STM32F0x1/STM32F0x2/STM32F0x8 Advanced ARM® Based 32 Bit MCUs Stm32f0x2 Reference Manual

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RM0091
Reference manual
STM32F0x1/STM32F0x2/STM32F0x8
advanced ARM®-based 32-bit MCUs
Introduction
This reference manual targets application developers. It provides complete information on
how to use the STM32F0x1/STM32F0x2/STM32F0x8 microcontroller memory and
peripherals.
It applies to the STM32F031x4/x6, STM32F051x4/x6/x8, STM32F071x8/xB,
STM32F091xB/xC, STM32F042x4/x6, STM32F072x8/xB, STM32F038x6, STM32F048x6,
STM32F058x8, STM32F078xB and STM32F098xC devices.
For the purpose of this manual, STM32F0x1/STM32F0x2/STM32F0x8 microcontrollers are
referred to as “STM32F0xx”.
The STM32F0xx is a family of microcontrollers with different memory sizes, packages and
peripherals.
For ordering information, mechanical and electrical device characteristics, please refer to
the corresponding datasheet.
For information on the ARM® CORTEX®-M0 core, please refer to the Cortex®-M0 technical
reference manual.

Related documents
• Cortex®-M0 technical reference manual, available from: http://infocenter.arm.com
• STM32F0xx Cortex-M0 programming manual (PM0215)
• STM32F0xx datasheets available from STMicroelectronics website: www.st.com

January 2017

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Contents

RM0091

Contents
1

2

3

Documentation conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.1

List of abbreviations for registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

1.2

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

1.3

Peripheral availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

System and memory overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.1

System architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.2

Memory organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.2.2

Memory map and register boundary addresses . . . . . . . . . . . . . . . . . . 46

2.3

Embedded SRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.4

Flash memory overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.5

Boot configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Embedded Flash memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.1

Flash main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.2

Flash memory functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.3

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2.2.1

3.2.1

Flash memory organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.2.2

Flash program and erase operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Memory protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.3.1

Read protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

3.3.2

Write protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

3.3.3

Option byte write protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

3.4

Flash interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

3.5

Flash register description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.5.1

Flash access control register (FLASH_ACR) . . . . . . . . . . . . . . . . . . . . 67

3.5.2

Flash key register (FLASH_KEYR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

3.5.3

Flash option key register (FLASH_OPTKEYR) . . . . . . . . . . . . . . . . . . . 68

3.5.4

Flash status register (FLASH_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

3.5.5

Flash control register (FLASH_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

3.5.6

Flash address register (FLASH_AR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

3.5.7

Flash Option byte register (FLASH_OBR) . . . . . . . . . . . . . . . . . . . . . . . 71

3.5.8

Write protection register (FLASH_WRPR) . . . . . . . . . . . . . . . . . . . . . . . 72

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4

Option byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.1

5

Option byte description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.1.1

User and read protection option byte . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.1.2

User data option byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.1.3

Write protection option byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

4.1.4

Option byte map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Power control (PWR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.1

5.2

5.3

5.4

6

Flash register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Power supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.1.1

Independent A/D and D/A converter supply and reference voltage . . . . 80

5.1.2

Independent I/O supply rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

5.1.3

Battery backup domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

5.1.4

Voltage regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Power supply supervisor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.2.1

Power on reset (POR) / power down reset (PDR) . . . . . . . . . . . . . . . . . 81

5.2.2

Programmable voltage detector (PVD) . . . . . . . . . . . . . . . . . . . . . . . . . 82

Low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.3.1

Slowing down system clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

5.3.2

Peripheral clock gating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

5.3.3

Sleep mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

5.3.4

Stop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

5.3.5

Standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

5.3.6

Auto-wakeup from low-power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Power control registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
5.4.1

Power control register (PWR_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

5.4.2

Power control/status register (PWR_CSR) . . . . . . . . . . . . . . . . . . . . . . 91

5.4.3

PWR register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Reset and clock control (RCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.1

6.2

Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
6.1.1

Power reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

6.1.2

System reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

6.1.3

RTC domain reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.2.1

HSE clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
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6.2.2

HSI clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

6.2.3

HSI48 clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

6.2.4

PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

6.2.5

LSE clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.2.6

LSI clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.2.7

System clock (SYSCLK) selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

6.2.8

Clock security system (CSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

6.2.9

ADC clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

6.2.10

RTC clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

6.2.11

Independent watchdog clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

6.2.12

Clock-out capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

6.2.13

Internal/external clock measurement with TIM14 . . . . . . . . . . . . . . . . 105

6.3

Low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

6.4

RCC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6.4.1

Clock control register (RCC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.4.2

Clock configuration register (RCC_CFGR) . . . . . . . . . . . . . . . . . . . . . 110

6.4.3

Clock interrupt register (RCC_CIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

6.4.4

APB peripheral reset register 2 (RCC_APB2RSTR) . . . . . . . . . . . . . . 116

6.4.5

APB peripheral reset register 1 (RCC_APB1RSTR) . . . . . . . . . . . . . . 117

6.4.6

AHB peripheral clock enable register (RCC_AHBENR) . . . . . . . . . . . 120

6.4.7

APB peripheral clock enable register 2 (RCC_APB2ENR) . . . . . . . . . 121

6.4.8

APB peripheral clock enable register 1 (RCC_APB1ENR) . . . . . . . . . 123

6.4.9

RTC domain control register (RCC_BDCR) . . . . . . . . . . . . . . . . . . . . . 126

6.4.10

Control/status register (RCC_CSR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

6.4.11

AHB peripheral reset register (RCC_AHBRSTR) . . . . . . . . . . . . . . . . 129

6.4.12

Clock configuration register 2 (RCC_CFGR2) . . . . . . . . . . . . . . . . . . . 131

6.4.13

Clock configuration register 3 (RCC_CFGR3) . . . . . . . . . . . . . . . . . . . 132

6.4.14

Clock control register 2 (RCC_CR2) . . . . . . . . . . . . . . . . . . . . . . . . . . 133

6.4.15

RCC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

Clock recovery system (CRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
7.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

7.2

CRS main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

7.3

CRS functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
7.3.1

CRS block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

7.3.2

Synchronization input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

7.3.3

Frequency error measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
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7.3.4

Frequency error evaluation and automatic trimming . . . . . . . . . . . . . . 140

7.3.5

CRS initialization and configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

7.4

CRS low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

7.5

CRS interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

7.6

CRS registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
7.6.1

CRS control register (CRS_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142

7.6.2

CRS configuration register (CRS_CFGR) . . . . . . . . . . . . . . . . . . . . . . 143

7.6.3

CRS interrupt and status register (CRS_ISR) . . . . . . . . . . . . . . . . . . . 144

7.6.4

CRS interrupt flag clear register (CRS_ICR) . . . . . . . . . . . . . . . . . . . . 146

7.6.5

CRS register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

General-purpose I/Os (GPIO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
8.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

8.2

GPIO main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

8.3

GPIO functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

8.4

8.3.1

General-purpose I/O (GPIO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

8.3.2

I/O pin alternate function multiplexer and mapping . . . . . . . . . . . . . . . 150

8.3.3

I/O port control registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

8.3.4

I/O port data registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

8.3.5

I/O data bitwise handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

8.3.6

GPIO locking mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

8.3.7

I/O alternate function input/output . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

8.3.8

External interrupt/wakeup lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

8.3.9

Input configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

8.3.10

Output configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

8.3.11

Alternate function configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

8.3.12

Analog configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155

8.3.13

Using the HSE or LSE oscillator pins as GPIOs . . . . . . . . . . . . . . . . . 156

8.3.14

Using the GPIO pins in the RTC supply domain . . . . . . . . . . . . . . . . . 156

GPIO registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
8.4.1

GPIO port mode register (GPIOx_MODER) (x =A..F) . . . . . . . . . . . . . 157

8.4.2

GPIO port output type register (GPIOx_OTYPER) (x = A..F) . . . . . . . 157

8.4.3

GPIO port output speed register (GPIOx_OSPEEDR)
(x = A..F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

8.4.4

GPIO port pull-up/pull-down register (GPIOx_PUPDR)
(x = A..F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

8.4.5

GPIO port input data register (GPIOx_IDR) (x = A..F) . . . . . . . . . . . . . 159

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GPIO port output data register (GPIOx_ODR) (x = A..F) . . . . . . . . . . . 159

8.4.7

GPIO port bit set/reset register (GPIOx_BSRR) (x = A..F) . . . . . . . . . 159

8.4.8

GPIO port configuration lock register (GPIOx_LCKR)
(x = A..B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

8.4.9

GPIO alternate function low register (GPIOx_AFRL)
(x = A..F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

8.4.10

GPIO alternate function high register (GPIOx_AFRH)
(x = A..F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

8.4.11

GPIO port bit reset register (GPIOx_BRR) (x =A..F) . . . . . . . . . . . . . . 162

8.4.12

GPIO register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

System configuration controller (SYSCFG) . . . . . . . . . . . . . . . . . . . . 165
9.1

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8.4.6

SYSCFG registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
9.1.1

SYSCFG configuration register 1 (SYSCFG_CFGR1) . . . . . . . . . . . . 165

9.1.2

SYSCFG external interrupt configuration register 1
(SYSCFG_EXTICR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

9.1.3

SYSCFG external interrupt configuration register 2
(SYSCFG_EXTICR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

9.1.4

SYSCFG external interrupt configuration register 3
(SYSCFG_EXTICR3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

9.1.5

SYSCFG external interrupt configuration register 4
(SYSCFG_EXTICR4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

9.1.6

SYSCFG configuration register 2 (SYSCFG_CFGR2) . . . . . . . . . . . . 172

9.1.7

SYSCFG interrupt line 0 status register (SYSCFG_ITLINE0) . . . . . . . 172

9.1.8

SYSCFG interrupt line 1 status register (SYSCFG_ITLINE1) . . . . . . . 173

9.1.9

SYSCFG interrupt line 2 status register (SYSCFG_ITLINE2) . . . . . . . 173

9.1.10

SYSCFG interrupt line 3 status register (SYSCFG_ITLINE3) . . . . . . . 174

9.1.11

SYSCFG interrupt line 4 status register (SYSCFG_ITLINE4) . . . . . . . 174

9.1.12

SYSCFG interrupt line 5 status register (SYSCFG_ITLINE5) . . . . . . . 175

9.1.13

SYSCFG interrupt line 6 status register (SYSCFG_ITLINE6) . . . . . . . 175

9.1.14

SYSCFG interrupt line 7 status register (SYSCFG_ITLINE7) . . . . . . . 175

9.1.15

SYSCFG interrupt line 8 status register (SYSCFG_ITLINE8) . . . . . . . 176

9.1.16

SYSCFG interrupt line 9 status register (SYSCFG_ITLINE9) . . . . . . . 176

9.1.17

SYSCFG interrupt line 10 status register (SYSCFG_ITLINE10) . . . . . 177

9.1.18

SYSCFG interrupt line 11 status register (SYSCFG_ITLINE11) . . . . . 177

9.1.19

SYSCFG interrupt line 12 status register (SYSCFG_ITLINE12) . . . . . 178

9.1.20

SYSCFG interrupt line 13 status register (SYSCFG_ITLINE13) . . . . . 178

9.1.21

SYSCFG interrupt line 14 status register (SYSCFG_ITLINE14) . . . . . 179

9.1.22

SYSCFG interrupt line 15 status register (SYSCFG_ITLINE15) . . . . . 179

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9.1.23

SYSCFG interrupt line 16 status register (SYSCFG_ITLINE16) . . . . . 179

9.1.24

SYSCFG interrupt line 17 status register (SYSCFG_ITLINE17) . . . . . 180

9.1.25

SYSCFG interrupt line 18 status register (SYSCFG_ITLINE18) . . . . . 180

9.1.26

SYSCFG interrupt line 19 status register (SYSCFG_ITLINE19) . . . . . 180

9.1.27

SYSCFG interrupt line 20 status register (SYSCFG_ITLINE20) . . . . . 181

9.1.28

SYSCFG interrupt line 21 status register (SYSCFG_ITLINE21) . . . . . 181

9.1.29

SYSCFG interrupt line 22 status register (SYSCFG_ITLINE22) . . . . . 181

9.1.30

SYSCFG interrupt line 23 status register (SYSCFG_ITLINE23) . . . . . 182

9.1.31

SYSCFG interrupt line 24 status register (SYSCFG_ITLINE24) . . . . . 182

9.1.32

SYSCFG interrupt line 25 status register (SYSCFG_ITLINE25) . . . . . 182

9.1.33

SYSCFG interrupt line 26 status register (SYSCFG_ITLINE26) . . . . . 183

9.1.34

SYSCFG interrupt line 27 status register (SYSCFG_ITLINE27) . . . . . 183

9.1.35

SYSCFG interrupt line 28 status register (SYSCFG_ITLINE28) . . . . . 183

9.1.36

SYSCFG interrupt line 29 status register (SYSCFG_ITLINE29) . . . . . 184

9.1.37

SYSCFG interrupt line 30 status register (SYSCFG_ITLINE30) . . . . . 184

9.1.38

SYSCFG register maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Direct memory access controller (DMA) . . . . . . . . . . . . . . . . . . . . . . . 188
10.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

10.2

DMA main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

10.3

DMA functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

10.4

10.3.1

DMA transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

10.3.2

Arbiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

10.3.3

DMA channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

10.3.4

Programmable data width, data alignment and endians . . . . . . . . . . . 192

10.3.5

Error management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

10.3.6

DMA interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

DMA registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
10.4.1

DMA interrupt status register (DMA_ISR and DMA2_ISR) . . . . . . . . . 199

10.4.2

DMA interrupt flag clear register (DMA_IFCR and DMA2_IFCR) . . . . 200

10.4.3

DMA channel x configuration register (DMA_CCRx and DMA2_CCRx)
(x = 1..7 for DMA and x = 1..5 for DMA2, where x = channel number) 201

10.4.4

DMA channel x number of data register (DMA_CNDTRx and
DMA2_CNDTRx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

10.4.5

DMA channel x peripheral address register (DMA_CPARx and
DMA2_CPARx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

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RM0091

11.2

11.3

10.4.7

DMA channel selection register (DMA_CSELR and DMA2_CSELR) . 205

10.4.8

DMA register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

Nested vectored interrupt controller (NVIC) . . . . . . . . . . . . . . . . . . . . . . 209
11.1.1

NVIC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

11.1.2

SysTick calibration value register . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

11.1.3

Interrupt and exception vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Extended interrupts and events controller (EXTI) . . . . . . . . . . . . . . . . . .211
11.2.1

Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

11.2.2

Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

11.2.3

Event management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

11.2.4

Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212

11.2.5

External and internal interrupt/event line mapping . . . . . . . . . . . . . . . 214

EXTI registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
11.3.1

Interrupt mask register (EXTI_IMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

11.3.2

Event mask register (EXTI_EMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

11.3.3

Rising trigger selection register (EXTI_RTSR) . . . . . . . . . . . . . . . . . . 216

11.3.4

Falling trigger selection register (EXTI_FTSR) . . . . . . . . . . . . . . . . . . 217

11.3.5

Software interrupt event register (EXTI_SWIER) . . . . . . . . . . . . . . . . 217

11.3.6

Pending register (EXTI_PR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

11.3.7

EXTI register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Cyclic redundancy check calculation unit (CRC) . . . . . . . . . . . . . . . . 220
12.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

12.2

CRC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

12.3

CRC implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

12.4

CRC functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

12.5

8/1004

DMA channel x memory address register (DMA_CMARx and
DMA2_CMARx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

Interrupts and events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
11.1

12

10.4.6

12.4.1

CRC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

12.4.2

CRC internal signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

12.4.3

CRC operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

CRC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
12.5.1

Data register (CRC_DR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223

12.5.2

Independent data register (CRC_IDR) . . . . . . . . . . . . . . . . . . . . . . . . 223

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12.5.3

Control register (CRC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

12.5.4

Initial CRC value (CRC_INIT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

12.5.5

CRC polynomial (CRC_POL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

12.5.6

CRC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

Analog-to-digital converter (ADC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
13.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

13.2

ADC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

13.3

ADC pins and internal signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

13.4

ADC functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
13.4.1

Calibration (ADCAL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

13.4.2

ADC on-off control (ADEN, ADDIS, ADRDY) . . . . . . . . . . . . . . . . . . . 231

13.4.3

ADC clock (CKMODE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

13.4.4

Configuring the ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

13.4.5

Channel selection (CHSEL, SCANDIR) . . . . . . . . . . . . . . . . . . . . . . . . 235

13.4.6

Programmable sampling time (SMP) . . . . . . . . . . . . . . . . . . . . . . . . . . 235

13.4.7

Single conversion mode (CONT=0) . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

13.4.8

Continuous conversion mode (CONT=1) . . . . . . . . . . . . . . . . . . . . . . . 236

13.4.9

Starting conversions (ADSTART) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

13.4.10 Timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
13.4.11 Stopping an ongoing conversion (ADSTP) . . . . . . . . . . . . . . . . . . . . . 238

13.5

13.6

13.7

Conversion on external trigger and trigger polarity (EXTSEL, EXTEN) . 238
13.5.1

Discontinuous mode (DISCEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

13.5.2

Programmable resolution (RES) - fast conversion mode . . . . . . . . . . 240

13.5.3

End of conversion, end of sampling phase (EOC, EOSMP flags) . . . . 241

13.5.4

End of conversion sequence (EOSEQ flag) . . . . . . . . . . . . . . . . . . . . 242

13.5.5

Example timing diagrams (single/continuous modes . . . . . . . . . . . . . . . . .
hardware/software triggers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242

Data management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
13.6.1

Data register and data alignment (ADC_DR, ALIGN) . . . . . . . . . . . . . 244

13.6.2

ADC overrun (OVR, OVRMOD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

13.6.3

Managing a sequence of data converted without using the DMA . . . . 245

13.6.4

Managing converted data without using the DMA without overrun . . . 245

13.6.5

Managing converted data using the DMA . . . . . . . . . . . . . . . . . . . . . . 245

Low-power features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
13.7.1

Wait mode conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

13.7.2

Auto-off mode (AUTOFF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
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13.8

Analog window watchdog (AWDEN, AWDSGL, AWDCH,
AWD_HTR/LTR, AWD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

13.9

Temperature sensor and internal reference voltage . . . . . . . . . . . . . . . . 250

13.10 Battery voltage monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
13.11 ADC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
13.12 ADC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
13.12.1 ADC interrupt and status register (ADC_ISR) . . . . . . . . . . . . . . . . . . . 254
13.12.2 ADC interrupt enable register (ADC_IER) . . . . . . . . . . . . . . . . . . . . . . 255
13.12.3 ADC control register (ADC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
13.12.4 ADC configuration register 1 (ADC_CFGR1) . . . . . . . . . . . . . . . . . . . 259
13.12.5 ADC configuration register 2 (ADC_CFGR2) . . . . . . . . . . . . . . . . . . . 263
13.12.6 ADC sampling time register (ADC_SMPR) . . . . . . . . . . . . . . . . . . . . . 263
13.12.7 ADC watchdog threshold register (ADC_TR) . . . . . . . . . . . . . . . . . . . 264
13.12.8 ADC channel selection register (ADC_CHSELR) . . . . . . . . . . . . . . . . 265
13.12.9 ADC data register (ADC_DR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
13.12.10 ADC common configuration register (ADC_CCR) . . . . . . . . . . . . . . . . 266
13.12.11 ADC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267

14

Digital-to-analog converter (DAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
14.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

14.2

DAC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

14.3

DAC output buffer enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

14.4

DAC channel enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

14.5

Single mode functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

14.6

14.7

10/1004

14.5.1

DAC data format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

14.5.2

DAC channel conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

14.5.3

DAC output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

14.5.4

DAC trigger selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Dual-mode functional description (STM32F07x and
STM32F09x devices) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
14.6.1

DAC data format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

14.6.2

DAC channel conversion in dual mode . . . . . . . . . . . . . . . . . . . . . . . . 273

14.6.3

Description of dual conversion modes . . . . . . . . . . . . . . . . . . . . . . . . . 273

14.6.4

DAC output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277

14.6.5

DAC trigger selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

Noise generation(STM32F07x and STM32F09x devices) . . . . . . . . . . . 278

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14.8

Triangle-wave generation (STM32F07x and STM32F09x
devices) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279

14.9

DMA request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

14.10 DAC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
14.10.1 DAC control register (DAC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
14.10.2 DAC software trigger register (DAC_SWTRIGR) . . . . . . . . . . . . . . . . . 285
14.10.3 DAC channel1 12-bit right-aligned data holding register
(DAC_DHR12R1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
14.10.4 DAC channel1 12-bit left-aligned data holding register
(DAC_DHR12L1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
14.10.5 DAC channel1 8-bit right-aligned data holding register
(DAC_DHR8R1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
14.10.6 DAC channel2 12-bit right-aligned data holding register
(DAC_DHR12R2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
14.10.7 DAC channel2 12-bit left-aligned data holding register
(DAC_DHR12L2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
14.10.8 DAC channel2 8-bit right-aligned data holding register
(DAC_DHR8R2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
14.10.9 Dual DAC 12-bit right-aligned data holding register
(DAC_DHR12RD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
14.10.10 Dual DAC 12-bit left-aligned data holding register
(DAC_DHR12LD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
14.10.11 Dual DAC 8-bit right-aligned data holding register
(DAC_DHR8RD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288
14.10.12 DAC channel1 data output register (DAC_DOR1) . . . . . . . . . . . . . . . . 289
14.10.13 DAC channel2 data output register (DAC_DOR2) . . . . . . . . . . . . . . . . 289
14.10.14 DAC status register (DAC_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
14.10.15 DAC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

15

Comparator (COMP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
15.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

15.2

COMP main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

15.3

COMP functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
15.3.1

COMP block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

15.3.2

COMP pins and internal signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

15.3.3

COMP reset and clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

15.3.4

Comparator LOCK mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

15.3.5

Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

15.3.6

Power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

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15.4

COMP interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

15.5

COMP registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
15.5.1

COMP control and status register (COMP_CSR) . . . . . . . . . . . . . . . . 297

15.5.2

COMP register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Touch sensing controller (TSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
16.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

16.2

TSC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301

16.3

TSC functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
16.3.1

TSC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302

16.3.2

Surface charge transfer acquisition overview . . . . . . . . . . . . . . . . . . . 302

16.3.3

Reset and clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304

16.3.4

Charge transfer acquisition sequence . . . . . . . . . . . . . . . . . . . . . . . . . 305

16.3.5

Spread spectrum feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

16.3.6

Max count error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

16.3.7

Sampling capacitor I/O and channel I/O mode selection . . . . . . . . . . . 307

16.3.8

Acquisition mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

16.3.9

I/O hysteresis and analog switch control . . . . . . . . . . . . . . . . . . . . . . . 308

16.4

TSC low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

16.5

TSC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

16.6

TSC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
16.6.1

TSC control register (TSC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310

16.6.2

TSC interrupt enable register (TSC_IER) . . . . . . . . . . . . . . . . . . . . . . 312

16.6.3

TSC interrupt clear register (TSC_ICR) . . . . . . . . . . . . . . . . . . . . . . . . 313

16.6.4

TSC interrupt status register (TSC_ISR) . . . . . . . . . . . . . . . . . . . . . . . 314

16.6.5

TSC I/O hysteresis control register (TSC_IOHCR) . . . . . . . . . . . . . . . 314

16.6.6

TSC I/O analog switch control register (TSC_IOASCR) . . . . . . . . . . . 315

16.6.7

TSC I/O sampling control register (TSC_IOSCR) . . . . . . . . . . . . . . . . 315

16.6.8

TSC I/O channel control register (TSC_IOCCR) . . . . . . . . . . . . . . . . . 316

16.6.9

TSC I/O group control status register (TSC_IOGCSR) . . . . . . . . . . . . 316

16.6.10 TSC I/O group x counter register (TSC_IOGxCR) (x = 1..8) . . . . . . . . 317
16.6.11 TSC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

17

12/1004

Advanced-control timers (TIM1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
17.1

TIM1 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

17.2

TIM1 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

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17.3

TIM1 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
17.3.1

Time-base unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

17.3.2

Counter modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324

17.3.3

Repetition counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

17.3.4

Clock sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336

17.3.5

Capture/compare channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

17.3.6

Input capture mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

17.3.7

PWM input mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343

17.3.8

Forced output mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

17.3.9

Output compare mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

17.3.10 PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
17.3.11 Complementary outputs and dead-time insertion . . . . . . . . . . . . . . . . 349
17.3.12 Using the break function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
17.3.13 Clearing the OCxREF signal on an external event . . . . . . . . . . . . . . . 354
17.3.14 6-step PWM generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
17.3.15 One-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
17.3.16 Encoder interface mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
17.3.17 Timer input XOR function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
17.3.18 Interfacing with Hall sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
17.3.19 TIMx and external trigger synchronization . . . . . . . . . . . . . . . . . . . . . . 363
17.3.20 Timer synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
17.3.21 Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

17.4

TIM1 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
17.4.1

TIM1 control register 1 (TIM1_CR1) . . . . . . . . . . . . . . . . . . . . . . . . . . 367

17.4.2

TIM1 control register 2 (TIM1_CR2) . . . . . . . . . . . . . . . . . . . . . . . . . . 368

17.4.3

TIM1 slave mode control register (TIM1_SMCR) . . . . . . . . . . . . . . . . 370

17.4.4

TIM1 DMA/interrupt enable register (TIM1_DIER) . . . . . . . . . . . . . . . 372

17.4.5

TIM1 status register (TIM1_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

17.4.6

TIM1 event generation register (TIM1_EGR) . . . . . . . . . . . . . . . . . . . 375

17.4.7

TIM1 capture/compare mode register 1 (TIM1_CCMR1) . . . . . . . . . . 376

17.4.8

TIM1 capture/compare mode register 2 (TIM1_CCMR2) . . . . . . . . . . 380

17.4.9

TIM1 capture/compare enable register (TIM1_CCER) . . . . . . . . . . . . 381

17.4.10 TIM1 counter (TIM1_CNT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
17.4.11 TIM1 prescaler (TIM1_PSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
17.4.12 TIM1 auto-reload register (TIM1_ARR) . . . . . . . . . . . . . . . . . . . . . . . . 385
17.4.13 TIM1 repetition counter register (TIM1_RCR) . . . . . . . . . . . . . . . . . . . 385
17.4.14 TIM1 capture/compare register 1 (TIM1_CCR1) . . . . . . . . . . . . . . . . . 386

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17.4.15 TIM1 capture/compare register 2 (TIM1_CCR2) . . . . . . . . . . . . . . . . . 386
17.4.16 TIM1 capture/compare register 3 (TIM1_CCR3) . . . . . . . . . . . . . . . . . 387
17.4.17 TIM1 capture/compare register 4 (TIM1_CCR4) . . . . . . . . . . . . . . . . . 387
17.4.18 TIM1 break and dead-time register (TIM1_BDTR) . . . . . . . . . . . . . . . 388
17.4.19 TIM1 DMA control register (TIM1_DCR) . . . . . . . . . . . . . . . . . . . . . . . 389
17.4.20 TIM1 DMA address for full transfer (TIM1_DMAR) . . . . . . . . . . . . . . . 390
17.4.21 TIM1 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

18

General-purpose timers (TIM2 and TIM3) . . . . . . . . . . . . . . . . . . . . . . 393
18.1

TIM2 and TIM3 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

18.2

TIM2 and TIM3 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393

18.3

TIM2 and TIM3 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . 394
18.3.1

Time-base unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394

18.3.2

Counter modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

18.3.3

Clock sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

18.3.4

Capture/compare channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410

18.3.5

Input capture mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412

18.3.6

PWM input mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414

18.3.7

Forced output mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

18.3.8

Output compare mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415

18.3.9

PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416

18.3.10 One-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
18.3.11 Clearing the OCxREF signal on an external event . . . . . . . . . . . . . . . 421
18.3.12 Encoder interface mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
18.3.13 Timer input XOR function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
18.3.14 Timers and external trigger synchronization . . . . . . . . . . . . . . . . . . . . 425
18.3.15 Timer synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
18.3.16 Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434

18.4

14/1004

TIM2 and TIM3 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
18.4.1

TIM2 and TIM3 control register 1 (TIM2_CR1 and TIM3_CR1) . . . . . 435

18.4.2

TIM2 and TIM3 control register 2 (TIM2_CR2 and TIM3_CR2) . . . . . 437

18.4.3

TIM2 and TIM3 slave mode control register (TIM2_SMCR and
TIM3_SMCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

18.4.4

TIM2 and TIM3 DMA/Interrupt enable register (TIM2_DIER and
TIM3_DIER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441

18.4.5

TIM2 and TIM3 status register (TIM2_SR and TIM3_SR) . . . . . . . . . . 442

18.4.6

TIM2 and TIM3 event generation register (TIM2_EGR and
TIM3_EGR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
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18.4.7

TIM2 and TIM3 capture/compare mode register 1 (TIM2_CCMR1 and
TIM3_CCMR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445

18.4.8

TIM2 and TIM3 capture/compare mode register 2 (TIM2_CCMR2 and
TIM3_CCMR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448

18.4.9

TIM2 and TIM3 capture/compare enable register (TIM2_CCER and
TIM3_CCER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449

18.4.10 TIM2 and TIM3 counter (TIM2_CNT and TIM3_CNT) . . . . . . . . . . . . . 451
18.4.11 TIM2 and TIM3 prescaler (TIM2_PSC and TIM3_PSC) . . . . . . . . . . . 451
18.4.12 TIM2 and TIM3 auto-reload register (TIM2_ARR and TIM3_ARR) . . . 451
18.4.13 TIM2 and TIM3 capture/compare register 1 (TIM2_CCR1 and
TIM3_CCR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
18.4.14 TIM2 and TIM3 capture/compare register 2 (TIM2_CCR2 and
TIM3_CCR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
18.4.15 TIM2 and TIM3 capture/compare register 3 (TIM2_CCR3 and
TIM3_CCR3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
18.4.16 TIM2 and TIM3 capture/compare register 4 (TIM2_CCR4 and
TIM3_CCR4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
18.4.17 TIM2 and TIM3 DMA control register (TIM2_DCR and TIM3_DCR) . . 454
18.4.18 TIM2 and TIM3 DMA address for full transfer (TIM2_DMAR and
TIM3_DMAR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455
18.4.19 TIM2 and TIM3 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457

19

General-purpose timer (TIM14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
19.1

TIM14 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

19.2

TIM14 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459

19.3

TIM14 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

19.4

19.3.1

Time-base unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460

19.3.2

Counter modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462

19.3.3

Clock source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464

19.3.4

Capture/compare channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465

19.3.5

Input capture mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466

19.3.6

Forced output mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467

19.3.7

Output compare mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468

19.3.8

PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469

19.3.9

Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470

TIM14 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
19.4.1

TIM14 control register 1 (TIM14_CR1) . . . . . . . . . . . . . . . . . . . . . . . . 470

19.4.2

TIM14 interrupt enable register (TIM14_DIER) . . . . . . . . . . . . . . . . . . 471

19.4.3

TIM14 status register (TIM14_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

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19.4.4

TIM14 event generation register (TIM14_EGR) . . . . . . . . . . . . . . . . . 472

19.4.5

TIM14 capture/compare mode register 1 (TIM14_CCMR1) . . . . . . . . 473

19.4.6

TIM14 capture/compare enable register (TIM14_CCER) . . . . . . . . . . 475

19.4.7

TIM14 counter (TIM14_CNT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

19.4.8

TIM14 prescaler (TIM14_PSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

19.4.9

TIM14 auto-reload register (TIM14_ARR) . . . . . . . . . . . . . . . . . . . . . . 477

19.4.10 TIM14 capture/compare register 1 (TIM14_CCR1) . . . . . . . . . . . . . . . 477
19.4.11 TIM14 option register (TIM14_OR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
19.4.12 TIM14 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

20

General-purpose timers (TIM15/16/17) . . . . . . . . . . . . . . . . . . . . . . . . 480
20.1

TIM15/16/17 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

20.2

TIM15 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

20.3

TIM16 and TIM17 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

20.4

TIM15/16/17 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
20.4.1

Time-base unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483

20.4.2

Counter modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

20.4.3

Repetition counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

20.4.4

Clock sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490

20.4.5

Capture/compare channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492

20.4.6

Input capture mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

20.4.7

PWM input mode (only for TIM15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

20.4.8

Forced output mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

20.4.9

Output compare mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497

20.4.10 PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
20.4.11 Complementary outputs and dead-time insertion . . . . . . . . . . . . . . . . 500
20.4.12 Using the break function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
20.4.13 One-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
20.4.14 TIM15 external trigger synchronization . . . . . . . . . . . . . . . . . . . . . . . . 506
20.4.15 Timer synchronization (TIM15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
20.4.16 Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509

20.5

16/1004

TIM15 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
20.5.1

TIM15 control register 1 (TIM15_CR1) . . . . . . . . . . . . . . . . . . . . . . . . 510

20.5.2

TIM15 control register 2 (TIM15_CR2) . . . . . . . . . . . . . . . . . . . . . . . . 511

20.5.3

TIM15 slave mode control register (TIM15_SMCR) . . . . . . . . . . . . . . 512

20.5.4

TIM15 DMA/interrupt enable register (TIM15_DIER) . . . . . . . . . . . . . 514

20.5.5

TIM15 status register (TIM15_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
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20.5.6

TIM15 event generation register (TIM15_EGR) . . . . . . . . . . . . . . . . . 517

20.5.7

TIM15 capture/compare mode register 1 (TIM15_CCMR1) . . . . . . . . 518

20.5.8

TIM15 capture/compare enable register (TIM15_CCER) . . . . . . . . . . 521

20.5.9

TIM15 counter (TIM15_CNT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523

20.5.10 TIM15 prescaler (TIM15_PSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523
20.5.11 TIM15 auto-reload register (TIM15_ARR) . . . . . . . . . . . . . . . . . . . . . . 524
20.5.12 TIM15 repetition counter register (TIM15_RCR) . . . . . . . . . . . . . . . . . 524
20.5.13 TIM15 capture/compare register 1 (TIM15_CCR1) . . . . . . . . . . . . . . . 524
20.5.14 TIM15 capture/compare register 2 (TIM15_CCR2) . . . . . . . . . . . . . . . 525
20.5.15 TIM15 break and dead-time register (TIM15_BDTR) . . . . . . . . . . . . . 525
20.5.16 TIM15 DMA control register (TIM15_DCR) . . . . . . . . . . . . . . . . . . . . . 527
20.5.17 TIM15 DMA address for full transfer (TIM15_DMAR) . . . . . . . . . . . . . 528
20.5.18 TIM15 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528

20.6

TIM16 and TIM17 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
20.6.1

TIM16 and TIM17 control register 1 (TIM16_CR1 and TIM17_CR1) . 530

20.6.2

TIM16 and TIM17 control register 2 (TIM16_CR2 and TIM17_CR2) . 531

20.6.3

TIM16 and TIM17 DMA/interrupt enable register (TIM16_DIER and
TIM17_DIER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532

20.6.4

TIM16 and TIM17 status register (TIM16_SR and TIM17_SR) . . . . . . 533

20.6.5

TIM16 and TIM17 event generation register (TIM16_EGR and
TIM17_EGR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534

20.6.6

TIM16 and TIM17 capture/compare mode register 1 (TIM16_CCMR1
and TIM17_CCMR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 535

20.6.7

TIM16 and TIM17 capture/compare enable register (TIM16_CCER
and TIM17_CCER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538

20.6.8

TIM16 and TIM17 counter (TIM16_CNT and TIM17_CNT) . . . . . . . . . 540

20.6.9

TIM16 and TIM17 prescaler (TIM16_PSC and TIM17_PSC) . . . . . . . 540

20.6.10 TIM16 and TIM17 auto-reload register (TIM16_ARR and
TIM17_ARR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540
20.6.11 TIM16 and TIM17 repetition counter register (TIM16_RCR and
TIM17_RCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540
20.6.12 TIM16 and TIM17 capture/compare register 1 (TIM16_CCR1 and
TIM17_CCR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
20.6.13 TIM16 and TIM17 break and dead-time register (TIM16_BDTR and
TIM17_BDTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
20.6.14 TIM16 and TIM17 DMA control register (TIM16_DCR and
TIM17_DCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
20.6.15 TIM16 and TIM17 DMA address for full transfer (TIM16_DMAR and
TIM17_DMAR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
20.6.16 TIM16 and TIM17 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545

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Basic timer (TIM6/TIM7) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
21.1

TIM6/TIM7 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547

21.2

TIM6/TIM7 main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547

21.3

TIM6/TIM7 functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548

21.4

21.3.1

Time-base unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548

21.3.2

Counter modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550

21.3.3

Clock source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

21.3.4

Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

TIM6/TIM7 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
21.4.1

TIM6/TIM7 control register 1 (TIMx_CR1) . . . . . . . . . . . . . . . . . . . . . . 555

21.4.2

TIM6/TIM7 control register 2 (TIMx_CR2) . . . . . . . . . . . . . . . . . . . . . . 556

21.4.3

TIM6/TIM7 DMA/Interrupt enable register (TIMx_DIER) . . . . . . . . . . . 556

21.4.4

TIM6/TIM7 status register (TIMx_SR) . . . . . . . . . . . . . . . . . . . . . . . . . 557

21.4.5

TIM6/TIM7 event generation register (TIMx_EGR) . . . . . . . . . . . . . . . 557

21.4.6

TIM6/TIM7 counter (TIMx_CNT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557

21.4.7

TIM6/TIM7 prescaler (TIMx_PSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558

21.4.8

TIM6/TIM7 auto-reload register (TIMx_ARR) . . . . . . . . . . . . . . . . . . . 558

21.4.9

TIM6/TIM7 register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559

22

Infrared interface (IRTIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560

23

Independent watchdog (IWDG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
23.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

23.2

IWDG main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

23.3

IWDG functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

23.4

18/1004

23.3.1

IWDG block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561

23.3.2

Window option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562

23.3.3

Hardware watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

23.3.4

Behavior in Stop and Standby modes . . . . . . . . . . . . . . . . . . . . . . . . . 563

23.3.5

Register access protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

23.3.6

Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563

IWDG registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
23.4.1

Key register (IWDG_KR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564

23.4.2

Prescaler register (IWDG_PR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565

23.4.3

Reload register (IWDG_RLR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566

23.4.4

Status register (IWDG_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567

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Window register (IWDG_WINR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568

23.4.6

IWDG register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569

System window watchdog (WWDG) . . . . . . . . . . . . . . . . . . . . . . . . . . 570
24.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570

24.2

WWDG main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570

24.3

WWDG functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570

24.4

25

23.4.5

24.3.1

Enabling the watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571

24.3.2

Controlling the downcounter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571

24.3.3

Advanced watchdog interrupt feature . . . . . . . . . . . . . . . . . . . . . . . . . 571

24.3.4

How to program the watchdog timeout . . . . . . . . . . . . . . . . . . . . . . . . 572

24.3.5

Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573

WWDG registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
24.4.1

Control register (WWDG_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573

24.4.2

Configuration register (WWDG_CFR) . . . . . . . . . . . . . . . . . . . . . . . . . 574

24.4.3

Status register (WWDG_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574

24.4.4

WWDG register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575

Real-time clock (RTC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576
25.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 576

25.2

RTC main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577

25.3

RTC implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577

25.4

RTC functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578
25.4.1

RTC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578

25.4.2

GPIOs controlled by the RTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580

25.4.3

Clock and prescalers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

25.4.4

Real-time clock and calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

25.4.5

Programmable alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583

25.4.6

Periodic auto-wakeup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583

25.4.7

RTC initialization and configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 584

25.4.8

Reading the calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586

25.4.9

Resetting the RTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587

25.4.10 RTC synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587
25.4.11 RTC reference clock detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
25.4.12 RTC smooth digital calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588
25.4.13 Time-stamp function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590

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25.4.14 Tamper detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
25.4.15 Calibration clock output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
25.4.16 Alarm output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

25.5

RTC low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594

25.6

RTC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594

25.7

RTC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
25.7.1

RTC time register (RTC_TR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595

25.7.2

RTC date register (RTC_DR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596

25.7.3

RTC control register (RTC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597

25.7.4

RTC initialization and status register (RTC_ISR) . . . . . . . . . . . . . . . . . 600

25.7.5

RTC prescaler register (RTC_PRER) . . . . . . . . . . . . . . . . . . . . . . . . . 602

25.7.6

RTC wakeup timer register (RTC_WUTR) . . . . . . . . . . . . . . . . . . . . . . 603

25.7.7

RTC alarm A register (RTC_ALRMAR) . . . . . . . . . . . . . . . . . . . . . . . . 604

25.7.8

RTC write protection register (RTC_WPR) . . . . . . . . . . . . . . . . . . . . . 605

25.7.9

RTC sub second register (RTC_SSR) . . . . . . . . . . . . . . . . . . . . . . . . . 605

25.7.10 RTC shift control register (RTC_SHIFTR) . . . . . . . . . . . . . . . . . . . . . . 606
25.7.11 RTC timestamp time register (RTC_TSTR) . . . . . . . . . . . . . . . . . . . . . 607
25.7.12 RTC timestamp date register (RTC_TSDR) . . . . . . . . . . . . . . . . . . . . 608
25.7.13 RTC time-stamp sub second register (RTC_TSSSR) . . . . . . . . . . . . . 609
25.7.14 RTC calibration register (RTC_CALR) . . . . . . . . . . . . . . . . . . . . . . . . . 610
25.7.15 RTC tamper and alternate function configuration register
(RTC_TAFCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
25.7.16 RTC alarm A sub second register (RTC_ALRMASSR) . . . . . . . . . . . . 614
25.7.17 RTC backup registers (RTC_BKPxR) . . . . . . . . . . . . . . . . . . . . . . . . . 615
25.7.18 RTC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615

26

20/1004

Inter-integrated circuit (I2C) interface . . . . . . . . . . . . . . . . . . . . . . . . . 617
26.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617

26.2

I2C main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617

26.3

I2C implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618

26.4

I2C functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
26.4.1

I2C1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619

26.4.2

I2C2 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620

26.4.3

I2C clock requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620

26.4.4

Mode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621

26.4.5

I2C initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622

26.4.6

Software reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
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26.4.7

Data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627

26.4.8

I2C slave mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629

26.4.9

I2C master mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638

26.4.10 I2C_TIMINGR register configuration examples . . . . . . . . . . . . . . . . . . 650
26.4.11 SMBus specific features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
26.4.12 SMBus initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
26.4.13 SMBus: I2C_TIMEOUTR register configuration examples . . . . . . . . . 656
26.4.14 SMBus slave mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657
26.4.15 Wakeup from Stop mode on address match . . . . . . . . . . . . . . . . . . . . 665
26.4.16 Error conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665
26.4.17 DMA requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667
26.4.18 Debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668

26.5

I2C low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668

26.6

I2C interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668

26.7

I2C registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670
26.7.1

Control register 1 (I2C_CR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670

26.7.2

Control register 2 (I2C_CR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673

26.7.3

Own address 1 register (I2C_OAR1) . . . . . . . . . . . . . . . . . . . . . . . . . . 676

26.7.4

Own address 2 register (I2C_OAR2) . . . . . . . . . . . . . . . . . . . . . . . . . . 677

26.7.5

Timing register (I2C_TIMINGR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678

26.7.6

Timeout register (I2C_TIMEOUTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 679

26.7.7

Interrupt and status register (I2C_ISR) . . . . . . . . . . . . . . . . . . . . . . . . 680

26.7.8

Interrupt clear register (I2C_ICR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682

26.7.9

PEC register (I2C_PECR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 683

26.7.10 Receive data register (I2C_RXDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
26.7.11 Transmit data register (I2C_TXDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
26.7.12 I2C register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685

27

Universal synchronous asynchronous receiver
transmitter (USART) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687
27.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

27.2

USART main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687

27.3

USART extended features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688

27.4

USART implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689

27.5

USART functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690
27.5.1

USART character description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692

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27.5.2

USART transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694

27.5.3

USART receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697

27.5.4

USART baud rate generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703

27.5.5

Tolerance of the USART receiver to clock deviation . . . . . . . . . . . . . . 705

27.5.6

USART auto baud rate detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706

27.5.7

Multiprocessor communication using USART . . . . . . . . . . . . . . . . . . . 707

27.5.8

Modbus communication using USART . . . . . . . . . . . . . . . . . . . . . . . . 709

27.5.9

USART parity control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710

27.5.10 USART LIN (local interconnection network) mode . . . . . . . . . . . . . . . 711
27.5.11 USART synchronous mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
27.5.12 USART Single-wire Half-duplex communication . . . . . . . . . . . . . . . . . 716
27.5.13 USART Smartcard mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
27.5.14 USART IrDA SIR ENDEC block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721
27.5.15 USART continuous communication in DMA mode . . . . . . . . . . . . . . . 723
27.5.16 RS232 hardware flow control and RS485 driver enable
using USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
27.5.17 Wakeup from Stop mode using USART . . . . . . . . . . . . . . . . . . . . . . . . 728

27.6

USART low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729

27.7

USART interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729

27.8

USART registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
27.8.1

Control register 1 (USART_CR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732

27.8.2

Control register 2 (USART_CR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735

27.8.3

Control register 3 (USART_CR3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739

27.8.4

Baud rate register (USART_BRR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743

27.8.5

Guard time and prescaler register (USART_GTPR) . . . . . . . . . . . . . . 743

27.8.6

Receiver timeout register (USART_RTOR) . . . . . . . . . . . . . . . . . . . . . 744

27.8.7

Request register (USART_RQR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745

27.8.8

Interrupt and status register (USART_ISR) . . . . . . . . . . . . . . . . . . . . . 746

27.8.9

Interrupt flag clear register (USART_ICR) . . . . . . . . . . . . . . . . . . . . . . 751

27.8.10 Receive data register (USART_RDR) . . . . . . . . . . . . . . . . . . . . . . . . . 752
27.8.11 Transmit data register (USART_TDR) . . . . . . . . . . . . . . . . . . . . . . . . . 752
27.8.12 USART register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753

28

22/1004

Serial peripheral interface / inter-IC sound (SPI/I2S) . . . . . . . . . . . . . 755
28.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755

28.2

SPI main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755

28.3

I2S main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
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28.4

SPI/I2S implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756

28.5

SPI functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757
28.5.1

General description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757

28.5.2

Communications between one master and one slave . . . . . . . . . . . . . 758

28.5.3

Standard multi-slave communication . . . . . . . . . . . . . . . . . . . . . . . . . . 760

28.5.4

Multi-master communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761

28.5.5

Slave select (NSS) pin management . . . . . . . . . . . . . . . . . . . . . . . . . . 762

28.5.6

Communication formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763

28.5.7

Configuration of SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765

28.5.8

Procedure for enabling SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766

28.5.9

Data transmission and reception procedures . . . . . . . . . . . . . . . . . . . 766

28.5.10 SPI status flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
28.5.11 SPI error flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
28.5.12 NSS pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
28.5.13 TI mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
28.5.14 CRC calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779

28.6

SPI interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781

28.7

I2S functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782
28.7.1

I2S general description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782

28.7.2

I2S full duplex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783

28.7.3

Supported audio protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784

28.7.4

Start-up description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791

28.7.5

Clock generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793

28.7.6

I2S master mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795

28.7.7

I2S slave mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797

28.7.8

I2S status flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798

28.7.9

I2S error flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799

28.7.10 DMA features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800

28.8

I2S interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800

28.9

SPI and I2S registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
28.9.1

SPI control register 1 (SPIx_CR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801

28.9.2

SPI control register 2 (SPIx_CR2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803

28.9.3

SPI status register (SPIx_SR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806

28.9.4

SPI data register (SPIx_DR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807

28.9.5

SPI CRC polynomial register (SPIx_CRCPR) . . . . . . . . . . . . . . . . . . . 807

28.9.6

SPI Rx CRC register (SPIx_RXCRCR) . . . . . . . . . . . . . . . . . . . . . . . . 809

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28.9.7

SPI Tx CRC register (SPIx_TXCRCR) . . . . . . . . . . . . . . . . . . . . . . . . 809

28.9.8

SPIx_I2S configuration register (SPIx_I2SCFGR) . . . . . . . . . . . . . . . . 810

28.9.9

SPIx_I2S prescaler register (SPIx_I2SPR) . . . . . . . . . . . . . . . . . . . . . 812

28.9.10 SPI/I2S register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813

29

Controller area network (bxCAN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814
29.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814

29.2

bxCAN main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814

29.3

bxCAN general description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815

29.4

29.5

24/1004

29.3.1

CAN 2.0B active core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815

29.3.2

Control, status and configuration registers . . . . . . . . . . . . . . . . . . . . . 815

29.3.3

Tx mailboxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815

29.3.4

Acceptance filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816

bxCAN operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
29.4.1

Initialization mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816

29.4.2

Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817

29.4.3

Sleep mode (low-power) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817

Test mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818
29.5.1

Silent mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818

29.5.2

Loop back mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819

29.5.3

Loop back combined with silent mode . . . . . . . . . . . . . . . . . . . . . . . . . 819

29.6

Behavior in debug mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820

29.7

bxCAN functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
29.7.1

Transmission handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820

29.7.2

Time triggered communication mode . . . . . . . . . . . . . . . . . . . . . . . . . . 822

29.7.3

Reception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822

29.7.4

Identifier filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823

29.7.5

Message storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827

29.7.6

Error management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829

29.7.7

Bit timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829

29.8

bxCAN interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832

29.9

CAN registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833
29.9.1

Register access protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

29.9.2

CAN control and status registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

29.9.3

CAN mailbox registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843

29.9.4

CAN filter registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850

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29.9.5

30

Universal serial bus full-speed device interface (USB) . . . . . . . . . . . 858
30.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858

30.2

USB main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858

30.3

USB implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858

30.4

USB functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
30.4.1

30.5

30.6

31

bxCAN register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854

Description of USB blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861

Programming considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862
30.5.1

Generic USB device programming . . . . . . . . . . . . . . . . . . . . . . . . . . . 862

30.5.2

System and power-on reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863

30.5.3

Double-buffered endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868

30.5.4

Isochronous transfers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870

30.5.5

Suspend/Resume events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871

USB registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
30.6.1

Common registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874

30.6.2

Buffer descriptor table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887

30.6.3

USB register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890

HDMI-CEC controller (HDMI-CEC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892
31.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892

31.2

HDMI-CEC controller main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892

31.3

HDMI-CEC functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893

31.4

31.3.1

HDMI-CEC pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893

31.3.2

HDMI-CEC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893

31.3.3

Message description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894

31.3.4

Bit timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894

Arbitration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
31.4.1

31.5

SFT option bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896

Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897
31.5.1

Bit error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897

31.5.2

Message error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897

31.5.3

Bit Rising Error (BRE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898

31.5.4

Short Bit Period Error (SBPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898

31.5.5

Long Bit Period Error (LBPE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898

31.5.6

Transmission Error Detection (TXERR) . . . . . . . . . . . . . . . . . . . . . . . . 900

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31.6

HDMI-CEC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901

31.7

HDMI-CEC registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902
31.7.1

CEC control register (CEC_CR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902

31.7.2

CEC configuration register (CEC_CFGR) . . . . . . . . . . . . . . . . . . . . . . 903

31.7.3

CEC Tx data register (CEC_TXDR) . . . . . . . . . . . . . . . . . . . . . . . . . . 906

31.7.4

CEC Rx Data Register (CEC_RXDR) . . . . . . . . . . . . . . . . . . . . . . . . . 906

31.7.5

CEC Interrupt and Status Register (CEC_ISR) . . . . . . . . . . . . . . . . . . 906

31.7.6

CEC interrupt enable register (CEC_IER) . . . . . . . . . . . . . . . . . . . . . . 908

31.7.7

HDMI-CEC register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910

Debug support (DBG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 911
32.1

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .911

32.2

Reference ARM documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912

32.3

Pinout and debug port pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 912

32.4

32.3.1

SWD port pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913

32.3.2

SW-DP pin assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913

32.3.3

Internal pull-up & pull-down on SWD pins . . . . . . . . . . . . . . . . . . . . . . 913

ID codes and locking mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913
32.4.1

32.5

SWD port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915
32.5.1

SWD protocol introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915

32.5.2

SWD protocol sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915

32.5.3

SW-DP state machine (reset, idle states, ID code) . . . . . . . . . . . . . . . 916

32.5.4

DP and AP read/write accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916

32.5.5

SW-DP registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917

32.5.6

SW-AP registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918

32.6

Core debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918

32.7

BPU (Break Point Unit) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
32.7.1

32.8

32.9

26/1004

MCU device ID code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914

BPU functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919

DWT (Data Watchpoint) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
32.8.1

DWT functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919

32.8.2

DWT Program Counter Sample Register . . . . . . . . . . . . . . . . . . . . . . 919

MCU debug component (DBGMCU) . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
32.9.1

Debug support for low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . 920

32.9.2

Debug support for timers, watchdog and I2C . . . . . . . . . . . . . . . . . . . . 920

32.9.3

Debug MCU configuration register (DBGMCU_CR) . . . . . . . . . . . . . . 920

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32.9.4

Debug MCU APB1 freeze register (DBGMCU_APB1_FZ) . . . . . . . . . 921

32.9.5

Debug MCU APB2 freeze register (DBGMCU_APB2_FZ) . . . . . . . . . 923

32.9.6

DBG register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 924

Device electronic signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925
33.1

Unique device ID register (96 bits) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925

33.2

Memory size data register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926
33.2.1

Flash size data register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926

Appendix A Code examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927
A.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927

A.2

Flash operation code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 927

A.3

A.4

A.5

A.2.1

Flash memory unlocking sequence code . . . . . . . . . . . . . . . . . . . . . . . 927

A.2.2

Main Flash programming sequence code example . . . . . . . . . . . . . . . 927

A.2.3

Page erase sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . . 928

A.2.4

Mass erase sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . . 929

A.2.5

Option byte unlocking sequence code example . . . . . . . . . . . . . . . . . . 929

A.2.6

Option byte programming sequence code example . . . . . . . . . . . . . . . 930

A.2.7

Option byte erasing sequence code example. . . . . . . . . . . . . . . . . . . . 930

Clock controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 931
A.3.1

HSE start sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . . . 931

A.3.2

PLL configuration modification code example . . . . . . . . . . . . . . . . . . . 932

A.3.3

MCO selection code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932

A.3.4

Clock measurement configuration with TIM14 code example . . . . . . . 933

GPIO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934
A.4.1

Lock sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934

A.4.2

Alternate function selection sequence code example. . . . . . . . . . . . . . 934

A.4.3

Analog GPIO configuration code example . . . . . . . . . . . . . . . . . . . . . . 935

DMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 935
A.5.1

A.6

A.7

DMA Channel Configuration sequence code example . . . . . . . . . . . . . 935

Interrupts and event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 936
A.6.1

NVIC initialization example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 936

A.6.2

External interrupt selection code example . . . . . . . . . . . . . . . . . . . . . . 936

ADC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937
A.7.1

ADC Calibration code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 937

A.7.2

ADC enable sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . 937

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A.8

A.9

28/1004

A.7.3

ADC disable sequence code example . . . . . . . . . . . . . . . . . . . . . . . . . 938

A.7.4

ADC Clock selection code example . . . . . . . . . . . . . . . . . . . . . . . . . . . 938

A.7.5

Single conversion sequence code example - Software trigger . . . . . . . 939

A.7.6

Continuous conversion sequence code example - Software trigger. . . 939

A.7.7

Single conversion sequence code example - Hardware trigger . . . . . . 940

A.7.8

Continuous conversion sequence code example - Hardware trigger . . 940

A.7.9

DMA one shot mode sequence code example . . . . . . . . . . . . . . . . . . . 941

A.7.10

DMA circular mode sequence code example . . . . . . . . . . . . . . . . . . . . 941

A.7.11

Wait mode sequence code example. . . . . . . . . . . . . . . . . . . . . . . . . . . 941

A.7.12

Auto Off and no wait mode sequence code example . . . . . . . . . . . . . . 942

A.7.13

Auto Off and wait mode sequence code example . . . . . . . . . . . . . . . . 942

A.7.14

Analog watchdog code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942

A.7.15

Temperature configuration code example. . . . . . . . . . . . . . . . . . . . . . . 943

A.7.16

Temperature computation code example . . . . . . . . . . . . . . . . . . . . . . . 943

DAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 943
A.8.1

Independent trigger without wave generation code example . . . . . . . . 943

A.8.2

Independent trigger with single LFSR generation code example . . . . . 944

A.8.3

Independent trigger with different LFSR generation code example . . . 944

A.8.4

Independent trigger with single triangle generation code example. . . . 945

A.8.5

Independent trigger with different triangle generation code example . . 945

A.8.6

Simultaneous software start code example . . . . . . . . . . . . . . . . . . . . . 945

A.8.7

Simultaneous trigger without wave generation code example . . . . . . . 946

A.8.8

Simultaneous trigger with single LFSR generation code example . . . . 946

A.8.9

Simultaneous trigger with different LFSR generation code example . . 946

A.8.10

Simultaneous trigger with single triangle generation code example . . . 947

A.8.11

Simultaneous trigger with different triangle generation code example . 947

A.8.12

DMA initialization code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948

Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949
A.9.1

Upcounter on TI2 rising edge code example . . . . . . . . . . . . . . . . . . . . 949

A.9.2

Up counter on each 2 ETR rising edges code example . . . . . . . . . . . . 950

A.9.3

Input capture configuration code example . . . . . . . . . . . . . . . . . . . . . . 950

A.9.4

Input capture data management code example . . . . . . . . . . . . . . . . . . 951

A.9.5

PWM input configuration code example . . . . . . . . . . . . . . . . . . . . . . . . 952

A.9.6

PWM input with DMA configuration code example . . . . . . . . . . . . . . . . 952

A.9.7

Output compare configuration code example . . . . . . . . . . . . . . . . . . . . 953

A.9.8

Edge-aligned PWM configuration example. . . . . . . . . . . . . . . . . . . . . . 953

A.9.9

Center-aligned PWM configuration example . . . . . . . . . . . . . . . . . . . . 954

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A.10

A.11

A.12

A.13

A.14

A.9.10

ETR configuration to clear OCxREF code example . . . . . . . . . . . . . . . 955

A.9.11

Encoder interface code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955

A.9.12

Reset mode code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956

A.9.13

Gated mode code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 956

A.9.14

Trigger mode code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 957

A.9.15

External clock mode 2 + trigger mode code example. . . . . . . . . . . . . . 957

A.9.16

One-Pulse mode code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958

A.9.17

Timer prescaling another timer code example . . . . . . . . . . . . . . . . . . . 958

A.9.18

Timer enabling another timer code example. . . . . . . . . . . . . . . . . . . . . 959

A.9.19

Master and slave synchronization code example . . . . . . . . . . . . . . . . . 960

A.9.20

Two timers synchronized by an external trigger code example . . . . . . 961

A.9.21

DMA burst feature code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 962

IRTIM code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
A.10.1

TIM16 and TIM17 configuration code example . . . . . . . . . . . . . . . . . . 963

A.10.2

IRQHandler for IRTIM code example . . . . . . . . . . . . . . . . . . . . . . . . . . 964

bxCAN code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965
A.11.1

bxCAN initialization mode code example . . . . . . . . . . . . . . . . . . . . . . . 965

A.11.2

bxCAN transmit code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965

A.11.3

bxCAN receive code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966

DBG code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
A.12.1

DBG read device ID code example . . . . . . . . . . . . . . . . . . . . . . . . . . . 966

A.12.2

DBG debug in Low-power mode code example . . . . . . . . . . . . . . . . . . 966

HDMI-CEC code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966
A.13.1

HDMI-CEC configure CEC code example . . . . . . . . . . . . . . . . . . . . . . 966

A.13.2

HDMI-CEC transmission with interrupt enabled code example . . . . . . 967

A.13.3

HDMI-CEC interrupt management code example . . . . . . . . . . . . . . . . 967

I2C code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967
A.14.1

I2C configured in master mode to receive code example. . . . . . . . . . . 967

A.14.2

I2C configured in master mode to transmit code example . . . . . . . . . . 968

A.14.3

I2C configured in slave mode code example . . . . . . . . . . . . . . . . . . . . 968

A.14.4

I2C master transmitter code example . . . . . . . . . . . . . . . . . . . . . . . . . . 968

A.14.5

I2C master receiver code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968

A.14.6

I2C slave transmitter code example . . . . . . . . . . . . . . . . . . . . . . . . . . . 969

A.14.7

I2C slave receiver code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 969

A.14.8

I2C configured in master mode to transmit with DMA code example . . 969

A.14.9

I2C configured in slave mode to receive with DMA code example . . . . 970

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A.15

A.16

A.17

A.18

A.19

IWDG code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970
A.15.1

IWDG configuration code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 970

A.15.2

IWDG configuration with window code example. . . . . . . . . . . . . . . . . . 971

RTC code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 971
A.16.1

RTC calendar configuration code example. . . . . . . . . . . . . . . . . . . . . . 971

A.16.2

RTC alarm configuration code example . . . . . . . . . . . . . . . . . . . . . . . . 972

A.16.3

RTC WUT configuration code example . . . . . . . . . . . . . . . . . . . . . . . . 972

A.16.4

RTC read calendar code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972

A.16.5

RTC calibration code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 973

A.16.6

RTC tamper and time stamp configuration code example . . . . . . . . . . 973

A.16.7

RTC tamper and time stamp code example . . . . . . . . . . . . . . . . . . . . . 974

A.16.8

RTC clock output code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974

SPI code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 974
A.17.1

SPI master configuration code example . . . . . . . . . . . . . . . . . . . . . . . . 974

A.17.2

SPI slave configuration code example . . . . . . . . . . . . . . . . . . . . . . . . . 975

A.17.3

SPI full duplex communication code example . . . . . . . . . . . . . . . . . . . 975

A.17.4

SPI interrupt code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 975

A.17.5

SPI master configuration with DMA code example. . . . . . . . . . . . . . . . 975

A.17.6

SPI slave configuration with DMA code example . . . . . . . . . . . . . . . . . 976

TSC code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976
A.18.1

TSC configuration code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976

A.18.2

TSC interrupt code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 976

USART code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
A.19.1

USART transmitter configuration code example. . . . . . . . . . . . . . . . . . 977

A.19.2

USART transmit byte code example. . . . . . . . . . . . . . . . . . . . . . . . . . . 977

A.19.3

USART transfer complete code example . . . . . . . . . . . . . . . . . . . . . . . 977

A.19.4

USART receiver configuration code example . . . . . . . . . . . . . . . . . . . . 977

A.19.5

USART receive byte code example . . . . . . . . . . . . . . . . . . . . . . . . . . . 977

A.19.6

USART LIN mode code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 978

A.19.7

USART synchronous mode code example . . . . . . . . . . . . . . . . . . . . . . 978

A.19.8

USART single-wire half-duplex code example . . . . . . . . . . . . . . . . . . . 979

A.19.9

USART smartcard mode code example . . . . . . . . . . . . . . . . . . . . . . . . 979

A.19.10 USART IrDA mode code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980
A.19.11 USART DMA code example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980
A.19.12 USART hardware flow control code example . . . . . . . . . . . . . . . . . . . . 981

A.20

30/1004

WWDG code example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 981

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A.20.1

WWDG configuration code example. . . . . . . . . . . . . . . . . . . . . . . . . . . 981

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 982

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List of tables

RM0091

List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Table 16.
Table 17.
Table 18.
Table 19.
Table 20.
Table 21.
Table 22.
Table 23.
Table 24.
Table 25.
Table 26.
Table 27.
Table 28.
Table 29.
Table 30.
Table 31.
Table 32.
Table 33.
Table 34.
Table 35.
Table 36.
Table 37.
Table 38.
Table 39.
Table 40.
Table 41.
Table 42.
Table 43.
Table 44.

32/1004

STM32F0xx peripheral register boundary addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
STM32F0xx memory boundary addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Boot modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Flash memory organization (STM32F03x, STM32F04x and
STM32F05x devices) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Flash memory organization (STM32F07x, STM32F09x devices). . . . . . . . . . . . . . . . . . . . 56
Flash memory read protection status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Access status versus protection level and execution modes . . . . . . . . . . . . . . . . . . . . . . . 65
Flash interrupt request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Flash interface - register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Option byte format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Option byte organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Option byte map and ST production values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Low-power mode summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Sleep-now . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Sleep-on-exit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Stop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Standby mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
PWR register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
RCC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Effect of low-power modes on CRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Interrupt control bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
CRS register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Port bit configuration table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
GPIO register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
SYSCFG register map and reset values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
SYSCFG register map and reset values for STM32F09x devices . . . . . . . . . . . . . . . . . . 185
Programmable data width & endian behavior (when bits PINC = MINC = 1) . . . . . . . . . . 192
DMA interrupt requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Summary of the DMA requests for each channel
on STM32F03x, STM32F04x and STM32F05x devices . . . . . . . . . . . . . . . . . . . . . . . . . . 194
Summary of the DMA requests for each channel on STM32F07x devices . . . . . . . . . . . 194
Summary of the DMA1 requests for each channel on STM32F09x devices . . . . . . . . . . 197
Summary of the DMA2 requests for each channel on STM32F09x devices . . . . . . . . . . 198
DMA register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
DMA register map and reset values (registers available on STM32F07x and STM32F09x
devices only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
DMA register map and reset values (register available on STM32F09x
devices only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
Vector table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
External interrupt/event controller register map and reset values. . . . . . . . . . . . . . . . . . . 219
STM32F0xx CRC implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
CRC internal input/output signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
CRC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
ADC internal signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
ADC pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
Latency between trigger and start of conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
Configuring the trigger polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

DocID018940 Rev 9

RM0091
Table 45.
Table 46.
Table 47.
Table 48.
Table 49.
Table 50.
Table 51.
Table 52.
Table 53.
Table 54.
Table 55.
Table 56.
Table 57.
Table 58.
Table 59.
Table 60.
Table 61.
Table 62.
Table 63.
Table 64.
Table 65.
Table 66.
Table 67.
Table 68.
Table 69.
Table 70.
Table 71.
Table 72.
Table 73.
Table 74.
Table 75.
Table 76.
Table 77.
Table 78.
Table 79.
Table 80.
Table 81.
Table 82.
Table 83.
Table 84.
Table 85.
Table 86.
Table 87.
Table 88.
Table 89.
Table 90.
Table 91.
Table 92.
Table 93.
Table 94.
Table 95.
Table 96.

List of tables
External triggers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
tSAR timings depending on resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Analog watchdog comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Analog watchdog channel selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
ADC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
ADC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
DAC pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
External triggers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
DAC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
COMP register map and reset values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
Acquisition sequence summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
Spread spectrum deviation versus AHB clock frequency . . . . . . . . . . . . . . . . . . . . . . . . . 306
I/O state depending on its mode and IODEF bit value . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
Effect of low-power modes on TSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
Interrupt control bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
TSC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Counting direction versus encoder signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
TIMx Internal trigger connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
Output control bits for complementary OCx and OCxN channels. . . . . . . . . . . . . . . . . . . 384
TIM1 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
Counting direction versus encoder signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
TIM2 and TIM3 internal trigger connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
Output control bit for standard OCx channels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
TIM2 and TIM3 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
Output control bit for standard OCx channels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
TIM14 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
TIMx Internal trigger connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
Output control bits for complementary OCx and OCxN channels with break feature . . . . 522
TIM15 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
Output control bits for complementary OCx and OCxN channels with break feature . . . . 539
TIM16 and TIM17 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
TIM6/TIM7 register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
IWDG register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
WWDG register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575
STM32F0xx RTC implementation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
RTC pin PC13 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
LSE pin PC14 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
LSE pin PC15 configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
Effect of low-power modes on RTC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594
Interrupt control bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 594
RTC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615
STM32F0xx I2C implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618
Comparison of analog vs. digital filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622
I2C-SMBUS specification data setup and hold times . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625
I2C configuration table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629
I2C-SMBUS specification clock timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640
Examples of timings settings for fI2CCLK = 8 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Examples of timings settings for fI2CCLK = 16 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Examples of timings settings for fI2CCLK = 48 MHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
SMBus timeout specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
SMBUS with PEC configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655
Examples of TIMEOUTA settings for various I2CCLK frequencies

DocID018940 Rev 9

33/1004
34

List of tables

Table 97.
Table 98.
Table 99.
Table 100.
Table 101.
Table 102.
Table 103.
Table 104.
Table 105.
Table 106.
Table 107.
Table 108.
Table 109.
Table 110.
Table 111.
Table 112.
Table 113.
Table 114.
Table 115.
Table 116.
Table 117.
Table 118.
Table 119.
Table 120.
Table 121.
Table 122.
Table 123.
Table 124.
Table 125.
Table 126.
Table 127.
Table 128.
Table 129.
Table 130.
Table 131.
Table 132.
Table 133.
Table 134.
Table 135.
Table 136.
Table 137.
Table 138.
Table 139.
Table 140.
Table 141.
Table 142.
Table 143.
Table 144.

34/1004

RM0091

(max tTIMEOUT = 25 ms) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656
Examples of TIMEOUTB settings for various I2CCLK frequencies . . . . . . . . . . . . . . . . . 656
Examples of TIMEOUTA settings for various I2CCLK frequencies
(max tIDLE = 50 µs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 657
low-power modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668
I2C Interrupt requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
I2C register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
STM32F0xx USART implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689
Noise detection from sampled data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
Error calculation for programmed baud rates at fCK = 48 MHz in both cases of
oversampling by 16 or by 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 704
Tolerance of the USART receiver when BRR [3:0] = 0000. . . . . . . . . . . . . . . . . . . . . . . . 706
Tolerance of the USART receiver when BRR [3:0] is different from 0000 . . . . . . . . . . . . 706
Frame formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710
Effect of low-power modes on the USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
USART interrupt requests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
USART register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753
STM32F0xx SPI implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
SPI interrupt requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781
Audio-frequency precision using standard 8 MHz HSE . . . . . . . . . . . . . . . . . . . . . . . . . . 794
I2S interrupt requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
SPI register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 813
Transmit mailbox mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
Receive mailbox mapping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
bxCAN register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
STM32F0xx USB implementation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 858
Double-buffering buffer flag definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
Bulk double-buffering memory buffers usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
Isochronous memory buffers usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
Resume event detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
Reception status encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
Endpoint type encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
Endpoint kind meaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
Transmission status encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886
Definition of allocated buffer memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
USB register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 890
HDMI pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893
Error handling timing parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
TXERR timing parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900
HDMI-CEC interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901
HDMI-CEC register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 910
SW debug port pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 913
DEV_ID and REV_ID field values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
Packet request (8-bits) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915
ACK response (3 bits). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
DATA transfer (33 bits) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
SW-DP registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
32-bit debug port registers addressed through the shifted value A[3:2] . . . . . . . . . . . . . . 918
Core debug registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918
DBG register map and reset values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 924
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 982

DocID018940 Rev 9

RM0091

List of figures

List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.

System architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Memory map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Programming procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Flash memory Page Erase procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Flash memory Mass Erase procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Power supply overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Power on reset/power down reset waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
PVD thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Simplified diagram of the reset circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Clock tree (STM32F03x and STM32F05x devices) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Clock tree (STM32F04x, STM32F07x and STM32F09x devices) . . . . . . . . . . . . . . . . . . . 98
HSE/ LSE clock sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Frequency measurement with TIM14 in capture mode. . . . . . . . . . . . . . . . . . . . . . . . . . . 105
CRS block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
CRS counter behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Basic structure of an I/O port bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Input floating/pull up/pull down configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Output configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Alternate function configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
High impedance-analog configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
DMA block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
DMAx request routing architecture on STM32F09x devices. . . . . . . . . . . . . . . . . . . . . . . 196
Extended interrupts and events controller (EXTI) block diagram . . . . . . . . . . . . . . . . . . . 212
External interrupt/event GPIO mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
CRC calculation unit block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
ADC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
ADC calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Enabling/disabling the ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
ADC clock scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Analog to digital conversion time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
ADC conversion timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Stopping an ongoing conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Single conversions of a sequence, software trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Continuous conversion of a sequence, software trigger . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Single conversions of a sequence, hardware trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Continuous conversions of a sequence, hardware trigger . . . . . . . . . . . . . . . . . . . . . . . . 243
Data alignment and resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Example of overrun (OVR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Wait mode conversion (continuous mode, software trigger). . . . . . . . . . . . . . . . . . . . . . . 247
Behavior with WAIT=0, AUTOFF=1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
Behavior with WAIT=1, AUTOFF=1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
Analog watchdog guarded area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Temperature sensor and VREFINT channel block diagram . . . . . . . . . . . . . . . . . . . . . . 251
DAC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Data registers in single DAC channel mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Timing diagram for conversion with trigger disabled TEN = 0 . . . . . . . . . . . . . . . . . . . . . 271
Data registers in dual DAC channel mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
DAC LFSR register calculation algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278

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41

List of figures
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
Figure 54.
Figure 55.
Figure 56.
Figure 57.
Figure 58.
Figure 59.
Figure 60.
Figure 61.
Figure 62.
Figure 63.
Figure 64.
Figure 65.
Figure 66.
Figure 67.
Figure 68.
Figure 69.
Figure 70.
Figure 71.
Figure 72.
Figure 73.
Figure 74.
Figure 75.
Figure 76.
Figure 77.
Figure 78.
Figure 79.
Figure 80.
Figure 81.
Figure 82.
Figure 83.
Figure 84.
Figure 85.
Figure 86.
Figure 87.
Figure 88.
Figure 89.
Figure 90.
Figure 91.
Figure 92.
Figure 93.
Figure 94.
Figure 95.
Figure 96.
Figure 97.
Figure 98.

36/1004

RM0091

DAC conversion (SW trigger enabled) with LFSR wave generation. . . . . . . . . . . . . . . . . 278
DAC triangle wave generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
DAC conversion (SW trigger enabled) with triangle wave generation . . . . . . . . . . . . . . . 279
Comparator 1 and 2 block diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
Comparator hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
TSC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
Surface charge transfer analog I/O group structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
Sampling capacitor voltage variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
Charge transfer acquisition sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
Spread spectrum variation principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
Advanced-control timer block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Counter timing diagram with prescaler division change from 1 to 2 . . . . . . . . . . . . . . . . . 323
Counter timing diagram with prescaler division change from 1 to 4 . . . . . . . . . . . . . . . . . 323
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
Counter timing diagram, update event when ARPE=0
(TIMx_ARR not preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Counter timing diagram, update event when repetition counter is not used . . . . . . . . . . . 330
Counter timing diagram, internal clock divided by 1, TIMx_ARR = 0x6 . . . . . . . . . . . . . . 331
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
Counter timing diagram, internal clock divided by 4, TIMx_ARR=0x36 . . . . . . . . . . . . . . 332
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
Counter timing diagram, update event with ARPE=1 (counter underflow) . . . . . . . . . . . . 333
Counter timing diagram, Update event with ARPE=1 (counter overflow) . . . . . . . . . . . . . 334
Update rate examples depending on mode and TIMx_RCR register settings . . . . . . . . . 335
Control circuit in normal mode, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . 336
TI2 external clock connection example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
Control circuit in external clock mode 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
External trigger input block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
Control circuit in external clock mode 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Capture/compare channel (example: channel 1 input stage) . . . . . . . . . . . . . . . . . . . . . . 340
Capture/compare channel 1 main circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
Output stage of capture/compare channel (channel 1 to 3) . . . . . . . . . . . . . . . . . . . . . . . 341
Output stage of capture/compare channel (channel 4). . . . . . . . . . . . . . . . . . . . . . . . . . . 341
PWM input mode timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
Output compare mode, toggle on OC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
Edge-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
Center-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
Complementary output with dead-time insertion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Dead-time waveforms with delay greater than the negative pulse. . . . . . . . . . . . . . . . . . 350
Dead-time waveforms with delay greater than the positive pulse. . . . . . . . . . . . . . . . . . . 350
Output behavior in response to a break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
Clearing TIMx OCxREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
6-step generation, COM example (OSSR=1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356

DocID018940 Rev 9

RM0091
Figure 99.
Figure 100.
Figure 101.
Figure 102.
Figure 103.
Figure 104.
Figure 105.
Figure 106.
Figure 107.
Figure 108.
Figure 109.
Figure 110.
Figure 111.
Figure 112.
Figure 113.
Figure 114.
Figure 115.
Figure 116.
Figure 117.
Figure 118.
Figure 119.
Figure 120.
Figure 121.
Figure 122.
Figure 123.
Figure 124.
Figure 125.
Figure 126.
Figure 127.
Figure 128.
Figure 129.
Figure 130.
Figure 131.
Figure 132.
Figure 133.
Figure 134.
Figure 135.
Figure 136.
Figure 137.
Figure 138.
Figure 139.
Figure 140.
Figure 141.
Figure 142.
Figure 143.
Figure 144.
Figure 145.
Figure 146.
Figure 147.
Figure 148.

List of figures
Example of one pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
Example of counter operation in encoder interface mode. . . . . . . . . . . . . . . . . . . . . . . . . 360
Example of encoder interface mode with TI1FP1 polarity inverted. . . . . . . . . . . . . . . . . . 360
Example of hall sensor interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
Control circuit in reset mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
Control circuit in gated mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
Control circuit in trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
Control circuit in external clock mode 2 + trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . 366
General-purpose timer block diagram (TIM2 and TIM3) . . . . . . . . . . . . . . . . . . . . . . . . . 394
Counter timing diagram with prescaler division change from 1 to 2 . . . . . . . . . . . . . . . . . 395
Counter timing diagram with prescaler division change from 1 to 4 . . . . . . . . . . . . . . . . . 396
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
Counter timing diagram, Update event when ARPE=0
(TIMx_ARR not preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
Counter timing diagram, Update event when ARPE=1
(TIMx_ARR preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
Counter timing diagram, Update event when repetition counter is not used . . . . . . . . . . 402
Counter timing diagram, internal clock divided by 1, TIMx_ARR=0x6 . . . . . . . . . . . . . . . 404
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
Counter timing diagram, internal clock divided by 4, TIMx_ARR=0x36 . . . . . . . . . . . . . . 405
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
Counter timing diagram, Update event with ARPE=1 (counter underflow). . . . . . . . . . . . 406
Counter timing diagram, Update event with ARPE=1 (counter overflow) . . . . . . . . . . . . . 406
Control circuit in normal mode, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . 407
TI2 external clock connection example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
Control circuit in external clock mode 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
External trigger input block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
Control circuit in external clock mode 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
Capture/compare channel (example: channel 1 input stage) . . . . . . . . . . . . . . . . . . . . . . 411
Capture/compare channel 1 main circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
Output stage of capture/compare channel (channel 1). . . . . . . . . . . . . . . . . . . . . . . . . . . 412
PWM input mode timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Output compare mode, toggle on OC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416
Edge-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
Center-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Example of one-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
Clearing TIMx OCxREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Example of counter operation in encoder interface mode . . . . . . . . . . . . . . . . . . . . . . . . 424
Example of encoder interface mode with TI1FP1 polarity inverted . . . . . . . . . . . . . . . . . 424
Control circuit in reset mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
Control circuit in gated mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
Control circuit in trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
Control circuit in external clock mode 2 + trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . 428
Master/Slave timer example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
Gating timer 2 with OC1REF of timer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430

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41

List of figures
Figure 149.
Figure 150.
Figure 151.
Figure 152.
Figure 153.
Figure 154.
Figure 155.
Figure 156.
Figure 157.
Figure 158.
Figure 159.
Figure 160.
Figure 161.
Figure 162.
Figure 163.
Figure 164.
Figure 165.
Figure 166.
Figure 167.
Figure 168.
Figure 169.
Figure 170.
Figure 171.
Figure 172.
Figure 173.
Figure 174.
Figure 175.
Figure 176.
Figure 177.
Figure 178.
Figure 179.
Figure 180.
Figure 181.
Figure 182.
Figure 183.
Figure 184.
Figure 185.
Figure 186.
Figure 187.
Figure 188.
Figure 189.
Figure 190.
Figure 191.
Figure 192.
Figure 193.
Figure 194.
Figure 195.
Figure 196.

38/1004

RM0091

Gating timer 2 with Enable of timer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
Triggering timer 2 with update of timer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
Triggering timer 2 with Enable of timer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
Triggering timer 1 and 2 with timer 1 TI1 input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
General-purpose timer block diagram (TIM14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Counter timing diagram with prescaler division change from 1 to 2 . . . . . . . . . . . . . . . . . 461
Counter timing diagram with prescaler division change from 1 to 4 . . . . . . . . . . . . . . . . . 461
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
Counter timing diagram, update event when ARPE=0
(TIMx_ARR not preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
Control circuit in normal mode, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . 465
Capture/compare channel (example: channel 1 input stage) . . . . . . . . . . . . . . . . . . . . . . 465
Capture/compare channel 1 main circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
Output stage of capture/compare channel (channel 1). . . . . . . . . . . . . . . . . . . . . . . . . . . 466
Output compare mode, toggle on OC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
Edge-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
TIM15 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
TIM16 and TIM17 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
Counter timing diagram with prescaler division change from 1 to 2 . . . . . . . . . . . . . . . . . 484
Counter timing diagram with prescaler division change from 1 to 4 . . . . . . . . . . . . . . . . . 485
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
Counter timing diagram, update event when ARPE=0
(TIMx_ARR not preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Update rate examples depending on mode and TIMx_RCR register settings . . . . . . . . . 490
Control circuit in normal mode, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . 491
TI2 external clock connection example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
Control circuit in external clock mode 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
Capture/compare channel (example: channel 1 input stage) . . . . . . . . . . . . . . . . . . . . . . 493
Capture/compare channel 1 main circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Output stage of capture/compare channel (channel 1). . . . . . . . . . . . . . . . . . . . . . . . . . . 494
Output stage of capture/compare channel (channel 2 for TIM15) . . . . . . . . . . . . . . . . . . 494
PWM input mode timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496
Output compare mode, toggle on OC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
Edge-aligned PWM waveforms (ARR=8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
Complementary output with dead-time insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
Dead-time waveforms with delay greater than the negative pulse . . . . . . . . . . . . . . . . . . 501
Dead-time waveforms with delay greater than the positive pulse. . . . . . . . . . . . . . . . . . . 502
Output behavior in response to a break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
Example of One-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
Control circuit in reset mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
Control circuit in gated mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
Control circuit in trigger mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509

DocID018940 Rev 9

RM0091
Figure 197.
Figure 198.
Figure 199.
Figure 200.
Figure 201.
Figure 202.
Figure 203.
Figure 204.
Figure 205.
Figure 206.
Figure 207.
Figure 208.
Figure 209.
Figure 210.
Figure 211.
Figure 212.
Figure 213.
Figure 214.
Figure 215.
Figure 216.
Figure 217.
Figure 218.
Figure 219.
Figure 220.
Figure 221.
Figure 222.
Figure 223.
Figure 224.
Figure 225.
Figure 226.
Figure 227.
Figure 228.
Figure 229.
Figure 230.
Figure 231.
Figure 232.
Figure 233.
Figure 234.
Figure 235.
Figure 236.
Figure 237.
Figure 238.
Figure 239.
Figure 240.
Figure 241.
Figure 242.
Figure 243.
Figure 244.
Figure 245.
Figure 246.

List of figures
Basic timer block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
Counter timing diagram with prescaler division change from 1 to 2 . . . . . . . . . . . . . . . . . 549
Counter timing diagram with prescaler division change from 1 to 4 . . . . . . . . . . . . . . . . . 549
Counter timing diagram, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
Counter timing diagram, internal clock divided by 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
Counter timing diagram, internal clock divided by 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
Counter timing diagram, internal clock divided by N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
Counter timing diagram, update event when ARPE = 0
(TIMx_ARR not preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
Control circuit in normal mode, internal clock divided by 1 . . . . . . . . . . . . . . . . . . . . . . . . 554
IR internal hardware connections with TIM16 and TIM17 . . . . . . . . . . . . . . . . . . . . . . . . 560
Independent watchdog block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
Watchdog block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
Window watchdog timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
RTC block diagram in STM32F03x, STM32F04x and STM32F05x devices
. . . . . . . . 578
RTC block diagram for STM32F07x and STM32F09x devices. . . . . . . . . . . . . . . . . . . . . 579
I2C1 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619
I2C2 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620
I2C bus protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621
Setup and hold timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623
I2C initialization flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
Data reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
Data transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628
Slave initialization flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
Transfer sequence flowchart for I2C slave transmitter, NOSTRETCH=0. . . . . . . . . . . . . 633
Transfer sequence flowchart for I2C slave transmitter, NOSTRETCH=1. . . . . . . . . . . . . 634
Transfer bus diagrams for I2C slave transmitter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635
Transfer sequence flowchart for slave receiver with NOSTRETCH=0 . . . . . . . . . . . . . . . 636
Transfer sequence flowchart for slave receiver with NOSTRETCH=1 . . . . . . . . . . . . . . . 637
Transfer bus diagrams for I2C slave receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 637
Master clock generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639
Master initialization flowchart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
10-bit address read access with HEAD10R=0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
10-bit address read access with HEAD10R=1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
Transfer sequence flowchart for I2C master transmitter for N≤255 bytes . . . . . . . . . . . . 643
Transfer sequence flowchart for I2C master transmitter for N>255 bytes . . . . . . . . . . . . 644
Transfer bus diagrams for I2C master transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
Transfer sequence flowchart for I2C master receiver for N≤255 bytes. . . . . . . . . . . . . . . 647
Transfer sequence flowchart for I2C master receiver for N >255 bytes . . . . . . . . . . . . . . 648
Transfer bus diagrams for I2C master receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
Timeout intervals for tLOW:SEXT, tLOW:MEXT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
Transfer sequence flowchart for SMBus slave transmitter N bytes + PEC. . . . . . . . . . . . 658
Transfer bus diagrams for SMBus slave transmitter (SBC=1) . . . . . . . . . . . . . . . . . . . . . 658
Transfer sequence flowchart for SMBus slave receiver N Bytes + PEC . . . . . . . . . . . . . 660
Bus transfer diagrams for SMBus slave receiver (SBC=1) . . . . . . . . . . . . . . . . . . . . . . . 661
Bus transfer diagrams for SMBus master transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662
Bus transfer diagrams for SMBus master receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664
I2C interrupt mapping diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670
USART block diagram
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691
Word length programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693

DocID018940 Rev 9

39/1004
41

List of figures
Figure 247.
Figure 248.
Figure 249.
Figure 250.
Figure 251.
Figure 252.
Figure 253.
Figure 254.
Figure 255.
Figure 256.
Figure 257.
Figure 258.
Figure 259.
Figure 260.
Figure 261.
Figure 262.
Figure 263.
Figure 264.
Figure 265.
Figure 266.
Figure 267.
Figure 268.
Figure 269.
Figure 270.
Figure 271.
Figure 272.
Figure 273.
Figure 274.
Figure 275.
Figure 276.
Figure 277.
Figure 278.
Figure 279.
Figure 280.
Figure 281.
Figure 282.
Figure 283.
Figure 284.
Figure 285.
Figure 286.
Figure 287.
Figure 288.
Figure 289.
Figure 290.
Figure 291.
Figure 292.
Figure 293.
Figure 294.
Figure 295.
Figure 296.
Figure 297.

40/1004

RM0091

Configurable stop bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
TC/TXE behavior when transmitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
Start bit detection when oversampling by 16 or 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
Data sampling when oversampling by 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
Data sampling when oversampling by 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
Mute mode using Idle line detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
Mute mode using address mark detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
Break detection in LIN mode (11-bit break length - LBDL bit is set) . . . . . . . . . . . . . . . . . 712
Break detection in LIN mode vs. Framing error detection. . . . . . . . . . . . . . . . . . . . . . . . . 713
USART example of synchronous transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
USART data clock timing diagram (M bits = 00). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
USART data clock timing diagram (M bits = 01) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
RX data setup/hold time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
ISO 7816-3 asynchronous protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
Parity error detection using the 1.5 stop bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
IrDA SIR ENDEC- block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722
IrDA data modulation (3/16) -Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
Transmission using DMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
Reception using DMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
Hardware flow control between 2 USARTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
RS232 RTS flow control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 726
RS232 CTS flow control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727
USART interrupt mapping diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
SPI block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 757
Full-duplex single master/ single slave application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
Half-duplex single master/ single slave application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
Simplex single master/single slave application (master in transmit-only/
slave in receive-only mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
Master and three independent slaves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761
Multi-master application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
Hardware/software slave select management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
Data clock timing diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
Data alignment when data length is not equal to 8-bit or 16-bit . . . . . . . . . . . . . . . . . . . . 765
Packing data in FIFO for transmission and reception . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
Master full-duplex communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
Slave full-duplex communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
Master full-duplex communication with CRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
Master full-duplex communication in packed mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
NSSP pulse generation in Motorola SPI master mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
TI mode transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
I2S block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782
Full-duplex communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784
I2S Philips protocol waveforms (16/32-bit full accuracy). . . . . . . . . . . . . . . . . . . . . . . . . . 785
I2S Philips standard waveforms (24-bit frame) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
Transmitting 0x8EAA33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786
Receiving 0x8EAA33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 786
I2S Philips standard (16-bit extended to 32-bit packet frame) . . . . . . . . . . . . . . . . . . . . . 786
Example of 16-bit data frame extended to 32-bit channel frame . . . . . . . . . . . . . . . . . . . 786
MSB Justified 16-bit or 32-bit full-accuracy length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
MSB justified 24-bit frame length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
MSB justified 16-bit extended to 32-bit packet frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
LSB justified 16-bit or 32-bit full-accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788

DocID018940 Rev 9

RM0091
Figure 298.
Figure 299.
Figure 300.
Figure 301.
Figure 302.
Figure 303.
Figure 304.
Figure 305.
Figure 306.
Figure 307.
Figure 308.
Figure 309.
Figure 310.
Figure 311.
Figure 312.
Figure 313.
Figure 314.
Figure 315.
Figure 316.
Figure 317.
Figure 318.
Figure 319.
Figure 320.
Figure 321.
Figure 322.
Figure 323.
Figure 324.
Figure 325.
Figure 326.
Figure 327.
Figure 328.
Figure 329.
Figure 330.
Figure 331.
Figure 332.
Figure 333.
Figure 334.
Figure 335.

List of figures
LSB justified 24-bit frame length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
Operations required to transmit 0x3478AE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
Operations required to receive 0x3478AE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
LSB justified 16-bit extended to 32-bit packet frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
Example of 16-bit data frame extended to 32-bit channel frame . . . . . . . . . . . . . . . . . . . 790
PCM standard waveforms (16-bit) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790
PCM standard waveforms (16-bit extended to 32-bit packet frame). . . . . . . . . . . . . . . . . 791
Start sequence in master mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792
Audio sampling frequency definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
I2S clock generator architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
CAN network topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815
bxCAN operating modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818
bxCAN in silent mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819
bxCAN in loop back mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819
bxCAN in combined mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820
Transmit mailbox states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821
Receive FIFO states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822
Filter bank scale configuration - register organization . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
Example of filter numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
Filtering mechanism - example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 827
CAN error state diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 828
Bit timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
CAN frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
Event flags and interrupt generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
Can mailbox registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
USB peripheral block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
Packet buffer areas with examples of buffer description table locations . . . . . . . . . . . . . 864
HDMI-CEC block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893
Message structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 894
Bit timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
Signal free time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895
Arbitration phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896
SFT of three nominal bit periods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896
Error bit timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 897
Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
TXERR detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900
Block diagram of STM32F0xx MCU and Cortex®-M0-level debug support . . . . . . . . . . . 911

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1

Documentation conventions

1.1

List of abbreviations for registers
The following abbreviations are used in register descriptions:

read/write (rw)

Software can read and write to this bit.

read-only (r)

Software can only read this bit.

write-only (w)

Software can only write to this bit. Reading this bit returns the reset value.

read/clear (rc_w1) Software can read as well as clear this bit by writing 1. Writing ‘0’ has no effect on the
bit value.
read/clear (rc_w0) Software can read as well as clear this bit by writing 0. Writing ‘1’ has no effect on the
bit value.
read/clear by read Software can read this bit. Reading this bit automatically clears it to ‘0’. Writing this bit
(rc_r)
has no effect on the bit value.
read/set (rs)

Software can read as well as set this bit. Writing ‘0’ has no effect on the bit value.

Reserved (Res.)

Reserved bit, must be kept at reset value.

1.2

Glossary
This section gives a brief definition of acronyms and abbreviations used in this document:

1.3

•

Word: data of 32-bit length.

•

Half-word: data of 16-bit length.

•

Byte: data of 8-bit length.

•

SWD-DP (SWD DEBUG PORT): SWD-DP provides a 2-pin (clock and data) interface
based on the Serial Wire Debug (SWD) protocol. Please refer to the Cortex®-M0
technical reference manual.

•

IAP (in-application programming): IAP is the ability to re-program the Flash memory
of a microcontroller while the user program is running.

•

ICP (in-circuit programming): ICP is the ability to program the Flash memory of a
microcontroller using the JTAG protocol, the SWD protocol or the bootloader while the
device is mounted on the user application board.

•

Option bytes: product configuration bits stored in the Flash memory.

•

OBL: option byte loader.

•

AHB: advanced high-performance bus.

•

APB: advanced peripheral bus.

Peripheral availability
For peripheral availability and number across all sales types, please refer to the particular
device datasheet.

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System and memory overview

2

System and memory overview

2.1

System architecture
The main system consists of:
•

•

Up to three masters:
–

Cortex®-M0 core

–

General-purpose DMA1

–

General purpose DMA2 (available on STM32F09x devices only)

Four slaves:
–

Internal SRAM

–

Internal Flash memory

–

AHB1 with AHB to APB bridge which connects all the APB peripherals

–

AHB2 dedicated to GPIO ports

These are interconnected using a multilayer AHB bus architecture as shown in Figure 1:
Figure 1. System architecture

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System bus
This bus connects the system bus of the Cortex®-M0 core (peripherals bus) to a BusMatrix
which manages the arbitration between the core and the DMA.

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System and memory overview

RM0091

DMA bus
This bus connects the AHB master interface of the DMA to the BusMatrix which manages
the access of CPU and DMA to SRAM, Flash memory and peripherals.

BusMatrix
The BusMatrix manages the access arbitration between the core system bus and the DMA
master bus. The arbitration uses a Round Robin algorithm. The BusMatrix is composed of
up to three masters (CPU, DMA1, DMA2) and four slaves (FLITF, SRAM, AHB1 with AHB to
APB bridge and AHB2).
AHB peripherals are connected on system bus through a BusMatrix to allow DMA access.

AHB to APB bridge (APB)
The AHB to APB bridge provides full synchronous connections between the AHB and the
APB bus.
Refer to Section 2.2.2: Memory map and register boundary addresses for the address
mapping of the peripherals connected to this bridge.
After each device reset, all peripheral clocks are disabled (except for the SRAM and Flash).
Before using a peripheral you have to enable its clock in the RCC_AHBENR,
RCC_APB2ENR or RCC_APB1ENR register.
Note:

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When a 16- or 8-bit access is performed on an APB register, the access is transformed into
a 32-bit access: the bridge duplicates the 16- or 8-bit data to feed the 32-bit vector.

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2.2

Memory organization

2.2.1

Introduction
Program memory, data memory, registers and I/O ports are organized within the same linear
4-Gbyte address space.
The bytes are coded in memory in Little Endian format. The lowest numbered byte in a word
is considered the word’s least significant byte and the highest numbered byte the most
significant.
The addressable memory space is divided into 8 main blocks, of 512 Mbytes each.
Figure 2. Memory map
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All the memory areas that are not allocated to on-chip memories and peripherals are
considered “Reserved”. For the detailed mapping of available memory and register areas,
please refer to Memory map and register boundary addresses and peripheral sections.

2.2.2

Memory map and register boundary addresses
See the datasheet corresponding to your device for a comprehensive diagram of the
memory map.
The following table gives the boundary addresses of the peripherals available in the
devices.
Table 1. STM32F0xx peripheral register boundary addresses

Bus

AHB2

AHB1

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Boundary address

Size

Peripheral

Peripheral register map

0xE000 0000 - 0xE00F FFFF

1MB

Cortex®-M0 internal
peripherals

0x4800 1800 - 0x5FFF FFFF

~384 MB

Reserved

0x4800 1400 - 0x4800 17FF

1KB

GPIOF

Section 8.4.12 on page 163

0x4800 1000 - 0x4800 13FF

1KB

GPIOE

Section 8.4.12 on page 163

0x4800 0C00 - 0x4800 0FFF

1KB

GPIOD

Section 8.4.12 on page 163

0x4800 0800 - 0x4800 0BFF

1KB

GPIOC

Section 8.4.12 on page 163

0x4800 0400 - 0x4800 07FF

1KB

GPIOB

Section 8.4.12 on page 163

0x4800 0000 - 0x4800 03FF

1KB

GPIOA

Section 8.4.12 on page 163

0x4002 4400 - 0x47FF FFFF

~128 MB

Reserved

0x4002 4000 - 0x4002 43FF

1 KB

TSC

0x4002 3400 - 0x4002 3FFF

3 KB

Reserved

0x4002 3000 - 0x4002 33FF

1 KB

CRC

0x4002 2400 - 0x4002 2FFF

3 KB

Reserved

0x4002 2000 - 0x4002 23FF

1 KB

FLASH interface

0x4002 1400 - 0x4002 1FFF

3 KB

Reserved

0x4002 1000 - 0x4002 13FF

1 KB

RCC

0x4002 0800 - 0x4002 0FFF

2 KB

Reserved

0x4002 0400 - 0x4002 07FF

1 KB

DMA2

Section 10.4.8 on page 206

0x4002 0000 - 0x4002 03FF

1 KB

DMA

Section 10.4.8 on page 206

0x4001 8000 - 0x4001 FFFF

32 KB

Reserved

DocID018940 Rev 9

Section 16.6.11 on page 318

Section 12.5.6 on page 226

Section 3.5.9 on page 73

Section 6.4.15 on page 135

RM0091
Table 1. STM32F0xx peripheral register boundary addresses (continued)
Bus

APB

Boundary address

Size

Peripheral

Peripheral register map

0x4001 5C00 - 0x4001 7FFF

9 KB

Reserved

0x4001 5800 - 0x4001 5BFF

1 KB

DBGMCU

0x4001 4C00 - 0x4001 57FF

3 KB

Reserved

0x4001 4800 - 0x4001 4BFF

1 KB

TIM17

Section 20.6.16 on page 545

0x4001 4400 - 0x4001 47FF

1 KB

TIM16

Section 20.6.16 on page 545

0x4001 4000 - 0x4001 43FF

1 KB

TIM15

Section 20.5.18 on page 528

0x4001 3C00 - 0x4001 3FFF

1 KB

Reserved

0x4001 3800 - 0x4001 3BFF

1 KB

USART1

0x4001 3400 - 0x4001 37FF

1 KB

Reserved

0x4001 3000 - 0x4001 33FF

1 KB

SPI1/I2S1

Section 28.9.10 on page 813

0x4001 2C00 - 0x4001 2FFF

1 KB

TIM1

Section 17.4.21 on page 391

0x4001 2800 - 0x4001 2BFF

1 KB

Reserved

0x4001 2400 - 0x4001 27FF

1 KB

ADC

0x4001 2000 - 0x4001 23FF

1 KB

Reserved

0x4001 1C00 -0x4001 1FFF

1 KB

USART8

Section 27.8.12 on page 753

0x4001 1800 - 0x4001 1BFF

1 KB

USART7

Section 27.8.12 on page 753

0x4001 1400 - 0x4001 17FF

1 KB

USART6

Section 27.8.12 on page 753

0x4001 0800 - 0x4001 13FF

3 KB

Reserved

0x4001 0400 - 0x4001 07FF

1 KB

EXTI

Section 11.3.7 on page 219

0x4001 0000 - 0x4001 03FF

1 KB

SYSCFG
COMP

Section 9.1.38 on page 185

0x4000 8000 - 0x4000 FFFF

32 KB

Section 32.9.6 on page 924

Section 27.8.12 on page 753

Section 13.12.11 on page 267

Section 15.5.2 on page 300

Reserved

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Table 1. STM32F0xx peripheral register boundary addresses (continued)
Bus

APB

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Boundary address

Size

Peripheral

Peripheral register map

0x4000 7C00 - 0x4000 7FFF

1 KB

Reserved

0x4000 7800 - 0x4000 7BFF

1 KB

CEC

Section 31.7.7 on page 910

0x4000 7400 - 0x4000 77FF

1 KB

DAC

Section 14.10.15 on page 291

0x4000 7000 - 0x4000 73FF

1 KB

PWR

Section 5.4.3 on page 92

0x4000 6C00 - 0x4000 6FFF

1 KB

CRS

Section 7.6.5 on page 147

0x4000 6800 - 0x4000 6BFF

1 KB

Reserved

0x4000 6400 - 0x4000 67FF

1 KB

CAN

Section 29.9.5 on page 854

0x4000 6000 - 0x4000 63FF

1 KB

USB/CAN SRAM

Section 30.6.3 on page 890

0x4000 5C00 - 0x4000 5FFF

1 KB

USB

Section 30.6.3 on page 890

0x4000 5800 - 0x4000 5BFF

1 KB

I2C2

Section 26.7.12 on page 685

0x4000 5400 - 0x4000 57FF

1 KB

I2C1

Section 26.7.12 on page 685

0x4000 5000 - 0x4000 53FF

1 KB

USART5

Section 27.8.12 on page 753

0x4000 4C00 - 0x4000 4FFF

1 KB

USART4

Section 27.8.12 on page 753

0x4000 4800 - 0x4000 4BFF

1 KB

USART3

Section 27.8.12 on page 753

0x4000 4400 - 0x4000 47FF

1 KB

USART2

Section 27.8.12 on page 753

0x4000 3C00 - 0x4000 43FF

2 KB

Reserved

0x4000 3800 - 0x4000 3BFF

1 KB

SPI2

0x4000 3400 - 0x4000 37FF

1 KB

Reserved

0x4000 3000 - 0x4000 33FF

1 KB

IWDG

Section 23.4.6 on page 569

0x4000 2C00 - 0x4000 2FFF

1 KB

WWDG

Section 24.4.4 on page 575

0x4000 2800 - 0x4000 2BFF

1 KB

RTC

Section 25.7.18 on page 615

0x4000 2400 - 0x4000 27FF

1 KB

Reserved

0x4000 2000 - 0x4000 23FF

1 KB

TIM14

0x4000 1800 - 0x4000 1FFF

2 KB

Reserved

0x4000 1400 - 0x4000 17FF

1 KB

TIM7

Section 21.4.9 on page 559

0x4000 1000 - 0x4000 13FF

1 KB

TIM6

Section 21.4.9 on page 559

0x4000 0800 - 0x4000 0FFF

2 KB

Reserved

0x4000 0400 - 0x4000 07FF

1 KB

TIM3

Section 18.4.19 on page 457

0x4000 0000 - 0x4000 03FF

1 KB

TIM2

Section 18.4.19 on page 457

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Section 19.4.12 on page 478

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Table 2. STM32F0xx memory boundary addresses
Device

STM32F03x

STM32F04x

STM32F05x

Boundary address

Size

Memory Area

0x2000 1000 - 0x3FFF FFFF

~512 MB

Reserved

0x2000 0000 - 0x2000 0FFF

4 KB

SRAM

0x1FFF FC00 - 0x1FFF FFFF 1 KB

Reserved

0x1FFF F800 - 0x1FFF FBFF 1 KB

Option bytes

0x1FFF EC00 - 0x1FFF F7FF 3 KB

System memory

0x0800 8000 - 0x1FFF EBFF

~384 MB

Reserved

0x0800 0000 - 0x0800 7FFF

32 KB

Main Flash memory

0x0000 8000 - 0x07FF FFFF

~128 MB

Reserved

0x0000 0000 - 0x0000 7FFF

32 KB

Main Flash memory,
system memory or SRAM
depending on BOOT
configuration

0x2000 1800 - 0x3FFF FFFF

~512 MB

Reserved

0x2000 0000 - 0x2000 17FF

6 KB

SRAM

0x1FFF FC00 - 0x1FFF FFFF 1 KB

Reserved

0x1FFF F800 - 0x1FFF FBFF 1 KB

Option bytes

0x1FFF C400 - 0x1FFF F7FF 13 KB

System memory

0x0801 8000- 0x1FFF C7FF

~384 MB

Reserved

0x0800 0000 - 0x0801 7FFF

32 KB

Main Flash memory

0x0001 8000 - 0x07FF FFFF

~128 MB

Reserved

0x0000 0000 - 0x0000 7FFF

32 KB

Main Flash memory,
system memory or SRAM
depending on BOOT
configuration

0x2000 2000 - 0x3FFF FFFF

~512 MB

Reserved

0x2000 0000 - 0x2000 1FFF

8 KB

SRAM

0x1FFF FC00 - 0x1FFF FFFF 1 KB

Reserved

0x1FFF F800 - 0x1FFF FBFF 1 KB

Option bytes

0x1FFF EC00 - 0x1FFF F7FF 3 KB

System memory

0x0801 0000 - 0x1FFF EBFF

~384 MB

Reserved

0x0800 0000 - 0x0800 FFFF

64 KB

Main Flash memory

0x0001 0000 - 0x07FF FFFF

~128 MB

Reserved

64 KB

Main Flash memory,
system memory or SRAM
depending on BOOT
configuration

0x0000 0000 - 0x0000 FFFF

DocID018940 Rev 9

Register description

Section 2.3 on page 50

Section 4 on page 74

Section 3 on page 54

Section 2.3 on page 50

Section 4 on page 74

Section 3 on page 54

Section 2.3 on page 50

Section 4 on page 74

Section 3 on page 54

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Table 2. STM32F0xx memory boundary addresses (continued)
Device

STM32F07x

STM32F09x

Boundary address

Size

0x2000 4000 - 0x3FFF FFFF

~512 MB

Reserved

0x2000 0000 - 0x2000 3FFF

16 KB

SRAM

Section 2.3 on page 50

0x1FFF F800 - 0x1FFF FFFF 2 KB

Option bytes

Section 4 on page 74

0x1FFF C800 - 0x1FFF F7FF 12 KB

System memory

0x0802 0000 - 0x1FFF C7FF

~384 MB

Reserved

0x0800 0000 - 0x0801 FFFF

128 KB

Main Flash memory

0x0002 0000 - 0x07FF FFFF

~128 MB

Reserved

0x0000 0000 - 0x0001 FFFF

128 KB

Main Flash memory,
system memory or SRAM
depending on BOOT
configuration

0x2000 8000 - 0x3FFF FFFF

~512 MB

Reserved

0x2000 0000 - 0x2000 7FFF

32 KB

SRAM

Section 2.3 on page 50

0x1FFF F800 - 0x1FFF FFFF 2 KB

Option bytes

Section 4 on page 74

0x1FFF D800 - 0x1FFF F7FF 8 KB

System memory

0x0804 0000 - 0x1FFF D7FF

~384 MB

Reserved

0x0800 0000 - 0x0803 FFFF

256 KB

Main Flash memory

0x0004 0000 - 0x07FF FFFF

~128 MB

Reserved

256 KB

Main Flash memory,
system memory or SRAM
depending on BOOT
configuration

0x0000 0000 - 0x0003 FFFF

2.3

Memory Area

Register description

Section 3 on page 54

Section 3 on page 54

Embedded SRAM
STM32F03x devices feature 4 Kbytes of static SRAM. STM32F04x devices feature
6 Kbytes of static SRAM. STM32F05x devices feature 8 Kbytes of static SRAM.
STM32F07xS devices feature 16 Kbytes of static SRAM. STM32F09x devices feature
32 Kbytes of static SRAM.
This RAM can be accessed as bytes, half-words (16 bits) or full words (32 bits). This
memory can be addressed at maximum system clock frequency without wait state and thus
by both CPU and DMA.
Parity check
The user can enable the parity check using the option bit RAM_PARITY_CHECK in the user
option byte (refer to Section 4: Option byte).
The data bus width is 36 bits because 4 bits are available for parity check (1 bit per byte) in
order to increase memory robustness, as required for instance by Class B or SIL norms.
The parity bits are computed and stored when writing into the SRAM. Then, they are
automatically checked when reading. If one bit fails, an NMI is generated. The same error
can also be linked to the BRK_IN Break input of TIM1/15/16/17, with the

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SRAM_PARITY_LOCK control bit in the SYSCFG configuration register 2
(SYSCFG_CFGR2). The SRAM Parity Error flag (SRAM_PEF) is available in the SYSCFG
configuration register 2 (SYSCFG_CFGR2).
Note:

When enabling the RAM parity check, it is advised to initialize by software the whole RAM
memory at the beginning of the code, to avoid getting parity errors when reading noninitialized locations.

2.4

Flash memory overview
The Flash memory is composed of two distinct physical areas:
•

The main Flash memory block. It contains the application program and user data if
necessary.

•

The information block. It is composed of two parts:
–

Option bytes for hardware and memory protection user configuration.

–

System memory which contains the proprietary boot loader code.
Please, refer to Section 3: Embedded Flash memory for more details.

The Flash interface implements instruction access and data access based on the AHB
protocol. It implements the prefetch buffer that speeds up CPU code execution. It also
implements the logic necessary to carry out the Flash memory operations (Program/Erase)
controlled through the Flash registers.

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2.5

Boot configuration
In the STM32F0xx, three different boot modes can be selected through the BOOT0 pin and
boot configuration bits nBOOT1, BOOT_SEL and nBOOT0 in the User option byte, as
shown in the following table.
Table 3. Boot modes (1)
Boot mode configuration
Mode

nBOOT1
bit

BOOT0
pin

BOOT_SEL
bit

nBOOT0
bit

x

0

1

x

Main Flash memory is selected as boot area(2)

1

1

1

x

System memory is selected as boot area

0

1

1

x

Embedded SRAM is selected as boot area

x

x

0

1

Main Flash memory is selected as boot area

1

x

0

0

System memory is selected as boot area

0

x

0

0

Embedded SRAM is selected as boot area

1. Grey options are available on STM32F04x and STM32F09x devices only.
2. For STM32F04x and STM32F09x devices, see also Empty check description.

The boot mode configuration is latched on the 4th rising edge of SYSCLK after a reset. It is
up to the user to set boot mode configuration related to the required boot mode.
The boot mode configuration is also re-sampled when exiting from Standby mode.
Consequently they must be kept in the required Boot mode configuration in Standby mode.
After this startup delay has elapsed, the CPU fetches the top-of-stack value from address
0x0000 0000, then starts code execution from the boot memory at 0x0000 0004.
Depending on the selected boot mode, main Flash memory, system memory or SRAM is
accessible as follows:
•

Boot from main Flash memory: the main Flash memory is aliased in the boot memory
space (0x0000 0000), but still accessible from its original memory space
(0x0800 0000). In other words, the Flash memory contents can be accessed starting
from address 0x0000 0000 or 0x0800 0000.

•

Boot from system memory: the system memory is aliased in the boot memory space
(0x0000 0000), but still accessible from its original memory space (0x1FFF EC00 on
STM32F03x and STM32F05x devices, 0x1FFF C400 on STM32F04x devices, 0x1FFF
C800 on STM32F07x and 0x1FFF D800 on STM32F09x devices).

•

Boot from the embedded SRAM: the SRAM is aliased in the boot memory space
(0x0000 0000), but it is still accessible from its original memory space (0x2000 0000).

Empty check
On STM32F04x and STM32F09x devices only, internal empty check flag is implemented to
allow easy programming of the virgin devices by the boot loader. This flag is used when
BOOT0 pin is defining Main Flash memory as the target boot area. When the flag is set, the
device is considered as empty and System memory (boot loader) is selected instead of the
Main Flash as a boot area to allow user to program the Flash memory.

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This flag is updated only during Option bytes loading: it is set when the content of the
address 0x08000 0000 is read as 0xFFFF FFFF, otherwise it is cleared. It means a power
on or setting of OBL_LAUNCH bit in FLASH_CR register is needed to clear this flag after
programming of a virgin device to execute user code after System reset.
Note:

If the device is programmed for a first time but the Option bytes are not reloaded, the device
will still select System memory as a boot area after a System reset. In the STM32F04x, the
boot loader code is able to detect this situation. It then changes the boot memory mapping
to Main Flash and performs a jump to user code programmed there. In the STM32F09x, a
POR must be performed or the Option bytes reloaded before applying the system reset.

Physical remap
Once the boot mode is selected, the application software can modify the memory accessible
in the code area. This modification is performed by programming the MEM_MODE bits in
the SYSCFG configuration register 1 (SYSCFG_CFGR1). Unlike Cortex® M3 and M4, the
M0 CPU does not support the vector table relocation. For application code which is located
in a different address than 0x0800 0000, some additional code must be added in order to be
able to serve the application interrupts. A solution will be to relocate by software the vector
table to the internal SRAM:
•

Copy the vector table from the Flash (mapped at the base of the application load
address) to the base address of the SRAM at 0x2000 0000.

•

Remap SRAM at address 0x0000 0000, using SYSCFG configuration register 1.

•

Then once an interrupt occurs, the Cortex®-M0 processor will fetch the interrupt
handler start address from the relocated vector table in SRAM, then it will jump to
execute the interrupt handler located in the Flash.

This operation should be done at the initialization phase of the application. Please refer to
AN4065 and attached IAP code from www.st.com for more details.

Embedded boot loader
The embedded boot loader is located in the System memory, programmed by ST during
production. It is used to reprogram the Flash memory using one of the following serial
interfaces:
•

USART on pins PA14/PA15 or PA9/PA10

•

I2C on pins PB6/PB7 (STM32F04xxx, STM32F07xxx and STM32F09xxx devices only)

•

USB DFU interface (STM32F04xxx and STM32F07xxx devices only)

For further details, please refer to AN2606.

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3

Embedded Flash memory

3.1

Flash main features
•

Up to 256 Kbyte of Flash memory

•

Memory organization:
–

Main Flash memory block:
Up to 64 Kword (64 K × 32 bits)

–

Information block:
Up to 3 Kword (3 K × 32 bits) for the system memory

–

Up to 2 x 8 byte for the option byte

Flash memory interface features:
•

Read interface with prefetch buffer

•

Option byte Loader

•

Flash Program / Erase operation

•

Read / Write protection

•

Low-power mode

3.2

Flash memory functional description

3.2.1

Flash memory organization
The Flash memory is organized as 32-bit wide memory cells that can be used for storing
both code and data constants.
The memory organization of STM32F03x, STM32F04x and STM32F05x devices is based
on a main Flash memory block containing up to 64 pages of 1 Kbyte or up to 16 sectors of 4
Kbytes (4 pages). The sector is the granularity of the write protection (see Section 3.3:
Memory protection on page 64).
The memory organization of STM32F07x and STM32F09x devices is based on a main
Flash memory block containing up to 128 pages of 2 Kbytes or up to 64 sectors of 4 Kbytes
(2 pages). The sector is the granularity of the write protection (see Section 3.3: Memory
protection on page 64).
The information block is divided into two parts:

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1.

System memory: used to boot the device in System memory boot mode. The area is
reserved for use by STMicroelectronics and contains the boot loader which is used to
reprogram the Flash memory through the selected communication interface. It is
programmed by ST when the device is manufactured, and protected against spurious
write/erase operations. For further details, please refer to AN2606.

2.

Option byte

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Table 4. Flash memory organization (STM32F03x, STM32F04x and
STM32F05x devices)

Flash area

Main Flash
memory

Flash memory addresses

Size (byte)

Name

0x0800 0000 - 0x0800 03FF

1 Kbyte

Page 0

0x0800 0400 - 0x0800 07FF

1 Kbyte

Page 1

0x0800 0800 - 0x0800 0BFF

1 Kbyte

Page 2

0x0800 0C00 - 0x0800 0FFF

1 Kbyte

Page 3

.
.
.

.
.
.

.
.
.

0x0800 7000 - 0x0800 73FF

1 Kbyte

Page 28

0x0800 7400 - 0x0800 77FF

1 Kbyte

Page 29

0x0800 7800 - 0x0800 7BFF

1 Kbyte

Page 30

0x0800 7C00 - 0x0800 7FFF

1 Kbyte

Page 31

.
.
.

.
.
.

.
.
.

0x0800 F000 - 0x0800 F3FF

1 Kbyte

Page 60

0x0800 F400 - 0x0800 F7FF

1 Kbyte

Page 61

0x0800 F800 - 0x0800 FBFF

1 Kbyte

Page 62

0x0800 FC00 - 0x0800 FFFF

1 Kbyte

Page 63

Description

Sector 0

.
.
.

Sector 7 (1)

.
.
.

Sector 15

0x1FFF EC00 - 0x1FFF F7FF

3

Kbyte(2)

-

System memory

0x1FFF C400 -0x1FFF F7FF

13 Kbyte(3)

-

System memory

0x1FFF F800 - 0x1FFF F80F

2 x 8 byte

-

Option byte

Information
block

1. Main Flash memory space of STM32F03x and STM32F04x devices is limited to sector 7.
2. STM32F03x and STM32F05xdevices
3. STM32F04x devices

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Table 5. Flash memory organization (STM32F07x, STM32F09x devices)
Flash area

Main Flash
memory

Flash memory addresses

Size (byte)

Name

0x0800 0000 - 0x0800 07FF

2 Kbytes

Page 0

0x0800 0800 - 0x0800 0FFF

2 Kbytes

Page 1

.
.
.

.
.
.

.
.
.

0x0801 F000 - 0x0801 F7FF

2 Kbytes

Page 62

0x0801 F800 - 0x0801 FFFF

2 Kbytes

Page 63

.
.
.

.
.
.

.
.
.

.
.
.

0x0803 F000 - 0x0803 F7FF

2 Kbytes

Page 126

-

0x0803 F800 - 0x0803 FFFF

2 Kbytes

Page 127

-

-

System memory

0x1FFF C800 - 0x1FFF F7FF
Information
block

(2)

12 Kbytes

(3)

Description
Sector 0
.
.
.
Sector 31(1)

0x1FFF D800 - 0x1FFF F7FF

8 Kbytes

-

System memory

0x1FFF F800 - 0x1FFF F80F

2 x 8 byte

-

Option byte

1. The main Flash memory space of STM32F07x is limited to sector 31.
2. STM32F07x devices only.
3. STM32F09x devices only.

Read operations
The embedded Flash module can be addressed directly, as a common memory space. Any
data read operation accesses the content of the Flash module through dedicated read
senses and provides the requested data.
The instruction fetch and the data access are both done through the same AHB bus. Read
accesses can be performed with the following options managed through the Flash access
control register (FLASH_ACR):
•

Instruction fetch: Prefetch buffer enabled for a faster CPU execution

•

Latency: number of wait states for a correct read operation (from 0 to 1)

Instruction fetch
The Cortex®-M0 fetches the instruction over the AHB bus. The prefetch block aims at
increasing the efficiency of instruction fetching.

Prefetch buffer
The prefetch buffer is 3-block wide where each block consists of 4 bytes. The prefetch
blocks are direct-mapped. A block can be completely replaced on a single read to the Flash
memory as the size of the block matches the bandwidth of the Flash memory.
The implementation of this prefetch buffer makes a faster CPU execution possible as the
CPU fetches one word at a time with the next word readily available in the prefetch buffer.
This implies that the acceleration ratio will be of the order of 2 assuming that the code is
aligned at a 32-bit boundary for the jumps.

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However the prefetch buffer has an impact on the performance only when the wait state
number is 1. In the other case (no wait state) the performance remains the same whatever
the prefetch buffer status. There could be some impacts on the power consumption but this
is strongly dependent from the actual application code.

Prefetch controller
The prefetch controller decides to access the Flash memory depending on the available
space in the prefetch buffer. The Controller initiates a read request when there is at least
one block free in the prefetch buffer.
After reset, the state of the prefetch buffer is on.
The prefetch buffer is usually switched on/off during the initialization routine, while the
microcontroller is running on the internal 8 MHz RC (HSI) oscillator.

Access latency
In order to maintain the control signals to read the Flash memory, the ratio of the prefetch
controller clock period to the access time of the Flash memory has to be programmed in the
Flash access control register with the LATENCY[2:0] bits. This value gives the number of
cycles needed to maintain the control signals of the Flash memory and correctly read the
required data. After reset, the value is zero and only one cycle without additional wait states
is required to access the Flash memory.

3.2.2

Flash program and erase operations
The STM32F0xx embedded Flash memory can be programmed using in-circuit
programming or in-application programming.
The in-circuit programming (ICP) method is used to update the entire contents of the
Flash memory, using the SWD protocol or the boot loader to load the user application into
the microcontroller. ICP offers quick and efficient design iterations and eliminates
unnecessary package handling or socketing of devices.
In contrast to the ICP method, in-application programming (IAP) can use any
communication interface supported by the microcontroller (I/Os, USB, CAN, USART, I2C,
SPI, etc.) to download programming data into memory. IAP allows the user to re-program
the Flash memory while the application is running. Nevertheless, part of the application has
to have been previously programmed in the Flash memory using ICP.
The program and erase operations can be performed over the whole product voltage range.
They are managed through the following seven Flash registers:
•

Key register (FLASH_KEYR)

•

Option byte key register (FLASH_OPTKEYR)

•

Flash control register (FLASH_CR)

•

Flash status register (FLASH_SR)

•

Flash address register (FLASH_AR)

•

Option byte register (FLASH_OBR)

•

Write protection register (FLASH_WRPR)

An ongoing Flash memory operation will not block the CPU as long as the CPU does not
access the Flash memory.

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On the contrary, during a program/erase operation to the Flash memory, any attempt to read
the Flash memory will stall the bus. The read operation will proceed correctly once the
program/erase operation has completed. This means that code or data fetches cannot be
made while a program/erase operation is ongoing.
For program and erase operations on the Flash memory (write/erase), the internal RC
oscillator (HSI) must be ON.

Unlocking the Flash memory
After reset, the Flash memory is protected against unwanted write or erase operations. The
FLASH_CR register is not accessible in write mode, except for the OBL_LAUNCH bit, used
to reload the option bits. An unlocking sequence should be written to the FLASH_KEYR
register to open the access to the FLASH_CR register. This sequence consists of two write
operations:
•

Write KEY1 = 0x45670123

•

Write KEY2 = 0xCDEF89AB

Any wrong sequence locks up the FLASH_CR register until the next reset.
In the case of a wrong key sequence, a bus error is detected and a Hard Fault interrupt is
generated. This is done after the first write cycle if KEY1 does not match, or during the
second write cycle if KEY1 has been correctly written but KEY2 does not match.
The FLASH_CR register can be locked again by user software by writing the LOCK bit in the
FLASH_CR register to 1.
For code example refer to the Appendix section A.2.1: Flash memory unlocking sequence
code.

Main Flash memory programming
The main Flash memory can be programmed 16 bits at a time. The program operation is
started when the CPU writes a half-word into a main Flash memory address with the PG bit
of the FLASH_CR register set. Any attempt to write data that are not half-word long will
result in a bus error generating a Hard Fault interrupt.

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Figure 3. Programming procedure

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 VBAT +
0.6 V, a current may be injected into VBAT through an internal diode
connected between VDD and the power switch (VBAT).
If the power supply/battery connected to the VBAT pin cannot support

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Power control (PWR)
this current injection, it is strongly recommended to connect an
external low-drop diode between this power supply and the VBAT pin.

If no external battery is used in the application, it is recommended to connect VBAT
externally to VDD with a 100 nF external ceramic decoupling capacitor (for more details refer
to AN4080).
When the RTC domain is supplied by VDD (analog switch connected to VDD), the following
functions are available:

Note:

•

PC13, PC14 and PC15 can be used as GPIO pins

•

PC13, PC14 and PC15 can be configured by RTC or LSE (refer to Section 25.4: RTC
functional description on page 578)

Due to the fact that the analog switch can transfer only a limited amount of current (3 mA),
the use of GPIOs PC13 to PC15 in output mode is restricted: the speed has to be limited to
2 MHz with a maximum load of 30 pF and these IOs must not be used as a current source
(e.g. to drive an LED).
When the RTC domain is supplied by VBAT (analog switch connected to VBAT because VDD
is not present), the following functions are available:
•

5.1.4

PC13, PC14 and PC15 can be controlled only by RTC or LSE (refer to Section 25.4:
RTC functional description on page 578)

Voltage regulator
The voltage regulator is always enabled after Reset. It works in three different modes
depending on the application modes.
•

In Run mode, the regulator supplies full power to the 1.8 V domain (core, memories
and digital peripherals).

•

In Stop mode the regulator supplies low-power to the 1.8 V domain, preserving
contents of registers and SRAM

•

In Standby Mode, the regulator is powered off. The contents of the registers and SRAM
are lost except for the Standby circuitry and the RTC domain.

Note:

In STM32F0x8 devices, the voltage regulator is bypassed and the microcontroller must be
powered from a nominal VDD = 1.8 V ±8% supply.

5.2

Power supply supervisor

5.2.1

Power on reset (POR) / power down reset (PDR)
The device has an integrated power-on reset (POR) and power-down reset (PDR) circuits
which are always active and ensure proper operation above a threshold of 2 V.
The device remains in Reset mode when the monitored supply voltage is below a specified
threshold, VPOR/PDR, without the need for an external reset circuit.
•

The POR monitors only the VDD supply voltage. During the startup phase VDDA must
arrive first and be greater than or equal to VDD.

•

The PDR monitors both the VDD and VDDA supply voltages. However, the VDDA power
supply supervisor can be disabled (by programming a dedicated option bit

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VDDA_MONITOR) to reduce the power consumption if the application is designed to
make sure that VDDA is higher than or equal to VDD.
For more details on the power on / power down reset threshold, refer to the electrical
characteristics section in the datasheet.
Figure 7. Power on reset/power down reset waveform

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External NPOR signal
In STM32F0x8 devices, the PB2 I/O (or PB1 on small packages) is not available and is
replaced by the NPOR functionality used for power on reset.
To guarantee a proper power on and power down reset to the device, the NPOR pin must be
held low until VDD is stable or before turning off the supply. When VDD is stable, the reset
state can be exited by putting the NPOR pin in high impedance. The NPOR pin has an
internal pull-up connected to VDDA.

5.2.2

Programmable voltage detector (PVD)
You can use the PVD to monitor the VDD power supply by comparing it to a threshold
selected by the PLS[2:0] bits in the Power control register (PWR_CR).
The PVD is enabled by setting the PVDE bit.
A PVDO flag is available, in the Power control/status register (PWR_CSR), to indicate if VDD
is higher or lower than the PVD threshold. This event is internally connected to the EXTI
line16 and can generate an interrupt if enabled through the EXTI registers. The PVD output
interrupt can be generated when VDD drops below the PVD threshold and/or when VDD
rises above the PVD threshold depending on EXTI line16 rising/falling edge configuration.
As an example the service routine could perform emergency shutdown tasks.

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Figure 8. PVD thresholds
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5.3

Low-power modes
By default, the microcontroller is in Run mode after a system or a power Reset. Several lowpower modes are available to save power when the CPU does not need to be kept running,
for example when waiting for an external event. It is up to the user to select the mode that
gives the best compromise between low-power consumption, short startup time and
available wakeup sources.
The device features three low-power modes:
•

Sleep mode (CPU clock off, all peripherals including Cortex®-M0 core peripherals like
NVIC, SysTick, etc. are kept running)

•

Stop mode (all clocks are stopped)

•

Standby mode (1.8V domain powered-off)

In addition, the power consumption in Run mode can be reduce by one of the following
means:
•

Slowing down the system clocks

•

Gating the clocks to the APB and AHB peripherals when they are unused.

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Table 13. Low-power mode summary

Mode name

Entry

Sleep
WFI
(Sleep now or
Sleep-on WFE
exit)

Stop

Standby

wakeup

Any interrupt
Wakeup event

Effect on 1.8V
domain clocks

CPU clock OFF
no effect on other None
clocks or analog
clock sources

Any EXTI line
(configured in the
EXTI registers)
PDDS and LPDS
Specific
bits +
SLEEPDEEP bit communication
peripherals on
+ WFI or WFE
reception events All 1.8V domain
(CEC, USART,
clocks OFF
I2C)
PDDS bit +
SLEEPDEEP bit
+ WFI or WFE

WKUP pin rising
edge, RTC alarm,
external reset in
NRST pin,
IWDG reset

Effect on
VDD
domain
clocks

HSI and
HSE
oscillators
OFF

Voltage
regulator

ON

ON or in lowpower mode
(depends on
Power control
register
(PWR_CR))

OFF

Caution:

On STM32F0x8 devices, the Stop mode is available, but it is meaningless to distinguish
between voltage regulator in low-power mode and voltage regulator in Run mode because
the regulator is not used and the core is supplied directly from an external source.
Consequently, the Standby mode is not available on those devices.

5.3.1

Slowing down system clocks
In Run mode the speed of the system clocks (SYSCLK, HCLK, PCLK) can be reduced by
programming the prescaler registers. These prescalers can also be used to slow down
peripherals before entering Sleep mode.
For more details refer to Section 6.4.2: Clock configuration register (RCC_CFGR).

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5.3.2

Power control (PWR)

Peripheral clock gating
In Run mode, the AHB clock (HCLK) and the APB clock (PCLK) for individual peripherals
and memories can be stopped at any time to reduce power consumption.
To further reduce power consumption in Sleep mode the peripheral clocks can be disabled
prior to executing the WFI or WFE instructions.
Peripheral clock gating is controlled by the AHB peripheral clock enable register
(RCC_AHBENR), the APB peripheral clock enable register 2 (RCC_APB2ENR) and the
APB peripheral clock enable register 1 (RCC_APB1ENR).

5.3.3

Sleep mode
Entering Sleep mode
The Sleep mode is entered by executing the WFI (Wait For Interrupt) or WFE (Wait for
Event) instructions. Two options are available to select the Sleep mode entry mechanism,
depending on the SLEEPONEXIT bit in the Cortex®-M0 System Control register:
•

Sleep-now: if the SLEEPONEXIT bit is cleared, the MCU enters Sleep mode as soon
as WFI or WFE instruction is executed.

•

Sleep-on-exit: if the SLEEPONEXIT bit is set, the MCU enters Sleep mode as soon as
it exits the lowest priority ISR.

In the Sleep mode, all I/O pins keep the same state as in the Run mode.
Refer to Table 14 and Table 15 for details on how to enter Sleep mode.

Exiting Sleep mode
If the WFI instruction is used to enter Sleep mode, any peripheral interrupt acknowledged by
the nested vectored interrupt controller (NVIC) can wake up the device from Sleep mode.
If the WFE instruction is used to enter Sleep mode, the MCU exits Sleep mode as soon as
an event occurs. The wakeup event can be generated either by:
•

enabling an interrupt in the peripheral control register but not in the NVIC, and enabling
the SEVONPEND bit in the Cortex®-M0 System Control register. When the MCU
resumes from WFE, the peripheral interrupt pending bit and the peripheral NVIC IRQ
channel pending bit (in the NVIC interrupt clear pending register) have to be cleared.

•

or configuring an external or internal EXTI line in event mode. When the CPU resumes
from WFE, it is not necessary to clear the peripheral interrupt pending bit or the NVIC
IRQ channel pending bit as the pending bit corresponding to the event line is not set.

This mode offers the lowest wakeup time as no time is wasted in interrupt entry/exit.
Refer to Table 14 and Table 15 for more details on how to exit Sleep mode.

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Table 14. Sleep-now

Sleep-now mode

Description

Mode entry

WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– SLEEPDEEP = 0 and
– SLEEPONEXIT = 0
Refer to the Cortex®-M0 System Control register.

Mode exit

If WFI was used for entry:
Interrupt: Refer to Table 36: Vector table
If WFE was used for entry
Wakeup event: Refer to Section 11.2.3: Event management

Wakeup latency

None

Table 15. Sleep-on-exit
Sleep-on-exit

5.3.4

Description

Mode entry

WFI (wait for interrupt) while:
– SLEEPDEEP = 0 and
– SLEEPONEXIT = 1
Refer to the Cortex®-M0 System Control register.

Mode exit

Interrupt: Refer to Table 36: Vector table.

Wakeup latency

None

Stop mode
The Stop mode is based on the Cortex®-M0 deep sleep mode combined with peripheral
clock gating. The voltage regulator can be configured either in normal or low-power mode.
In Stop mode, all clocks in the 1.8 V domain are stopped, the PLL, the HSI and the HSE
oscillators are disabled. SRAM and register contents are preserved.
In the Stop mode, all I/O pins keep the same state as in the Run mode.

Entering Stop mode
Refer to Table 16 for details on how to enter the Stop mode.
To further reduce power consumption in Stop mode, the internal voltage regulator can be put
in low-power mode. This is configured by the LPDS bit of the Power control register
(PWR_CR).
If Flash memory programming is ongoing, the Stop mode entry is delayed until the memory
access is finished.
If an access to the APB domain is ongoing, The Stop mode entry is delayed until the APB
access is finished.
In Stop mode, the following features can be selected by programming individual control bits:
•

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Independent watchdog (IWDG): the IWDG is started by writing to its Key register or by
hardware option. Once started it cannot be stopped except by a Reset. See
Section 23.3: IWDG functional description in Section 23: Independent watchdog
(IWDG).

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Power control (PWR)
•

real-time clock (RTC): this is configured by the RTCEN bit in the RTC domain control
register (RCC_BDCR)

•

Internal RC oscillator (LSI): this is configured by the LSION bit in the Control/status
register (RCC_CSR).

•

External 32.768 kHz oscillator (LSE): this is configured by the LSEON bit in the RTC
domain control register (RCC_BDCR).

The ADC or DAC can also consume power during Stop mode, unless they are disabled
before entering this mode. Refer to ADC control register (ADC_CR) and DAC control
register (DAC_CR) for details on how to disable them.

Exiting Stop mode
Refer to Table 16 for more details on how to exit Stop mode.
When exiting Stop mode by issuing an interrupt or a wakeup event, the HSI oscillator is
selected as system clock.
When the voltage regulator operates in low-power mode, an additional startup delay is
incurred when waking up from Stop mode. By keeping the internal regulator ON during Stop
mode, the consumption is higher although the startup time is reduced.
Table 16. Stop mode
Stop mode

Description
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP bit in Cortex®-M0 System Control register
– Clear PDDS bit in Power Control register (PWR_CR)
– Select the voltage regulator mode by configuring LPDS bit in PWR_CR

Mode entry

Note: To enter Stop mode, all EXTI Line pending bits (in Pending register
(EXTI_PR)), all peripherals interrupt pending bits and RTC Alarm flag must
be reset. Otherwise, the Stop mode entry procedure is ignored and
program execution continues.
If the application needs to disable the external oscillator (external clock)
before entering Stop mode, the system clock source must be first switched
to HSI and then clear the HSEON bit.
Otherwise, if before entering Stop mode the HSEON bit is kept at 1, the
security system (CSS) feature must be enabled to detect any external
oscillator (external clock) failure and avoid a malfunction when entering
Stop mode.

Mode exit

If WFI was used for entry:
– Any EXTI Line configured in Interrupt mode (the corresponding EXTI
Interrupt vector must be enabled in the NVIC).
– Some specific communication peripherals (CEC, USART, I2C) interrupts,
when programmed in wakeup mode (the peripheral must be
programmed in wakeup mode and the corresponding interrupt vector
must be enabled in the NVIC).
Refer to Table 36: Vector table.
If WFE was used for entry:
Any EXTI Line configured in event mode. Refer to Section 11.2.3: Event
management on page 212

Wakeup latency

HSI wakeup time + regulator wakeup time from Low-power mode

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Power control (PWR)

5.3.5

RM0091

Standby mode
The Standby mode allows to achieve the lowest power consumption. It is based on the
Cortex®-M0 deepsleep mode, with the voltage regulator disabled. The 1.8 V domain is
consequently powered off. The PLL, the HSI oscillator and the HSE oscillator are also
switched off. SRAM and register contents are lost except for registers in the RTC domain
and Standby circuitry (see Figure 6).

Caution:

The Standby mode is not available on STM32F0x8 devices.

Entering Standby mode
Refer to Table 17 for more details on how to enter Standby mode.
In Standby mode, the following features can be selected by programming individual control
bits:
•

Independent watchdog (IWDG): the IWDG is started by writing to its Key register or by
hardware option. Once started it cannot be stopped except by a reset. See
Section 23.3: IWDG functional description in Section 23: Independent watchdog
(IWDG).

•

Real-time clock (RTC): this is configured by the RTCEN bit in the RTC domain control
register (RCC_BDCR).

•

Internal RC oscillator (LSI): this is configured by the LSION bit in the Control/status
register (RCC_CSR).

•

External 32.768 kHz oscillator (LSE): this is configured by the LSEON bit in the RTC
domain control register (RCC_BDCR).

Exiting Standby mode
The microcontroller exits the Standby mode when an external reset (NRST pin), an IWDG
reset, a rising edge on one of the enabled WKUPx pins or an RTC event occurs. All
registers are reset after wakeup from Standby except for Power control/status register
(PWR_CSR).
After waking up from Standby mode, program execution restarts in the same way as after a
Reset (boot pin sampling, option bytes loading, reset vector is fetched, etc.). The SBF status
flag in the Power control/status register (PWR_CSR) indicates that the MCU was in Standby
mode.
Refer to Table 17 for more details on how to exit Standby mode.
Table 17. Standby mode
Standby mode

88/1004

Description

Mode entry

WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP in Cortex®-M0 System Control register
– Set PDDS bit in Power Control register (PWR_CR)
– Clear WUF bit in Power Control/Status register (PWR_CSR)

Mode exit

WKUP pin rising edge, RTC alarm event’s rising edge, external Reset in
NRST pin, IWDG Reset.

Wakeup latency

Reset phase

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RM0091

Power control (PWR)

I/O states in Standby mode
In Standby mode, all I/O pins are high impedance except:
•

Reset pad (still available)

•

PC13, PC14 and PC15 if configured by RTC or LSE

•

WKUPx pins

Debug mode
By default, the debug connection is lost if the application puts the MCU in Stop or Standby
mode while the debug features are used. This is due to the fact that the Cortex®-M0 core is
no longer clocked.
However, by setting some configuration bits in the DBGMCU_CR register, the software can
be debugged even when using the low-power modes extensively.

5.3.6

Auto-wakeup from low-power mode
The RTC can be used to wakeup the MCU from low-power mode by means of the RTC
alarm.from low-power mode without depending on an external interrupt (Auto-wakeup
mode). The RTC provides a programmable time base for waking up from Stop or Standby
mode at regular intervals. For this purpose, two of the three alternative RTC clock sources
can be selected by programming the RTCSEL[1:0] bits in the RTC domain control register
(RCC_BDCR):
•

Low-power 32.768 kHz external crystal oscillator (LSE OSC)
This clock source provides a precise time base with very low-power consumption (less
than 1µA added consumption in typical conditions)

•

Low-power internal RC Oscillator (LSI)
This clock source has the advantage of saving the cost of the 32.768 kHz crystal. This
internal RC Oscillator is designed to add minimum power consumption.

To wakeup from Stop mode with an RTC alarm event, it is necessary to:
•

Configure the EXTI Line 17 to be sensitive to rising edge

•

Configure the RTC to generate the RTC alarm

To wakeup from Standby mode, there is no need to configure the EXTI Line 17.

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5.4

RM0091

Power control registers
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

5.4.1

Power control register (PWR_CR)
Address offset: 0x00
Reset value: 0x0000 0000 (reset by wakeup from Standby mode)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res

Res

Res

Res

Res

Res

Res

DBP

PVDE

CSBF

CWUF

PDDS

LPDS

rw

rc_w1

rc_w1

rw

rw

rw

PLS[2:0]
rw

rw

rw

Bits 31:9 Reserved, must be kept at reset value.
Bit 8 DBP: Disable RTC domain write protection.
In reset state, the RTC and backup registers are protected against parasitic write access. This
bit must be set to enable write access to these registers.
0: Access to RTC and Backup registers disabled
1: Access to RTC and Backup registers enabled
Bits 7:5 PLS[2:0]: PVD level selection.
These bits are written by software to select the voltage threshold detected by the Power
Voltage Detector.
Once the PVD_LOCK is enabled in the SYSCFG configuration register 2 (SYSCFG_CFGR2),
the PLS[2:0] bits cannot be programmed anymore.
000: PVD threshold 0
001: PVD threshold 1
010: PVD threshold 2
011: PVD threshold 3
100: PVD threshold 4
101: PVD threshold 5
110: PVD threshold 6
111: PVD threshold 7
Refer to the electrical characteristics of the datasheet for more details.
Bit 4 PVDE: Power voltage detector enable.
This bit is set and cleared by software. Once the PVD_LOCK is enabled in the SYSCFG
configuration register 2 (SYSCFG_CFGR2) register, the PVDE bit cannot be programmed
anymore.
0: PVD disabled
1: PVD enabled
Bit 3 CSBF: Clear standby flag.
This bit is always read as 0.
0: No effect
1: Clear the SBF Standby Flag (write).

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RM0091

Power control (PWR)

Bit 2 CWUF: Clear wakeup flag.
This bit is always read as 0.
0: No effect
1: Clear the WUF Wakeup Flag after 2 System clock cycles. (write)
Bit 1 PDDS: Power down deepsleep.
This bit is set and cleared by software. It works together with the LPDS bit.
0: Enter Stop mode when the CPU enters Deepsleep. The regulator status depends on the
LPDS bit.
1: Enter Standby mode when the CPU enters Deepsleep.
Bit 0 LPDS: Low-power deepsleep.
This bit is set and cleared by software. It works together with the PDDS bit.
0: Voltage regulator on during Stop mode
1: Voltage regulator in low-power mode during Stop mode
Note: When a peripheral that can work in STOP mode requires a clock, the Power controller
automatically switch the voltage regulator from Low-power mode to Normal mode and
remains in this mode until the request disappears.

5.4.2

Power control/status register (PWR_CSR)
Address offset: 0x04
Reset value: 0x0000 000X (not reset by wakeup from Standby mode)
Additional APB cycles are needed to read this register versus a standard APB read.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

EWUP
8

EWUP
7

EWUP
6

EWUP
5

EWUP
4

EWUP
3

EWUP
2

EWUP
1

Res

Res

Res

Res

VREF
INT
RDY

PVDO

SBF

WUF

rw

rw

rw

rw

rw

rw

rw

rw

r

r

r

r

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:8 EWUPx: Enable WKUPx pin
These bits are set and cleared by software.
0: WKUPx pin is used for general purpose I/O. An event on the WKUPx pin does not wakeup
the device from Standby mode.
1: WKUPx pin is used for wakeup from Standby mode and forced in input pull down
configuration (rising edge on WKUPx pin wakes-up the system from Standby mode).
Note: These bits are reset by a system Reset.
Bits 7:4 Reserved, must be kept at reset value.

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RM0091

Bit 3 VREFINTRDY: VREFINT reference voltage ready
This bit is set and cleared by hardware to indicate the state of the internal voltage reference
VREFINT.
0: VREFINT is not ready
1: VREFINT is ready
Note: This flag is useful only for STM32F0x8 devices where POR is provided externally
(through the NPOR pin). In STM32F0x1/F0x2 devices, the internal POR waits for
VREFINT to stabilize before releasing the reset.
Bit 2 PVDO: PVD output
This bit is set and cleared by hardware. It is valid only if PVD is enabled by the PVDE bit.
0: VDD is higher than the PVD threshold selected with the PLS[2:0] bits.
1: VDD is lower than the PVD threshold selected with the PLS[2:0] bits.
Notes:
1.
The PVD is stopped by Standby mode. For this reason, this bit is equal to 0 after Standby
or reset until the PVDE bit is set.
2.
Once the PVD is enabled and configured in the PWR_CR register, PVDO can be used to
generate an interrupt through the External Interrupt controller.
Bit 1 SBF: Standby flag
This bit is set by hardware when the device enters Standby mode and it is cleared only by a
POR/PDR (power on reset/power down reset) or by setting the CSBF bit in the Power control
register (PWR_CR)
0: Device has not been in Standby mode
1: Device has been in Standby mode
Bit 0 WUF: Wakeup flag
This bit is set by hardware to indicate that the device received a wakeup event. It is cleared by
a system reset or by setting the CWUF bit in the Power control register (PWR_CR)
0: No wakeup event occurred
1: A wakeup event was received from one of the enabled WKUPx pins or from the RTC
alarm.
Note: An additional wakeup event is detected if one WKUPx pin is enabled (by setting the
EWUPx bit) when its pin level is already high.

5.4.3

PWR register map
The following table summarizes the PWR register map and reset values.

PVDE

CSBF

CWUF

PDDS

LPDS

0

0

0

0

0

0

0

Res.

Res.

Res.

VREFINTRDY

PVDO

SBF

WUF

X

0

0

0

DBP

Res.

EWUP7

EWUP6

EWUP5

EWUP4

EWUP3

EWUP2

Reset value

EWUP8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PWR_CSR

Res.

0x004

0

0

Res.

Reset value

EWUP1
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PWR_CR

Res.

0x000

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 18. PWR register map and reset values

0

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

92/1004

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PLS[2:0]

RM0091

Reset and clock control (RCC)

6

Reset and clock control (RCC)

6.1

Reset
There are three types of reset, defined as system reset, power reset and RTC domain reset.

6.1.1

Power reset
A power reset is generated when one of the following events occurs:
1.

Power-on/power-down reset (POR/PDR reset)

2.

When exiting Standby mode

A power reset sets all registers to their reset values except the RTC domain (Figure 6:
Power supply overview).
In STM32F0x8 devices, the POR/PDR reset is not functional and the Standby mode is not
available. Power reset must be provided from an external NPOR pin (active low and
released by the application when all supply voltages are stabilized).

6.1.2

System reset
A system reset sets all registers to their reset values except the reset flags in the clock
controller CSR register and the registers in the RTC domain (see Figure 6: Power supply
overview).
A system reset is generated when one of the following events occurs:
1.

A low level on the NRST pin (external reset)

2.

Window watchdog event (WWDG reset)

3.

Independent watchdog event (IWDG reset)

4.

A software reset (SW reset) (see Software reset)

5.

Low-power management reset (see Low-power management reset)

6.

Option byte loader reset (see Option byte loader reset)

7.

A power reset

The reset source can be identified by checking the reset flags in the Control/Status register,
RCC_CSR (see Section 6.4.10: Control/status register (RCC_CSR)).
These sources act on the NRST pin and it is always kept low during the delay phase. The
RESET service routine vector is fixed at address 0x0000_0004 in the memory map.
The system reset signal provided to the device is output on the NRST pin. The pulse
generator guarantees a minimum reset pulse duration of 20 µs for each internal reset
source. In case of an external reset, the reset pulse is generated while the NRST pin is
asserted low.

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RM0091
Figure 9. Simplified diagram of the reset circuit
9 ''
5 38

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1567

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PLQ—V

6\VWHPUHVHW

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069

Software reset
The SYSRESETREQ bit in Cortex®-M0 Application Interrupt and Reset Control Register
must be set to force a software reset on the device. Refer to the Cortex™-M0 technical
reference manual for more details.

Low-power management reset
There are two ways to generate a low-power management reset:
1.

Reset generated when entering Standby mode:
This type of reset is enabled by resetting nRST_STDBY bit in User Option Bytes. In this
case, whenever a Standby mode entry sequence is successfully executed, the device
is reset instead of entering Standby mode.

2.

Reset when entering Stop mode:
This type of reset is enabled by resetting nRST_STOP bit in User Option Bytes. In this
case, whenever a Stop mode entry sequence is successfully executed, the device is
reset instead of entering Stop mode.

For further information on the User Option Bytes, refer to Section 4: Option byte.

Option byte loader reset
The option byte loader reset is generated when the OBL_LAUNCH bit (bit 13) is set in the
FLASH_CR register. This bit is used to launch the option byte loading by software.

6.1.3

RTC domain reset
The RTC domain has two specific resets that affect only the RTC domain (Figure 6: Power
supply overview).
An RTC domain reset only affects the LSE oscillator, the RTC, the Backup registers and the
RCC RTC domain control register (RCC_BDCR). It is generated when one of the following
events occurs.

94/1004

1.

Software reset, triggered by setting the BDRST bit in the RTC domain control register
(RCC_BDCR).

2.

VDD power-up if VBAT has been disconnected when it was low.

DocID018940 Rev 9

RM0091

Reset and clock control (RCC)
The Backup registers are also reset when one of the following events occurs:

6.2

1.

RTC tamper detection event.

2.

Change of the read out protection from level 1 to level 0.

Clocks
Various clock sources can be used to drive the system clock (SYSCLK):
•

HSI 8 MHz RC oscillator clock

•

HSE oscillator clock

•

PLL clock

•

HSI48 48 MHz RC oscillator clock (available on STM32F04x, STM32F07x and
STM32F09x devices only)

The devices have the following additional clock sources:
•

40 kHz low speed internal RC (LSI RC) which drives the independent watchdog and
optionally the RTC used for Auto-wakeup from Stop/Standby mode.

•

32.768 kHz low speed external crystal (LSE crystal) which optionally drives the realtime clock (RTCCLK)

•

14 MHz high speed internal RC (HSI14) dedicated for ADC.

Each clock source can be switched on or off independently when it is not used, to optimize
power consumption.
Several prescalers can be used to configure the frequency of the AHB and the APB
domains. The AHB and the APB domains maximum frequency is 48 MHz.

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RM0091

All the peripheral clocks are derived from their bus clock (HCLK for AHB or PCLK for APB)
except:
•

The Flash memory programming interface clock (FLITFCLK) which is always the HSI
clock.

•

The option byte loader clock which is always the HSI clock

•

The ADC clock which is derived (selected by software) from one of the two following
sources:

•

•

•

–

dedicated HSI14 clock, to run always at the maximum sampling rate

–

APB clock (PCLK) divided by 2 or 4

The USART1 clock, USART2 clock (on STM32F07x and STM32F09x devices only)
and USART3 clock (on STM32F09x devices only) which is derived (selected by
software) from one of the four following sources:
–

system clock

–

HSI clock

–

LSE clock

–

APB clock (PCLK)

The I2C1 clock which is derived (selected by software) from one of the two following
sources:
–

system clock

–

HSI clock

The USB clock which is derived (selected by software) from one of the two following
sources:
–

PLL clock

–

HSI48 clock

•

The CEC clock which is derived from the HSI clock divided by 244 or from the LSE
clock.

•

The I2S1 and I2S2 clock which is always the system clock.

•

The RTC clock which is derived from the LSE, LSI or from the HSE clock divided by 32.

•

The timer clock frequencies are automatically fixed by hardware. There are two cases:

•

–

if the APB prescaler is 1, the timer clock frequencies are set to the same
frequency as that of the APB domain;

–

otherwise, they are set to twice (x2) the frequency of the APB domain.

The IWDG clock which is always the LSI clock.

The RCC feeds the Cortex System Timer (SysTick) external clock with the AHB clock
(HCLK) divided by 8. The SysTick can work either with this clock or directly with the Cortex
clock (HCLK), configurable in the SysTick Control and Status Register.

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RM0091

Reset and clock control (RCC)
Figure 10. Clock tree (STM32F03x and STM32F05x devices)
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069

1. Not available on STM32F05x devices.

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136

Reset and clock control (RCC)

RM0091

Figure 11. Clock tree (STM32F04x, STM32F07x and STM32F09x devices)
)/,7)&/.
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069

1. Not available on STM32F04x devices.
2. Not available on STM32F04x and STM32F07x devices
®

FCLK acts as Cortex -M0’s free-running clock. For more details refer to the ARM Cortex™M0 r0p0 technical reference manual (TRM).

98/1004

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RM0091

6.2.1

Reset and clock control (RCC)

HSE clock
The high speed external clock signal (HSE) can be generated from two possible clock
sources:
•

HSE external crystal/ceramic resonator

•

HSE user external clock

The resonator and the load capacitors have to be placed as close as possible to the
oscillator pins in order to minimize output distortion and startup stabilization time. The
loading capacitance values must be adjusted according to the selected oscillator.
Figure 12. HSE/ LSE clock sources
Clock source

Hardware configuration

26&B,1

26&B287

External clock

*3,2
([WHUQDO
VRXUFH
06Y9

26&B,1

26&B287

Crystal/Ceramic
resonators

&/

/RDG
FDSDFLWRUV

&/

06Y9

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Reset and clock control (RCC)

RM0091

External crystal/ceramic resonator (HSE crystal)
The 4 to 32 MHz external oscillator has the advantage of producing a very accurate rate on
the main clock.
The associated hardware configuration is shown in Figure 12. Refer to the electrical
characteristics section of the datasheet for more details.
The HSERDY flag in the Clock control register (RCC_CR) indicates if the HSE oscillator is
stable or not. At startup, the clock is not released until this bit is set by hardware. An
interrupt can be generated if enabled in the Clock interrupt register (RCC_CIR).
The HSE Crystal can be switched on and off using the HSEON bit in the Clock control
register (RCC_CR).
For code example refer to the Appendix section A.3.1: HSE start sequence code example.
Caution:

To switch ON the HSE oscillator, 512 HSE clock pulses need to be seen by an internal
stabilization counter after the HSEON bit is set. Even in the case that no crystal or resonator
is connected to the device, excessive external noise on the OSC_IN pin may still lead the
oscillator to start. Once the oscillator is started, it needs another 6 HSE clock pulses to
complete a switching OFF sequence. If for any reason the oscillations are no more present
on the OSC_IN pin, the oscillator cannot be switched OFF, locking the OSC pins from any
other use and introducing unwanted power consumption. To avoid such situation, it is
strongly recommended to always enable the Clock Security System (CSS) which is able to
switch OFF the oscillator even in this case.

External source (HSE bypass)
In this mode, an external clock source must be provided. It can have a frequency of up to
32 MHz. You select this mode by setting the HSEBYP and HSEON bits in the Clock control
register (RCC_CR). The external clock signal (square, sinus or triangle) with ~40-60% duty
cycle depending on the frequency (refer to the datasheet) has to drive the OSC_IN pin while
the OSC_OUT pin can be used a GPIO. See Figure 12.

6.2.2

HSI clock
The HSI clock signal is generated from an internal 8 MHz RC oscillator and can be used
directly as a system clock or for PLL input
The HSI RC oscillator has the advantage of providing a clock source at low cost (no external
components). It also has a faster startup time than the HSE crystal oscillator however, even
with calibration the frequency is less accurate than an external crystal oscillator or ceramic
resonator.

Calibration
RC oscillator frequencies can vary from one chip to another due to manufacturing process
variations, this is why each device is factory calibrated by ST for 1% accuracy at TA=25°C.
After reset, the factory calibration value is loaded in the HSICAL[7:0] bits in the Clock control
register (RCC_CR).
If the application is subject to voltage or temperature variations this may affect the RC
oscillator speed. You can trim the HSI frequency in the application using the HSITRIM[4:0]
bits in the Clock control register (RCC_CR).

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For more details on how to measure the HSI frequency variation please refer to
Section 6.2.13: Internal/external clock measurement with TIM14 on page 105.
The HSIRDY flag in the Clock control register (RCC_CR) indicates if the HSI RC is stable or
not. At startup, the HSI RC output clock is not released until this bit is set by hardware.
The HSI RC can be switched on and off using the HSION bit in the Clock control register
(RCC_CR).
The HSI signal can also be used as a backup source (Auxiliary clock) if the HSE crystal
oscillator fails. Refer to Section 6.2.8: Clock security system (CSS) on page 103.
Furthermore it is possible to drive the HSI clock to the MCO multiplexer. Then the clock
could be driven to the Timer 14 giving the ability to the user to calibrate the oscillator.

6.2.3

HSI48 clock
On STM32F04x, STM32F07x and STM32F09x devices only, the HSI48 clock signal is
generated from an internal 48 MHz RC oscillator and can be used directly as a system clock
or divided and be used as PLL input.
The internal 48MHz RC oscillator is mainly dedicated to provide a high precision clock to the
USB peripheral by means of a special Clock Recovery System (CRS) circuitry, which could
use the USB SOF signal or the LSE or an external signal to automatically adjust the
oscillator frequency on-fly, in a very small steps. This oscillator can also be used as a
system clock source when the system is in run mode; it will be disabled as soon as the
system enters in Stop or Standby mode. When the CRS is not used, the HSI48 RC oscillator
runs on its default frequency which is subject to manufacturing process variations, this is
why each device is factory calibrated by ST for ~3% accuracy at TA = 25°C.
For more details on how to configure and use the CRS peripheral please refer to Section 7.
The HSI48RDY flag in the Clock control register (RCC_CR) indicates if the HSI48 RC is
stable or not. At startup, the HSI48 RC output clock is not released until this bit is set by
hardware.
The HSI48 RC can be switched on and off using the HSI48ON bit in the Clock control
register (RCC_CR). This oscillator will be also automatically enabled (by hardware forcing
HSI48ON bit to one) as soon as it is chosen as a clock source for the USB and the
peripheral is enabled.
Furthermore it is possible to drive the HSI48 clock to the MCO multiplexer and use it as a
clock source for other application components.

6.2.4

PLL
The internal PLL can be used to multiply the HSI, a divided HSI48 or the HSE output clock
frequency. Refer to Figure 9: Simplified diagram of the reset circuit, Figure 12: HSE/ LSE
clock sources and Clock control register (RCC_CR).
The PLL configuration (selection of the input clock, predivider and multiplication factor) must
be done before enabling the PLL. Once the PLL is enabled, these parameters cannot be
changed.

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To modify the PLL configuration, proceed as follows:
1.

Disable the PLL by setting PLLON to 0.

2.

Wait until PLLRDY is cleared. The PLL is now fully stopped.

3.

Change the desired parameter.

4.

Enable the PLL again by setting PLLON to 1.

5.

Wait until PLLRDY is set.

An interrupt can be generated when the PLL is ready, if enabled in the Clock interrupt
register (RCC_CIR).
The PLL output frequency must be set in the range 16-48 MHz.
For code example refer to the Appendix section A.3.2: PLL configuration modification code
example.

6.2.5

LSE clock
The LSE crystal is a 32.768 kHz Low Speed External crystal or ceramic resonator. It has the
advantage of providing a low-power but highly accurate clock source to the real-time clock
peripheral (RTC) for clock/calendar or other timing functions.
The LSE crystal is switched on and off using the LSEON bit in RTC domain control register
(RCC_BDCR). The crystal oscillator driving strength can be changed at runtime using the
LSEDRV[1:0] bits in the RTC domain control register (RCC_BDCR) to obtain the best
compromise between robustness and short start-up time on one side and low-power
consumption on the other.
The LSERDY flag in the RTC domain control register (RCC_BDCR) indicates whether the
LSE crystal is stable or not. At startup, the LSE crystal output clock signal is not released
until this bit is set by hardware. An interrupt can be generated if enabled in the Clock
interrupt register (RCC_CIR).

Caution:

To switch ON the LSE oscillator, 4096 LSE clock pulses need to be seen by an internal
stabilization counter after the LSEON bit is set. Even in the case that no crystal or resonator
is connected to the device, excessive external noise on the OSC32_IN pin may still lead the
oscillator to start. Once the oscillator is started, it needs another 6 LSE clock pulses to
complete a switching OFF sequence. If for any reason the oscillations are no more present
on the OSC_IN pin, the oscillator cannot be switched OFF, locking the OSC32 pins from any
other use and introducing unwanted power consumption. The only way to recover such
situation is to perform the RTC domain reset by software.

External source (LSE bypass)
In this mode, an external clock source must be provided. It can have a frequency of up to
1 MHz. You select this mode by setting the LSEBYP and LSEON bits in the RTC domain
control register (RCC_BDCR). The external clock signal (square, sinus or triangle) with
~50% duty cycle has to drive the OSC32_IN pin while the OSC32_OUT pin can be used as
GPIO. See Figure 12.

6.2.6

LSI clock
The LSI RC acts as a low-power clock source that can be kept running in Stop and Standby
mode for the independent watchdog (IWDG) and RTC. The clock frequency is around 40
kHz. For more details, refer to the electrical characteristics section of the datasheets.

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The LSI RC can be switched on and off using the LSION bit in the Control/status register
(RCC_CSR).
The LSIRDY flag in the Control/status register (RCC_CSR) indicates if the LSI oscillator is
stable or not. At startup, the clock is not released until this bit is set by hardware. An
interrupt can be generated if enabled in the Clock interrupt register (RCC_CIR).

6.2.7

System clock (SYSCLK) selection
Various clock sources can be used to drive the system clock (SYSCLK):
•

HSI oscillator

•

HSE oscillator

•

PLL

•

HSI48 oscillator (available only on STM32F04x, STM32F07x and STM32F09x devices)

After a system reset, the HSI oscillator is selected as system clock. When a clock source is
used directly or through the PLL as a system clock, it is not possible to stop it.
A switch from one clock source to another occurs only if the target clock source is ready
(clock stable after startup delay or PLL locked). If a clock source which is not yet ready is
selected, the switch will occur when the clock source becomes ready. Status bits in the
Clock control register (RCC_CR) indicate which clock(s) is (are) ready and which clock is
currently used as a system clock.

6.2.8

Clock security system (CSS)
Clock Security System can be activated by software. In this case, the clock detector is
enabled after the HSE oscillator startup delay, and disabled when this oscillator is stopped.
If a failure is detected on the HSE clock, the HSE oscillator is automatically disabled, a clock
failure event is sent to the break input of the advanced-control timers (TIM1) and generalpurpose timers (TIM15, TIM16 and TIM17) and an interrupt is generated to inform the
software about the failure (Clock Security System Interrupt CSSI), allowing the MCU to
perform rescue operations. The CSSI is linked to the Cortex®-M0 NMI (Non-Maskable
Interrupt) exception vector.

Note:

Once the CSS is enabled and if the HSE clock fails, the CSS interrupt occurs and an NMI is
automatically generated. The NMI will be executed indefinitely unless the CSS interrupt
pending bit is cleared. As a consequence, in the NMI ISR user must clear the CSS interrupt
by setting the CSSC bit in the Clock interrupt register (RCC_CIR).
If the HSE oscillator is used directly or indirectly as the system clock (indirectly means: it is
used as PLL input clock, and the PLL clock is used as system clock), a detected failure
causes a switch of the system clock to the HSI oscillator and the disabling of the HSE
oscillator. If the HSE clock (divided or not) is the clock entry of the PLL used as system clock
when the failure occurs, the PLL is disabled too.

6.2.9

ADC clock
The ADC clock selection is done inside the ADC_CFGR2 (refer to Section 13.12.5: ADC
configuration register 2 (ADC_CFGR2) on page 263). It can be either the dedicated 14 MHz
RC oscillator (HSI14) connected on the ADC asynchronous clock input or PCLK divided by
2 or 4. The 14 MHz RC oscillator can be configured by software either to be turned on/off
(“auto-off mode”) by the ADC interface or to be always enabled. The HSI 14 MHz RC

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oscillator cannot be turned on by ADC interface when the APB clock is selected as an ADC
kernel clock.

6.2.10

RTC clock
The RTCCLK clock source can be either the HSE/32, LSE or LSI clocks. This is selected by
programming the RTCSEL[1:0] bits in the RTC domain control register (RCC_BDCR). This
selection cannot be modified without resetting the RTC domain. The system must be always
configured in a way that the PCLK frequency is greater then or equal to the RTCCLK
frequency for proper operation of the RTC.
The LSE clock is in the RTC domain, whereas the HSE and LSI clocks are not.
Consequently:
•

•

If LSE is selected as RTC clock:
–

The RTC continues to work even if the VDD supply is switched off, provided the
VBAT supply is maintained.

–

The RTC remains clocked and functional under system reset

If LSI is selected as the RTC clock:
–

•

The RTC state is not guaranteed if the VDD supply is powered off. Refer to
Section 6.2.6: LSI clock on page 102 for more details on LSI calibration.

If the HSE clock divided by 32 is used as the RTC clock:
–

The RTC state is not guaranteed if the VDD supply is powered off or if the internal
voltage regulator is powered off (removing power from the 1.8 V domain).

When the RTC clock is LSE, the RTC remains clocked and functional under system reset.

6.2.11

Independent watchdog clock
If the Independent watchdog (IWDG) is started by either hardware option or software
access, the LSI oscillator is forced ON and cannot be disabled. After the LSI oscillator
temporization, the clock is provided to the IWDG.

6.2.12

Clock-out capability
The microcontroller clock output (MCO) capability allows the clock to be output onto the
external MCO pin. The configuration registers of the corresponding GPIO port must be
programmed in alternate function mode. One of the following clock signals can be selected
as the MCO clock:
•

HSI14

•

SYSCLK

•

HSI

•

HSE

•

PLL clock divided by 2 or direct (direct connection is not available on STM32F05x
devices)

•

LSE

•

LSI

•

HSI48 (on STM32F04x, STM32F07x and STM32F09x devices only)

The selection is controlled by the MCO[3:0] bits of the Clock configuration register
(RCC_CFGR).

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For code example refer to the Appendix section A.3.3: MCO selection code example.
On STM32F03x, STM32F04x, STM32F07x and STM32F09x devices, the additional bit
PLLNODIV of this register controls the divider bypass for a PLL clock input to MCO. The
MCO frequency can be reduced by a configurable binary divider, controlled by the
MCOPRE[2..0] bits of the Clock configuration register (RCC_CFGR).

6.2.13

Internal/external clock measurement with TIM14
It is possible to indirectly measure the frequency of all on-board clock sources by mean of
the TIM14 channel 1 input capture. As represented on Figure 13.
Figure 13. Frequency measurement with TIM14 in capture mode
7,0

7,B503>@
*3,2
57&&/.
+6(
0&2

7,

069

The input capture channel of the Timer 14 can be a GPIO line or an internal clock of the
MCU. This selection is performed through the TI1_RMP [1:0] bits in the TIM14_OR register.
The possibilities available are the following ones.
•

TIM14 Channel1 is connected to the GPIO. Refer to the alternate function mapping in
the device datasheets.

•

TIM14 Channel1 is connected to the RTCCLK.

•

TIM14 Channel1 is connected to the HSE/32 Clock.

•

TIM14 Channel1 is connected to the microcontroller clock output (MCO). Refer to
Section 6.2.12: Clock-out capability for MCO clock configuration.

For code example refer to the Appendix section A.3.4: Clock measurement configuration
with TIM14 code example.

Calibration of the HSI
The primary purpose of connecting the LSE, through the MCO multiplexer, to the channel 1
input capture is to be able to precisely measure the HSI system clocks (for this, the HSI
should be used as the system clock source). The number of HSI clock counts between
consecutive edges of the LSE signal provides a measure of the internal clock period. Taking
advantage of the high precision of LSE crystals (typically a few tens of ppm), it is possible to
determine the internal clock frequency with the same resolution, and trim the source to
compensate for manufacturing-process- and/or temperature- and voltage-related frequency
deviations.
The HSI oscillator has dedicated user-accessible calibration bits for this purpose.
The basic concept consists in providing a relative measurement (e.g. the HSI/LSE ratio): the
precision is therefore closely related to the ratio between the two clock sources. The higher
the ratio is, the better the measurement will be.
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If LSE is not available, HSE/32 will be the better option in order to reach the most precise
calibration possible.

Calibration of the LSI
The calibration of the LSI will follow the same pattern that for the HSI, but changing the
reference clock. It will be necessary to connect LSI clock to the channel 1 input capture of
the TIM14. Then define the HSE as system clock source, the number of its clock counts
between consecutive edges of the LSI signal provides a measure of the internal low speed
clock period.
The basic concept consists in providing a relative measurement (e.g. the HSE/LSI ratio): the
precision is therefore closely related to the ratio between the two clock sources. The higher
the ratio is, the better the measurement will be.

Calibration of the HSI14
For the HSI14, because of its high frequency, it is not possible to have a precise resolution.
However a solution could be to clock Timer 14 with HSE through PLL to reach 48 MHz, and
to use the input capture line with the HSI14 and the capture prescaler defined to the higher
value. In that configuration, we got a ratio of 27 events. It is still a bit low to have an accurate
calibration. In order to increase the measure accuracy, it is advised to count the HSI periods
after multiple cycles of Timer 14. Using polling to treat the capture event will be necessary in
this case.

6.3

Low-power modes
APB peripheral clocks and DMA clock can be disabled by software.
Sleep mode stops the CPU clock. The memory interface clocks (Flash and RAM interfaces)
can be stopped by software during sleep mode. The AHB to APB bridge clocks are disabled
by hardware during Sleep mode when all the clocks of the peripherals connected to them
are disabled.
Stop mode stops all the clocks in the core supply domain and disables the PLL and the HSI,
HSI48, HSI14 and HSE oscillators.
HDMI CEC, USART1, USART2 (only on STM32F07x and STM32F09x devices), USART3
(only on STM32F09x devices) and I2C1 have the capability to enable the HSI oscillator
even when the MCU is in Stop mode (if HSI is selected as the clock source for that
peripheral). When the system is in Stop mode, with the regulator in LP mode, the clock
request coming from any of those three peripherals moves the regulator to MR mode in
order to have the proper current drive capability for the core logic. The regulator moves back
to LP mode once this request is removed without waking up the MCU.
HDMI CEC, USART1, USART2 (only on STM32F07x and STM32F09x devices) and
USART3 (only on STM32F09x devices) can also be driven by the LSE oscillator when the
system is in Stop mode (if LSE is selected as clock source for that peripheral) and the LSE
oscillator is enabled (LSEON) but they do not have the capability to turn on the LSE
oscillator.
Standby mode stops all the clocks in the core supply domain and disables the PLL and the
HSI, HSI48, HSI14 and HSE oscillators.
The CPU’s deepsleep mode can be overridden for debugging by setting the DBG_STOP or
DBG_STANDBY bits in the DBGMCU_CR register.

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When waking up from deepsleep after an interrupt (Stop mode) or reset (Standby mode),
the HSI oscillator is selected as system clock.
If a Flash programming operation is on going, deepsleep mode entry is delayed until the
Flash interface access is finished. If an access to the APB domain is ongoing, deepsleep
mode entry is delayed until the APB access is finished.

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RCC registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

6.4.1

Clock control register (RCC_CR)
Address offset: 0x00
Reset value: 0x0000 XX83 where X is undefined.
Access: no wait state, word, half-word and byte access

31
Res.

30
Res.

15

14

29
Res.

13

28
Res.

12

27
Res.

11

26

25

Res.

PLL
RDY

PLLON

r

rw

9

8

10

24

23
Res.

22
Res.

7

r

r

r

r

Res.

6

HSICAL[7:0]
r

21

5

20

19

18

17

16

Res.

CSS
ON

HSE
BYP

HSE
RDY

HSE
ON

rw

rw

r

rw

3

2

1

0

Res.

HSI
RDY

HSION

r

rw

4

HSITRIM[4:0]
r

r

r

rw

rw

rw

rw

rw

Bits 31:26 Reserved, must be kept at reset value.
Bit 25 PLLRDY: PLL clock ready flag
Set by hardware to indicate that the PLL is locked.
0: PLL unlocked
1: PLL locked
Bit 24 PLLON: PLL enable
Set and cleared by software to enable PLL.
Cleared by hardware when entering Stop or Standby mode. This bit can not be reset if the PLL
clock is used as system clock or is selected to become the system clock.
0: PLL OFF
1: PLL ON
Bits 23:20 Reserved, must be kept at reset value.
Bit 19 CSSON: Clock security system enable
Set and cleared by software to enable the clock security system. When CSSON is set, the
clock detector is enabled by hardware when the HSE oscillator is ready, and disabled by
hardware if a HSE clock failure is detected.
0: Clock security system disabled (clock detector OFF).
1: Clock security system enabled (clock detector ON if the HSE is ready, OFF if not).
Bit 18 HSEBYP: HSE crystal oscillator bypass
Set and cleared by software to bypass the oscillator with an external clock. The external clock
must be enabled with the HSEON bit set, to be used by the device. The HSEBYP bit can be
written only if the HSE oscillator is disabled.
0: HSE crystal oscillator not bypassed
1: HSE crystal oscillator bypassed with external clock

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Bit 17 HSERDY: HSE clock ready flag
Set by hardware to indicate that the HSE oscillator is stable. This bit needs 6 cycles of the HSE
oscillator clock to fall down after HSEON reset.
0: HSE oscillator not ready
1: HSE oscillator ready
Bit 16 HSEON: HSE clock enable
Set and cleared by software.
Cleared by hardware to stop the HSE oscillator when entering Stop or Standby mode. This bit
cannot be reset if the HSE oscillator is used directly or indirectly as the system clock.
0: HSE oscillator OFF
1: HSE oscillator ON
Bits 15:8 HSICAL[7:0]: HSI clock calibration
These bits are initialized automatically at startup. They are adjusted by SW through the
HSITRIM setting.
Bits 7:3 HSITRIM[4:0]: HSI clock trimming
These bits provide an additional user-programmable trimming value that is added to the
HSICAL[7:0] bits. It can be programmed to adjust to variations in voltage and temperature that
influence the frequency of the HSI.
The default value is 16, which, when added to the HSICAL value, should trim the HSI to 8 MHz
± 1%. The trimming step is around 40 kHz between two consecutive HSICAL steps.
Note: Increased value in the register results to higher clock frequency.
Bit 2 Reserved, must be kept at reset value.
Bit 1 HSIRDY: HSI clock ready flag
Set by hardware to indicate that HSI oscillator is stable. After the HSION bit is cleared,
HSIRDY goes low after 6 HSI oscillator clock cycles.
0: HSI oscillator not ready
1: HSI oscillator ready
Bit 0 HSION: HSI clock enable
Set and cleared by software.
Set by hardware to force the HSI oscillator ON when leaving Stop or Standby mode or in case
of failure of the HSE crystal oscillator used directly or indirectly as system clock. This bit
cannot be reset if the HSI is used directly or indirectly as system clock or is selected to become
the system clock.
0: HSI oscillator OFF
1: HSI oscillator ON

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Clock configuration register (RCC_CFGR)
Address offset: 0x04
Reset value: 0x0000 0000
Access: 0 ≤ wait state ≤ 2, word, half-word and byte access
1 or 2 wait states inserted only if the access occurs during clock source switch.

31

30

PLL
NODIV

29

28

27

MCOPRE[2:0]

26

25

24

MCO[3:0]

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

PLL
SRC[0]

ADC
PRE

Res.

Res.

Res.

rw

rw

23

22

Res.

Res.

7

PPRE[2:0]
rw

rw

6

21

20

rw

rw

18

PLLMUL[3:0]

17

16

PLL
XTPRE

PLL
SRC[1]

rw

rw

rw

rw

rw

rw

5

4

3

2

1

0

HPRE[3:0]
rw

19

rw

SWS[1:0]
rw

r

r

SW[1:0]
rw

rw

Bit 31 PLLNODIV: PLL clock not divided for MCO (not available on STM32F05x devices)
This bit is set and cleared by software. It switches off divider by 2 for PLL connection to MCO.
0: PLL is divided by 2 for MCO
1: PLL is not divided for MCO
Bits 30:28 MCOPRE[2:0]: Microcontroller Clock Output Prescaler (not available on STM32F05x
devices)
These bits are set and cleared by software to select the MCO prescaler division factor. To
avoid glitches, it is highly recommended to change this prescaler only when the MCO output is
disabled.
000: MCO is divided by 1
001: MCO is divided by 2
010: MCO is divided by 4
.....
111: MCO is divided by 128
Bits 27:24 MCO[3:0]: Microcontroller clock output
Set and cleared by software.
0000: MCO output disabled, no clock on MCO
0001: Internal RC 14 MHz (HSI14) oscillator clock selected
0010: Internal low speed (LSI) oscillator clock selected
0011: External low speed (LSE) oscillator clock selected
0100: System clock selected
0101: Internal RC 8 MHz (HSI) oscillator clock selected
0110: External 4-32 MHz (HSE) oscillator clock selected
0111: PLL clock selected (divided by 1 or 2, depending on PLLNODIV)
1000: Internal RC 48 MHz (HSI48) oscillator clock selected
Note: This clock output may have some truncated cycles at startup or during MCO clock
source switching.
Bits 23:22 Reserved, must be kept at reset value.

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Bits 21:18 PLLMUL[3:0]: PLL multiplication factor
These bits are written by software to define the PLL multiplication factor. These bits can be
written only when PLL is disabled.
Caution: The PLL output frequency must not exceed 48 MHz.
0000: PLL input clock x 2
0001: PLL input clock x 3
0010: PLL input clock x 4
0011: PLL input clock x 5
0100: PLL input clock x 6
0101: PLL input clock x 7
0110: PLL input clock x 8
0111: PLL input clock x 9
1000: PLL input clock x 10
1001: PLL input clock x 11
1010: PLL input clock x 12
1011: PLL input clock x 13
1100: PLL input clock x 14
1101: PLL input clock x 15
1110: PLL input clock x 16
1111: PLL input clock x 16
Bit 17 PLLXTPRE: HSE divider for PLL input clock
This bit is the same bit as bit PREDIV[0] from RCC_CFGR2. Refer to RCC_CFGR2 PREDIV
bits description for its meaning.
Bits 16:15 PLLSRC[1:0]: PLL input clock source
Set and cleared by software to select PLL or PREDIV clock source. These bits can be written
only when PLL is disabled.
00: HSI/2 selected as PLL input clock (PREDIV forced to divide by 2 on STM32F04x,
STM32F07x and STM32F09x devices)
01: HSI/PREDIV selected as PLL input clock
10: HSE/PREDIV selected as PLL input clock
11: HSI48/PREDIV selected as PLL input clock
Note: Bit PLLSRC[0] is available only on STM32F04x, STM32F07x and STM32F09x
devices, otherwise it is reserved (with value zero).
Bit 14 ADCPRE: ADC prescaler
Obsolete setting. Proper ADC clock selection is done inside the ADC_CFGR2 (refer to
Section 13.12.5: ADC configuration register 2 (ADC_CFGR2) on page 263).
Bits 13:11 Reserved, must be kept at reset value.
Bits 10:8 PPRE[2:0]: PCLK prescaler
Set and cleared by software to control the division factor of the APB clock (PCLK).
0xx: HCLK not divided
100: HCLK divided by 2
101: HCLK divided by 4
110: HCLK divided by 8
111: HCLK divided by 16

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Bits 7:4 HPRE[3:0]: HCLK prescaler
Set and cleared by software to control the division factor of the AHB clock.
0xxx: SYSCLK not divided
1000: SYSCLK divided by 2
1001: SYSCLK divided by 4
1010: SYSCLK divided by 8
1011: SYSCLK divided by 16
1100: SYSCLK divided by 64
1101: SYSCLK divided by 128
1110: SYSCLK divided by 256
1111: SYSCLK divided by 512
Bits 3:2 SWS[1:0]: System clock switch status
Set and cleared by hardware to indicate which clock source is used as system clock.
00: HSI oscillator used as system clock
01: HSE oscillator used as system clock
10: PLL used as system clock
11: HSI48 oscillator used as system clock (when available)
Bits 1:0 SW[1:0]: System clock switch
Set and cleared by software to select SYSCLK source.
Cleared by hardware to force HSI selection when leaving Stop and Standby mode or in case
of failure of the HSE oscillator used directly or indirectly as system clock (if the Clock Security
System is enabled).
00: HSI selected as system clock
01: HSE selected as system clock
10: PLL selected as system clock
11: HSI48 selected as system clock (when available)

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6.4.3

Clock interrupt register (RCC_CIR)
Address offset: 0x08
Reset value: 0x0000 0000
Access: no wait state, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CSSC

HSI48
RDYC

HSI14
RDYC

PLL
RDYC

HSE
RDYC

HSI
RDYC

LSE
RDYC

LSI
RDYC

w

w

w

w

w

w

w

w

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

HSI48
RDYIE

HSI14
RDYIE

PLL
RDYIE

HSE
RDYIE

HSI
RDYIE

LSE
RDYIE

LSI
RDYIE

CSSF

HSI48
RDYF

HSI14
RDYF

PLL
RDYF

HSE
RDYF

HSI
RDYF

LSE
RDYF

LSI
RDYF

rw

rw

rw

rw

rw

rw

rw

r

r

r

r

r

r

r

r

Bits 31:24 Reserved, must be kept at reset value.
Bit 23 CSSC: Clock security system interrupt clear
This bit is set by software to clear the CSSF flag.
0: No effect
1: Clear CSSF flag
Bit 22 HSI48RDYC: HSI48 Ready Interrupt Clear
This bit is set by software to clear the HSI48RDYF flag.
0: No effect
1: Clear HSI48RDYF flag
Bit 21 HSI14RDYC: HSI14 ready interrupt clear
This bit is set by software to clear the HSI14RDYF flag.
0: No effect
1: Clear HSI14RDYF flag
Bit 20 PLLRDYC: PLL ready interrupt clear
This bit is set by software to clear the PLLRDYF flag.
0: No effect
1: Clear PLLRDYF flag
Bit 19 HSERDYC: HSE ready interrupt clear
This bit is set by software to clear the HSERDYF flag.
0: No effect
1: Clear HSERDYF flag
Bit 18 HSIRDYC: HSI ready interrupt clear
This bit is set software to clear the HSIRDYF flag.
0: No effect
1: Clear HSIRDYF flag
Bit 17 LSERDYC: LSE ready interrupt clear
This bit is set by software to clear the LSERDYF flag.
0: No effect
1: LSERDYF cleared

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Reset and clock control (RCC)

RM0091

Bit 16 LSIRDYC: LSI ready interrupt clear
This bit is set by software to clear the LSIRDYF flag.
0: No effect
1: LSIRDYF cleared
Bit 15 Reserved, must be kept at reset value.
Bit 14 HSI48RDYIE: HSI48 ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the HSI48 oscillator
stabilization.
0: HSI48 ready interrupt disabled
1: HSI48 ready interrupt enabled
Bit 13 HSI14RDYIE: HSI14 ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the HSI14 oscillator
stabilization.
0: HSI14 ready interrupt disabled
1: HSI14 ready interrupt enabled
Bit 12 PLLRDYIE: PLL ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by PLL lock.
0: PLL lock interrupt disabled
1: PLL lock interrupt enabled
Bit 11 HSERDYIE: HSE ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the HSE oscillator
stabilization.
0: HSE ready interrupt disabled
1: HSE ready interrupt enabled
Bit 10 HSIRDYIE: HSI ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the HSI oscillator
stabilization.
0: HSI ready interrupt disabled
1: HSI ready interrupt enabled
Bit 9 LSERDYIE: LSE ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the LSE oscillator
stabilization.
0: LSE ready interrupt disabled
1: LSE ready interrupt enabled
Bit 8 LSIRDYIE: LSI ready interrupt enable
Set and cleared by software to enable/disable interrupt caused by the LSI oscillator
stabilization.
0: LSI ready interrupt disabled
1: LSI ready interrupt enabled
Bit 7 CSSF: Clock security system interrupt flag
Set by hardware when a failure is detected in the HSE oscillator.
Cleared by software setting the CSSC bit.
0: No clock security interrupt caused by HSE clock failure
1: Clock security interrupt caused by HSE clock failure

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RM0091

Reset and clock control (RCC)

Bit 6 HSI48RDYF: HSI48 ready interrupt flag
Set by hardware when the HSI48 becomes stable and HSI48RDYDIE is set in a response to
setting the HSI48ON bit in Clock control register 2 (RCC_CR2). When HSI48ON is not set
but the HSI48 oscillator is enabled by the peripheral through a clock request, this bit is not set
and no interrupt is generated.
Cleared by software setting the HSI48RDYC bit.
0: No clock ready interrupt caused by the HSI48 oscillator
1: Clock ready interrupt caused by the HSI48 oscillator
Bit 5 HSI14RDYF: HSI14 ready interrupt flag
Set by hardware when the HSI14 becomes stable and HSI14RDYDIE is set in a response to
setting the HSI14ON bit in Clock control register 2 (RCC_CR2). When HSI14ON is not set
but the HSI14 oscillator is enabled by the peripheral through a clock request, this bit is not set
and no interrupt is generated.
Cleared by software setting the HSI14RDYC bit.
0: No clock ready interrupt caused by the HSI14 oscillator
1: Clock ready interrupt caused by the HSI14 oscillator
Bit 4 PLLRDYF: PLL ready interrupt flag
Set by hardware when the PLL locks and PLLRDYDIE is set.
Cleared by software setting the PLLRDYC bit.
0: No clock ready interrupt caused by PLL lock
1: Clock ready interrupt caused by PLL lock
Bit 3 HSERDYF: HSE ready interrupt flag
Set by hardware when the HSE clock becomes stable and HSERDYDIE is set.
Cleared by software setting the HSERDYC bit.
0: No clock ready interrupt caused by the HSE oscillator
1: Clock ready interrupt caused by the HSE oscillator
Bit 2 HSIRDYF: HSI ready interrupt flag
Set by hardware when the HSI clock becomes stable and HSIRDYDIE is set in a response to
setting the HSION (refer to Clock control register (RCC_CR)). When HSION is not set but the
HSI oscillator is enabled by the peripheral through a clock request, this bit is not set and no
interrupt is generated.
Cleared by software setting the HSIRDYC bit.
0: No clock ready interrupt caused by the HSI oscillator
1: Clock ready interrupt caused by the HSI oscillator
Bit 1 LSERDYF: LSE ready interrupt flag
Set by hardware when the LSE clock becomes stable and LSERDYDIE is set.
Cleared by software setting the LSERDYC bit.
0: No clock ready interrupt caused by the LSE oscillator
1: Clock ready interrupt caused by the LSE oscillator
Bit 0 LSIRDYF: LSI ready interrupt flag
Set by hardware when the LSI clock becomes stable and LSIRDYDIE is set.
Cleared by software setting the LSIRDYC bit.
0: No clock ready interrupt caused by the LSI oscillator
1: Clock ready interrupt caused by the LSI oscillator

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Reset and clock control (RCC)

6.4.4

RM0091

APB peripheral reset register 2 (RCC_APB2RSTR)
Address offset: 0x0C
Reset value: 0x00000 0000
Access: no wait state, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DBGMCU
RST

Res.

Res.

Res.

TIM17
RST

TIM16
RST

TIM15
RST

rw

rw

rw

2

1

0

Res.

SYSCFG
RST

rw
15

14

Res.

USART1
RST
rw

13

12

11

Res.

SPI1
RST

TIM1
RST

rw

rw

10

9

Res.

ADC
RST

8

7

6

5

Res.

USART8
RST

USART7R
ST

USART6
RST

rw

rw

rw

rw

Bits 31:23 Reserved, must be kept at reset value.
Bits 22 DBGMCURST: Debug MCU reset
Set and cleared by software.
0: No effect
1: Reset Debug MCU
Bits 21:19 Reserved, must be kept at reset value.
Bit 18 TIM17RST: TIM17 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM17 timer
Bit 17 TIM16RST: TIM16 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM16 timer
Bit 16 TIM15RST: TIM15 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM15 timer
Bit 15 Reserved, must be kept at reset value.
Bit 14 USART1RST: USART1 reset
Set and cleared by software.
0: No effect
1: Reset USART1
Bit 13 Reserved, must be kept at reset value.
Bit 12 SPI1RST: SPI1 reset
Set and cleared by software.
0: No effect
1: Reset SPI1

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4
Res.

3
Res.

Res.

rw

RM0091

Reset and clock control (RCC)

Bit 11 TIM1RST: TIM1 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM1 timer
Bit 10 Reserved, must be kept at reset value.
Bit 9 ADCRST: ADC interface reset
Set and cleared by software.
0: No effect
1: Reset ADC interface
Bit 8 Reserved, must be kept at reset value.
Bit 7 USART8RST: USART8 reset
Set and cleared by software
0: No effect
1: Reset USART8
Bit 6 USART7RST: USART7 reset
Set and cleared by software
0: No effect
1: Reset USART7
Bit 5 USART6RST: USART6 reset
Set and cleared by software
0: No effect
1: Reset USART6
Bits 4:1 Reserved, must be kept at reset value.
Bit 0 SYSCFGRST: SYSCFG reset
Set and cleared by software.
0: No effect
1: Reset SYSCFG

6.4.5

APB peripheral reset register 1 (RCC_APB1RSTR)
Address offset: 0x10
Reset value: 0x0000 0000
Access: no wait state, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

Res.

CEC
RST

DAC
RST

PWR
RST

CRS
RST

Res
.

CAN
RST

Res.

USB
RST

I2C2
RST

I2C1
RST

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

SPI2
RST

Res.

Res.

WWDG
RST

Res
.

Res.

TIM14
RST

Res.

Res.

TIM7
RST

TIM6
RST

Res.

Res.

TIM3
RST

TIM2
RST

rw

rw

rw

rw

rw

rw

rw

rw

DocID018940 Rev 9

20

19

18

17

USART5 USART4 USART3 USART2
RST
RST
RST
RST

16
Res.

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Reset and clock control (RCC)

RM0091

Bit 31 Reserved, must be kept at reset value.
Bit 30 CECRST: HDMI CEC reset
Set and cleared by software.
0: No effect
1: Reset HDMI CEC
Bit 29 DACRST: DAC interface reset
Set and cleared by software.
0: No effect
1: Reset DAC interface
Bit 28 PWRRST: Power interface reset
Set and cleared by software.
0: No effect
1: Reset power interface
Bit 27 CRSRST: Clock Recovery System interface reset
Set and cleared by software.
0: No effect
1: Reset CRS interface
Bit 26 Reserved, must be kept at reset value.
Bit 25 CANRST: CAN interface reset
Set and cleared by software.
0: No effect
1: Reset CAN interface
Bit 24 Reserved, must be kept at reset value.
Bit 23 USBRST: USB interface reset
Set and cleared by software.
0: No effect
1: Reset USB interface
Bit 22 I2C2RST: I2C2 reset
Set and cleared by software.
0: No effect
1: Reset I2C2
Bit 21 I2C1RST: I2C1 reset
Set and cleared by software.
0: No effect
1: Reset I2C1
Bit 20 USART5RST: USART5 reset
Set and cleared by software.
0: No effect
1: Reset USART4
Bit 19 USART4RST: USART4 reset
Set and cleared by software.
0: No effect
1: Reset USART4

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RM0091

Reset and clock control (RCC)

Bit 18 USART3RST: USART3 reset
Set and cleared by software.
0: No effect
1: Reset USART3
Bit 17 USART2RST: USART2 reset
Set and cleared by software.
0: No effect
1: Reset USART2
Bits 16:15 Reserved, must be kept at reset value.
Bit 14 SPI2RST: SPI2 reset
Set and cleared by software.
0: No effect
1: Reset SPI2
Bits 13:12 Reserved, must be kept at reset value.
Bit 11 WWDGRST: Window watchdog reset
Set and cleared by software.
0: No effect
1: Reset window watchdog
Bits 10:9 Reserved, must be kept at reset value.
Bit 8 TIM14RST: TIM14 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM14
Bits 7:6 Reserved, must be kept at reset value.
Bit 5 TIM7RST: TIM7 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM7
Bit 4 TIM6RST: TIM6 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM6
Bit 3:2 Reserved, must be kept at reset value.
Bit 1 TIM3RST: TIM3 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM3
Bit 0 TIM2RST: TIM2 timer reset
Set and cleared by software.
0: No effect
1: Reset TIM2

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Reset and clock control (RCC)

6.4.6

RM0091

AHB peripheral clock enable register (RCC_AHBENR)
Address offset: 0x14
Reset value: 0x0000 0014
Access: no wait state, word, half-word and byte access

Note:

When the peripheral clock is not active, the peripheral register values may not be readable
by software and the returned value is always 0x0.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSCEN

Res.

IOPF
EN

IOPE
EN

IOPD
EN

IOPC
EN

IOPB
EN

IOPA
EN

Res.

rw

rw

rw

rw

rw

rw

rw
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CRC
EN

Res.

FLITF
EN

Res.

SRAM
EN

DMA2
EN

DMA
EN

rw

rw

rw

rw

Bits 31:25 Reserved, must be kept at reset value.
Bit 24 TSCEN: Touch sensing controller clock enable
Set and cleared by software.
0: TSC clock disabled
1: TSC clock enabled
Bit 23 Reserved, must be kept at reset value.
Bit 22 IOPFEN: I/O port F clock enable
Set and cleared by software.
0: I/O port F clock disabled
1: I/O port F clock enabled
Bit 21 IOPEEN: I/O port E clock enable
Set and cleared by software.
0: I/O port E clock disabled
1: I/O port E clock enabled
Bit 20 IOPDEN: I/O port D clock enable
Set and cleared by software.
0: I/O port D clock disabled
1: I/O port D clock enabled
Bit 19 IOPCEN: I/O port C clock enable
Set and cleared by software.
0: I/O port C clock disabled
1: I/O port C clock enabled
Bit 18 IOPBEN: I/O port B clock enable
Set and cleared by software.
0: I/O port B clock disabled
1: I/O port B clock enabled

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RM0091

Reset and clock control (RCC)

Bit 17 IOPAEN: I/O port A clock enable
Set and cleared by software.
0: I/O port A clock disabled
1: I/O port A clock enabled
Bits 16:7 Reserved, must be kept at reset value.
Bit 6 CRCEN: CRC clock enable
Set and cleared by software.
0: CRC clock disabled
1: CRC clock enabled
Bit 5 Reserved, must be kept at reset value.
Bit 4 FLITFEN: FLITF clock enable
Set and cleared by software to disable/enable FLITF clock during Sleep mode.
0: FLITF clock disabled during Sleep mode
1: FLITF clock enabled during Sleep mode
Bit 3 Reserved, must be kept at reset value.
Bit 2 SRAMEN: SRAM interface clock enable
Set and cleared by software to disable/enable SRAM interface clock during Sleep mode.
0: SRAM interface clock disabled during Sleep mode.
1: SRAM interface clock enabled during Sleep mode
Bit 1 DMA2EN: DMA2 clock enable
Set and cleared by software.
0: DMA2 clock disabled
1: DMA2 clock enabled
Bit 0 DMAEN: DMA clock enable
Set and cleared by software.
0: DMA clock disabled
1: DMA clock enabled

6.4.7

APB peripheral clock enable register 2 (RCC_APB2ENR)
Address: 0x18
Reset value: 0x0000 0000
Access: word, half-word and byte access
No wait states, except if the access occurs while an access to a peripheral in the APB
domain is on going. In this case, wait states are inserted until the access to APB peripheral
is finished.

Note:

When the peripheral clock is not active, the peripheral register values may not be readable
by software and the returned value is always 0x0.

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Reset and clock control (RCC)

31
Res.

30
Res.

29
Res.

28
Res.

27
Res.

RM0091

26
Res.

25

24

Res.

Res.

23

22

Res.

DBG
MCUEN

21
Res.

20
Res.

19

18

17

16

Res.

TIM17
EN

TIM16
EN

TIM15EN

rw

rw

rw

rw
15

14

13

12

11

10

9

8

Res.

USART1
EN

Res.

SPI1EN

TIM1EN

Res.

ADCEN

Res.

rw

rw

rw

7

6

USART8 USART7 USART6
EN
EN
EN

rw

rw

rw

Bits 31:23 Reserved, must be kept at reset value.
Bit 22 DBGMCUEN MCU debug module clock enable
Set and reset by software.
0: MCU debug module clock disabled
1: MCU debug module enabled
Bits 21:19 Reserved, must be kept at reset value.
Bit 18 TIM17EN: TIM17 timer clock enable
Set and cleared by software.
0: TIM17 timer clock disabled
1: TIM17 timer clock enabled
Bit 17 TIM16EN: TIM16 timer clock enable
Set and cleared by software.
0: TIM16 timer clock disabled
1: TIM16 timer clock enabled
Bit 16 TIM15EN: TIM15 timer clock enable
Set and cleared by software.
0: TIM15 timer clock disabled
1: TIM15 timer clock enabled
Bit 15 Reserved, must be kept at reset value.
Bit 14 USART1EN: USART1 clock enable
Set and cleared by software.
0: USART1clock disabled
1: USART1clock enabled
Bit 13 Reserved, must be kept at reset value.
Bit 12 SPI1EN: SPI1 clock enable
Set and cleared by software.
0: SPI1 clock disabled
1: SPI1 clock enabled
Bit 11 TIM1EN: TIM1 timer clock enable
Set and cleared by software.
0: TIM1 timer clock disabled
1: TIM1P timer clock enabled
Bit 10 Reserved, must be kept at reset value.

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rw

4

3

2

1

0

Res.

Res.

Res.

Res.

SYSCFG
COMPEN
rw

RM0091

Reset and clock control (RCC)

Bit 9 ADCEN: ADC interface clock enable
Set and cleared by software.
0: ADC interface disabled
1: ADC interface clock enabled
Bit 8 Reserved, must be kept at reset value.
Bit 7 USART8EN: USART8 clock enable
Set and cleared by software.
0: USART8clock disabled
1: USART8clock enabled
Bit 6 USART7EN: USART7 clock enable
Set and cleared by software.
0: USART7clock disabled
1: USART7clock enabled
Bit 5 USART6EN: USART6 clock enable
Set and cleared by software.
0: USART6clock disabled
1: USART6clock enabled
Bits 4:1 Reserved, must be kept at reset value.
Bit 0 SYSCFGCOMPEN: SYSCFG & COMP clock enable
Set and cleared by software.
0: SYSCFG & COMP clock disabled
1: SYSCFG & COMP clock enabled

6.4.8

APB peripheral clock enable register 1 (RCC_APB1ENR)
Address: 0x1C
Reset value: 0x0000 0000
Access: word, half-word and byte access
No wait state, except if the access occurs while an access to a peripheral on APB domain is
on going. In this case, wait states are inserted until this access to APB peripheral is finished.

Note:

When the peripheral clock is not active, the peripheral register values may not be readable
by software and the returned value is always 0x0.

31

30

29

28

27

26

25

24

23

22

21

Res.

CEC
EN

DAC
EN

PWR
EN

CRS
EN

Res.

CAN
EN

Res.

USB
EN

I2C2
EN

I2C1
EN

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

SPI2
EN

Res.

Res.

WWDG
EN

Res.

Res.

TIM14
EN

Res.

Res.

TIM7
EN

TIM6
EN

Res.

Res.

TIM3
EN

TIM2
EN

rw

rw

rw

rw

rw

rw

rw

rw

DocID018940 Rev 9

20

19

18

USART5 USART4 USART3
EN
EN
EN

17

16

USART2
EN

Res.

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Reset and clock control (RCC)

RM0091

Bit 31 Reserved, must be kept at reset value.
Bit 30 CECEN: HDMI CEC clock enable
Set and cleared by software.
0: HDMI CEC clock disabled
1: HDMI CEC clock enabled
Bit 29 DACEN: DAC interface clock enable
Set and cleared by software.
0: DAC interface clock disabled
1: DAC interface clock enabled
Bit 28 PWREN: Power interface clock enable
Set and cleared by software.
0: Power interface clock disabled
1: Power interface clock enabled
Bit 27 CRSEN: Clock Recovery System interface clock enable
Set and cleared by software.
0: CRS interface clock disabled
1: CRS interface clock enabled
Bit 26 Reserved, must be kept at reset value.
Bit 25 CANEN: CAN interface clock enable
Set and cleared by software.
0: CAN interface clock disabled
1: CAN interface clock enabled
Bit 24 Reserved, must be kept at reset value.
Bit 23 USBEN: USB interface clock enable
Set and cleared by software.
0: USB interface clock disabled
1: USB interface clock enabled
Bit 22 I2C2EN: I2C2 clock enable
Set and cleared by software.
0: I2C2 clock disabled
1: I2C2 clock enabled
Bit 21 I2C1EN: I2C1 clock enable
Set and cleared by software.
0: I2C1 clock disabled
1: I2C1 clock enabled
Bit 20 USART5EN: USART5 clock enable
Set and cleared by software.
0: USART5 clock disabled
1: USART5 clock enabled
Bit 19 USART4EN: USART4 clock enable
Set and cleared by software.
0: USART4 clock disabled
1: USART4 clock enabled

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RM0091

Reset and clock control (RCC)

Bit 18 USART3EN: USART3 clock enable
Set and cleared by software.
0: USART3 clock disabled
1: USART3 clock enabled
Bit 17 USART2EN: USART2 clock enable
Set and cleared by software.
0: USART2 clock disabled
1: USART2 clock enabled
Bits 16:15 Reserved, must be kept at reset value.
Bit 14 SPI2EN: SPI2 clock enable
Set and cleared by software.
0: SPI2 clock disabled
1: SPI2 clock enabled
Bits 13:12 Reserved, must be kept at reset value.
Bit 11 WWDGEN: Window watchdog clock enable
Set and cleared by software.
0: Window watchdog clock disabled
1: Window watchdog clock enabled
Bits 10:9 Reserved, must be kept at reset value.
Bit 8 TIM14EN: TIM14 timer clock enable
Set and cleared by software.
0: TIM14 clock disabled
1: TIM14 clock enabled
Bits 7:6 Reserved, must be kept at reset value.
Bit 5 TIM7EN: TIM7 timer clock enable
Set and cleared by software.
0: TIM7 clock disabled
1: TIM7 clock enabled
Bit 4 TIM6EN: TIM6 timer clock enable
Set and cleared by software.
0: TIM6 clock disabled
1: TIM6 clock enabled
Bits 3:2 Reserved, must be kept at reset value.
Bit 1 TIM3EN: TIM3 timer clock enable
Set and cleared by software.
0: TIM3 clock disabled
1: TIM3 clock enabled
Bit 0 TIM2EN: TIM2 timer clock enable
Set and cleared by software.
0: TIM2 clock disabled
1: TIM2 clock enabled

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Reset and clock control (RCC)

6.4.9

RM0091

RTC domain control register (RCC_BDCR)
Address offset: 0x20
Reset value: 0x0000 0018, reset by RTC domain reset.
Access: 0 ≤ wait state ≤ 3, word, half-word and byte access
Wait states are inserted in case of successive accesses to this register.

Note:

The LSEON, LSEBYP, RTCSEL and RTCEN bits of the RTC domain control register
(RCC_BDCR) are in the RTC domain. As a result, after Reset, these bits are write-protected
and the DBP bit in the Power control register (PWR_CR) has to be set before these can be
modified. Refer to Section 5.1.3: Battery backup domain for further information. These bits
are only reset after a RTC domain reset (see Section 6.1.3: RTC domain reset). Any internal
or external Reset will not have any effect on these bits.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

BDRST
rw

15
RTC
EN

14
Res.

rw

13
Res.

12
Res.

11
Res.

10
Res.

9

8

RTCSEL[1:0]
rw

7
Res.

6
Res.

rw

5
Res.

4

3

LSEDRV[1:0]
rw

rw

2

1

0

LSE
BYP

LSE
RDY

LSEON

rw

r

rw

Bits 31:17 Reserved, must be kept at reset value.
Bit 16 BDRST: RTC domain software reset
Set and cleared by software.
0: Reset not activated
1: Resets the entire RTC domain
Bit 15 RTCEN: RTC clock enable
Set and cleared by software.
0: RTC clock disabled
1: RTC clock enabled
Bits 14:10 Reserved, must be kept at reset value.
Bits 9:8 RTCSEL[1:0]: RTC clock source selection
Set by software to select the clock source for the RTC. Once the RTC clock source has been
selected, it cannot be changed anymore unless the RTC domain is reset. The BDRST bit can
be used to reset them.
00: No clock
01: LSE oscillator clock used as RTC clock
10: LSI oscillator clock used as RTC clock
11: HSE oscillator clock divided by 32 used as RTC clock
Bits 7:5 Reserved, must be kept at reset value.

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RM0091

Reset and clock control (RCC)

Bits 4:3 LSEDRV LSE oscillator drive capability
Set and reset by software to modulate the LSE oscillator’s drive capability. A reset of the RTC
domain restores the default value.
00: ‘Xtal mode’ low drive capability
01: ‘Xtal mode’ medium-high drive capability
10: ‘Xtal mode’ medium-low drive capability
11: ‘Xtal mode’ high drive capability (reset value)
Note: The oscillator is in Xtal mode when it is not in bypass mode.
Bit 2 LSEBYP: LSE oscillator bypass
Set and cleared by software to bypass oscillator in debug mode. This bit can be written only
when the external 32 kHz oscillator is disabled.
0: LSE oscillator not bypassed
1: LSE oscillator bypassed
Bit 1 LSERDY: LSE oscillator ready
Set and cleared by hardware to indicate when the external 32 kHz oscillator is stable. After the
LSEON bit is cleared, LSERDY goes low after 6 external low-speed oscillator clock cycles.
0: LSE oscillator not ready
1: LSE oscillator ready
Bit 0 LSEON: LSE oscillator enable
Set and cleared by software.
0: LSE oscillator OFF
1: LSE oscillator ON

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Reset and clock control (RCC)

6.4.10

RM0091

Control/status register (RCC_CSR)
Address: 0x24
Reset value: 0xXXX0 0000, reset by system Reset, except reset flags by power Reset only.
Access: 0 ≤ wait state ≤ 3, word, half-word and byte access
Wait states are inserted in case of successive accesses to this register.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

LPWR
RSTF

WWDG
RSTF

IWDG
RSTF

SFT
RSTF

POR
RSTF

PIN
RSTF

OB
LRSTF

RMVF

V18PWR
RSTF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

r

r

r

r

r

r

r

rt_w

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

LSI
RDY

LSION

r

rw

Bit 31 LPWRRSTF: Low-power reset flag
Set by hardware when a Low-power management reset occurs.
Cleared by writing to the RMVF bit.
0: No Low-power management reset occurred
1: Low-power management reset occurred
For further information on Low-power management reset, refer to Low-power management
reset.
Bit 30 WWDGRSTF: Window watchdog reset flag
Set by hardware when a window watchdog reset occurs.
Cleared by writing to the RMVF bit.
0: No window watchdog reset occurred
1: Window watchdog reset occurred
Bit 29 IWDGRSTF: Independent watchdog reset flag
Set by hardware when an independent watchdog reset from VDD domain occurs.
Cleared by writing to the RMVF bit.
0: No watchdog reset occurred
1: Watchdog reset occurred
Bit 28 SFTRSTF: Software reset flag
Set by hardware when a software reset occurs.
Cleared by writing to the RMVF bit.
0: No software reset occurred
1: Software reset occurred
Bit 27 PORRSTF: POR/PDR reset flag
Set by hardware when a POR/PDR reset occurs.
Cleared by writing to the RMVF bit.
0: No POR/PDR reset occurred
1: POR/PDR reset occurred

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RM0091

Reset and clock control (RCC)

Bit 26 PINRSTF: PIN reset flag
Set by hardware when a reset from the NRST pin occurs.
Cleared by writing to the RMVF bit.
0: No reset from NRST pin occurred
1: Reset from NRST pin occurred
Bit 25 OBLRSTF: Option byte loader reset flag
Set by hardware when a reset from the OBL occurs.
Cleared by writing to the RMVF bit.
0: No reset from OBL occurred
1: Reset from OBL occurred
Bit 24 RMVF: Remove reset flag
Set by software to clear the reset flags including RMVF.
0: No effect
1: Clear the reset flags
Bit 23 V18PWRRSTF: Reset flag of the 1.8 V domain.
Set by hardware when a POR/PDR of the 1.8 V domain occurred.
Cleared by writing to the RMVF bit.
0: No POR/PDR reset of the 1.8 V domain occurred
1: POR/PDR reset of the 1.8 V domain occurred
Caution: On the STM32F0x8 family, this flag must be read as reserved.
Bits 22:2 Reserved, must be kept at reset value.
Bit 1 LSIRDY: LSI oscillator ready
Set and cleared by hardware to indicate when the LSI oscillator is stable. After the LSION bit is
cleared, LSIRDY goes low after 3 LSI oscillator clock cycles.
0: LSI oscillator not ready
1: LSI oscillator ready
Bit 0 LSION: LSI oscillator enable
Set and cleared by software.
0: LSI oscillator OFF
1: LSI oscillator ON

6.4.11

AHB peripheral reset register (RCC_AHBRSTR)
Address: 0x28
Reset value: 0x0000 0000
Access: no wait states, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC
RST

Res.

IOPF
RST

IOPE
RST

IOPD
RST

IOPC
RST

IOPB
RST

IOPA
RST

Res.

rw

rw

rw

rw

rw

rw

rw
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

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Reset and clock control (RCC)

RM0091

Bits 31:25 Reserved, must be kept at reset value.
Bit 24 TSCRST: Touch sensing controller reset
Set and cleared by software.
0: No effect
1: Reset TSC
Bit 23 Reserved, must be kept at reset value.
Bit 22 IOPFRST: I/O port F reset
Set and cleared by software.
0: No effect
1: Reset I/O port F
Bit 21 IOPERST: I/O port E reset
Set and cleared by software.
0: No effect
1: Reset I/O port E
Bit 20 IOPDRST: I/O port D reset
Set and cleared by software.
0: No effect
1: Reset I/O port D
Bit 19 IOPCRST: I/O port C reset
Set and cleared by software.
0: No effect
1: Reset I/O port C
Bit 18 IOPBRST: I/O port B reset
Set and cleared by software.
0: No effect
1: Reset I/O port B
Bit 17 IOPARST: I/O port A reset
Set and cleared by software.
0: No effect
1: Reset I/O port A
Bits 16:0 Reserved, must be kept at reset value.

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DocID018940 Rev 9

RM0091

Reset and clock control (RCC)

6.4.12

Clock configuration register 2 (RCC_CFGR2)
Address: 0x2C
Reset value: 0x0000 0000
Access: no wait states, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

3

2

1

0

15

14

13

12

11

10

9

8

7

6

5

4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PREDIV[3:0]
rw

rw

rw

rw

Bits 31:4 Reserved, must be kept at reset value.
Bits 3:0 PREDIV[3:0] PREDIV division factor
These bits are set and cleared by software to select PREDIV division factor. They can be
written only when the PLL is disabled.
Note: Bit 0 is the same bit as bit 17 in Clock configuration register (RCC_CFGR), so
modifying bit 17 Clock configuration register (RCC_CFGR) also modifies bit 0 in Clock
configuration register 2 (RCC_CFGR2) (for compatibility with other STM32 products)
0000: PREDIV input clock not divided
0001: PREDIV input clock divided by 2
0010: PREDIV input clock divided by 3
0011: PREDIV input clock divided by 4
0100: PREDIV input clock divided by 5
0101: PREDIV input clock divided by 6
0110: PREDIV input clock divided by 7
0111: PREDIV input clock divided by 8
1000: PREDIV input clock divided by 9
1001: PREDIV input clock divided by 10
1010: PREDIV input clock divided by 11
1011: PREDIV input clock divided by 12
1100: PREDIV input clock divided by 13
1101: PREDIV input clock divided by 14
1110: PREDIV input clock divided by 15
1111: PREDIV input clock divided by 16

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Reset and clock control (RCC)

6.4.13

RM0091

Clock configuration register 3 (RCC_CFGR3)
Address: 0x30
Reset value: 0x0000 0000
Access: no wait states, word, half-word and byte access

31

30

29

28

27

26

25

24

23

22

21

20

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15
Res.

14
Res.

13
Res.

12
Res.

11
Res.

10
Res.

9

8

7

6

Res.

ADC
SW

USB
SW

CEC
SW

rw

rw

rw

19

18

USART3SW[1:0]

17

16

USART2SW[1:0]

rw

rw

rw

rw

1

0

5

4

3

2

Res.

I2C1
SW

Res.

Res.

rw

USART1SW[1:0]
rw

rw

Bits 31:20 Reserved, must be kept at reset value.
Bits 19:18 USART3SW[1:0]: USART3 clock source selection (available only on STM32F09x devices)
This bit is set and cleared by software to select the USART3 clock source.
00: PCLK selected as USART3 clock source (default)
01: System clock (SYSCLK) selected as USART3 clock
10: LSE clock selected as USART3 clock
11: HSI clock selected as USART3 clock
Bits 17:16 USART2SW[1:0]: USART2 clock source selection (available only on STM32F07x and
STM32F09x devices)
This bit is set and cleared by software to select the USART2 clock source.
00: PCLK selected as USART2 clock source (default)
01: System clock (SYSCLK) selected as USART2 clock
10: LSE clock selected as USART2 clock
11: HSI clock selected as USART2 clock
Bits 15:9 Reserved, must be kept at reset value.
Bit 8 ADCSW: ADC clock source selection
Obsolete setting. To be kept at reset value, connecting the HSI14 clock to the ADC
asynchronous clock input. Proper ADC clock selection is done inside the ADC_CFGR2 (refer
to Section 13.12.5: ADC configuration register 2 (ADC_CFGR2) on page 263).
Bit 7 USBSW: USB clock source selection
This bit is set and cleared by software to select the USB clock source.
0: HSI48 clock selected as USB clock source (default)
1: PLL clock (PLLCLK) selected as USB clock
Bit 6 CECSW: HDMI CEC clock source selection
This bit is set and cleared by software to select the CEC clock source.
0: HSI clock, divided by 244, selected as CEC clock (default)
1: LSE clock selected as CEC clock
Bit 5 Reserved, must be kept at reset value.

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RM0091

Reset and clock control (RCC)

Bit 4 I2C1SW: I2C1 clock source selection
This bit is set and cleared by software to select the I2C1 clock source.
0: HSI clock selected as I2C1 clock source (default)
1: System clock (SYSCLK) selected as I2C1 clock
Bits 3:2 Reserved, must be kept at reset value.
Bits 1:0 USART1SW[1:0]: USART1 clock source selection
This bit is set and cleared by software to select the USART1 clock source.
00: PCLK selected as USART1 clock source (default)
01: System clock (SYSCLK) selected as USART1 clock
10: LSE clock selected as USART1 clock
11: HSI clock selected as USART1 clock

6.4.14

Clock control register 2 (RCC_CR2)
Address: 0x34
Reset value: 0xXX00 XX80, where X is undefined.
Access: no wait states, word, half-word and byte access

31

30

29

28

27

26

25

24

HSI48CAL[7:0]

23
Res.

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

22
Res.

7

6

HSI14CAL[7:0]
r

r

r

r

r

21
Res.

20
Res.

5

4

19
Res.

3

HSI14TRIM[4:0]
r

r

r

rw

rw

rw

rw

rw

18

17

16

Res.

HSI48
RDY

HSI48
ON

r

rw

2

1

0

HSI14
DIS

HSI14
RDY

HSI14
ON

rw

r

rw

Bits 31:24 HSI48CAL[7:0]: HSI48 factory clock calibration
These bits are initialized automatically at startup and are read-only.
Bits 23:18 Reserved, must be kept at reset value.
Bit 17 HSI48RDY: HSI48 clock ready flag
Set by hardware to indicate that HSI48 oscillator is stable. After the HSI48ON bit is cleared,
HSI48RDY goes low after 6 HSI48 oscillator clock cycles.
0: HSI48 oscillator not ready
1: HSI48 oscillator ready
Bit 16 HSI48ON: HSI48 clock enable
Set and cleared either by software or by hardware. Set by hardware when the USB peripheral
is enabled and switched on this source; reset by hardware to stop the oscillator when entering
in Stop or Standby mode. This bit cannot be reset if the HSI48 is used directly or indirectly as
system clock or is selected to become the system clock.
0: HSI48 oscillator OFF
1: HSI48 oscillator ON
Bits 15:8 HSI14CAL[7:0]: HSI14 clock calibration
These bits are initialized automatically at startup.

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Reset and clock control (RCC)

RM0091

Bits 7:3 HSI14TRIM[4:0]: HSI14 clock trimming
These bits provide an additional user-programmable trimming value that is added to the
HSI14CAL[7:0] bits. It can be programmed to adjust to variations in voltage and temperature
that influence the frequency of the HSI14.
The default value is 16, which, when added to the HSI14CAL value, should trim the HSI14 to
14 MHz ± 1%. The trimming step is around 50 kHz between two consecutive HSI14CAL steps.
Bit 2 HSI14DIS HSI14 clock request from ADC disable
Set and cleared by software.
When set this bit prevents the ADC interface from enabling the HSI14 oscillator.
0: ADC interface can turn on the HSI14 oscillator
1: ADC interface can not turn on the HSI14 oscillator
Bit 1 HSI14RDY: HSI14 clock ready flag
Set by hardware to indicate that HSI14 oscillator is stable. After the HSI14ON bit is cleared,
HSI14RDY goes low after 6 HSI14 oscillator clock cycles. When HSI14ON is not set but the
HSI14 oscillator is enabled by the peripheral through a clock request, this bit is not set.
0: HSI14 oscillator not ready
1: HSI14 oscillator ready
Bit 0 HSI14ON: HSI14 clock enable
Set and cleared by software. When the HSI14 oscillator is enabled by the peripheral through a
clock request, this bit is not set and resetting it does not stop the HSI14 oscillator.
0: HSI14 oscillator OFF
1: HSI14 oscillator ON

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0x24

RCC_CSR

Reset value

X

X X X

X X

Reset value

DocID018940 Rev 9

0

0

0

0

0

LSEON

0

0

0

0

LSION

LSE
DRV
[1:0]

0
TIM2EN

Res.

SRAMEN
DAM2EN
DMAEN

1
0
0

Res.
Res.
SYSCFGCOMPEN

TIM2RST

Res.
TIM3RST

0

TIM3EN

1

LSEBYP

HSI14 RDYF
PLLRDYF
HSERDYF
HSIRDYF
LSERDYF
LSIRDYF

0
0
0
0
0
0

USART6RST
Res.
Res.
Res.
Res.
SYSCFGRST

HSION

0
1
1

SWS
[1:0]
SW
[1:0]

Res.
HSIRDY

HPRE[3:0]

LSERDY

0

TM6RST
Res.

TM7RST

CSSF
HSI48RDYF
USART7RST

Res.

HSITRIM[4:0]

Res.

0

0

Res.

0

FLITFEN
Res.

0

Res.

0
0

USART6EN
Res.

0

TIM7EN

CRCEN
Res.

0

TIM6EN
Res.

USART7EN

0

Res.

0

Res.

Res.

LSIRDYIE
USART8RST

0

0

Res.

0

RTC
SEL
[1:0]

0

Res.

0
Res.

0

Res.

PPRE
[2:0]

1

Res.

USART8EN

0

LSERDYIE

0

0

ADCRST
Res.
0

TIM14RST
Res.

Res.

0

Res.

0

Res.

HSIRDYIE

Res.
Res.

0

Res.

0
Res.

0

ADCEN
Res.

HSERDYIE
0

TIM1RST
Res.

0

Res.

WWDGRST
Res.

0

TIM14EN
Res.

Res.

Res.

0

Res.

TIM1EN
Res.

PLLRDYIE

0

Res.

0

WWDGEN
Res.

0

Res.

0

Res.

0

0

Res.

0

0

Res.

0

0
SPI1RST

HSICAL[7:0]

LSIRDY

X X
0

Res.

0

Res.

0

SPI1EN

ADC PRE

0
HSI48RDYIE

0
HSI14 RDYIE

0

USART1RST
Res.

0

Res.

0
SPI2RST
Res.

0

Res.

0

0

Res.

0
Res.

HSEON
PLLSRC[0]

PLLMUL[3:0]
PLLSRC[1]

0

Res.

LSIRDYC

0

Res.

0
USART1EN
Res.

0

SPI2EN
Res.

0
Res.

TIM15RST

HSEBYP
HSERDY
0

Res.
CSSON

0

Res.

0
Res.

0

Res.

TIM16RST

0

Res.

0

TIM15 EN

TIM17RST

0

Res.

HSIRDYC
LSERDYC

0

Res.

Res.

Res.

PLL ON
Res.

0
PLLXTPRE

HSERDYC

0

Res.

Res.

Res.

PLL RDY

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0
USART2RST
Res.

PLLRDYC

0

Res.

0

BDRST

0

TIM16 EN

USART3RST

0
IOPAEN
Res.

IOPBEN

0

TIM17 EN

USART4RST

Res.

0

RTCEN
Res.

0

Res.

0

Res.

0

USART2EN
Res.

USART3EN

0

Res.

Res.

0

Res.

Reset value
IOPCEN
0

Res.

0
0

DBGMCURST
Res.

0

Res.

USART4EN

Res.

0

Res.

USART5RST

0

USART4RST
0

Res.

Res.

HSI48RDYC

Res.

HSI14 RDYC

Res.

0

Res.

USART5EN

I2C1RST

Res.

0

Res.

I2C2RST

0

IOPFEN
0

IOPEEN

Reset value

DBGMCUEN
Res.

Res.

0

Res.

I2C1EN

0
I2C2EN

Reset value

Res.

0

Res.

0

Res.

0

CSSC

0

Res.

0

Res.

USBRST

Res.

0

Res.

CANRST
Res.

0

TSCEN
Res.

Res.

0

USBEN

Res.

0

Res.

Res.

Res.

Res.

Res.

0
MCO [3:0]

Res.

CANEN
Res.

Reset value

Res.

Res.
Res.

Res.

PLL NODIV

Reset value

Res.

0

RMVF
Res.

OBLRSTF

0
Res.

Res.

0

CRSRST
Res.

DACRST
PWRRST

0

Res.

Res.

Res.

Reset value

Res.

0
Res.

Res.

Res.
0

Res.

0
CRSEN
Res.

0

Res.

DACEN
PWREN

Res.
CECRST

0

Res.

RCC_CFGR
MCOPRE
[2:0]

PINRSTF

RCC_BDCR

Res.

Reset value

PORRSTF

0x20
RCC_APB1ENR

Res.

0x1C
RCC_APB2ENR

SFTRSTF

0x18
RCC_AHBENR
Res.

Reset value

IWDGRSTF

0x14
RCC_APB1RSTR

Res.

0x010
RCC_APB2RSTR

Res.

0x0C
RCC_CIR

Res.

0x08

CECEN

0x04
RCC_CR

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

LPWRSTF

6.4.15

WWDGRSTF

RM0091
Reset and clock control (RCC)

RCC register map
The following table gives the RCC register map and the reset values.
Table 19. RCC register map and reset values

0
0
0
0
0
0
0
0
0
0
0

0

0
0

0

0

0

0

0

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0x34

136/1004
RCC_CR2

Reset value
X
X X X
X X

HSI48CAL[7:0]
HSI48ON

0
0

0
0

DocID018940 Rev 9
X X X
X X X

USBSW

0
0

HSI14CAL[7:0]
X X

Refer to Section 2.2.2 on page 46 for the register boundary addresses.
1

0

0
0
0
0

0

HSI14ON

HSI14TRIM[14:0]

0

HSI14RDY

0
HSI14DIS

0
USART1SW[1:0]

0

Res.

Reset value

I2C1SW
Res.

CECSW
Res.

ADCSW

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

IOPA RST
0

Res.

IOPB RST
0
Res.

IOPC RST
0
Res.

.IOPERST
IOPD RST
0

Res.

Res.
IOPF RST
0

Res.

Res.

TSC RST

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

USART2SW[1:0]

Res.

Res.

USART3SW[1:0]

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

HSI48RDY

X X

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

RCC_CFGR3

Res.

0x30
Res.

0x2C
RCC_CFGR2
Res.

RCC_AHBRSTR

Res.

0x28

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

Reset and clock control (RCC)
RM0091

Table 19. RCC register map and reset values (continued)

PREDIV[3:0]
0
0

0
0
0

RM0091

7

Clock recovery system (CRS)

Clock recovery system (CRS)
This section applies to STM32F04x, STM32F07x and STM32F09x devices only.

7.1

Introduction
The clock recovery system (CRS) is an advanced digital controller acting on the internal
fine-granularity trimmable RC oscillator HSI48. The CRS provides a powerful means for
oscillator output frequency evaluation, based on comparison with a selectable
synchronization signal. It is capable of doing automatic adjustment of oscillator trimming
based on the measured frequency error value, while keeping the possibility of a manual
trimming.
The CRS is ideally suited to provide a precise clock to the USB peripheral. In such case, the
synchronization signal can be derived from the start-of-frame (SOF) packet signalization on
the USB bus, which is sent by a USB host at precise 1-ms intervals.
The synchronization signal can also be derived from the LSE oscillator output, from an
external pin, or it can be generated by user software.

7.2

CRS main features
•

Selectable synchronization source with programmable prescaler and polarity:
–

External pin

–

LSE oscillator output

–

USB SOF packet reception

•

Possibility to generate synchronization pulses by software

•

Automatic oscillator trimming capability with no need of CPU action

•

Manual control option for faster start-up convergence

•

16-bit frequency error counter with automatic error value capture and reload

•

Programmable limit for automatic frequency error value evaluation and status reporting

•

Maskable interrupts/events:
–

Expected synchronization (ESYNC)

–

Synchronization OK (SYNCOK)

–

Synchronization warning (SYNCWARN)

–

Synchronization or trimming error (ERR)

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RM0091

7.3

CRS functional description

7.3.1

CRS block diagram
Figure 14. CRS block diagram
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7.3.2

Synchronization input
The CRS synchronization (SYNC) source, selectable through the CRS_CFGR register, can
be the signal from the external CRS_SYNC pin, the LSE clock or the USB SOF signal.For a
better robustness of the SYNC input, a simple digital filter (2 out of 3 majority votes,
sampled by the HSI48 clock) is implemented to filter out any glitches. This source signal
also has a configurable polarity and can then be divided by a programmable binary
prescaler to obtain a synchronization signal in a suitable frequency range (usually around
1 kHz).
For more information on the CRS synchronization source configuration, refer to
Section 7.6.2: CRS configuration register (CRS_CFGR).

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Clock recovery system (CRS)
It is also possible to generate a synchronization event by software, by setting the SWSYNC
bit in the CRS_CR register.

7.3.3

Frequency error measurement
The frequency error counter is a 16-bit down/up counter which is reloaded with the RELOAD
value on each SYNC event. It starts counting down till it reaches the zero value, where the
ESYNC (expected synchronization) event is generated. Then it starts counting up to the
OUTRANGE limit where it eventually stops (if no SYNC event is received) and generates a
SYNCMISS event. The OUTRANGE limit is defined as the frequency error limit (FELIM field
of the CRS_CFGR register) multiplied by 128.
When the SYNC event is detected, the actual value of the frequency error counter and its
counting direction are stored in the FECAP (frequency error capture) field and in the FEDIR
(frequency error direction) bit of the CRS_ISR register. When the SYNC event is detected
during the downcounting phase (before reaching the zero value), it means that the actual
frequency is lower than the target (and so, that the TRIM value should be incremented),
while when it is detected during the upcounting phase it means that the actual frequency is
higher (and that the TRIM value should be decremented).
Figure 15. CRS counter behavior
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Clock recovery system (CRS)

7.3.4

RM0091

Frequency error evaluation and automatic trimming
The measured frequency error is evaluated by comparing its value with a set of limits:
–

TOLERANCE LIMIT, given directly in the FELIM field of the CRS_CFGR register

–

WARNING LIMIT, defined as 3 * FELIM value

–

OUTRANGE (error limit), defined as 128 * FELIM value

The result of this comparison is used to generate the status indication and also to control the
automatic trimming which is enabled by setting the AUTOTRIMEN bit in the CRS_CR
register:
•

•

•

•

Note:

When the frequency error is below the tolerance limit, it means that the actual trimming
value in the TRIM field is the optimal one and that then, no trimming action is
necessary.
–

SYNCOK status indicated

–

TRIM value not changed in AUTOTRIM mode

When the frequency error is below the warning limit but above or equal to the tolerance
limit, it means that some trimming action is necessary but that adjustment by one
trimming step is enough to reach the optimal TRIM value.
–

SYNCOK status indicated

–

TRIM value adjusted by one trimming step in AUTOTRIM mode

When the frequency error is above or equal to the warning limit but below the error
limit, it means that a stronger trimming action is necessary, and there is a risk that the
optimal TRIM value will not be reached for the next period.
–

SYNCWARN status indicated

–

TRIM value adjusted by two trimming steps in AUTOTRIM mode

When the frequency error is above or equal to the error limit, it means that the
frequency is out of the trimming range. This can also happen when the SYNC input is
not clean or when some SYNC pulse is missing (for example when one USB SOF is
corrupted).
–

SYNCERR or SYNCMISS status indicated

–

TRIM value not changed in AUTOTRIM mode

If the actual value of the TRIM field is so close to its limits that the automatic trimming would
force it to overflow or underflow, then the TRIM value is set just to the limit and the
TRIMOVF status is indicated.
In AUTOTRIM mode (AUTOTRIMEN bit set in the CRS_CR register), the TRIM field of
CRS_CR is adjusted by hardware and is read-only.

7.3.5

CRS initialization and configuration
RELOAD value
The RELOAD value should be selected according to the ratio between the target frequency
and the frequency of the synchronization source after prescaling. It is then decreased by
one in order to reach the expected synchronization on the zero value. The formula is the
following:
RELOAD = (fTARGET / fSYNC) -1
The reset value of the RELOAD field corresponds to a target frequency of 48 MHz and a
synchronization signal frequency of 1 kHz (SOF signal from USB).

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Clock recovery system (CRS)

FELIM value
The selection of the FELIM value is closely coupled with the HSI48 oscillator characteristics
and its typical trimming step size. The optimal value corresponds to half of the trimming step
size, expressed as a number of HSI48 oscillator clock ticks. The following formula can be
used:
FELIM = (fTARGET / fSYNC) * STEP[%] / 100% / 2
The result should be always rounded up to the nearest integer value in order to obtain the
best trimming response. If frequent trimming actions are not wanted in the application, the
trimming hysteresis can be increased by increasing slightly the FELIM value.
The reset value of the FELIM field corresponds to (fTARGET / fSYNC) = 48000 and to a typical
trimming step size of 0.14%.
Caution:

There is no hardware protection from a wrong configuration of the RELOAD and FELIM
fields which can lead to an erratic trimming response. The expected operational mode
requires proper setup of the RELOAD value (according to the synchronization source
frequency), which is also greater than 128 * FELIM value (OUTRANGE limit).

7.4

CRS low-power modes
Table 20. Effect of low-power modes on CRS
Mode
Sleep

Description
No effect.
CRS interrupts cause the device to exit the Sleep mode.

Stop

CRS registers are frozen.
The CRS stops operating until the Stop or Standby mode is exited and the HSI48 oscillator
Standby restarted.

7.5

CRS interrupts
Table 21. Interrupt control bits
Interrupt event

Event flag

Enable
control bit

Clear
flag bit

Expected synchronization

ESYNCF

ESYNCIE

ESYNCC

Synchronization OK

SYNCOKF

SYNCOKIE

SYNCOKC

Synchronization warning

SYNCWARNF

SYNCWARNIE

SYNCWARNC

Synchronization or trimming error
(TRIMOVF, SYNCMISS, SYNCERR)

ERRF

ERRIE

ERRC

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Clock recovery system (CRS)

7.6

RM0091

CRS registers
Refer to Section 1.1 on page 42 of the reference manual for a list of abbreviations used in
register descriptions.
The peripheral registers can be accessed by words (32-bit).

7.6.1

CRS control register (CRS_CR)
Address offset: 0x00
Reset value: 0x0000 2000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

SWSY AUTOT
NC
RIMEN

TRIM[5:0]
rw

rw

rw

rw

rw

rw

rt_w

rw

CEN
rw

Res.

SYNC
ESYNC
SYNCO
ERRIE WARNI
IE
KIE
E
rw

rw

rw

rw

Bits 31:14 Reserved, must be kept at reset value.
Bits 13:8 TRIM[5:0]: HSI48 oscillator smooth trimming
These bits provide a user-programmable trimming value to the HSI48 oscillator. They can be
programmed to adjust to variations in voltage and temperature that influence the frequency
of the HSI48.
The default value is 32, which corresponds to the middle of the trimming interval. The
trimming step is around 67 kHz between two consecutive TRIM steps. A higher TRIM value
corresponds to a higher output frequency.
When the AUTOTRIMEN bit is set, this field is controlled by hardware and is read-only.
Bit 7 SWSYNC: Generate software SYNC event
This bit is set by software in order to generate a software SYNC event. It is automatically
cleared by hardware.
0: No action
1: A software SYNC event is generated.
Bit 6 AUTOTRIMEN: Automatic trimming enable
This bit enables the automatic hardware adjustment of TRIM bits according to the measured
frequency error between two SYNC events. If this bit is set, the TRIM bits are read-only. The
TRIM value can be adjusted by hardware by one or two steps at a time, depending on the
measured frequency error value. Refer to Section 7.3.4: Frequency error evaluation and
automatic trimming for more details.
0: Automatic trimming disabled, TRIM bits can be adjusted by the user.
1: Automatic trimming enabled, TRIM bits are read-only and under hardware control.
Bit 5 CEN: Frequency error counter enable
This bit enables the oscillator clock for the frequency error counter.
0: Frequency error counter disabled
1: Frequency error counter enabled
When this bit is set, the CRS_CFGR register is write-protected and cannot be modified.
Bit 4 Reserved, must be kept at reset value.

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Clock recovery system (CRS)

Bit 3 ESYNCIE: Expected SYNC interrupt enable
0: Expected SYNC (ESYNCF) interrupt disabled
1: Expected SYNC (ESYNCF) interrupt enabled
Bit 2 ERRIE: Synchronization or trimming error interrupt enable
0: Synchronization or trimming error (ERRF) interrupt disabled
1: Synchronization or trimming error (ERRF) interrupt enabled
Bit 1 SYNCWARNIE: SYNC warning interrupt enable
0: SYNC warning (SYNCWARNF) interrupt disabled
1: SYNC warning (SYNCWARNF) interrupt enabled
Bit 0 SYNCOKIE: SYNC event OK interrupt enable
0: SYNC event OK (SYNCOKF) interrupt disabled
1: SYNC event OK (SYNCOKF) interrupt enabled

7.6.2

CRS configuration register (CRS_CFGR)
This register can be written only when the frequency error counter is disabled (CEN bit is
cleared in CRS_CR). When the counter is enabled, this register is write-protected.
Address offset: 0x04
Reset value: 0x2022 BB7F

31

30

SYNCP
OL

Res.

rw

29

28

SYNCSRC[1:0]

27

26

Res.

25

24

23

22

21

SYNCDIV[2:0]

20

19

18

17

16

FELIM[7:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

RELOAD[15:0]
rw

rw

Bit 31 SYNCPOL: SYNC polarity selection
This bit is set and cleared by software to select the input polarity for the SYNC signal source.
0: SYNC active on rising edge (default)
1: SYNC active on falling edge
Bit 30 Reserved, must be kept at reset value.
Bits 29:28 SYNCSRC[1:0]: SYNC signal source selection
These bits are set and cleared by software to select the SYNC signal source.
00: GPIO selected as SYNC signal source
01: LSE selected as SYNC signal source
10: USB SOF selected as SYNC signal source (default).
11: Reserved
Note: When using USB LPM (Link Power Management) and the device is in Sleep mode, the
periodic USB SOF will not be generated by the host. No SYNC signal will therefore be
provided to the CRS to calibrate the HSI48 on the run. To guarantee the required clock
precision after waking up from Sleep mode, the LSE or reference clock on the GPIOs
should be used as SYNC signal.
Bit 27 Reserved, must be kept at reset value.

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Bits 26:24 SYNCDIV[2:0]: SYNC divider
These bits are set and cleared by software to control the division factor of the SYNC signal.
000: SYNC not divided (default)
001: SYNC divided by 2
010: SYNC divided by 4
011: SYNC divided by 8
100: SYNC divided by 16
101: SYNC divided by 32
110: SYNC divided by 64
111: SYNC divided by 128
Bits 23:16 FELIM[7:0]: Frequency error limit
FELIM contains the value to be used to evaluate the captured frequency error value latched
in the FECAP[15:0] bits of the CRS_ISR register. Refer to Section 7.3.4: Frequency error
evaluation and automatic trimming for more details about FECAP evaluation.
Bits 15:0 RELOAD[15:0]: Counter reload value
RELOAD is the value to be loaded in the frequency error counter with each SYNC event.
Refer to Section 7.3.3: Frequency error measurement for more details about counter
behavior.

7.6.3

CRS interrupt and status register (CRS_ISR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

r

r

r

r

r

r

r

FECAP[15:0]
r
15

r
14

r
13

12

r

r

11

10

r

r
9

r
8

r
7

6

5

4

3

2

1

0

FEDIR Res. Res. Res. Res. TRIMOVF SYNCMISS SYNCERR Res. Res. Res. Res. ESYNCF ERRF SYNCWARNF SYNCOKF
r

r

r

r

r

r

r

r

Bits 31:16 FECAP[15:0]: Frequency error capture
FECAP is the frequency error counter value latched in the time of the last SYNC event.
Refer to Section 7.3.4: Frequency error evaluation and automatic trimming for more details
about FECAP usage.
Bit 15 FEDIR: Frequency error direction
FEDIR is the counting direction of the frequency error counter latched in the time of the last
SYNC event. It shows whether the actual frequency is below or above the target.
0: Upcounting direction, the actual frequency is above the target.
1: Downcounting direction, the actual frequency is below the target.
Bits 14:11 Reserved, must be kept at reset value.
Bit 10 TRIMOVF: Trimming overflow or underflow
This flag is set by hardware when the automatic trimming tries to over- or under-flow the
TRIM value. An interrupt is generated if the ERRIE bit is set in the CRS_CR register. It is
cleared by software by setting the ERRC bit in the CRS_ICR register.
0: No trimming error signalized
1: Trimming error signalized

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Clock recovery system (CRS)

Bit 9 SYNCMISS: SYNC missed
This flag is set by hardware when the frequency error counter reached value FELIM * 128
and no SYNC was detected, meaning either that a SYNC pulse was missed or that the
frequency error is too big (internal frequency too high) to be compensated by adjusting the
TRIM value, and that some other action should be taken. At this point, the frequency error
counter is stopped (waiting for a next SYNC) and an interrupt is generated if the ERRIE bit is
set in the CRS_CR register. It is cleared by software by setting the ERRC bit in the
CRS_ICR register.
0: No SYNC missed error signalized
1: SYNC missed error signalized
Bit 8 SYNCERR: SYNC error
This flag is set by hardware when the SYNC pulse arrives before the ESYNC event and the
measured frequency error is greater than or equal to FELIM * 128. This means that the
frequency error is too big (internal frequency too low) to be compensated by adjusting the
TRIM value, and that some other action should be taken. An interrupt is generated if the
ERRIE bit is set in the CRS_CR register. It is cleared by software by setting the ERRC bit in
the CRS_ICR register.
0: No SYNC error signalized
1: SYNC error signalized
Bits 7:4 Reserved, must be kept at reset value.
Bit 3 ESYNCF: Expected SYNC flag
This flag is set by hardware when the frequency error counter reached a zero value. An
interrupt is generated if the ESYNCIE bit is set in the CRS_CR register. It is cleared by
software by setting the ESYNCC bit in the CRS_ICR register.
0: No expected SYNC signalized
1: Expected SYNC signalized
Bit 2 ERRF: Error flag
This flag is set by hardware in case of any synchronization or trimming error. It is the logical
OR of the TRIMOVF, SYNCMISS and SYNCERR bits. An interrupt is generated if the ERRIE
bit is set in the CRS_CR register. It is cleared by software in reaction to setting the ERRC bit
in the CRS_ICR register, which clears the TRIMOVF, SYNCMISS and SYNCERR bits.
0: No synchronization or trimming error signalized
1: Synchronization or trimming error signalized
Bit 1 SYNCWARNF: SYNC warning flag
This flag is set by hardware when the measured frequency error is greater than or equal to
FELIM * 3, but smaller than FELIM * 128. This means that to compensate the frequency
error, the TRIM value must be adjusted by two steps or more. An interrupt is generated if the
SYNCWARNIE bit is set in the CRS_CR register. It is cleared by software by setting the
SYNCWARNC bit in the CRS_ICR register.
0: No SYNC warning signalized
1: SYNC warning signalized
Bit 0 SYNCOKF: SYNC event OK flag
This flag is set by hardware when the measured frequency error is smaller than FELIM * 3.
This means that either no adjustment of the TRIM value is needed or that an adjustment by
one trimming step is enough to compensate the frequency error. An interrupt is generated if
the SYNCOKIE bit is set in the CRS_CR register. It is cleared by software by setting the
SYNCOKC bit in the CRS_ICR register.
0: No SYNC event OK signalized
1: SYNC event OK signalized

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Clock recovery system (CRS)

7.6.4

RM0091

CRS interrupt flag clear register (CRS_ICR)
Address offset: 0x0C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

ESYNCC

ERRC

SYNCWARNC

SYNCOKC

rw

rw

rw

rw

Bits 31:4 Reserved, must be kept at reset value
Bit 3 ESYNCC: Expected SYNC clear flag
Writing 1 to this bit clears the ESYNCF flag in the CRS_ISR register.
Bit 2 ERRC: Error clear flag
Writing 1 to this bit clears TRIMOVF, SYNCMISS and SYNCERR bits and consequently also
the ERRF flag in the CRS_ISR register.
Bit 1 SYNCWARNC: SYNC warning clear flag
Writing 1 to this bit clears the SYNCWARNF flag in the CRS_ISR register.
Bit 0 SYNCOKC: SYNC event OK clear flag
Writing 1 to this bit clears the SYNCOKF flag in the CRS_ISR register.

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7.6.5

Clock recovery system (CRS)

CRS register map

SWSYNC

CEN

Res.

ESYNCIE

ERRIE

SYNCWARNIE

SYNCOKIE

0

0

0

0

0

0

0

0

0

0

0

0

CRS_ICR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

Reset value

SYNCOKF

0

0

0

0

0
SYNCOKC

0

ERRF

0

1

SYNCWARNF

0

1

ERRC

0

1

SYNCWARNC

0

1
ESYNCF

0

1

ESYNCC

0

1

Res.

0

1

Res.

0

0

Res.

0

1
SYNCERR

0

1

Res.

0

0

SYNCMISS

0

1

Res.

0

Res.

1

Res.

1

Res.

0

Res.

FECAP[15:0]

1

Res.

0

Res.

1

TRIMOVF

0

Reset value

0x0C

0

Res.

0

Res.

0

Res.

1

Res.

0

Res.

0

Res.

0

Res.

CRS_ISR

0

Res.

0

0

RELOAD[15:0]

FEDIR

0

0

FELIM[7:0]

Res.

1

SYNC
DIV
[2:0]

Res.

0

Res.

Reset value

SYNC
SRC
[1:0]

Res.

0x08

CRS_CFGR

Res.

0x04

1
SYNCPOL

Reset value

TRIM[5:0]

AUTOTRIMEN

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CRS_CR

Res.

0x00

Res.

Offset Register

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 22. CRS register map and reset values

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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General-purpose I/Os (GPIO)

RM0091

8

General-purpose I/Os (GPIO)

8.1

Introduction
Each general-purpose I/O port has four 32-bit configuration registers (GPIOx_MODER,
GPIOx_OTYPER, GPIOx_OSPEEDR and GPIOx_PUPDR), two 32-bit data registers
(GPIOx_IDR and GPIOx_ODR) and a 32-bit set/reset register (GPIOx_BSRR). Ports A and
B also have a 32-bit locking register (GPIOx_LCKR) and two 32-bit alternate function
selection registers (GPIOx_AFRH and GPIOx_AFRL).
On STM32F07x and STM32F09x devices, also ports C, D and E have two 32-bit alternate
function selection registers (GPIOx_AFRH and GPIOx_AFRL).
Port E is available on STM32F07x and STM32F09x devices only.

8.2

8.3

GPIO main features
•

Output states: push-pull or open drain + pull-up/down

•

Output data from output data register (GPIOx_ODR) or peripheral (alternate function
output)

•

Speed selection for each I/O

•

Input states: floating, pull-up/down, analog

•

Input data to input data register (GPIOx_IDR) or peripheral (alternate function input)

•

Bit set and reset register (GPIOx_ BSRR) for bitwise write access to GPIOx_ODR

•

Locking mechanism (GPIOx_LCKR) provided to freeze the port A or B I/O port
configuration.

•

Analog function

•

Alternate function selection registers(at most 16 AFs possible per I/O)

•

Fast toggle capable of changing every two clock cycles

•

Highly flexible pin multiplexing allows the use of I/O pins as GPIOs or as one of several
peripheral functions

GPIO functional description
Subject to the specific hardware characteristics of each I/O port listed in the datasheet, each
port bit of the general-purpose I/O (GPIO) ports can be individually configured by software in
several modes:

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•

Input floating

•

Input pull-up

•

Input-pull-down

•

Analog

•

Output open-drain with pull-up or pull-down capability

•

Output push-pull with pull-up or pull-down capability

•

Alternate function push-pull with pull-up or pull-down capability

•

Alternate function open-drain with pull-up or pull-down capability

DocID018940 Rev 9

RM0091

General-purpose I/Os (GPIO)
Each I/O port bit is freely programmable, however the I/O port registers have to be
accessed as 32-bit words, half-words or bytes. The purpose of the GPIOx_BSRR and
GPIOx_BRR registers is to allow atomic read/modify accesses to any of the GPIOx_ODR
registers. In this way, there is no risk of an IRQ occurring between the read and the modify
access.
Figure 16 shows the basic structures of a standard I/O port bit. Table 23 gives the possible
port bit configurations.
Figure 16. Basic structure of an I/O port bit
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Table 23. Port bit configuration table(1)
MODER(i)
[1:0]

01

OTYPER(i)

OSPEEDR(i)
[1:0]

PUPDR(i)
[1:0]

I/O configuration

0

0

0

GP output

PP

0

0

1

GP output

PP + PU

0

1

0

GP output

PP + PD

1

1

Reserved

0

0

GP output

OD

1

0

1

GP output

OD + PU

1

1

0

GP output

OD + PD

1

1

1

Reserved (GP output OD)

0
1

SPEED
[1:0]

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RM0091
Table 23. Port bit configuration table(1) (continued)

MODER(i)
[1:0]

10

00

11

OTYPER(i)

OSPEEDR(i)
[1:0]

PUPDR(i)
[1:0]

I/O configuration

0

0

0

AF

PP

0

0

1

AF

PP + PU

0

1

0

AF

PP + PD

1

1

Reserved

0

0

AF

OD

1

0

1

AF

OD + PU

1

1

0

AF

OD + PD

1

1

1

Reserved

0

SPEED
[1:0]

1

x

x

x

0

0

Input

Floating

x

x

x

0

1

Input

PU

x

x

x

1

0

Input

PD

x

x

x

1

1

Reserved (input floating)

x

x

x

0

0

Input/output

x

x

x

0

1

x

x

x

1

0

x

x

x

1

1

Analog

Reserved

1. GP = general-purpose, PP = push-pull, PU = pull-up, PD = pull-down, OD = open-drain, AF = alternate
function.

8.3.1

General-purpose I/O (GPIO)
During and just after reset, the alternate functions are not active and most of the I/O ports
are configured in input floating mode.
The debug pins are in AF pull-up/pull-down after reset:
•

PA14: SWCLK in pull-down

•

PA13: SWDIO in pull-up

When the pin is configured as output, the value written to the output data register
(GPIOx_ODR) is output on the I/O pin. It is possible to use the output driver in push-pull
mode or open-drain mode (only the low level is driven, high level is HI-Z).
The input data register (GPIOx_IDR) captures the data present on the I/O pin at every AHB
clock cycle.
All GPIO pins have weak internal pull-up and pull-down resistors, which can be activated or
not depending on the value in the GPIOx_PUPDR register.

8.3.2

I/O pin alternate function multiplexer and mapping
The device I/O pins are connected to on-board peripherals/modules through a multiplexer
that allows only one peripheral alternate function (AF) connected to an I/O pin at a time. In
this way, there can be no conflict between peripherals available on the same I/O pin.

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General-purpose I/Os (GPIO)
Each I/O pin has a multiplexer with up to sixteen alternate function inputs (AF0 to AF15) that
can be configured through the GPIOx_AFRL (for pin 0 to 7) and GPIOx_AFRH (for pin 8 to
15) registers:
•

After reset the multiplexer selection is alternate function 0 (AF0). The I/Os are
configured in alternate function mode through GPIOx_MODER register.

•

The specific alternate function assignments for each pin are detailed in the device
datasheet.

In addition to this flexible I/O multiplexing architecture, each peripheral has alternate
functions mapped onto different I/O pins to optimize the number of peripherals available in
smaller packages.
To use an I/O in a given configuration, the user has to proceed as follows:
•

Debug function: after each device reset these pins are assigned as alternate function
pins immediately usable by the debugger host

•

GPIO: configure the desired I/O as output, input or analog in the GPIOx_MODER
register.

•

Peripheral alternate function:

•

–

Connect the I/O to the desired AFx in one of the GPIOx_AFRL or GPIOx_AFRH
register.

–

Select the type, pull-up/pull-down and output speed via the GPIOx_OTYPER,
GPIOx_PUPDR and GPIOx_OSPEEDER registers, respectively.

–

Configure the desired I/O as an alternate function in the GPIOx_MODER register.

Additional functions:
–

ADC and DAC connection could be enabled in ADC or DAC registers regardless
the configured GPIO mode. It is recommended to configure GPIO in analog mode
in the GPIOx_MODER register when ADC or DAC is used.

–

For the additional functions like RTC, WKUPx and oscillators, configure the
required function in the related RTC, PWR and RCC registers. These functions
have priority over the configuration in the standard GPIO registers.

Please refer to the “Alternate function mapping” table in the device datasheet for the
detailed mapping of the alternate function I/O pins.

8.3.3

I/O port control registers
Each of the GPIO ports has four 32-bit memory-mapped control registers (GPIOx_MODER,
GPIOx_OTYPER, GPIOx_OSPEEDR, GPIOx_PUPDR) to configure up to 16 I/Os. The
GPIOx_MODER register is used to select the I/O mode (input, output, AF, analog). The
GPIOx_OTYPER and GPIOx_OSPEEDR registers are used to select the output type (pushpull or open-drain) and speed. The GPIOx_PUPDR register is used to select the pullup/pull-down whatever the I/O direction.

8.3.4

I/O port data registers
Each GPIO has two 16-bit memory-mapped data registers: input and output data registers
(GPIOx_IDR and GPIOx_ODR). GPIOx_ODR stores the data to be output, it is read/write
accessible. The data input through the I/O are stored into the input data register
(GPIOx_IDR), a read-only register.
See Section 8.4.5: GPIO port input data register (GPIOx_IDR) (x = A..F) and Section 8.4.6:
GPIO port output data register (GPIOx_ODR) (x = A..F) for the register descriptions.
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8.3.5

RM0091

I/O data bitwise handling
The bit set reset register (GPIOx_BSRR) is a 32-bit register which allows the application to
set and reset each individual bit in the output data register (GPIOx_ODR). The bit set reset
register has twice the size of GPIOx_ODR.
To each bit in GPIOx_ODR, correspond two control bits in GPIOx_BSRR: BS(i) and BR(i).
When written to 1, bit BS(i) sets the corresponding ODR(i) bit. When written to 1, bit BR(i)
resets the ODR(i) corresponding bit.
Writing any bit to 0 in GPIOx_BSRR does not have any effect on the corresponding bit in
GPIOx_ODR. If there is an attempt to both set and reset a bit in GPIOx_BSRR, the set
action takes priority.
Using the GPIOx_BSRR register to change the values of individual bits in GPIOx_ODR is a
“one-shot” effect that does not lock the GPIOx_ODR bits. The GPIOx_ODR bits can always
be accessed directly. The GPIOx_BSRR register provides a way of performing atomic
bitwise handling.
There is no need for the software to disable interrupts when programming the GPIOx_ODR
at bit level: it is possible to modify one or more bits in a single atomic AHB write access.

8.3.6

GPIO locking mechanism
It is possible to freeze the port A and B GPIO control registers by applying a specific write
sequence to the GPIOx_LCKR register. The frozen registers are GPIOx_MODER,
GPIOx_OTYPER, GPIOx_OSPEEDR, GPIOx_PUPDR, GPIOx_AFRL and GPIOx_AFRH.
To write the GPIOx_LCKR register, a specific write / read sequence has to be applied. When
the right LOCK sequence is applied to bit 16 in this register, the value of LCKR[15:0] is used
to lock the configuration of the I/Os (during the write sequence the LCKR[15:0] value must
be the same). When the LOCK sequence has been applied to a port bit, the value of the port
bit can no longer be modified until the next MCU reset or peripheral reset. Each
GPIOx_LCKR bit freezes the corresponding bit in the control registers (GPIOx_MODER,
GPIOx_OTYPER, GPIOx_OSPEEDR, GPIOx_PUPDR, GPIOx_AFRL and GPIOx_AFRH.
The LOCK sequence (refer to Section 8.4.8: GPIO port configuration lock register
(GPIOx_LCKR) (x = A..B)) can only be performed using a word (32-bit long) access to the
GPIOx_LCKR register due to the fact that GPIOx_LCKR bit 16 has to be set at the same
time as the [15:0] bits.
For more details please refer to LCKR register description in Section 8.4.8: GPIO port
configuration lock register (GPIOx_LCKR) (x = A..B).

8.3.7

I/O alternate function input/output
Two registers are provided to select one of the alternate function inputs/outputs available for
each I/O. With these registers, the user can connect an alternate function to some other pin
as required by the application.
This means that a number of possible peripheral functions are multiplexed on each GPIO
using the GPIOx_AFRL and GPIOx_AFRH alternate function registers. The application can
thus select any one of the possible functions for each I/O. The AF selection signal being
common to the alternate function input and alternate function output, a single channel is
selected for the alternate function input/output of a given I/O.

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General-purpose I/Os (GPIO)
For code example refer to the Appendix section A.4.2: Alternate function selection
sequence code example.
To know which functions are multiplexed on each GPIO pin, refer to the device datasheet.

8.3.8

External interrupt/wakeup lines
All ports have external interrupt capability. To use external interrupt lines, the given pin must
not be configured in analog mode or being used as oscillator pin, so the input trigger is kept
enabled. Refer to Section 11.2: Extended interrupts and events controller (EXTI) and to
Section 11.2.3: Event management.

Input configuration
When the I/O port is programmed as input:
•

The output buffer is disabled

•

The Schmitt trigger input is activated

•

The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register

•

The data present on the I/O pin are sampled into the input data register every AHB
clock cycle

•

A read access to the input data register provides the I/O state

Figure 17 shows the input configuration of the I/O port bit.
Figure 17. Input floating/pull up/pull down configurations
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8.3.10

RM0091

Output configuration
When the I/O port is programmed as output:
•

The output buffer is enabled:
–

Open drain mode: A “0” in the Output register activates the N-MOS whereas a “1”
in the Output register leaves the port in Hi-Z (the P-MOS is never activated)

–

Push-pull mode: A “0” in the Output register activates the N-MOS whereas a “1” in
the Output register activates the P-MOS

•

The Schmitt trigger input is activated

•

The pull-up and pull-down resistors are activated depending on the value in the
GPIOx_PUPDR register

•

The data present on the I/O pin are sampled into the input data register every AHB
clock cycle

•

A read access to the input data register gets the I/O state

•

A read access to the output data register gets the last written value

Figure 18 shows the output configuration of the I/O port bit.
Figure 18. Output configuration
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8.3.11

Alternate function configuration
When the I/O port is programmed as alternate function:
•

The output buffer can be configured in open-drain or push-pull mode

•

The output buffer is driven by the signals coming from the peripheral (transmitter
enable and data)

•

The Schmitt trigger input is activated

•

The weak pull-up and pull-down resistors are activated or not depending on the value
in the GPIOx_PUPDR register

•

The data present on the I/O pin are sampled into the input data register every AHB
clock cycle

•

A read access to the input data register gets the I/O state

Figure 19 shows the Alternate function configuration of the I/O port bit.

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General-purpose I/Os (GPIO)
Figure 19. Alternate function configuration
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8.3.12

Analog configuration
When the I/O port is programmed as analog configuration:
•

The output buffer is disabled

•

The Schmitt trigger input is deactivated, providing zero consumption for every analog
value of the I/O pin. The output of the Schmitt trigger is forced to a constant value (0).

•

The weak pull-up and pull-down resistors are disabled by hardware

•

Read access to the input data register gets the value “0”

For code example refer to the Appendix section A.4.3: Analog GPIO configuration code
example.
Figure 20 shows the high-impedance, analog-input configuration of the I/O port bit.

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RM0091
Figure 20. High impedance-analog configuration

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8.3.13

Using the HSE or LSE oscillator pins as GPIOs
When the HSE or LSE oscillator is switched OFF (default state after reset), the related
oscillator pins can be used as normal GPIOs.
When the HSE or LSE oscillator is switched ON (by setting the HSEON or LSEON bit in the
RCC_CSR register) the oscillator takes control of its associated pins and the GPIO
configuration of these pins has no effect.
When the oscillator is configured in a user external clock mode, only the pin is reserved for
clock input and the OSC_OUT or OSC32_OUT pin can still be used as normal GPIO.

8.3.14

Using the GPIO pins in the RTC supply domain
The PC13/PC14/PC15 GPIO functionality is lost when the core supply domain is powered
off (when the device enters Standby mode). In this case, if their GPIO configuration is not
bypassed by the RTC configuration, these pins are set in an analog input mode.
For details about I/O control by the RTC, refer to Section 25.4: RTC functional description
on page 578.

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General-purpose I/Os (GPIO)

8.4

GPIO registers
This section gives a detailed description of the GPIO registers.
For a summary of register bits, register address offsets and reset values, refer to Table 24.
The peripheral registers can be written in word, half word or byte mode.

8.4.1

GPIO port mode register (GPIOx_MODER) (x =A..F)
Address offset:0x00
Reset values:

31

30

•

0x2800 0000 for port A

•

0x0000 0000 for other ports
29

MODER15[1:0]

28

MODER14[1:0]

27

26

MODER13[1:0]

25

24

MODER12[1:0]

23

22

MODER11[1:0]

21

20

MODER10[1:0]

19

18

MODER9[1:0]

17

16

MODER8[1:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

MODER7[1:0]
rw

rw

MODER6[1:0]
rw

rw

MODER5[1:0]
rw

rw

MODER4[1:0]
rw

rw

MODER3[1:0]
rw

rw

MODER2[1:0]
rw

rw

MODER1[1:0]
rw

rw

MODER0[1:0]
rw

rw

Bits 2y+1:2y MODERy[1:0]: Port x configuration bits (y = 0..15)
These bits are written by software to configure the I/O mode.
00: Input mode (reset state)
01: General purpose output mode
10: Alternate function mode
11: Analog mode

8.4.2

GPIO port output type register (GPIOx_OTYPER) (x = A..F)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

OT15

OT14

OT13

OT12

OT11

OT10

OT9

OT8

OT7

OT6

OT5

OT4

OT3

OT2

OT1

OT0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 OTy: Port x configuration bits (y = 0..15)
These bits are written by software to configure the I/O output type.
0: Output push-pull (reset state)
1: Output open-drain

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GPIO port output speed register (GPIOx_OSPEEDR)
(x = A..F)
Address offset: 0x08
Reset value:

31

•

0x0C00 0000 for port A

•

0x0000 0000 for other ports

30

29

OSPEEDR15
[1:0]

28

27

OSPEEDR14
[1:0]

26

25

OSPEEDR13
[1:0]

24

OSPEEDR12
[1:0]

23

22

OSPEEDR11
[1:0]

21

20

OSPEEDR10
[1:0]

19

18

17

16

OSPEEDR9
[1:0]

OSPEEDR8
[1:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

OSPEEDR7
[1:0]

OSPEEDR6
[1:0]

OSPEEDR5
[1:0]

OSPEEDR4
[1:0]

OSPEEDR3
[1:0]

OSPEEDR2
[1:0]

OSPEEDR1
[1:0]

OSPEEDR0
[1:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 2y+1:2y OSPEEDRy[1:0]: Port x configuration bits (y = 0..15)
These bits are written by software to configure the I/O output speed.
x0: Low speed
01: Medium speed
11: High speed
Note: Refer to the device datasheet for the frequency specifications and the power supply
and load conditions for each speed.

8.4.4

GPIO port pull-up/pull-down register (GPIOx_PUPDR)
(x = A..F)
Address offset: 0x0C
Reset values:

31

30

PUPDR15[1:0]

•

0x2400 0000 for port A

•

0x0000 0000 for other ports
29

28

PUPDR14[1:0]

27

26

PUPDR13[1:0]

25

24

PUPDR12[1:0]

23

22

PUPDR11[1:0]

21

20

PUPDR10[1:0]

19

18

PUPDR9[1:0]

17

16

PUPDR8[1:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

PUPDR7[1:0]
rw

rw

PUPDR6[1:0]
rw

rw

PUPDR5[1:0]
rw

rw

PUPDR4[1:0]
rw

rw

PUPDR3[1:0]
rw

rw

PUPDR2[1:0]
rw

rw

PUPDR1[1:0]
rw

Bits 2y+1:2y PUPDRy[1:0]: Port x configuration bits (y = 0..15)
These bits are written by software to configure the I/O pull-up or pull-down
00: No pull-up, pull-down
01: Pull-up
10: Pull-down
11: Reserved

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RM0091

General-purpose I/Os (GPIO)

8.4.5

GPIO port input data register (GPIOx_IDR) (x = A..F)
Address offset: 0x10
Reset value: 0x0000 XXXX (where X means undefined)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

IDR15

IDR14

IDR13

IDR12

IDR11

IDR10

IDR9

IDR8

IDR7

IDR6

IDR5

IDR4

IDR3

IDR2

IDR1

IDR0

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 IDRy: Port input data bit (y = 0..15)
These bits are read-only. They contain the input value of the corresponding I/O port.

8.4.6

GPIO port output data register (GPIOx_ODR) (x = A..F)
Address offset: 0x14
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

ODR15 ODR14 ODR13 ODR12 ODR11 ODR10
rw

rw

rw

rw

rw

rw

9

8

7

6

5

4

3

2

1

0

ODR9

ODR8

ODR7

ODR6

ODR5

ODR4

ODR3

ODR2

ODR1

ODR0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 ODRy: Port output data bit (y = 0..15)
These bits can be read and written by software.
Note: For atomic bit set/reset, the ODR bits can be individually set and/or reset by writing to
the GPIOx_BSRR or GPIOx_BRR registers (x = A..F).

8.4.7

GPIO port bit set/reset register (GPIOx_BSRR) (x = A..F)
Address offset: 0x18
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

BR15

BR14

BR13

BR12

BR11

BR10

BR9

BR8

BR7

BR6

BR5

BR4

BR3

BR2

BR1

BR0

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

BS15

BS14

BS13

BS12

BS11

BS10

BS9

BS8

BS7

BS6

BS5

BS4

BS3

BS2

BS1

BS0

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

DocID018940 Rev 9

159/1004
164

General-purpose I/Os (GPIO)

RM0091

Bits 31:16 BRy: Port x reset bit y (y = 0..15)
These bits are write-only. A read to these bits returns the value 0x0000.
0: No action on the corresponding ODRx bit
1: Resets the corresponding ODRx bit
Note: If both BSx and BRx are set, BSx has priority.
Bits 15:0 BSy: Port x set bit y (y= 0..15)
These bits are write-only. A read to these bits returns the value 0x0000.
0: No action on the corresponding ODRx bit
1: Sets the corresponding ODRx bit

8.4.8

GPIO port configuration lock register (GPIOx_LCKR)
(x = A..B)
This register is used to lock the configuration of the port bits when a correct write sequence
is applied to bit 16 (LCKK). The value of bits [15:0] is used to lock the configuration of the
GPIO. During the write sequence, the value of LCKR[15:0] must not change. When the
LOCK sequence has been applied on a port bit, the value of this port bit can no longer be
modified until the next MCU reset or peripheral reset.

Note:

A specific write sequence is used to write to the GPIOx_LCKR register. Only word access
(32-bit long) is allowed during this locking sequence.
Each lock bit freezes a specific configuration register (control and alternate function
registers).
Address offset: 0x1C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

LCKK
rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

LCK15

LCK14

LCK13

LCK12

LCK11

LCK10

LCK9

LCK8

LCK7

LCK6

LCK5

LCK4

LCK3

LCK2

LCK1

LCK0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

160/1004

DocID018940 Rev 9

RM0091

General-purpose I/Os (GPIO)

Bits 31:17 Reserved, must be kept at reset value.
Bit 16 LCKK: Lock key
This bit can be read any time. It can only be modified using the lock key write sequence.
0: Port configuration lock key not active
1: Port configuration lock key active. The GPIOx_LCKR register is locked until the next MCU
reset or peripheral reset.
LOCK key write sequence:
WR LCKR[16] = ‘1’ + LCKR[15:0]
WR LCKR[16] = ‘0’ + LCKR[15:0]
WR LCKR[16] = ‘1’ + LCKR[15:0]
RD LCKR
RD LCKR[16] = ‘1’ (this read operation is optional but it confirms that the lock is active)
Note: During the LOCK key write sequence, the value of LCK[15:0] must not change.
Any error in the lock sequence aborts the lock.
After the first lock sequence on any bit of the port, any read access on the LCKK bit will
return ‘1’ until the next MCU reset or peripheral reset.
For code example refer to the Appendix section A.4.1: Lock sequence code example.
Bits 15:0 LCKy: Port x lock bit y (y= 0..15)
These bits are read/write but can only be written when the LCKK bit is ‘0.
0: Port configuration not locked
1: Port configuration locked

8.4.9

GPIO alternate function low register (GPIOx_AFRL)
(x = A..F)
Address offset: 0x20
Reset value: 0x0000 0000

31

30

29

28

27

AFSEL7[3:0]
rw
15

rw

rw

rw

rw

14

13

12

11

AFSEL3[3:0]
rw

rw

rw

26

25

24

23

AFSEL6[3:0]
rw

rw

rw

rw

10

9

8

7

AFSEL2[3:0]
rw

rw

rw

rw

22

21

20

19

AFSEL5[3:0]
rw

rw

rw

rw

6

5

4

3

AFSEL1[3:0]
rw

rw

rw

rw

18

17

16

AFSEL4[3:0]
rw

rw

rw

2

1

0

AFSEL0[3:0]
rw

rw

rw

rw

rw

Bits 31:0 AFSELy[3:0]: Alternate function selection for port x pin y (y = 0..7)
These bits are written by software to configure alternate function I/Os
AFSELy selection:
0000: AF0
0001: AF1
0010: AF2
0011: AF3
0100: AF4
0101: AF5
0110: AF6
0111: AF7

1000: Reserved
1001: Reserved
1010: Reserved
1011: Reserved
1100: Reserved
1101: Reserved
1110: Reserved
1111: Reserved

DocID018940 Rev 9

161/1004
164

General-purpose I/Os (GPIO)

8.4.10

RM0091

GPIO alternate function high register (GPIOx_AFRH)
(x = A..F)
Address offset: 0x24
Reset value: 0x0000 0000

31

30

29

28

27

AFSEL15[3:0]

26

25

24

23

AFSEL14[3:0]

22

21

20

19

AFSEL13[3:0]

18

17

16

AFSEL12[3:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

AFSEL11[3:0]
rw

rw

rw

AFSEL10[3:0]
rw

rw

rw

rw

AFSEL9[3:0]
rw

rw

rw

rw

AFSEL8[3:0]
rw

rw

rw

rw

rw

Bits 31:0 AFSELy[3:0]: Alternate function selection for port x pin y (y = 8..15)
These bits are written by software to configure alternate function I/Os
AFSELy selection:
0000: AF0
0001: AF1
0010: AF2
0011: AF3
0100: AF4
0101: AF5
0110: AF6
0111: AF7

8.4.11

1000: Reserved
1001: Reserved
1010: Reserved
1011: Reserved
1100: Reserved
1101: Reserved
1110: Reserved
1111: Reserved

GPIO port bit reset register (GPIOx_BRR) (x =A..F)
Address offset: 0x28
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

BR15

BR14

BR13

BR12

BR11

BR10

BR9

BR8

BR7

BR6

BR5

BR4

BR3

BR2

BR1

BR0

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

Bits 31:16 Reserved
Bits 15:0 BRy: Port x Reset bit y (y= 0..15)
These bits are write-only. A read to these bits returns the value 0x0000
0: No action on the corresponding ODx bit
1: Reset the corresponding ODx bit

162/1004

DocID018940 Rev 9

DocID018940 Rev 9

ODR0

0

ODR1

0

0

0

0

0

0

0

0

0

BS0

0

0

BS1

0

ODR2

0

ODR3

0

0

BS2

0

0

BS3

0

ODR4

0

ODR5

0

0

BS4

0

0

BS5

0

ODR6

0

ODR7

0

0

BS6

0

0

BS7

0

ODR8

0

ODR9

0

0

BS8

BS11

BS10

Reset value

BS9

BS12

0
0
0
0
0
0

0x10

IDR0

0

IDR1

0

IDR2

0

IDR3

0

IDR4

0

IDR5

0

IDR6

0

IDR7

0

IDR8

0

IDR9

0

IDR11

0

IDR10

0

IDR12

0

IDR13

Reset value

ODR11

BS13

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

GPIOx_OTYPER
(where x = A..F)

0
0

0
0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

0

0
0
0

0
0

0
0
0
0

0
0

0
0

0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

OT1
OT0

0
0
0
0

0
0

0
0

0
0

OSPEEDR0[1:0]

MODER0[1:0]

MODER1[1:0]

0

OSPEEDR0[1:0]

OT2

0

PUPDR0[1:0]

OT3
OSPEEDR1[1:0]

MODER2[1:0]

0

OSPEEDR1[1:0]

OT4

0

PUPDR1[1:0]

OT5
OSPEEDR2[1:0]

MODER3[1:0]

0

OSPEEDR2[1:0]

OT6

MODER4[1:0]

0

PUPDR2[1:0]

OT7
OSPEEDR3[1:0]

0

OSPEEDR3[1:0]

OT8

MODER5[1:0]

MODER6[1:0]

MODER7[1:0]

MODER8[1:0]

MODER9[1:0]

MODER10[1:0]

MODER11[1:0]

MODER12[1:0]

MODER13[1:0]

MODER14[1:0]

MODER15[1:0]

0

PUPDR3[1:0]

OT9
OSPEEDR4[1:0]

0

OSPEEDR4[1:0]

0

PUPDR4[1:0]

OT11
OT10

OSPEEDR5[1:0]

0
OSPEEDR5[1:0]

OT12
0

PUPDR5[1:0]

OT13

OSPEEDR6[1:0]

0
OSPEEDR6[1:0]

0

PUPDR6[1:0]

0

0

0

PUPDR0[1:0]

0

0

0

PUPDR1[1:0]

0

0

0

PUPDR2[1:0]

0

0

PUPDR3[1:0]

0

0

PUPDR4[1:0]

0

Res.

0

PUPDR5[1:0]

0

OT14

0

OT15

OSPEEDR7[1:0]

OSPEEDR8[1:0]

Reset value

Res.

0

PUPDR6[1:0]

0
OSPEEDR7[1:0]

0
PUPDR7[1:0]

0

PUPDR7[1:0]

0

IDR14

0

IDR15

OSPEEDR8[1:0]

0
PUPDR8[1:0]

0
PUPDR8[1:0]

0
0

ODR10

BS14

0

Res.

OSPEEDR9[1:0]

OSPEEDR10[1:0]

OSPEEDR11[1:0]

OSPEEDR12[1:0]

OSPEEDR13[1:0]

OSPEEDR14[1:0]

OSPEEDR15[1:0]

Reset value

ODR12

BS15

0

Res.

0

0

Res.

0

Res.

0
OSPEEDR9[1:0]

0
PUPDR9[1:0]

0

PUPDR9[1:0]

0
0

0

ODR13

BR0

0

Res.

0

0

ODR14

BR1

0

Res.

0
OSPEEDR10[1:0]

0
PUPDR10[1:0]

0

PUPDR10[1:0]

0
0

0

Res.

0

Res.

0

0

Res.

0

Res.

OSPEEDR11[1:0]

0
PUPDR11[1:0]

1
PUPDR11[1:0]

0
0

0

Res.

0

Res.

0
0

Res.

0

Res.

0

0

Res.

0
OSPEEDR12[1:0]

0
PUPDR12[1:0]

0

PUPDR12[1:0]

0
1

Res.

0

Res.

1
0

ODR15

BR2

0

BR3

0

BR4

0

BR5

0

BR6

Reset value

BR7

0

Res.

0
0

Res.

1
OSPEEDR13[1:0]

0
PUPDR13[1:0]

OSPEEDR14[1:0]

0

PUPDR13[1:0]

PUPDR14[1:0]

0
1

Res.

0

Res.

0
0

BR8

0

Res.

Reset value

PUPDR14[1:0]

GPIOA_PUPDR
0
0
0

Res.

0

Res.

Reset value
1

Res.

Reset value

GPIOx_IDR
(where x = A..F)

Res.

0x0C
GPIOx_OSPEEDR
(where x = B..F)
0
0

Res.

Reset value

Res.

0x08
GPIOA_OSPEEDR
0

BR9

BR12

0x08

OSPEEDR15[1:0]

0x04
GPIOx_MODER
(where x = B..F)

PUPDR15[1:0]

Reset value

BR11

0x18

GPIOx_BSRR
(where x = A..F)

BR13

GPIOx_PUPDR
(where x = B..F)

Res.

0x00
MODER0[1:0]

MODER1[1:0]

MODER2[1:0]

MODER3[1:0]

MODER4[1:0]

MODER5[1:0]

MODER6[1:0]

MODER7[1:0]

MODER8[1:0]

MODER9[1:0]

MODER10[1:0]

MODER11[1:0]

MODER12[1:0]

MODER13[1:0]

MODER14[1:0]

MODER15[1:0]

GPIOA_MODER

PUPDR15[1:0]

0x0C

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

BR10

GPIOx_ODR
(where x = A..F)

BR14

8.4.12

Res.

0x14

BR15

RM0091
General-purpose I/Os (GPIO)

GPIO register map
The following table gives the GPIO register map and reset values.
Table 24. GPIO register map and reset values

0
0
0

0

0

0

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

0

0

0

0

0

0

0

0

0

0

163/1004

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General-purpose I/Os (GPIO)

RM0091

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0x28

Res.

Res.

BR15

BR14

BR13

BR12

BR11

BR10

BR9

BR8

BR7

BR6

BR5

BR4

BR3

BR2

BR1

BR0

LCK0

0

Res.

LCK1

0

Res.

LCK2

0

Res.

LCK3

0

Res.

LCK4

0

Res.

LCK5

Reset value
GPIOx_BRR
(where x = A..F)

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

0x24

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

AFSEL14
[3:0]

0

0

AFSEL4
[3:0]

0

GPIOx_AFRH
(where x = A..F)

AFSEL15
[3:0]

AFSEL5
[3:0]

0

GPIOx_AFRL
(where x = A..F)
0

AFSEL6
[3:0]

0

0x20

Reset value

AFSEL7
[3:0]

LCK6

0

LCK7

0

LCK8

LCK12

0

LCK9

LCK13

0

LCK11

LCK14

0

Reset value

LCK10

LCK15

Res.

LCKK

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

GPIOx_LCKR
(where x = A..B)

Res.

0x1C

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 24. GPIO register map and reset values (continued)

0

0

AFSEL13
[3:0]

0

0

AFSEL3
[3:0]
0

0

AFSEL12
[3:0]

0

0

AFSEL2
[3:0]
0

0

AFSEL11
[3:0]

Reset value

0

0

AFSEL1
[3:0]
0

DocID018940 Rev 9

0

0

0

0

AFSEL9
[3:0]

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

164/1004

0

AFSEL10
[3:0]

AFSEL0
[3:0]
0

0

0

AFSEL8
[3:0]

RM0091

9

System configuration controller (SYSCFG)

System configuration controller (SYSCFG)
The devices feature a set of configuration registers. The main purposes of the system
configuration controller are the following:
•

Enabling/disabling I2C Fast Mode Plus on some IO ports

•

Remapping some DMA trigger sources to different DMA channels

•

Remapping the memory located at the beginning of the code area

•

Pending interrupt status registers for each interrupt line on STM32F09x devices

•

Managing the external interrupt line connection to the GPIOs

•

Managing robustness feature

9.1

SYSCFG registers

9.1.1

SYSCFG configuration register 1 (SYSCFG_CFGR1)
This register is used for specific configurations of memory and DMA requests remap and to
control special I/O features.
Two bits are used to configure the type of memory accessible at address 0x0000 0000.
These bits are used to select the physical remap by software and so, bypass the hardware
BOOT selection.
After reset these bits take the value selected by the actual boot mode configuration.
Address offset: 0x00
Reset value: 0x0000 000X (X is the memory mode selected by the actual boot mode
configuration

31

30

29

28

27

Res.

TIM3_
DMA_
RMP

TIM2_
DMA_
RMP

TIM1_
DMA_
RMP

I2C1_
DMA_
RMP

rw

rw

rw

rw

rw

15

14

13

12

11

10

Res.

TIM17
_DMA
_RMP
2
rw

26

25

24

23

22

SPI2_
DMA_
RMP

I2C_
PA10_
FMP

I2C_
PA9_
FMP

rw

rw

rw

9

8

7

USART3 USART2
_DMA_ _DMA_
RMP
RMP

TIM16
USART1 USART1
TIM17_ TIM16_
_DMA
_RX_
_TX_
DMA_ DMA_
_RMP
DMA_
DMA_
RMP
RMP
2
RMP
RMP
rw

rw

rw

rw

rw

20

19

18

17

16

I2C2_
FMP

I2C1_
FMP

I2C_
PB9_
FMP

I2C_
PB8_
FMP

I2C_
PB7_
FMP

I2C_
PB6_
FMP

rw

rw

rw

rw

rw

rw

rw

6

5

4

3

2

1

0

Res.

PA11_
PA12_
RMP

Res.

Res.

ADC_
DMA_
RMP

IR_MOD
[1:0]

rw

rw

DocID018940 Rev 9

21

rw

MEM_MODE
[1:0]
rw

rw

165/1004
187

System configuration controller (SYSCFG)

RM0091

Bit 31 Reserved, must be kept at reset value.
Bit 30 TIM3_DMA_RMP: TIM3 DMA request remapping bit. Available on STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of TIM3 DMA requests.
0: No remap (TIM3_CH1 and TIM3_TRIG DMA requests mapped on DMA channel 4)
1: Remap (TIM3_CH1 and TIM3_TRIG DMA requests mapped on DMA channel 6)
Bit 29 TIM2_DMA_RMP: TIM2 DMA request remapping bit. Available on STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of TIM2 DMA requests.
0: No remap (TIM2_CH2 and TIM2_CH4 DMA requests mapped on DMA channel 3 and 4
respectively)
1: Remap (TIM2_CH2 and TIM2_CH4 DMA requests mapped on DMA channel 7)
Bit 28 TIM1_DMA_RMP: TIM1 DMA request remapping bit. Available on STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of TIM1 DMA requests.
0: No remap (TIM1_CH1, TIM1_CH2 and TIM1_CH3 DMA requests mapped on DMA
channel 2, 3 and 4 respectively)
1: Remap (TIM1_CH1, TIM1_CH2 and TIM1_CH3 DMA requests mapped on DMA channel
6)
Bit 27 I2C1_DMA_RMP: I2C1 DMA request remapping bit. Available on STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of I2C1 DMA requests.
0: No remap (I2C1_RX and I2C1_TX DMA requests mapped on DMA channel 3 and 2
respectively)
1: Remap (I2C1_RX and I2C1_TX DMA requests mapped on DMA channel 7 and 6
respectively)
Bit 26 USART3_DMA_RMP: USART3 DMA request remapping bit. Available on STM32F07x
devices only.
This bit is set and cleared by software. It controls the remapping of USART3 DMA requests.
0: (USART3_RX and USART3_TX DMA requests mapped on DMA channel 6 and 7
respectively)
1: Remap (USART3_RX and USART3_TX DMA requests mapped on DMA channel 3 and 2
respectively)
Bit 25 USART2_DMA_RMP: USART2 DMA request remapping bit. Available on STM32F07x
devices only.
This bit is set and cleared by software. It controls the remapping of USART2 DMA requests.
0: No remap (USART2_RX and USART2_TX DMA requests mapped on DMA channel 5 and
4 respectively)
1: Remap (USART2_RX and USART2_TX DMA requests mapped on DMA channel 6 and 7
respectively)
Bit 24 SPI2_DMA_RMP: SPI2 DMA request remapping bit. Available on STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of SPI2 DMA requests.
0: No remap (SPI2_RX and SPI2_TX DMA requests mapped on DMA channel 4 and 5
respectively)
1: Remap (SPI2_RX and SPI2_TX DMA requests mapped on DMA channel 6 and 7
respectively)
Bits 23:22 I2C_PAx_FMP: Fast Mode Plus (FM+) driving capability activation bits. Available on
STM32F03x, STM32F04x and STM32F09x devices only.
These bits are set and cleared by software. Each bit enables I2C FM+ mode for PA10 and PA9
I/Os.
0: PAx pin operates in standard mode.
1: I2C FM+ mode enabled on PAx pin and the Speed control is bypassed.

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Bit 21 I2C2_FMP: FM+ driving capability activation for I2C2. Available on STM32F07x and
STM32F09x devices only.
This bit is set and cleared by software. This bit is OR-ed with I2C_Pxx_FM+ bits.
0: FM+ mode is controlled by I2C_Pxx_FM+ bits only.
1: FM+ mode is enabled on all I2C2 pins selected through selection bits in GPIOx_AFR
registers. This is the only way to enable the FM+ mode for pads without a dedicated
I2C_Pxx_FM+ control bit.
Bit 20 I2C1_FMP: FM+ driving capability activation for I2C1. Not available on STM32F05x devices.
This bit is set and cleared by software. This bit is OR-ed with I2C_Pxx_FM+ bits.
0: FM+ mode is controlled by I2C_Pxx_FM+ bits only.
1: FM+ mode is enabled on all I2C1 pins selected through selection bits in GPIOx_AFR
registers. This is the only way to enable the FM+ mode for pads without a dedicated
I2C_Pxx_FM+ control bit.
Bits 19:16 I2C_PBx_FMP: Fast Mode Plus (FM+) driving capability activation bits.
These bits are set and cleared by software. Each bit enables I2C FM+ mode for PB6, PB7,
PB8, and PB9 I/Os.
0: PBx pin operates in standard mode.
1: I2C FM+ mode enabled on PBx pin and the Speed control is bypassed.
Bit 15 Reserved, must be kept at reset value.
Bit 14 TIM17_DMA_RMP2: TIM17 alternate DMA request remapping bit. Available on STM32F07x
devices only.
This bit is set and cleared by software. It controls the alternate remapping of TIM17 DMA
requests.
0: No alternate remap (TIM17 DMA requests mapped according to TIM17_DMA_RMP bit)
1: Alternate remap (TIM17_CH1 and TIM17_UP DMA requests mapped on DMA channel 7)
Bit 13 TIM16_DMA_RMP2: TIM16 alternate DMA request remapping bit. Available on STM32F07x
devices only.
This bit is set and cleared by software. It controls the alternate remapping of TIM16 DMA
requests.
0: No alternate remap (TIM16 DMA requests mapped according to TIM16_DMA_RMP bit)
1: Alternate remap (TIM16_CH1 and TIM16_UP DMA requests mapped on DMA channel 6)
Bit 12 TIM17_DMA_RMP: TIM17 DMA request remapping bit. Available on STM32F03x,
STM32F04x, STM32F05x and STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of TIM17 DMA requests.
0: No remap (TIM17_CH1 and TIM17_UP DMA requests mapped on DMA channel 1)
1: Remap (TIM17_CH1 and TIM17_UP DMA requests mapped on DMA channel 2)
Bit 11 TIM16_DMA_RMP: TIM16 DMA request remapping bit. Available on STM32F03x,
STM32F04x, STM32F05x and STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of TIM16 DMA requests.
0: No remap (TIM16_CH1 and TIM16_UP DMA requests mapped on DMA channel 3)
1: Remap (TIM16_CH1 and TIM16_UP DMA requests mapped on DMA channel 4)
Bit 10 USART1_RX_DMA_RMP: USART1_RX DMA request remapping bit. Available on
STM32F03x, STM32F04x, STM32F05x and STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of USART1_RX DMA
requests.
0: No remap (USART1_RX DMA request mapped on DMA channel 3)
1: Remap (USART1_RX DMA request mapped on DMA channel 5)

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Bit 9 USART1_TX_DMA_RMP: USART1_TX DMA request remapping bit. Available on
STM32F03x, STM32F04x, STM32F05x and STM32F07x devices only.
This bit is set and cleared by software. It bit controls the remapping of USART1_TX DMA
requests.
0: No remap (USART1_TX DMA request mapped on DMA channel 2)
1: Remap (USART1_TX DMA request mapped on DMA channel 4)
Bit 8 ADC_DMA_RMP: ADC DMA request remapping bit. Available on STM32F03x, STM32F04x,
STM32F05x and STM32F07x devices only.
This bit is set and cleared by software. It controls the remapping of ADC DMA requests.
0: No remap (ADC DMA request mapped on DMA channel 1)
1: Remap (ADC DMA request mapped on DMA channel 2)
Bits 7:6 IR_MOD[1:0]: IR Modulation Envelope signal selection. Available on STM32F09x devices
only.
Those bits allow to select the modulation envelope signal between TIM16, USART1 and
USART4:
00: TIM16 selected
01: USART1 selected
10: USART4 selected
11: Reserved
Bit 5 Reserved, must be kept at reset value.
Bit 4 PA11_PA12_RMP: PA11 and PA12 remapping bit for small packages (28 and 20 pins).
Available on STM32F04x devices only.
This bit is set and cleared by software. It controls the mapping of either PA9/10 or PA11/12 pin
pair on small pin-count packages.
0: No remap (pin pair PA9/10 mapped on the pins)
1: Remap (pin pair PA11/12 mapped instead of PA9/10)
Bits 3:2 Reserved, must be kept at reset value.
Bits 1:0 MEM_MODE[1:0]: Memory mapping selection bits
These bits are set and cleared by software. They control the memory internal mapping at
address 0x0000 0000. After reset these bits take on the value selected by the actual boot
mode configuration. Refer to Chapter 2.5: Boot configuration for more details.
x0: Main Flash memory mapped at 0x0000 0000
01: System Flash memory mapped at 0x0000 0000
11: Embedded SRAM mapped at 0x0000 0000

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9.1.2

SYSCFG external interrupt configuration register 1
(SYSCFG_EXTICR1)
Address offset: 0x08
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

EXTI3[3:0]
rw

rw

rw

EXTI2[3:0]
rw

rw

rw

EXTI1[3:0]

rw

rw

rw

rw

rw

EXTI0[3:0]
rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 EXTIx[3:0]: EXTI x configuration bits (x = 0 to 3)
These bits are written by software to select the source input for the EXTIx external interrupt.
x000: PA[x] pin
x001: PB[x] pin
x010: PC[x] pin
x011: PD[x] pin
x100: PE[x] pin
x101: PF[x] pin
other configurations: reserved

Note:

Some of the I/O pins mentioned in the above register may not be available on small
packages.

9.1.3

SYSCFG external interrupt configuration register 2
(SYSCFG_EXTICR2)
Address offset: 0x0C
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

EXTI7[3:0]
rw

rw

rw

EXTI6[3:0]
rw

rw

rw

EXTI5[3:0]

rw

rw

rw

rw

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Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 EXTIx[3:0]: EXTI x configuration bits (x = 4 to 7)
These bits are written by software to select the source input for the EXTIx external interrupt.
x000: PA[x] pin
x001: PB[x] pin
x010: PC[x] pin
x011: PD[x] pin
x100: PE[x] pin
x101: PF[x] pin
other configurations: reserved

Note:

Some of the I/O pins mentioned in the above register may not be available on small
packages.

9.1.4

SYSCFG external interrupt configuration register 3
(SYSCFG_EXTICR3)
Address offset: 0x10
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

EXTI11[3:0]
rw

rw

rw

EXTI10[3:0]
rw

rw

rw

rw

EXTI9[3:0]
rw

rw

rw

rw

EXTI8[3:0]
rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 EXTIx[3:0]: EXTI x configuration bits (x = 8 to 11)
These bits are written by software to select the source input for the EXTIx external interrupt.
x000: PA[x] pin
x001: PB[x] pin
x010: PC[x] pin
x011: PD[x] pin
x100: PE[x] pin
x101: PF[x] pin
other configurations: reserved

Note:

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9.1.5

SYSCFG external interrupt configuration register 4
(SYSCFG_EXTICR4)
Address offset: 0x14
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

15

EXTI15[3:0]
rw

rw

rw

EXTI14[3:0]
rw

rw

rw

rw

EXTI13[3:0]
rw

rw

rw

rw

EXTI12[3:0]
rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 EXTIx[3:0]: EXTI x configuration bits (x = 12 to 15)
These bits are written by software to select the source input for the EXTIx external interrupt.
x000: PA[x] pin
x001: PB[x] pin
x010: PC[x] pin
x011: PD[x] pin
x100: PE[x] pin
x101: PF[x] pin
other configurations: reserved

Note:

Some of the I/O pins mentioned in the above register may not be available on small
packages.

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9.1.6

RM0091

SYSCFG configuration register 2 (SYSCFG_CFGR2)
Address offset: 0x18
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SRAM_
PEF

Res.

Res.

Res.

Res.

Res.

rc_w1

SRAM_
PVD_
LOCKUP
PARITY
LOCK
_LOCK
_LOCK
rw

rw

rw

Bits 31:9 Reserved, must be kept at reset value
Bit 8 SRAM_PEF: SRAM parity error flag
This bit is set by hardware when an SRAM parity error is detected. It is cleared by software by
writing ‘1’.
0: No SRAM parity error detected
1: SRAM parity error detected
Bits 7:3 Reserved, must be kept at reset value
Bit 2 PVD_LOCK: PVD lock enable bit
This bit is set by software and cleared by a system reset. It can be used to enable and lock the
PVD connection to TIM1/15/16/17 Break input, as well as the PVDE and PLS[2:0] in the
PWR_CR register.
0: PVD interrupt disconnected from TIM1/15/16/17 Break input. PVDE and PLS[2:0] bits can
be programmed by the application.
1: PVD interrupt connected to TIM1/15/16/17 Break input, PVDE and PLS[2:0] bits are read
only.
Bit 1 SRAM_PARITY_LOCK: SRAM parity lock bit
This bit is set by software and cleared by a system reset. It can be used to enable and lock the
SRAM parity error signal connection to TIM1/15/16/17 Break input.
0: SRAM parity error disconnected from TIM1/15/16/17 Break input
1: SRAM parity error connected to TIM1/15/16/17 Break input
Bit 0 LOCKUP_LOCK: Cortex-M0 LOCKUP bit enable bit
This bit is set by software and cleared by a system reset. It can be use to enable and lock the
connection of Cortex-M0 LOCKUP (Hardfault) output to TIM1/15/16/17 Break input.
0: Cortex-M0 LOCKUP output disconnected from TIM1/15/16/17 Break input
1: Cortex-M0 LOCKUP output connected to TIM1/15/16/17 Break input

9.1.7

SYSCFG interrupt line 0 status register (SYSCFG_ITLINE0)
A dedicated set of registers is implemented on STM32F09x to collect all pending interrupt
sources associated with each interrupt line into a single register. This allows users to check
by single read which peripheral requires service in case more than one source is associated
to the interrupt line.
All bits in those registers are read only, set by hardware when there is corresponding
interrupt request pending and cleared by resetting the interrupt source flags in the
peripheral registers.

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Address offset: 80h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

WWDG
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 WWDG: Window watchdog interrupt pending flag

9.1.8

SYSCFG interrupt line 1 status register (SYSCFG_ITLINE1)
Address offset: 84h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

VDDIO2

PVDOUT

r

r

Bits 31:2 Reserved (read as ‘0’)
Bit 1 VDDIO2: VDDIO2 supply monitoring interrupt request pending (EXTI line 31)
Bit 0 PVDOUT: PVD supply monitoring interrupt request pending (EXTI line 16). This bit is not
available on STM32F0x8 devices.

9.1.9

SYSCFG interrupt line 2 status register (SYSCFG_ITLINE2)
Address offset: 88h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

RTC_ALRA

RTC_
TSTAMP

RTC_
WAKEUP

r

r

r

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Bits 31:3 Reserved (read as ‘0’)

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Bit 2 RTC_ALRA: RTC Alarm interrupt request pending (EXTI line 17)
Bit 1 RTC_TSTAMP: RTC Tamper and TimeStamp interrupt request pending (EXTI line 19)
Bit 0 RTC_WAKEUP: RTC Wake Up interrupt request pending (EXTI line 20)

9.1.10

SYSCFG interrupt line 3 status register (SYSCFG_ITLINE3)
Address offset: 8Ch
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

FLASH_
ITF

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 FLASH_ITF: Flash interface interrupt request pending

9.1.11

SYSCFG interrupt line 4 status register (SYSCFG_ITLINE4)
Address offset: 90h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

CRS

RCC

r

r

Bits 31:2 Reserved (read as ‘0’)
Bit 1 CRS: Clock recovery system interrupt request pending
Bit 0 RCC: Reset and clock control interrupt request pending

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9.1.12

SYSCFG interrupt line 5 status register (SYSCFG_ITLINE5)
Address offset: 94h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

EXTI1

EXTI0

r

r

Bits 31:2 Reserved (read as ‘0’)
Bit 1 EXTI1: EXTI line 1 interrupt request pending
Bit 0 EXTI0: EXTI line 0 interrupt request pending

9.1.13

SYSCFG interrupt line 6 status register (SYSCFG_ITLINE6)
Address offset: 98h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

EXTI3

EXTI2

r

r

Bits 31:2 Reserved (read as ‘0’)
Bit 1 EXTI3: EXTI line 3 interrupt request pending
Bit 0 EXTI2: EXTI line 2 interrupt request pending

9.1.14

SYSCFG interrupt line 7 status register (SYSCFG_ITLINE7)
Address offset: 9Ch
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

EXTI8

EXTI7

EXTI6

EXTI5

EXTI4

r

r

r

r

r

EXTI15 EXTI14 EXTI13 EXTI12 EXTI11 EXTI10 EXTI9
r

r

r

r

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Bits 31:10 Reserved (read as ‘0’)
Bit 11 EXTI15: EXTI line 15 interrupt request pending
Bit 10 EXTI14: EXTI line 14 interrupt request pending
Bit 9 EXTI13: EXTI line 13 interrupt request pending
Bit 8 EXTI12: EXTI line 12 interrupt request pending
Bit 7 EXTI11: EXTI line 11 interrupt request pending
Bit 6 EXTI10: EXTI line 10 interrupt request pending
Bit 5 EXTI9: EXTI line 9 interrupt request pending
Bit 4 EXTI8: EXTI line 8 interrupt request pending
Bit 3 EXTI7: EXTI line 7 interrupt request pending
Bit 2 EXTI6: EXTI line 6 interrupt request pending
Bit 1 EXTI5: EXTI line 5 interrupt request pending
Bit 0 EXTI4: EXTI line 4 interrupt request pending

9.1.15

SYSCFG interrupt line 8 status register (SYSCFG_ITLINE8)
Address offset: A0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

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9

8

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6

5

4

3

2

1

0

Res..

TCS_
EOA

TCS_
MCE

r

r

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Bits 31:2 Reserved (read as ‘0’)
Bit 1 TCS_EOA: Touch sensing controller end of acquisition interrupt request pending
Bit 0 TCS_MCE: Touch sensing controller max count error interrupt request pending

9.1.16

SYSCFG interrupt line 9 status register (SYSCFG_ITLINE9)
Address offset: A4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

DMA1_
CH1

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

r

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RM0091

System configuration controller (SYSCFG)

Bits 31:1 Reserved (read as ‘0’)
Bit 0 DMA1_CH1: DMA1 channel 1 interrupt request pending

9.1.17

SYSCFG interrupt line 10 status register (SYSCFG_ITLINE10)
Address offset: A8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

DMA2
_CH2

DMA2
_CH1

DMA1
_CH3

DMA1
_CH2

r

r

r

r

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Bits 31:4 Reserved (read as ‘0’)
Bit 3 DMA2_CH2: DMA2 channel 2 interrupt request pending
Bit 2 DMA2_CH1: DMA2 channel 1 interrupt request pending
Bit 1 DMA1_CH3: DMA1 channel 3 interrupt request pending
Bit 0 DMA1_CH2: DMA1 channel 2 interrupt request pending

9.1.18

SYSCFG interrupt line 11 status register (SYSCFG_ITLINE11)
Address offset: ACh
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

DMA2
_CH5

DMA2
_CH4

DMA2
_CH3

DMA1
_CH7

DMA1
_CH6

DMA1
_CH5

DMA1
_CH4

r

r

r

r

r

r

r

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Bits 31:7 Reserved (read as ‘0’)
Bit 6 DMA2_CH5: DMA2 channel 5 interrupt request pending
Bit 5 DMA2_CH4: DMA2 channel 4 interrupt request pending
Bit 4 DMA2_CH3: DMA2 channel 3 interrupt request pending
Bit 3 DMA1_CH7: DMA1 channel 7 interrupt request pending
Bit 2 DMA1_CH6: DMA1 channel 6 interrupt request pending
Bit 1 DMA1_CH5: DMA1 channel 5 interrupt request pending
Bit 0 DMA1_CH4: DMA1 channel 4 interrupt request pending

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System configuration controller (SYSCFG)

9.1.19

RM0091

SYSCFG interrupt line 12 status register (SYSCFG_ITLINE12)
Address offset: B0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

COMP2

COMP1

ADC

r

r

r

Bits 31:3 Reserved (read as ‘0’)
Bit 2 COMP2: Comparator 2 interrupt request pending (EXTI line 22)
Bit 1 COMP1: Comparator 1 interrupt request pending (EXTI line 21)
Bit 0 ADC: ADC interrupt request pending

9.1.20

SYSCFG interrupt line 13 status register (SYSCFG_ITLINE13)
Address offset: B4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

TIM1_
BRK

TIM1_
UPD

TIM1_
TRG

TIM1_
CCU

r

r

r

r

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Bits 31:4 Reserved (read as ‘0’)
Bit 3 TIM1_BRK: Timer 1 break interrupt request pending
Bit 2 TIM1_UPD: Timer 1 update interrupt request pending
Bit 1 TIM1_TRG: Timer 1 trigger interrupt request pending
Bit 0 TIM1_CCU: Timer 1 commutation interrupt request pending

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System configuration controller (SYSCFG)

9.1.21

SYSCFG interrupt line 14 status register (SYSCFG_ITLINE14)
Address offset: B8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM1_
CC
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM1_CC: Timer 1 capture compare interrupt request pending

9.1.22

SYSCFG interrupt line 15 status register (SYSCFG_ITLINE15)
Address offset: BCh
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM2
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM2: Timer 2 interrupt request pending

9.1.23

SYSCFG interrupt line 16 status register (SYSCFG_ITLINE16)
Address offset: C0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM3
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM3: Timer 3 interrupt request pending

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System configuration controller (SYSCFG)

9.1.24

RM0091

SYSCFG interrupt line 17 status register (SYSCFG_ITLINE17)
Address offset: C4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

DAC

TIM6

r

r

Bits 31:1 Reserved (read as ‘0’)
Bit 1 DAC: DAC underrun interrupt request pending
Bit 0 TIM6: Timer 6 interrupt request pending

9.1.25

SYSCFG interrupt line 18 status register (SYSCFG_ITLINE18)
Address offset: C8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM7
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM7: Timer 7 interrupt request pending

9.1.26

SYSCFG interrupt line 19 status register (SYSCFG_ITLINE19)
Address offset: CCh
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM14
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM14: Timer 14 interrupt request pending

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System configuration controller (SYSCFG)

9.1.27

SYSCFG interrupt line 20 status register (SYSCFG_ITLINE20)
Address offset: D0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM15
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM15: Timer 15 interrupt request pending

9.1.28

SYSCFG interrupt line 21 status register (SYSCFG_ITLINE21)
Address offset: D4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM16
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM16: Timer 16 interrupt request pending

9.1.29

SYSCFG interrupt line 22 status register (SYSCFG_ITLINE22)
Address offset: D8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

TIM17
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 TIM17: Timer 17 interrupt request pending

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System configuration controller (SYSCFG)

9.1.30

RM0091

SYSCFG interrupt line 23 status register (SYSCFG_ITLINE23)
Address offset: DCh
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

I2C1
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 I2C1: I2C1 interrupt request pending, combined with EXTI line 23

9.1.31

SYSCFG interrupt line 24 status register (SYSCFG_ITLINE24)
Address offset: E0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

I2C2
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 I2C2: I2C2 interrupt request pending

9.1.32

SYSCFG interrupt line 25 status register (SYSCFG_ITLINE25)
Address offset: E4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

SPI1
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 SPI1: SPI1 interrupt request pending

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System configuration controller (SYSCFG)

9.1.33

SYSCFG interrupt line 26 status register (SYSCFG_ITLINE26)
Address offset: E8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

SPI2
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 SPI2: SPI2 interrupt request pending

9.1.34

SYSCFG interrupt line 27 status register (SYSCFG_ITLINE27)
Address offset: ECh
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

USART1
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 USART1: USART1 interrupt request pending, combined with EXTI line 25

9.1.35

SYSCFG interrupt line 28 status register (SYSCFG_ITLINE28)
Address offset: F0h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

USART2
r

Bits 31:1 Reserved (read as ‘0’)
Bit 0 USART2: USART2 interrupt request pending, combined with EXTI line 26

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System configuration controller (SYSCFG)

9.1.36

RM0091

SYSCFG interrupt line 29 status register (SYSCFG_ITLINE29)
Address offset: F4h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

USART8 USART7 USART6 USART5 USART4 USART3
r

r

r

r

r

r

Bits 31:6 Reserved (read as ‘0’)
Bit 5 USART8: USART8 interrupt request pending
Bit 4 USART7: USART7 interrupt request pending
Bit 3 USART6: USART6 interrupt request pending
Bit 2 USART5: USART5 interrupt request pending
Bit 1 USART4: USART4 interrupt request pending
Bit 0 USART3: USART3 interrupt request pending, combined with EXTI line 28.

9.1.37

SYSCFG interrupt line 30 status register (SYSCFG_ITLINE30)
Address offset: F8h
System reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

Res..

CAN

CEC

r

r

Bits 31:2 Reserved (read as ‘0’)
Bit 1 CAN: CAN interrupt request pending
Bit 0 CEC: CEC interrupt request pending, combined with EXTI line 27

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0x84

0x88

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

VDDIO2

PVDOUT

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_ALRA

RTC_TSTAMP

RTC_WAKEUP

SYSCFG_ITLINE2

Res.

Reset value

Res.

SYSCFG_ITLINE1

Res.

SYSCFG_ITLINE0

Res.

0x80

DocID018940 Rev 9
0
0
0
0

Reset value
0

EXTI13[3:0]
EXTI12[3:0]

0
0
0
0
0
0
0
0
0
0

LOCUP_LOCK

0

0

0

EXTI6[3:0]
0

0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

EXTI1[3:0]

0

0

0

ADC_DMA_RMP

0

0

0

0

0

0

0

EXTI5[3:0]
0

EXTI9[3:0]
0

0

0
0

0
0

0
0

MEM_MODE[1:0]

Res.

PA11_PA12_RMP
Res.

Res.

IR_MOD

USART1_TX_DMA_RMP

TIM17_DMA_RMP
TIM16_DMA_RMP

TIM16_DMA_RMP2

USART1_RX_DMA_RMP

TIM17_DMA_RMP2

0

0

0

0

WWDG

EXTI14[3:0]

0

SRAM_PARITY_LOCK

0

0

Res.

EXTI15[3:0]

0

Res.

0

PVD_LOCK

Res.

0

Res.

I2C_PB7_FMP

Res.

0

Res.

0

Res.

0

0

0

Res.

EXTI10[3:0]

0

0

0

0

Res.

EXTI7[3:0]

0

Res.

EXTI11[3:0]

0
0

0

0

EXTI2[3:0]

Res.

Reset value
0

0

0

Res.

Reset value
0

Res.

0

0

Res.

Reset value
0

Res.

0

0

SRAM_PEF

Reset value
EXTI3[3:0]

Res.

I2C_PB8_FMP

0

Res.

I2C1_FMP
I2C_PB9_FMP

0

Res.

I2C2_FMP

0

Res.

I2C_PA9_FMP

0

Res.

I2C_PA10_FMP

0

Res.

SPI2_DMA_RMP

0

Res.

USART2_DMA_RMP

0

Res.

I2C1_DMA_RMP
USART3_DMA_RMP

0

Res.

TIM1_DMA_RMP

0

I2C_PB6_FMP
Res.

TIM2_DMA_RMP

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
TIM3_DMA_RMP

0

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_CFGR2

Res.

0x18
SYSCFG_EXTICR4

Res.

0x14
SYSCFG_EXTICR3

Res.

0x10
SYSCFG_EXTICR2

Res.

Offset
Register
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Reset value

Res.

0x0C
SYSCFG_EXTICR1

Res.

0x08
SYSCFG_CFGR1

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

9.1.38

Res.

RM0091
System configuration controller (SYSCFG)

SYSCFG register maps
The following table gives the SYSCFG register map and the reset values.
Table 25. SYSCFG register map and reset values

EXTI0[3:0]

X X

0

EXTI4[3:0]
0

EXTI8[3:0]
0

0
0
0

Table 26. SYSCFG register map and reset values for STM32F09x devices

0x1D to
0x7F
Reserved
Reserved

Reset value

Reset value

Reset value

185/1004

187

0xBC

0xC0

186/1004

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM3

SYSCFG_ITLINE16

Res.

Reset value

Res.

SYSCFG_ITLINE15

Res.

SYSCFG_ITLINE14

Res.

0xB8

Reset value

DocID018940 Rev 9

TIM1_CC

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE13

Res.

0xB4
TIM1_CCU

TIM1_TRG

TIM1_UPD

TIM1_BRK

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE12

Res.

0xB0
ADC

COMP1

COMP2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DMA1_CH4

DMA1_CH5

DMA1_CH6

DMA1_CH7

DMA2_CH3

DMA2_CH4

DMA2_CH5

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE11

Res.

0xAC
DMA1_CH2

DMA1_CH3

DMA2_CH1

DMA2_CH2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE10

Res.

0xA8
DMA1_CH1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE9

Res.

0xA4
TCS_MCE

TCS_EOA

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE8

Res.

0xA0
EXTI4

EXTI5

EXTI6

EXTI7

EXTI8

EXTI9

EXTI10

EXTI11

EXTI12

EXTI13

EXTI14

EXTI15

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE7

Res.

0x9C
EXTI2

EXTI3

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE6

Res.

0x98
EXTI0

EXTI1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE5

Res.

0x94
RCC

CRS

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE4

Res.

0x90
FLASH_ITF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE3

Res.

0x8C

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

System configuration controller (SYSCFG)
RM0091

Table 26. SYSCFG register map and reset values for STM32F09x devices

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

0xF4

0xF8
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
USART3

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
CAN
CEC

SYSCFG_ITLINE30
Res.

Reset value
Res.

SYSCFG_ITLINE29

Res.

SYSCFG_ITLINE28

Res.

0xF0

DocID018940 Rev 9
USART2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE27

Res.

0xEC
USART1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE26

Res.

0xE8
SPI2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SPI1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE25

Res.

0xE4
I2C2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE24

Res.

0xE0
I2C1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE23

Res.

0xDC
TIM17

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE22

Res.

0xD8
TIM16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE21

Res.

0xD4
TIM15

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE20

Res.

0xD0
TIM14

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE19

Res.

0xCC
TIM7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE18

Res.

0xC8
TIM6

DAC

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SYSCFG_ITLINE17

Res.

0xC4

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

RM0091
System configuration controller (SYSCFG)

Table 26. SYSCFG register map and reset values for STM32F09x devices

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Reset value

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

187/1004

187

Direct memory access controller (DMA)

RM0091

10

Direct memory access controller (DMA)

10.1

Introduction
Direct memory access (DMA) is used in order to provide high-speed data transfer between
peripherals and memory as well as memory to memory. Data can be quickly moved by DMA
without any CPU actions. This keeps CPU resources free for other operations.
The DMA controller has up to 12 channels, each dedicated to managing memory access
requests from one or more peripherals. It has an arbiter for handling the priority between
DMA requests.

10.2

188/1004

DMA main features
•

Up to 7 independently configurable channels (requests) on DMA

•

STM32F09x provides 5 additional independently configurable channels (requests) on
DMA2

•

Each channel is connected to dedicated hardware DMA requests, software trigger is
also supported on each channel. This configuration is done by software.

•

Priorities between requests from the DMA channels are software programmable (4
levels consisting of very high, high, medium, low) or hardware in case of equality
(request 1 has priority over request 2, etc.)

•

Independent source and destination transfer size (byte, half word, word), emulating
packing and unpacking. Source/destination addresses must be aligned on the data
size.

•

Support for circular buffer management

•

3 event flags (DMA Half Transfer, DMA Transfer complete and DMA Transfer Error)
logically ORed together in a single interrupt request for each channel

•

Memory-to-memory transfer

•

Peripheral-to-memory and memory-to-peripheral, and peripheral-to-peripheral
transfers

•

Access to Flash, SRAM, APB and AHB peripherals as source and destination

•

Programmable number of data to be transferred: up to 65535

DocID018940 Rev 9

RM0091

10.3

Direct memory access controller (DMA)

DMA functional description
The block diagram is shown in the following figure.
Figure 21. DMA block diagram
FLITF

DMA

Ch.1
Ch.2

DMA

Bus matrix

Cortex-M0

Flash

System

SRAM
Reset & clock
CRC GPIOA GPIOB
control (RCC)

up to
Ch.7

Bridge
APB

Arbiter
GPIOC GPIOD GPIOE GPIOF
AHB Slave
DMA request

ADC
DAC
USART1
USART2
I2C2
I2C1
TIM7
USART3
USART4

SPI1/I2S1
SPI2/I2S2
TIM1
TIM2
TIM3
TIM6
TIM15
TIM16
TIM17

MS19218V5

The DMA controller performs direct memory transfer by sharing the system bus with the
Cortex®-M0 core. The DMA request may stop the CPU access to the system bus for some
bus cycles, when the CPU and DMA are targeting the same destination (memory or
peripheral). The bus matrix implements round-robin scheduling, thus ensuring at least half
of the system bus bandwidth (both to memory and peripheral) for the CPU.

10.3.1

DMA transactions
After an event, the peripheral sends a request signal to the DMA Controller. The DMA
controller serves the request depending on the channel priorities. As soon as the DMA
Controller accesses the peripheral, an Acknowledge is sent to the peripheral by the DMA
Controller. The peripheral releases its request as soon as it gets the Acknowledge from the
DMA Controller. Once the request is de-asserted by the peripheral, the DMA Controller
release the Acknowledge. If there are more requests, the peripheral can initiate the next
transaction.
In summary, each DMA transfer consists of three operations:
•

The loading of data from the peripheral data register or a location in memory addressed
through an internal current peripheral/memory address register. The start address used
for the first transfer is the base peripheral/memory address programmed in the
DMA_CPARx or DMA_CMARx register.

DocID018940 Rev 9

189/1004
208

Direct memory access controller (DMA)

10.3.2

RM0091

•

The storage of the data loaded to the peripheral data register or a location in memory
addressed through an internal current peripheral/memory address register. The start
address used for the first transfer is the base peripheral/memory address programmed
in the DMA_CPARx or DMA_CMARx register.

•

The post-decrementing of the DMA_CNDTRx register, which contains the number of
transactions that have still to be performed.

Arbiter
The arbiter manages the channel requests based on their priority and launches the
peripheral/memory access sequences.
The priorities are managed in two stages:
•

Software: each channel priority can be configured in the DMA_CCRx register. There
are four levels:
–

•

10.3.3

Very high priority

–

High priority

–

Medium priority

–

Low priority

Hardware: if 2 requests have the same software priority level, the channel with the
lowest number will get priority versus the channel with the highest number. For
example, channel 2 gets priority over channel 4.

DMA channels
Each channel can handle DMA transfer between a peripheral register located at a fixed
address and a memory address. The amount of data to be transferred (up to 65535) is
programmable. The register which contains the amount of data items to be transferred is
decremented after each transaction.

Programmable data sizes
Transfer data sizes of the peripheral and memory are fully programmable through the
PSIZE and MSIZE bits in the DMA_CCRx register.

Pointer incrementation
Peripheral and memory pointers can optionally be automatically post-incremented after
each transaction depending on the PINC and MINC bits in the DMA_CCRx register. If
incremented mode is enabled, the address of the next transfer will be the address of the
previous one incremented by 1, 2 or 4 depending on the chosen data size. The first transfer
address is the one programmed in the DMA_CPARx/DMA_CMARx registers. During
transfer operations, these registers keep the initially programmed value. The current
transfer addresses (in the current internal peripheral/memory address register) are not
accessible by software.
If the channel is configured in non-circular mode, no DMA request is served after the last
transfer (that is once the number of data items to be transferred has reached zero). In order
to reload a new number of data items to be transferred into the DMA_CNDTRx register, the
DMA channel must be disabled.

190/1004

DocID018940 Rev 9

RM0091
Note:

Direct memory access controller (DMA)
If a DMA channel is disabled, the DMA registers are not reset. The DMA channel registers
(DMA_CCRx, DMA_CPARx and DMA_CMARx) retain the initial values programmed during
the channel configuration phase.
In circular mode, after the last transfer, the DMA_CNDTRx register is automatically reloaded
with the initially programmed value. The current internal address registers are reloaded with
the base address values from the DMA_CPARx/DMA_CMARx registers.

Channel configuration procedure
The following sequence should be followed to configure a DMA channel x (where x is the
channel number).
1.

Set the peripheral register address in the DMA_CPARx register. The data will be
moved from/ to this address to/ from the memory after the peripheral event.

2.

Set the memory address in the DMA_CMARx register. The data will be written to or
read from this memory after the peripheral event.

3.

Configure the total number of data to be transferred in the DMA_CNDTRx register.
After each peripheral event, this value will be decremented.

4.

Configure the channel priority using the PL[1:0] bits in the DMA_CCRx register

5.

Configure data transfer direction, circular mode, peripheral & memory incremented
mode, peripheral & memory data size, and interrupt after half and/or full transfer in the
DMA_CCRx register

6.

Activate the channel by setting the ENABLE bit in the DMA_CCRx register.

For code example refer to the Appendix section A.5.1: DMA Channel Configuration
sequence code example.
As soon as the channel is enabled, it can serve any DMA request from the peripheral
connected on the channel.
Once half of the bytes are transferred, the half-transfer flag (HTIF) is set and an interrupt is
generated if the Half-Transfer Interrupt Enable bit (HTIE) is set. At the end of the transfer,
the Transfer Complete Flag (TCIF) is set and an interrupt is generated if the Transfer
Complete Interrupt Enable bit (TCIE) is set.

Circular mode
Circular mode is available to handle circular buffers and continuous data flows (e.g. ADC
scan mode). This feature can be enabled using the CIRC bit in the DMA_CCRx register.
When circular mode is activated, the number of data to be transferred is automatically
reloaded with the initial value programmed during the channel configuration phase, and the
DMA requests continue to be served.

Memory-to-memory mode
The DMA channels can also work without being triggered by a request from a peripheral.
This mode is called Memory to Memory mode.
If the MEM2MEM bit in the DMA_CCRx register is set, then the channel initiates transfers
as soon as it is enabled by software by setting the Enable bit (EN) in the DMA_CCRx
register. The transfer stops once the DMA_CNDTRx register reaches zero. Memory to
Memory mode may not be used at the same time as Circular mode.

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10.3.4

RM0091

Programmable data width, data alignment and endians
When PSIZE and MSIZE are not equal, the DMA performs some data alignments as
described in Table 27: Programmable data width & endian behavior (when bits PINC =
MINC = 1).

Table 27. Programmable data width & endian behavior (when bits PINC = MINC = 1)
Number
Source
of data
Destination
port
items to
port width
width
transfer
(NDT)

Source content:
address / data

Transfer operations

Destination
content:
address / data

8

8

4

@0x0 / B0
@0x1 / B1
@0x2 / B2
@0x3 / B3

1: READ B0[7:0] @0x0 then WRITE B0[7:0] @0x0
2: READ B1[7:0] @0x1 then WRITE B1[7:0] @0x1
3: READ B2[7:0] @0x2 then WRITE B2[7:0] @0x2
4: READ B3[7:0] @0x3 then WRITE B3[7:0] @0x3

@0x0 / B0
@0x1 / B1
@0x2 / B2
@0x3 / B3

8

16

4

@0x0 / B0
@0x1 / B1
@0x2 / B2
@0x3 / B3

1: READ B0[7:0] @0x0 then WRITE 00B0[15:0] @0x0
2: READ B1[7:0] @0x1 then WRITE 00B1[15:0] @0x2
3: READ B2[7:0] @0x2 then WRITE 00B2[15:0] @0x4
4: READ B3[7:0] @0x3 then WRITE 00B3[15:0] @0x6

@0x0 / 00B0
@0x2 / 00B1
@0x4 / 00B2
@0x6 / 00B3

8

32

4

@0x0 / B0
@0x1 / B1
@0x2 / B2
@0x3 / B3

1: READ B0[7:0] @0x0 then WRITE 000000B0[31:0] @0x0
2: READ B1[7:0] @0x1 then WRITE 000000B1[31:0] @0x4
3: READ B2[7:0] @0x2 then WRITE 000000B2[31:0] @0x8
4: READ B3[7:0] @0x3 then WRITE 000000B3[31:0] @0xC

@0x0 / 000000B0
@0x4 / 000000B1
@0x8 / 000000B2
@0xC / 000000B3

16

8

4

@0x0 / B1B0
@0x2 / B3B2
@0x4 / B5B4
@0x6 / B7B6

1: READ B1B0[15:0] @0x0 then WRITE B0[7:0] @0x0
2: READ B3B2[15:0] @0x2 then WRITE B2[7:0] @0x1
3: READ B5B4[15:0] @0x4 then WRITE B4[7:0] @0x2
4: READ B7B6[15:0] @0x6 then WRITE B6[7:0] @0x3

@0x0 / B0
@0x1 / B2
@0x2 / B4
@0x3 / B6

16

16

4

@0x0 / B1B0
@0x2 / B3B2
@0x4 / B5B4
@0x6 / B7B6

1: READ B1B0[15:0] @0x0 then WRITE B1B0[15:0] @0x0
2: READ B3B2[15:0] @0x2 then WRITE B3B2[15:0] @0x2
3: READ B5B4[15:0] @0x4 then WRITE B5B4[15:0] @0x4
4: READ B7B6[15:0] @0x6 then WRITE B7B6[15:0] @0x6

@0x0 / B1B0
@0x2 / B3B2
@0x4 / B5B4
@0x6 / B7B6

16

32

4

@0x0 / B1B0
@0x2 / B3B2
@0x4 / B5B4
@0x6 / B7B6

1: READ B1B0[15:0] @0x0 then WRITE 0000B1B0[31:0] @0x0
2: READ B3B2[15:0] @0x2 then WRITE 0000B3B2[31:0] @0x4
3: READ B5B4[15:0] @0x4 then WRITE 0000B5B4[31:0] @0x8
4: READ B7B6[15:0] @0x6 then WRITE 0000B7B6[31:0] @0xC

@0x0 / 0000B1B0
@0x4 / 0000B3B2
@0x8 / 0000B5B4
@0xC / 0000B7B6

32

8

4

@0x0 / B3B2B1B0
@0x4 / B7B6B5B4
@0x8 / BBBAB9B8
@0xC / BFBEBDBC

1: READ B3B2B1B0[31:0] @0x0 then WRITE B0[7:0] @0x0
2: READ B7B6B5B4[31:0] @0x4 then WRITE B4[7:0] @0x1
3: READ BBBAB9B8[31:0] @0x8 then WRITE B8[7:0] @0x2
4: READ BFBEBDBC[31:0] @0xC then WRITE BC[7:0] @0x3

@0x0 / B0
@0x1 / B4
@0x2 / B8
@0x3 / BC

32

16

4

@0x0 / B3B2B1B0
@0x4 / B7B6B5B4
@0x8 / BBBAB9B8
@0xC / BFBEBDBC

1: READ B3B2B1B0[31:0] @0x0 then WRITE B1B0[15:0] @0x0
2: READ B7B6B5B4[31:0] @0x4 then WRITE B5B4[15:0] @0x2
3: READ BBBAB9B8[31:0] @0x8 then WRITE B9B8[15:0] @0x4
4: READ BFBEBDBC[31:0] @0xC then WRITE BDBC[15:0] @0x6

@0x0 / B1B0
@0x2 / B5B4
@0x4 / B9B8
@0x6 / BDBC

32

32

4

@0x0 / B3B2B1B0
@0x4 / B7B6B5B4
@0x8 / BBBAB9B8
@0xC / BFBEBDBC

@0x0 / B3B2B1B0
1: READ B3B2B1B0[31:0] @0x0 then WRITE B3B2B1B0[31:0] @0x0
2: READ B7B6B5B4[31:0] @0x4 then WRITE B7B6B5B4[31:0] @0x4
@0x4 / B7B6B5B4
3: READ BBBAB9B8[31:0] @0x8 then WRITE BBBAB9B8[31:0] @0x8 @0x8 / BBBAB9B8
4: READ BFBEBDBC[31:0] @0xC then WRITE BFBEBDBC[31:0] @0xC @0xC / BFBEBDBC

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Direct memory access controller (DMA)

Addressing an AHB peripheral that does not support byte or halfword
write operations
When the DMA initiates an AHB byte or halfword write operation, the data are duplicated on
the unused lanes of the HWDATA[31:0] bus. So when the used AHB slave peripheral does
not support byte or halfword write operations (when HSIZE is not used by the peripheral)
and does not generate any error, the DMA writes the 32 HWDATA bits as shown in the two
examples below:
•

To write the halfword “0xABCD”, the DMA sets the HWDATA bus to “0xABCDABCD”
with HSIZE = HalfWord

•

To write the byte “0xAB”, the DMA sets the HWDATA bus to “0xABABABAB” with
HSIZE = Byte

Assuming that the AHB/APB bridge is an AHB 32-bit slave peripheral that does not take the
HSIZE data into account, it will transform any AHB byte or halfword operation into a 32-bit
APB operation in the following manner:
•

An AHB byte write operation of the data “0xB0” to 0x0 (or to 0x1, 0x2 or 0x3) will be
converted to an APB word write operation of the data “0xB0B0B0B0” to 0x0

•

An AHB halfword write operation of the data “0xB1B0” to 0x0 (or to 0x2) will be
converted to an APB word write operation of the data “0xB1B0B1B0” to 0x0

For instance, to write the APB backup registers (16-bit registers aligned to a 32-bit address
boundary), the software must configure the memory source size (MSIZE) to “16-bit” and the
peripheral destination size (PSIZE) to “32-bit”.

10.3.5

Error management
A DMA transfer error can be generated by reading from or writing to a reserved address
space. When a DMA transfer error occurs during a DMA read or a write access, the faulty
channel is automatically disabled through a hardware clear of its EN bit in the corresponding
Channel configuration register (DMA_CCRx). The channel's transfer error interrupt flag
(TEIF) in the DMA_IFR register is set and an interrupt is generated if the transfer error
interrupt enable bit (TEIE) in the DMA_CCRx register is set.

10.3.6

DMA interrupts
An interrupt can be produced on a Half-transfer, Transfer complete or Transfer error for
each DMA channel. Separate interrupt enable bits are available for flexibility.
Table 28. DMA interrupt requests
Interrupt event

Event flag

Enable control bit

Half-transfer

HTIF

HTIE

Transfer complete

TCIF

TCIE

Transfer error

TEIF

TEIE

DMA controller
The hardware requests from the peripherals (TIMx, ADC, DAC, SPI, I2C, and USARTx) are
simply logically ORed before entering the DMA. This means that on one channel, only one
request must be enabled at a time.

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The peripheral DMA requests can be independently activated/de-activated by programming
the DMA control bit in the registers of the corresponding peripheral.
Table 29 and Table 30 list the DMA requests for each channel.
Table 29. Summary of the DMA requests for each channel
on STM32F03x, STM32F04x and STM32F05x devices
Peripherals

Channel 1

Channel 2

(1)

ADC

Channel 4

Channel 5

-

-

-

ADC

ADC

SPI

Channel 3

(2)

-

SPI1_RX

SPI1_TX

SPI2_RX

SPI2_TX
USART1_RX(2)
USART2_RX

USART

-

USART1_TX(1)

USART1_RX(1)

USART1_TX(2)
USART2_TX

I2C

-

I2C1_TX

I2C1_RX

I2C2_TX

I2C2_RX

TIM1

-

TIM1_CH1

TIM1_CH2

TIM1_CH4
TIM1_TRIG
TIM1_COM

TIM1_CH3
TIM1_UP

TIM2

TIM2_CH3

TIM2_UP

TIM2_CH2

TIM2_CH4

TIM2_CH1

TIM3

-

TIM3_CH3

TIM3_CH4
TIM3_UP

TIM3_CH1
TIM3_TRIG

-

TIM6 / DAC

-

-

TIM6_UP
DAC_Channel1

-

-

TIM15

-

-

-

-

TIM15_CH1
TIM15_UP
TIM15_TRIG
TIM15_COM

TIM16

-

-

TIM16_CH1(1)
TIM16_UP(1)

TIM16_CH1(2)
TIM16_UP(2)

-

TIM17

TIM17_CH1(1)
TIM17_UP(1)

TIM17_CH1(2)
TIM17_UP(2)

-

-

-

1. DMA request mapped on this DMA channel only if the corresponding remapping bit is cleared in the SYSCFG_CFGR1
register. For more details, please refer to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page 165.
2. DMA request mapped on this DMA channel only if the corresponding remapping bit is set in the SYSCFG_CFGR1 register.
For more details, please refer to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page 165.

Table 30. Summary of the DMA requests for each channel on STM32F07x devices
Peripherals
ADC
SPI
USART

Channel 1
ADC

(1)

Reserved

Reserved

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

(2)
ADC

Reserved

Reserved

Reserved

Reserved

Reserved

SPI1_TX

(1)
SPI2_RX

(1)
SPI2_TX

(2)
SPI2_RX

(2)
SPI2_TX

SPI1_RX
USART1_TX
USART3_TX

(1)
(2)

Reserved

(1)
I2C1_TX

TIM1

Reserved

(1)
TIM1_CH1

TIM2

TIM2_CH3

TIM2_UP

TIM3

Reserved

TIM3_CH3

I2C

194/1004

(1)
USART1_RX
(2)
USART3_RX
I2C1_RX

(1)

(1)
TIM1_CH2

TIM2_CH2

(1)

TIM3_CH4
TIM3_UP

USART1_TX
USART2_TX

(2)

USART1_RX

(1) USART2_RX

(2) USART2_TX(2)
(2) USART2_RX
(1) USART3_TX(1)
(1) USART3_RX
USART4_RX

USART4_TX

(2)
I2C1_TX

(2)
I2C1_RX

(2)
TIM1_CH1
(2)
TIM1_CH2
(2)
TIM1_CH3

Reserved

TIM2_CH1

Reserved

(2)
TIM2_CH2
(2)
TIM2_CH4

Reserved

(2)
TIM3_CH1
(2)
TIM3_TRIG

Reserved

I2C2_TX

I2C2_RX

TIM1_CH4
TIM1_TRIG
TIM1_COM

(1)
TIM1_CH3

TIM2_CH4

(1)

(1)
TIM3_CH1
(1)
TIM3_TRIG

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RM0091

Direct memory access controller (DMA)

Table 30. Summary of the DMA requests for each channel on STM32F07x devices (continued)
Peripherals

Channel 1

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

TIM6 / DAC

Reserved

Reserved

TIM6_UP
DAC_Channel1

Reserved

Reserved

Reserved

Reserved

TIM7 / DAC

Reserved

Reserved

Reserved

TIM7_UP
DAC_Channel2

Reserved

Reserved

Reserved

TIM15

Reserved

Reserved

Reserved

Reserved

TIM15_CH1
TIM15_UP
TIM15_TRIG
TIM15_COM

Reserved

Reserved

TIM16

Reserved

Reserved

(1)
TIM16_CH1
(1)
TIM16_UP

(2)
TIM16_CH1
(2)
TIM16_UP

Reserved

(3)
TIM16_CH1
(3)
TIM16_UP

Reserved

TIM17

(1)
TIM17_CH1
(1)
TIM17_UP

(2)
TIM17_CH1
(2)
TIM17_UP

Reserved

Reserved

Reserved

Reserved

(3)
TIM17_CH1
(3)
TIM17_UP

1. DMA request mapped on this DMA channel only if the corresponding remapping bit is cleared in the SYSCFG_CFGR1
register. For more details, please refer to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page 165.
2. DMA request mapped on this DMA channel only if the corresponding remapping bit is set in the SYSCFG_CFGR1 register.
For more details, please refer to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page 165.
3. DMA request mapped on this DMA channel only if the additional RMP2 remapping bit is set in the SYSCFG_CFGR1
register. For more details, please refer to Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1) on page 165.

DMA1/DMA2 controllers on STM32F09x devices
This chapter is valid for STM32F09x devices only.
STM32F09x embeds two independent DMA controllers named DMA1 and DMA2.
The hardware requests from the peripherals (TIMx, ADC, DAC, SPI, I2C, and USARTx) are
mapped to the DMAx channels (DMA1 1 to 7 and DMA2 1 to 5) through the DMAx channel
selection registers. On one channel, only one request must be enabled at a time. Refer to
Figure 22: DMAx request routing architecture on STM32F09x devices.
The peripheral DMA requests can be independently activated/de-activated by programming
the DMA control bit in the registers of the corresponding peripheral.
The default mapping position 0 ensures the compatibility with the DMA mapping used on
other STM32F0xx products. The hardware requests from the peripherals (TIMx, ADC, DAC,
SPI, I2C, and USARTx) are simply logically ORed before entering the DMA. This means
that on one channel, only one request must be enabled at a time.
Alternate mapping positions 1 to 15 brings higher flexibility to map hardware requests on
DMA channels. When alternate mapping position is used for some peripheral, the same
request is removed from the default mapping position to avoid conflicts.
Table 31 and Table 32 list the DMA requests for each channel and alternate position.

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RM0091



Figure 22. DMAx request routing architecture on STM32F09x devices

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1. Channels 6 and 7 are not available on DMA2.
2. Once some DMA request is selected on position 1 to 15, it disappears from the default location on position
0.

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Table 31. Summary of the DMA1 requests for each channel on STM32F09x devices
CxS
[3:0]

Channel 1

Channel 2

Channel 3

Channel 4

TIM2_CH3
-

TIM2_UP
TIM3_CH3

TIM3_CH4
TIM3_UP

-

-

-

TIM1_CH4
TIM1_TRIG
TIM1_COM

ADC

-

TIM6_UP
DAC_
Channel1

-

USART1_TX

USART1_RX

-

-

-

-

-

-

SPI1_RX

SPI1_TX

SPI2_RX

SPI2_TX

-

-

-

I2C1_TX

I2C1_RX

I2C2_TX

I2C2_RX

-

-

-

TIM1_CH1

TIM1_CH2

-

TIM1_CH3

-

-

-

-

TIM2_CH2

TIM2_CH4

-

-

-

TIM17_CH1
TIM17_UP

-

TIM16_CH1
TIM16_UP

TIM3_CH1
TIM3_TRIG

-

-

-

0001

ADC

ADC

TIM6_UP
DAC_
Channel1

TIM7_UP
DAC_
Channel2

-

-

-

0010

-

I2C1_TX

I2C1_RX

I2C2_TX

I2C2_RX

I2C1_TX

I2C1_RX

0011

-

SPI1_RX

SPI1_TX

SPI2_RX

SPI2_TX

SPI2_RX

SPI2_TX

0100

-

TIM1_CH1

TIM1_CH2

-

TIM1_CH3

TIM1_CH1
TIM1_CH2
TIM1_CH3

-

0101

-

-

TIM2_CH2

TIM2_CH4

-

-

TIM2_CH2
TIM2_CH4

0110

-

-

-

TIM3_CH1
TIM3_TRIG

-

TIM3_CH1
TIM3_TRIG

-

0111

TIM17_CH1
TIM17_UP

TIM17_CH1
TIM17_UP

TIM16_CH1
TIM16_UP

TIM16_CH1
TIM16_UP

-

TIM16_CH1
TIM16_UP

TIM17_CH1
TIM17_UP

1000

USART1_
RX

USART1_TX

USART1_RX

USART1_TX USART1_ RX USART1_ RX USART1_TX

1001

USART2_
RX

USART2_TX USART2_ RX USART2_TX USART2_ RX USART2_ RX USART2_TX

1010

USART3_
RX

USART3_TX USART3_ RX USART3_TX USART3_ RX USART3_ RX USART3_TX

1011

USART4_
RX

USART4_TX USART4_ RX USART4_TX USART4_ RX USART4_ RX USART4_TX

1100

USART5_
RX

USART5_TX USART5_ RX USART5_TX USART5_ RX USART5_ RX USART5_TX

1101

USART6_
RX

USART6_TX USART6_ RX USART6_TX USART6_ RX USART6_ RX USART6_TX

0000

TIM7_UP
DAC_
Channel2

Channel 5

Channel 6

Channel 7

TIM1_UP

-

-

TIM2_CH1

-

-

TIM15_CH1
TIM15_UP
TIM15_TRIG
TIM15_COM

-

-

-

-

USART2_TX USART2_ RX USART3_ RX USART3_TX

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Table 31. Summary of the DMA1 requests for each channel on STM32F09x devices (continued)
CxS
[3:0]

Channel 1

1110

USART7_
RX

USART7_TX USART7_ RX USART7_TX USART7_ RX USART7_ RX USART7_TX

1111

USART8_
RX

USART8_TX USART8_ RX USART8_TX USART8_ RX USART8_ RX USART8_TX

Channel 2

Channel 3

Channel 4

Channel 5

Channel 6

Channel 7

Table 32. Summary of the DMA2 requests for each channel on STM32F09x devices
CxS[3:0]

Channel 1

Channel 2

0000

Channel 3

Channel 4

Channel 5

none

0001

-

-

TIM6_UP
DAC_Channel1

TIM7_UP
DAC_Channel2

ADC

0010

I2C2_TX

I2C2_RX

-

-

-

0011

-

-

SPI1_RX

SPI1_TX

-

0100

-

-

-

-

-

0101

-

-

-

-

-

0110

-

-

-

-

-

0111

-

-

-

-

-

1000

USART1_TX

USART1_RX

USART1_RX

USART1_TX

USART1_TX

1001

USART2_TX

USART2_RX

USART2_RX

USART2_TX

USART2_TX

1010

USART3_TX

USART3_RX

USART3_RX

USART3_TX

USART3_TX

1011

USART4_TX

USART4_RX

USART4_RX

USART4_TX

USART4_TX

1100

USART5_TX

USART5_RX

USART5_RX

USART5_TX

USART5_TX

1101

USART6_TX

USART6_RX

USART6_RX

USART6_TX

USART6_TX

1110

USART7_TX

USART7_RX

USART7_RX

USART7_TX

USART7_TX

1111

USART8_TX

USART8_RX

USART8_RX

USART8_TX

USART8_TX

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10.4

DMA registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by bytes (8-bit), half-words (16-bit) or words (32bit).

10.4.1

DMA interrupt status register (DMA_ISR and DMA2_ISR)
Address offset: 0x00
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

TEIF7

HTIF7

TCIF7

GIF7

TEIF6

HTIF6

TCIF6

GIF6

TEIF5

HTIF5

TCIF5

GIF5

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

TEIF4

HTIF4

TCIF4

GIF4

TEIF3

HTIF3

TCIF3

GIF3

TEIF2

HTIF2

TCIF2

GIF2

TEIF1

HTIF1

TCIF1

GIF1

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

Bits 31:28 Reserved, must be kept at reset value.
Bits 27, 23, 19, 15, TEIFx: Channel x transfer error flag (x = 1..7 for DMA and x = 1..5 for DMA2)
11, 7, 3 This bit is set by hardware. It is cleared by software writing 1 to the corresponding bit in the
DMA_IFCR register.
0: No transfer error (TE) on channel x
1: A transfer error (TE) occurred on channel x
Bits 26, 22, 18, 14, HTIFx: Channel x half transfer flag (x = 1..7 for DMA and x = 1..5 for DMA2)
10, 6, 2 This bit is set by hardware. It is cleared by software writing 1 to the corresponding bit in the
DMA_IFCR register.
0: No half transfer (HT) event on channel x
1: A half transfer (HT) event occurred on channel x
Bits 25, 21, 17, 13, TCIFx: Channel x transfer complete flag (x = 1..7 for DMA and x = 1..5 for DMA2)
9, 5, 1 This bit is set by hardware. It is cleared by software writing 1 to the corresponding bit in the
DMA_IFCR register.
0: No transfer complete (TC) event on channel x
1: A transfer complete (TC) event occurred on channel x
Bits 24, 20, 16, 12, GIFx: Channel x global interrupt flag (x = 1..7 for DMA and x = 1..5 for DMA2)
8, 4, 0 This bit is set by hardware. It is cleared by software writing 1 to the corresponding bit in the
DMA_IFCR register.
0: No TE, HT or TC event on channel x
1: A TE, HT or TC event occurred on channel x

DocID018940 Rev 9

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Direct memory access controller (DMA)

10.4.2

RM0091

DMA interrupt flag clear register (DMA_IFCR and DMA2_IFCR)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

Res.

Res.

Res.

Res.

15

14

13

12

27

26

25

24

23

22

21

20

19

18

17

16

CTEIF7 CHTIF7 CTCIF7 CGIF7 CTEIF6 CHTIF6 CTCIF6 CGIF6 CTEIF5 CHTIF5 CTCIF5 CGIF5
w

w

w

w

w

w

w

w

w

w

w

w

11

10

9

8

7

6

5

4

3

2

1

0

CTEIF4 CHTIF4 CTCIF4 CGIF4 CTEIF3 CHTIF3 CTCIF3 CGIF3 CTEIF2 CHTIF2 CTCIF2 CGIF2 CTEIF1 CHTIF1 CTCIF1 CGIF1
w

w

w

w

w

w

w

w

w

w

w

w

w

w

w

Bits 31:28 Reserved, must be kept at reset value.
Bits 27, 23, 19, 15, CTEIFx: Channel x transfer error clear (x = 1..7 for DMA and x = 1..5 for DMA2)
11, 7, 3 This bit is set by software.
0: No effect
1: Clears the corresponding TEIF flag in the DMA_ISR register
Bits 26, 22, 18, 14, CHTIFx: Channel x half transfer clear (x = 1..7 for DMA and x = 1..5 for DMA2)
10, 6, 2 This bit is set by software.
0: No effect
1: Clears the corresponding HTIF flag in the DMA_ISR register
Bits 25, 21, 17, 13, CTCIFx: Channel x transfer complete clear (x = 1..7 for DMA and x = 1..5 for DMA2)
9, 5, 1 This bit is set by software.
0: No effect
1: Clears the corresponding TCIF flag in the DMA_ISR register
Bits 24, 20, 16, 12, CGIFx: Channel x global interrupt clear (x = 1..7 for DMA and x = 1..5 for DMA2)
8, 4, 0 This bit is set by software.
0: No effect
1: Clears the GIF, TEIF, HTIF and TCIF flags in the DMA_ISR register

200/1004

DocID018940 Rev 9

w

RM0091

Direct memory access controller (DMA)

10.4.3

DMA channel x configuration register (DMA_CCRx and DMA2_CCRx)
(x = 1..7 for DMA and x = 1..5 for DMA2, where x = channel number)
Address offset: 0x08 + 0d20 × (channel number – 1)
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

MEM2
MEM

MINC

PINC

CIRC

DIR

TEIE

HTIE

TCIE

EN

rw

rw

rw

rw

rw

rw

rw

rw

rw

PL[1:0]
rw

rw

MSIZE[1:0]

PSIZE[1:0]

rw

rw

rw

rw

Bits 31:15 Reserved, must be kept at reset value.
Bit 14 MEM2MEM: Memory to memory mode
This bit is set and cleared by software.
0: Memory to memory mode disabled
1: Memory to memory mode enabled
Bits 13:12 PL[1:0]: Channel priority level
These bits are set and cleared by software.
00: Low
01: Medium
10: High
11: Very high
Bits 11:10 MSIZE[1:0]: Memory size
These bits are set and cleared by software.
00: 8-bits
01: 16-bits
10: 32-bits
11: Reserved
Bits 9:8 PSIZE[1:0]: Peripheral size
These bits are set and cleared by software.
00: 8-bits
01: 16-bits
10: 32-bits
11: Reserved
Bit 7 MINC: Memory increment mode
This bit is set and cleared by software.
0: Memory increment mode disabled
1: Memory increment mode enabled
Bit 6 PINC: Peripheral increment mode
This bit is set and cleared by software.
0: Peripheral increment mode disabled
1: Peripheral increment mode enabled

DocID018940 Rev 9

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Direct memory access controller (DMA)

RM0091

Bit 5 CIRC: Circular mode
This bit is set and cleared by software.
0: Circular mode disabled
1: Circular mode enabled
Bit 4 DIR: Data transfer direction
This bit is set and cleared by software.
0: Read from peripheral
1: Read from memory
Bit 3 TEIE: Transfer error interrupt enable
This bit is set and cleared by software.
0: TE interrupt disabled
1: TE interrupt enabled
Bit 2 HTIE: Half transfer interrupt enable
This bit is set and cleared by software.
0: HT interrupt disabled
1: HT interrupt enabled
Bit 1 TCIE: Transfer complete interrupt enable
This bit is set and cleared by software.
0: TC interrupt disabled
1: TC interrupt enabled
Bit 0 EN: Channel enable
This bit is set and cleared by software.
0: Channel disabled
1: Channel enabled

202/1004

DocID018940 Rev 9

RM0091

Direct memory access controller (DMA)

10.4.4

DMA channel x number of data register (DMA_CNDTRx and
DMA2_CNDTRx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number)
Address offset: 0x0C + 0d20 × (channel number – 1)
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

NDT[15:0]
rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 NDT[15:0]: Number of data to transfer
Number of data to be transferred (0 up to 65535). This register can only be written when the
channel is disabled. Once the channel is enabled, this register is read-only, indicating the
remaining bytes to be transmitted. This register decrements after each DMA transfer.
Once the transfer is completed, this register can either stay at zero or be reloaded
automatically by the value previously programmed if the channel is configured in circular
mode.
If this register is zero, no transaction can be served whether the channel is enabled or not.

10.4.5

DMA channel x peripheral address register (DMA_CPARx and
DMA2_CPARx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number)
Address offset: 0x10 + 0d20 × (channel number – 1)
Reset value: 0x0000 0000
This register must not be written when the channel is enabled.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

PA [31:16]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

PA [15:0]
rw

Bits 31:0 PA[31:0]: Peripheral address
Base address of the peripheral data register from/to which the data will be read/written.
When PSIZE is 01 (16-bit), the PA[0] bit is ignored. Access is automatically aligned to a halfword address.
When PSIZE is 10 (32-bit), PA[1:0] are ignored. Access is automatically aligned to a word
address.

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Direct memory access controller (DMA)

10.4.6

RM0091

DMA channel x memory address register (DMA_CMARx and
DMA2_CMARx) (x = 1..7 for DMA and x = 1..5 for DMA2,
where x = channel number)
Address offset: 0x14 + 0d20 × (channel number – 1)
Reset value: 0x0000 0000
This register must not be written when the channel is enabled.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

MA [31:16]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

MA [15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 MA[31:0]: Memory address
Base address of the memory area from/to which the data will be read/written.
When MSIZE is 01 (16-bit), the MA[0] bit is ignored. Access is automatically aligned to a halfword address.
When MSIZE is 10 (32-bit), MA[1:0] are ignored. Access is automatically aligned to a word
address.

204/1004

DocID018940 Rev 9

RM0091

Direct memory access controller (DMA)

10.4.7

DMA channel selection register (DMA_CSELR and DMA2_CSELR)
This register is present only on STM32F09x devices.
Address offset: 0xA8
Reset value: 0x0000 0000
This register is used to manage the remapping of DMA channels (see Figure 22).

31

30

29

28

Res.

Res.

Res.

Res.

27

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

25

24

23

22

rw

rw

rw

rw

rw

rw

rw

rw

rw

C7S [3:0]

C4S [3:0]
rw

26

21

20

19

C6S [3:0]

C3S [3:0]

rw

17

16

C5S [3:0]

C2S [3:0]

rw

18

C1S [3:0]
rw

rw

Bits 31:28 Reserved, must be kept at reset value.
Bits 27:24 C7S[3:0]: DMA channel 7 selection
DMA request mapping for channel 7 (1). Not available on DMA2
Bits 23:20 C6S[3:0]: DMA channel 6 selection
DMA request mapping for channel 6 (1). Not available on DMA2
Bits 19:16 C5S[3:0]: DMA channel 5 selection
DMA request mapping for channel 5 (1)
Bits 15:12 C4S[3:0]: DMA channel 4 selection
DMA request mapping for channel 4 (1)
Bits 11:8 C3S[3:0]: DMA channel 3 selection
DMA request mapping for channel 3 (1)
Bits 7:4 C2S[3:0]: DMA channel 2 selection
DMA request mapping for channel 2 (1)
Bits 3:0 C1S[3:0]: DMA channel 1 selection
DMA request mapping for channel 1 (1)
1. For concrete DMA requests mapping, refer to Table 31: Summary of the DMA1 requests for each channel on
STM32F09x devices and Table 32: Summary of the DMA2 requests for each channel on STM32F09x
devices.

DocID018940 Rev 9

205/1004
208

0x34

0x38

0x3C

206/1004

DMA_CNDTR3

Reset value

Reset value

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0
0
0

Reset value
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Reserved
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

MEM2MEM Res.
Res.
Res.
Res.
Res.
Res.
Res.

0

0

0

0

0

0

0

0
0
0

Reserved
Res.
Res.

MEM2MEM Res.
Res.
Res.
Res.
Res.
Res.
Res.

0
0

0

DMA_CPAR3

DMA_CMAR3

0

0
0

Reset value

0

0

DocID018940 Rev 9
0

0

0

0

PL
[1:0]

0
0

0
0

0
0

0

0

Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

PINC
CIRC
DIR
TEIE
HTIE
TCIE
EN

PSIZE [1:0]

MSIZE [1:0]

MINC

0

Res.

0

0

EN

0

PL
[1:0]

Res.

TCIF4
GIF4
TEIF3
HTIF3
TCIF3
GIF3
TEIF2
HTIF2
TCIF2
GIF2
TEIF1
HTIF1
TCIF1
GIF1

0
0
0
0
0
0
0
0
0
0

CHTIF7
CTCIF7
CGIF7
CTEIF6
CHTIF6
CTCIF6
CGIF6
CTEIF5
CHTIF5
CTCIF5

0
0
0
0
0
0
0
0
0
0
0

CGIF4

HTIF4

0

CTCIF4

0

CHTIF4

0

MEM2MEM

GIF5
TEIF4

0

CTEIF4

TCIF5

0

Res.

HTIF5

0

CGIF5

Res.

Res.

Res.

0
CTCIF3

CTCIF1
CGIF1

0
0
0

MINC
0

EN

CHTIF1

0
TCIE

CTEIF1

0
HTIE

CGIF2

0
TEIE

CTCIF2

0

DIR

CHTIF2

0
PINC

CTEIF2

0
CIRC

CGIF3

PSIZE [1:0]

CHTIF3

MSIZE [1:0]

CTEIF3

0

Res.

0

Res.

Res.

Res.

GIF6
TEIF5

0

0

Res.

0

Res.

Res.

TCIF6

0

0

TCIE

Reset value
0

0

HTIE

DMA_CPAR2
0

0

Res.

0

Res.

0
0

TEIE

0

Res.

0

Res.

0

Res.

Res.

Reset value
PL
[1:0]

DIR

0

Res.

Res.

0

0

Res.

0

Res.

Res.

HTIF6

0

0

Res.

0

Res.

Res.

Res.

GIF7
TEIF6

0

0

PINC

0

Res.

Res.

Res.

TCIF7

0

0

CIRC

0

Res.

HTIF7

0

0

Res.

0

Res.

TEIF7

Res.

Res.

Res.

Res.

0

CTEIF7

Res.

Res.

Res.

Res.

0

0

MINC

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

PSIZE [1:0]

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

MSIZE [1:0]

0

Res.

Reset value

Res.

0

Res.

0

Res.

0

Res.

DMA_CMAR1

Res.

Res.

Res.

0

Res.

0

Res.

Res.

Res.

Res.

Res.
0

Res.

0

Res.

Res.

Res.

Res.

0

Res.

DMA_CPAR1

Res.

0

Res.

Res.
0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Res.

0

Res.

Reset value
0

Res.

0

Res.

0

Res.

Res.

Res.

0

Res.

0

Res.

Reset value
0

Res.

DMA_CCR3
0

Res.

0x30
0

Res.

0x2C
0

Res.

DMA_CMAR2
0

Res.

Reset value
0

Res.

DMA_CNDTR2
0

Res.

DMA_CCR2
0

Res.

Reset value

Res.

0x28
Reset value

Res.

Reset value

Res.

0x24
DMA_CNDTR1

Res.

0x20
DMA_CCR1

Res.

0x1C
0

Res.

0x18
Reset value

Res.

0x14
DMA_IFCR

Res.

0x10
DMA_ISR

Res.

0x08

Res.

0x04

Res.

0x00

Res.

0x0C

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

10.4.8

Res.

Direct memory access controller (DMA)
RM0091

DMA register map
The following table gives the DMA register map and the reset values.
Table 33. DMA register map and reset values

0
0
0
0
0
0
0

NDT[15:0]

PA[31:0]
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

MA[31:0]
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0

NDT[15:0]

PA[31:0]
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

MA[31:0]

0

0

0

0

0

0

0

0

NDT[15:0]

PA[31:0]

MA[31:0]

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0x80

DMA_CCR7

0

0

0

0

0

0

0

0

0x7C

0

0

0

0

0

DMA_CPAR6

DMA_CMAR6

0

0

Reset value

Reset value

DocID018940 Rev 9

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

EN

0

0

TCIE

0

0

HTIE

Reserved

0

TEIE

0

0

DIR

MA[31:0]

0

CIRC

0

PINC

PA[31:0]

MINC

0

0

0

Reset value
0

0
PL
[1:0]

0

0

0

0

0

0

0

0

0

0

0

0
0

PL
[1:0]

0
0

0
0
0
0

0
EN

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Reserved
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

MEM2MEM Res.
Res.
Res.
Res.
Res.
Res.
Res.

0
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

PINC
CIRC
DIR
TEIE
HTIE
TCIE
EN

PSIZE [1:0]

MSIZE [1:0]

MINC

0

TCIE

0

0

HTIE

0

0

TEIE

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

PINC
CIRC
DIR
TEIE
HTIE
TCIE
EN

Res.

Res.

Res.

Res.

MINC

PSIZE [1:0]

MSIZE [1:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

MEM2MEM Res.

0

DIR

0

0

0

CIRC

0

PL
[1:0]

0

PINC

0

Res.

0

0

MINC

0

Res.

0
0

PSIZE [1:0]

0

0

PSIZE [1:0]

0
0

0

MSIZE [1:0]

0

Res.

Res.

Res.

Reset value
PL
[1:0]

MSIZE [1:0]

0

MEM2MEM

Reset value

MEM2MEM

DMA_CMAR5
0

Res.

0

Res.

Reset value

Res.

DMA_CPAR5
Res.

0

Res.

DMA_CMAR4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Reset value
0

Res.

DMA_CPAR4

Res.

0

0
0
0

0

Res.

0

0
0
0

0

Res.

0

0
0

0

Res.

0

0
0

0

Res.

0

0
0
0

Res.

0

0
0
0
0

Res.

0

0
0
0
0

Res.

Reset value

0
0
0
0

Res.

0x78

Reset value
0
0
0

Res.

0x74
DMA_CNDTR6
0
0
0

Res.

0x70
DMA_CCR6
0
0
0

Res.

0x6C

Register
0
0

Res.

Offset
Reset value
0

Res.

0x64
Reset value

Res.

0x60
DMA_CNDTR5
0

Res.

0x5C
DMA_CCR5
0

Res.

0x58
Reset value

Res.

0x54
0

Res.

0x50
Reset value

Res.

0x4C
DMA_CNDTR4

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

0x48
DMA_CCR4

Res.

0x44

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Reserved

Res.

0x40

Res.

Register

Res.

Offset

Res.

RM0091
Direct memory access controller (DMA)

Table 33. DMA register map and reset values (continued)

0
0
0
0
0
0
0
0

NDT[15:0]

PA[31:0]

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

MA[31:0]

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0

NDT[15:0]

PA[31:0]

MA[31:0]
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Table 34. DMA register map and reset values (registers available on STM32F07x and STM32F09x
devices only)

0
0
0
0
0
0
0
0

NDT[15:0]

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Direct memory access controller (DMA)

RM0091

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DMA_CNDTR7

Res.

0x84

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 34. DMA register map and reset values (registers available on STM32F07x and STM32F09x
devices only) (continued)

Reset value
0x88
0x8C

0

DMA_CPAR7
Reset value

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

PA[31:0]
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

DMA_CMAR7
Reset value

NDT[15:0]

0

0

MA[31:0]
0

0

0

0

0

0

0

0

0

0

0

0

0x90

0

0

0

0

0

Reserved

Reset value

Res.

Res.

DMA_CSELR

Res.

0xA8

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 35. DMA register map and reset values (register available on STM32F09x
devices only)

C7S[3:0]
0

0

0

C6S[3:0]
0

0

0

0

C5S[3:0]
0

0

0

0

C4S[3:0]
0

0

0

0

C3S[3:0]
0

0

0

0

C2S[3:0]
0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

208/1004

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0

0

0

C1S[3:0]
0

0

0

0

0

RM0091

Interrupts and events

11

Interrupts and events

11.1

Nested vectored interrupt controller (NVIC)

11.1.1

NVIC main features
•

32 maskable interrupt channels (not including the sixteen Cortex®-M0 interrupt lines)

•

4 programmable priority levels (2 bits of interrupt priority are used)

•

Low-latency exception and interrupt handling

•

Power management control

•

Implementation of System Control Registers

The NVIC and the processor core interface are closely coupled, which enables low latency
interrupt processing and efficient processing of late arriving interrupts.
All interrupts including the core exceptions are managed by the NVIC. For more information
on exceptions and NVIC programming, refer to the PM0215 programming manual.
For code example refer to the Appendix section A.6.1: NVIC initialization example.

11.1.2

SysTick calibration value register
The SysTick calibration value is set to 6000, which gives a reference time base of 1 ms with
the SysTick clock set to 6 MHz (max fHCLK/8).

11.1.3

Interrupt and exception vectors
Table 36 is the vector table for STM32F0xx devices. Please consider peripheral availability
on given device.

Position

Priority

Table 36. Vector table
Type of
priority

-

-

-

-

-3

-

Acronym

Description

Address

-

Reserved

0x0000 0000

fixed

Reset

Reset

0x0000 0004

-2

fixed

NMI

Non maskable interrupt. The RCC Clock Security
System (CSS) is linked to the NMI vector.

0x0000 0008

-

-1

fixed

HardFault

All class of fault

0x0000 000C

-

3

settable

SVCall

System service call via SWI instruction

0x0000 002C

-

5

settable

PendSV

Pendable request for system service

0x0000 0038

-

6

settable

SysTick

System tick timer

0x0000 003C

0

7

settable

WWDG

Window watchdog interrupt

0x0000 0040

1

8

settable

PVD_VDDIO2

PVD and VDDIO2 supply comparator interrupt
(combined EXTI lines 16 and 31)

0x0000 0044

2

9

settable

RTC

RTC interrupts (combined EXTI lines 17, 19 and
20)

0x0000 0048

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Position

Priority

Table 36. Vector table (continued)
Type of
priority

3

10

settable

FLASH

Flash global interrupt

0x0000 004C

4

11

settable

RCC_CRS

RCC and CRS global interrupts

0x0000 0050

5

12

settable

EXTI0_1

EXTI Line[1:0] interrupts

0x0000 0054

6

13

settable

EXTI2_3

EXTI Line[3:2] interrupts

0x0000 0058

7

14

settable

EXTI4_15

EXTI Line[15:4] interrupts

0x0000 005C

8

15

settable

TSC

Touch sensing interrupt

0x0000 0060

9

16

settable

DMA_CH1

DMA channel 1 interrupt

0x0000 0064

10

17

settable

DMA_CH2_3
DMA2_CH1_2

DMA channel 2 and 3 interrupts
DMA2 channel 1 and 2 interrupts

0x0000 0068

11

18

settable

DMA_CH4_5_6_7
DMA2_CH3_4_5

DMA channel 4, 5, 6 and 7 interrupts
DMA2 channel 3, 4 and 5 interrupts

0x0000 006C

12

19

settable

ADC_COMP

ADC and COMP interrupts (ADC interrupt
combined with EXTI lines 21 and 22)

0x0000 0070

13

20

settable

TIM1_BRK_UP_
TRG_COM

TIM1 break, update, trigger and commutation
interrupt

0x0000 0074

14

21

settable

TIM1_CC

TIM1 capture compare interrupt

0x0000 0078

15

22

settable

TIM2

TIM2 global interrupt

0x0000 007C

16

23

settable

TIM3

TIM3 global interrupt

0x0000 0080

17

24

settable

TIM6_DAC

TIM6 global interrupt and DAC underrun interrupt

0x0000 0084

18

25

settable

TIM7

TIM7 global interrupt

0x0000 0088

19

26

settable

TIM14

TIM14 global interrupt

0x0000 008C

20

27

settable

TIM15

TIM15 global interrupt

0x0000 0090

21

28

settable

TIM16

TIM16 global interrupt

0x0000 0094

22

29

settable

TIM17

TIM17 global interrupt

0x0000 0098

23

30

settable

Acronym

I2C1

Description

I

2C1

global interrupt (combined with EXTI line 23)

2

Address

0x0000 009C

24

31

settable

I2C2

I C2 global interrupt

0x0000 00A0

25

32

settable

SPI1

SPI1 global interrupt

0x0000 00A4

26

33

settable

SPI2

SPI2 global interrupt

0x0000 00A8

27

34

settable

USART1

USART1 global interrupt (combined with EXTI
line 25)

0x0000 00AC

28

35

settable

USART2

USART2 global interrupt (combined with EXTI
line 26)

0x0000 00B0

29

36

settable

USART3_4_5_6_7_
8

USART3, USART4, USART5, USART6,
USART7, USART8 global interrupts
(combined with EXTI line 28)

0x0000 00B4

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Interrupts and events

Position

Priority

Table 36. Vector table (continued)
Type of
priority

30

37

settable

CEC_CAN

CEC and CAN global interrupts (combined with
EXTI line 27)

0x0000 00B8

31

38

settable

USB

USB global interrupt (combined with EXTI line 18)

0x0000 00BC

11.2

Acronym

Description

Address

Extended interrupts and events controller (EXTI)
The extended interrupts and events controller (EXTI) manages the external and internal
asynchronous events/interrupts and generates the event request to the CPU/Interrupt
Controller and a wake-up request to the Power Manager.
The EXTI allows the management of up to 32 external/internal event line (23 external event
lines and 9 internal event lines).
The active edge of each external interrupt line can be chosen independently, whilst for
internal interrupt the active edge is always the rising one. An interrupt could be left pending:
in case of an external one, a status register is instantiated and indicates the source of the
interrupt; an event is always a simple pulse and it’s used for triggering the core Wake-up
(e.g. Cortex-M0 RXEV pin). For internal interrupts, the pending status is assured by the
generating IP, so no need for a specific flag. Each input line can be masked independently
for interrupt or event generation, in addition the internal lines are sampled only in STOP
mode. This controller allows also to emulate the (only) external events by software,
multiplexed with the corresponding hardware event line, by writing to a dedicated register.

11.2.1

Main features
The EXTI main features are the following:
•

Supports generation of up to 32 event/interrupt requests

•

Independent mask on each event/interrupt line

•

Automatic disable of internal lines when system is not in STOP mode

•

Independent trigger for external event/interrupt line

•

Dedicated status bit for external interrupt line

•

Emulation for all the external event requests

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Interrupts and events

11.2.2

RM0091

Block diagram
The extended interrupt/event block diagram is shown in Figure 23.
Figure 23. Extended interrupts and events controller (EXTI) block diagram
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11.2.3

Event management
The STM32F0xx is able to handle external or internal events in order to wake up the core
(WFE). The wakeup event can be generated either by:

11.2.4

•

enabling an interrupt in the peripheral control register but not in the NVIC, and enabling
the SEVONPEND bit in the Cortex-M0 System Control register. When the MCU
resumes from WFE, the EXTI peripheral interrupt pending bit and the peripheral NVIC
IRQ channel pending bit (in the NVIC interrupt clear pending register) have to be
cleared.

•

or by configuring an external or internal EXTI line in event mode. When the CPU
resumes from WFE, it is not necessary to clear the peripheral interrupt pending bit or
the NVIC IRQ channel pending bit as the pending bit corresponding to the event line is
not set.

Functional description
For the external interrupt lines, to generate the interrupt, the interrupt line should be
configured and enabled. This is done by programming the two trigger registers with the
desired edge detection and by enabling the interrupt request by writing a ‘1’ to the
corresponding bit in the interrupt mask register. When the selected edge occurs on the
external interrupt line, an interrupt request is generated. The pending bit corresponding to
the interrupt line is also set. This request is reset by writing a ‘1’ in the pending register.

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Interrupts and events
For the internal interrupt lines, the active edge is always the rising edge, the interrupt is
enabled by default in the interrupt mask register and there is no corresponding pending bit
in the pending register.
To generate the event, the event line should be configured and enabled. This is done by
programming the two trigger registers with the desired edge detection and by enabling the
event request by writing a ‘1’ to the corresponding bit in the event mask register. When the
selected edge occurs on the event line, an event pulse is generated. The pending bit
corresponding to the event line is not set.
For the external lines, an interrupt/event request can also be generated by software by
writing a ‘1’ in the software interrupt/event register.

Note:

The interrupts or events associated to the internal lines can be triggered only when the
system is in STOP mode. If the system is still running, no interrupt/event is generated.
For code example refer to the Appendix section A.6.2: External interrupt selection code
example.

Hardware interrupt selection
To configure a line as interrupt source, use the following procedure:
•

Configure the corresponding mask bit in the EXTI_IMR register.

•

Configure the Trigger Selection bits of the Interrupt line (EXTI_RTSR and EXTI_FTSR)

•

Configure the enable and mask bits that control the NVIC IRQ channel mapped to the
EXTI so that an interrupt coming from one of the EXTI line can be correctly
acknowledged.

Hardware event selection
To configure a line as event source, use the following procedure:
•

Configure the corresponding mask bit in the EXTI_EMR register.

•

Configure the Trigger Selection bits of the Event line (EXTI_RTSR and EXTI_FTSR)

Software interrupt/event selection
Any of the external lines can be configured as software interrupt/event lines. The following is
the procedure to generate a software interrupt.
•

Configure the corresponding mask bit (EXTI_IMR, EXTI_EMR)

•

Set the required bit of the software interrupt register (EXTI_SWIER)

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11.2.5

RM0091

External and internal interrupt/event line mapping
The GPIOs are connected to the 16 external interrupt/event lines in the following manner:
Figure 24. External interrupt/event GPIO mapping
EXTI0[3:0] bits in the SYSCFG_EXTICR1 register

PA0
PB0
PC0
PD0
PE0
PF0

EXTI0

EXTI1[3:0] bits in the SYSCFG_EXTICR1 register

PA1
PB1
PC1
PD1
PE1
PF1

EXTI1

...

EXTI15[3:0] bits in the SYSCFG_EXTICR4 register

PA15
PB15
PC15
PD15
PE15
PF15

EXTI15

MS19951V2

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Interrupts and events
The remaining lines are connected as follow:
•

EXTI line 16 is connected to the PVD output

•

EXTI line 17 is connected to the RTC Alarm event

•

EXTI line 18 is connected to the internal USB wakeup event

•

EXTI line 19 is connected to the RTC Tamper and TimeStamp events

•

EXTI line 20 is connected to the RTC Wakeup event (available only on STM32F07x
and STM32F09x devices)

•

EXTI line 21 is connected to the Comparator 1 output

•

EXTI line 22 is connected to the Comparator 2 output

•

EXTI line 23 is connected to the internal I2C1 wakeup event

•

EXTI line 24 is reserved (internally held low)

•

EXTI line 25 is connected to the internal USART1 wakeup event

•

EXTI line 26 is connected to the internal USART2 wakeup event (available only on
STM32F07x and STM32F09x devices)

•

EXTI line 27 is connected to the internal CEC wakeup event

•

EXTI line 28 is connected to the internal USART3 wakeup event (available only on
STM32F09x devices)

•

EXTI line 29 is reserved (internally held low)

•

EXTI line 30 is reserved (internally held low)

•

EXTI line 31 is connected to the VDDIO2 supply comparator output (available only on
STM32F04x, STM32F07x and STM32F09x devices

Note:

EXTI lines which are reserved or not used on some devices are considered as internal.

11.3

EXTI registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers have to be accessed by words (32-bit).

11.3.1

Interrupt mask register (EXTI_IMR)
Address offset: 0x00
Reset value: 0x0FF4 0000 (STM32F03x devices)
0x7FF4 0000 (STM32F04x devices)
0x0F94 0000 (STM32F05x devices)
0x7F84 0000 (STM32F07x and STM32F09x devices)

Note:

The reset value for the internal lines is set to ‘1’ in order to enable the interrupt by default.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

IM31

IM30

IM29

IM28

IM27

IM26

IM25

IM24

IM23

IM22

IM21

IM20

IM19

IM18

IM17

IM16

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

IM15

IM14

IM13

IM12

IM11

IM10

IM9

IM8

IM7

IM6

IM5

IM4

IM3

IM2

IM1

IM0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

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RM0091

Bits 31:0 IMx: Interrupt Mask on line x (x = 31 to 0)
0: Interrupt request from Line x is masked
1: Interrupt request from Line x is not masked

11.3.2

Event mask register (EXTI_EMR)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

EM31

EM30

EM29

EM28

EM27

EM26

EM25

EM24

EM23

EM22

EM21

EM20

EM19

EM18

EM17

EM16

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

EM15

EM14

EM13

EM12

EM11

EM10

EM9

EM8

EM7

EM6

EM5

EM4

EM3

EM2

EM1

EM0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 EMx: Event mask on line x (x = 31 to 0)
0: Event request from Line x is masked
1: Event request from Line x is not masked

11.3.3

Rising trigger selection register (EXTI_RTSR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

RT31

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RT22

RT21

RT20

RT19

Res.

RT17

RT16

rw

rw

rw

rw

rw

rw

rw
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

RT15

RT14

RT13

RT12

RT11

RT10

RT9

RT8

RT7

RT6

RT5

RT4

RT3

RT2

RT1

RT0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bit 31 RT31: Rising trigger event configuration bit of line 31
0: Rising trigger disabled (for Event and Interrupt) for input line
1: Rising trigger enabled (for Event and Interrupt) for input line.
Bits 30:23 Reserved, must be kept at reset value.
Bits 22:19 RTx: Rising trigger event configuration bit of line x (x = 22 to 19)
0: Rising trigger disabled (for Event and Interrupt) for input line
1: Rising trigger enabled (for Event and Interrupt) for input line.
Bits 18 Reserved, must be kept at reset value.
Bits 17:0 RTx: Rising trigger event configuration bit of line x (x = 17 to 0)
0: Rising trigger disabled (for Event and Interrupt) for input line
1: Rising trigger enabled (for Event and Interrupt) for input line.

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Interrupts and events

Note:

The external wakeup lines are edge triggered. No glitches must be generated on these
lines. If a rising edge on an external interrupt line occurs during a write operation to the
EXTI_RTSR register, the pending bit is not set.
Rising and falling edge triggers can be set for the same interrupt line. In this case, both
generate a trigger condition.

11.3.4

Falling trigger selection register (EXTI_FTSR)
Address offset: 0x0C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

FT31

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FT22

FT21

FT20

FT19

Res.

FT17

FT16

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

FT15

FT14

FT13

FT12

FT11

FT10

FT9

FT8

FT7

FT6

FT5

FT4

FT3

FT2

FT1

FT0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bit 31 FT31: Falling trigger event configuration bit of line 31
0: Falling trigger disabled (for Event and Interrupt) for input line
1: Falling trigger enabled (for Event and Interrupt) for input line.
Bits 30:23 Reserved, must be kept at reset value.
Bits 22:19 FTx: Falling trigger event configuration bit of line x (x = 22 to 19)
0: Falling trigger disabled (for Event and Interrupt) for input line.
1: Falling trigger enabled (for Event and Interrupt) for input line.
Bits 18 Reserved, must be kept at reset value.
Bits 17:0 FTx: Falling trigger event configuration bit of line x (x = 17 to 0)
0: Falling trigger disabled (for Event and Interrupt) for input line.
1: Falling trigger enabled (for Event and Interrupt) for input line.

Note:

The external wakeup lines are edge triggered. No glitches must be generated on these
lines. If a falling edge on an external interrupt line occurs during a write operation to the
EXTI_FTSR register, the pending bit is not set.
Rising and falling edge triggers can be set for the same interrupt line. In this case, both
generate a trigger condition.

11.3.5

Software interrupt event register (EXTI_SWIER)
Address offset: 0x10
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

SWI31

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SWI22

SWI21

SWI20

SWI19

Res.

SWI17

SWI16

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

SWI15

SWI14

SWI13

SWI12

SWI11

SWI10

SWI9

SWI8

SWI7

SWI6

SWI5

SWI4

SWI3

SWI2

SWI1

SWI0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

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Interrupts and events

RM0091

Bit 31 SWI31: Software interrupt on line 31
If the interrupt is enabled on this line in the EXTI_IMR, writing a ‘1’ to this bit when it is at ‘0’
sets the corresponding pending bit in EXTI_PR resulting in an interrupt request generation.
This bit is cleared by clearing the corresponding bit of EXTI_PR (by writing a ‘1’ to the bit)
Bits 30:23 Reserved, must be kept at reset value.
Bits 22:19 SWIx: Software interrupt on line x (x = 22 to 19)
If the interrupt is enabled on this line in the EXTI_IMR, writing a ‘1’ to this bit when it is at ‘0’
sets the corresponding pending bit in EXTI_PR resulting in an interrupt request generation.
This bit is cleared by clearing the corresponding bit of EXTI_PR (by writing a ‘1’ to the bit)
Bits 18 Reserved, must be kept at reset value.
Bits 17:0 SWIx: Software interrupt on line x (x = 17 to 0)
If the interrupt is enabled on this line in the EXTI_IMR, writing a ‘1’ to this bit when it is at ‘0’
sets the corresponding pending bit in EXTI_PR resulting in an interrupt request generation.
This bit is cleared by clearing the corresponding bit of EXTI_PR (by writing a ‘1’ to the bit).

11.3.6

Pending register (EXTI_PR)
Address offset: 0x14
Reset value: undefined

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

PIF31

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PIF22

PIF21

PIF20

PIF19

Res.

PIF17

PIF16

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

PIF15

PIF14

PIF13

PIF12

PIF11

PIF10

PIF9

PIF8

PIF7

PIF6

PIF5

PIF4

PIF3

PIF2

PIF1

PIF0

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

Bit 31 PIF31: Pending interrupt flag on line 31
0: no trigger request occurred
1: selected trigger request occurred
This bit is set when the selected edge event arrives on the external interrupt line. This bit is
cleared by writing a 1 to the bit.
Bits 30:23 Reserved, must be kept at reset value.
Bits 22:19 PIFx: Pending interrupt flag on line x (x = 22 to 19)
0: no trigger request occurred
1: selected trigger request occurred
This bit is set when the selected edge event arrives on the external interrupt line. This bit is
cleared by writing a 1 to the bit.
Bits 18 Reserved, must be kept at reset value.
Bits 17:0 PIFx: Pending interrupt flag on line x (x = 17 to 0)
0: no trigger request occurred
1: selected trigger request occurred
This bit is set when the selected edge event arrives on the external interrupt line. This bit is
cleared by writing a 1 to the bit.

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11.3.7

Interrupts and events

EXTI register map
The following table gives the EXTI register map and the reset values.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Res.

0

0

0

0

0

0

0

0

0

0

RT[17:0]
0

0

0

0

0

0

0

0

Res.

RT19

0

0

0

0

FT[17:0]
0

0

0

0

0

0

0

0

Res.

0

0

0

0

SWI[17:0]
0

0

0

0

0

0

0

0

Res.

RT20
0

SWI19

0

PIF19

FT19

RT21

0

SWI20

FT20

RT22

0

PIF20

Res.
Res.

Res.
Res.

Res.
Res.

Res.

Res.
Res.

Res.

FT21

0

0

FT22

Reset value

0

SWI21

EXTI_PR

0

SWI22

0

0

PIF21

Reset value

0

PIF22

EXTI_SWIER

0

Res.

0

0

RT23

Reset value

0

FT23

Res.

EXTI_FTSR

0

SWI23

Res.

0

0

PIF23

Res.

Reset value

0

Res.

EXTI_RTSR

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Reset value

Res.

EM[31:0]

Res.

EXTI_EMR

Res.

0x14

0

RT31

0x10

0

FT31

0x0C

0

Res.

0x08

IM[31:0]
0

SWI31

0x04

EXTI_IMR
Reset value

Res.

0x00

Register

PIF31

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 37. External interrupt/event controller register map and reset values

0

0

PIF[17:0]
0

0

0

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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Cyclic redundancy check calculation unit (CRC)

RM0091

12

Cyclic redundancy check calculation unit (CRC)

12.1

Introduction
The CRC (cyclic redundancy check) calculation unit is used to get a CRC code from 8-, 16or 32-bit data word and a generator polynomial.
Among other applications, CRC-based techniques are used to verify data transmission or
storage integrity. In the scope of the functional safety standards, they offer a means of
verifying the Flash memory integrity. The CRC calculation unit helps compute a signature of
the software during runtime, to be compared with a reference signature generated at link
time and stored at a given memory location.

12.2

CRC main features
•

Uses CRC-32 (Ethernet) polynomial: 0x4C11DB7
X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 +X8 + X7 + X5 + X4 + X2+ X +1

12.3

•

Alternatively, uses fully programmable polynomial with programmable size (7, 8, 16, 32
bits) (STM32F07x and STM32F09x devices only)

•

Handles 8-,16-, 32-bit data size

•

Programmable CRC initial value

•

Single input/output 32-bit data register

•

Input buffer to avoid bus stall during calculation

•

CRC computation done in 4 AHB clock cycles (HCLK) for the 32-bit data size

•

General-purpose 8-bit register (can be used for temporary storage)

•

Reversibility option on I/O data

CRC implementation
Table 38. STM32F0xx CRC implementation(1)
CRC
modes/features

STM32F03x

STM32F04x

STM32F05x

STM32F07x

STM32F09x

Programmable
polynomial

-

-

-

X

X

Input buffer

X

X

X

X

X

1. X = supported

220/1004

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Cyclic redundancy check calculation unit (CRC)

12.4

CRC functional description

12.4.1

CRC block diagram
Figure 25. CRC calculation unit block diagram
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12.4.2

CRC internal signals
Table 39. CRC internal input/output signals

12.4.3

Signal name

Signal type

crc_hclk

Digital input

Description
AHB clock

CRC operation
The CRC calculation unit has a single 32-bit read/write data register (CRC_DR). It is used to
input new data (write access), and holds the result of the previous CRC calculation (read
access).
Each write operation to the data register creates a combination of the previous CRC value
(stored in CRC_DR) and the new one. CRC computation is done on the whole 32-bit data
word or byte by byte depending on the format of the data being written.
The CRC_DR register can be accessed by word, right-aligned half-word and right-aligned
byte. For the other registers only 32-bit access is allowed.
The duration of the computation depends on data width:
•

4 AHB clock cycles for 32-bit

•

2 AHB clock cycles for 16-bit

•

1 AHB clock cycles for 8-bit

An input buffer allows to immediately write a second data without waiting for any wait states
due to the previous CRC calculation.
The data size can be dynamically adjusted to minimize the number of write accesses for a
given number of bytes. For instance, a CRC for 5 bytes can be computed with a word write
followed by a byte write.

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Cyclic redundancy check calculation unit (CRC)

RM0091

The input data can be reversed, to manage the various endianness schemes. The reversing
operation can be performed on 8 bits, 16 bits and 32 bits depending on the REV_IN[1:0] bits
in the CRC_CR register.
For example: input data 0x1A2B3C4D is used for CRC calculation as:
0x58D43CB2 with bit-reversal done by byte
0xD458B23C with bit-reversal done by half-word
0xB23CD458 with bit-reversal done on the full word
The output data can also be reversed by setting the REV_OUT bit in the CRC_CR register.
The operation is done at bit level: for example, output data 0x11223344 is converted into
0x22CC4488.
The CRC calculator can be initialized to a programmable value using the RESET control bit
in the CRC_CR register (the default value is 0xFFFFFFFF).
The initial CRC value can be programmed with the CRC_INIT register. The CRC_DR
register is automatically initialized upon CRC_INIT register write access.
The CRC_IDR register can be used to hold a temporary value related to CRC calculation. It
is not affected by the RESET bit in the CRC_CR register.

Polynomial programmability (STM32F07x and STM32F09x devices only)
The polynomial coefficients are fully programmable through the CRC_POL register, and the
polynomial size can be configured to be 7, 8, 16 or 32 bits by programming the
POLYSIZE[1:0] bits in the CRC_CR register. Even polynomials are not supported.
If the CRC data is less than 32-bit, its value can be read from the least significant bits of the
CRC_DR register.
To obtain a reliable CRC calculation, the change on-fly of the polynomial value or size can
not be performed during a CRC calculation. As a result, if a CRC calculation is ongoing, the
application must either reset it or perform a CRC_DR read before changing the polynomial.
The default polynomial value is the CRC-32 (Ethernet) polynomial: 0x4C11DB7.

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Cyclic redundancy check calculation unit (CRC)

12.5

CRC registers

12.5.1

Data register (CRC_DR)
Address offset: 0x00
Reset value: 0xFFFF FFFF

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

6

5

4

3

2

1

0

DR[31:16]
rw
15

14

13

12

11

10

9

8

7

DR[15:0]
rw

Bits 31:0 DR[31:0]: Data register bits
This register is used to write new data to the CRC calculator.
It holds the previous CRC calculation result when it is read.
If the data size is less than 32 bits, the least significant bits are used to write/read the
correct value.

12.5.2

Independent data register (CRC_IDR)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

IDR[7:0]
rw

Bits 31:8 Reserved, must be kept cleared.
Bits 7:0 IDR[7:0]: General-purpose 8-bit data register bits
These bits can be used as a temporary storage location for one byte.
This register is not affected by CRC resets generated by the RESET bit in the CRC_CR register

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12.5.3

RM0091

Control register (CRC_CR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

REV_
OUT

Res.

Res.

RESET

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rw

REV_IN[1:0]
rw

rw

POLYSIZE[1:0]
rw

rw

rs

Bits 31:8 Reserved, must be kept cleared.
Bit 7 REV_OUT: Reverse output data
This bit controls the reversal of the bit order of the output data.
0: Bit order not affected
1: Bit-reversed output format
Bits 6:5 REV_IN[1:0]: Reverse input data
These bits control the reversal of the bit order of the input data
00: Bit order not affected
01: Bit reversal done by byte
10: Bit reversal done by half-word
11: Bit reversal done by word
Bits 4:3 Reserved, must be kept cleared (for STM32F03x, STM32F04x, and STM32F05x)
POLYSIZE[1:0]: Polynomial size (for STM32F07x and STM32F09x)
These bits control the size of the polynomial.
00: 32 bit polynomial
01: 16 bit polynomial
10: 8 bit polynomial
11: 7 bit polynomial
Bits 2:1 Reserved, must be kept cleared.
Bit 0 RESET: RESET bit
This bit is set by software to reset the CRC calculation unit and set the data register to the value
stored in the CRC_INIT register. This bit can only be set, it is automatically cleared by hardware

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12.5.4

Cyclic redundancy check calculation unit (CRC)

Initial CRC value (CRC_INIT)
Address offset: 0x10
Reset value: 0xFFFF FFFF

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

6

5

4

3

2

1

0

22

21

20

19

18

17

16

6

5

4

3

2

1

0

CRC_INIT[31:16]
rw
15

14

13

12

11

10

9

8

7

CRC_INIT[15:0]
rw

Bits 31:0 CRC_INIT: Programmable initial CRC value
This register is used to write the CRC initial value.

12.5.5

CRC polynomial (CRC_POL)
Address offset: 0x14
Reset value: 0x04C11DB7

31

30

29

28

27

26

25

24

23

POL[31:16]
r / rw
15

14

13

12

11

10

9

8

7
POL[15:0]
r / rw

Bits 31:0 POL[31:0]: Programmable polynomial (for STM32F07x and STM32F09x)
This register is used to write the coefficients of the polynomial to be used for CRC calculation.
If the polynomial size is less than 32 bits, the least significant bits have to be used to program the
correct value.
For STM32F03x, STM32F04x, and STM32F05x, the field is read-only.

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12.5.6

RM0091

CRC register map

Offset

Register

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 40. CRC register map and reset values

CRC_DR

DR[31:0]
1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

CRC_IDR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CRC_CR

0

Res.

0x08

Reset value

0x10

CRC_INIT
Reset value

0x14

1

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

1

1

1

1

1

0

CRC_INIT[31:0]
1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

CRC_POL

POL[31:0]

Reset value

0x04C11DB7

1

1

1

1

1

1

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

226/1004

1

IDR[7:0]

REV_OUT

0x04

1

Res.

1

RESET

1

Res.

1

POLYSIZE[1:0]

1

REV_IN[1:0]

Reset value

Res.

0x00

DocID018940 Rev 9

1

1

1

RM0091

Analog-to-digital converter (ADC)

13

Analog-to-digital converter (ADC)

13.1

Introduction
The 12-bit ADC is a successive approximation analog-to-digital converter. It has up to 19
multiplexed channels allowing it to measure signals from 16 external and 3 internal sources.
A/D conversion of the various channels can be performed in single, continuous, scan or
discontinuous mode. The result of the ADC is stored in a left-aligned or right-aligned 16-bit
data register.
The analog watchdog feature allows the application to detect if the input voltage goes
outside the user-defined higher or lower thresholds.
An efficient low-power mode is implemented to allow very low consumption at low
frequency.

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Analog-to-digital converter (ADC)

13.2

RM0091

ADC main features
•

•

•

•

•

High performance
–

12-bit, 10-bit, 8-bit or 6-bit configurable resolution

–

ADC conversion time: 1.0 µs for 12-bit resolution (1 MHz), 0.93 µs conversion
time for 10-bit resolution, faster conversion times can be obtained by lowering
resolution.

–

Self-calibration

–

Programmable sampling time

–

Data alignment with built-in data coherency

–

DMA support

Low-power
–

Application can reduce PCLK frequency for low-power operation while still
keeping optimum ADC performance. For example, 1.0 µs conversion time is kept,
whatever the frequency of PCLK)

–

Wait mode: prevents ADC overrun in applications with low frequency PCLK

–

Auto off mode: ADC is automatically powered off except during the active
conversion phase. This dramatically reduces the power consumption of the ADC.

Analog input channels
–

16 external analog inputs

–

1 channel for internal temperature sensor (VSENSE)

–

1 channel for internal reference voltage (VREFINT)

–

1 channel for monitoring external VBAT power supply pin.

Start-of-conversion can be initiated:
–

By software

–

By hardware triggers with configurable polarity (internal timer events from TIM1,
TIM2, TIM3 and TIM15)

Conversion modes
–

Can convert a single channel or can scan a sequence of channels.

–

Single mode converts selected inputs once per trigger

–

Continuous mode converts selected inputs continuously

–

Discontinuous mode

•

Interrupt generation at the end of sampling, end of conversion, end of sequence
conversion, and in case of analog watchdog or overrun events

•

Analog watchdog

•

ADC supply requirements: 2.4 V to 3.6 V

•

ADC input range: VSSA ≤ VIN ≤ VDDA

Figure 26 shows the block diagram of the ADC.

228/1004

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RM0091

13.3

Analog-to-digital converter (ADC)

ADC pins and internal signals
Table 41. ADC internal signals
Internal signal
name

Signal type

TRGx

Input

ADC conversion triggers

VSENSE

Input

Internal temperature sensor output voltage

VREFINT

Input

Internal voltage reference output voltage

VBAT/2

Input

VBAT pin input voltage divided by 2

Description

Table 42. ADC pins
Name

Signal type

Remarks

VDDA

Input, analog power
supply

Analog power supply and positive reference voltage
for the ADC, VDDA ≥ VDD

VSSA

Input, analog supply
ground

Ground for analog power supply. Must be at VSS
potential

ADC_IN[15:0]

Analog input signals

16 analog input channels

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267

Analog-to-digital converter (ADC)

13.4

RM0091

ADC functional description
Figure 26 shows the ADC block diagram and Table 42 gives the ADC pin description.
Figure 26. ADC block diagram
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13.4.1

Calibration (ADCAL)
The ADC has a calibration feature. During the procedure, the ADC calculates a calibration
factor which is internally applied to the ADC until the next ADC power-off. The application
must not use the ADC during calibration and must wait until it is complete.
Calibration should be performed before starting A/D conversion. It removes the offset error
which may vary from chip to chip due to process variation.
The calibration is initiated by software by setting bit ADCAL=1. Calibration can only be
initiated when the ADC is disabled (when ADEN=0). ADCAL bit stays at 1 during all the
calibration sequence. It is then cleared by hardware as soon the calibration completes. After
this, the calibration factor can be read from the ADC_DR register (from bits 6 to 0).
The internal analog calibration is kept if the ADC is disabled (ADEN=0). When the ADC
operating conditions change (VDDA changes are the main contributor to ADC offset
variations and temperature change to a lesser extend), it is recommended to re-run a
calibration cycle.

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Analog-to-digital converter (ADC)
The calibration factor is lost each time power is removed from the ADC (for example when
the product enters STANDBY mode).
Calibration software procedure
1.

Ensure that ADEN=0 and DMAEN=0

2.

Set ADCAL=1

3.

Wait until ADCAL=0

4.

The calibration factor can be read from bits 6:0 of ADC_DR.

For code example refer to the Appendix section A.7.1: ADC Calibration code example.
Figure 27. ADC calibration
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13.4.2

ADC on-off control (ADEN, ADDIS, ADRDY)
At MCU power-up, the ADC is disabled and put in power-down mode (ADEN=0).
As shown in Figure 28, the ADC needs a stabilization time of tSTAB before it starts
converting accurately.
Two control bits are used to enable or disable the ADC:
•

Set ADEN=1 to enable the ADC. The ADRDY flag is set as soon as the ADC is ready
for operation.

•

Set ADDIS=1 to disable the ADC and put the ADC in power down mode. The ADEN
and ADDIS bits are then automatically cleared by hardware as soon as the ADC is fully
disabled.

Conversion can then start either by setting ADSTART=1 (refer to Section 13.5: Conversion
on external trigger and trigger polarity (EXTSEL, EXTEN) on page 238) or when an external
trigger event occurs if triggers are enabled.
Follow this procedure to enable the ADC:
1.

Clear the ADRDY bit in ADC_ISR register by programming this bit to 1.

2.

Set ADEN=1 in the ADC_CR register.

3.

Wait until ADRDY=1 in the ADC_ISR register and continue to write ADEN=1 (ADRDY
is set after the ADC startup time). This can be handled by interrupt if the interrupt is
enabled by setting the ADRDYIE bit in the ADC_IER register.

For code example refer to the Appendix section A.7.2: ADC enable sequence code
example.

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Follow this procedure to disable the ADC:
1.

Check that ADSTART=0 in the ADC_CR register to ensure that no conversion is
ongoing. If required, stop any ongoing conversion by writing 1 to the ADSTP bit in the
ADC_CR register and waiting until this bit is read at 0.

2.

Set ADDIS=1 in the ADC_CR register.

3.

If required by the application, wait until ADEN=0 in the ADC_CR register, indicating that
the ADC is fully disabled (ADDIS is automatically reset once ADEN=0).

4.

Clear the ADRDY bit in ADC_ISR register by programming this bit to 1 (optional).

For code example refer to the Appendix section A.7.3: ADC disable sequence code
example.
Caution:

ADEN bit cannot be set when ADCAL=1 and during four ADC clock cycles after the ADCAL
bit is cleared by hardware (end of calibration).
Figure 28. Enabling/disabling the ADC
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In auto-off mode (AUTOFF=1) the power-on/off phases are performed automatically, by
hardware and the ADRDY flag is not set.

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13.4.3

Analog-to-digital converter (ADC)

ADC clock (CKMODE)
The ADC has a dual clock-domain architecture, so that the ADC can be fed with a clock
(ADC asynchronous clock) independent from the APB clock (PCLK).
Figure 29. ADC clock scheme
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1. Refer to Section 6: Reset and clock control (RCC) on page 93 to see how PCLK and ADC asynchronous
clock are enabled.

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The input clock of the analog ADC can be selected between two different clock sources (see
Figure 29: ADC clock scheme to see how PCLK and the ADC asynchronous clock are
enabled):
a)

The ADC clock can be a specific clock source, named “ADC asynchronous clock“
which is independent and asynchronous with the APB clock.
Refer to RCC Section for more information on generating this clock source.
To select this scheme, bits CKMODE[1:0] of the ADC_CFGR2 register must be
reset.
For code example refer to the Appendix section A.7.4: ADC Clock selection code
example.

b)

The ADC clock can be derived from the APB clock of the ADC bus interface,
divided by a programmable factor (2 or 4) according to bits CKMODE[1:0].
To select this scheme, bits CKMODE[1:0] of the ADC_CFGR2 register must be
different from “00”.

Option a) has the advantage of reaching the maximum ADC clock frequency whatever the
APB clock scheme selected.
Option b) has the advantage of bypassing the clock domain resynchronizations. This can be
useful when the ADC is triggered by a timer and if the application requires that the ADC is
precisely triggered without any uncertainty (otherwise, an uncertainty of the trigger instant is
added by the resynchronizations between the two clock domains).
Table 43. Latency between trigger and start of conversion
ADC clock source

13.4.4

CKMODE[1:0]

Latency between the trigger event
and the start of conversion

Dedicated 14MHz clock

00

Latency is not deterministic (jitter)

PCLK divided by 2

01

Latency is deterministic (no jitter) and equal to
2.75 ADC clock cycles

PCLK divided by 4

10

Latency is deterministic (no jitter) and equal to
2.625 ADC clock cycles

Configuring the ADC
Software must write to the ADCAL and ADEN bits in the ADC_CR register if the ADC is
disabled (ADEN must be 0).
Software must only write to the ADSTART and ADDIS bits in the ADC_CR register only if
the ADC is enabled and there is no pending request to disable the ADC (ADEN = 1 and
ADDIS = 0).
For all the other control bits in the ADC_IER, ADC_CFGRi, ADC_SMPR, ADC_TR,
ADC_CHSELR and ADC_CCR registers, software must only write to the configuration
control bits if the ADC is enabled (ADEN = 1) and if there is no conversion ongoing
(ADSTART = 0).
Software must only write to the ADSTP bit in the ADC_CR register if the ADC is enabled
(and possibly converting) and there is no pending request to disable the ADC (ADSTART =
1 and ADDIS = 0)

Note:

234/1004

There is no hardware protection preventing software from making write operations forbidden
by the above rules. If such a forbidden write access occurs, the ADC may enter an

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Analog-to-digital converter (ADC)
undefined state. To recover correct operation in this case, the ADC must be disabled (clear
ADEN=0 and all the bits in the ADC_CR register).

13.4.5

Channel selection (CHSEL, SCANDIR)
There are up to 19 multiplexed channels:
•

16 analog inputs from GPIO pins (ADC_IN0...ADC_IN15)

•

3 internal analog inputs (Temperature Sensor, Internal Reference Voltage, VBAT
channel)

It is possible to convert a single channel or to automatically scan a sequence of channels.
The sequence of the channels to be converted must be programmed in the ADC_CHSELR
channel selection register: each analog input channel has a dedicated selection bit
(CHSEL0...CHSEL18).
The order in which the channels will be scanned can be configured by programming the bit
SCANDIR bit in the ADC_CFGR1 register:
•

SCANDIR=0: forward scan Channel 0 to Channel 18

•

SCANDIR=1: backward scan Channel 18 to Channel 0

Temperature sensor, VREFINT and VBAT internal channels
The temperature sensor is connected to channel ADC_IN16. The internal voltage reference
VREFINT is connected to channel ADC_IN17. The VBAT channel is connected to channel
ADC_IN18.

13.4.6

Programmable sampling time (SMP)
Before starting a conversion, the ADC needs to establish a direct connection between the
voltage source to be measured and the embedded sampling capacitor of the ADC. This
sampling time must be enough for the input voltage source to charge the sample and hold
capacitor to the input voltage level.
Having a programmable sampling time allows to trim the conversion speed according to the
input resistance of the input voltage source.
The ADC samples the input voltage for a number of ADC clock cycles that can be modified
using the SMP[2:0] bits in the ADC_SMPR register.
This programmable sampling time is common to all channels. If required by the application,
the software can change and adapt this sampling time between each conversions.
The total conversion time is calculated as follows:
tCONV = Sampling time + 12.5 x ADC clock cycles
Example:
With ADC_CLK = 14 MHz and a sampling time of 1.5 ADC clock cycles:
tCONV = 1.5 + 12.5 = 14 ADC clock cycles = 1 µs
The ADC indicates the end of the sampling phase by setting the EOSMP flag.

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13.4.7

RM0091

Single conversion mode (CONT=0)
In Single conversion mode, the ADC performs a single sequence of conversions, converting
all the channels once. This mode is selected when CONT=0 in the ADC_CFGR1 register.
Conversion is started by either:
•

Setting the ADSTART bit in the ADC_CR register

•

Hardware trigger event

Inside the sequence, after each conversion is complete:
•

The converted data are stored in the 16-bit ADC_DR register

•

The EOC (end of conversion) flag is set

•

An interrupt is generated if the EOCIE bit is set

After the sequence of conversions is complete:
•

The EOSEQ (end of sequence) flag is set

•

An interrupt is generated if the EOSEQIE bit is set

Then the ADC stops until a new external trigger event occurs or the ADSTART bit is set
again.
Note:

To convert a single channel, program a sequence with a length of 1.

13.4.8

Continuous conversion mode (CONT=1)
In continuous conversion mode, when a software or hardware trigger event occurs, the ADC
performs a sequence of conversions, converting all the channels once and then
automatically re-starts and continuously performs the same sequence of conversions. This
mode is selected when CONT=1 in the ADC_CFGR1 register. Conversion is started by
either:
•

Setting the ADSTART bit in the ADC_CR register

•

Hardware trigger event

Inside the sequence, after each conversion is complete:
•

The converted data are stored in the 16-bit ADC_DR register

•

The EOC (end of conversion) flag is set

•

An interrupt is generated if the EOCIE bit is set

After the sequence of conversions is complete:
•

The EOSEQ (end of sequence) flag is set

•

An interrupt is generated if the EOSEQIE bit is set

Then, a new sequence restarts immediately and the ADC continuously repeats the
conversion sequence.
Note:

To convert a single channel, program a sequence with a length of 1.
It is not possible to have both discontinuous mode and continuous mode enabled: it is
forbidden to set both bits DISCEN=1 and CONT=1.

13.4.9

Starting conversions (ADSTART)
Software starts ADC conversions by setting ADSTART=1.

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When ADSTART is set, the conversion:
•

Starts immediately if EXTEN = 00 (software trigger)

•

At the next active edge of the selected hardware trigger if EXTEN ≠ 00

The ADSTART bit is also used to indicate whether an ADC operation is currently ongoing. It
is possible to re-configure the ADC while ADSTART=0, indicating that the ADC is idle.
The ADSTART bit is cleared by hardware:
•

In single mode with software trigger (CONT=0, EXTEN=00)
–

•

At any end of conversion sequence (EOSEQ=1)

In discontinuous mode with software trigger (CONT=0, DISCEN=1, EXTEN=00)
–

•

At end of conversion (EOC=1)

In all cases (CONT=x, EXTEN=XX)
–

Note:

After execution of the ADSTP procedure invoked by software (see
Section 13.4.11: Stopping an ongoing conversion (ADSTP) on page 238)

In continuous mode (CONT=1), the ADSTART bit is not cleared by hardware when the
EOSEQ flag is set because the sequence is automatically relaunched.
When hardware trigger is selected in single mode (CONT=0 and EXTEN = 01), ADSTART is
not cleared by hardware when the EOSEQ flag is set. This avoids the need for software
having to set the ADSTART bit again and ensures the next trigger event is not missed.

13.4.10

Timings
The elapsed time between the start of a conversion and the end of conversion is the sum of
the configured sampling time plus the successive approximation time depending on data
resolution:
tADC = tSMPL + tSAR = [1.5 |min + 12.5 |12bit] x tADC_CLK
tADC = tSMPL + tSAR = 107.1 ns |min + 892.8 ns |12bit = 1 µs |min (for fADC_CLK = 14 MHz)

Figure 30. Analog to digital conversion time
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RM0091
Figure 31. ADC conversion timings

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2. Trigger latency (refer to datasheet for more details)
3. ADC_DR register write latency (refer to datasheet for more details)

13.4.11

Stopping an ongoing conversion (ADSTP)
The software can decide to stop any ongoing conversions by setting ADSTP=1 in the
ADC_CR register.
This will reset the ADC operation and the ADC will be idle, ready for a new operation.
When the ADSTP bit is set by software, any ongoing conversion is aborted and the result is
discarded (ADC_DR register is not updated with the current conversion).
The scan sequence is also aborted and reset (meaning that restarting the ADC would restart a new sequence).
Once this procedure is complete, the ADSTP and ADSTART bits are both cleared by
hardware and the software must wait until ADSTART=0 before starting new conversions.
Figure 32. Stopping an ongoing conversion
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13.5

Conversion on external trigger and trigger polarity (EXTSEL,
EXTEN)
A conversion or a sequence of conversion can be triggered either by software or by an
external event (for example timer capture). If the EXTEN[1:0] control bits are not equal to
“0b00”, then external events are able to trigger a conversion with the selected polarity. The
trigger selection is effective once software has set bit ADSTART=1.
Any hardware triggers which occur while a conversion is ongoing are ignored.

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Analog-to-digital converter (ADC)
If bit ADSTART=0, any hardware triggers which occur are ignored.
Table 44 provides the correspondence between the EXTEN[1:0] values and the trigger
polarity.
Table 44. Configuring the trigger polarity
Source

Note:

EXTEN[1:0]

Trigger detection disabled

00

Detection on rising edge

01

Detection on falling edge

10

Detection on both rising and falling edges

11

The polarity of the external trigger can be changed only when the ADC is not converting
(ADSTART= 0).
The EXTSEL[2:0] control bits are used to select which of 8 possible events can trigger
conversions.
Table 45 gives the possible external trigger for regular conversion.
Software source trigger events can be generated by setting the ADSTART bit in the
ADC_CR register.
Table 45. External triggers
Name

Source

EXTSEL[2:0]

TRG0

TIM1_TRGO

000

TRG1

TIM1_CC4

001

TRG2

TIM2_TRGO

010

TRG3

TIM3_TRGO

011

TRG4

TIM15_TRGO

100

TRG5

Reserved

101

TRG6

Reserved

110

TRG7

Reserved

111

Note:

The trigger selection can be changed only when the ADC is not converting (ADSTART= 0).

13.5.1

Discontinuous mode (DISCEN)
This mode is enabled by setting the DISCEN bit in the ADC_CFGR1 register.
In this mode (DISCEN=1), a hardware or software trigger event is required to start each
conversion defined in the sequence. On the contrary, if DISCEN=0, a single hardware or
software trigger event successively starts all the conversions defined in the sequence.

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Example:
•

•

DISCEN=1, channels to be converted = 0, 3, 7, 10
–

1st trigger: channel 0 is converted and an EOC event is generated

–

2nd trigger: channel 3 is converted and an EOC event is generated

–

3rd trigger: channel 7 is converted and an EOC event is generated

–

4th trigger: channel 10 is converted and both EOC and EOSEQ events are
generated.

–

5th trigger: channel 0 is converted an EOC event is generated

–

6th trigger: channel 3 is converted and an EOC event is generated

–

...

DISCEN=0, channels to be converted = 0, 3, 7, 10
–

1st trigger: the complete sequence is converted: channel 0, then 3, 7 and 10. Each
conversion generates an EOC event and the last one also generates an EOSEQ
event.

–

Any subsequent trigger events will restart the complete sequence.

Note:

It is not possible to have both discontinuous mode and continuous mode enabled: it is
forbidden to set both bits DISCEN=1 and CONT=1.

13.5.2

Programmable resolution (RES) - fast conversion mode
It is possible to obtain faster conversion times (tSAR) by reducing the ADC resolution.
The resolution can be configured to be either 12, 10, 8, or 6 bits by programming the
RES[1:0] bits in the ADC_CFGR1 register. Lower resolution allows faster conversion times
for applications where high data precision is not required.

Note:

The RES[1:0] bit must only be changed when the ADEN bit is reset.
The result of the conversion is always 12 bits wide and any unused LSB bits are read as
zeros.
Lower resolution reduces the conversion time needed for the successive approximation
steps as shown in Table 46.
Table 46. tSAR timings depending on resolution
RES[1:0]
bits

240/1004

tSAR
(ADC clock
cycles)

tSAR (ns) at
fADC = 14 MHz

tSMPL (min)

tCONV

(ADC clock
cycles)

(ADC clock cycles)
(with min. tSMPL)

tCONV at fADC =
14 MHz

12

12.5

893 ns

1.5

14

1000 ns

10

11.5

821 ns

1.5

13

928 ns

8

9.5

678 ns

1.5

11

785 ns

6

7.5

535 ns

1.5

9

643 ns

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13.5.3

Analog-to-digital converter (ADC)

End of conversion, end of sampling phase (EOC, EOSMP flags)
The ADC indicates each end of conversion (EOC) event.
The ADC sets the EOC flag in the ADC_ISR register as soon as a new conversion data
result is available in the ADC_DR register. An interrupt can be generated if the EOCIE bit is
set in the ADC_IER register. The EOC flag is cleared by software either by writing 1 to it, or
by reading the ADC_DR register.
The ADC also indicates the end of sampling phase by setting the EOSMP flag in the
ADC_ISR register. The EOSMP flag is cleared by software by writing1 to it. An interrupt can
be generated if the EOSMPIE bit is set in the ADC_IER register.
The aim of this interrupt is to allow the processing to be synchronized with the conversions.
Typically, an analog multiplexer can be accessed in hidden time during the conversion
phase, so that the multiplexer is positioned when the next sampling starts.

Note:

As there is only a very short time left between the end of the sampling and the end of the
conversion, it is recommenced to use polling or a WFE instruction rather than an interrupt
and a WFI instruction.

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13.5.4

RM0091

End of conversion sequence (EOSEQ flag)
The ADC notifies the application of each end of sequence (EOSEQ) event.
The ADC sets the EOSEQ flag in the ADC_ISR register as soon as the last data result of a
conversion sequence is available in the ADC_DR register. An interrupt can be generated if
the EOSEQIE bit is set in the ADC_IER register. The EOSEQ flag is cleared by software by
writing 1 to it.

13.5.5

Example timing diagrams (single/continuous modes
hardware/software triggers)
Figure 33. Single conversions of a sequence, software trigger


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2. CHSEL=0x20601, WAIT=0, AUTOFF=0

For code example refer to the Appendix section A.7.5: Single conversion sequence code
example - Software trigger.
Figure 34. Continuous conversion of a sequence, software trigger
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2. CHSEL=0x20601, WAIT=0, AUTOFF=0

For code example refer to the Appendix section A.7.6: Continuous conversion sequence
code example - Software trigger.

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Analog-to-digital converter (ADC)
Figure 35. Single conversions of a sequence, hardware trigger

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1. EXTSEL=TRGx (over-frequency), EXTEN=01 (rising edge), CONT=0
2. CHSEL=0xF, SCANDIR=0, WAIT=0, AUTOFF=0

For code example refer to the Appendix section A.7.7: Single conversion sequence code
example - Hardware trigger.
Figure 36. Continuous conversions of a sequence, hardware trigger
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2. CHSEL=0xF, SCANDIR=0, WAIT=0, AUTOFF=0

For code example refer to the Appendix section A.7.8: Continuous conversion sequence
code example - Hardware trigger.

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13.6

Data management

13.6.1

Data register and data alignment (ADC_DR, ALIGN)
At the end of each conversion (when an EOC event occurs), the result of the converted data
is stored in the ADC_DR data register which is 16-bit wide.
The format of the ADC_DR depends on the configured data alignment and resolution.
The ALIGN bit in the ADC_CFGR1 register selects the alignment of the data stored after
conversion. Data can be right-aligned (ALIGN=0) or left-aligned (ALIGN=1) as shown in
Figure 37.
Figure 37. Data alignment and resolution


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13.6.2

ADC overrun (OVR, OVRMOD)
The overrun flag (OVR) indicates a data overrun event, when the converted data was not
read in time by the CPU or the DMA, before the data from a new conversion is available.
The OVR flag is set in the ADC_ISR register if the EOC flag is still at ‘1’ at the time when a
new conversion completes. An interrupt can be generated if the OVRIE bit is set in the
ADC_IER register.
When an overrun condition occurs, the ADC keeps operating and can continue to convert
unless the software decides to stop and reset the sequence by setting the ADSTP bit in the
ADC_CR register.
The OVR flag is cleared by software by writing 1 to it.
It is possible to configure if the data is preserved or overwritten when an overrun event
occurs by programming the OVRMOD bit in the ADC_CFGR1 register:
•

OVRMOD=0
–

•

OVRMOD=1
–

244/1004

An overrun event preserves the data register from being overwritten: the old data
is maintained and the new conversion is discarded. If OVR remains at 1, further
conversions can be performed but the resulting data is discarded.
The data register is overwritten with the last conversion result and the previous
unread data is lost. If OVR remains at 1, further conversions can be performed
and the ADC_DR register always contains the data from the latest conversion.

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Analog-to-digital converter (ADC)
Figure 38. Example of overrun (OVR)

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13.6.3

Managing a sequence of data converted without using the DMA
If the conversions are slow enough, the conversion sequence can be handled by software.
In this case the software must use the EOC flag and its associated interrupt to handle each
data result. Each time a conversion is complete, the EOC bit is set in the ADC_ISR register
and the ADC_DR register can be read. The OVRMOD bit in the ADC_CFGR1 register
should be configured to 0 to manage overrun events as an error.

13.6.4

Managing converted data without using the DMA without overrun
It may be useful to let the ADC convert one or more channels without reading the data after
each conversion. In this case, the OVRMOD bit must be configured at 1 and the OVR flag
should be ignored by the software. When OVRMOD=1, an overrun event does not prevent
the ADC from continuing to convert and the ADC_DR register always contains the latest
conversion data.

13.6.5

Managing converted data using the DMA
Since all converted channel values are stored in a single data register, it is efficient to use
DMA when converting more than one channel. This avoids losing the conversion data
results stored in the ADC_DR register.
When DMA mode is enabled (DMAEN bit set to 1 in the ADC_CFGR1 register), a DMA
request is generated after the conversion of each channel. This allows the transfer of the
converted data from the ADC_DR register to the destination location selected by the
software.

Note:

The DMAEN bit in the ADC_CFGR1 register must be set after the ADC calibration phase.

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Despite this, if an overrun occurs (OVR=1) because the DMA could not serve the DMA
transfer request in time, the ADC stops generating DMA requests and the data
corresponding to the new conversion is not transferred by the DMA. Which means that all
the data transferred to the RAM can be considered as valid.
Depending on the configuration of OVRMOD bit, the data is either preserved or overwritten
(refer to Section 13.6.2: ADC overrun (OVR, OVRMOD) on page 244).
The DMA transfer requests are blocked until the software clears the OVR bit.
Two different DMA modes are proposed depending on the application use and are
configured with bit DMACFG in the ADC_CFGR1 register:
•

DMA one shot mode (DMACFG=0).
This mode should be selected when the DMA is programmed to transfer a fixed
number of data words.

•

DMA circular mode (DMACFG=1)
This mode should be selected when programming the DMA in circular mode or double
buffer mode.

DMA one shot mode (DMACFG=0)
In this mode, the ADC generates a DMA transfer request each time a new conversion data
word is available and stops generating DMA requests once the DMA has reached the last
DMA transfer (when a DMA_EOT interrupt occurs, see Section 10: Direct memory access
controller (DMA) on page 188) even if a conversion has been started again.
For code example refer to the Appendix section A.7.9: DMA one shot mode sequence code
example.
When the DMA transfer is complete (all the transfers configured in the DMA controller have
been done):
•

The content of the ADC data register is frozen.

•

Any ongoing conversion is aborted and its partial result discarded

•

No new DMA request is issued to the DMA controller. This avoids generating an
overrun error if there are still conversions which are started.

•

The scan sequence is stopped and reset

•

The DMA is stopped

DMA circular mode (DMACFG=1)
In this mode, the ADC generates a DMA transfer request each time a new conversion data
word is available in the data register, even if the DMA has reached the last DMA transfer.
This allows the DMA to be configured in circular mode to handle a continuous analog input
data stream.
For code example refer to the Appendix section A.7.10: DMA circular mode sequence code
example.

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Analog-to-digital converter (ADC)

13.7

Low-power features

13.7.1

Wait mode conversion
Wait mode conversion can be used to simplify the software as well as optimizing the
performance of applications clocked at low frequency where there might be a risk of ADC
overrun occurring.
When the WAIT bit is set to 1 in the ADC_CFGR1 register, a new conversion can start only
if the previous data has been treated, once the ADC_DR register has been read or if the
EOC bit has been cleared.
This is a way to automatically adapt the speed of the ADC to the speed of the system that
reads the data.

Note:

Any hardware triggers which occur while a conversion is ongoing or during the wait time
preceding the read access are ignored.
Figure 39. Wait mode conversion (continuous mode, software trigger)
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1. EXTEN=00, CONT=1
2. CHSEL=0x3, SCANDIR=0, WAIT=1, AUTOFF=0

For code example refer to the Appendix section A.7.11: Wait mode sequence code
example.

13.7.2

Auto-off mode (AUTOFF)
The ADC has an automatic power management feature which is called auto-off mode, and
is enabled by setting AUTOFF=1 in the ADC_CFGR1 register.
When AUTOFF=1, the ADC is always powered off when not converting and automatically
wakes-up when a conversion is started (by software or hardware trigger). A startup-time is
automatically inserted between the trigger event which starts the conversion and the
sampling time of the ADC. The ADC is then automatically disabled once the sequence of
conversions is complete.
Auto-off mode can cause a dramatic reduction in the power consumption of applications
which need relatively few conversions or when conversion requests are timed far enough
apart (for example with a low frequency hardware trigger) to justify the extra power and
extra time used for switching the ADC on and off.

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Auto-off mode can be combined with the wait mode conversion (WAIT=1) for applications
clocked at low frequency. This combination can provide significant power savings if the ADC
is automatically powered-off during the wait phase and restarted as soon as the ADC_DR
register is read by the application (see Figure 41: Behavior with WAIT=1, AUTOFF=1).
Note:

Please refer to the Section 6: Reset and clock control (RCC) on page 93 for the description
of how to manage the dedicated 14 MHz internal oscillator. The ADC interface can
automatically switch ON/OFF the 14 MHz internal oscillator to save power.
Figure 40. Behavior with WAIT=0, AUTOFF=1

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1. EXTSEL=TRGx, EXTEN=01 (rising edge), CONT=x, ADSTART=1, CHSEL=0xF, SCANDIR=0, WAIT=1, AUTOFF=1

For code example refer to the Appendix section A.7.12: Auto Off and no wait mode
sequence code example.
Figure 41. Behavior with WAIT=1, AUTOFF=1
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1. EXTSEL=TRGx, EXTEN=01 (rising edge), CONT=x, ADSTART=1, CHSEL=0xF, SCANDIR=0, WAIT=1, AUTOFF=1

For code example refer to the Appendix section A.7.13: Auto Off and wait mode sequence
code example.

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13.8

Analog-to-digital converter (ADC)

Analog window watchdog (AWDEN, AWDSGL, AWDCH,
AWD_HTR/LTR, AWD)
The AWD analog watchdog feature is enabled by setting the AWDEN bit in the
ADC_CFGR1 register. It is used to monitor that either one selected channel or all enabled
channels (see Table 48: Analog watchdog channel selection) remain within a configured
voltage range (window) as shown in Figure 42.
The AWD analog watchdog status bit is set if the analog voltage converted by the ADC is
below a lower threshold or above a higher threshold. These thresholds are programmed in
the 12 least significant bits of the ADC_HTR and ADC_LTR 16-bit registers. An interrupt can
be enabled by setting the AWDIE bit in the ADC_IER register.
The AWD flag is cleared by software by writing 1 to it.
When converting a data with a resolution of less than 12-bit (according to bits DRES[1:0]),
the LSB of the programmed thresholds must be kept cleared because the internal
comparison is always performed on the full 12-bit raw converted data (left aligned).
For code example refer to the Appendix section A.7.14: Analog watchdog code example.
Table 47 describes how the comparison is performed for all the possible resolutions.
Table 47. Analog watchdog comparison

Resolution
bits
RES[1:0]

Analog Watchdog comparison between:
Comments

Raw converted
data, left aligned(1)

Thresholds

00: 12-bit

DATA[11:0]

LT[11:0] and HT[11:0]

-

01: 10-bit

DATA[11:2],00

LT[11:0] and HT[11:0]

The user must configure LT1[1:0] and HT1[1:0] to “00”

10: 8-bit

DATA[11:4],0000

LT[11:0] and HT[11:0]

The user must configure LT1[3:0] and HT1[3:0] to
“0000”

11: 6-bit

DATA[11:6],000000

LT[11:0] and HT[11:0]

The user must configure LT1[5:0] and HT1[5:0] to
“000000”

1. The watchdog comparison is performed on the raw converted data before any alignment calculation.

Table 48 shows how to configure the AWDSGL and AWDEN bits in the ADC_CFGR1
register to enable the analog watchdog on one or more channels.
Figure 42. Analog watchdog guarded area

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Table 48. Analog watchdog channel selection

Channels guarded by the analog watchdog
None
All channels
(1)

Single

channel

AWDSGL bit

AWDEN bit

x

0

0

1

1

1

1. Selected by the AWDCH[4:0] bits

13.9

Temperature sensor and internal reference voltage
The temperature sensor can be used to measure the junction temperature (TJ) of the
device. The temperature sensor is internally connected to the ADC_IN16 input channel
which is used to convert the sensor’s output voltage to a digital value. The sampling time for
the temperature sensor analog pin must be greater than the minimum TS_temp value
specified in the datasheet. When not in use, the sensor can be put in power down mode.
The temperature sensor output voltage changes linearly with temperature, however its
characteristics may vary significantly from chip to chip due to the process variations. To
improve the accuracy of the temperature sensor (especially for absolute temperature
measurement), calibration values are individually measured for each part by ST during
production test and stored in the system memory area. Refer to the specific device
datasheet for additional information.
The internal voltage reference (VREFINT) provides a stable (bandgap) voltage output for the
ADC and Comparators. VREFINT is internally connected to the ADC_IN17 input channel. The
precise voltage of VREFINT is individually measured for each part by ST during production
test and stored in the system memory area.
Figure 43 shows the block diagram of connections between the temperature sensor, the
internal voltage reference and the ADC.
The TSEN bit must be set to enable the conversion of ADC_IN16 (temperature sensor) and
the VREFEN bit must be set to enable the conversion of ADC_IN17 (VREFINT).

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Figure 43. Temperature sensor and VREFINT channel block diagram
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Reading the temperature
1.

Select the ADC_IN16 input channel

2.

Select an appropriate sampling time specified in the device datasheet (TS_temp).

3.

Set the TSEN bit in the ADC_CCR register to wake up the temperature sensor from
power down mode and wait for its stabilization time (tSTART)
For code example refer to the Appendix section A.7.15: Temperature configuration
code example.

4.

Start the ADC conversion by setting the ADSTART bit in the ADC_CR register (or by
external trigger)

5.

Read the resulting data in the ADC_DR register

6.

Calculate the actual temperature using the following formula:
110 °C – 30 °C
Temperature ( in °C ) = ---------------------------------------------------------- × ( TS_DATA – TS_CAL1 ) + 30 °C
TS_CAL2 – TS_CAL1

Where:
•

TS_CAL2 is the temperature sensor calibration value acquired at 110°C

•

TS_CAL1 is the temperature sensor calibration value acquired at 30°C

•

TS_DATA is the actual temperature sensor output value converted by ADC
Refer to the specific device datasheet for more information about TS_CAL1 and
TS_CAL2 calibration points.

For code example refer to the A.7.16: Temperature computation code example.
Note:

The sensor has a startup time after waking from power down mode before it can output
VSENSE at the correct level. The ADC also has a startup time after power-on, so to minimize
the delay, the ADEN and TSEN bits should be set at the same time.

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Calculating the actual VDDA voltage using the internal reference voltage
The VDDA power supply voltage applied to the microcontroller may be subject to variation or
not precisely known. The embedded internal voltage reference (VREFINT) and its
calibration data acquired by the ADC during the manufacturing process at VDDA = .3 V can
be used to evaluate the actual VDDA voltage level.
The following formula gives the actual VDDA voltage supplying the device:
VDDA = .3 V x VREFINT_CAL / VREFINT_DATA
Where:
•

VREFINT_CAL is the VREFINT calibration value

•

VREFINT_DATA is the actual VREFINT output value converted by ADC

Converting a supply-relative ADC measurement to an absolute voltage value
The ADC is designed to deliver a digital value corresponding to the ratio between the analog
power supply and the voltage applied on the converted channel. For most application use
cases, it is necessary to convert this ratio into a voltage independent of VDDA. For
applications where VDDA is known and ADC converted values are right-aligned you can use
the following formula to get this absolute value:
V DDA
V CHANNELx = ------------------------------------- × ADC_DATA x
FULL_SCALE

For applications where VDDA value is not known, you must use the internal voltage
reference and VDDA can be replaced by the expression provided in the section Calculating
the actual VDDA voltage using the internal reference voltage, resulting in the following
formula:
3.3 V × VREFINT_CAL × ADC_DATA x
V CHANNELx = ------------------------------------------------------------------------------------------------------VREFINT_DATA × FULL_SCALE

Where:
•

VREFINT_CAL is the VREFINT calibration value

•

ADC_DATAx is the value measured by the ADC on channel x (right-aligned)

•

VREFINT_DATA is the actual VREFINT output value converted by the ADC

•

full_SCALE is the maximum digital value of the ADC output. For example with 12-bit
resolution, it will be 212 - 1 = 4095 or with 8-bit resolution, 28 - 1 = 255.

Note:

If ADC measurements are done using an output format other than 12 bit right-aligned, all the
parameters must first be converted to a compatible format before the calculation is done.

13.10

Battery voltage monitoring
The VBATEN bit in the ADC_CCR register allows the application to measure the backup
battery voltage on the VBAT pin. As the VBAT voltage could be higher than VDDA, to ensure
the correct operation of the ADC, the VBAT pin is internally connected to a bridge divider by
2. This bridge is automatically enabled when VBATEN is set, to connect VBAT/2 to the
ADC_IN18 input channel. As a consequence, the converted digital value is half the VBAT
voltage. To prevent any unwanted consumption on the battery, it is recommended to enable
the bridge divider only when needed for ADC conversion.

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13.11

Analog-to-digital converter (ADC)

ADC interrupts
An interrupt can be generated by any of the following events:
•

ADC power-up, when the ADC is ready (ADRDY flag)

•

End of any conversion (EOC flag)

•

End of a sequence of conversions (EOSEQ flag)

•

When an analog watchdog detection occurs (AWD flag)

•

When the end of sampling phase occurs (EOSMP flag)

•

when a data overrun occurs (OVR flag)

Separate interrupt enable bits are available for flexibility.
Table 49. ADC interrupts
Interrupt event

Event flag

Enable control bit

ADRDY

ADRDYIE

EOC

EOCIE

End of sequence of conversions

EOSEQ

EOSEQIE

Analog watchdog status bit is set

AWD

AWDIE

EOSMP

EOSMPIE

OVR

OVRIE

ADC ready
End of conversion

End of sampling phase
Overrun

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13.12

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ADC registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

13.12.1

ADC interrupt and status register (ADC_ISR)
Address offset: 0x00
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

AWD

Res.

Res.

OVR

EOSEQ

EOC

rc_w1

rc_w1

rc_w1

rc_w1

EOSMP ADRDY
rc_w1

rc_w1

Bits 31:8 Reserved, must be kept at reset value.
Bit 7 AWD: Analog watchdog flag
This bit is set by hardware when the converted voltage crosses the values programmed in the
ADC_LTR and ADC_HTR registers. It is cleared by software writing 1 to it.
0: No analog watchdog event occurred (or the flag event was already acknowledged and cleared by
software)
1: Analog watchdog event occurred
Bit 6:5 Reserved, must be kept at reset value.
Bit 4 OVR: ADC overrun
This bit is set by hardware when an overrun occurs, meaning that a new conversion has complete
while the EOC flag was already set. It is cleared by software writing 1 to it.
0: No overrun occurred (or the flag event was already acknowledged and cleared by software)
1: Overrun has occurred
Bit 3 EOSEQ: End of sequence flag
This bit is set by hardware at the end of the conversion of a sequence of channels selected by the
CHSEL bits. It is cleared by software writing 1 to it.
0: Conversion sequence not complete (or the flag event was already acknowledged and cleared by
software)
1: Conversion sequence complete

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Bit 2 EOC: End of conversion flag
This bit is set by hardware at the end of each conversion of a channel when a new data result is
available in the ADC_DR register. It is cleared by software writing 1 to it or by reading the ADC_DR
register.
0: Channel conversion not complete (or the flag event was already acknowledged and cleared by
software)
1: Channel conversion complete
Bit 1 EOSMP: End of sampling flag
This bit is set by hardware during the conversion, at the end of the sampling phase.It is cleared by
software by programming it to ‘1’.
0: Not at the end of the sampling phase (or the flag event was already acknowledged and cleared by
software)
1: End of sampling phase reached
Bit 0 ADRDY: ADC ready
This bit is set by hardware after the ADC has been enabled (bit ADEN=1) and when the ADC reaches
a state where it is ready to accept conversion requests.
It is cleared by software writing 1 to it.
0: ADC not yet ready to start conversion (or the flag event was already acknowledged and cleared
by software)
1: ADC is ready to start conversion

Note:

In auto-off mode (AUTOFF=1) the power-on/off phases are performed automatically, by
hardware and the ADRDY flag is not set.

13.12.2

ADC interrupt enable register (ADC_IER)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

AWD
IE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rw

Res.

EOSEQ
EOSMP ADRDY
OVRIE
EOCIE
IE
IE
IE
rw

rw

rw

rw

rw

Bits 31:8 Reserved, must be kept at reset value.
Bit 7 AWDIE: Analog watchdog interrupt enable
This bit is set and cleared by software to enable/disable the analog watchdog interrupt.
0: Analog watchdog interrupt disabled
1: Analog watchdog interrupt enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 6:5 Reserved, must be kept at reset value.

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Bit 4 OVRIE: Overrun interrupt enable
This bit is set and cleared by software to enable/disable the overrun interrupt.
0: Overrun interrupt disabled
1: Overrun interrupt enabled. An interrupt is generated when the OVR bit is set.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 3 EOSEQIE: End of conversion sequence interrupt enable
This bit is set and cleared by software to enable/disable the end of sequence of conversions interrupt.
0: EOSEQ interrupt disabled
1: EOSEQ interrupt enabled. An interrupt is generated when the EOSEQ bit is set.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 2 EOCIE: End of conversion interrupt enable
This bit is set and cleared by software to enable/disable the end of conversion interrupt.
0: EOC interrupt disabled
1: EOC interrupt enabled. An interrupt is generated when the EOC bit is set.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 1 EOSMPIE: End of sampling flag interrupt enable
This bit is set and cleared by software to enable/disable the end of the sampling phase interrupt.
0: EOSMP interrupt disabled.
1: EOSMP interrupt enabled. An interrupt is generated when the EOSMP bit is set.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bits 0 ADRDYIE: ADC ready interrupt enable
This bit is set and cleared by software to enable/disable the ADC Ready interrupt.
0: ADRDY interrupt disabled.
1: ADRDY interrupt enabled. An interrupt is generated when the ADRDY bit is set.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).

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13.12.3

Analog-to-digital converter (ADC)

ADC control register (ADC_CR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

AD
CAL

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

ADSTA
RT

ADDIS

ADEN

rs

rs

rs

rs
15
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

ADSTP
rs

Bit 31 ADCAL: ADC calibration
This bit is set by software to start the calibration of the ADC.
It is cleared by hardware after calibration is complete.
0: Calibration complete
1: Write 1 to calibrate the ADC. Read at 1 means that a calibration is in progress.
Note: Software is allowed to set ADCAL only when the ADC is disabled (ADCAL=0, ADSTART=0,
ADSTP=0, ADDIS=0 and ADEN=0).
Bits 30:5

Reserved, must be kept at reset value.

Bit 4 ADSTP: ADC stop conversion command
This bit is set by software to stop and discard an ongoing conversion (ADSTP Command).
It is cleared by hardware when the conversion is effectively discarded and the ADC is ready to accept
a new start conversion command.
0: No ADC stop conversion command ongoing
1: Write 1 to stop the ADC. Read 1 means that an ADSTP command is in progress.
Note: Setting ADSTP to ‘1’ is only effective when ADSTART=1 and ADDIS=0 (ADC is enabled and
may be converting and there is no pending request to disable the ADC)
Bit 3

Reserved, must be kept at reset value.

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Bit 2 ADSTART: ADC start conversion command
This bit is set by software to start ADC conversion. Depending on the EXTEN [1:0] configuration bits, a
conversion either starts immediately (software trigger configuration) or once a hardware trigger event
occurs (hardware trigger configuration).
It is cleared by hardware:
– In single conversion mode (CONT=0, DISCEN=0), when software trigger is selected (EXTEN=00):
at the assertion of the end of Conversion Sequence (EOSEQ) flag.
– In discontinuous conversion mode(CONT=0, DISCEN=1), when the software trigger is selected
(EXTEN=00): at the assertion of the end of Conversion (EOC) flag.
– In all other cases: after the execution of the ADSTP command, at the same time as the ADSTP bit is
cleared by hardware.
0: No ADC conversion is ongoing.
1: Write 1 to start the ADC. Read 1 means that the ADC is operating and may be converting.
Note: Software is allowed to set ADSTART only when ADEN=1 and ADDIS=0 (ADC is enabled and
there is no pending request to disable the ADC)
Bit 1 ADDIS: ADC disable command
This bit is set by software to disable the ADC (ADDIS command) and put it into power-down state
(OFF state).
It is cleared by hardware once the ADC is effectively disabled (ADEN is also cleared by hardware at
this time).
0: No ADDIS command ongoing
1: Write 1 to disable the ADC. Read 1 means that an ADDIS command is in progress.
Note: Setting ADDIS to ‘1’ is only effective when ADEN=1 and ADSTART=0 (which ensures that no
conversion is ongoing)
Bit 0 ADEN: ADC enable command
This bit is set by software to enable the ADC. The ADC will be effectively ready to operate once the
ADRDY flag has been set.
It is cleared by hardware when the ADC is disabled, after the execution of the ADDIS command.
0: ADC is disabled (OFF state)
1: Write 1 to enable the ADC.
Note: Software is allowed to set ADEN only when all bits of ADC_CR registers are 0 (ADCAL=0,
ADSTP=0, ADSTART=0, ADDIS=0 and ADEN=0)

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Analog-to-digital converter (ADC)

13.12.4

ADC configuration register 1 (ADC_CFGR1)
Address offset: 0x0C
Reset value: 0x0000 0000

31

30

29

Res.

15

28

26

AWDCH[4:0]
rw

rw

rw

rw

rw

14

13

12

11

10

AUTOFF WAIT CONT OVRMOD
rw

27

rw

rw

rw

EXTEN[1:0]

25

24

Res.

Res.

9

8

Res.

23

22

AWDEN AWDSGL
rw

rw

7

6

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

DISCEN

5

4

3

2

1

rw

EXTSEL[2:0]

ALIGN

RES[1:0]

rw

rw

rw

rw

SCAND DMAC
IR
FG
rw

rw

0
DMAEN
rw

Bit 31 Reserved, must be kept at reset value.
Bits 30:26 AWDCH[4:0]: Analog watchdog channel selection
These bits are set and cleared by software. They select the input channel to be guarded by the
analog watchdog.
00000: ADC analog input Channel 0 monitored by AWD
00001: ADC analog input Channel 1 monitored by AWD
.....
10010: ADC analog input Channel 18 monitored by AWD
other values: Reserved, must not be used
Note: The channel selected by the AWDCH[4:0] bits must be also set into the CHSELR
register
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bits 25:24

Reserved, must be kept at reset value.

Bit 23 AWDEN: Analog watchdog enable
This bit is set and cleared by software.
0: Analog watchdog disabled
1: Analog watchdog enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 22 AWDSGL: Enable the watchdog on a single channel or on all channels
This bit is set and cleared by software to enable the analog watchdog on the channel identified
by the AWDCH[4:0] bits or on all the channels
0: Analog watchdog enabled on all channels
1: Analog watchdog enabled on a single channel
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bits 21:17 Reserved, must be kept at reset value.

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Bit 16 DISCEN: Discontinuous mode
This bit is set and cleared by software to enable/disable discontinuous mode.
0: Discontinuous mode disabled
1: Discontinuous mode enabled
Note: It is not possible to have both discontinuous mode and continuous mode enabled: it is
forbidden to set both bits DISCEN=1 and CONT=1.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 15 AUTOFF: Auto-off mode
This bit is set and cleared by software to enable/disable auto-off mode..
0: Auto-off mode disabled
1: Auto-off mode enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 14 WAIT: Wait conversion mode
This bit is set and cleared by software to enable/disable wait conversion mode..
0: Wait conversion mode off
1: Wait conversion mode on
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 13 CONT: Single / continuous conversion mode
This bit is set and cleared by software. If it is set, conversion takes place continuously until it is
cleared.
0: Single conversion mode
1: Continuous conversion mode
Note: It is not possible to have both discontinuous mode and continuous mode enabled: it is
forbidden to set both bits DISCEN=1 and CONT=1.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 12 OVRMOD: Overrun management mode
This bit is set and cleared by software and configure the way data overruns are managed.
0: ADC_DR register is preserved with the old data when an overrun is detected.
1: ADC_DR register is overwritten with the last conversion result when an overrun is
detected.
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bits 11:10 EXTEN[1:0]: External trigger enable and polarity selection
These bits are set and cleared by software to select the external trigger polarity and enable the
trigger.
00: Hardware trigger detection disabled (conversions can be started by software)
01: Hardware trigger detection on the rising edge
10: Hardware trigger detection on the falling edge
11: Hardware trigger detection on both the rising and falling edges
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 9 Reserved, must be kept at reset value.

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Analog-to-digital converter (ADC)

Bits 8:6 EXTSEL[2:0]: External trigger selection
These bits select the external event used to trigger the start of conversion (refer to Table 45:
External triggers for details):
000: TRG0
001: TRG1
010: TRG2
011: TRG3
100: TRG4
101: TRG5
110: TRG6
111: TRG7
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 5 ALIGN: Data alignment
This bit is set and cleared by software to select right or left alignment. Refer to Figure 37: Data
alignment and resolution on page 244
0: Right alignment
1: Left alignment
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 4:3 RES[1:0]: Data resolution
These bits are written by software to select the resolution of the conversion.
00: 12 bits
01: 10 bits
10: 8 bits
11: 6 bits
Note: Software is allowed to write these bits only when ADEN=0.

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Bit 2 SCANDIR: Scan sequence direction
This bit is set and cleared by software to select the direction in which the channels will be
scanned in the sequence.
0: Upward scan (from CHSEL0 to CHSEL18)
1: Backward scan (from CHSEL18 to CHSEL0)
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 1 DMACFG: Direct memory access configuration
This bit is set and cleared by software to select between two DMA modes of operation and is
effective only when DMAEN=1.
0: DMA one shot mode selected
1: DMA circular mode selected
For more details, refer to Section 13.6.5: Managing converted data using the DMA on
page 245
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bit 0 DMAEN: Direct memory access enable
This bit is set and cleared by software to enable the generation of DMA requests. This allows to
use the DMA controller to manage automatically the converted data. For more details, refer to
Section 13.6.5: Managing converted data using the DMA on page 245.
0: DMA disabled
1: DMA enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no
conversion is ongoing).

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Analog-to-digital converter (ADC)

13.12.5

ADC configuration register 2 (ADC_CFGR2)
Address offset: 0x10
Reset value: 0x0000 0000

31

30

CKMODE[1:0]

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Bits 31:30 CKMODE[1:0]: ADC clock mode
These bits are set and cleared by software to define how the analog ADC is clocked:
00: ADCCLK (Asynchronous clock mode), generated at product level (refer to RCC section)
01: PCLK/2 (Synchronous clock mode)
10: PCLK/4 (Synchronous clock mode)
11: Reserved
In all synchronous clock modes, there is no jitter in the delay from a timer trigger to the start of a
conversion.
Note: Software is allowed to write these bits only when the ADC is disabled (ADCAL=0, ADSTART=0,
ADSTP=0, ADDIS=0 and ADEN=0).
Bits 29:0

13.12.6

Reserved, must be kept at reset value.

ADC sampling time register (ADC_SMPR)
Address offset: 0x14
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SMP[2:0]
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Bits 31:3 Reserved, must be kept at reset value.
Bits 2:0 SMP[2:0]: Sampling time selection
These bits are written by software to select the sampling time that applies to all channels.
000: 1.5 ADC clock cycles
001: 7.5 ADC clock cycles
010: 13.5 ADC clock cycles
011: 28.5 ADC clock cycles
100: 41.5 ADC clock cycles
101: 55.5 ADC clock cycles
110: 71.5 ADC clock cycles
111: 239.5 ADC clock cycles
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).

13.12.7

ADC watchdog threshold register (ADC_TR)
Address offset: 0x20
Reset value: 0x0FFF 0000

31

30

29

28

Res.

Res.

Res.

Res.

15

14

13

12

Res.

Res.

Res.

Res.

27

25

24

23

22

21

20

19

18

17

16

HT[11:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

LT[11:0]
rw

Bits 31:28

26

rw

rw

rw

rw

rw

Reserved, must be kept at reset value.

Bit 27:16 HT[11:0]: Analog watchdog higher threshold
These bits are written by software to define the higher threshold for the analog watchdog. Refer to
Section 13.8: Analog window watchdog (AWDEN, AWDSGL, AWDCH, AWD_HTR/LTR, AWD) on
page 249
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).
Bits 15:12

Reserved, must be kept at reset value.

Bit 11:0 LT[11:0]: Analog watchdog lower threshold
These bits are written by software to define the lower threshold for the analog watchdog.
Refer to Section 13.8: Analog window watchdog (AWDEN, AWDSGL, AWDCH, AWD_HTR/LTR,
AWD) on page 249
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).

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Analog-to-digital converter (ADC)

13.12.8

ADC channel selection register (ADC_CHSELR)
Address offset: 0x28
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

18

17

16

CHSEL CHSEL CHSEL
18
17
16
rw

rw

rw

2

1

0

CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL CHSEL
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:19 Reserved, must be kept at reset value.
Bits 18:0 CHSELx: Channel-x selection
These bits are written by software and define which channels are part of the sequence of channels to
be converted.
0: Input Channel-x is not selected for conversion
1: Input Channel-x is selected for conversion
Note: Software is allowed to write these bits only when ADSTART=0 (which ensures that no
conversion is ongoing).

13.12.9

ADC data register (ADC_DR)
Address offset: 0x40
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

DATA[15:0]
r

r

r

r

r

r

r

r

r

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 DATA[15:0]: Converted data
These bits are read-only. They contain the conversion result from the last converted channel. The data
are left- or right-aligned as shown in Figure 37: Data alignment and resolution on page 244.
Just after a calibration is complete, DATA[6:0] contains the calibration factor.

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13.12.10 ADC common configuration register (ADC_CCR)
Address offset: 0x308
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

VBAT
EN

TS
EN

VREF
EN

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Bits 31:25 Reserved, must be kept at reset value.
Bit 24 VBATEN: VBAT enable
This bit is set and cleared by software to enable/disable the VBAT channel.
0: VBAT channel disabled
1: VBAT channel enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 23 TSEN: Temperature sensor enable
This bit is set and cleared by software to enable/disable the temperature sensor.
0: Temperature sensor disabled
1: Temperature sensor enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bit 22 VREFEN: VREFINT enable
This bit is set and cleared by software to enable/disable the VREFINT.
0: VREFINT disabled
1: VREFINT enabled
Note: Software is allowed to write this bit only when ADSTART=0 (which ensures that no conversion
is ongoing).
Bits 21:0 Reserved, must be kept at reset value.

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ADC_CCR

0

0

0

Reset value

Reserved

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0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

CHSEL12
CHSEL11
CHSEL10
CHSEL9
CHSEL8
CHSEL7

0
0
0
0
0
0

Reserved

DATA[15:0]

0
CHSEL0

0

Res.

0
1
Reserved

0
0
0
0
0
0
0

0

0

0

Res.

0

Res.

CHSEL13

OVRMOD

Res.
Res.
Res.

Res.

SCANDIR
DMACFG
DMAEN

0
0
0
0
0
0
0
0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

ALIGN

0

Res.

ADRDYIE

0
0

0
RES
[1:0]

ADEN

EOSMPIE

0
ADDIS

EOCIE

0
ADSTART

EOSEQIE

Res.

Res.

AWDIE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0
Res.

0

OVRIE

ADSTP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

EOSEQ
EOC
EOSMP
ADRDY

Res.

Res.

AWD

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

OVR

0

Res.

Res.

CONT

Res.

Res.

WAIT

Res.

EXTEN[1:0]

AUTOFF

Res.

EXTSEL
[2:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Reserved
Reserved

Res.

Res.

Res.

0

CHSEL1

0

Res.

CHSEL14

Res.

DISCEN

0

Res.

Res.

0

Res.

0

Res.

CHSEL15

Res.

Res.

Res.

0

CHSEL2

0

Res.

CHSEL16

Res.

Res.

Res.

0

CHSEL3

0

Res.

1

CHSEL17

Res.

Res.

Res.

0

Res.

0

Res.

1

CHSEL18

Res.

Res.

0

CHSEL4

0

Res.

1

Res.

Res.

Res.

AWDSGL

Res.
Res.

AWDEN

Res.

Res.

Res.

Res.

Res.

Reset value

CHSEL5

0

Res.

1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

CHSEL6

0

Res.

Reserved

0

Res.

0

Res.

1

Res.

HT[11:0]

Res.

Reserved

Res.

Res.

Res.

Res.

Res.

1

Res.

Reset value
Reserved
Reserved

Res.

Res.

Res.

Res.

Res.

1

Res.

Res.

Res.
Res.

Res.

0

Res.

Res.

1

Res.

Res.

Res.

Res.

ADCAL

Res.

0

Res.

VREFEN

Res.

1

Res.

Res.

Res.

Res.

Res.

0

Res.

1

Res.

Reset value
1

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

CKMODE[1:0]

0

TSEN

Reset value
0

VBATEN

ADC_DR
AWDCH[4:0]

Res.

0x44
...
0x304
ADC_CHSELR

Res.

0x40
Reset value
Reserved

Res.

0x2C
0x30
0x34
0x38
0x3C
ADC_TR
0

Res.

Reset value
0

Res.

0x28
ADC_SMPR
Res.

Reset value

Res.

0x24
ADC_CFGR1

Res.

0x20
0

Res.

0x18
0x1C
Reset value

Res.

0x14
ADC_CFGR2

Res.

0x10
ADC_CR

Res.

0x0C

Res.

0x08
ADC_IER

Res.

0x04
ADC_ISR

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

RM0091
Analog-to-digital converter (ADC)

13.12.11 ADC register map
The following table summarizes the ADC registers.
Table 50. ADC register map and reset values

0
0
0
0
0

0
0
0

0

SMP
[2:0]
0 0 0

LT[11:0]

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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Digital-to-analog converter (DAC)
This section applies to STM32F05x, STM32F07x and STM32F09x devices only. The
second DAC channel (DAC_OUT2) and some other features are available only on
STM32F07x and STM32F09x devices.

14.1

Introduction
The DAC module is a 12-bit, voltage output digital-to-analog converter. The DAC can be
configured in 8- or 12-bit mode and may be used in conjunction with the DMA controller. In
12-bit mode, the data could be left- or right-aligned. An input reference voltage, VDDA
(shared with ADC), is available. The output can optionally be buffered for higher current
drive.

14.2

DAC main features
The devices integrate one 12-bit DAC channel DAC_OUT1. A second channel DAC_OUT2
is available on STM32F07x and STM32F09x devices.
DAC main features are the following:
•

Left or right data alignment in 12-bit mode

•

Synchronized update capability

•

Noise-wave generation (STM32F07x and STM32F09x devices)

•

Triangular-wave generation (STM32F07x and STM32F09x devices)

•

Independent or simultaneous conversions (dual mode only)

•

DMA capability

•

DMA underrun error detection

•

External triggers for conversion

•

Programmable internal buffer

•

Input voltage reference, VDDA

Figure 44 shows the block diagram of a DAC channel and Table 51 gives the pin
description.

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Digital-to-analog converter (DAC)
Figure 44. DAC block diagram

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Table 51. DAC pins
Name

Signal type

Remarks

VDDA

Input, analog supply

Analog power supply

VSSA

Input, analog supply ground

Ground for analog power supply

DAC_OUT

Analog output signal

DAC channelx analog output

Note:

Once DAC_Channelx is enabled, the corresponding GPIO pin (PA4 or PA5) is automatically
connected to the analog converter output (DAC_OUTx). In order to avoid parasitic
consumption, the PA4 or PA5 pin should first be configured to analog (AIN).

14.3

DAC output buffer enable
The DAC integrates one output buffer that can be used to reduce the output impedance and
to drive external loads directly without having to add an external operational amplifier.
The DAC channel output buffers can be enabled and disabled through the corresponding
BOFFx bit in the DAC_CR register.

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14.4

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DAC channel enable
Each DAC channel can be powered on by setting the corresponding ENx bit in the DAC_CR
register. Each DAC channel is then enabled after a startup time tWAKEUP.

Note:

The ENx bit enables the analog DAC Channelx macrocell only. The DAC Channelx digital
interface is enabled even if the ENx bit is reset.

14.5

Single mode functional description

14.5.1

DAC data format
There are three possibilities:
•

8-bit right alignment: the software has to load data into the DAC_DHR8Rx [7:0] bits
(stored into the DHRx[11:4] bits)

•

12-bit left alignment: the software has to load data into the DAC_DHR12Lx [15:4] bits
(stored into the DHRx[11:0] bits)

•

12-bit right alignment: the software has to load data into the DAC_DHR12Rx [11:0] bits
(stored into the DHRx[11:0] bits)

Depending on the loaded DAC_DHRyyyx register, the data written by the user is shifted and
stored into the corresponding DHRx (data holding registerx, which are internal non-memorymapped registers). The DHRx register is then loaded into the DORx register either
automatically, by software trigger or by an external event trigger.
Figure 45. Data registers in single DAC channel mode










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14.5.2

DAC channel conversion
The DAC_DORx cannot be written directly and any data transfer to the DAC channelx must
be performed by loading the DAC_DHRx register (write to DAC_DHR8Rx, DAC_DHR12Lx,
DAC_DHR12Rx).
Data stored in the DAC_DHRx register are automatically transferred to the DAC_DORx
register after one APB clock cycle, if no hardware trigger is selected (TENx bit in DAC_CR
register is reset). However, when a hardware trigger is selected (TENx bit in DAC_CR
register is set) and a trigger occurs, the transfer is performed three PCLK clock cycles later.
When DAC_DORx is loaded with the DAC_DHRx contents, the analog output voltage
becomes available after a time tSETTLING that depends on the power supply voltage and the
analog output load.

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Digital-to-analog converter (DAC)
Figure 46. Timing diagram for conversion with trigger disabled TEN = 0
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Independent trigger with single LFSR generation
To configure the DAC in this conversion mode (see Section 14.7: Noise
generation(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the DAC channel trigger enable bit TENx.

2.

Configure the trigger source by setting TSELx[2:0] bits.

3.

Configure the DAC channel WAVEx[1:0] bits as “01” and the same LFSR mask value in
the MAMPx[3:0] bits

4.

Load the DAC channel data into the desired DAC_DHRx register (DHR12RD,
DHR12LD or DHR8RD).

When a DAC channelx trigger arrives, the LFSRx counter, with the same mask, is added to
the DHRx register and the sum is transferred into DAC_DORx (three APB clock cycles
later). Then the LFSRx counter is updated.

Independent trigger with single triangle generation
To configure the DAC in this conversion mode (see Section 14.8: Triangle-wave generation
(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the DAC channelx trigger enable TENx bits.

2.

Configure the trigger source by setting TSELx[2:0] bits.

3.

Configure the DAC channelx WAVEx[1:0] bits as “1x” and the same maximum
amplitude value in the MAMPx[3:0] bits

4.

Load the DAC channelx data into the desired DAC_DHRx register. (DHR12RD,
DHR12LD or DHR8RD).

When a DAC channelx trigger arrives, the DAC channelx triangle counter, with the same
triangle amplitude, is added to the DHRx register and the sum is transferred into
DAC_DORx (three APB clock cycles later). The DAC channelx triangle counter is then
updated.

14.5.3

DAC output voltage
Digital inputs are converted to output voltages on a linear conversion between 0 and VDDA.
The analog output voltages on each DAC channel pin are determined by the following
equation:
DOR
DACoutput = V DDA × -------------4096

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14.5.4

RM0091

DAC trigger selection
If the TENx control bit is set, conversion can then be triggered by an external event (timer
counter, external interrupt line). The TSELx[2:0] control bits determine which possible
events will trigger conversion as shown in Table 52.
Table 52. External triggers
Source

Type

TSEL[2:0]

TIM6_TRGO event

000

TIM3_TRGO event

001

TIM7_TRGO event
TIM15_TRGO event

Internal signal from on-chip
timers

010
011

TIM2_TRGO event

100

Reserved

101

EXTI line9

External pin

110

SWTRIG

Software control bit

111

Each time a DAC interface detects a rising edge on the selected timer TRGO output, or on
the selected external interrupt line 9, the last data stored into the DAC_DHRx register are
transferred into the DAC_DORx register. The DAC_DORx register is updated three APB
cycles after the trigger occurs.
If the software trigger is selected, the conversion starts once the SWTRIG bit is set.
SWTRIG is reset by hardware once the DAC_DORx register has been loaded with the
DAC_DHRx register contents.
Note:

TSELx[2:0] bit cannot be changed when the ENx bit is set. When software trigger is
selected, the transfer from the DAC_DHRx register to the DAC_DORx register takes only
one APB clock cycle.

14.6

Dual-mode functional description (STM32F07x and
STM32F09x devices)

14.6.1

DAC data format
In Dual DAC channel mode, there are three possibilities:

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•

8-bit right alignment: data for DAC channel1 to be loaded in the DAC_DHR8RD [7:0]
bits (stored in the DHR1[11:4] bits) and data for DAC channel2 to be loaded in the
DAC_DHR8RD [15:8] bits (stored in the DHR2[11:4] bits)

•

12-bit left alignment: data for DAC channel1 to be loaded into the DAC_DHR12LD
[15:4] bits (stored into the DHR1[11:0] bits) and data for DAC channel2 to be loaded
into the DAC_DHR12LD [31:20] bits (stored in the DHR2[11:0] bits)

•

12-bit right alignment: data for DAC channel1 to be loaded into the DAC_DHR12RD
[11:0] bits (stored in the DHR1[11:0] bits) and data for DAC channel2 to be loaded into
the DAC_DHR12LD [27:16] bits (stored in the DHR2[11:0] bits)

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Digital-to-analog converter (DAC)
Depending on the loaded DAC_DHRyyyD register, the data written by the user is shifted
and stored in DHR1 and DHR2 (data holding registers, which are internal non-memorymapped registers). The DHR1 and DHR2 registers are then loaded into the DOR1 and
DOR2 registers, respectively, either automatically, by software trigger or by an external
event trigger.
Figure 47. Data registers in dual DAC channel mode










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14.6.2

DAC channel conversion in dual mode
The DAC channel conversion in dual mode is performed in the same way as in single mode
(refer to Section 14.5.2) except that the data have to be loaded by writing to DAC_DHR8Rx,
DAC_DHR12Lx, DAC_DHR12Rx, DAC_DHR8RD, DAC_DHR12LD or DAC_DHR12RD.

14.6.3

Description of dual conversion modes
To efficiently use the bus bandwidth in applications that require the two DAC channels at the
same time, three dual registers are implemented: DHR8RD, DHR12RD and DHR12LD. A
unique register access is then required to drive both DAC channels at the same time.
Eleven conversion modes are possible using the two DAC channels and these dual
registers. All the conversion modes can nevertheless be obtained using separate DHRx
registers if needed.
All modes are described in the paragraphs below.
Refer to Section 14.5.2: DAC channel conversion for details on the APB bus (APB or APB1)
that clocks the DAC conversions.

Independent trigger without wave generation
To configure the DAC in this conversion mode, the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure different trigger sources by setting different values in the TSEL1[2:0] and
TSEL2[2:0] bits

3.

Load the dual DAC channel data into the desired DHR register (DAC_DHR12RD,
DAC_DHR12LD or DAC_DHR8RD)

When a DAC channel1 trigger arrives, the DHR1 register is transferred into DAC_DOR1
(three APB clock cycles later).
When a DAC channel2 trigger arrives, the DHR2 register is transferred into DAC_DOR2
(three APB clock cycles later).
For code example refer to the Appendix section A.8.1: Independent trigger without wave
generation code example

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Independent trigger with single LFSR generation
To configure the DAC in this conversion mode (refer to Section 14.7: Noise
generation(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure different trigger sources by setting different values in the TSEL1[2:0] and
TSEL2[2:0] bits

3.

Configure the two DAC channel WAVEx[1:0] bits as “01” and the same LFSR mask
value in the MAMPx[3:0] bits

4.

Load the dual DAC channel data into the desired DHR register (DHR12RD, DHR12LD
or DHR8RD)

For code example refer to the Appendix section A.8.2: Independent trigger with single LFSR
generation code example
When a DAC channel1 trigger arrives, the LFSR1 counter, with the same mask, is added to
the DHR1 register and the sum is transferred into DAC_DOR1 (three APB clock cycles
later). Then the LFSR1 counter is updated.
When a DAC channel2 trigger arrives, the LFSR2 counter, with the same mask, is added to
the DHR2 register and the sum is transferred into DAC_DOR2 (three APB clock cycles
later). Then the LFSR2 counter is updated.

Independent trigger with different LFSR generation
To configure the DAC in this conversion mode (refer to Section 14.7: Noise
generation(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure different trigger sources by setting different values in the TSEL1[2:0] and
TSEL2[2:0] bits

3.

Configure the two DAC channel WAVEx[1:0] bits as “01” and set different LFSR masks
values in the MAMP1[3:0] and MAMP2[3:0] bits

4.

Load the dual DAC channel data into the desired DHR register (DAC_DHR12RD,
DAC_DHR12LD or DAC_DHR8RD)

For code example refer to the Appendix section A.8.3: Independent trigger with different
LFSR generation code example.
When a DAC channel1 trigger arrives, the LFSR1 counter, with the mask configured by
MAMP1[3:0], is added to the DHR1 register and the sum is transferred into DAC_DOR1
(three APB clock cycles later). Then the LFSR1 counter is updated.
When a DAC channel2 trigger arrives, the LFSR2 counter, with the mask configured by
MAMP2[3:0], is added to the DHR2 register and the sum is transferred into DAC_DOR2
(three APB clock cycles later). Then the LFSR2 counter is updated.

Independent trigger with single triangle generation
To configure the DAC in this conversion mode (refer to Section 14.8: Triangle-wave
generation (STM32F07x and STM32F09x devices)), the following sequence is required:

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Digital-to-analog converter (DAC)
1.

Set the DAC channelx trigger enable TENx bits.

2.

Configure different trigger sources by setting different values in the TSELx[2:0] bits

3.

Configure the DAC channelx WAVEx[1:0] bits as “1x” and the same maximum
amplitude value in the MAMPx[3:0] bits

4.

Load the DAC channelx data into the desired DAC_DHRx register.

For code example refer to the Appendix section A.8.4: Independent trigger with single
triangle generation code example.
Refer to Section 14.5.2: DAC channel conversion for details on the APB bus (APB or APB1)
that clocks the DAC conversions.
When a DAC channelx trigger arrives, the DAC channelx triangle counter, with the same
triangle amplitude, is added to the DHRx register and the sum is transferred into
DAC_DORx (three APB clock cycles later). The DAC channelx triangle counter is then
updated.

Independent trigger with different triangle generation
To configure the DAC in this conversion mode (refer to Section 14.8: Triangle-wave
generation (STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the DAC channelx trigger enable TENx bits.

2.

Configure different trigger sources by setting different values in the TSELx[2:0] bits

3.

Configure the DAC channelx WAVEx[1:0] bits as “1x” and set different maximum
amplitude values in the MAMPx[3:0] bits

4.

Load the DAC channelx data into the desired DAC_DHRx register.

For code example refer to the Appendix section A.8.5: Independent trigger with different
triangle generation code example.
When a DAC channelx trigger arrives, the DAC channelx triangle counter, with a triangle
amplitude configured by MAMPx[3:0], is added to the DHRx register and the sum is
transferred into DAC_DORx (three APB clock cycles later). The DAC channelx triangle
counter is then updated.

Simultaneous software start
To configure the DAC in this conversion mode, the following sequence is required:
1.

Load the dual DAC channel data to the desired DHR register (DAC_DHR12RD,
DAC_DHR12LD or DAC_DHR8RD)

In this configuration, one APB clock cycles).
For code example refer to the Appendix section A.8.6: Simultaneous software start code
example.

Simultaneous trigger without wave generation
To configure the DAC in this conversion mode, the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure the same trigger source for both DAC channels by setting the same value in
the TSEL1[2:0] and TSEL2[2:0] bits

3.

Load the dual DAC channel data to the desired DHR register (DAC_DHR12RD,
DAC_DHR12LD or DAC_DHR8RD)

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When a trigger arrives, the DHR1 and DHR2 registers are transferred into DAC_DOR1 and
DAC_DOR2, respectively (after three APB clock cycles).
For code example refer to the Appendix section A.8.7: Simultaneous trigger without wave
generation code example.

Simultaneous trigger with single LFSR generation
To configure the DAC in this conversion mode (refer to Section 14.7: Noise
generation(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure the same trigger source for both DAC channels by setting the same value in
the TSEL1[2:0] and TSEL2[2:0] bits

3.

Configure the two DAC channel WAVEx[1:0] bits as “01” and the same LFSR mask
value in the MAMPx[3:0] bits

4.

Load the dual DAC channel data to the desired DHR register (DHR12RD, DHR12LD or
DHR8RD)

For code example refer to the Appendix section A.8.8: Simultaneous trigger with single
LFSR generation code example.
When a trigger arrives, the LFSR1 counter, with the same mask, is added to the DHR1
register and the sum is transferred into DAC_DOR1 (three APB clock cycles later). The
LFSR1 counter is then updated. At the same time, the LFSR2 counter, with the same mask,
is added to the DHR2 register and the sum is transferred into DAC_DOR2 (three APB clock
cycles later). The LFSR2 counter is then updated.

Simultaneous trigger with different LFSR generation
To configure the DAC in this conversion mode (refer to Section 14.7: Noise
generation(STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the two DAC channel trigger enable bits TEN1 and TEN2

2.

Configure the same trigger source for both DAC channels by setting the same value in
the TSEL1[2:0] and TSEL2[2:0] bits

3.

Configure the two DAC channel WAVEx[1:0] bits as “01” and set different LFSR mask
values using the MAMP1[3:0] and MAMP2[3:0] bits

4.

Load the dual DAC channel data into the desired DHR register (DAC_DHR12RD,
DAC_DHR12LD or DAC_DHR8RD)

For code example refer to the Appendix section A.8.9: Simultaneous trigger with different
LFSR generation code example.
When a trigger arrives, the LFSR1 counter, with the mask configured by MAMP1[3:0], is
added to the DHR1 register and the sum is transferred into DAC_DOR1 (three APB clock
cycles later). The LFSR1 counter is then updated.
At the same time, the LFSR2 counter, with the mask configured by MAMP2[3:0], is added to
the DHR2 register and the sum is transferred into DAC_DOR2 (three APB clock cycles
later). The LFSR2 counter is then updated.

Simultaneous trigger with single triangle generation
To configure the DAC in this conversion mode (refer to Section 14.8: Triangle-wave
generation (STM32F07x and STM32F09x devices)), the following sequence is required:

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Digital-to-analog converter (DAC)
1.

Set the DAC channelx trigger enable TEN1x bits.

2.

Configure the same trigger source for both DAC channels by setting the same value in
the TSELx[2:0] bits.

3.

Configure the DAC channelx WAVEx[1:0] bits as “1x” and the same maximum
amplitude value using the MAMPx[3:0] bits

4.

Load the DAC channelx data into the desired DAC_DHRx registers.

For code example refer to the Appendix section A.8.10: Simultaneous trigger with single
triangle generation code example.
When a trigger arrives, the DAC channelx triangle counter, with the same triangle amplitude,
is added to the DHRx register and the sum is transferred into DAC_DORx (three APB clock
cycles later). The DAC channelx triangle counter is then updated.

Simultaneous trigger with different triangle generation
To configure the DAC in this conversion mode ‘refer to Section 14.8: Triangle-wave
generation (STM32F07x and STM32F09x devices)), the following sequence is required:
1.

Set the DAC channelx trigger enable TENx bits.

2.

Configure the same trigger source for DAC channelx by setting the same value in the
TSELx[2:0] bits

3.

Configure the DAC channelx WAVEx[1:0] bits as “1x” and set different maximum
amplitude values in the MAMPx[3:0] bits.

4.

Load the DAC channelx data into the desired DAC_DHRx registers.

For code example refer to the Appendix section A.8.11: Simultaneous trigger with different
triangle generation code example.
When a trigger arrives, the DAC channelx triangle counter, with a triangle amplitude
configured by MAMPx[3:0], is added to the DHRx register and the sum is transferred into
DAC_DORx (three APB clock cycles later). Then the DAC channelx triangle counter is
updated.

14.6.4

DAC output voltage
Refer to Section 14.5.3: DAC output voltage.

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14.6.5

RM0091

DAC trigger selection
Refer to Section 14.5.4: DAC trigger selection

14.7

Noise generation(STM32F07x and STM32F09x devices)
In order to generate a variable-amplitude pseudonoise, an LFSR (linear feedback shift
register) is available. DAC noise generation is selected by setting WAVEx[1:0] to “01”. The
preloaded value in LFSR is 0xAAA. This register is updated three APB clock cycles after
each trigger event, following a specific calculation algorithm.
Figure 48. DAC LFSR register calculation algorithm
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;




;

;









125

DLF

The LFSR value, that may be masked partially or totally by means of the MAMPx[3:0] bits in
the DAC_CR register, is added up to the DAC_DHRx contents without overflow and this
value is then stored into the DAC_DORx register.
If LFSR is 0x0000, a ‘1 is injected into it (antilock-up mechanism).
It is possible to reset LFSR wave generation by resetting the WAVEx[1:0] bits.
Figure 49. DAC conversion (SW trigger enabled) with LFSR wave generation

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Note:

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The DAC trigger must be enabled for noise generation by setting the TENx bit in the
DAC_CR register.

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14.8

Digital-to-analog converter (DAC)

Triangle-wave generation (STM32F07x and STM32F09x
devices)
It is possible to add a small-amplitude triangular waveform on a DC or slowly varying signal.
DAC triangle-wave generation is selected by setting WAVEx[1:0] to “10”. The amplitude is
configured through the MAMPx[3:0] bits in the DAC_CR register. An internal triangle counter
is incremented three APB clock cycles after each trigger event. The value of this counter is
then added to the DAC_DHRx register without overflow and the sum is stored into the
DAC_DORx register. The triangle counter is incremented as long as it is less than the
maximum amplitude defined by the MAMPx[3:0] bits. Once the configured amplitude is
reached, the counter is decremented down to 0, then incremented again and so on.
It is possible to reset triangle wave generation by resetting the WAVEx[1:0] bits.
Figure 50. DAC triangle wave generation

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Figure 51. DAC conversion (SW trigger enabled) with triangle wave generation
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Note:

The DAC trigger must be enabled for triangle generation by setting the TENx bit in the
DAC_CR register.
The MAMPx[3:0] bits must be configured before enabling the DAC, otherwise they cannot
be changed.

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RM0091

DMA request
Each DAC channel has a DMA capability. Two DMA channels are used to service DAC
channel DMA requests.
A DAC DMA request is generated when an external trigger (but not a software trigger)
occurs while the DMAENx bit is set. The value of the DAC_DHRx register is then transferred
to the DAC_DORx register.
In dual mode, if both DMAENx bits are set, two DMA requests are generated. If only one
DMA request is needed, user should set only the corresponding DMAENx bit. In this way,
the application can manage both DAC channels in dual mode by using one DMA request
and a unique DMA channel.
For code example refer to the Appendix section A.8.12: DMA initialization code example.

DMA underrun
The DAC DMA request is not queued so that if a second external trigger arrives before the
acknowledgment for the first external trigger is received (first request), then no new request
is issued and the DMA channelx underrun flag DMAUDRx in the DAC_SR register is set,
reporting the error condition. DMA data transfers are then disabled and no further DMA
request is treated. The DAC channelx continues to convert old data.
The software should clear the DMAUDRx flag by writing “1”, clear the DMAEN bit of the
used DMA stream and re-initialize both DMA and DAC channelx to restart the transfer
correctly. The software should modify the DAC trigger conversion frequency or lighten the
DMA workload to avoid a new DMA. Finally, the DAC conversion can be resumed by
enabling both DMA data transfer and conversion trigger.
For each DAC channel, an interrupt is also generated if the corresponding DMAUDRIEx bit
in the DAC_CR register is enabled.

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14.10

DAC registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers have to be accessed by words (32-bit).

14.10.1

DAC control register (DAC_CR)
Address offset: 0x00
Reset value: 0x0000 0000

31

30

29

28

Res.

Res.

DMAU
DRIE2

DMA
EN2

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

Res.

DMAU
DRIE1

DMA
EN1

rw

rw

Res.

27

26

25

24

MAMP2[3:0]

rw

rw

22

21

WAVE2[1:0]

MAMP1[3:0]
rw

23

rw

rw

19

18

17

16

TEN2

BOFF2

EN2

rw

rw

rw

rw

3

2

1

0

TEN1

BOFF1

EN1

rw

rw

rw

TSEL2[2:0]

WAVE1[1:0]
rw

20

TSEL1[2:0]
rw

rw

rw

Bits 31:30 Reserved, must be kept at reset value.
Bit 29 DMAUDRIE2: DAC channel2 DMA underrun interrupt enable
This bit is set and cleared by software.
0: DAC channel2 DMA underrun interrupt disabled
1: DAC channel2 DMA underrun interrupt enabled
Note: This bit is available in dual mode only. It is reserved in single mode.
Bit 28 DMAEN2: DAC channel2 DMA enable
This bit is set and cleared by software.
0: DAC channel2 DMA mode disabled
1: DAC channel2 DMA mode enabled
Note: This bit is available in dual mode only. It is reserved in single mode.
Bits 27:24 MAMP2[3:0]: DAC channel2 mask/amplitude selector
These bits are written by software to select mask in wave generation mode or amplitude in
triangle generation mode.
0000: Unmask bit0 of LFSR/ triangle amplitude equal to 1
0001: Unmask bits[1:0] of LFSR/ triangle amplitude equal to 3
0010: Unmask bits[2:0] of LFSR/ triangle amplitude equal to 7
0011: Unmask bits[3:0] of LFSR/ triangle amplitude equal to 15
0100: Unmask bits[4:0] of LFSR/ triangle amplitude equal to 31
0101: Unmask bits[5:0] of LFSR/ triangle amplitude equal to 63
0110: Unmask bits[6:0] of LFSR/ triangle amplitude equal to 127
0111: Unmask bits[7:0] of LFSR/ triangle amplitude equal to 255
1000: Unmask bits[8:0] of LFSR/ triangle amplitude equal to 511
1001: Unmask bits[9:0] of LFSR/ triangle amplitude equal to 1023
1010: Unmask bits[10:0] of LFSR/ triangle amplitude equal to 2047
≥1011: Unmask bits[11:0] of LFSR/ triangle amplitude equal to 4095
Note: These bits are available only in dual mode when wave generation is supported.
Otherwise, they are reserved and must be kept at reset value.

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Bits 23:22 WAVE2[1:0]: DAC channel2 noise/triangle wave generation enable
These bits are set/reset by software.
00: wave generation disabled
01: Noise wave generation enabled
1x: Triangle wave generation enabled
Note: Only used if bit TEN2 = 1 (DAC channel2 trigger enabled)
These bits are available only in dual mode when wave generation is supported.
Otherwise, they are reserved and must be kept at reset value.
Bits 21:19 TSEL2[2:0]: DAC channel2 trigger selection
These bits select the external event used to trigger DAC channel2
000: Timer 6 TRGO event
001: Timer 3 TRGO event
010: Timer 7 TRGO event
011: Timer 15 TRGO event
100: Timer 2 TRGO event
101: Reserved
110: EXTI line9
111: Software trigger
Note: Only used if bit TEN2 = 1 (DAC channel2 trigger enabled).
These bits are available in dual mode only. They are reserved in single mode.
Bit 18 TEN2: DAC channel2 trigger enable
This bit is set and cleared by software to enable/disable DAC channel2 trigger
0: DAC channel2 trigger disabled and data written into the DAC_DHRx register are
transferred one APBclock cycle later to the DAC_DOR2 register
1: DAC channel2 trigger enabled and data from the DAC_DHRx register are transferred
three APB clock cycles later to the DAC_DOR2 register
Note: When software trigger is selected, the transfer from the DAC_DHRx register to the
DAC_DOR2 register takes only one APB clock cycle.
Note: This bit is available in dual mode only. It is reserved in single mode.
Bit 17 BOFF2: DAC channel2 output buffer disable
This bit is set and cleared by software to enable/disable DAC channel2 output buffer.
0: DAC channel2 output buffer enabled
1: DAC channel2 output buffer disabled
Note: This bit is available in dual mode only. It is reserved in single mode.
Bit 16 EN2: DAC channel2 enable
This bit is set and cleared by software to enable/disable DAC channel2.
0: DAC channel2 disabled
1: DAC channel2 enabled
Note: This bit is available in dual mode only. It is reserved in single mode.
Bits 15:14 Reserved, must be kept at reset value.
Bit 13 DMAUDRIE1: DAC channel1 DMA Underrun Interrupt enable
This bit is set and cleared by software.
0: DAC channel1 DMA Underrun Interrupt disabled
1: DAC channel1 DMA Underrun Interrupt enabled

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Digital-to-analog converter (DAC)

Bit 12 DMAEN1: DAC channel1 DMA enable
This bit is set and cleared by software.
0: DAC channel1 DMA mode disabled
1: DAC channel1 DMA mode enabled
Bits 11:8 MAMP1[3:0]: DAC channel1 mask/amplitude selector
These bits are written by software to select mask in wave generation mode or amplitude in
triangle generation mode.
0000: Unmask bit0 of LFSR/ triangle amplitude equal to 1
0001: Unmask bits[1:0] of LFSR/ triangle amplitude equal to 3
0010: Unmask bits[2:0] of LFSR/ triangle amplitude equal to 7
0011: Unmask bits[3:0] of LFSR/ triangle amplitude equal to 15
0100: Unmask bits[4:0] of LFSR/ triangle amplitude equal to 31
0101: Unmask bits[5:0] of LFSR/ triangle amplitude equal to 63
0110: Unmask bits[6:0] of LFSR/ triangle amplitude equal to 127
0111: Unmask bits[7:0] of LFSR/ triangle amplitude equal to 255
1000: Unmask bits[8:0] of LFSR/ triangle amplitude equal to 511
1001: Unmask bits[9:0] of LFSR/ triangle amplitude equal to 1023
1010: Unmask bits[10:0] of LFSR/ triangle amplitude equal to 2047
≥ 1011: Unmask bits[11:0] of LFSR/ triangle amplitude equal to 4095
Bits 7:6 WAVE1[1:0]: DAC channel1 noise/triangle wave generation enable
These bits are set and cleared by software.
00: Wave generation disabled
01: Noise wave generation enabled
1x: Triangle wave generation enabled
Note: Only used if bit TEN1 = 1 (DAC channel1 trigger enabled).
Bits 5:3 TSEL1[2:0]: DAC channel1 trigger selection
These bits select the external event used to trigger DAC channel1.
000: Timer 6 TRGO event
001: Timer 3 TRGO event
010: Timer 7 TRGO event
011: Timer 15 TRGO event
100: Timer 2 TRGO event
101: Reserved
110: EXTI line9
111: Software trigger
Note: Only used if bit TEN1 = 1 (DAC channel1 trigger enabled).

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Bit 2 TEN1: DAC channel1 trigger enable
This bit is set and cleared by software to enable/disable DAC channel1 trigger.
0: DAC channel1 trigger disabled and data written into the DAC_DHRx register are
transferred one APB clock cycle later to the DAC_DOR1 register
1: DAC channel1 trigger enabled and data from the DAC_DHRx register are transferred
three APB clock cycles later to the DAC_DOR1 register
Note: When software trigger is selected, the transfer from the DAC_DHRx register to the
DAC_DOR1 register takes only one APB clock cycle.
Bit 1 BOFF1: DAC channel1 output buffer disable
This bit is set and cleared by software to enable/disable DAC channel1 output buffer.
0: DAC channel1 output buffer enabled
1: DAC channel1 output buffer disabled
Bit 0 EN1: DAC channel1 enable
This bit is set and cleared by software to enable/disable DAC channel1.
0: DAC channel1 disabled
1: DAC channel1 enabled

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Digital-to-analog converter (DAC)

14.10.2

DAC software trigger register (DAC_SWTRIGR)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

1

0

SWTRIG2 SWTRIG1
w

w

Bits 31:2 Reserved, must be kept at reset value.
Bit 1 SWTRIG2: DAC channel2 software trigger
This bit is set and cleared by software to enable/disable the software trigger.
0: Software trigger disabled
1: Software trigger enabled
Note: This bit is cleared by hardware (one APB clock cycle later) once the DAC_DHR2
register value has been loaded into the DAC_DOR2 register.
This bit is available in dual mode only. It is reserved in single mode.
Bit 0 SWTRIG1: DAC channel1 software trigger
This bit is set and cleared by software to enable/disable the software trigger.
0: Software trigger disabled
1: Software trigger enabled
Note: This bit is cleared by hardware (one APB clock cycle later) once the DAC_DHR1
register value has been loaded into the DAC_DOR1 register.

14.10.3

DAC channel1 12-bit right-aligned data holding register
(DAC_DHR12R1)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

15

14

13

12

Res.

Res.

Res.

Res.

DACC1DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

Bits 31:12 Reserved, must be kept at reset value.
Bits 11:0 DACC1DHR[11:0]: DAC channel1 12-bit right-aligned data
These bits are written by software which specifies 12-bit data for DAC channel1.

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14.10.4

RM0091

DAC channel1 12-bit left-aligned data holding register
(DAC_DHR12L1)
Address offset: 0x0C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

v

Res.

Res.

Res.

DACC1DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:4 DACC1DHR[11:0]: DAC channel1 12-bit left-aligned data
These bits are written by software which specifies 12-bit data for DAC channel1.
Bits 3:0 Reserved, must be kept at reset value.

14.10.5

DAC channel1 8-bit right-aligned data holding register
(DAC_DHR8R1)
Address offset: 0x10
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

3

2

1

0

rw

rw

rw

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DACC1DHR[7:0]
rw

rw

rw

rw

rw

Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 DACC1DHR[7:0]: DAC channel1 8-bit right-aligned data
These bits are written by software which specifies 8-bit data for DAC channel1.

14.10.6

DAC channel2 12-bit right-aligned data holding register
(DAC_DHR12R2)
Address offset: 0x14
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

15

14

13

12

Res.

Res.

Res.

Res.

DACC2DHR[11:0]
rw

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RM0091

Digital-to-analog converter (DAC)

Bits 31:12 Reserved, must be kept at reset value.
Bits 11:0 DACC2DHR[11:0]: DAC channel2 12-bit right-aligned data
These bits are written by software which specifies 12-bit data for DAC channel2.

14.10.7

DAC channel2 12-bit left-aligned data holding register
(DAC_DHR12L2)
Address offset: 0x18
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

DACC2DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

3

2

1

0

Res.

Res.

Res.

Res.

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:4 DACC2DHR[11:0]: DAC channel2 12-bit left-aligned data
These bits are written by software which specify 12-bit data for DAC channel2.
Bits 3:0 Reserved, must be kept at reset value.

14.10.8

DAC channel2 8-bit right-aligned data holding register
(DAC_DHR8R2)
Address offset: 0x1C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
rw

rw

rw

rw

rw

rw

DACC2DHR[7:0]
rw

rw

Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 DACC2DHR[7:0]: DAC channel2 8-bit right-aligned data
These bits are written by software which specifies 8-bit data for DAC channel2.

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14.10.9

RM0091

Dual DAC 12-bit right-aligned data holding register
(DAC_DHR12RD)
Address offset: 0x20
Reset value: 0x0000 0000

31

30

29

28

Res.

Res.

Res.

Res.

15

14

13

12

Res.

Res.

Res.

Res.

27

26

25

24

23

22

21

20

19

18

17

16

DACC2DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

DACC1DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

Bits 31:28 Reserved, must be kept at reset value.
Bits 27:16 DACC2DHR[11:0]: DAC channel2 12-bit right-aligned data
These bits are written by software which specifies 12-bit data for DAC channel2.
Bits 15:12 Reserved, must be kept at reset value.
Bits 11:0 DACC1DHR[11:0]: DAC channel1 12-bit right-aligned data
These bits are written by software which specifies 12-bit data for DAC channel1.

14.10.10 Dual DAC 12-bit left-aligned data holding register
(DAC_DHR12LD)
Address offset: 0x24
Reset value: 0x0000 0000
31

30

29

28

27

rw

rw

rw

rw

rw

15

14

13

12

11

26

25

24

23

22

21

20

DACC2DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

10

9

8

7

6

5

4

DACC1DHR[11:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

19

18

17

16

Res.

Res.

Res.

Res.

3

2

1

0

Res.

Res.

Res.

Res.

rw

Bits 31:20 DACC2DHR[11:0]: DAC channel2 12-bit left-aligned data
These bits are written by software which specifies 12-bit data for DAC channel2.
Bits 19:16 Reserved, must be kept at reset value.
Bits 15:4 DACC1DHR[11:0]: DAC channel1 12-bit left-aligned data
These bits are written by software which specifies 12-bit data for DAC channel1.
Bits 3:0 Reserved, must be kept at reset value.

14.10.11 Dual DAC 8-bit right-aligned data holding register
(DAC_DHR8RD)
Address offset: 0x28
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

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15

Digital-to-analog converter (DAC)

14

13

12

11

10

9

8

7

6

5

DACC2DHR[7:0]
rw

rw

rw

rw

4

3

2

1

0

rw

rw

rw

DACC1DHR[7:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:8 DACC2DHR[7:0]: DAC channel2 8-bit right-aligned data
These bits are written by software which specifies 8-bit data for DAC channel2.
Bits 7:0 DACC1DHR[7:0]: DAC channel1 8-bit right-aligned data
These bits are written by software which specifies 8-bit data for DAC channel1.

14.10.12 DAC channel1 data output register (DAC_DOR1)
Address offset: 0x2C
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

15

14

13

12

Res.

Res.

Res.

Res.

DACC1DOR[11:0]
r

r

r

r

r

r

r

Bits 31:12 Reserved, must be kept at reset value.
Bits 11:0 DACC1DOR[11:0]: DAC channel1 data output
These bits are read-only, they contain data output for DAC channel1.

14.10.13 DAC channel2 data output register (DAC_DOR2)
Address offset: 0x30
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

15

14

13

12

Res.

Res.

Res.

Res.

DACC2DOR[11:0]
r

r

r

r

r

r

r

Bits 31:12 Reserved, must be kept at reset value.
Bits 11:0 DACC2DOR[11:0]: DAC channel2 data output
These bits are read-only, they contain data output for DAC channel2.

14.10.14 DAC status register (DAC_SR)
Address offset: 0x34
Reset value: 0x0000 0000

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31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

DMAUDR2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rc_w1
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

DMAUDR1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rc_w1

Bits 31:30 Reserved, must be kept at reset value.
Bit 29 DMAUDR2: DAC channel2 DMA underrun flag. Available on STM32F07x and STM32F09x
devices.
This bit is set by hardware and cleared by software (by writing it to 1).
0: No DMA underrun error condition occurred for DAC channel2
1: DMA underrun error condition occurred for DAC channel2 (the currently selected trigger is
driving DAC channel2 conversion at a frequency higher than the DMA service capability rate)
Note: This bit is available in dual mode only. It is reserved in single mode.
Bits 28:14 Reserved, must be kept at reset value.
Bit 13 DMAUDR1: DAC channel1 DMA underrun flag
This bit is set by hardware and cleared by software (by writing it to 1).
0: No DMA underrun error condition occurred for DAC channel1
1: DMA underrun error condition occurred for DAC channel1 (the currently selected trigger is
driving DAC channel1 conversion at a frequency higher than the DMA service capability rate)
Bits 12:0 Reserved, must be kept at reset value.

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DAC_DOR2

Reset value

Reset value

DocID018940 Rev 9

0

0

0

0

Res.

0
0
0

Res.

Res.

0
0
0
0
0
0
0
0

Res.
Res.
Res.
Res.
Res.

Reset value

Res.
0

0

0

Reset value
0

0

0

0
0

0

0

0

0

0
0

0

0

0

0

0

0
0
0
0

Reset value

0

Reset value

0

0

0

0

0

Res.
Res.
Res.

0

DACC1DHR[11:0]
0

0

0

0

0

0

0

0

0

0

DACC1DHR[7:0]

0

0

DACC2DHR[7:0]

0

0

0

0

0

0

0

0

0

DACC2DHR[11:0]

DACC2DHR[11:0]
0
0
0

0
0
0

DACC1DHR[11:0]
0
0
0

0
0
0

0

Res.

0
Res.

0

0
0
0

Res.

0

0

Res.

0

0
0
0
0

0
0
0
0

Res.

0

Res.

0

DACC2DHR[7:0]

0

DACC1DHR[11:0]
Res.

0

Res.

0

Res.

0

Res.

0

0
0
0
0

0
0
0
0

DACC1DHR[7:0]

0

DACC1DOR[11:0]

0

DACC2DOR[11:0]
Res.

Reset value
0

Res.

0

Res.

0

Res.

0

Res.

Reset value

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

EN2
0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

DMAEN1
0
0
0
0
0
0
0
0
0
0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

EN1
0

Reset value
SWTRIG1

TEN1
BOFF1
0

SWTRIG2

0

Res.

TSEL1[2:0]

WAVE1[1:0]

MAMP1[3:0].

DMAUDRIE1

Res.

Res.

TSEL2[2:0]

WAVE2[1:0]

0

Res.

Res.

Res.

0

Res.

Res.

0

Res.

Res.

TEN2
BOFF2

0

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

DMAEN2

0

MAMP2[3:0]

DMAUDRIE2

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

DACC2DHR[11:0]
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.
0

Res.

Res.

Res.

DAC_
DHR8RD

Res.

0

Res.

0

Res.

0

Res.

0

Res.

DACC2DHR[11:0]

Res.

0

Res.
0

Res.

Res.

Res.

0

Res.
0

Res.

0

Res.
0

Res.

Res.

0

Res.
0

Res.

Res.

Res.

0

Res.
0

Res.

0

Res.
0

Res.

Res.

Res.

0

Res.
0

Res.

DAC_DOR1
0

Res.

0

Res.

DAC_
DHR12LD

Res.

Reset value

Res.

Reset value

Res.

0x2C
DAC_
DHR12RD

Res.

0x28
DAC_
DHR8R2

Res.

0x24
DAC_
DHR12L2

Res.

0x20
DAC_
DHR12R2

Res.

Reset value

Res.

0x1C
DAC_
DHR8R1

Res.

0x18
DAC_
DHR12L1

Res.

0x14
DAC_
DHR12R1

Res.

0x10

Res.

0x0C

Res.

0x08
DAC_
SWTRIGR

Res.

0x04
DAC_CR

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register
name

Res.

Offset

Res.

RM0091
Digital-to-analog converter (DAC)

14.10.15 DAC register map
Table 53 summarizes the DAC registers.
Table 53. DAC register map and reset values

0
0

DACC1DHR[11:0]

0

0

0

0

0

0

0

0

0

0

0

0

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RM0091

Reset value

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DMAUDR1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DMAUDR2

DAC_SR

Res.

0x34

Register
name

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 53. DAC register map (continued)and reset values (continued)

RM0091

15

Comparator (COMP)

Comparator (COMP)
This section applies to STM32F05x and STM32F07x and STM32F09x devices only.

15.1

Introduction
STM32F05x and STM32F07x and STM32F09x devices embed two general purpose
comparators COMP1 and COMP2,that can be used either as standalone devices (all
terminal are available on I/Os) or combined with the timers.
The comparators can be used for a variety of functions including:

15.2

•

Wake-up from low-power mode triggered by an analog signal,

•

Analog signal conditioning,

•

Cycle-by-cycle current control loop when combined with the DAC and a PWM output
from a timer.

COMP main features
•

Rail-to-rail comparators

•

Each comparator has positive and configurable negative inputs used for flexible voltage
selection:
–

3 I/O pins

–

DAC

–

Internal reference voltage and three submultiple values (1/4, 1/2, 3/4) provided by
scaler (buffered voltage divider)

•

Programmable hysteresis

•

Programmable speed / consumption

•

The outputs can be redirected to an I/O or to timer inputs for triggering:
–

OCREF_CLR events (for cycle-by-cycle current control)

–

Break events for fast PWM shutdowns

•

COMP1 and COMP2 comparators can be combined in a window comparator.

•

Each comparator has interrupt generation capability with wake-up from Sleep and Stop
modes (through the EXTI controller)

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RM0091

15.3

COMP functional description

15.3.1

COMP block diagram
The block diagram of the comparators is shown in Figure 52: Comparator 1 and 2 block
diagrams.
Figure 52. Comparator 1 and 2 block diagrams
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15.3.2

COMP pins and internal signals
The I/Os used as comparators inputs must be configured in analog mode in the GPIOs
registers.
The comparator output can be connected to the I/Os using the alternate function channel
given in “Alternate function mapping” table in the datasheet.
The output can also be internally redirected to a variety of timer input for the following
purposes:
•

Emergency shut-down of PWM signals, using BKIN

•

Cycle-by-cycle current control, using OCREF_CLR inputs

•

Input capture for timing measures

It is possible to have the comparator output simultaneously redirected internally and
externally.

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15.3.3

Comparator (COMP)

COMP reset and clocks
The COMP clock provided by the clock controller is synchronous with the PCLK (APB
clock).
There is no clock enable control bit provided in the RCC controller. Clock enable bit is
common for COMP and SYSCFG. COMP is only reset by system reset.

Note:

Important: The polarity selection logic and the output redirection to the port works
independently from the PCLK clock. This allows the comparator to work even in Stop mode.

15.3.4

Comparator LOCK mechanism
The comparators can be used for safety purposes, such as over-current or thermal
protection. For applications having specific functional safety requirements, it is necessary to
insure that the comparator programming cannot be altered in case of spurious register
access or program counter corruption.
For this purpose, the comparator control and status registers can be write-protected (readonly).
Once the programming is completed, using bits 30:16 and 15:0 of COMP_CSR, the
COMPxLOCK bit can be set to 1. This causes the whole COMP_CSR register to become
read-only, including the COMPxLOCK bit.
The write protection can only be reset by a MCU reset.

15.3.5

Hysteresis
The comparator includes a programmable hysteresis to avoid spurious output transitions in
case of noisy signals. The hysteresis can be disabled if it is not needed (for instance when
exiting from low-power mode) to be able to force the hysteresis value using external
components.
Figure 53. Comparator hysteresis
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15.3.6

RM0091

Power mode
The comparator power consumption versus propagation delay can be adjusted to have the
optimum trade-off for a given application.The bits COMPxMODE[1:0] in COMP_CSR
register can be programmed as follows:

15.4

•

00: High speed / full power

•

01: Medium speed / medium power

•

10: Low speed / low-power

•

11: Very-low speed / ultra-low-power

COMP interrupts
The comparator outputs are internally connected to the Extended interrupts and events
controller. Each comparator has its own EXTI line and can generate either interrupts or
events. The same mechanism is used to exit from low-power modes.
Refer to Interrupt and events section for more details.

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Comparator (COMP)

15.5

COMP registers

15.5.1

COMP control and status register (COMP_CSR)
Address offset: 0x1C
Reset value: 0x0000 0000

31

30

COMP COMP
2LOCK 2OUT

29

28

COMP2HYST
[1:0]

27
COMP
2POL

26

25

24

COMP2OUTSEL[2:0]

23
WNDW
EN

22

21

20

COMP2INSEL[2:0]

19

18

COMP2MODE
[1:0]

rwo

r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

rw/r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

COMP COMP
1LOCK 1OUT
rwo

r

COMP1HYST
[1:0]
rw/r

rw/r

COMP
1POL
rw/r

COMP1OUTSEL[2:0]
rw/r

rw/r

Res.

rw/r

COMP1INSEL[2:0]
rw/r

rw/r

rw/r

COMP1MODE
[1:0]
rw/r

rw/r

17

16

Res.

COMP2
EN
rw/r

1

0

COMP1 COMP1
SW1
EN
rw/r

rw/r

Bit 31 COMP2LOCK: Comparator 2 lock
This bit is write-once. It is set by software. It can only be cleared by a system reset.
It allows to have all control bits of comparator 2 as read-only.
0: COMP_CSR[31:16] bits are read-write.
1: COMP_CSR[31:16] bits are read-only.
Bit 30 COMP2OUT: Comparator 2 output
This read-only bit is a copy of comparator 2 output state.
0: Output is low (non-inverting input below inverting input).
1: Output is high (non-inverting input above inverting input).
Bits 29:28 COMP2HYST[1:0] Comparator 2 hysteresis
These bits control the hysteresis level.
00: No hysteresis
01: Low hysteresis
10: Medium hysteresis
11: High hysteresis
Please refer to the electrical characteristics for the hysteresis values.
Bit 27 COMP2POL: Comparator 2 output polarity
This bit is used to invert the comparator 2 output.
0: Output is not inverted
1: Output is inverted
Bits 26:24 COMP2OUTSEL[2:0]: Comparator 2 output selection
These bits select the destination of the comparator output.
000: No selection
001: Timer 1 break input
010: Timer 1 Input capture 1
011: Timer 1 OCrefclear input
100: Timer 2 input capture 4
101: Timer 2 OCrefclear input
110: Timer 3 input capture 1
111: Timer 3 OCrefclear input

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Bit 23 WNDWEN: Window mode enable
This bit connects the non-inverting input of COMP2 to COMP1’s non-inverting input, which is
simultaneously disconnected from PA3.
0: Window mode disabled
1: Window mode enabled
Bits 22:20 COMP2INSEL[2:0]: Comparator 2 inverting input selection
These bits allows to select the source connected to the inverting input of the comparator 2.
000: 1/4 of VREFINT
001: 1/2 of VREFINT
010: 3/4 of VREFINT
011: VREFINT
100: COMP2_INM4 (PA4 with DAC_OUT1 if enabled)
101: COMP2_INM5 (PA5 with DAC_OUT2 if present and enabled)
110: COMP2_INM6 (PA2)
111: Reserved
Bits 19:18 COMP2MODE[1:0]: Comparator 2 mode
These bits control the operating mode of the comparator 2 and allows to adjust the
speed/consumption.
00: High speed / full power
01: Medium speed / medium power
10: Low speed / low-power
11: Very-low speed / ultra-low power
Bit 17 Reserved, must be kept at reset value.
Bit 16 COMP2EN: Comparator 2 enable
This bit switches ON/OFF the comparator2.
0: Comparator 2 disabled
1: Comparator 2 enabled
Bit 15 COMP1LOCK: Comparator 1 lock
This bit is write-once. It is set by software. It can only be cleared by a system reset.
It allows to have all control bits of comparator 1 as read-only.
0: COMP_CSR[15:0] bits are read-write.
1: COMP_CSR[15:0] bits are read-only.
Bit 14 COMP1OUT: Comparator 1 output
This read-only bit is a copy of comparator 1 output state.
0: Output is low (non-inverting input below inverting input).
1: Output is high (non-inverting input above inverting input).
Bits 13:12 COMP1HYST[1:0] Comparator 1 hysteresis
These bits are controlling the hysteresis level.
00: No hysteresis
01: Low hysteresis
10: Medium hysteresis
11: High hysteresis
Please refer to the electrical characteristics for the hysteresis values.
Bit 11 COMP1POL: Comparator 1 output polarity
This bit is used to invert the comparator 1 output.
0: output is not inverted
1: output is inverted

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Comparator (COMP)

Bits 10:8 COMP1OUTSEL[2:0]: Comparator 1 output selection
These bits selects the destination of the comparator 1 output.
000: no selection
001: Timer 1 break input
010: Timer 1 Input capture 1
011: Timer 1 OCrefclear input
100: Timer 2 input capture 4
101: Timer 2 OCrefclear input
110: Timer 3 input capture 1
111: Timer 3 OCrefclear input
Bit 7 Reserved, must be kept at reset value.
Bits 6:4 COMP1INSEL[2:0]: Comparator 1 inverting input selection
These bits select the source connected to the inverting input of the comparator 1.
000: 1/4 of VREFINT
001: 1/2 of VREFINT
010: 3/4 of VREFINT
011: VREFINT
100: COMP1_INM4 (PA4 with DAC_OUT1 if enabled)
101: COMP1_INM5 (PA5 with DAC_OUT2 if present and enabled)
110: COMP1_INM6 (PA0)
111: Reserved
Bits 3:2 COMP1MODE[1:0]: Comparator 1 mode
These bits control the operating mode of the comparator 1 and allows to adjust the
speed/consumption.
00: High speed / full power
01: Medium speed / medium power
10: Low speed / low-power
11: Very-low speed / ultra-low power
Bit 1 COMP1SW1: Comparator 1 non inverting input DAC switch
This bit closes a switch between comparator 1 non-inverting input on PA1 and PA4 (DAC) I/O.
0: Switch open
1: Switch closed
Note: This switch is solely intended to redirect signals onto high impedance input, such as COMP1
non-inverting input (highly resistive switch).
Bit 0 COMP1EN: Comparator 1 enable
This bit switches COMP1 ON/OFF.
0: Comparator 1 disabled
1: Comparator 1 enabled

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15.5.2

RM0091

COMP register map
The following table summarizes the comparator registers.

0

0

0

0

0

0

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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COMP1MODE[1:0]

COMP1INSEL[2:0]

Res.

0

COMP1OUTSEL[2:0]

0

COMP1POL

0

COMP1HYST[1:0]

Res.

COMP2INSEL[2:0]
0

0

0

0

0

0

COMP1EN

0

COMP1SW1

0

WNDWEN

COMP2POL
0

COMP1OUT

0

COMP1LOCK

0

COMP2EN

0

COMP2MODE[1:0]

Reset value

COMP2OUTSEL[2:0]

COMP_CSR

COMP2HYST[1:0]

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

0x1C

Register

COMP2OUT

Offset

COMP2LOCK

Table 54. COMP register map and reset values

0

0

RM0091

16

Touch sensing controller (TSC)

Touch sensing controller (TSC)
This section applies to STM32F05x, STM32F04x, STM32F07x and STM32F09x devices
only.

16.1

Introduction
The touch sensing controller provides a simple solution for adding capacitive sensing
functionality to any application. Capacitive sensing technology is able to detect finger
presence near an electrode which is protected from direct touch by a dielectric (for example
glass, plastic). The capacitive variation introduced by the finger (or any conductive object) is
measured using a proven implementation based on a surface charge transfer acquisition
principle.
The touch sensing controller is fully supported by the STMTouch touch sensing firmware
library which is free to use and allows touch sensing functionality to be implemented reliably
in the end application.

16.2

TSC main features
The touch sensing controller has the following main features:

Note:

•

Proven and robust surface charge transfer acquisition principle

•

Supports up to 24 capacitive sensing channels

•

Up to 8 capacitive sensing channels can be acquired in parallel offering a very good
response time

•

Spread spectrum feature to improve system robustness in noisy environments

•

full hardware management of the charge transfer acquisition sequence

•

Programmable charge transfer frequency

•

Programmable sampling capacitor I/O pin

•

Programmable channel I/O pin

•

Programmable max count value to avoid long acquisition when a channel is faulty

•

Dedicated end of acquisition and max count error flags with interrupt capability

•

One sampling capacitor for up to 3 capacitive sensing channels to reduce the system
components

•

Compatible with proximity, touchkey, linear and rotary touch sensor implementation

•

Designed to operate with STMTouch touch sensing firmware library

The number of capacitive sensing channels is dependent on the size of the packages and
subject to IO availability.

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16.3

TSC functional description

16.3.1

TSC block diagram
The block diagram of the touch sensing controller is shown in Figure 54: TSC block
diagram.
Figure 54. TSC block diagram

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16.3.2

Surface charge transfer acquisition overview
The surface charge transfer acquisition is a proven, robust and efficient way to measure a
capacitance. It uses a minimum number of external components to operate with a single
ended electrode type. This acquisition is designed around an analog I/O group which is
composed of four GPIOs (see Figure 55). Several analog I/O groups are available to allow
the acquisition of several capacitive sensing channels simultaneously and to support a
larger number of capacitive sensing channels. Within a same analog I/O group, the
acquisition of the capacitive sensing channels is sequential.
One of the GPIOs is dedicated to the sampling capacitor CS. Only one sampling capacitor
I/O per analog I/O group must be enabled at a time.

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Touch sensing controller (TSC)
The remaining GPIOs are dedicated to the electrodes and are commonly called channels.
For some specific needs (such as proximity detection), it is possible to simultaneously
enable more than one channel per analog I/O group.
Figure 55. Surface charge transfer analog I/O group structure

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Note:

Gx_IOy where x is the analog I/O group number and y the GPIO number within the selected
group.
The surface charge transfer acquisition principle consists of charging an electrode
capacitance (CX) and transferring a part of the accumulated charge into a sampling
capacitor (CS). This sequence is repeated until the voltage across CS reaches a given
threshold (VIH in our case). The number of charge transfers required to reach the threshold
is a direct representation of the size of the electrode capacitance.
The Table 55 details the charge transfer acquisition sequence of the capacitive sensing
channel 1. States 3 to 7 are repeated until the voltage across CS reaches the given
threshold. The same sequence applies to the acquisition of the other channels. The
electrode serial resistor RS improves the ESD immunity of the solution.

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RM0091
Table 55. Acquisition sequence summary

State

G1_IO1
(electrode)

G1_IO2
(sampling)

#1

Input floating
with analog
switch closed

Output opendrain low with
analog switch
closed

#2
#3

G1_IO4
(electrode)

State description

Input floating with analog switch Discharge all CX and
CS
closed

Input floating
Output pushpull high

Dead time

Input floating

#4
#5

G1_IO3
(electrode)

Charge CX1

Input floating
Input floating with analog switch
closed

Dead time
Input floating

Charge transfer from
CX1 to CS

#6

Input floating

Dead time

#7

Input floating

Measure CS voltage

The voltage variation over the time on the sampling capacitor CS is detailed below:
Figure 56. Sampling capacitor voltage variation

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16.3.3

Reset and clocks
The TSC clock source is the AHB clock (HCLK). Two programmable prescalers are used to
generate the pulse generator and the spread spectrum internal clocks:
•

The pulse generator clock (PGCLK) is defined using the PGPSC[2:0] bits of the
TSC_CR register

•

The spread spectrum clock (SSCLK) is defined using the SSPSC bit of the TSC_CR
register

The Reset and Clock Controller (RCC) provides dedicated bits to enable the touch sensing
controller clock and to reset this peripheral. For more information, please refer to Section 6:
Reset and clock control (RCC).

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16.3.4

Touch sensing controller (TSC)

Charge transfer acquisition sequence
An example of a charge transfer acquisition sequence is detailed in Figure 57.
Figure 57. Charge transfer acquisition sequence
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For higher flexibility, the charge transfer frequency is fully configurable. Both the pulse high
state (charge of CX) and the pulse low state (transfer of charge from CX to CS) duration can
be defined using the CTPH[3:0] and CTPL[3:0] bits in the TSC_CR register. The standard
range for the pulse high and low states duration is 500 ns to 2 µs. To ensure a correct
measurement of the electrode capacitance, the pulse high state duration must be set to
ensure that CX is always fully charged.
A dead time where both the sampling capacitor I/O and the channel I/O are in input floating
state is inserted between the pulse high and low states to ensure an optimum charge
transfer acquisition sequence. This state duration is 2 periods of HCLK.
At the end of the pulse high state and if the spread spectrum feature is enabled, a variable
number of periods of the SSCLK clock are added.
The reading of the sampling capacitor I/O, to determine if the voltage across CS has
reached the given threshold, is performed at the end of the pulse low state and its duration
is one period of HCLK.
Note:

The following TSC control register configurations are forbidden:

•
•
•

bits PGPSC are set to ‘000’ and bits CTPL are set to ‘0000’
bits PGPSC are set to ‘000’ and bits CTPL are set to ‘0001’
bits PGPSC are set to ‘001’ and bits CTPL are set to ‘0000’

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16.3.5

RM0091

Spread spectrum feature
The spread spectrum feature allows to generate a variation of the charge transfer
frequency. This is done to improve the robustness of the charge transfer acquisition in noisy
environments and also to reduce the induced emission. The maximum frequency variation
is in the range of 10% to 50% of the nominal charge transfer period. For instance, for a
nominal charge transfer frequency of 250 kHz (4 µs), the typical spread spectrum deviation
is 10% (400 ns) which leads to a minimum charge transfer frequency of ~227 kHz.
In practice, the spread spectrum consists of adding a variable number of SSCLK periods to
the pulse high state using the principle shown below:
Figure 58. Spread spectrum variation principle

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The table below details the maximum frequency deviation with different HCLK settings:
Table 56. Spread spectrum deviation versus AHB clock frequency
fHCLK

Spread spectrum step

Maximum spread spectrum deviation

24 MHz

41.6 ns

10666.6 ns

48 MHz

20.8 ns

5333.3 ns

The spread spectrum feature can be disabled/enabled using the SSE bit in the TSC_CR
register. The frequency deviation is also configurable to accommodate the device HCLK
clock frequency and the selected charge transfer frequency through the SSPSC and
SSD[6:0] bits in the TSC_CR register.

16.3.6

Max count error
The max count error prevents long acquisition times resulting from a faulty capacitive
sensing channel. It consists of specifying a maximum count value for the analog I/O group
counters. This maximum count value is specified using the MCV[2:0] bits in the TSC_CR
register. As soon as an acquisition group counter reaches this maximum value, the ongoing
acquisition is stopped and the end of acquisition (EOAF bit) and max count error (MCEF bit)
flags are both set. An interrupt can also be generated if the corresponding end of acquisition
(EOAIE bit) or/and max count error (MCEIE bit) interrupt enable bits are set.

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16.3.7

Touch sensing controller (TSC)

Sampling capacitor I/O and channel I/O mode selection
To allow the GPIOs to be controlled by the touch sensing controller, the corresponding
alternate function must be enabled through the standard GPIO registers and the GPIOxAFR
registers.
The GPIOs modes controlled by the TSC are defined using the TSC_IOSCR and
TSC_IOCCR register.
When there is no ongoing acquisition, all the I/Os controlled by the touch sensing controller
are in default state. While an acquisition is ongoing, only unused I/Os (neither defined as
sampling capacitor I/O nor as channel I/O) are in default state. The IODEF bit in the
TSC_CR register defines the configuration of the I/Os which are in default state. The table
below summarizes the configuration of the I/O depending on its mode.
Table 57. I/O state depending on its mode and IODEF bit value
IODEF bit

Acquisition
status

Unused I/O
mode

Electrode I/O
mode

Sampling
capacitor I/O
mode

0
(output push-pull
low)

No

Output push-pull
low

Output push-pull
low

Output push-pull
low

0
(output push-pull
low)

ongoing

Output push-pull
low

-

-

1
(input floating)

No

Input floating

Input floating

Input floating

1
(input floating)

ongoing

Input floating

-

-

Unused I/O mode
An unused I/O corresponds to a GPIO controlled by the TSC peripheral but not defined as
an electrode I/O nor as a sampling capacitor I/O.
Sampling capacitor I/O mode
To allow the control of the sampling capacitor I/O by the TSC peripheral, the corresponding
GPIO must be first set to alternate output open drain mode and then the corresponding
Gx_IOy bit in the TSC_IOSCR register must be set.
Only one sampling capacitor per analog I/O group must be enabled at a time.
Channel I/O mode
To allow the control of the channel I/O by the TSC peripheral, the corresponding GPIO must
be first set to alternate output push-pull mode and the corresponding Gx_IOy bit in the
TSC_IOCCR register must be set.
For proximity detection where a higher equivalent electrode surface is required or to speedup the acquisition process, it is possible to enable and simultaneously acquire several
channels belonging to the same analog I/O group.

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Note:

During the acquisition phase and even if the TSC peripheral alternate function is not
enabled, as soon as the TSC_IOSCR or TSC_IOCCR bit is set, the corresponding GPIO
analog switch is automatically controlled by the touch sensing controller.

16.3.8

Acquisition mode
The touch sensing controller offers two acquisition modes:
•

Normal acquisition mode: the acquisition starts as soon as the START bit in the
TSC_CR register is set.

•

Synchronized acquisition mode: the acquisition is enabled by setting the START bit in
the TSC_CR register but only starts upon the detection of a falling edge or a rising
edge and high level on the SYNC input pin. This mode is useful for synchronizing the
capacitive sensing channels acquisition with an external signal without additional CPU
load.

The GxE bits in the TSC_IOGCSR registers specify which analog I/O groups are enabled
(corresponding counter is counting). The CS voltage of a disabled analog I/O group is not
monitored and this group does not participate in the triggering of the end of acquisition flag.
However, if the disabled analog I/O group contains some channels, they will be pulsed.
When the CS voltage of an enabled analog I/O group reaches the given threshold, the
corresponding GxS bit of the TSC_IOGCSR register is set. When the acquisition of all
enabled analog I/O groups is complete (all GxS bits of all enabled analog I/O groups are
set), the EOAF flag in the TSC_ISR register is set. An interrupt request is generated if the
EOAIE bit in the TSC_IER register is set.
In the case that a max count error is detected, the ongoing acquisition is stopped and both
the EOAF and MCEF flags in the TSC_ISR register are set. Interrupt requests can be
generated for both events if the corresponding bits (EOAIE and MCEIE bits of the TSCIER
register) are set. Note that when the max count error is detected the remaining GxS bits in
the enabled analog I/O groups are not set.
To clear the interrupt flags, the corresponding EOAIC and MCEIC bits in the TSC_ICR
register must be set.
The analog I/O group counters are cleared when a new acquisition is started. They are
updated with the number of charge transfer cycles generated on the corresponding
channel(s) upon the completion of the acquisition.
For code example refer to the Appendix section A.18.1: TSC configuration code example.

16.3.9

I/O hysteresis and analog switch control
In order to offer a higher flexibility, the touch sensing controller also allows to take the control
of the Schmitt trigger hysteresis and analog switch of each Gx_IOy. This control is available
whatever the I/O control mode is (controlled by standard GPIO registers or other
peripherals) assuming that the touch sensing controller is enabled. This may be useful to
perform a different acquisition sequence or for other purposes.
In order to improve the system immunity, the Schmitt trigger hysteresis of the GPIOs
controlled by the TSC must be disabled by resetting the corresponding Gx_IOy bit in the
TSC_IOHCR register.

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16.4

Touch sensing controller (TSC)

TSC low-power modes
Table 58. Effect of low-power modes on TSC
Mode
Sleep

Description
No effect
TSC interrupts cause the device to exit Sleep mode.

Stop

TSC registers are frozen
Standby The TSC stops its operation until the Stop or Standby mode is exited.

16.5

TSC interrupts
Table 59. Interrupt control bits
Interrupt event

Enable
control bit

Event flag

Clear flag
bit

Exit the
Sleep
mode

Exit the
Stop mode

Exit the
Standby
mode

End of acquisition

EOAIE

EOAIF

EOAIC

yes

no

no

Max count error

MCEIE

MCEIF

MCEIC

yes

no

no

For code example refer to the Appendix section A.18.2: TSC interrupt code example.

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TSC registers
Refer to Section 1.1 on page 42 of the reference manual for a list of abbreviations used in
register descriptions.
The peripheral registers can be accessed by words (32-bit).

16.6.1

TSC control register (TSC_CR)
Address offset: 0x00
Reset value: 0x0000 0000

31

30

29

28

27

CTPH[3:0]

26

25

24

23

22

21

CTPL[3:0]

20

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

rw

PGPSC[2:0]
rw

rw

Res.
rw

Res.

18

17

SSD[6:0]

rw

SSPSC

19

Res.

Res.

MCV[2:0]
rw

rw

rw

16
SSE

rw

rw

rw

rw

4

3

2

1

0

IODEF

SYNC
POL

AM

START

TSCE

rw

rw

rw

rw

rw

Bits 31:28 CTPH[3:0]: Charge transfer pulse high
These bits are set and cleared by software. They define the duration of the high state of the
charge transfer pulse (charge of CX).
0000: 1x tPGCLK
0001: 2x tPGCLK
...
1111: 16x tPGCLK
Note: These bits must not be modified when an acquisition is ongoing.
Bits 27:24 CTPL[3:0]: Charge transfer pulse low
These bits are set and cleared by software. They define the duration of the low state of the
charge transfer pulse (transfer of charge from CX to CS).
0000: 1x tPGCLK
0001: 2x tPGCLK
...
1111: 16x tPGCLK
Note: These bits must not be modified when an acquisition is ongoing.
Note: Some configurations are forbidden. Please refer to the Section 16.3.4: Charge transfer
acquisition sequence for details.
Bits 23:17 SSD[6:0]: Spread spectrum deviation
These bits are set and cleared by software. They define the spread spectrum deviation which
consists in adding a variable number of periods of the SSCLK clock to the charge transfer
pulse high state.
0000000: 1x tSSCLK
0000001: 2x tSSCLK
...
1111111: 128x tSSCLK
Note: These bits must not be modified when an acquisition is ongoing.

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Touch sensing controller (TSC)

Bit 16 SSE: Spread spectrum enable
This bit is set and cleared by software to enable/disable the spread spectrum feature.
0: Spread spectrum disabled
1: Spread spectrum enabled
Note: This bit must not be modified when an acquisition is ongoing.
Bit 15 SSPSC: Spread spectrum prescaler
This bit is set and cleared by software. It selects the AHB clock divider used to generate the
spread spectrum clock (SSCLK).
0: fHCLK
1: fHCLK /2
Note: This bit must not be modified when an acquisition is ongoing.
Bits 14:12 PGPSC[2:0]: Pulse generator prescaler
These bits are set and cleared by software.They select the AHB clock divider used to generate
the pulse generator clock (PGCLK).
000: fHCLK
001: fHCLK /2
010: fHCLK /4
011: fHCLK /8
100: fHCLK /16
101: fHCLK /32
110: fHCLK /64
111: fHCLK /128
Note: These bits must not be modified when an acquisition is ongoing.
Note: Some configurations are forbidden. Please refer to the Section 16.3.4: Charge transfer
acquisition sequence for details.
Bits 11:8 Reserved, must be kept at reset value.
Bits 7:5 MCV[2:0]: Max count value
These bits are set and cleared by software. They define the maximum number of charge
transfer pulses that can be generated before a max count error is generated.
000: 255
001: 511
010: 1023
011: 2047
100: 4095
101: 8191
110: 16383
111: reserved
Note: These bits must not be modified when an acquisition is ongoing.
Bit 4 IODEF: I/O Default mode
This bit is set and cleared by software. It defines the configuration of all the TSC I/Os when
there is no ongoing acquisition. When there is an ongoing acquisition, it defines the
configuration of all unused I/Os (not defined as sampling capacitor I/O or as channel I/O).
0: I/Os are forced to output push-pull low
1: I/Os are in input floating
Note: This bit must not be modified when an acquisition is ongoing.
Bit 3 SYNCPOL: Synchronization pin polarity
This bit is set and cleared by software to select the polarity of the synchronization input pin.
0: Falling edge only
1: Rising edge and high level

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Bit 2 AM: Acquisition mode
This bit is set and cleared by software to select the acquisition mode.
0: Normal acquisition mode (acquisition starts as soon as START bit is set)
1: Synchronized acquisition mode (acquisition starts if START bit is set and when the
selected signal is detected on the SYNC input pin)
Note: This bit must not be modified when an acquisition is ongoing.
Bit 1 START: Start a new acquisition
This bit is set by software to start a new acquisition. It is cleared by hardware as soon as the
acquisition is complete or by software to cancel the ongoing acquisition.
0: Acquisition not started
1: Start a new acquisition
Bit 0 TSCE: Touch sensing controller enable
This bit is set and cleared by software to enable/disable the touch sensing controller.
0: Touch sensing controller disabled
1: Touch sensing controller enabled
Note: When the touch sensing controller is disabled, TSC registers settings have no effect.

16.6.2

TSC interrupt enable register (TSC_IER)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

MCEIE

EOAIE

rw

rw

Bits 31:2 Reserved, must be kept at reset value.
Bit 1 MCEIE: Max count error interrupt enable
This bit is set and cleared by software to enable/disable the max count error interrupt.
0: Max count error interrupt disabled
1: Max count error interrupt enabled
Bit 0 EOAIE: End of acquisition interrupt enable
This bit is set and cleared by software to enable/disable the end of acquisition interrupt.
0: End of acquisition interrupt disabled
1: End of acquisition interrupt enabled

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Touch sensing controller (TSC)

16.6.3

TSC interrupt clear register (TSC_ICR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

MCEIC EOAIC
rw

rw

Bits 31:2 Reserved, must be kept at reset value.
Bit 1 MCEIC: Max count error interrupt clear
This bit is set by software to clear the max count error flag and it is cleared by hardware when
the flag is reset. Writing a ‘0’ has no effect.
0: No effect
1: Clears the corresponding MCEF of the TSC_ISR register
Bit 0 EOAIC: End of acquisition interrupt clear
This bit is set by software to clear the end of acquisition flag and it is cleared by hardware
when the flag is reset. Writing a ‘0’ has no effect.
0: No effect
1: Clears the corresponding EOAF of the TSC_ISR register

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16.6.4

RM0091

TSC interrupt status register (TSC_ISR)
Address offset: 0x0C
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

MCEF

EOAF

r

r

Bits 31:2 Reserved, must be kept at reset value.
Bit 1 MCEF: Max count error flag
This bit is set by hardware as soon as an analog I/O group counter reaches the max count
value specified. It is cleared by software writing 1 to the bit MCEIC of the TSC_ICR register.
0: No max count error (MCE) detected
1: Max count error (MCE) detected
Bit 0 EOAF: End of acquisition flag
This bit is set by hardware when the acquisition of all enabled group is complete (all GxS bits
of all enabled analog I/O groups are set or when a max count error is detected). It is cleared by
software writing 1 to the bit EOAIC of the TSC_ICR register.
0: Acquisition is ongoing or not started
1: Acquisition is complete

16.6.5

TSC I/O hysteresis control register (TSC_IOHCR)
Address offset: 0x10
Reset value: 0xFFFF FFFF

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

G8_IO4 G8_IO3 G8_IO2 G8_IO1 G7_IO4 G7_IO3 G7_IO2 G7_IO1 G6_IO4 G6_IO3 G6_IO2 G6_IO1 G5_IO4 G5_IO3 G5_IO2 G5_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

G4_IO4 G4_IO3 G4_IO2 G4_IO1 G3_IO4 G3_IO3 G3_IO2 G3_IO1 G2_IO4 G2_IO3 G2_IO2 G2_IO1 G1_IO4 G1_IO3 G1_IO2 G1_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 Gx_IOy: Gx_IOy Schmitt trigger hysteresis mode
These bits are set and cleared by software to enable/disable the Gx_IOy Schmitt trigger
hysteresis.
0: Gx_IOy Schmitt trigger hysteresis disabled
1: Gx_IOy Schmitt trigger hysteresis enabled
Note: These bits control the I/O Schmitt trigger hysteresis whatever the I/O control mode is
(even if controlled by standard GPIO registers).

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Touch sensing controller (TSC)

16.6.6

TSC I/O analog switch control register (TSC_IOASCR)
Address offset: 0x18
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

G8_IO4 G8_IO3 G8_IO2 G8_IO1 G7_IO4 G7_IO3 G7_IO2 G7_IO1 G6_IO4 G6_IO3 G6_IO2 G6_IO1 G5_IO4 G5_IO3 G5_IO2 G5_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

G4_IO4 G4_IO3 G4_IO2 G4_IO1 G3_IO4 G3_IO3 G3_IO2 G3_IO1 G2_IO4 G2_IO3 G2_IO2 G2_IO1 G1_IO4 G1_IO3 G1_IO2 G1_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 Gx_IOy: Gx_IOy analog switch enable
These bits are set and cleared by software to enable/disable the Gx_IOy analog switch.
0: Gx_IOy analog switch disabled (opened)
1: Gx_IOy analog switch enabled (closed)
Note: These bits control the I/O analog switch whatever the I/O control mode is (even if
controlled by standard GPIO registers).

16.6.7

TSC I/O sampling control register (TSC_IOSCR)
Address offset: 0x20
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

G8_IO4 G8_IO3 G8_IO2 G8_IO1 G7_IO4 G7_IO3 G7_IO2 G7_IO1 G6_IO4 G6_IO3 G6_IO2 G6_IO1 G5_IO4 G5_IO3 G5_IO2 G5_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

G4_IO4 G4_IO3 G4_IO2 G4_IO1 G3_IO4 G3_IO3 G3_IO2 G3_IO1 G2_IO4 G2_IO3 G2_IO2 G2_IO1 G1_IO4 G1_IO3 G1_IO2 G1_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 Gx_IOy: Gx_IOy sampling mode
These bits are set and cleared by software to configure the Gx_IOy as a sampling capacitor
I/O. Only one I/O per analog I/O group must be defined as sampling capacitor.
0: Gx_IOy unused
1: Gx_IOy used as sampling capacitor
Note: These bits must not be modified when an acquisition is ongoing.
During the acquisition phase and even if the TSC peripheral alternate function is not
enabled, as soon as the TSC_IOSCR bit is set, the corresponding GPIO analog switch
is automatically controlled by the touch sensing controller.

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16.6.8

RM0091

TSC I/O channel control register (TSC_IOCCR)
Address offset: 0x28
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

G8_IO4 G8_IO3 G8_IO2 G8_IO1 G7_IO4 G7_IO3 G7_IO2 G7_IO1 G6_IO4 G6_IO3 G6_IO2 G6_IO1 G5_IO4 G5_IO3 G5_IO2 G5_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

G4_IO4 G4_IO3 G4_IO2 G4_IO1 G3_IO4 G3_IO3 G3_IO2 G3_IO1 G2_IO4 G2_IO3 G2_IO2 G2_IO1 G1_IO4 G1_IO3 G1_IO2 G1_IO1
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 Gx_IOy: Gx_IOy channel mode
These bits are set and cleared by software to configure the Gx_IOy as a channel I/O.
0: Gx_IOy unused
1: Gx_IOy used as channel
Note: These bits must not be modified when an acquisition is ongoing.
During the acquisition phase and even if the TSC peripheral alternate function is not
enabled, as soon as the TSC_IOCCR bit is set, the corresponding GPIO analog switch
is automatically controlled by the touch sensing controller.

16.6.9

TSC I/O group control status register (TSC_IOGCSR)
Address offset: 0x30
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

G8S

G7S

G6S

G5S

G4S

G3S

G2S

G1S

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

G8E

G7E

G6E

G5E

G4E

G3E

G2E

G1E

rw

rw

rw

rw

rw

rw

rw

rw

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Touch sensing controller (TSC)

Bits 31:24 Reserved, must be kept at reset value.
Bits 23:16 GxS: Analog I/O group x status
These bits are set by hardware when the acquisition on the corresponding enabled analog I/O
group x is complete. They are cleared by hardware when a new acquisition is started.
0: Acquisition on analog I/O group x is ongoing or not started
1: Acquisition on analog I/O group x is complete
Note: When a max count error is detected the remaining GxS bits of the enabled analog I/O
groups are not set.
Bits 15:8 Reserved, must be kept at reset value.
Bits 7:0 GxE: Analog I/O group x enable
These bits are set and cleared by software to enable/disable the acquisition (counter is
counting) on the corresponding analog I/O group x.
0: Acquisition on analog I/O group x disabled
1: Acquisition on analog I/O group x enabled

16.6.10

TSC I/O group x counter register (TSC_IOGxCR) (x = 1..8)
Address offset: 0x30 + 0x04 x Analog I/O group number
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

r

r

r

r

r

r

CNT[13:0]
r

r

r

r

r

r

r

r

Bits 31:14 Reserved, must be kept at reset value.
Bits 13:0 CNT[13:0]: Counter value
These bits represent the number of charge transfer cycles generated on the analog I/O group
x to complete its acquisition (voltage across CS has reached the threshold).

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318/1004

TSC_IOG2CR
0
0
0
0
0
0
0
0
0
0

0x002C
Reserved

Reset value

DocID018940 Rev 9

Reset value

0

0
G1_IO3
G1_IO2
G1_IO1

G2_IO4
G2_IO3
G2_IO2
G2_IO1
G1_IO4
G1_IO3
G1_IO2
G1_IO1

G3_IO4
G3_IO3
G3_IO2
G3_IO1
G2_IO4
G2_IO3
G2_IO2

0

0

0

0

0

0

0

0

0

0

0

0

0

0

G2_IO1

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

0

0

CNT[13:0]

CNT[13:0]

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

G1_IO4
G1_IO3
G1_IO2
G1_IO1

Reset value

Reset value
EOAIC

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

TSCE

0
0
0

EOAIE

AM

Res.

START

Res.

0
Res.

Res.

IODEF

Res.

Res.

Res.

Res.

Res.

SYNCPOL

Res.

Res.

Res.

Res.

PGPSC[2:0]

0
MCEIE

Reset value

EOAF

Res.

Res.

0

MCEIC

Res.

0

MCEF

Res.

Res.

0

Res.

Res.

Res.

Res.

MCV
[2:0]

Res.

Res.

Res.

TSC_IER

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0
Res.

0

Res.

0

Res.

0

Res.

Res.

0

Res.

Res.

Res.

Res.

0

G1E

G1_IO4

G3_IO1

G4_IO1

Res.

Res.

SSE
SSPSC

0

G2E

G2_IO1

G3_IO2

G4_IO2

Res.

0

G3E

G2_IO2

G3_IO3

G4_IO3

Res.

Res.

Res.

Res.

0

G4E

G2_IO3

G3_IO4

G4_IO4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

G5E

G1_IO1

0
G1_IO2

0
G1_IO3

0
G1_IO4

0
G2_IO1

Reset value
G2_IO2

0

G2_IO3

0x0024
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

G6E

0

G7E

0
G2_IO4

0

G2_IO4

0

G8E

0
G3_IO1

0

G3_IO1

0

Res.

0
G3_IO2

0

G3_IO2

0

Res.

0
G3_IO3

0
G3_IO4

0

G3_IO3

Reset value

G3_IO4

0

Res.

0

Res.

0
G4_IO1

0

G4_IO1

0

G4_IO1

0

Res.

0
G4_IO2

0
G4_IO3

0

G4_IO2

0

G4_IO3

0

G4_IO2

0

G4_IO3

0

Res.

0

Res.

Reset value
G4_IO4

1

G4_IO4

1
G5_IO1

G5_IO3

1
G5_IO2

G5_IO4

1

G5_IO1

G5_IO3

G6_IO1

1

G5_IO2

G5_IO4

G6_IO2

1

G5_IO1

G5_IO3

G6_IO1

G6_IO3

1

G5_IO2

G5_IO4

G6_IO2

G6_IO4

1

Res.

G5_IO3

G6_IO1

G6_IO3

G7_IO1

1

Res.

G5_IO4

G6_IO2

G6_IO4

G7_IO2

1

G4_IO4

G6_IO1

G6_IO3

G7_IO1

G7_IO3

1

Res.

G6_IO2

G6_IO4

G7_IO2

G7_IO4

1

Res.

G6_IO3

G7_IO1

G7_IO3

G8_IO1

1

Res.

G1S

0

Res.

G6_IO4

G7_IO2

G7_IO4

G8_IO2

1

G5_IO1

G2S

0

Res.

G7_IO1

G7_IO3

G8_IO1

G8_IO3
0
SSD[6:0]

Res.

G3S

0

Res.

G7_IO2

G7_IO4

G8_IO2

G8_IO4

Reset value

G5_IO2

G4S

0

Res.

G7_IO3

G8_IO1

TSC_IOHCR

Res.

G5S

0

Res.

G7_IO4

G8_IO2

0x001C

Res.

G6S

0

Res.

G8_IO1

0x0014

Res.

Res.

G7S

0

Res.

TSC_IOCCR
G8_IO2

G8_IO3

0
CTPL[3:0]

Res.

Res.

G8S

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

TSC_IOG1CR

Res.

TSC_IOASCR
G8_IO4

Reset value
CTPH[3:0]

Res.

0x0034

TSC_IOGCSR

Res.

0x0030
TSC_ISR

Res.

0x0028
TSC_IOSCR
G8_IO3

0x0020
G8_IO4

0x0018

G8_IO3

0x0010

G8_IO4

0x000C
TSC_ICR

Res.

0x0008

Res.

0x0004
TSC_CR

Res.

0x0000

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

16.6.11

Res.

Touch sensing controller (TSC)
RM0091

TSC register map
Table 60. TSC register map and reset values

0
0

0
0

0
0

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

Reserved

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Reserved

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Reserved

RM0091

Touch sensing controller (TSC)

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG3CR

Res.

0x003C

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 60. TSC register map and reset values (continued)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

CNT[13:0]
0

Reset value

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG8CR

0

CNT[13:0]
0

Reset value

0x0050

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG7CR

0

CNT[13:0]
0

Reset value

0x004C

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG6CR

0

CNT[13:0]
0

Reset value

0x0048

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG5CR

0

CNT[13:0]
0

Reset value

0x0044

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TSC_IOG4CR

Res.

Reset value

0x0040

CNT[13:0]

0

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

DocID018940 Rev 9

319/1004
319

Advanced-control timers (TIM1)

RM0091

17

Advanced-control timers (TIM1)

17.1

TIM1 introduction
The advanced-control timers (TIM1) consist of a 16-bit auto-reload counter driven by a
programmable prescaler.
It may be used for a variety of purposes, including measuring the pulse lengths of input
signals (input capture) or generating output waveforms (output compare, PWM,
complementary PWM with dead-time insertion).
Pulse lengths and waveform periods can be modulated from a few microseconds to several
milliseconds using the timer prescaler and the RCC clock controller prescalers.
The advanced-control (TIM1) and general-purpose (TIMx) timers are completely
independent, and do not share any resources. They can be synchronized together as
described in Section 17.3.20.

17.2

TIM1 main features
TIM1 timer features include:

320/1004

•

16-bit up, down, up/down auto-reload counter.

•

16-bit programmable prescaler allowing dividing (also “on the fly”) the counter clock
frequency either by any factor between 1 and 65535.

•

Up to 4 independent channels for:
–

Input Capture

–

Output Compare

–

PWM generation (Edge- and Center-aligned modes)

–

One-pulse mode output

•

Complementary outputs with programmable dead-time

•

Synchronization circuit to control the timer with external signals and to interconnect
several timers together.

•

Repetition counter to update the timer registers only after a given number of cycles of
the counter.

•

Break input to put the timer’s output signals in reset state or in a known state.

•

Interrupt/DMA generation on the following events:
–

Update: counter overflow/underflow, counter initialization (by software or
internal/external trigger)

–

Trigger event (counter start, stop, initialization or count by internal/external trigger)

–

Input capture

–

Output compare

–

Break input

•

Supports incremental (quadrature) encoder and hall-sensor circuitry for positioning
purposes

•

Trigger input for external clock or cycle-by-cycle current management

DocID018940 Rev 9

RM0091

Advanced-control timers (TIM1)
Figure 59. Advanced-control timer block diagram
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DocID018940 Rev 9

321/1004
392

Advanced-control timers (TIM1)

RM0091

17.3

TIM1 functional description

17.3.1

Time-base unit
The main block of the programmable advanced-control timer is a 16-bit counter with its
related auto-reload register. The counter can count up, down or both up and down. The
counter clock can be divided by a prescaler.
The counter, the auto-reload register and the prescaler register can be written or read by
software. This is true even when the counter is running.
The time-base unit includes:
•

Counter register (TIMx_CNT)

•

Prescaler register (TIMx_PSC)

•

Auto-reload register (TIMx_ARR)

•

Repetition counter register (TIMx_RCR)

The auto-reload register is preloaded. Writing to or reading from the auto-reload register
accesses the preload register. The content of the preload register are transferred into the
shadow register permanently or at each update event (UEV), depending on the auto-reload
preload enable bit (ARPE) in TIMx_CR1 register. The update event is sent when the counter
reaches the overflow (or underflow when downcounting) and if the UDIS bit equals 0 in the
TIMx_CR1 register. It can also be generated by software. The generation of the update
event is described in detailed for each configuration.
The counter is clocked by the prescaler output CK_CNT, which is enabled only when the
counter enable bit (CEN) in TIMx_CR1 register is set (refer also to the slave mode controller
description to get more details on counter enabling).
Note that the counter starts counting 1 clock cycle after setting the CEN bit in the TIMx_CR1
register.

Prescaler description
The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It
is based on a 16-bit counter controlled through a 16-bit register (in the TIMx_PSC register).
It can be changed on the fly as this control register is buffered. The new prescaler ratio is
taken into account at the next update event.
Figure 61 and Figure 62 give some examples of the counter behavior when the prescaler
ratio is changed on the fly:

322/1004

DocID018940 Rev 9

RM0091

Advanced-control timers (TIM1)
Figure 60. Counter timing diagram with prescaler division change from 1 to 2

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Figure 61. Counter timing diagram with prescaler division change from 1 to 4

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069

DocID018940 Rev 9

323/1004
392

Advanced-control timers (TIM1)

17.3.2

RM0091

Counter modes
Upcounting mode
In upcounting mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register), then restarts from 0 and generates a counter overflow event.
If the repetition counter is used, the update event (UEV) is generated after upcounting is
repeated for the number of times programmed in the repetition counter register
(TIMx_RCR). Else the update event is generated at each counter overflow.
Setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event.
The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until the UDIS bit has been written to 0.
However, the counter restarts from 0, as well as the counter of the prescaler (but the
prescale rate does not change). In addition, if the URS bit (update request selection) in
TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without
setting the UIF flag (thus no interrupt or DMA request is sent). This is to avoid generating
both update and capture interrupts when clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The repetition counter is reloaded with the content of TIMx_RCR register,

•

The auto-reload shadow register is updated with the preload value (TIMx_ARR),

•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register).

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.

324/1004

DocID018940 Rev 9

RM0091

Advanced-control timers (TIM1)
Figure 62. Counter timing diagram, internal clock divided by 1

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Figure 63. Counter timing diagram, internal clock divided by 2

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DocID018940 Rev 9

325/1004
392

Advanced-control timers (TIM1)

RM0091

Figure 64. Counter timing diagram, internal clock divided by 4

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Figure 65. Counter timing diagram, internal clock divided by N

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326/1004

DocID018940 Rev 9

RM0091

Advanced-control timers (TIM1)
Figure 66. Counter timing diagram, update event when ARPE=0
(TIMx_ARR not preloaded)
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Figure 67. Counter timing diagram, update event when ARPE=1
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DocID018940 Rev 9



069

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392

Advanced-control timers (TIM1)

RM0091

Downcounting mode
In downcounting mode, the counter counts from the auto-reload value (content of the
TIMx_ARR register) down to 0, then restarts from the auto-reload value and generates a
counter underflow event.
If the repetition counter is used, the update event (UEV) is generated after downcounting is
repeated for the number of times programmed in the repetition counter register
(TIMx_RCR). Else the update event is generated at each counter underflow.
Setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event.
The UEV update event can be disabled by software by setting the UDIS bit in TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until UDIS bit has been written to 0.
However, the counter restarts from the current auto-reload value, whereas the counter of the
prescaler restarts from 0 (but the prescale rate doesn’t change).
In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the
UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or
DMA request is sent). This is to avoid generating both update and capture interrupts when
clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The repetition counter is reloaded with the content of TIMx_RCR register

•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register)

•

The auto-reload active register is updated with the preload value (content of the
TIMx_ARR register). Note that the auto-reload is updated before the counter is
reloaded, so that the next period is the expected one

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.
Figure 68. Counter timing diagram, internal clock divided by 1
CK_PSC
CNT_EN
Timer clock = CK_CNT
Counter register

05

04 03 02 01 00 36 35 34 33 32 31 30 2F

Counter underflow (cnt_udf)
Update event (UEV)
Update interrupt flag (UIF)

328/1004

DocID018940 Rev 9

RM0091

Advanced-control timers (TIM1)
Figure 69. Counter timing diagram, internal clock divided by 2
CK_PSC
CNT_EN
Timer clock = CK_CNT
Counter register

0002

0001 0000

0036

0035

0034

0033

Counter underflow
Update event (UEV)
Update interrupt flag (UIF)

Figure 70. Counter timing diagram, internal clock divided by 4
CK_PSC
CNT_EN
Timer clock = CK_CNT
Counter register

0001

0000

0036

0035

Counter underflow
Update event (UEV)
Update interrupt flag (UIF)

Figure 71. Counter timing diagram, internal clock divided by N
CK_PSC
Timer clock = CK_CNT
Counter register

20

1F

00

36

Counter underflow
Update event (UEV)
Update interrupt flag (UIF)

DocID018940 Rev 9

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392

Advanced-control timers (TIM1)

RM0091

Figure 72. Counter timing diagram, update event when repetition counter is not used
CK_PSC
CEN
Timer clock = CK_CNT
Counter register

05

04 03 02 01 00 36 35 34 33 32 31 30 2F

Counter underflow
Update event (UEV)
Update interrupt flag (UIF)
Auto-reload register

FF

36

Write a new value in TIMx_ARR

Center-aligned mode (up/down counting)
In center-aligned mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register) – 1, generates a counter overflow event, then counts from the autoreload value down to 1 and generates a counter underflow event. Then it restarts counting
from 0.
Center-aligned mode is active when the CMS bits in TIMx_CR1 register are not equal to
'00'. The Output compare interrupt flag of channels configured in output is set when: the
counter counts down (Center aligned mode 1, CMS = “01”), the counter counts up (Center
aligned mode 2, CMS = “10”) the counter counts up and down (Center aligned mode 3,
CMS = “11”).
In this mode, the DIR direction bit in the TIMx_CR1 register cannot be written. It is updated
by hardware and gives the current direction of the counter.
The update event can be generated at each counter overflow and at each counter underflow
or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event. In this case, the counter restarts counting from
0, as well as the counter of the prescaler.
The UEV update event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until UDIS bit has been written to 0.
However, the counter continues counting up and down, based on the current auto-reload
value.
In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the
UG bit generates an UEV update event but without setting the UIF flag (thus no interrupt or
DMA request is sent). This is to avoid generating both update and capture interrupts when
clearing the counter on the capture event.

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Advanced-control timers (TIM1)
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The repetition counter is reloaded with the content of TIMx_RCR register

•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register)

•

The auto-reload active register is updated with the preload value (content of the
TIMx_ARR register). Note that if the update source is a counter overflow, the autoreload is updated before the counter is reloaded, so that the next period is the expected
one (the counter is loaded with the new value).

The following figures show some examples of the counter behavior for different clock
frequencies.
Figure 73. Counter timing diagram, internal clock divided by 1, TIMx_ARR = 0x6
CK_PSC
CNT_EN
Timer clock = CK_CNT
Counter register

04

03 02 01 00 01 02 03 04 05 06 05 04 03

Counter underflow
Counter overflow
Update event (UEV)
Update interrupt flag (UIF)

1. Here, center-aligned mode 1 is used (for more details refer to Section 17.4: TIM1 registers on page 367).

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Figure 74. Counter timing diagram, internal clock divided by 2

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Figure 75. Counter timing diagram, internal clock divided by 4, TIMx_ARR=0x36

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069

1. Center-aligned mode 2 or 3 is used with an UIF on overflow.

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Figure 76. Counter timing diagram, internal clock divided by N

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Figure 77. Counter timing diagram, update event with ARPE=1 (counter underflow)
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Figure 78. Counter timing diagram, Update event with ARPE=1 (counter overflow)
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17.3.3

Repetition counter
Section 17.3.1: Time-base unit describes how the update event (UEV) is generated with
respect to the counter overflows/underflows. It is actually generated only when the repetition
counter has reached zero. This can be useful when generating PWM signals.
This means that data are transferred from the preload registers to the shadow registers
(TIMx_ARR auto-reload register, TIMx_PSC prescaler register, but also TIMx_CCRx
capture/compare registers in compare mode) every N counter overflows or underflows,
where N is the value in the TIMx_RCR repetition counter register.
The repetition counter is decremented:
•

At each counter overflow in upcounting mode,

•

At each counter underflow in downcounting mode,

•

At each counter overflow and at each counter underflow in center-aligned mode.
Although this limits the maximum number of repetition to 128 PWM cycles, it makes it
possible to update the duty cycle twice per PWM period. When refreshing compare
registers only once per PWM period in center-aligned mode, maximum resolution is
2xTck, due to the symmetry of the pattern.

The repetition counter is an auto-reload type; the repetition rate is maintained as defined by
the TIMx_RCR register value (refer to Figure 79). When the update event is generated by
software (by setting the UG bit in TIMx_EGR register) or by hardware through the slave
mode controller, it occurs immediately whatever the value of the repetition counter is and the
repetition counter is reloaded with the content of the TIMx_RCR register.

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Advanced-control timers (TIM1)
In center-aligned mode, for odd values of RCR, the update event occurs either on the
overflow or on the underflow depending on when the RCR register was written and when
the counter was started. If the RCR was written before starting the counter, the UEV occurs
on the overflow. If the RCR was written after starting the counter, the UEV occurs on the
underflow. For example for RCR = 3, the UEV is generated on each 4th overflow or
underflow event depending on when RCR was written.

Figure 79. Update rate examples depending on mode and TIMx_RCR register settings

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17.3.4

RM0091

Clock sources
The counter clock can be provided by the following clock sources:
•

Internal clock (CK_INT)

•

External clock mode1: external input pin

•

External clock mode2: external trigger input ETR

•

Internal trigger inputs (ITRx): using one timer as prescaler for another timer, for
example, you can configure Timer 1 to act as a prescaler for Timer 2. Refer to Using
one timer as prescaler for another on page 429 for more details.

Internal clock source (CK_INT)
If the slave mode controller is disabled (SMS=000), then the CEN, DIR (in the TIMx_CR1
register) and UG bits (in the TIMx_EGR register) are actual control bits and can be changed
only by software (except UG which remains cleared automatically). As soon as the CEN bit
is written to 1, the prescaler is clocked by the internal clock CK_INT.
Figure 80 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 80. Control circuit in normal mode, internal clock divided by 1

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Advanced-control timers (TIM1)

External clock source mode 1
This mode is selected when SMS=111 in the TIMx_SMCR register. The counter can count at
each rising or falling edge on a selected input.
Figure 81. TI2 external clock connection example
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For example, to configure the upcounter to count in response to a rising edge on the TI2
input, use the following procedure:

Note:

1.

Configure channel 2 to detect rising edges on the TI2 input by writing CC2S = ‘01’ in
the TIMx_CCMR1 register.

2.

Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1
register (if no filter is needed, keep IC2F=0000).

3.

Select rising edge polarity by writing CC2P=0 in the TIMx_CCER register.

4.

Configure the timer in external clock mode 1 by writing SMS=111 in the TIMx_SMCR
register.

5.

Select TI2 as the trigger input source by writing TS=110 in the TIMx_SMCR register.

6.

Enable the counter by writing CEN=1 in the TIMx_CR1 register.

The capture prescaler is not used for triggering, so you don’t need to configure it.
For code examples refer to the Appendix section A.9.1: Upcounter on TI2 rising edge code
example.
When a rising edge occurs on TI2, the counter counts once and the TIF flag is set.
The delay between the rising edge on TI2 and the actual clock of the counter is due to the
resynchronization circuit on TI2 input.

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Figure 82. Control circuit in external clock mode 1

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External clock source mode 2
This mode is selected by writing ECE=1 in the TIMx_SMCR register.
The counter can count at each rising or falling edge on the external trigger input ETR.
The Figure 83 gives an overview of the external trigger input block.
Figure 83. External trigger input block

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For example, to configure the upcounter to count each 2 rising edges on ETR, use the
following procedure:

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Advanced-control timers (TIM1)
1.

As no filter is needed in this example, write ETF[3:0]=0000 in the TIMx_SMCR register.

2.

Set the prescaler by writing ETPS[1:0]=01 in the TIMx_SMCR register

3.

Select rising edge detection on the ETR pin by writing ETP=0 in the TIMx_SMCR
register

4.

Enable external clock mode 2 by writing ECE=1 in the TIMx_SMCR register.

5.

Enable the counter by writing CEN=1 in the TIMx_CR1 register.

The counter counts once each 2 ETR rising edges.
For code example refer to the Appendix section A.9.2: Up counter on each 2 ETR rising
edges code example.
The delay between the rising edge on ETR and the actual clock of the counter is due to the
resynchronization circuit on the ETRP signal.
Figure 84. Control circuit in external clock mode 2

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17.3.5

Capture/compare channels
Each Capture/Compare channel is built around a capture/compare register (including a
shadow register), a input stage for capture (with digital filter, multiplexing and prescaler) and
an output stage (with comparator and output control).
Figure 85 to Figure 88 give an overview of one Capture/Compare channel.
The input stage samples the corresponding TIx input to generate a filtered signal TIxF.
Then, an edge detector with polarity selection generates a signal (TIxFPx) which can be
used as trigger input by the slave mode controller or as the capture command. It is
prescaled before the capture register (ICxPS).

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Figure 85. Capture/compare channel (example: channel 1 input stage)

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The output stage generates an intermediate waveform which is then used for reference:
OCxRef (active high). The polarity acts at the end of the chain.
Figure 86. Capture/compare channel 1 main circuit

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Advanced-control timers (TIM1)
Figure 87. Output stage of capture/compare channel (channel 1 to 3)
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The capture/compare block is made of one preload register and one shadow register. Write
and read always access the preload register.
In capture mode, captures are actually done in the shadow register, which is copied into the
preload register.
In compare mode, the content of the preload register is copied into the shadow register
which is compared to the counter.

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17.3.6

RM0091

Input capture mode
In Input capture mode, the Capture/Compare Registers (TIMx_CCRx) are used to latch the
value of the counter after a transition detected by the corresponding ICx signal. When a
capture occurs, the corresponding CCXIF flag (TIMx_SR register) is set and an interrupt or
a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was
already high, then the over-capture flag CCxOF (TIMx_SR register) is set. CCxIF can be
cleared by software by writing it to ‘0’ or by reading the captured data stored in the
TIMx_CCRx register. CCxOF is cleared when you write it to ‘0’.
The following example shows how to capture the counter value in TIMx_CCR1 when TI1
input rises. To do this, use the following procedure:
•

Select the active input: TIMx_CCR1 must be linked to the TI1 input, so write the CC1S
bits to 01 in the TIMx_CCMR1 register. As soon as CC1S becomes different from 00,
the channel is configured in input and the TIMx_CCR1 register becomes read-only.

•

Program the input filter duration you need with respect to the signal you connect to the
timer (when the input is one of the TIx (ICxF bits in the TIMx_CCMRx register). Let’s
imagine that, when toggling, the input signal is not stable during at must 5 internal clock
cycles. We must program a filter duration longer than these 5 clock cycles. We can
validate a transition on TI1 when 8 consecutive samples with the new level have been
detected (sampled at fDTS frequency). Then write IC1F bits to 0011 in the
TIMx_CCMR1 register.

•

Select the edge of the active transition on the TI1 channel by writing CC1P and CC1NP
bits to 0 in the TIMx_CCER register (rising edge in this case).

•

Program the input prescaler. In our example, we wish the capture to be performed at
each valid transition, so the prescaler is disabled (write IC1PS bits to ‘00’ in the
TIMx_CCMR1 register).

•

Enable capture from the counter into the capture register by setting the CC1E bit in the
TIMx_CCER register.

•

If needed, enable the related interrupt request by setting the CC1IE bit in the
TIMx_DIER register, and/or the DMA request by setting the CC1DE bit in the
TIMx_DIER register.

For code example refer to the Appendix section A.9.3: Input capture configuration code
example.
When an input capture occurs:
•

The TIMx_CCR1 register gets the value of the counter on the active transition.

•

CC1IF flag is set (interrupt flag). CC1OF is also set if at least two consecutive captures
occurred whereas the flag was not cleared.

•

An interrupt is generated depending on the CC1IE bit.

•

A DMA request is generated depending on the CC1DE bit.

For code example refer to the Appendix section A.9.4: Input capture data management
code example.
In order to handle the overcapture, it is recommended to read the data before the
overcapture flag. This is to avoid missing an overcapture which could happen after reading
the flag and before reading the data.
Note:

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IC interrupt and/or DMA requests can be generated by software by setting the
corresponding CCxG bit in the TIMx_EGR register.

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17.3.7

Advanced-control timers (TIM1)

PWM input mode
This mode is a particular case of input capture mode. The procedure is the same except:
•

Two ICx signals are mapped on the same TIx input.

•

These 2 ICx signals are active on edges with opposite polarity.

•

One of the two TIxFP signals is selected as trigger input and the slave mode controller
is configured in reset mode.

For example, you can measure the period (in TIMx_CCR1 register) and the duty cycle (in
TIMx_CCR2 register) of the PWM applied on TI1 using the following procedure (depending
on CK_INT frequency and prescaler value):
•

Select the active input for TIMx_CCR1: write the CC1S bits to 01 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP1 (used both for capture in TIMx_CCR1 and counter
clear): write the CC1P and CC1NP bits to ‘0’ (active on rising edge).

•

Select the active input for TIMx_CCR2: write the CC2S bits to 10 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP2 (used for capture in TIMx_CCR2): write the CC2P
bit to ‘1’ (active on falling edge).

•

Select the valid trigger input: write the TS bits to 101 in the TIMx_SMCR register
(TI1FP1 selected).

•

Configure the slave mode controller in reset mode: write the SMS bits to 100 in the
TIMx_SMCR register.

•

Enable the captures: write the CC1E and CC2E bits to ‘1’ in the TIMx_CCER register.

For code example refer to the Appendix section A.9.5: PWM input configuration code
example.
Figure 89. PWM input mode timing
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17.3.8

RM0091

Forced output mode
In output mode (CCxS bits = 00 in the TIMx_CCMRx register), each output compare signal
(OCxREF and then OCx/OCxN) can be forced to active or inactive level directly by software,
independently of any comparison between the output compare register and the counter.
To force an output compare signal (OCXREF/OCx) to its active level, you just need to write
101 in the OCxM bits in the corresponding TIMx_CCMRx register. Thus OCXREF is forced
high (OCxREF is always active high) and OCx get opposite value to CCxP polarity bit.
For example: CCxP=0 (OCx active high) => OCx is forced to high level.
The OCxREF signal can be forced low by writing the OCxM bits to 100 in the TIMx_CCMRx
register.
Anyway, the comparison between the TIMx_CCRx shadow register and the counter is still
performed and allows the flag to be set. Interrupt and DMA requests can be sent
accordingly. This is described in the output compare mode section below.

17.3.9

Output compare mode
This function is used to control an output waveform or indicating when a period of time has
elapsed.
When a match is found between the capture/compare register and the counter, the output
compare function:
•

Assigns the corresponding output pin to a programmable value defined by the output
compare mode (OCxM bits in the TIMx_CCMRx register) and the output polarity (CCxP
bit in the TIMx_CCER register). The output pin can keep its level (OCXM=000), be set
active (OCxM=001), be set inactive (OCxM=010) or can toggle (OCxM=011) on match.

•

Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).

•

Generates an interrupt if the corresponding interrupt mask is set (CCXIE bit in the
TIMx_DIER register).

•

Sends a DMA request if the corresponding enable bit is set (CCxDE bit in the
TIMx_DIER register, CCDS bit in the TIMx_CR2 register for the DMA request
selection).

The TIMx_CCRx registers can be programmed with or without preload registers using the
OCxPE bit in the TIMx_CCMRx register.
In output compare mode, the update event UEV has no effect on OCxREF and OCx output.
The timing resolution is one count of the counter. Output compare mode can also be used to
output a single pulse (in One Pulse mode).

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Advanced-control timers (TIM1)
Procedure:
1.

Select the counter clock (internal, external, prescaler).

2.

Write the desired data in the TIMx_ARR and TIMx_CCRx registers.

3.

Set the CCxIE bit if an interrupt request is to be generated.

4.

Select the output mode. For example:

5.

–

Write OCxM = 011 to toggle OCx output pin when CNT matches CCRx

–

Write OCxPE = 0 to disable preload register

–

Write CCxP = 0 to select active high polarity

–

Write CCxE = 1 to enable the output

Enable the counter by setting the CEN bit in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.7: Output compare configuration code
example.
The TIMx_CCRx register can be updated at any time by software to control the output
waveform, provided that the preload register is not enabled (OCxPE=’0’, else TIMx_CCRx
shadow register is updated only at the next update event UEV). An example is given in
Figure 90.
Figure 90. Output compare mode, toggle on OC1
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17.3.10

PWM mode
Pulse Width Modulation mode allows you to generate a signal with a frequency determined
by the value of the TIMx_ARR register and a duty cycle determined by the value of the
TIMx_CCRx register.
The PWM mode can be selected independently on each channel (one PWM per OCx
output) by writing ‘110’ (PWM mode 1) or ‘111’ (PWM mode 2) in the OCxM bits in the
TIMx_CCMRx register. You must enable the corresponding preload register by setting the

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OCxPE bit in the TIMx_CCMRx register, and eventually the auto-reload preload register (in
upcounting or center-aligned modes) by setting the ARPE bit in the TIMx_CR1 register.
As the preload registers are transferred to the shadow registers only when an update event
occurs, before starting the counter, you have to initialize all the registers by setting the UG
bit in the TIMx_EGR register.
OCx polarity is software programmable using the CCxP bit in the TIMx_CCER register. It
can be programmed as active high or active low. OCx output is enabled by a combination of
the CCxE, CCxNE, MOE, OSSI and OSSR bits (TIMx_CCER and TIMx_BDTR registers).
Refer to the TIMx_CCER register description for more details.
In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine
whether TIMx_CCRx ≤ TIMx_CNT or TIMx_CNT ≤ TIMx_CCRx (depending on the direction
of the counter).
The timer is able to generate PWM in edge-aligned mode or center-aligned mode
depending on the CMS bits in the TIMx_CR1 register.

PWM edge-aligned mode
•

Upcounting configuration
Upcounting is active when the DIR bit in the TIMx_CR1 register is low. Refer to the
Upcounting mode on page 324.
In the following example, we consider PWM mode 1. The reference PWM signal
OCxREF is high as long as TIMx_CNT < TIMx_CCRx else it becomes low. If the
compare value in TIMx_CCRx is greater than the auto-reload value (in TIMx_ARR)
then OCxREF is held at ‘1’. If the compare value is 0 then OCxRef is held at ‘0’.
Figure 91 shows some edge-aligned PWM waveforms in an example where
TIMx_ARR=8.

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Figure 91. Edge-aligned PWM waveforms (ARR=8)



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For code example refer to the Appendix section A.9.8: Edge-aligned PWM configuration
example.
•

Downcounting configuration
Downcounting is active when DIR bit in TIMx_CR1 register is high. Refer to the
Downcounting mode on page 328
In PWM mode 1, the reference signal OCxRef is low as long as
TIMx_CNT > TIMx_CCRx else it becomes high. If the compare value in TIMx_CCRx is
greater than the auto-reload value in TIMx_ARR, then OCxREF is held at ‘1’. 0% PWM
is not possible in this mode.

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PWM center-aligned mode
Center-aligned mode is active when the CMS bits in TIMx_CR1 register are different from
‘00’ (all the remaining configurations having the same effect on the OCxRef/OCx signals).
The compare flag is set when the counter counts up, when it counts down or both when it
counts up and down depending on the CMS bits configuration. The direction bit (DIR) in the
TIMx_CR1 register is updated by hardware and must not be changed by software. Refer to
the Center-aligned mode (up/down counting) on page 330.
Figure 92 shows some center-aligned PWM waveforms in an example where:
•

TIMx_ARR=8,

•

PWM mode is the PWM mode 1,

•

The flag is set when the counter counts down corresponding to the center-aligned
mode 1 selected for CMS=01 in TIMx_CR1 register.

For code example refer to the Appendix section A.9.9: Center-aligned PWM configuration
example.
Figure 92. Center-aligned PWM waveforms (ARR=8)
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Hints on using center-aligned mode:
•

When starting in center-aligned mode, the current up-down configuration is used. It
means that the counter counts up or down depending on the value written in the DIR bit
in the TIMx_CR1 register. Moreover, the DIR and CMS bits must not be changed at the
same time by the software.

•

Writing to the counter while running in center-aligned mode is not recommended as it
can lead to unexpected results. In particular:

•

17.3.11

–

The direction is not updated if you write a value in the counter that is greater than
the auto-reload value (TIMx_CNT>TIMx_ARR). For example, if the counter was
counting up, it continues to count up.

–

The direction is updated if you write 0 or write the TIMx_ARR value in the counter
but no Update Event UEV is generated.

The safest way to use center-aligned mode is to generate an update by software
(setting the UG bit in the TIMx_EGR register) just before starting the counter and not to
write the counter while it is running.

Complementary outputs and dead-time insertion
The advanced-control timers (TIM1) can output two complementary signals and manage the
switching-off and the switching-on instants of the outputs.
This time is generally known as dead-time and you have to adjust it depending on the
devices you have connected to the outputs and their characteristics (intrinsic delays of levelshifters, delays due to power switches...)
You can select the polarity of the outputs (main output OCx or complementary OCxN)
independently for each output. This is done by writing to the CCxP and CCxNP bits in the
TIMx_CCER register.
The complementary signals OCx and OCxN are activated by a combination of several
control bits: the CCxE and CCxNE bits in the TIMx_CCER register and the MOE, OISx,
OISxN, OSSI and OSSR bits in the TIMx_BDTR and TIMx_CR2 registers. Refer to
Table 63: Output control bits for complementary OCx and OCxN channels on page 384 for
more details. In particular, the dead-time is activated when switching to the IDLE state (MOE
falling down to 0).
Dead-time insertion is enabled by setting both CCxE and CCxNE bits, and the MOE bit if the
break circuit is present. There is one 10-bit dead-time generator for each channel. From a
reference waveform OCxREF, it generates 2 outputs OCx and OCxN. If OCx and OCxN are
active high:
•

The OCx output signal is the same as the reference signal except for the rising edge,
which is delayed relative to the reference rising edge.

•

The OCxN output signal is the opposite of the reference signal except for the rising
edge, which is delayed relative to the reference falling edge.

If the delay is greater than the width of the active output (OCx or OCxN) then the
corresponding pulse is not generated.
The following figures show the relationships between the output signals of the dead-time
generator and the reference signal OCxREF. (we suppose CCxP=0, CCxNP=0, MOE=1,
CCxE=1 and CCxNE=1 in these examples)

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Figure 93. Complementary output with dead-time insertion.

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Figure 94. Dead-time waveforms with delay greater than the negative pulse.

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Figure 95. Dead-time waveforms with delay greater than the positive pulse.

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The dead-time delay is the same for each of the channels and is programmable with the
DTG bits in the TIMx_BDTR register. Refer to Section 17.4.18: TIM1 break and dead-time
register (TIM1_BDTR) on page 388 for delay calculation.

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Re-directing OCxREF to OCx or OCxN
In output mode (forced, output compare or PWM), OCxREF can be re-directed to the OCx
output or to OCxN output by configuring the CCxE and CCxNE bits in the TIMx_CCER
register.
This allows you to send a specific waveform (such as PWM or static active level) on one
output while the complementary remains at its inactive level. Other alternative possibilities
are to have both outputs at inactive level or both outputs active and complementary with
dead-time.
Note:

When only OCxN is enabled (CCxE=0, CCxNE=1), it is not complemented and becomes
active as soon as OCxREF is high. For example, if CCxNP=0 then OCxN=OCxRef. On the
other hand, when both OCx and OCxN are enabled (CCxE=CCxNE=1) OCx becomes
active when OCxREF is high whereas OCxN is complemented and becomes active when
OCxREF is low.

17.3.12

Using the break function
When using the break function, the output enable signals and inactive levels are modified
according to additional control bits (MOE, OSSI and OSSR bits in the TIMx_BDTR register,
OISx and OISxN bits in the TIMx_CR2 register). In any case, the OCx and OCxN outputs
cannot be set both to active level at a given time. Refer to Table 63: Output control bits for
complementary OCx and OCxN channels on page 384 for more details.
The source for break (BRK) channel can be an external source connected to the BKIN pin or
one of the following internal sources:
•

the core LOCKUP output

•

the PVD output

•

the SRAM parity error signal

•

a clock failure event generated by the CSS detector

•

the output from a comparator

When exiting from reset, the break circuit is disabled and the MOE bit is low. You can enable
the break function by setting the BKE bit in the TIMx_BDTR register. The break input
polarity can be selected by configuring the BKP bit in the same register. BKE and BKP can
be modified at the same time. When the BKE and BKP bits are written, a delay of 1 APB
clock cycle is applied before the writing is effective. Consequently, it is necessary to wait 1
APB clock period to correctly read back the bit after the write operation.
Because MOE falling edge can be asynchronous, a resynchronization circuit has been
inserted between the actual signal (acting on the outputs) and the synchronous control bit
(accessed in the TIMx_BDTR register). It results in some delays between the asynchronous
and the synchronous signals. In particular, if you write MOE to 1 whereas it was low, you
must insert a delay (dummy instruction) before reading it correctly. This is because you write
the asynchronous signal and read the synchronous signal.

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When a break occurs (selected level on the break input):

Note:

•

The MOE bit is cleared asynchronously, putting the outputs in inactive state, idle state
or in reset state (selected by the OSSI bit). This feature functions even if the MCU
oscillator is off.

•

Each output channel is driven with the level programmed in the OISx bit in the
TIMx_CR2 register as soon as MOE=0. If OSSI=0 then the timer releases the enable
output else the enable output remains high.

•

When complementary outputs are used:
–

The outputs are first put in reset state inactive state (depending on the polarity).
This is done asynchronously so that it works even if no clock is provided to the
timer.

–

If the timer clock is still present, then the dead-time generator is reactivated in
order to drive the outputs with the level programmed in the OISx and OISxN bits
after a dead-time. Even in this case, OCx and OCxN cannot be driven to their
active level together. Note that because of the resynchronization on MOE, the
dead-time duration is a bit longer than usual (around 2 ck_tim clock cycles).

–

If OSSI=0 then the timer releases the enable outputs else the enable outputs
remain or become high as soon as one of the CCxE or CCxNE bits is high.

•

The break status flag (BIF bit in the TIMx_SR register) is set. An interrupt can be
generated if the BIE bit in the TIMx_DIER register is set.

•

If the AOE bit in the TIMx_BDTR register is set, the MOE bit is automatically set again
at the next update event UEV. This can be used to perform a regulation, for instance.
Else, MOE remains low until you write it to ‘1’ again. In this case, it can be used for
security and you can connect the break input to an alarm from power drivers, thermal
sensors or any security components.

The break inputs is acting on level. Thus, the MOE cannot be set while the break input is
active (neither automatically nor by software). In the meantime, the status flag BIF cannot
be cleared.
The break can be generated by the BRK input which has a programmable polarity and an
enable bit BKE in the TIMx_BDTR Register.
In addition to the break input and the output management, a write protection has been
implemented inside the break circuit to safeguard the application. It allows you to freeze the
configuration of several parameters (dead-time duration, OCx/OCxN polarities and state
when disabled, OCxM configurations, break enable and polarity). You can choose from 3
levels of protection selected by the LOCK bits in the TIMx_BDTR register. Refer to
Section 17.4.18: TIM1 break and dead-time register (TIM1_BDTR) on page 388. The LOCK
bits can be written only once after an MCU reset.
The Figure 96 shows an example of behavior of the outputs in response to a break.

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Figure 96. Output behavior in response to a break
BREAK (MOE

)

OCxREF

OCx
(OCxN not implemented, CCxP=0, OISx=1)

OCx
(OCxN not implemented, CCxP=0, OISx=0)

OCx
(OCxN not implemented, CCxP=1, OISx=1)

OCx
(OCxN not implemented, CCxP=1, OISx=0)

OCx
delay
delay
OCxN
(CCxE=1, CCxP=0, OISx=0, CCxNE=1, CCxNP=0, OISxN=1)

delay

OCx
delay
delay
OCxN
(CCxE=1, CCxP=0, OISx=1, CCxNE=1, CCxNP=1, OISxN=1)

delay

OCx
OCxN
(CCxE=1, CCxP=0, OISx=0, CCxNE=0, CCxNP=0, OISxN=1)

delay

OCx
OCxN
(CCxE=1, CCxP=0, OISx=1, CCxNE=0, CCxNP=0, OISxN=0)

delay

OCx
OCxN
(CCxE=1, CCxP=0, CCxNE=0, CCxNP=0, OISx=OISxN=0 or OISx=OISxN=1)

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17.3.13

RM0091

Clearing the OCxREF signal on an external event
The OCxREF signal of a given channel can be cleared when a high level is applied on the
OCREF_CLR_INPUT (OCxCE enable bit in the corresponding TIMx_CCMRx register set to
1). OCxREF remains low until the next update event (UEV) occurs. This function can only
be used in Output compare and PWM modes. It does not work in Forced mode.
OCREF_CLR_INPUT can be selected between the OCREF_CLR input and ETRF (ETR
after the filter) by configuring the OCCS bit in the TIMx_SMCR register.
When ETRF is chosen, ETR must be configured as follows:
The OCxREF signal for a given channel can be driven Low by applying a High level to the
ETRF input (OCxCE enable bit of the corresponding TIMx_CCMRx register set to ‘1’). The
OCxREF signal remains Low until the next update event, UEV, occurs.
This function can only be used in output compare and PWM modes, and does not work in
forced mode.
For example, the OCxREF signal can be connected to the output of a comparator to be
used for current handling. In this case, the ETR must be configured as follow:
1.

The External Trigger Prescaler should be kept off: bits ETPS[1:0] of the TIMx_SMCR
register set to ‘00’.

2.

The external clock mode 2 must be disabled: bit ECE of the TIMx_SMCR register set to
‘0’.

3.

The External Trigger Polarity (ETP) and the External Trigger Filter (ETF) can be
configured according to the user needs.

For code example refer to the Appendix section A.9.10: ETR configuration to clear OCxREF
code example.
Figure 97 shows the behavior of the OCxREF signal when the ETRF Input becomes High,
for both values of the enable bit OCxCE. In this example, the timer TIMx is programmed in
PWM mode.

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Figure 97. Clearing TIMx OCxREF

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Note:

In case of a PWM with a 100% duty cycle (if CCRx>ARR), then OCxREF is enabled again at
the next counter overflow.

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17.3.14

RM0091

6-step PWM generation
When complementary outputs are used on a channel, preload bits are available on the
OCxM, CCxE and CCxNE bits. The preload bits are transferred to the shadow bits at the
COM commutation event. Thus you can program in advance the configuration for the next
step and change the configuration of all the channels at the same time. COM can be
generated by software by setting the COM bit in the TIMx_EGR register or by hardware (on
TRGI rising edge).
A flag is set when the COM event occurs (COMIF bit in the TIMx_SR register), which can
generate an interrupt (if the COMIE bit is set in the TIMx_DIER register) or a DMA request
(if the COMDE bit is set in the TIMx_DIER register).
The Figure 98 describes the behavior of the OCx and OCxN outputs when a COM event
occurs, in 3 different examples of programmed configurations.
Figure 98. 6-step generation, COM example (OSSR=1)

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One-pulse mode
One-pulse mode (OPM) is a particular case of the previous modes. It allows the counter to
be started in response to a stimulus and to generate a pulse with a programmable length
after a programmable delay.
Starting the counter can be controlled through the slave mode controller. Generating the
waveform can be done in output compare mode or PWM mode. You select One-pulse mode
by setting the OPM bit in the TIMx_CR1 register. This makes the counter stop automatically
at the next update event UEV.
A pulse can be correctly generated only if the compare value is different from the counter
initial value. Before starting (when the timer is waiting for the trigger), the configuration must
be:
•

In upcounting: CNT < CCRx ≤ ARR (in particular, 0 < CCRx)

•

In downcounting: CNT > CCRx
Figure 99. Example of one pulse mode
TI2
OC1REF
OC1

Counter

17.3.15

Advanced-control timers (TIM1)

TIM1_ARR
TIM1_CCR1

0
tDELAY

tPULSE

t

For example you may want to generate a positive pulse on OC1 with a length of tPULSE and
after a delay of tDELAY as soon as a positive edge is detected on the TI2 input pin.
Let’s use TI2FP2 as trigger 1:
•

Map TI2FP2 to TI2 by writing CC2S=’01’ in the TIMx_CCMR1 register.

•

TI2FP2 must detect a rising edge, write CC2P=’0’ and CC2NP=’0’ in the TIMx_CCER
register.

•

Configure TI2FP2 as trigger for the slave mode controller (TRGI) by writing TS=’110’ in
the TIMx_SMCR register.

•

TI2FP2 is used to start the counter by writing SMS to ‘110’ in the TIMx_SMCR register
(trigger mode).

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The OPM waveform is defined by writing the compare registers (taking into account the
clock frequency and the counter prescaler).
•

The tDELAY is defined by the value written in the TIMx_CCR1 register.

•

The tPULSE is defined by the difference between the auto-reload value and the compare
value (TIMx_ARR - TIMx_CCR1+1).

•

Let’s say you want to build a waveform with a transition from ‘0’ to ‘1’ when a compare
match occurs and a transition from ‘1’ to ‘0’ when the counter reaches the auto-reload
value. To do this you enable PWM mode 2 by writing OC1M=111 in the TIMx_CCMR1
register. You can optionally enable the preload registers by writing OC1PE=’1’ in the
TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this case you have to
write the compare value in the TIMx_CCR1 register, the auto-reload value in the
TIMx_ARR register, generate an update by setting the UG bit and wait for external
trigger event on TI2. CC1P is written to ‘0’ in this example.

In our example, the DIR and CMS bits in the TIMx_CR1 register should be low.
For code example refer to the Appendix section A.9.16: One-Pulse mode code example.
You only want 1 pulse (Single mode), so you write '1 in the OPM bit in the TIMx_CR1
register to stop the counter at the next update event (when the counter rolls over from the
auto-reload value back to 0). When OPM bit in the TIMx_CR1 register is set to '0', so the
Repetitive Mode is selected.

Particular case: OCx fast enable
In One-pulse mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
output toggle. But several clock cycles are needed for these operations and it limits the
minimum delay tDELAY min we can get.
If you want to output a waveform with the minimum delay, you can set the OCxFE bit in the
TIMx_CCMRx register. Then OCxRef (and OCx) are forced in response to the stimulus,
without taking in account the comparison. Its new level is the same as if a compare match
had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.
For code example refer to the part of code, conditioned by PULSE_WITHOUT_DELAY > 0
in the Appendix section A.9.16: One-Pulse mode code example.

17.3.16

Encoder interface mode
To select Encoder Interface mode write SMS=‘001’ in the TIMx_SMCR register if the
counter is counting on TI2 edges only, SMS=’010’ if it is counting on TI1 edges only and
SMS=’011’ if it is counting on both TI1 and TI2 edges.
Select the TI1 and TI2 polarity by programming the CC1P and CC2P bits in the TIMx_CCER
register. When needed, you can program the input filter as well. CC1NP and CC2NP must
be kept low.
The two inputs TI1 and TI2 are used to interface to an incremental encoder. Refer to
Table 61. The counter is clocked by each valid transition on TI1FP1 or TI2FP2 (TI1 and TI2
after input filter and polarity selection, TI1FP1=TI1 if not filtered and not inverted,
TI2FP2=TI2 if not filtered and not inverted) assuming that it is enabled (CEN bit in
TIMx_CR1 register written to ‘1’). The sequence of transitions of the two inputs is evaluated
and generates count pulses as well as the direction signal. Depending on the sequence the
counter counts up or down, the DIR bit in the TIMx_CR1 register is modified by hardware

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accordingly. The DIR bit is calculated at each transition on any input (TI1 or TI2), whatever
the counter is counting on TI1 only, TI2 only or both TI1 and TI2.
Encoder interface mode acts simply as an external clock with direction selection. This
means that the counter just counts continuously between 0 and the auto-reload value in the
TIMx_ARR register (0 to ARR or ARR down to 0 depending on the direction). So you must
configure TIMx_ARR before starting. in the same way, the capture, compare, prescaler,
repetition counter, trigger output features continue to work as normal. Encoder mode and
External clock mode 2 are not compatible and must not be selected together.
In this mode, the counter is modified automatically following the speed and the direction of
the incremental encoder and its content, therefore, always represents the encoder’s
position. The count direction correspond to the rotation direction of the connected sensor.
The table summarizes the possible combinations, assuming TI1 and TI2 don’t switch at the
same time.
Table 61. Counting direction versus encoder signals

Active edge

Level on
opposite
signal (TI1FP1
for TI2,
TI2FP2 for
TI1)

TI1FP1 signal

TI2FP2 signal

Rising

Falling

Rising

Falling

Counting on
TI1 only

High

Down

Up

No Count

No Count

Low

Up

Down

No Count

No Count

Counting on
TI2 only

High

No Count

No Count

Up

Down

Low

No Count

No Count

Down

Up

Counting on
TI1 and TI2

High

Down

Up

Up

Down

Low

Up

Down

Down

Up

An external incremental encoder can be connected directly to the MCU without external
interface logic. However, comparators are normally be used to convert the encoder’s
differential outputs to digital signals. This greatly increases noise immunity. The third
encoder output which indicate the mechanical zero position, may be connected to an
external interrupt input and trigger a counter reset.
Figure 100 gives an example of counter operation, showing count signal generation and
direction control. It also shows how input jitter is compensated where both edges are
selected. This might occur if the sensor is positioned near to one of the switching points. For
this example we assume that the configuration is the following:
•

CC1S=’01’ (TIMx_CCMR1 register, TI1FP1 mapped on TI1).

•

CC2S=’01’ (TIMx_CCMR2 register, TI1FP2 mapped on TI2).

•

CC1P=’0’ (TIMx_CCER register, TI1FP1 non-inverted, TI1FP1=TI1).

•

CC2P=’0’ (TIMx_CCER register, TI1FP2 non-inverted, TI1FP2= TI2).

•

SMS=’011’ (TIMx_SMCR register, both inputs are active on both rising and falling
edges).

•

CEN=’1’ (TIMx_CR1 register, Counter enabled).

For code example refer to the Appendix section A.9.11: Encoder interface code example.

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Figure 100. Example of counter operation in encoder interface mode.
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Figure 101 gives an example of counter behavior when TI1FP1 polarity is inverted (same
configuration as above except CC1P=’1’).
Figure 101. Example of encoder interface mode with TI1FP1 polarity inverted.
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The timer, when configured in Encoder Interface mode provides information on the sensor’s
current position. You can obtain dynamic information (speed, acceleration, deceleration) by
measuring the period between two encoder events using a second timer configured in
capture mode. The output of the encoder which indicates the mechanical zero can be used
for this purpose. Depending on the time between two events, the counter can also be read
at regular times. You can do this by latching the counter value into a third input capture
register if available (then the capture signal must be periodic and can be generated by
another timer). when available, it is also possible to read its value through a DMA request
generated by a real-time clock.

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17.3.17

Advanced-control timers (TIM1)

Timer input XOR function
The TI1S bit in the TIMx_CR2 register, allows the input filter of channel 1 to be connected to
the output of a XOR gate, combining the three input pins TIMx_CH1, TIMx_CH2 and
TIMx_CH3.
The XOR output can be used with all the timer input functions such as trigger or input
capture. An example of this feature used to interface Hall sensors is given in
Section 17.3.18 below.

17.3.18

Interfacing with Hall sensors
This is done using the advanced-control timers (TIM1) to generate PWM signals to drive the
motor and another timer TIMx (TIM2 or TIM3) referred to as “interfacing timer” in Figure 102.
The “interfacing timer” captures the 3 timer input pins (CC1, CC2, CC3) connected through
a XOR to the TI1 input channel (selected by setting the TI1S bit in the TIMx_CR2 register).
The slave mode controller is configured in reset mode; the slave input is TI1F_ED. Thus,
each time one of the 3 inputs toggles, the counter restarts counting from 0. This creates a
time base triggered by any change on the Hall inputs.
On the “interfacing timer”, capture/compare channel 1 is configured in capture mode,
capture signal is TRC (See Figure 85: Capture/compare channel (example: channel 1 input
stage) on page 340). The captured value, which corresponds to the time elapsed between 2
changes on the inputs, gives information about motor speed.
The “interfacing timer” can be used in output mode to generate a pulse which changes the
configuration of the channels of the advanced-control timer (TIM1) (by triggering a COM
event). The TIM1 timer is used to generate PWM signals to drive the motor. To do this, the
interfacing timer channel must be programmed so that a positive pulse is generated after a
programmed delay (in output compare or PWM mode). This pulse is sent to the advancedcontrol timer (TIM1) through the TRGO output.
Example: you want to change the PWM configuration of your advanced-control timer TIM1
after a programmed delay each time a change occurs on the Hall inputs connected to one of
the TIMx timers.
•

Configure 3 timer inputs XORed to the TI1 input channel by writing the TI1S bit in the
TIMx_CR2 register to ‘1’,

•

Program the time base: write the TIMx_ARR to the max value (the counter must be
cleared by the TI1 change. Set the prescaler to get a maximum counter period longer
than the time between 2 changes on the sensors,

•

Program channel 1 in capture mode (TRC selected): write the CC1S bits in the
TIMx_CCMR1 register to ‘01’. You can also program the digital filter if needed,

•

Program channel 2 in PWM 2 mode with the desired delay: write the OC2M bits to ‘111’
and the CC2S bits to ‘00’ in the TIMx_CCMR1 register,

•

Select OC2REF as trigger output on TRGO: write the MMS bits in the TIMx_CR2
register to ‘101’,

In the advanced-control timer TIM1, the right ITR input must be selected as trigger input, the
timer is programmed to generate PWM signals, the capture/compare control signals are
preloaded (CCPC=1 in the TIMx_CR2 register) and the COM event is controlled by the
trigger input (CCUS=1 in the TIMx_CR2 register). The PWM control bits (CCxE, OCxM) are
written after a COM event for the next step (this can be done in an interrupt subroutine
generated by the rising edge of OC2REF).

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Figure 102 describes this example.
Figure 102. Example of hall sensor interface

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17.3.19

Advanced-control timers (TIM1)

TIMx and external trigger synchronization
The TIMx timer can be synchronized with an external trigger in several modes: Reset mode,
Gated mode and Trigger mode.

Slave mode: Reset mode
The counter and its prescaler can be reinitialized in response to an event on a trigger input.
Moreover, if the URS bit from the TIMx_CR1 register is low, an update event UEV is
generated. Then all the preloaded registers (TIMx_ARR, TIMx_CCRx) are updated.
In the following example, the upcounter is cleared in response to a rising edge on TI1 input:
•

Configure the channel 1 to detect rising edges on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits
select the input capture source only, CC1S = 01 in the TIMx_CCMR1 register. Write
CC1P=0 and CC1NP=’0’ in TIMx_CCER register to validate the polarity (and detect
rising edges only).

•

Configure the timer in reset mode by writing SMS=100 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Start the counter by writing CEN=1 in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.12: Reset mode code example.
The counter starts counting on the internal clock, then behaves normally until TI1 rising
edge. When TI1 rises, the counter is cleared and restarts from 0. In the meantime, the
trigger flag is set (TIF bit in the TIMx_SR register) and an interrupt request, or a DMA
request can be sent if enabled (depending on the TIE and TDE bits in TIMx_DIER register).
The following figure shows this behavior when the auto-reload register TIMx_ARR=0x36.
The delay between the rising edge on TI1 and the actual reset of the counter is due to the
resynchronization circuit on TI1 input.
Figure 103. Control circuit in reset mode
TI1
UG
Counter clock = ck_cnt = ck_psc
Counter register

30 31 32 33 34 35 36 00 01 02 03 00 01 02 03

TIF

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Slave mode: Gated mode
The counter can be enabled depending on the level of a selected input.
In the following example, the upcounter counts only when TI1 input is low:
•

Configure the channel 1 to detect low levels on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits
select the input capture source only, CC1S=01 in TIMx_CCMR1 register. Write
CC1P=1 and CC1NP=’0’ in TIMx_CCER register to validate the polarity (and detect
low level only).

•

Configure the timer in gated mode by writing SMS=101 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Enable the counter by writing CEN=1 in the TIMx_CR1 register (in gated mode, the
counter doesn’t start if CEN=0, whatever is the trigger input level).

For code example refer to the Appendix section A.9.13: Gated mode code example.
The counter starts counting on the internal clock as long as TI1 is low and stops as soon as
TI1 becomes high. The TIF flag in the TIMx_SR register is set both when the counter starts
or stops.
The delay between the rising edge on TI1 and the actual stop of the counter is due to the
resynchronization circuit on TI1 input.
Figure 104. Control circuit in gated mode
TI1
cnt_en
Counter clock = ck_cnt = ck_psc
Counter register

30 31 32 33

TIF

Write TIF=0

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Advanced-control timers (TIM1)

Slave mode: Trigger mode
The counter can start in response to an event on a selected input.
In the following example, the upcounter starts in response to a rising edge on TI2 input:
•

Configure the channel 2 to detect rising edges on TI2. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC2F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC2S bits are
configured to select the input capture source only, CC2S=01 in TIMx_CCMR1 register.
Write CC2P=1 and CC2NP=0 in TIMx_CCER register to validate the polarity (and
detect low level only).

•

Configure the timer in trigger mode by writing SMS=110 in TIMx_SMCR register. Select
TI2 as the input source by writing TS=110 in TIMx_SMCR register.

For code example refer to the Appendix section A.9.14: Trigger mode code example.
When a rising edge occurs on TI2, the counter starts counting on the internal clock and the
TIF flag is set.
The delay between the rising edge on TI2 and the actual start of the counter is due to the
resynchronization circuit on TI2 input.
Figure 105. Control circuit in trigger mode
TI2
cnt_en
Counter clock = ck_cnt = ck_psc
Counter register

34

35 36 37 38

TIF

Slave mode: external clock mode 2 + trigger mode
The external clock mode 2 can be used in addition to another slave mode (except external
clock mode 1 and encoder mode). In this case, the ETR signal is used as external clock
input, and another input can be selected as trigger input (in reset mode, gated mode or
trigger mode). It is recommended not to select ETR as TRGI through the TS bits of
TIMx_SMCR register.
In the following example, the upcounter is incremented at each rising edge of the ETR
signal as soon as a rising edge of TI1 occurs:
1.

Configure the external trigger input circuit by programming the TIMx_SMCR register as
follows:
–

ETF = 0000: no filter

–

ETPS=00: prescaler disabled

–

ETP=0: detection of rising edges on ETR and ECE=1 to enable the external clock
mode 2.

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2.

3.

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Configure the channel 1 as follows, to detect rising edges on TI:
–

IC1F=0000: no filter.

–

The capture prescaler is not used for triggering and does not need to be
configured.

–

CC1S=01in TIMx_CCMR1 register to select only the input capture source

–

CC1P=0 and CC1NP=’0’ in TIMx_CCER register to validate the polarity (and
detect rising edge only).

Configure the timer in trigger mode by writing SMS=110 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

For code example refer to the Appendix section A.9.15: External clock mode 2 + trigger
mode code example.
A rising edge on TI1 enables the counter and sets the TIF flag. The counter then counts on
ETR rising edges.
The delay between the rising edge of the ETR signal and the actual reset of the counter is
due to the resynchronization circuit on ETRP input.
Figure 106. Control circuit in external clock mode 2 + trigger mode

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17.3.20

Timer synchronization
The TIM timers are linked together internally for timer synchronization or chaining. Refer to
Section 18.3.15: Timer synchronization on page 428 for details.

17.3.21

Debug mode
When the microcontroller enters debug mode (Cortex™-M0 core halted), the TIMx counter
either continues to work normally or stops, depending on DBG_TIMx_STOP configuration
bit in DBG module.

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17.4

TIM1 registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

17.4.1

TIM1 control register 1 (TIM1_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

CKD[1:0]
rw

7

6

ARPE

rw

rw

5

CMS[1:0]
rw

rw

4

3

2

1

0

DIR

OPM

URS

UDIS

CEN

rw

rw

rw

rw

rw

Bits 15:10 Reserved, must be kept at reset value.
Bits 9:8 CKD[1:0]: Clock division
This bit-field indicates the division ratio between the timer clock (CK_INT) frequency and the
dead-time and sampling clock (tDTS)used by the dead-time generators and the digital filters
(ETR, TIx),
00: tDTS=tCK_INT
01: tDTS=2*tCK_INT
10: tDTS=4*tCK_INT
11: Reserved, do not program this value
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered
Bits 6:5 CMS[1:0]: Center-aligned mode selection
00: Edge-aligned mode. The counter counts up or down depending on the direction bit
(DIR).
01: Center-aligned mode 1. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
only when the counter is counting down.
10: Center-aligned mode 2. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
only when the counter is counting up.
11: Center-aligned mode 3. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
both when the counter is counting up or down.
Note: It is not allowed to switch from edge-aligned mode to center-aligned mode as long as
the counter is enabled (CEN=1).
Bit 4 DIR: Direction
0: Counter used as upcounter
1: Counter used as downcounter
Note: This bit is read only when the timer is configured in Center-aligned mode or Encoder
mode.
Bit 3 OPM: One pulse mode
0: Counter is not stopped at update event
1: Counter stops counting at the next update event (clearing the bit CEN)

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Bit 2 URS: Update request source
This bit is set and cleared by software to select the UEV event sources.
0: Any of the following events generate an update interrupt or DMA request if enabled.
These events can be:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
1: Only counter overflow/underflow generates an update interrupt or DMA request if
enabled.
Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable UEV event generation.
0: UEV enabled. The Update (UEV) event is generated by one of the following events:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
Buffered registers are then loaded with their preload values.
1: UEV disabled. The Update event is not generated, shadow registers keep their value
(ARR, PSC, CCRx). However the counter and the prescaler are reinitialized if the UG bit is
set or if a hardware reset is received from the slave mode controller.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled
Note: External clock, gated mode and encoder mode can work only if the CEN bit has been
previously set by software. However trigger mode can set the CEN bit automatically by
hardware.

17.4.2

TIM1 control register 2 (TIM1_CR2)
Address offset: 0x04
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

Res.

OIS4

OIS3N

OIS3

OIS2N

OIS2

OIS1N

OIS1

TI1S

rw

rw

rw

rw

rw

rw

rw

rw

6

4

MMS[2:0]
rw

Bit 15 Reserved, must be kept at reset value.
Bit 14 OIS4: Output Idle state 4 (OC4 output)
refer to OIS1 bit
Bit 13 OIS3N: Output Idle state 3 (OC3N output)
refer to OIS1N bit
Bit 12 OIS3: Output Idle state 3 (OC3 output)
refer to OIS1 bit
Bit 11 OIS2N: Output Idle state 2 (OC2N output)
refer to OIS1N bit
Bit 10 OIS2: Output Idle state 2 (OC2 output)
refer to OIS1 bit

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CCDS

CCUS

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Advanced-control timers (TIM1)

Bit 9 OIS1N: Output Idle state 1 (OC1N output)
0: OC1N=0 after a dead-time when MOE=0
1: OC1N=1 after a dead-time when MOE=0
Note: This bit cannot be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BDTR register).
Bit 8 OIS1: Output Idle state 1 (OC1 output)
0: OC1=0 (after a dead-time if OC1N is implemented) when MOE=0
1: OC1=1 (after a dead-time if OC1N is implemented) when MOE=0
Note: This bit cannot be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BDTR register).
Bit 7 TI1S: TI1 selection
0: The TIMx_CH1 pin is connected to TI1 input
1: The TIMx_CH1, CH2 and CH3 pins are connected to the TI1 input (XOR combination)
Bits 6:4 MMS[1:0]: Master mode selection
These bits allow to select the information to be sent in master mode to slave timers for
synchronization (TRGO). The combination is as follows:
000: Reset - the UG bit from the TIMx_EGR register is used as trigger output (TRGO). If the
reset is generated by the trigger input (slave mode controller configured in reset mode) then
the signal on TRGO is delayed compared to the actual reset.
001: Enable - the Counter Enable signal CNT_EN is used as trigger output (TRGO). It is
useful to start several timers at the same time or to control a window in which a slave timer is
enable. The Counter Enable signal is generated by a logic OR between CEN control bit and
the trigger input when configured in gated mode. When the Counter Enable signal is
controlled by the trigger input, there is a delay on TRGO, except if the master/slave mode is
selected (see the MSM bit description in TIMx_SMCR register).
010: Update - The update event is selected as trigger output (TRGO). For instance a master
timer can then be used as a prescaler for a slave timer.
011: Compare Pulse - The trigger output send a positive pulse when the CC1IF flag is to be
set (even if it was already high), as soon as a capture or a compare match occurred.
(TRGO).
100: Compare - OC1REF signal is used as trigger output (TRGO)
101: Compare - OC2REF signal is used as trigger output (TRGO)
110: Compare - OC3REF signal is used as trigger output (TRGO)
111: Compare - OC4REF signal is used as trigger output (TRGO)
Bit 3 CCDS: Capture/compare DMA selection
0: CCx DMA request sent when CCx event occurs
1: CCx DMA requests sent when update event occurs
Bit 2 CCUS: Capture/compare control update selection
0: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit only
1: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit or when an rising edge occurs on TRGI
Note: This bit acts only on channels that have a complementary output.
Bit 1 Reserved, must be kept at reset value.
Bit 0 CCPC: Capture/compare preloaded control
0: CCxE, CCxNE and OCxM bits are not preloaded
1: CCxE, CCxNE and OCxM bits are preloaded, after having been written, they are updated
only when a communication event (COM) occurs (COMG bit set or rising edge detected on
TRGI, depending on the CCUS bit).
Note: This bit acts only on channels that have a complementary output.

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17.4.3

RM0091

TIM1 slave mode control register (TIM1_SMCR)
Address offset: 0x08
Reset value: 0x0000

15

14

ETP

ECE

rw

rw

13

12

11

ETPS[1:0]
rw

rw

10

9

8

ETF[3:0]
rw

rw

7

6

MSM

rw

rw

rw

5

4

TS[2:0]
rw

rw

3

2

OCCS
rw

rw

1

0

SMS[2:0]
rw

rw

rw

Bit 15 ETP: External trigger polarity
This bit selects whether ETR or ETR is used for trigger operations
0: ETR is non-inverted, active at high level or rising edge.
1: ETR is inverted, active at low level or falling edge.
Bit 14 ECE: External clock enable
This bit enables External clock mode 2.
0: External clock mode 2 disabled
1: External clock mode 2 enabled. The counter is clocked by any active edge on the ETRF
signal.
Note: 1: Setting the ECE bit has the same effect as selecting external clock mode 1 with
TRGI connected to ETRF (SMS=111 and TS=111).
2: It is possible to simultaneously use external clock mode 2 with the following slave
modes: reset mode, gated mode and trigger mode. Nevertheless, TRGI must not be
connected to ETRF in this case (TS bits must not be 111).
3: If external clock mode 1 and external clock mode 2 are enabled at the same time,
the external clock input is ETRF.
Bits 13:12 ETPS[1:0]: External trigger prescaler
External trigger signal ETRP frequency must be at most 1/4 of TIMxCLK frequency. A
prescaler can be enabled to reduce ETRP frequency. It is useful when inputting fast external
clocks.
00: Prescaler OFF
01: ETRP frequency divided by 2
10: ETRP frequency divided by 4
11: ETRP frequency divided by 8

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Bits 11:8 ETF[3:0]: External trigger filter
This bit-field then defines the frequency used to sample ETRP signal and the length of the
digital filter applied to ETRP. The digital filter is made of an event counter in which N
consecutive events are needed to validate a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ETF[3:0] = 1,
2 or 3.
Bit 7 MSM: Master/slave mode
0: No action
1: The effect of an event on the trigger input (TRGI) is delayed to allow a perfect
synchronization between the current timer and its slaves (through TRGO). It is useful if we
want to synchronize several timers on a single external event.
Bits 6:4 TS[2:0]: Trigger selection
This bit-field selects the trigger input to be used to synchronize the counter.
000: Internal Trigger 0 (ITR0)
001: Internal Trigger 1 (ITR1)
010: Internal Trigger 2 (ITR2)
011: Internal Trigger 3 (ITR3)
100: TI1 Edge Detector (TI1F_ED)
101: Filtered Timer Input 1 (TI1FP1)
110: Filtered Timer Input 2 (TI2FP2)
111: External Trigger input (ETRF)
See Table 62: TIMx Internal trigger connection on page 372 for more details on ITRx meaning
for each Timer.
Note: These bits must be changed only when they are not used (e.g. when SMS=000) to
avoid wrong edge detections at the transition.
Bit 3 OCCS: OCREF clear selection.
This bit is used to select the OCREF clear source.
0:OCREF_CLR_INT is connected to the OCREF_CLR input
1: OCREF_CLR_INT is connected to ETRF

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Bits 2:0 SMS: Slave mode selection
When external signals are selected the active edge of the trigger signal (TRGI) is linked to the
polarity selected on the external input (see Input Control register and Control Register
description.
000: Slave mode disabled - if CEN = ‘1’ then the prescaler is clocked directly by the internal
clock.
001: Encoder mode 1 - Counter counts up/down on TI2FP1 edge depending on TI1FP2
level.
010: Encoder mode 2 - Counter counts up/down on TI1FP2 edge depending on TI2FP1
level.
011: Encoder mode 3 - Counter counts up/down on both TI1FP1 and TI2FP2 edges
depending on the level of the other input.
100: Reset Mode - Rising edge of the selected trigger input (TRGI) reinitializes the counter
and generates an update of the registers.
101: Gated Mode - The counter clock is enabled when the trigger input (TRGI) is high. The
counter stops (but is not reset) as soon as the trigger becomes low. Both start and stop of
the counter are controlled.
110: Trigger Mode - The counter starts at a rising edge of the trigger TRGI (but it is not
reset). Only the start of the counter is controlled.
111: External Clock Mode 1 - Rising edges of the selected trigger (TRGI) clock the counter.
Note: The gated mode must not be used if TI1F_ED is selected as the trigger input
(TS=’100’). Indeed, TI1F_ED outputs 1 pulse for each transition on TI1F, whereas the
gated mode checks the level of the trigger signal.
Note: The clock of the slave timer must be enabled prior to receive events from the master
timer, and must not be changed on-the-fly while triggers are received from the master
timer.

Table 62. TIMx Internal trigger connection

17.4.4

Slave TIM

ITR0 (TS = 000)

ITR1 (TS = 001)

ITR2 (TS = 010)

ITR3 (TS = 011)

TIM1

TIM15

TIM2

TIM3

TIM17

TIM1 DMA/interrupt enable register (TIM1_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

Res.

TDE
rw

13

12

11

10

9

COMDE CC4DE CC3DE CC2DE CC1DE
rw

rw

rw

rw

rw

8

7

6

5

4

3

2

1

0

UDE

BIE

TIE

COMIE

CC4IE

CC3IE

CC2IE

CC1IE

UIE

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bit 15 Reserved, must be kept at reset value.
Bit 14 TDE: Trigger DMA request enable
0: Trigger DMA request disabled
1: Trigger DMA request enabled
Bit 13 COMDE: COM DMA request enable
0: COM DMA request disabled
1: COM DMA request enabled
Bit 12 CC4DE: Capture/Compare 4 DMA request enable
0: CC4 DMA request disabled
1: CC4 DMA request enabled

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Bit 11 CC3DE: Capture/Compare 3 DMA request enable
0: CC3 DMA request disabled
1: CC3 DMA request enabled
Bit 10 CC2DE: Capture/Compare 2 DMA request enable
0: CC2 DMA request disabled
1: CC2 DMA request enabled
Bit 9 CC1DE: Capture/Compare 1 DMA request enable
0: CC1 DMA request disabled
1: CC1 DMA request enabled
Bit 8 UDE: Update DMA request enable
0: Update DMA request disabled
1: Update DMA request enabled
Bit 7 BIE: Break interrupt enable
0: Break interrupt disabled
1: Break interrupt enabled
Bit 6 TIE: Trigger interrupt enable
0: Trigger interrupt disabled
1: Trigger interrupt enabled
Bit 5 COMIE: COM interrupt enable
0: COM interrupt disabled
1: COM interrupt enabled
Bit 4 CC4IE: Capture/Compare 4 interrupt enable
0: CC4 interrupt disabled
1: CC4 interrupt enabled
Bit 3 CC3IE: Capture/Compare 3 interrupt enable
0: CC3 interrupt disabled
1: CC3 interrupt enabled
Bit 2 CC2IE: Capture/Compare 2 interrupt enable
0: CC2 interrupt disabled
1: CC2 interrupt enabled
Bit 1 CC1IE: Capture/Compare 1 interrupt enable
0: CC1 interrupt disabled
1: CC1 interrupt enabled
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled
1: Update interrupt enabled

17.4.5

TIM1 status register (TIM1_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

CC4OF CC3OF CC2OF CC1OF
rc_w0

rc_w0

rc_w0

rc_w0

8

7

6

5

4

3

2

1

0

Res.

BIF

TIF

COMIF

CC4IF

CC3IF

CC2IF

CC1IF

UIF

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

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Bits 15:13 Reserved, must be kept at reset value.
Bit 12 CC4OF: Capture/Compare 4 overcapture flag
refer to CC1OF description
Bit 11 CC3OF: Capture/Compare 3 overcapture flag
refer to CC1OF description
Bit 10 CC2OF: Capture/Compare 2 overcapture flag
refer to CC1OF description
Bit 9 CC1OF: Capture/Compare 1 overcapture flag
This flag is set by hardware only when the corresponding channel is configured in input
capture mode. It is cleared by software by writing it to ‘0’.
0: No overcapture has been detected.
1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was
already set
Bit 8 Reserved, must be kept at reset value.
Bit 7 BIF: Break interrupt flag
This flag is set by hardware as soon as the break input goes active. It can be cleared by
software if the break input is not active.
0: No break event occurred.
1: An active level has been detected on the break input.
Bit 6 TIF: Trigger interrupt flag
This flag is set by hardware on trigger event (active edge detected on TRGI input when the
slave mode controller is enabled in all modes but gated mode.It is cleared by software.
0: No trigger event occurred.
1: Trigger interrupt pending.
Bit 5 COMIF: COM interrupt flag
This flag is set by hardware on COM event (when Capture/compare Control bits - CCxE,
CCxNE, OCxM - have been updated). It is cleared by software by writing it to ‘0’.
0: No COM event occurred.
1: COM interrupt pending.
Bit 4 CC4IF: Capture/Compare 4 interrupt flag
refer to CC1IF description
Bit 3 CC3IF: Capture/Compare 3 interrupt flag
refer to CC1IF description

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Bit 2 CC2IF: Capture/Compare 2 interrupt flag
refer to CC1IF description
Bit 1 CC1IF: Capture/Compare 1 interrupt flag
If channel CC1 is configured as output:
This flag is set by hardware when the counter matches the compare value, with some
exception in center-aligned mode (refer to the CMS bits in the TIMx_CR1 register description).
It is cleared by software.
0: No match.
1: The content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register.
When the contents of TIMx_CCR1 are greater than the contents of TIMx_ARR, the CC1IF
bit goes high on the counter overflow (in upcounting and up/down-counting modes) or
underflow (in downcounting mode)
If channel CC1 is configured as input:
This bit is set by hardware on a capture. It is cleared by software or by reading the
TIMx_CCR1 register.
0: No input capture occurred
1: The counter value has been captured in TIMx_CCR1 register (An edge has been
detected on IC1 which matches the selected polarity)
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending. This bit is set by hardware when the registers are updated:
–At overflow or underflow regarding the repetition counter value (update if repetition
counter = 0) and if the UDIS=0 in the TIMx_CR1 register.
–When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if URS=0
and UDIS=0 in the TIMx_CR1 register.
–When CNT is reinitialized by a trigger event (refer to Section 17.4.3: TIM1 slave mode
control register (TIM1_SMCR)), if URS=0 and UDIS=0 in the TIMx_CR1 register.

17.4.6

TIM1 event generation register (TIM1_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

BG

TG

COMG

CC4G

CC3G

CC2G

CC1G

UG

w

w

w

w

w

w

w

w

Bits 15:8 Reserved, must be kept at reset value.
Bit 7 BG: Break generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: A break event is generated. MOE bit is cleared and BIF flag is set. Related interrupt or
DMA transfer can occur if enabled.

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Bit 6 TG: Trigger generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: The TIF flag is set in TIMx_SR register. Related interrupt or DMA transfer can occur if
enabled.
Bit 5 COMG: Capture/Compare control update generation
This bit can be set by software, it is automatically cleared by hardware
0: No action
1: When CCPC bit is set, it allows to update CCxE, CCxNE and OCxM bits
Note: This bit acts only on channels having a complementary output.
Bit 4 CC4G: Capture/Compare 4 generation
Refer to CC1G description
Bit 3 CC3G: Capture/Compare 3 generation
Refer to CC1G description
Bit 2 CC2G: Capture/Compare 2 generation
Refer to CC1G description
Bit 1 CC1G: Capture/Compare 1 generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: A capture/compare event is generated on channel 1:
If channel CC1 is configured as output:
CC1IF flag is set, Corresponding interrupt or DMA request is sent if enabled.
If channel CC1 is configured as input:
The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set, the
corresponding interrupt or DMA request is sent if enabled. The CC1OF flag is set if the CC1IF
flag was already high.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action
1: Reinitialize the counter and generates an update of the registers. Note that the prescaler
counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared if
the center-aligned mode is selected or if DIR=0 (upcounting), else it takes the auto-reload
value (TIMx_ARR) if DIR=1 (downcounting).

17.4.7

TIM1 capture/compare mode register 1 (TIM1_CCMR1)
Address offset: 0x18
Reset value: 0x0000
The channels can be used in input (capture mode) or in output (compare mode). The
direction of a channel is defined by configuring the corresponding CCxS bits. All the other
bits of this register have a different function in input and in output mode. For a given bit,
OCxx describes its function when the channel is configured in output, ICxx describes its

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function when the channel is configured in input. So you must take care that the same bit
can have a different meaning for the input stage and for the output stage.

15

14

OC2
CE

13

12

OC2M[2:0]
IC2F[3:0]

rw

rw

rw

11

10

OC2
PE

OC2
FE

9

8

CC2S[1:0]

7

6

OC1
CE

rw

rw

4

OC1M[2:0]

IC2PSC[1:0]
rw

5

IC1F[3:0]
rw

rw

rw

rw

rw

3

2

OC1
PE

OC1
FE

1

0

CC1S[1:0]

IC1PSC[1:0]
rw

rw

rw

rw

rw

Output compare mode
Bit 15 OC2CE: Output Compare 2 clear enable
Bits 14:12 OC2M[2:0]: Output Compare 2 mode
Bit 11 OC2PE: Output Compare 2 preload enable
Bit 10 OC2FE: Output Compare 2 fast enable
Bits 9:8 CC2S[1:0]: Capture/Compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output
01: CC2 channel is configured as input, IC2 is mapped on TI2
10: CC2 channel is configured as input, IC2 is mapped on TI1
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if
an internal trigger input is selected through the TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = ‘0’ in TIMx_CCER).
Bit 7 OC1CE: Output Compare 1 clear enable
OC1CE: Output Compare 1 Clear Enable
0: OC1Ref is not affected by the ETRF Input
1: OC1Ref is cleared as soon as a High level is detected on ETRF input

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Bits 6:4 OC1M: Output Compare 1 mode
These bits define the behavior of the output reference signal OC1REF from which OC1 and
OC1N are derived. OC1REF is active high whereas OC1 and OC1N active level depends on
CC1P and CC1NP bits.
000: Frozen - The comparison between the output compare register TIMx_CCR1 and the
counter TIMx_CNT has no effect on the outputs (this mode is used to generate a timing
base).
001: Set channel 1 to active level on match. OC1REF signal is forced high when the counter
TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
010: Set channel 1 to inactive level on match. OC1REF signal is forced low when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
011: Toggle - OC1REF toggles when TIMx_CNT=TIMx_CCR1.
100: Force inactive level - OC1REF is forced low.
101: Force active level - OC1REF is forced high.
110: PWM mode 1 - In upcounting, channel 1 is active as long as TIMx_CNTTIMx_CCR1 else active (OC1REF=’1’).
111: PWM mode 2 - In upcounting, channel 1 is inactive as long as TIMx_CNTTIMx_CCR1 else
inactive.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: In PWM mode 1 or 2, the OCREF level changes only when the result of the
comparison changes or when the output compare mode switches from “frozen” mode
to “PWM” mode.
3: On channels having a complementary output, this bit field is preloaded. If the CCPC
bit is set in the TIMx_CR2 register then the OC1M active bits take the new value from
the preloaded bits only when a COM event is generated.
Bit 3 OC1PE: Output Compare 1 preload enable
0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the
new value is taken in account immediately.
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded in the active register at each update event.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: The PWM mode can be used without validating the preload register only in one
pulse mode (OPM bit set in TIMx_CR1 register). Else the behavior is not guaranteed.
Bit 2 OC1FE: Output Compare 1 fast enable
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is
ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is
5 clock cycles.
1: An active edge on the trigger input acts like a compare match on CC1 output. Then, OC is
set to the compare level independently from the result of the comparison. Delay to sample
the trigger input and to activate CC1 output is reduced to 3 clock cycles. OCFE acts only if
the channel is configured in PWM1 or PWM2 mode.

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Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

Input capture mode
Bits 15:12 IC2F: Input capture 2 filter
Bits 11:10 IC2PSC[1:0]: Input capture 2 prescaler
Bits 9:8 CC2S: Capture/Compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output
01: CC2 channel is configured as input, IC2 is mapped on TI2
10: CC2 channel is configured as input, IC2 is mapped on TI1
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if an
internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = ‘0’ in TIMx_CCER).
Bits 7:4 IC1F[3:0]: Input capture 1 filter
This bit-field defines the frequency used to sample TI1 input and the length of the digital filter applied to
TI1. The digital filter is made of an event counter in which N consecutive events are needed to validate
a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ICxF[3:0] = 1, 2 or 3.
Bits 3:2 IC1PSC: Input capture 1 prescaler
This bit-field defines the ratio of the prescaler acting on CC1 input (IC1).
The prescaler is reset as soon as CC1E=’0’ (TIMx_CCER register).
00: no prescaler, capture is done each time an edge is detected on the capture input
01: capture is done once every 2 events
10: capture is done once every 4 events
11: capture is done once every 8 events

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Bits 1:0 CC1S: Capture/Compare 1 Selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if an
internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

17.4.8

TIM1 capture/compare mode register 2 (TIM1_CCMR2)
Address offset: 0x1C
Reset value: 0x0000
Refer to the above CCMR1 register description.

15

14

OC4
CE

13

12

OC4M[2:0]
IC4F[3:0]

rw

rw

rw

11

10

OC4
PE

OC4
FE

9

8

CC4S[1:0]

7

6

OC3
CE.

rw

rw

4

OC3M[2:0]

IC4PSC[1:0]
rw

5

IC3F[3:0]
rw

rw

rw

rw

rw

3

2

OC3
PE

OC3
FE

1

0

CC3S[1:0]

IC3PSC[1:0]
rw

rw

rw

rw

rw

Output compare mode
Bit 15 OC4CE: Output compare 4 clear enable
Bits 14:12 OC4M: Output compare 4 mode
Bit 11 OC4PE: Output compare 4 preload enable
Bit 10 OC4FE: Output compare 4 fast enable
Bits 9:8 CC4S: Capture/Compare 4 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC4 channel is configured as output
01: CC4 channel is configured as input, IC4 is mapped on TI4
10: CC4 channel is configured as input, IC4 is mapped on TI3
11: CC4 channel is configured as input, IC4 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC4S bits are writable only when the channel is OFF (CC4E = ‘0’ in TIMx_CCER).
Bit 7 OC3CE: Output compare 3 clear enable
Bits 6:4 OC3M: Output compare 3 mode
Bit 3 OC3PE: Output compare 3 preload enable
Bit 2 OC3FE: Output compare 3 fast enable
Bits 1:0 CC3S: Capture/Compare 3 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC3 channel is configured as output
01: CC3 channel is configured as input, IC3 is mapped on TI3
10: CC3 channel is configured as input, IC3 is mapped on TI4
11: CC3 channel is configured as input, IC3 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC3S bits are writable only when the channel is OFF (CC3E = ‘0’ in TIMx_CCER).

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Input capture mode
Bits 15:12 IC4F: Input capture 4 filter
Bits 11:10 IC4PSC: Input capture 4 prescaler
Bits 9:8 CC4S: Capture/Compare 4 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC4 channel is configured as output
01: CC4 channel is configured as input, IC4 is mapped on TI4
10: CC4 channel is configured as input, IC4 is mapped on TI3
11: CC4 channel is configured as input, IC4 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC4S bits are writable only when the channel is OFF (CC4E = ‘0’ in TIMx_CCER).
Bits 7:4 IC3F: Input capture 3 filter
Bits 3:2 IC3PSC: Input capture 3 prescaler
Bits 1:0 CC3S: Capture/compare 3 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC3 channel is configured as output
01: CC3 channel is configured as input, IC3 is mapped on TI3
10: CC3 channel is configured as input, IC3 is mapped on TI4
11: CC3 channel is configured as input, IC3 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC3S bits are writable only when the channel is OFF (CC3E = ‘0’ in TIMx_CCER).

17.4.9

TIM1 capture/compare enable register (TIM1_CCER)
Address offset: 0x20
Reset value: 0x0000

15

14

13

12

Res.

Res.

CC4P

CC4E

rw

rw

11

10

CC3NP CC3NE
rw

rw

9

8

CC3P

CC3E

rw

rw

7

6

CC2NP CC2NE
rw

rw

5

4

CC2P

CC2E

rw

rw

3

2

CC1NP CC1NE
rw

rw

1

0

CC1P

CC1E

rw

rw

Bits 15:14 Reserved, must be kept at reset value.
Bit 13 CC4P: Capture/Compare 4 output polarity
refer to CC1P description
Bit 12 CC4E: Capture/Compare 4 output enable
refer to CC1E description
Bit 11 CC3NP: Capture/Compare 3 complementary output polarity
refer to CC1NP description
Bit 10 CC3NE: Capture/Compare 3 complementary output enable
refer to CC1NE description
Bit 9 CC3P: Capture/Compare 3 output polarity
refer to CC1P description
Bit 8 CC3E: Capture/Compare 3 output enable
refer to CC1E description

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Bit 7 CC2NP: Capture/Compare 2 complementary output polarity
refer to CC1NP description
Bit 6 CC2NE: Capture/Compare 2 complementary output enable
refer to CC1NE description
Bit 5 CC2P: Capture/Compare 2 output polarity
refer to CC1P description
Bit 4 CC2E: Capture/Compare 2 output enable
refer to CC1E description
Bit 3 CC1NP: Capture/Compare 1 complementary output polarity
CC1 channel configuration as output:
0: OC1N active high.
1: OC1N active low.
CC1 channel configuration as input:
This bit is used in conjunction with CC1P to define the polarity of TI1FP1 and TI2FP1. Refer to
CC1P description.
Note: On channels having a complementary output, this bit is preloaded. If the CCPC bit is
set in the TIMx_CR2 register then the CC1NP active bit takes the new value from the
preloaded bits only when a Commutation event is generated.
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register) and CC1S=”00” (the channel is configured in output).
Bit 2 CC1NE: Capture/Compare 1 complementary output enable
0: Off - OC1N is not active. OC1N level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1E bits.
1: On - OC1N signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1E bits.
Note: On channels having a complementary output, this bit is preloaded. If the CCPC bit is
set in the TIMx_CR2 register then the CC1NE active bit takes the new value from the
preloaded bits only when a Commutation event is generated.

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Bit 1 CC1P: Capture/Compare 1 output polarity
CC1 channel configured as output:
0: OC1 active high
1: OC1 active low
CC1 channel configured as input:
CC1NP/CC1P bits select the active polarity of TI1FP1 and TI2FP1 for trigger or capture
operations.
00: non-inverted/rising edge
The circuit is sensitive to TIxFP1 rising edge (capture or trigger operations in reset, external
clock or trigger mode), TIxFP1 is not inverted (trigger operation in gated mode or encoder
mode).
01: inverted/falling edge
The circuit is sensitive to TIxFP1 falling edge (capture or trigger operations in reset, external
clock or trigger mode), TIxFP1 is inverted (trigger operation in gated mode or encoder
mode).
10: reserved, do not use this configuration.
11: non-inverted/both edges
The circuit is sensitive to both TIxFP1 rising and falling edges (capture or trigger operations
in reset, external clock or trigger mode), TIxFP1 is not inverted (trigger operation in gated
mode). This configuration must not be used in encoder mode.
Note: On channels having a complementary output, this bit is preloaded. If the CCPC bit is
set in the TIMx_CR2 register then the CC1P active bit takes the new value from the
preloaded bits only when a Commutation event is generated.
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register).
Bit 0 CC1E: Capture/Compare 1 output enable
CC1 channel configured as output:
0: Off - OC1 is not active. OC1 level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1NE bits.
1: On - OC1 signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1NE bits.
CC1 channel configured as input:
This bit determines if a capture of the counter value can actually be done into the input
capture/compare register 1 (TIMx_CCR1) or not.
0: Capture disabled.
1: Capture enabled.
Note: On channels having a complementary output, this bit is preloaded. If the CCPC bit is
set in the TIMx_CR2 register then the CC1E active bit takes the new value from the
preloaded bits only when a Commutation event is generated.

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Table 63. Output control bits for complementary OCx and OCxN channels
Output states(1)

Control bits
MOE
bit

OSSI
bit

1

OSSR
bit

CCxE
bit

CCxNE
OCx output state
bit

0

0

0

Output Disabled (not driven by Output Disabled (not driven by the
the timer)
timer)
OCx=0, OCx_EN=0
OCxN=0, OCxN_EN=0

0

0

1

Output Disabled (not driven by
OCxREF + Polarity OCxN=OCxREF
the timer)
xor CCxNP, OCxN_EN=1
OCx=0, OCx_EN=0

0

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

0

1

1

Complementary to OCREF (not
OCREF + Polarity + dead-time
OCREF) + Polarity + dead-time
OCx_EN=1
OCxN_EN=1

1

0

0

Output Disabled (not driven by Output Disabled (not driven by the
timer)
the timer)
OCx=CCxP, OCx_EN=0
OCxN=CCxNP, OCxN_EN=0

1

0

1

Off-State (output enabled with
inactive state)
OCx=CCxP, OCx_EN=1

OCxREF + Polarity
OCxN=OCxREF xor CCxNP,
OCxN_EN=1

1

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

Off-State (output enabled with
inactive state)
OCxN=CCxNP, OCxN_EN=1

1

1

1

Complementary to OCREF (not
OCREF + Polarity + dead-time
OCREF) + Polarity + dead-time
OCx_EN=1
OCxN_EN=1

0

0

0

Output Disabled (not driven by Output Disabled (not driven by the
the timer)
timer)
OCx=CCxP, OCx_EN=0
OCxN=CCxNP, OCxN_EN=0

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

X

0

X

OCxN output state

Output Disabled (not driven by the
timer)
OCxN=0, OCxN_EN=0

Output Disabled (not driven by the timer)
Asynchronously: OCx=CCxP, OCx_EN=0, OCxN=CCxNP,
OCxN_EN=0
Then if the clock is present: OCx=OISx and OCxN=OISxN after a
dead-time, assuming that OISx and OISxN do not correspond to OCX
and OCxN both in active state.
Output Disabled (not driven by Output Disabled (not driven by the
the timer)
timer)
OCx=CCxP, OCx_EN=0
OCxN=CCxNP, OCxN_EN=0
Off-State (output enabled with inactive state)
Asynchronously: OCx=CCxP, OCx_EN=1, OCxN=CCxNP,
OCxN_EN=1
Then if the clock is present: OCx=OISx and OCxN=OISxN after a
dead-time, assuming that OISx and OISxN do not correspond to OCX
and OCxN both in active state.

1. When both channel outputs are unused (CCxE=CCxNE=0), OISx, OISxN, CCxP and CCxNP bits must be kept cleared.

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Advanced-control timers (TIM1)

Note:

The state of the external I/O pins connected to the complementary OCx and OCxN channels
depends on the OCx and OCxN channel state and the GPIO registers.

17.4.10

TIM1 counter (TIM1_CNT)
Address offset: 0x24
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

CNT[15:0]
rw

rw

rw

Bits 15:0

17.4.11

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]: Counter value

TIM1 prescaler (TIM1_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

rw

PSC[15:0]
rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency (CK_CNT) is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded in the active prescaler register at each update event
(including when the counter is cleared through UG bit of TIMx_EGR register or through trigger
controller when configured in “reset mode”).

17.4.12

TIM1 auto-reload register (TIM1_ARR)
Address offset: 0x2C
Reset value: 0xFFFF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 ARR[15:0]: Auto-reload value
ARR is the value to be loaded in the actual auto-reload register.
Refer to the Section 17.3.1: Time-base unit on page 322 for more details about ARR update
and behavior.
The counter is blocked while the auto-reload value is null.

17.4.13

TIM1 repetition counter register (TIM1_RCR)
Address offset: 0x30
Reset value: 0x0000

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

rw

rw

rw

rw

3

2

1

0

rw

rw

rw

REP[7:0]

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Advanced-control timers (TIM1)

RM0091

Bits 15:8 Reserved, must be kept at reset value.
Bits 7:0 REP[7:0]: Repetition counter value
These bits allow the user to set-up the update rate of the compare registers (i.e. periodic
transfers from preload to active registers) when preload registers are enable, as well as the
update interrupt generation rate, if this interrupt is enable.
Each time the REP_CNT related downcounter reaches zero, an update event is generated
and it restarts counting from REP value. As REP_CNT is reloaded with REP value only at the
repetition update event U_RC, any write to the TIMx_RCR register is not taken in account until
the next repetition update event.
It means in PWM mode (REP+1) corresponds to:
–
the number of PWM periods in edge-aligned mode
–
the number of half PWM period in center-aligned mode.

17.4.14

TIM1 capture/compare register 1 (TIM1_CCR1)
Address offset: 0x34
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR1[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 CCR1[15:0]: Capture/Compare 1 value
If channel CC1 is configured as output:
CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit
OC1PE). Else the preload value is copied in the active capture/compare 1 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC1 output.
If channel CC1 is configured as input:
CCR1 is the counter value transferred by the last input capture 1 event (IC1).

17.4.15

TIM1 capture/compare register 2 (TIM1_CCR2)
Address offset: 0x38
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR2[15:0]

386/1004

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rw

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RM0091

Advanced-control timers (TIM1)

Bits 15:0 CCR2[15:0]: Capture/Compare 2 value
If channel CC2 is configured as output:
CCR2 is the value to be loaded in the actual capture/compare 2 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR2 register (bit
OC2PE). Else the preload value is copied in the active capture/compare 2 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signalled on OC2 output.
If channel CC2 is configured as input:
CCR2 is the counter value transferred by the last input capture 2 event (IC2).

17.4.16

TIM1 capture/compare register 3 (TIM1_CCR3)
Address offset: 0x3C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR3[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 CCR3[15:0]: Capture/Compare value
If channel CC3 is configured as output:
CCR3 is the value to be loaded in the actual capture/compare 3 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR3 register (bit
OC3PE). Else the preload value is copied in the active capture/compare 3 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signalled on OC3 output.
If channel CC3 is configured as input:
CCR3 is the counter value transferred by the last input capture 3 event (IC3).

17.4.17

TIM1 capture/compare register 4 (TIM1_CCR4)
Address offset: 0x40
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR4[15:0]
rw

rw

Bits 15:0 CCR4[15:0]: Capture/Compare value
If channel CC4 is configured as output:
CCR4 is the value to be loaded in the actual capture/compare 4 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR4 register (bit
OC4PE). Else the preload value is copied in the active capture/compare 4 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signalled on OC4 output.
If channel CC4 is configured as input:
CCR4 is the counter value transferred by the last input capture 4 event (IC4).

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Advanced-control timers (TIM1)

17.4.18

RM0091

TIM1 break and dead-time register (TIM1_BDTR)
Address offset: 0x44
Reset value: 0x0000

15

14

13

12

11

10

MOE

AOE

BKP

BKE

OSSR

OSSI

rw

rw

rw

rw

rw

rw

Note:

9

8

7

6

5

LOCK[1:0]
rw

rw

4

3

2

1

0

rw

rw

rw

DTG[7:0]
rw

rw

rw

rw

rw

As the bits AOE, BKP, BKE, OSSI, OSSR and DTG[7:0] can be write-locked depending on
the LOCK configuration, it can be necessary to configure all of them during the first write
access to the TIMx_BDTR register.
Bit 15 MOE: Main output enable
This bit is cleared asynchronously by hardware as soon as the break input is active. It is set by
software or automatically depending on the AOE bit. It is acting only on the channels which are
configured in output.
0: OC and OCN outputs are disabled or forced to idle state.
1: OC and OCN outputs are enabled if their respective enable bits are set (CCxE, CCxNE in
TIMx_CCER register).
See OC/OCN enable description for more details (Section 17.4.9: TIM1 capture/compare
enable register (TIM1_CCER) on page 381).
Bit 14 AOE: Automatic output enable
0: MOE can be set only by software
1: MOE can be set by software or automatically at the next update event (if the break input is
not be active)
Note: This bit cannot be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Bit 13 BKP: Break polarity
0: Break input BRK is active low
1: Break input BRK is active high
Note: This bit can not be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 12 BKE: Break enable
0: Break inputs (BRK and CCS clock failure event) disabled
1; Break inputs (BRK and CCS clock failure event) enabled
Note: This bit cannot be modified when LOCK level 1 has been programmed (LOCK bits in
TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 11 OSSR: Off-state selection for Run mode
This bit is used when MOE=1 on channels having a complementary output which are
configured as outputs. OSSR is not implemented if no complementary output is implemented in
the timer.
See OC/OCN enable description for more details (Section 17.4.9: TIM1 capture/compare
enable register (TIM1_CCER) on page 381).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0).
1: When inactive, OC/OCN outputs are enabled with their inactive level as soon as CCxE=1
or CCxNE=1. Then, OC/OCN enable output signal=1
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).

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Advanced-control timers (TIM1)

Bit 10 OSSI: Off-state selection for Idle mode
This bit is used when MOE=0 on channels configured as outputs.
See OC/OCN enable description for more details (Section 17.4.9: TIM1 capture/compare
enable register (TIM1_CCER) on page 381).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0).
1: When inactive, OC/OCN outputs are forced first with their idle level as soon as CCxE=1 or
CCxNE=1. OC/OCN enable output signal=1)
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).
Bits 9:8 LOCK[1:0]: Lock configuration
These bits offer a write protection against software errors.
00: LOCK OFF - No bit is write protected.
01: LOCK Level 1 = DTG bits in TIMx_BDTR register, OISx and OISxN bits in TIMx_CR2
register and BKE/BKP/AOE bits in TIMx_BDTR register can no longer be written.
10: LOCK Level 2 = LOCK Level 1 + CC Polarity bits (CCxP/CCxNP bits in TIMx_CCER
register, as long as the related channel is configured in output through the CCxS bits) as well
as OSSR and OSSI bits can no longer be written.
11: LOCK Level 3 = LOCK Level 2 + CC Control bits (OCxM and OCxPE bits in
TIMx_CCMRx registers, as long as the related channel is configured in output through the
CCxS bits) can no longer be written.
Note: The LOCK bits can be written only once after the reset. Once the TIMx_BDTR register
has been written, their content is frozen until the next reset.
Bits 7:0 DTG[7:0]: Dead-time generator setup
This bit-field defines the duration of the dead-time inserted between the complementary
outputs. DT correspond to this duration.
DTG[7:5]=0xx => DT=DTG[7:0]x tdtg with tdtg=tDTS.
DTG[7:5]=10x => DT=(64+DTG[5:0])xtdtg with Tdtg=2xtDTS.
DTG[7:5]=110 => DT=(32+DTG[4:0])xtdtg with Tdtg=8xtDTS.
DTG[7:5]=111 => DT=(32+DTG[4:0])xtdtg with Tdtg=16xtDTS.
Example if TDTS=125 ns (8 MHz), dead-time possible values are:
0 to 15875 ns by 125 ns steps,
16 us to 31750 ns by 250 ns steps,
32 us to 63 us by 1 us steps,
64 us to 126 us by 2 us steps
Note: This bit-field can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BDTR register).

17.4.19

TIM1 DMA control register (TIM1_DCR)
Address offset: 0x48
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

8

DBL[4:0]
rw

rw

rw

rw

7

6

5

Res.

Res.

Res.

rw

DocID018940 Rev 9

4

3

2

1

0

rw

rw

DBA[4:0]
rw

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Advanced-control timers (TIM1)

RM0091

Bits 15:13 Reserved, must be kept at reset value.
Bits 12:8 DBL[4:0]: DMA burst length
This 5-bit vector defines the number of DMA transfers (the timer recognizes a burst transfer
when a read or a write access is done to the TIMx_DMAR address)
00000: 1 transfer
00001: 2 transfers
00010: 3 transfers
...
10001: 18 transfers
Bits 7:5 Reserved, must be kept at reset value.
Bits 4:0 DBA[4:0]: DMA base address
This 5-bit vector defines the base-address for DMA transfers (when read/write access are
done through the TIMx_DMAR address). DBA is defined as an offset starting from the address
of the TIMx_CR1 register.
Example:
00000: TIMx_CR1,
00001: TIMx_CR2,
00010: TIMx_SMCR,
...
Example: Let us consider the following transfer: DBL = 7 transfers and DBA = TIMx_CR1. In
this case the transfer is done to/from 7 registers starting from the TIMx_CR1 address.

17.4.20

TIM1 DMA address for full transfer (TIM1_DMAR)
Address offset: 0x4C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

DMAB[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 DMAB[15:0]: DMA register for burst accesses
A read or write operation to the DMAR register accesses the register located at the address
(TIMx_CR1 address) + (DBA + DMA index) x 4
where TIMx_CR1 address is the address of the control register 1, DBA is the DMA base
address configured in TIMx_DCR register, DMA index is automatically controlled by the DMA
transfer, and ranges from 0 to DBL (DBL configured in TIMx_DCR).

Example of how to use the DMA burst feature
In this example the timer DMA burst feature is used to update the contents of the CCRx
registers (x = 2, 3, 4) with the DMA transferring half words into the CCRx registers.
This is done in the following steps:
1.

390/1004

Configure the corresponding DMA channel as follows:
–

DMA channel peripheral address is the DMAR register address

–

DMA channel memory address is the address of the buffer in the RAM containing
the data to be transferred by DMA into CCRx registers.

–

Number of data to transfer = 3 (See note below).

–

Circular mode disabled.

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RM0091

Advanced-control timers (TIM1)
2.

Configure the DCR register by configuring the DBA and DBL bit fields as follows:
DBL = 3 transfers, DBA = 0xE.

3.

Enable the TIMx update DMA request (set the UDE bit in the DIER register).

4.

Enable TIMx

5.

Enable the DMA channel

Note:

This example is for the case where every CCRx register to be updated once. If every CCRx
register is to be updated twice for example, the number of data to transfer should be 6. Let's
take the example of a buffer in the RAM containing data1, data2, data3, data4, data5 and
data6. The data is transferred to the CCRx registers as follows: on the first update DMA
request, data1 is transferred to CCR2, data2 is transferred to CCR3, data3 is transferred to
CCR4 and on the second update DMA request, data4 is transferred to CCR2, data5 is
transferred to CCR3 and data6 is transferred to CCR4.

17.4.21

TIM1 register map
TIM1 registers are mapped as 16-bit addressable registers as described in the table below:

CEN
CCPC

0

0

0

0

0

0

0
UIE

0

0

0

UG

0

CC1G

0

CC2G

0

0

0

0

0

0

0

OC1FE

0

CC3G

0

OC1PE

0

COM

0
CC4G

UIF

CC1IE

0

CC1IF

CC2IE

0

CC2IF

CC3IE

0

CC3IF

CC4IE

OC1M
[2:0]

0 0 0 0 0 0 0 0
IC2
CC2S
PSC
IC1F[3:0]
[1:0]
[1:0]
0 0 0 0 0 0 0 0
CC4S
[1:0]

OC3M
[2:0]

0 0 0 0 0 0 0 0
IC4
CC4S
PSC
IC3F[3:0]
[1:0]
[1:0]
0 0 0 0 0 0 0 0

CC1S
[1:0]

0 0 0 0
IC1
CC1S
PSC
[1:0]
[1:0]
0 0 0 0
OC3FE

0

0

OC3PE

0

OC4M
[2:0]

CC4IF

COMIE

0

COMIF

TIE

Res.

0

CC2S
[1:0]

0

OC3CE

0

OC4FE

0

OC4PE

Res.

OC2M
[2:0]

0

OC1CE

0

OC2FE

0

OC2PE

0

TIF

BIE

Res.

0

TG

UDE

0

BIF

0

BG

0

Res.

CC1DE

0

CC1OF

0

Res.

CC2DE

0

CC2OF

0

Res.

CC3DE

0

CC3OF

0

Res.

CC4DE

0

CC4OF

COMDE

0

Res.

TDE

0

Res.

SMS[2:0]

0

Res.

Res.

TS[2:0]

0

IC4F[3:0]
0

ETF[3:0]

0

IC2F[3:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

URS

0

O24CE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

UDIS

ECE

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

0

0

OC2CE

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.

Res.
Res.

Res.

Res.

Res.
Res.

Res.
Res.

Res.
Res.

0

0

0

DocID018940 Rev 9

0

0

0

0

Res.

Reset value
TIM1_CCMR2
Input capture
mode
Reset value

0

0

0

0

Res.

0x1C

Reset value
TIM1_CCMR1
Input capture
mode
Reset value
TIM1_CCMR2
Output compare
mode

Res.

0x18

Res.

Reset value
TIM1_CCMR1
Output compare
mode

Res.

TIM1_EGR

MMS[2:0]

0

Reset value
0x14

0

Res.

TI1S
0

0

CCUS

OIS1
0

DIR

OIS1N
0

OPM

OIS2
0

0

CCDS

OIS2N
0

0

0

OCCS

OIS3
0

MSM

OIS3N
0

ETPS
[1:0]

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_SR

0

0

Reset value
0x10

0

ETP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_DIER

Res.

0x0C

Res.

Reset value

0

CMS
[1:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_SMCR

Res.

0x08

0
Res.

Reset value

OIS4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_CR2

Res.

0x04

Res.

Reset value

CKD
[1:0]

ARPE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_CR1

Res.

0x00

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 64. TIM1 register map and reset values

CC3S
[1:0]

0 0 0 0
IC3
CC3S
PSC
[1:0]
[1:0]
0 0 0 0

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392/1004
TIM1_DMAR
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_DCR

Res.

0x48
Reset value

Reset value

DocID018940 Rev 9
1
1
1
1
1
1

Res.
Res.
Res.
Res.
Res.
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Reset value

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0

0

0

0

0

0

0

0

0

0

0

0

0
0
0
0
0

0

0

0

0

0

0

0

0
0

0
0

0

0

0

0

0

0

0

0

0

0

0

0
0
0
0

CNT[15:0]
0

DBL[4:0]

0

0
0

1

Reset value
0

0
0

0
0

0
0

0
0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.
0

0

PSC[15:0]
0

ARR[15:0]
1

0

0

0

0

0

0

CC1E

CC2E
CC1NP

0

CC1P

CC2P

0

CC1NE

CC2NE

CC3P
0

CC3E

CC3NE
0

CC2NP

CC4E
CC3NP

CC4P

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0
0
0

Res.

1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_CCER

0

Res.

1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Register

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

OSSI

BKE

Reset value

OSSR

Reset value

BKP

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

AOE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

MOE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM1_BDTR

Res.

0x44
TIM1_CCR4

Res.

0x40
TIM1_CCR3

Res.

0x3C
TIM1_CCR2

Res.

0x38
TIM1_CCR1

Res.

0x34
TIM1_RCR

Res.

0x30
TIM1_ARR

Res.

0x2C
TIM1_PSC

Res.

0x28
TIM1_CNT

Res.

0x24

Res.

0x20

Res.

Offset

Res.

Advanced-control timers (TIM1)
RM0091

Table 64. TIM1 register map and reset values (continued)

0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

1
1
1
1
1
1

REP[7:0]

CCR1[15:0]

CCR2[15:0]

CCR3[15:0]

CCR4[15:0]

LOCK
[1:0]
DT[7:0]

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0

0

0
0
0

DBA[4:0]

DMAB[15:0]
0
0
0
0
0

0
0
0
0
0

RM0091

General-purpose timers (TIM2 and TIM3)

18

General-purpose timers (TIM2 and TIM3)

18.1

TIM2 and TIM3 introduction
The general-purpose timers consist of a 16-bit or 32-bit auto-reload counter driven by a
programmable prescaler.
They may be used for a variety of purposes, including measuring the pulse lengths of input
signals (input capture) or generating output waveforms (output compare and PWM).
Pulse lengths and waveform periods can be modulated from a few microseconds to several
milliseconds using the timer prescaler and the RCC clock controller prescalers.
The timers are completely independent, and do not share any resources. They can be
synchronized together as described in Section 18.3.15.

18.2

TIM2 and TIM3 main features
General-purpose TIMx timer features include:
•

16-bit (TIM3) or 32-bit (TIM2) up, down, up/down auto-reload counter.

•

16-bit programmable prescaler used to divide (also “on the fly”) the counter clock
frequency by any factor between 1 and 65535.

•

Up to 4 independent channels for:
–

Input capture

–

Output compare

–

PWM generation (Edge- and Center-aligned modes)

–

One-pulse mode output

•

Synchronization circuit to control the timer with external signals and to interconnect
several timers.

•

Interrupt/DMA generation on the following events:
–

Update: counter overflow/underflow, counter initialization (by software or
internal/external trigger)

–

Trigger event (counter start, stop, initialization or count by internal/external trigger)

–

Input capture

–

Output compare

•

Supports incremental (quadrature) encoder and hall-sensor circuitry for positioning
purposes

•

Trigger input for external clock or cycle-by-cycle current management

DocID018940 Rev 9

393/1004
458

General-purpose timers (TIM2 and TIM3)

RM0091

Figure 107. General-purpose timer block diagram (TIM2 and TIM3)

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18.3

TIM2 and TIM3 functional description

18.3.1

Time-base unit
The main block of the programmable timer is a 16-bit/32-bit counter with its related autoreload register. The counter can count up but also down or both up and down. The counter
clock can be divided by a prescaler.
The counter, the auto-reload register and the prescaler register can be written or read by
software. This is true even when the counter is running.

394/1004

DocID018940 Rev 9

RM0091

General-purpose timers (TIM2 and TIM3)
The time-base unit includes:
•

Counter Register (TIMx_CNT)

•

Prescaler Register (TIMx_PSC)

•

Auto-Reload Register (TIMx_ARR)

The auto-reload register is preloaded. Writing to or reading from the auto-reload register
accesses the preload register. The content of the preload register are transferred into the
shadow register permanently or at each update event (UEV), depending on the auto-reload
preload enable bit (ARPE) in TIMx_CR1 register. The update event is sent when the counter
reaches the overflow (or underflow when downcounting) and if the UDIS bit equals 0 in the
TIMx_CR1 register. It can also be generated by software. The generation of the update
event is described in detail for each configuration.
The counter is clocked by the prescaler output CK_CNT, which is enabled only when the
counter enable bit (CEN) in TIMx_CR1 register is set (refer also to the slave mode controller
description to get more details on counter enabling).
Note that the actual counter enable signal CNT_EN is set 1 clock cycle after CEN.

Prescaler description
The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It
is based on a 16-bit counter controlled through a 16-bit/32-bit register (in the TIMx_PSC
register). It can be changed on the fly as this control register is buffered. The new prescaler
ratio is taken into account at the next update event.
Figure 108 and Figure 109 give some examples of the counter behavior when the prescaler
ratio is changed on the fly:
Figure 108. Counter timing diagram with prescaler division change from 1 to 2

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458

General-purpose timers (TIM2 and TIM3)

RM0091

Figure 109. Counter timing diagram with prescaler division change from 1 to 4

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18.3.2

Counter modes
Upcounting mode
In upcounting mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register), then restarts from 0 and generates a counter overflow event.
An Update event can be generated at each counter overflow or by setting the UG bit in the
TIMx_EGR register (by software or by using the slave mode controller).
The UEV event can be disabled by software by setting the UDIS bit in TIMx_CR1 register.
This is to avoid updating the shadow registers while writing new values in the preload
registers. Then no update event occurs until the UDIS bit has been written to 0. However,
the counter restarts from 0, as well as the counter of the prescaler (but the prescale rate
does not change). In addition, if the URS bit (update request selection) in TIMx_CR1
register is set, setting the UG bit generates an update event UEV but without setting the UIF
flag (thus no interrupt or DMA request is sent). This is to avoid generating both update and
capture interrupts when clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register)

•

The auto-reload shadow register is updated with the preload value (TIMx_ARR)

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.
396/1004

DocID018940 Rev 9

RM0091

General-purpose timers (TIM2 and TIM3)
Figure 110. Counter timing diagram, internal clock divided by 1

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069

Figure 111. Counter timing diagram, internal clock divided by 2

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DocID018940 Rev 9

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458

General-purpose timers (TIM2 and TIM3)

RM0091

Figure 112. Counter timing diagram, internal clock divided by 4

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Figure 113. Counter timing diagram, internal clock divided by N

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398/1004

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RM0091

General-purpose timers (TIM2 and TIM3)
Figure 114. Counter timing diagram, Update event when ARPE=0
(TIMx_ARR not preloaded)
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Figure 115. Counter timing diagram, Update event when ARPE=1
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069

399/1004
458

General-purpose timers (TIM2 and TIM3)

RM0091

Downcounting mode
In downcounting mode, the counter counts from the auto-reload value (content of the
TIMx_ARR register) down to 0, then restarts from the auto-reload value and generates a
counter underflow event.
An Update event can be generate at each counter underflow or by setting the UG bit in the
TIMx_EGR register (by software or by using the slave mode controller)
The UEV update event can be disabled by software by setting the UDIS bit in TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until UDIS bit has been written to 0.
However, the counter restarts from the current auto-reload value, whereas the counter of the
prescaler restarts from 0 (but the prescale rate doesn’t change).
In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the
UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or
DMA request is sent). This is to avoid generating both update and capture interrupts when
clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register).

•

The auto-reload active register is updated with the preload value (content of the
TIMx_ARR register). Note that the auto-reload is updated before the counter is
reloaded, so that the next period is the expected one.

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.
Figure 116. Counter timing diagram, internal clock divided by 1

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400/1004

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RM0091

General-purpose timers (TIM2 and TIM3)
Figure 117. Counter timing diagram, internal clock divided by 2

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Figure 118. Counter timing diagram, internal clock divided by 4

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458

General-purpose timers (TIM2 and TIM3)

RM0091

Figure 119. Counter timing diagram, internal clock divided by N

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069

Figure 120. Counter timing diagram, Update event when repetition counter is not
used
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RM0091

General-purpose timers (TIM2 and TIM3)

Center-aligned mode (up/down counting)
In center-aligned mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register) – 1, generates a counter overflow event, then counts from the autoreload value down to 1 and generates a counter underflow event. Then it restarts counting
from 0.
Center-aligned mode is active when the CMS bits in TIMx_CR1 register are not equal to
'00'. The Output compare interrupt flag of channels configured in output is set when: the
counter counts down (Center aligned mode 1, CMS = “01”), the counter counts up (Center
aligned mode 2, CMS = “10”) the counter counts up and down (Center aligned mode 3,
CMS = “11”).
In this mode, the direction bit (DIR from TIMx_CR1 register) cannot be written. It is updated
by hardware and gives the current direction of the counter.
The update event can be generated at each counter overflow and at each counter underflow
or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event. In this case, the counter restarts counting from
0, as well as the counter of the prescaler.
The UEV update event can be disabled by software by setting the UDIS bit in TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until the UDIS bit has been written to 0.
However, the counter continues counting up and down, based on the current auto-reload
value.
In addition, if the URS bit (update request selection) in TIMx_CR1 register is set, setting the
UG bit generates an update event UEV but without setting the UIF flag (thus no interrupt or
DMA request is sent). This is to avoid generating both update and capture interrupt when
clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register).

•

The auto-reload active register is updated with the preload value (content of the
TIMx_ARR register). Note that if the update source is a counter overflow, the autoreload is updated before the counter is reloaded, so that the next period is the expected
one (the counter is loaded with the new value).

The following figures show some examples of the counter behavior for different clock
frequencies.

DocID018940 Rev 9

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General-purpose timers (TIM2 and TIM3)

RM0091

Figure 121. Counter timing diagram, internal clock divided by 1, TIMx_ARR=0x6
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069

1. Here, center-aligned mode 1 is used (for more details refer to Section 18.4.1: TIM2 and TIM3 control
register 1 (TIM2_CR1 and TIM3_CR1) on page 435).

Figure 122. Counter timing diagram, internal clock divided by 2

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RM0091

General-purpose timers (TIM2 and TIM3)
Figure 123. Counter timing diagram, internal clock divided by 4, TIMx_ARR=0x36

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1. Center-aligned mode 2 or 3 is used with an UIF on overflow.

Figure 124. Counter timing diagram, internal clock divided by N

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DocID018940 Rev 9

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General-purpose timers (TIM2 and TIM3)

RM0091

Figure 125. Counter timing diagram, Update event with ARPE=1 (counter underflow)
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Figure 126. Counter timing diagram, Update event with ARPE=1 (counter overflow)
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RM0091

18.3.3

General-purpose timers (TIM2 and TIM3)

Clock sources
The counter clock can be provided by the following clock sources:
•

Internal clock (CK_INT)

•

External clock mode1: external input pin (TIx)

•

External clock mode2: external trigger input (ETR)

•

Internal trigger inputs (ITRx): using one timer as prescaler for another timer, for
example, you can configure Timer 1 to act as a prescaler for Timer 2. Refer to : Using
one timer as prescaler for another on page 429 for more details.

Internal clock source (CK_INT)
If the slave mode controller is disabled (SMS=000 in the TIMx_SMCR register), then the
CEN, DIR (in the TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual
control bits and can be changed only by software (except UG which remains cleared
automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal
clock CK_INT.
Figure 127 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 127. Control circuit in normal mode, internal clock divided by 1

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External clock source mode 1
This mode is selected when SMS=111 in the TIMx_SMCR register. The counter can count at
each rising or falling edge on a selected input.

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RM0091

Figure 128. TI2 external clock connection example
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For example, to configure the upcounter to count in response to a rising edge on the TI2
input, use the following procedure:

Note:

1.

Configure channel 2 to detect rising edges on the TI2 input by writing CC2S= ‘01 in the
TIMx_CCMR1 register.

2.

Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1
register (if no filter is needed, keep IC2F=0000).

The capture prescaler is not used for triggering, so you don’t need to configure it.
3.

Select rising edge polarity by writing CC2P=0 and CC2NP=0 in the TIMx_CCER
register.

4.

Configure the timer in external clock mode 1 by writing SMS=111 in the TIMx_SMCR
register.

5.

Select TI2 as the input source by writing TS=110 in the TIMx_SMCR register.

6.

Enable the counter by writing CEN=1 in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.2: Up counter on each 2 ETR rising
edges code example.
When a rising edge occurs on TI2, the counter counts once and the TIF flag is set.
The delay between the rising edge on TI2 and the actual clock of the counter is due to the
resynchronization circuit on TI2 input.

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Figure 129. Control circuit in external clock mode 1

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External clock source mode 2
This mode is selected by writing ECE=1 in the TIMx_SMCR register.
The counter can count at each rising or falling edge on the external trigger input ETR.
The Figure 130 gives an overview of the external trigger input block.
Figure 130. External trigger input block

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For example, to configure the upcounter to count each 2 rising edges on ETR, use the
following procedure:

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RM0091

1.

As no filter is needed in this example, write ETF[3:0]=0000 in the TIMx_SMCR register.

2.

Set the prescaler by writing ETPS[1:0]=01 in the TIMx_SMCR register

3.

Select rising edge detection on the ETR pin by writing ETP=0 in the TIMx_SMCR
register

4.

Enable external clock mode 2 by writing ECE=1 in the TIMx_SMCR register.

5.

Enable the counter by writing CEN=1 in the TIMx_CR1 register.

The counter counts once each 2 ETR rising edges.
The delay between the rising edge on ETR and the actual clock of the counter is due to the
resynchronization circuit on the ETRP signal.
Figure 131. Control circuit in external clock mode 2

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18.3.4

Capture/compare channels
Each Capture/Compare channel is built around a capture/compare register (including a
shadow register), a input stage for capture (with digital filter, multiplexing and prescaler) and
an output stage (with comparator and output control).
The following figure gives an overview of one Capture/Compare channel.
The input stage samples the corresponding TIx input to generate a filtered signal TIxF.
Then, an edge detector with polarity selection generates a signal (TIxFPx) which can be
used as trigger input by the slave mode controller or as the capture command. It is
prescaled before the capture register (ICxPS).

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Figure 132. Capture/compare channel (example: channel 1 input stage)

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The output stage generates an intermediate waveform which is then used for reference:
OCxRef (active high). The polarity acts at the end of the chain.
Figure 133. Capture/compare channel 1 main circuit

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RM0091

Figure 134. Output stage of capture/compare channel (channel 1)
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The capture/compare block is made of one preload register and one shadow register. Write
and read always access the preload register.
In capture mode, captures are actually done in the shadow register, which is copied into the
preload register.
In compare mode, the content of the preload register is copied into the shadow register
which is compared to the counter.

18.3.5

Input capture mode
In Input capture mode, the Capture/Compare Registers (TIMx_CCRx) are used to latch the
value of the counter after a transition detected by the corresponding ICx signal. When a
capture occurs, the corresponding CCXIF flag (TIMx_SR register) is set and an interrupt or
a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was
already high, then the over-capture flag CCxOF (TIMx_SR register) is set. CCxIF can be
cleared by software by writing it to 0 or by reading the captured data stored in the
TIMx_CCRx register. CCxOF is cleared when you write it to 0.
The following example shows how to capture the counter value in TIMx_CCR1 when TI1
input rises. To do this, use the following procedure:
•
•

412/1004

Select the active input: TIMx_CCR1 must be linked to the TI1 input, so write the CC1S
bits to 01 in the TIMx_CCMR1 register. As soon as CC1S becomes different from 00,
the channel is configured in input and the TIMx_CCR1 register becomes read-only.
Program the input filter duration you need with respect to the signal you connect to the
timer (when the input is one of the TIx (ICxF bits in the TIMx_CCMRx register). Let’s
imagine that, when toggling, the input signal is not stable during at must 5 internal clock
cycles. We must program a filter duration longer than these 5 clock cycles. We can
validate a transition on TI1 when 8 consecutive samples with the new level have been

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•
•
•
•

detected (sampled at fDTS frequency). Then write IC1F bits to 0011 in the
TIMx_CCMR1 register.
Select the edge of the active transition on the TI1 channel by writing the CC1P and
CC1NP bits to 0 in the TIMx_CCER register (rising edge in this case).
Program the input prescaler. In our example, we wish the capture to be performed at
each valid transition, so the prescaler is disabled (write IC1PS bits to 00 in the
TIMx_CCMR1 register).
Enable capture from the counter into the capture register by setting the CC1E bit in the
TIMx_CCER register.
If needed, enable the related interrupt request by setting the CC1IE bit in the
TIMx_DIER register, and/or the DMA request by setting the CC1DE bit in the
TIMx_DIER register.

For code example refer to the Appendix section A.9.3: Input capture configuration code
example.
When an input capture occurs:
•
•
•
•

The TIMx_CCR1 register gets the value of the counter on the active transition.
CC1IF flag is set (interrupt flag). CC1OF is also set if at least two consecutive captures
occurred whereas the flag was not cleared.
An interrupt is generated depending on the CC1IE bit.
A DMA request is generated depending on the CC1DE bit.

For code example refer to the Appendix section A.9.4: Input capture data management
code example.
In order to handle the overcapture, it is recommended to read the data before the
overcapture flag. This is to avoid missing an overcapture which could happen after reading
the flag and before reading the data.
Note:

IC interrupt and/or DMA requests can be generated by software by setting the
corresponding CCxG bit in the TIMx_EGR register.

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18.3.6

RM0091

PWM input mode
This mode is a particular case of input capture mode. The procedure is the same except:
•

Two ICx signals are mapped on the same TIx input.

•

These 2 ICx signals are active on edges with opposite polarity.

•

One of the two TIxFP signals is selected as trigger input and the slave mode controller
is configured in reset mode.

For example, you can measure the period (in TIMx_CCR1 register) and the duty cycle (in
TIMx_CCR2 register) of the PWM applied on TI1 using the following procedure (depending
on CK_INT frequency and prescaler value):
•

Select the active input for TIMx_CCR1: write the CC1S bits to 01 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP1 (used both for capture in TIMx_CCR1 and counter
clear): write the CC1P to ‘0’ and the CC1NP bit to ‘0’ (active on rising edge).

•

Select the active input for TIMx_CCR2: write the CC2S bits to 10 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP2 (used for capture in TIMx_CCR2): write the CC2P
bit to ‘1’ and the CC2NP bit to ’0’(active on falling edge).

•

Select the valid trigger input: write the TS bits to 101 in the TIMx_SMCR register
(TI1FP1 selected).

•

Configure the slave mode controller in reset mode: write the SMS bits to 100 in the
TIMx_SMCR register.

•

Enable the captures: write the CC1E and CC2E bits to ‘1 in the TIMx_CCER register.

For code example refer to the Appendix section A.9.5: PWM input configuration code
example.
Figure 135. PWM input mode timing
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18.3.7

General-purpose timers (TIM2 and TIM3)

Forced output mode
In output mode (CCxS bits = 00 in the TIMx_CCMRx register), each output compare signal
(OCxREF and then OCx) can be forced to active or inactive level directly by software,
independently of any comparison between the output compare register and the counter.
To force an output compare signal (ocxref/OCx) to its active level, you just need to write 101
in the OCxM bits in the corresponding TIMx_CCMRx register. Thus ocxref is forced high
(OCxREF is always active high) and OCx get opposite value to CCxP polarity bit.
e.g.: CCxP=0 (OCx active high) => OCx is forced to high level.
ocxref signal can be forced low by writing the OCxM bits to 100 in the TIMx_CCMRx
register.
Anyway, the comparison between the TIMx_CCRx shadow register and the counter is still
performed and allows the flag to be set. Interrupt and DMA requests can be sent
accordingly. This is described in the Output Compare Mode section.

18.3.8

Output compare mode
This function is used to control an output waveform or indicating when a period of time has
elapsed.
When a match is found between the capture/compare register and the counter, the output
compare function:
•

Assigns the corresponding output pin to a programmable value defined by the output
compare mode (OCxM bits in the TIMx_CCMRx register) and the output polarity (CCxP
bit in the TIMx_CCER register). The output pin can keep its level (OCXM=000), be set
active (OCxM=001), be set inactive (OCxM=010) or can toggle (OCxM=011) on match.

•

Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).

•

Generates an interrupt if the corresponding interrupt mask is set (CCXIE bit in the
TIMx_DIER register).

•

Sends a DMA request if the corresponding enable bit is set (CCxDE bit in the
TIMx_DIER register, CCDS bit in the TIMx_CR2 register for the DMA request
selection).

The TIMx_CCRx registers can be programmed with or without preload registers using the
OCxPE bit in the TIMx_CCMRx register.
In output compare mode, the update event UEV has no effect on ocxref and OCx output.
The timing resolution is one count of the counter. Output compare mode can also be used to
output a single pulse (in One-pulse mode).
Procedure:
1.

Select the counter clock (internal, external, prescaler).

2.

Write the desired data in the TIMx_ARR and TIMx_CCRx registers.

3.

Set the CCxIE and/or CCxDE bits if an interrupt and/or a DMA request is to be
generated.

4.

Select the output mode. For example, you must write OCxM=011, OCxPE=0, CCxP=0
and CCxE=1 to toggle OCx output pin when CNT matches CCRx, CCRx preload is not
used, OCx is enabled and active high.

5.

Enable the counter by setting the CEN bit in the TIMx_CR1 register.

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For code example refer to the Appendix section A.9.7: Output compare configuration code
example.
The TIMx_CCRx register can be updated at any time by software to control the output
waveform, provided that the preload register is not enabled (OCxPE=0, else TIMx_CCRx
shadow register is updated only at the next update event UEV). An example is given in
Figure 136.
Figure 136. Output compare mode, toggle on OC1
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18.3.9

PWM mode
Pulse width modulation mode allows you to generate a signal with a frequency determined
by the value of the TIMx_ARR register and a duty cycle determined by the value of the
TIMx_CCRx register.
The PWM mode can be selected independently on each channel (one PWM per OCx
output) by writing 110 (PWM mode 1) or ‘111 (PWM mode 2) in the OCxM bits in the
TIMx_CCMRx register. You must enable the corresponding preload register by setting the
OCxPE bit in the TIMx_CCMRx register, and eventually the auto-reload preload register (in
upcounting or center-aligned modes) by setting the ARPE bit in the TIMx_CR1 register.
As the preload registers are transferred to the shadow registers only when an update event
occurs, before starting the counter, you have to initialize all the registers by setting the UG
bit in the TIMx_EGR register.
OCx polarity is software programmable using the CCxP bit in the TIMx_CCER register. It
can be programmed as active high or active low. OCx output is enabled by the CCxE bit in
the TIMx_CCER register. Refer to the TIMx_CCERx register description for more details.
In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine
whether TIMx_CCRx ≤ TIMx_CNT or TIMx_CNT ≤ TIMx_CCRx (depending on the direction
of the counter). However, to comply with the OCREF_CLR functionality (OCREF can be

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General-purpose timers (TIM2 and TIM3)
cleared by an external event through the ETR signal until the next PWM period), the
OCREF signal is asserted only:
•

When the result of the comparison changes, or

•

When the output compare mode (OCxM bits in TIMx_CCMRx register) switches from
the “frozen” configuration (no comparison, OCxM=‘000) to one of the PWM modes
(OCxM=‘110 or ‘111).

This forces the PWM by software while the timer is running.
The timer is able to generate PWM in edge-aligned mode or center-aligned mode
depending on the CMS bits in the TIMx_CR1 register.

PWM edge-aligned mode
Upcounting configuration
Upcounting is active when the DIR bit in the TIMx_CR1 register is low. Refer to the Section :
Upcounting mode on page 396.
In the following example, we consider PWM mode 1. The reference PWM signal OCxREF is
high as long as TIMx_CNT TIMx_CCRx else
it becomes high. If the compare value in TIMx_CCRx is greater than the auto-reload value in
TIMx_ARR, then ocxref is held at ‘1. 0% PWM is not possible in this mode.

PWM center-aligned mode
Center-aligned mode is active when the CMS bits in TIMx_CR1 register are different from
‘00 (all the remaining configurations having the same effect on the ocxref/OCx signals). The
compare flag is set when the counter counts up, when it counts down or both when it counts
up and down depending on the CMS bits configuration. The direction bit (DIR) in the
TIMx_CR1 register is updated by hardware and must not be changed by software. Refer to
the Center-aligned mode (up/down counting) on page 403.
Figure 138 shows some center-aligned PWM waveforms in an example where:
•
•
•

418/1004

TIMx_ARR=8,
PWM mode is the PWM mode 1,
The flag is set when the counter counts down corresponding to the center-aligned
mode 1 selected for CMS=01 in TIMx_CR1 register.

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Figure 138. Center-aligned PWM waveforms (ARR=8)
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Hints on using center-aligned mode:
•

•

•

When starting in center-aligned mode, the current up-down configuration is used. It
means that the counter counts up or down depending on the value written in the DIR bit
in the TIMx_CR1 register. Moreover, the DIR and CMS bits must not be changed at the
same time by the software.
Writing to the counter while running in center-aligned mode is not recommended as it
can lead to unexpected results. In particular:
–
The direction is not updated if you write a value in the counter that is greater than
the auto-reload value (TIMx_CNT>TIMx_ARR). For example, if the counter was
counting up, it continues to count up.
–
The direction is updated if you write 0 or write the TIMx_ARR value in the counter
but no Update Event UEV is generated.
The safest way to use center-aligned mode is to generate an update by software
(setting the UG bit in the TIMx_EGR register) just before starting the counter and not to
write the counter while it is running.

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18.3.10

RM0091

One-pulse mode
One-pulse mode (OPM) is a particular case of the previous modes. It allows the counter to
be started in response to a stimulus and to generate a pulse with a programmable length
after a programmable delay.
Starting the counter can be controlled through the slave mode controller. Generating the
waveform can be done in output compare mode or PWM mode. You select One-pulse mode
by setting the OPM bit in the TIMx_CR1 register. This makes the counter stop automatically
at the next update event UEV.
A pulse can be correctly generated only if the compare value is different from the counter
initial value. Before starting (when the timer is waiting for the trigger), the configuration must
be:
•

In upcounting: CNTCCRx.
Figure 139. Example of one-pulse mode

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For example you may want to generate a positive pulse on OC1 with a length of tPULSE and
after a delay of tDELAY as soon as a positive edge is detected on the TI2 input pin.
Use TI2FP2 as trigger 1:

420/1004

•

Map TI2FP2 on TI2 by writing CC2S=01 in the TIMx_CCMR1 register.

•

TI2FP2 must detect a rising edge, write CC2P=0 and CC2NP=’0’ in the TIMx_CCER
register.

•

Configure TI2FP2 as trigger for the slave mode controller (TRGI) by writing TS=110 in
the TIMx_SMCR register.

•

TI2FP2 is used to start the counter by writing SMS to ‘110 in the TIMx_SMCR register
(trigger mode).

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General-purpose timers (TIM2 and TIM3)
The OPM waveform is defined by writing the compare registers (taking into account the
clock frequency and the counter prescaler).
•

The tDELAY is defined by the value written in the TIMx_CCR1 register.

•

The tPULSE is defined by the difference between the auto-reload value and the compare
value (TIMx_ARR - TIMx_CCR1 + 1).

•

Let’s say you want to build a waveform with a transition from ‘0 to ‘1 when a compare
match occurs and a transition from ‘1 to ‘0 when the counter reaches the auto-reload
value. To do this you enable PWM mode 2 by writing OC1M=111 in the TIMx_CCMR1
register. You can optionally enable the preload registers by writing OC1PE=1 in the
TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this case you have to
write the compare value in the TIMx_CCR1 register, the auto-reload value in the
TIMx_ARR register, generate an update by setting the UG bit and wait for external
trigger event on TI2. CC1P is written to ‘0 in this example.

In our example, the DIR and CMS bits in the TIMx_CR1 register should be low.
For code example refer to the Appendix section A.9.16: One-Pulse mode code example.
You only want 1 pulse (Single mode), so you write '1 in the OPM bit in the TIMx_CR1
register to stop the counter at the next update event (when the counter rolls over from the
auto-reload value back to 0). When OPM bit in the TIMx_CR1 register is set to '0', so the
Repetitive Mode is selected.

Particular case: OCx fast enable
In One-pulse mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
output toggle. But several clock cycles are needed for these operations and it limits the
minimum delay tDELAY min we can get.
If you want to output a waveform with the minimum delay, you can set the OCxFE bit in the
TIMx_CCMRx register. Then OCxRef (and OCx) are forced in response to the stimulus,
without taking in account the comparison. Its new level is the same as if a compare match
had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.
For code example refer to the part of code, conditioned by PULSE_WITHOUT_DELAY > 0
in the Appendix section A.9.16: One-Pulse mode code example.

18.3.11

Clearing the OCxREF signal on an external event
1.

The external trigger prescaler should be kept off: bits ETPS[1:0] in the TIMx_SMCR
register are cleared to 00.

2.

The external clock mode 2 must be disabled: bit ECE in the TIM1_SMCR register is
cleared to 0.

3.

The external trigger polarity (ETP) and the external trigger filter (ETF) can be
configured according to the application’s needs.

For code example refer to the Appendix section A.9.10: ETR configuration to clear OCxREF
code example.
Figure 140 shows the behavior of the OCxREF signal when the ETRF input becomes high,
for both values of the OCxCE enable bit. In this example, the timer TIMx is programmed in
PWM mode.

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RM0091

Figure 140. Clearing TIMx OCxREF

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1. In case of a PWM with a 100% duty cycle (if CCRx>ARR), OCxREF is enabled again at the next counter
overflow.

18.3.12

Encoder interface mode
To select Encoder Interface mode write SMS=‘001 in the TIMx_SMCR register if the counter
is counting on TI2 edges only, SMS=010 if it is counting on TI1 edges only and SMS=011 if
it is counting on both TI1 and TI2 edges.
Select the TI1 and TI2 polarity by programming the CC1P and CC2P bits in the TIMx_CCER
register. CC1NP and CC2NP must be kept cleared. When needed, you can program the
input filter as well.
The two inputs TI1 and TI2 are used to interface to an incremental encoder. Refer to
Table 65. The counter is clocked by each valid transition on TI1FP1 or TI2FP2 (TI1 and TI2
after input filter and polarity selection, TI1FP1=TI1 if not filtered and not inverted,
TI2FP2=TI2 if not filtered and not inverted) assuming that it is enabled (CEN bit in
TIMx_CR1 register written to ‘1). The sequence of transitions of the two inputs is evaluated
and generates count pulses as well as the direction signal. Depending on the sequence the
counter counts up or down, the DIR bit in the TIMx_CR1 register is modified by hardware
accordingly. The DIR bit is calculated at each transition on any input (TI1 or TI2), whatever
the counter is counting on TI1 only, TI2 only or both TI1 and TI2.
Encoder interface mode acts simply as an external clock with direction selection. This
means that the counter just counts continuously between 0 and the auto-reload value in the
TIMx_ARR register (0 to ARR or ARR down to 0 depending on the direction). So you must
configure TIMx_ARR before starting. In the same way, the capture, compare, prescaler,
trigger output features continue to work as normal.
In this mode, the counter is modified automatically following the speed and the direction of
the incremental encoder and its content, therefore, always represents the encoder’s

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position. The count direction correspond to the rotation direction of the connected sensor.
The table summarizes the possible combinations, assuming TI1 and TI2 don’t switch at the
same time.
Table 65. Counting direction versus encoder signals
Level on opposite
signal (TI1FP1 for
TI2, TI2FP2 for TI1)

Rising

Falling

Rising

Falling

Counting on
TI1 only

High

Down

Up

No Count

No Count

Low

Up

Down

No Count

No Count

Counting on
TI2 only

High

No Count

No Count

Up

Down

Low

No Count

No Count

Down

Up

Counting on
TI1 and TI2

High

Down

Up

Up

Down

Low

Up

Down

Down

Up

Active edge

TI1FP1 signal

TI2FP2 signal

An external incremental encoder can be connected directly to the MCU without external
interface logic. However, comparators are normally be used to convert the encoder’s
differential outputs to digital signals. This greatly increases noise immunity. The third
encoder output which indicate the mechanical zero position, may be connected to an
external interrupt input and trigger a counter reset.
Figure 141 gives an example of counter operation, showing count signal generation and
direction control. It also shows how input jitter is compensated where both edges are
selected. This might occur if the sensor is positioned near to one of the switching points. For
this example we assume that the configuration is the following:
•

CC1S= 01 (TIMx_CCMR1 register, TI1FP1 mapped on TI1)

•

CC2S= 01 (TIMx_CCMR2 register, TI2FP2 mapped on TI2)

•

CC1P=0, CC1NP = ‘0’ (TIMx_CCER register, TI1FP1 noninverted, TI1FP1=TI1)

•

CC2P=0, CC2NP = ‘0’ (TIMx_CCER register, TI2FP2 noninverted, TI2FP2=TI2)

•

SMS= 011 (TIMx_SMCR register, both inputs are active on both rising and falling
edges)

•

CEN= 1 (TIMx_CR1 register, Counter is enabled)

For code example refer to the Appendix section A.9.10: ETR configuration to clear OCxREF
code example.

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RM0091

Figure 141. Example of counter operation in encoder interface mode
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Figure 142 gives an example of counter behavior when TI1FP1 polarity is inverted (same
configuration as above except CC1P=1).
Figure 142. Example of encoder interface mode with TI1FP1 polarity inverted
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The timer, when configured in Encoder Interface mode provides information on the sensor’s
current position. You can obtain dynamic information (speed, acceleration, deceleration) by
measuring the period between two encoder events using a second timer configured in
capture mode. The output of the encoder which indicates the mechanical zero can be used
for this purpose. Depending on the time between two events, the counter can also be read
at regular times. You can do this by latching the counter value into a third input capture
register if available (then the capture signal must be periodic and can be generated by
another timer). when available, it is also possible to read its value through a DMA request
generated by a Real-Time clock.

18.3.13

Timer input XOR function
The TI1S bit in the TIM1_CR2 register, allows the input filter of channel 1 to be connected to
the output of a XOR gate, combining the three input pins TIMx_CH1 to TIMx_CH3.
The XOR output can be used with all the timer input functions such as trigger or input
capture.

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An example of this feature used to interface Hall sensors is given in Section 17.3.18 on
page 361.

18.3.14

Timers and external trigger synchronization
The TIMx Timers can be synchronized with an external trigger in several modes: Reset
mode, Gated mode and Trigger mode.

Slave mode: Reset mode
The counter and its prescaler can be reinitialized in response to an event on a trigger input.
Moreover, if the URS bit from the TIMx_CR1 register is low, an update event UEV is
generated. Then all the preloaded registers (TIMx_ARR, TIMx_CCRx) are updated.
In the following example, the upcounter is cleared in response to a rising edge on TI1 input:
•

Configure the channel 1 to detect rising edges on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits
select the input capture source only, CC1S = 01 in the TIMx_CCMR1 register. Write
CC1P=0 and CC1NP=0 in TIMx_CCER register to validate the polarity (and detect
rising edges only).

•

Configure the timer in reset mode by writing SMS=100 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Start the counter by writing CEN=1 in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.12: Reset mode code example.
The counter starts counting on the internal clock, then behaves normally until TI1 rising
edge. When TI1 rises, the counter is cleared and restarts from 0. In the meantime, the
trigger flag is set (TIF bit in the TIMx_SR register) and an interrupt request, or a DMA
request can be sent if enabled (depending on the TIE and TDE bits in TIMx_DIER register).
The following figure shows this behavior when the auto-reload register TIMx_ARR=0x36.
The delay between the rising edge on TI1 and the actual reset of the counter is due to the
resynchronization circuit on TI1 input.
Figure 143. Control circuit in reset mode

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RM0091

Slave mode: Gated mode
The counter can be enabled depending on the level of a selected input.
In the following example, the upcounter counts only when TI1 input is low:
•

Configure the channel 1 to detect low levels on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits
select the input capture source only, CC1S=01 in TIMx_CCMR1 register. Write
CC1P=1 and CC1NP=0 in TIMx_CCER register to validate the polarity (and detect low
level only).

•

Configure the timer in gated mode by writing SMS=101 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Enable the counter by writing CEN=1 in the TIMx_CR1 register (in gated mode, the
counter doesn’t start if CEN=0, whatever is the trigger input level).

For code example refer to the Appendix section A.9.13: Gated mode code example.
The counter starts counting on the internal clock as long as TI1 is low and stops as soon as
TI1 becomes high. The TIF flag in the TIMx_SR register is set both when the counter starts
or stops.
The delay between the rising edge on TI1 and the actual stop of the counter is due to the
resynchronization circuit on TI1 input.
Figure 144. Control circuit in gated mode

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1. The configuration “CCxP=CCxNP=1” (detection of both rising and falling edges) does not have any effect
in gated mode because gated mode acts on a level and not on an edge.

Slave mode: Trigger mode
The counter can start in response to an event on a selected input.
In the following example, the upcounter starts in response to a rising edge on TI2 input:
•

426/1004

Configure the channel 2 to detect rising edges on TI2. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC2F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. CC2S bits are
selecting the input capture source only, CC2S=01 in TIMx_CCMR1 register. Write

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General-purpose timers (TIM2 and TIM3)
CC2P=1 and CC2NP=0 in TIMx_CCER register to validate the polarity (and detect low
level only).
•

Configure the timer in trigger mode by writing SMS=110 in TIMx_SMCR register. Select
TI2 as the input source by writing TS=110 in TIMx_SMCR register.

For code example refer to the Appendix section A.9.14: Trigger mode code example.
When a rising edge occurs on TI2, the counter starts counting on the internal clock and the
TIF flag is set.
The delay between the rising edge on TI2 and the actual start of the counter is due to the
resynchronization circuit on TI2 input.
Figure 145. Control circuit in trigger mode
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Slave mode: External Clock mode 2 + trigger mode
The external clock mode 2 can be used in addition to another slave mode (except external
clock mode 1 and encoder mode). In this case, the ETR signal is used as external clock
input, and another input can be selected as trigger input when operating in reset mode,
gated mode or trigger mode. It is recommended not to select ETR as TRGI through the TS
bits of TIMx_SMCR register.
In the following example, the upcounter is incremented at each rising edge of the ETR
signal as soon as a rising edge of TI1 occurs:

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1.

2.

3.

RM0091

Configure the external trigger input circuit by programming the TIMx_SMCR register as
follows:
–

ETF = 0000: no filter

–

ETPS=00: prescaler disabled

–

ETP=0: detection of rising edges on ETR and ECE=1 to enable the external clock
mode 2.

Configure the channel 1 as follows, to detect rising edges on TI:
–

IC1F=0000: no filter.

–

The capture prescaler is not used for triggering and does not need to be
configured.

–

CC1S=01in TIMx_CCMR1 register to select only the input capture source

–

CC1P=0 and CC1NP=0 in TIMx_CCER register to validate the polarity (and detect
rising edge only).

Configure the timer in trigger mode by writing SMS=110 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

For code example refer to the Appendix section A.9.15: External clock mode 2 + trigger
mode code example.
A rising edge on TI1 enables the counter and sets the TIF flag. The counter then counts on
ETR rising edges.
The delay between the rising edge of the ETR signal and the actual reset of the counter is
due to the resynchronization circuit on ETRP input.
Figure 146. Control circuit in external clock mode 2 + trigger mode

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18.3.15

Timer synchronization
The TIMx timers are linked together internally for timer synchronization or chaining. When
one Timer is configured in Master Mode, it can reset, start, stop or clock the counter of
another Timer configured in Slave Mode.

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General-purpose timers (TIM2 and TIM3)
Figure 147: Master/Slave timer example presents an overview of the trigger selection and
the master mode selection blocks.

Using one timer as prescaler for another
Figure 147. Master/Slave timer example

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For example, you can configure Timer 1 to act as a prescaler for Timer 2. Refer to
Figure 147. To do this:
•

Configure Timer 1 in master mode so that it outputs a periodic trigger signal on each
update event UEV. If you write MMS=010 in the TIM1_CR2 register, a rising edge is
output on TRGO1 each time an update event is generated.

•

To connect the TRGO1 output of Timer 1 to Timer 2, Timer 2 must be configured in
slave mode using ITR1 as internal trigger. You select this through the TS bits in the
TIM2_SMCR register (writing TS=000).

•

Then the Timer2's slave mode controller should be configured in external clock mode 1
(write SMS=111 in the TIM2_SMCR register). This causes Timer 2 to be clocked by the
rising edge of the periodic Timer 1 trigger signal (which correspond to the timer 1
counter overflow).

•

Finally both timers must be enabled by setting their respective CEN bits within their
respective TIMx_CR1 registers. Make sure to enable Timer2 before enabling Timer1.

For code example refer to the Appendix section A.9.17: Timer prescaling another timer code
example.
Note:

If OCx is selected on Timer 1 as trigger output (MMS=1xx), its rising edge is used to clock
the counter of timer 2.

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RM0091

Using one timer to enable another timer
In this example, we control the enable of Timer 2 with the output compare 1 of Timer 1.
Refer to Figure 147 for connections. Timer 2 counts on the divided internal clock only when
OC1REF of Timer 1 is high. Both counter clock frequencies are divided by 3 by the
prescaler compared to CK_INT (fCK_CNT = fCK_INT/3).
•

Configure Timer 1 master mode to enable the slave timer(MMS=001 in the TIM1_CR2
register).

•

Configure the Timer 1 OC1REF waveform (TIM1_CCMR1 register).

•

Configure Timer 2 to get the input trigger from Timer 1 (TS=000 in the TIM2_SMCR
register).

•

Configure Timer 2 in gated mode (SMS=101 in TIM2_SMCR register).

•

Enable Timer 2 by writing ‘1 in the CEN bit (TIM2_CR1 register).

•

Start Timer 1 by writing ‘1 in the CEN bit (TIM1_CR1 register).

For code example refer to the Appendix section A.9.18: Timer enabling another timer code
example.
Note:

The counter 2 clock is not synchronized with counter 1, this mode only affects the Timer 2
counter enable signal.
Figure 148. Gating timer 2 with OC1REF of timer 1
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In the example in Figure 148, the Timer 2 counter and prescaler are not initialized before
being started. So they start counting from their current value. It is possible to start from a
given value by resetting both timers before starting Timer 1. You can then write any value
you want in the timer counters. The timers can easily be reset by software using the UG bit
in the TIMx_EGR registers.
In the next example, we synchronize Timer 1 and Timer 2. Timer 1 is the master and starts
from 0. Timer 2 is the slave and starts from 0xE7. The prescaler ratio is the same for both

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General-purpose timers (TIM2 and TIM3)
timers. Timer 2 stops when Timer 1 is disabled by writing ‘0 to the CEN bit in the TIM1_CR1
register:
•

Configure Timer 1 master mode to send its Counter Enable signal (CNT_EN) as a
trigger output (MMS=001 in the TIM1_CR2 register).

•

Configure the Timer 1 OC1REF waveform (TIM1_CCMR1 register).

•

Configure Timer 2 to get the input trigger from Timer 1 (TS=000 in the TIM2_SMCR
register).

•

Configure Timer 2 in gated mode (SMS=101 in TIM2_SMCR register).

•

Reset Timer 1 by writing ‘1 in UG bit (TIM1_EGR register).

•

Reset Timer 2 by writing ‘1 in UG bit (TIM2_EGR register).

•

Initialize Timer 2 to 0xE7 by writing ‘0xE7’ in the timer 2 counter (TIM2_CNTL).

•

Enable Timer 2 by writing ‘1 in the CEN bit (TIM2_CR1 register).

•

Start Timer 1 by writing ‘1 in the CEN bit (TIM1_CR1 register).

•

Stop Timer 1 by writing ‘0 in the CEN bit (TIM1_CR1 register).

For code example refer to the Appendix section A.9.19: Master and slave synchronization
code example.
Figure 149. Gating timer 2 with Enable of timer 1
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RM0091

Using one timer to start another timer
In this example, we set the enable of Timer 2 with the update event of Timer 1. Refer to
Figure 147 for connections. Timer 2 starts counting from its current value (which can be
nonzero) on the divided internal clock as soon as the update event is generated by Timer 1.
When Timer 2 receives the trigger signal its CEN bit is automatically set and the counter
counts until we write ‘0 to the CEN bit in the TIM2_CR1 register. Both counter clock
frequencies are divided by 3 by the prescaler compared to CK_INT (fCK_CNT = fCK_INT/3).
•

Configure Timer 1 master mode to send its Update Event (UEV) as trigger output
(MMS=010 in the TIM1_CR2 register).

•

Configure the Timer 1 period (TIM1_ARR registers).

•

Configure Timer 2 to get the input trigger from Timer 1 (TS=000 in the TIM2_SMCR
register).

•

Configure Timer 2 in trigger mode (SMS=110 in TIM2_SMCR register).

•

Start Timer 1 by writing ‘1 in the CEN bit (TIM1_CR1 register).
Figure 150. Triggering timer 2 with update of timer 1
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As in the previous example, you can initialize both counters before starting counting.
Figure 151 shows the behavior with the same configuration as in Figure 150 but in trigger
mode instead of gated mode (SMS=110 in the TIM2_SMCR register).

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Figure 151. Triggering timer 2 with Enable of timer 1
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Starting 2 timers synchronously in response to an external trigger
In this example, we set the enable of timer 1 when its TI1 input rises, and the enable of
Timer 2 with the enable of Timer 1. Refer to Figure 147 for connections. To ensure the
counters are aligned, Timer 1 must be configured in Master/Slave mode (slave with respect
to TI1, master with respect to Timer 2):
•

Configure Timer 1 master mode to send its Enable as trigger output (MMS=001 in the
TIM1_CR2 register).

•

Configure Timer 1 slave mode to get the input trigger from TI1 (TS=100 in the
TIM1_SMCR register).

•

Configure Timer 1 in trigger mode (SMS=110 in the TIM1_SMCR register).

•

Configure the Timer 1 in Master/Slave mode by writing MSM=1 (TIM1_SMCR register).

•

Configure Timer 2 to get the input trigger from Timer 1 (TS=000 in the TIM2_SMCR
register).

•

Configure Timer 2 in trigger mode (SMS=110 in the TIM2_SMCR register).

For code example refer to the Appendix section A.9.20: Two timers synchronized by an
external trigger code example.
When a rising edge occurs on TI1 (Timer 1), both counters starts counting synchronously on
the internal clock and both TIF flags are set.
Note:

In this example both timers are initialized before starting (by setting their respective UG
bits). Both counters starts from 0, but you can easily insert an offset between them by
writing any of the counter registers (TIMx_CNT). You can see that the master/slave mode
insert a delay between CNT_EN and CK_PSC on timer 1.

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RM0091

Figure 152. Triggering timer 1 and 2 with timer 1 TI1 input
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18.3.16

Debug mode
When the microcontroller enters debug mode (ARM® Cortex®-M0 core - halted), the TIMx
counter either continues to work normally or stops, depending on DBG_TIMx_STOP
configuration bit in DBGMCU module.

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18.4

TIM2 and TIM3 registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

18.4.1

TIM2 and TIM3 control register 1 (TIM2_CR1 and TIM3_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

CKD[1:0]
rw

7

6

ARPE

rw

rw

5
CMS

rw

rw

4

3

2

1

0

DIR

OPM

URS

UDIS

CEN

rw

rw

rw

rw

rw

Bits 15:10 Reserved, always read as 0.
Bits 9:8 CKD: Clock division
This bit-field indicates the division ratio between the timer clock (CK_INT) frequency and
sampling clock used by the digital filters (ETR, TIx),
00: tDTS = tCK_INT
01: tDTS = 2 × tCK_INT
10: tDTS = 4 × tCK_INT
11: Reserved
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered
Bits 6:5 CMS: Center-aligned mode selection
00: Edge-aligned mode. The counter counts up or down depending on the direction bit
(DIR).
01: Center-aligned mode 1. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
only when the counter is counting down.
10: Center-aligned mode 2. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
only when the counter is counting up.
11: Center-aligned mode 3. The counter counts up and down alternatively. Output compare
interrupt flags of channels configured in output (CCxS=00 in TIMx_CCMRx register) are set
both when the counter is counting up or down.
Note: It is not allowed to switch from edge-aligned mode to center-aligned mode as long as
the counter is enabled (CEN=1)
Bit 4 DIR: Direction
0: Counter used as upcounter
1: Counter used as downcounter
Note: This bit is read only when the timer is configured in Center-aligned mode or Encoder
mode.
Bit 3 OPM: One-pulse mode
0: Counter is not stopped at update event
1: Counter stops counting at the next update event (clearing the bit CEN)

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Bit 2 URS: Update request source
This bit is set and cleared by software to select the UEV event sources.
0: Any of the following events generate an update interrupt or DMA request if enabled.
These events can be:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
1: Only counter overflow/underflow generates an update interrupt or DMA request if
enabled.
Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable UEV event generation.
0: UEV enabled. The Update (UEV) event is generated by one of the following events:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
Buffered registers are then loaded with their preload values.
1: UEV disabled. The Update event is not generated, shadow registers keep their value
(ARR, PSC, CCRx). However the counter and the prescaler are reinitialized if the UG bit is
set or if a hardware reset is received from the slave mode controller.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled
Note: External clock, gated mode and encoder mode can work only if the CEN bit has been
previously set by software. However trigger mode can set the CEN bit automatically by
hardware.
CEN is cleared automatically in one-pulse mode, when an update event occurs.

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18.4.2

TIM2 and TIM3 control register 2 (TIM2_CR2 and TIM3_CR2)
Address offset: 0x04
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TI1S
rw

6

5

4

MMS[2:0]
rw

rw

rw

3

2

1

0

CCDS

Res.

Res.

Res.

rw

Bits 15:8 Reserved, must be kept at reset value.
Bit 7 TI1S: TI1 selection
0: The TIMx_CH1 pin is connected to TI1 input
1: The TIMx_CH1, CH2 and CH3 pins are connected to the TI1 input (XOR combination)
See also Section 17.3.18: Interfacing with Hall sensors on page 361
Bits 6:4 MMS: Master mode selection
These bits allow to select the information to be sent in master mode to slave timers for
synchronization (TRGO). The combination is as follows:
000: Reset - the UG bit from the TIMx_EGR register is used as trigger output (TRGO). If the
reset is generated by the trigger input (slave mode controller configured in reset mode) then
the signal on TRGO is delayed compared to the actual reset.
001: Enable - the Counter enable signal, CNT_EN, is used as trigger output (TRGO). It is
useful to start several timers at the same time or to control a window in which a slave timer is
enabled. The Counter Enable signal is generated by a logic OR between CEN control bit
and the trigger input when configured in gated mode.
When the Counter Enable signal is controlled by the trigger input, there is a delay on TRGO,
except if the master/slave mode is selected (see the MSM bit description in TIMx_SMCR
register).
010: Update - The update event is selected as trigger output (TRGO). For instance a master
timer can then be used as a prescaler for a slave timer.
011: Compare Pulse - The trigger output send a positive pulse when the CC1IF flag is to be
set (even if it was already high), as soon as a capture or a compare match occurred.
(TRGO)
100: Compare - OC1REF signal is used as trigger output (TRGO)
101: Compare - OC2REF signal is used as trigger output (TRGO)
110: Compare - OC3REF signal is used as trigger output (TRGO)
111: Compare - OC4REF signal is used as trigger output (TRGO)
Bit 3 CCDS: Capture/compare DMA selection
0: CCx DMA request sent when CCx event occurs
1: CCx DMA requests sent when update event occurs
Bits 2:0 Reserved, always read as 0.

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18.4.3

RM0091

TIM2 and TIM3 slave mode control register (TIM2_SMCR and
TIM3_SMCR)
Address offset: 0x08
Reset value: 0x0000

15

14

ETP

ECE

rw

rw

13

12

11

ETPS[1:0]
rw

rw

10

9

8

ETF[3:0]
rw

rw

7

6

MSM

rw

rw

rw

5

4

TS[2:0]
rw

rw

3

2

OCCS
rw

rw

1

0

SMS[2:0]
rw

rw

rw

Bit 15 ETP: External trigger polarity
This bit selects whether ETR or ETR is used for trigger operations
0: ETR is noninverted, active at high level or rising edge
1: ETR is inverted, active at low level or falling edge
Bit 14 ECE: External clock enable
This bit enables External clock mode 2.
0: External clock mode 2 disabled
1: External clock mode 2 enabled. The counter is clocked by any active edge on the ETRF
signal.
1: Setting the ECE bit has the same effect as selecting external clock mode 1 with TRGI
connected to ETRF (SMS=111 and TS=111).
2: It is possible to simultaneously use external clock mode 2 with the following slave modes:
reset mode, gated mode and trigger mode. Nevertheless, TRGI must not be connected to
ETRF in this case (TS bits must not be 111).
3: If external clock mode 1 and external clock mode 2 are enabled at the same time, the
external clock input is ETRF.
Bits 13:12 ETPS: External trigger prescaler
External trigger signal ETRP frequency must be at most 1/4 of CK_INT frequency. A prescaler
can be enabled to reduce ETRP frequency. It is useful when inputting fast external clocks.
00: Prescaler OFF
01: ETRP frequency divided by 2
10: ETRP frequency divided by 4
11: ETRP frequency divided by 8

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Bits 11:8 ETF[3:0]: External trigger filter
This bit-field defines the frequency used to sample ETRP signal and the length of the digital
filter applied to ETRP. The digital filter is made of an event counter in which N consecutive
events are needed to validate a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ETF[3:0] = 1,
2 or 3.
Bit 7 MSM: Master/Slave mode
0: No action
1: The effect of an event on the trigger input (TRGI) is delayed to allow a perfect
synchronization between the current timer and its slaves (through TRGO). It is useful if we
want to synchronize several timers on a single external event.

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Bits 6:4 TS: Trigger selection
This bit-field selects the trigger input to be used to synchronize the counter.
000: Internal Trigger 0 (ITR0).
001: Internal Trigger 1 (ITR1).
010: Internal Trigger 2 (ITR2).
011: Internal Trigger 3 (ITR3).
100: TI1 Edge Detector (TI1F_ED)
101: Filtered Timer Input 1 (TI1FP1)
110: Filtered Timer Input 2 (TI2FP2)
111: External Trigger input (ETRF)
See Table 66: TIM2 and TIM3 internal trigger connection on page 440 for more details on
ITRx meaning for each Timer.
Note: These bits must be changed only when they are not used (e.g. when SMS=000) to
avoid wrong edge detections at the transition.
Bit 3 OCCS: OCREF clear selection.
This bit is used to select the OCREF clear source.
0:OCREF_CLR_INT is connected to the OCREF_CLR input
1: OCREF_CLR_INT is connected to ETRF
Bits 2:0 SMS: Slave mode selection
When external signals are selected the active edge of the trigger signal (TRGI) is linked to the
polarity selected on the external input (see Input Control register and Control Register
description.
000: Slave mode disabled - if CEN = ‘1 then the prescaler is clocked directly by the internal
clock.
001: Encoder mode 1 - Counter counts up/down on TI2FP1 edge depending on TI1FP2
level.
010: Encoder mode 2 - Counter counts up/down on TI1FP2 edge depending on TI2FP1
level.
011: Encoder mode 3 - Counter counts up/down on both TI1FP1 and TI2FP2 edges
depending on the level of the other input.
100: Reset Mode - Rising edge of the selected trigger input (TRGI) reinitializes the counter
and generates an update of the registers.
101: Gated Mode - The counter clock is enabled when the trigger input (TRGI) is high. The
counter stops (but is not reset) as soon as the trigger becomes low. Both start and stop of
the counter are controlled.
110: Trigger Mode - The counter starts at a rising edge of the trigger TRGI (but it is not
reset). Only the start of the counter is controlled.
111: External Clock Mode 1 - Rising edges of the selected trigger (TRGI) clock the counter.
Note: The gated mode must not be used if TI1F_ED is selected as the trigger input (TS=100).
Indeed, TI1F_ED outputs 1 pulse for each transition on TI1F, whereas the gated mode
checks the level of the trigger signal.
Note: The clock of the slave timer must be enabled prior to receive events from the master
timer, and must not be changed on-the-fly while triggers are received from the master
timer.

Table 66. TIM2 and TIM3 internal trigger connection

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Slave TIM

ITR0 (TS = 000)

ITR1 (TS = 001)

ITR2 (TS = 010)

ITR3 (TS = 011)

TIM2

TIM1

TIM15

TIM3

TIM14

TIM3

TIM1

TIM2

TIM15

TIM14

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18.4.4

TIM2 and TIM3 DMA/Interrupt enable register (TIM2_DIER and
TIM3_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

Res.

TDE

Res.

rw

12

11

10

9

CC4DE CC3DE CC2DE CC1DE
rw

rw

rw

rw

8

7

6

5

4

3

2

1

0

UDE

Res.

TIE

Res.

CC4IE

CC3IE

CC2IE

CC1IE

UIE

rw

rw

rw

rw

rw

rw

rw

Bit 15 Reserved, must be kept at reset value.
Bit 14 TDE: Trigger DMA request enable
0: Trigger DMA request disabled.
1: Trigger DMA request enabled.
Bit 13 Reserved, always read as 0
Bit 12 CC4DE: Capture/Compare 4 DMA request enable
0: CC4 DMA request disabled.
1: CC4 DMA request enabled.
Bit 11 CC3DE: Capture/Compare 3 DMA request enable
0: CC3 DMA request disabled.
1: CC3 DMA request enabled.
Bit 10 CC2DE: Capture/Compare 2 DMA request enable
0: CC2 DMA request disabled.
1: CC2 DMA request enabled.
Bit 9 CC1DE: Capture/Compare 1 DMA request enable
0: CC1 DMA request disabled.
1: CC1 DMA request enabled.
Bit 8 UDE: Update DMA request enable
0: Update DMA request disabled.
1: Update DMA request enabled.
Bit 7 Reserved, must be kept at reset value.
Bit 6 TIE: Trigger interrupt enable
0: Trigger interrupt disabled.
1: Trigger interrupt enabled.
Bit 5 Reserved, must be kept at reset value.
Bit 4 CC4IE: Capture/Compare 4 interrupt enable
0: CC4 interrupt disabled.
1: CC4 interrupt enabled.
Bit 3 CC3IE: Capture/Compare 3 interrupt enable
0: CC3 interrupt disabled
1: CC3 interrupt enabled

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Bit 2 CC2IE: Capture/Compare 2 interrupt enable
0: CC2 interrupt disabled
1: CC2 interrupt enabled
Bit 1 CC1IE: Capture/Compare 1 interrupt enable
0: CC1 interrupt disabled
1: CC1 interrupt enabled
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled
1: Update interrupt enabled

18.4.5

TIM2 and TIM3 status register (TIM2_SR and TIM3_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

CC4OF CC3OF CC2OF CC1OF
rc_w0

rc_w0

rc_w0

8

7

6

5

4

3

2

1

0

Res.

Res.

TIF

Res.

CC4IF

CC3IF

CC2IF

CC1IF

UIF

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

Bit 15:13 Reserved, always read as 0.
Bit 12 CC4OF: Capture/Compare 4 overcapture flag
Refer to CC1OF description
Bit 11 CC3OF: Capture/Compare 3 overcapture flag
Refer to CC1OF description
Bit 10 CC2OF: Capture/compare 2 overcapture flag
Refer to CC1OF description
Bit 9 CC1OF: Capture/Compare 1 overcapture flag
This flag is set by hardware only when the corresponding channel is configured in input capture
mode. It is cleared by software by writing it to ‘0.
0: No overcapture has been detected
1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was
already set
Bits 8:7 Reserved, always read as 0.
Bit 6 TIF: Trigger interrupt flag
This flag is set by hardware on trigger event (active edge detected on TRGI input when the
slave mode controller is enabled in all modes but gated mode. It is set when the counter starts
or stops when gated mode is selected. It is cleared by software.
0: No trigger event occurred
1: Trigger interrupt pending
Bit 5 Reserved, always read as 0.
Bit 4 CC4IF: Capture/Compare 4 interrupt flag
Refer to CC1IF description
Bit 3 CC3IF: Capture/Compare 3 interrupt flag
Refer to CC1IF description

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Bit 2 CC2IF: Capture/Compare 2 interrupt flag
Refer to CC1IF description
Bit 1 CC1IF: Capture/compare 1 interrupt flag
If channel CC1 is configured as output:
This flag is set by hardware when the counter matches the compare value, with some
exception in center-aligned mode (refer to the CMS bits in the TIMx_CR1 register description).
It is cleared by software.
0: No match
1: The content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register.
When the contents of TIMx_CCR1 are greater than the contents of TIMx_ARR, the CC1IF bit
goes high on the counter overflow (in upcounting and up/down-counting modes) or underflow
(in downcounting mode)
If channel CC1 is configured as input:
This bit is set by hardware on a capture. It is cleared by software or by reading the
TIMx_CCR1 register.
0: No input capture occurred
1: The counter value has been captured in TIMx_CCR1 register (An edge has been detected
on IC1 which matches the selected polarity)
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending.
This bit is set by hardware when the registers are updated:
At overflow or underflow and if UDIS=0 in the TIMx_CR1 register.
When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if URS=0 and
UDIS=0 in the TIMx_CR1 register.
When CNT is reinitialized by a trigger event (refer to the synchro control register description), if
URS=0 and UDIS=0 in the TIMx_CR1 register.

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18.4.6

RM0091

TIM2 and TIM3 event generation register (TIM2_EGR and
TIM3_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TG

Res.

CC4G

CC3G

CC2G

CC1G

UG

w

w

w

w

w

w

Bits 15:7 Reserved, must be kept at reset value.
Bit 6 TG: Trigger generation
This bit is set by software in order to generate an event, it is automatically cleared by hardware.
0: No action
1: The TIF flag is set in TIMx_SR register. Related interrupt or DMA transfer can occur if
enabled.
Bit 5 Reserved, must be kept at reset value.
Bit 4 CC4G: Capture/compare 4 generation
Refer to CC1G description
Bit 3 CC3G: Capture/compare 3 generation
Refer to CC1G description
Bit 2 CC2G: Capture/compare 2 generation
Refer to CC1G description
Bit 1 CC1G: Capture/compare 1 generation
This bit is set by software in order to generate an event, it is automatically cleared by hardware.
0: No action
1: A capture/compare event is generated on channel 1:
If channel CC1 is configured as output:
CC1IF flag is set, Corresponding interrupt or DMA request is sent if enabled.
If channel CC1 is configured as input:
The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set,
the corresponding interrupt or DMA request is sent if enabled. The CC1OF flag is set if the
CC1IF flag was already high.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action
1: Re-initialize the counter and generates an update of the registers. Note that the prescaler
counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared if
the center-aligned mode is selected or if DIR=0 (upcounting), else it takes the auto-reload
value (TIMx_ARR) if DIR=1 (downcounting).

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18.4.7

TIM2 and TIM3 capture/compare mode register 1 (TIM2_CCMR1 and
TIM3_CCMR1)
Address offset: 0x18
Reset value: 0x0000
The channels can be used in input (capture mode) or in output (compare mode). The
direction of a channel is defined by configuring the corresponding CCxS bits. All the other
bits of this register have a different function in input and in output mode. For a given bit,
OCxx describes its function when the channel is configured in output, ICxx describes its
function when the channel is configured in input. So you must take care that the same bit
can have a different meaning for the input stage and for the output stage.

15

14

OC2CE

13

12

OC2M[2:0]
IC2F[3:0]

rw

rw

rw

11

10

OC2PE OC2FE
IC2PSC[1:0]
rw

rw

rw

9

8

CC2S[1:0]
rw

7

6

OC1CE

rw

5

4

OC1M[2:0]
IC1F[3:0]

rw

rw

rw

3

2

OC1PE OC1FE
IC1PSC[1:0]
rw

rw

rw

1

0

CC1S[1:0]
rw

rw

Output compare mode
Bit 15 OC2CE: Output compare 2 clear enable
Bits 14:12 OC2M[2:0]: Output compare 2 mode
Bit 11 OC2PE: Output compare 2 preload enable
Bit 10 OC2FE: Output compare 2 fast enable
Bits 9:8 CC2S[1:0]: Capture/Compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output
01: CC2 channel is configured as input, IC2 is mapped on TI2
10: CC2 channel is configured as input, IC2 is mapped on TI1
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if
an internal trigger input is selected through the TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = 0 in TIMx_CCER).
Bit 7 OC1CE: Output compare 1 clear enable
OC1CE: Output Compare 1 Clear Enable
0: OC1Ref is not affected by the ETRF input
1: OC1Ref is cleared as soon as a High level is detected on ETRF input

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Bits 6:4 OC1M: Output compare 1 mode
These bits define the behavior of the output reference signal OC1REF from which OC1 and
OC1N are derived. OC1REF is active high whereas OC1 and OC1N active level depends on
CC1P and CC1NP bits.
000: Frozen - The comparison between the output compare register TIMx_CCR1 and the
counter TIMx_CNT has no effect on the outputs.(this mode is used to generate a timing base).
001: Set channel 1 to active level on match. OC1REF signal is forced high when the counter
TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
010: Set channel 1 to inactive level on match. OC1REF signal is forced low when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
011: Toggle - OC1REF toggles when TIMx_CNT=TIMx_CCR1.
100: Force inactive level - OC1REF is forced low.
101: Force active level - OC1REF is forced high.
110: PWM mode 1 - In upcounting, channel 1 is active as long as TIMx_CNTTIMx_CCR1 else active (OC1REF=1).
111: PWM mode 2 - In upcounting, channel 1 is inactive as long as TIMx_CNTTIMx_CCR1 else
inactive.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=00 (the channel is configured in
output).
2: In PWM mode 1 or 2, the OCREF level changes only when the result of the
comparison changes or when the output compare mode switches from “frozen” mode
to “PWM” mode.
Bit 3 OC1PE: Output compare 1 preload enable
0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the
new value is taken in account immediately.
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded in the active register at each update event.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=00 (the channel is configured in
output).
2: The PWM mode can be used without validating the preload register only in onepulse mode (OPM bit set in TIMx_CR1 register). Else the behavior is not guaranteed.
Bit 2 OC1FE: Output compare 1 fast enable
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is
ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is
5 clock cycles.
1: An active edge on the trigger input acts like a compare match on CC1 output. Then, OC
is set to the compare level independently from the result of the comparison. Delay to sample
the trigger input and to activate CC1 output is reduced to 3 clock cycles. OCFE acts only if
the channel is configured in PWM1 or PWM2 mode.
Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output.
01: CC1 channel is configured as input, IC1 is mapped on TI1.
10: CC1 channel is configured as input, IC1 is mapped on TI2.
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

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Input capture mode
Bits 15:12 IC2F: Input capture 2 filter
Bits 11:10 IC2PSC[1:0]: Input capture 2 prescaler
Bits 9:8 CC2S: Capture/compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output.
01: CC2 channel is configured as input, IC2 is mapped on TI2.
10: CC2 channel is configured as input, IC2 is mapped on TI1.
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = 0 in TIMx_CCER).
Bits 7:4 IC1F: Input capture 1 filter
This bit-field defines the frequency used to sample TI1 input and the length of the digital filter
applied to TI1. The digital filter is made of an event counter in which N consecutive events are
needed to validate a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ICxF[3:0] = 1,
2 or 3.
Bits 3:2 IC1PSC: Input capture 1 prescaler
This bit-field defines the ratio of the prescaler acting on CC1 input (IC1).
The prescaler is reset as soon as CC1E=0 (TIMx_CCER register).
00: no prescaler, capture is done each time an edge is detected on the capture input
01: capture is done once every 2 events
10: capture is done once every 4 events
11: capture is done once every 8 events
Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

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18.4.8

RM0091

TIM2 and TIM3 capture/compare mode register 2 (TIM2_CCMR2 and
TIM3_CCMR2)
Address offset: 0x1C
Reset value: 0x0000
Refer to the above CCMR1 register description.

15

14

OC4CE

13

12

OC4M[2:0]
IC4F[3:0]

rw

rw

rw

11

10

OC4PE OC4FE
IC4PSC[1:0]
rw

rw

rw

9

8

CC4S[1:0]
rw

7

6

OC3CE

rw

5

4

OC3M[2:0]
IC3F[3:0]

rw

rw

rw

3

2

OC3PE OC3FE
IC3PSC[1:0]
rw

rw

rw

1

0

CC3S[1:0]
rw

rw

Output compare mode
Bit 15 OC4CE: Output compare 4 clear enable
Bits 14:12 OC4M: Output compare 4 mode
Bit 11 OC4PE: Output compare 4 preload enable
Bit 10 OC4FE: Output compare 4 fast enable
Bits 9:8 CC4S: Capture/Compare 4 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC4 channel is configured as output
01: CC4 channel is configured as input, IC4 is mapped on TI4
10: CC4 channel is configured as input, IC4 is mapped on TI3
11: CC4 channel is configured as input, IC4 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC4S bits are writable only when the channel is OFF (CC4E = 0 in TIMx_CCER).
Bit 7 OC3CE: Output compare 3 clear enable
Bits 6:4 OC3M: Output compare 3 mode
Bit 3 OC3PE: Output compare 3 preload enable
Bit 2 OC3FE: Output compare 3 fast enable
Bits 1:0 CC3S: Capture/Compare 3 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC3 channel is configured as output
01: CC3 channel is configured as input, IC3 is mapped on TI3
10: CC3 channel is configured as input, IC3 is mapped on TI4
11: CC3 channel is configured as input, IC3 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC3S bits are writable only when the channel is OFF (CC3E = 0 in TIMx_CCER).

448/1004

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RM0091

General-purpose timers (TIM2 and TIM3)

Input capture mode
Bits 15:12 IC4F: Input capture 4 filter
Bits 11:10 IC4PSC: Input capture 4 prescaler
Bits 9:8 CC4S: Capture/Compare 4 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC4 channel is configured as output
01: CC4 channel is configured as input, IC4 is mapped on TI4
10: CC4 channel is configured as input, IC4 is mapped on TI3
11: CC4 channel is configured as input, IC4 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC4S bits are writable only when the channel is OFF (CC4E = 0 in TIMx_CCER).
Bits 7:4 IC3F: Input capture 3 filter
Bits 3:2 IC3PSC: Input capture 3 prescaler
Bits 1:0 CC3S: Capture/Compare 3 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC3 channel is configured as output
01: CC3 channel is configured as input, IC3 is mapped on TI3
10: CC3 channel is configured as input, IC3 is mapped on TI4
11: CC3 channel is configured as input, IC3 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC3S bits are writable only when the channel is OFF (CC3E = 0 in TIMx_CCER).

18.4.9

TIM2 and TIM3 capture/compare enable register (TIM2_CCER and
TIM3_CCER)
Address offset: 0x20
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

CC4NP

Res.

CC4P

CC4E

CC3NP

Res.

CC3P

CC3E

CC2NP

Res.

CC2P

CC2E

CC1NP

Res.

CC1P

CC1E

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bit 15 CC4NP: Capture/Compare 4 output Polarity.
Refer to CC1NP description
Bit 14

Reserved, always read as 0.

Bit 13 CC4P: Capture/Compare 4 output Polarity.
Refer to CC1P description
Bit 12 CC4E: Capture/Compare 4 output enable.
Refer to CC1E description
Bit 11 CC3NP: Capture/Compare 3 output Polarity.
Refer to CC1NP description
Bit 10

Reserved, always read as 0.

Bit 9 CC3P: Capture/Compare 3 output Polarity.
Refer to CC1P description

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RM0091

Bit 8 CC3E: Capture/Compare 3 output enable.
Refer to CC1E description
Bit 7 CC2NP: Capture/Compare 2 output Polarity.
Refer to CC1NP description
Bit 6 Reserved, always read as 0.
Bit 5 CC2P: Capture/Compare 2 output Polarity.
Refer to CC1P description
Bit 4 CC2E: Capture/Compare 2 output enable.
Refer to CC1E description
Bit 3 CC1NP: Capture/Compare 1 output Polarity.
CC1 channel configured as output:
CC1NP must be kept cleared in this case.
CC1 channel configured as input:
This bit is used in conjunction with CC1P to define TI1FP1/TI2FP1 polarity. refer to CC1P
description.
Bit 2

Reserved, always read as 0.

Bit 1 CC1P: Capture/Compare 1 output Polarity.
CC1 channel configured as output:
0: OC1 active high
1: OC1 active low
CC1 channel configured as input:
CC1NP/CC1P bits select TI1FP1 and TI2FP1 polarity for trigger or capture operations.
00: noninverted/rising edge
Circuit is sensitive to TIxFP1 rising edge (capture, trigger in reset, external clock or trigger
mode), TIxFP1 is not inverted (trigger in gated mode, encoder mode).
01: inverted/falling edge
Circuit is sensitive to TIxFP1 falling edge (capture, trigger in reset, external clock or trigger
mode), TIxFP1 is inverted (trigger in gated mode, encoder mode).
10: reserved, do not use this configuration.
11: noninverted/both edges
Circuit is sensitive to both TIxFP1 rising and falling edges (capture, trigger in reset, external
clock or trigger mode), TIxFP1 is not inverted (trigger in gated mode). This configuration
must not be used for encoder mode.
Bit 0 CC1E: Capture/Compare 1 output enable.
CC1 channel configured as output:
0: Off - OC1 is not active
1: On - OC1 signal is output on the corresponding output pin
CC1 channel configured as input:
This bit determines if a capture of the counter value can actually be done into the input
capture/compare register 1 (TIMx_CCR1) or not.
0: Capture disabled
1: Capture enabled

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RM0091

General-purpose timers (TIM2 and TIM3)
Table 67. Output control bit for standard OCx channels
CCxE bit

OCx output state

0

Output Disabled (OCx=0, OCx_EN=0)

1

OCx=OCxREF + Polarity, OCx_EN=1

Note:

The state of the external IO pins connected to the standard OCx channels depends on the
OCx channel state and the GPIO registers.

18.4.10

TIM2 and TIM3 counter (TIM2_CNT and TIM3_CNT)
Address offset: 0x24
Reset value: 0x00000000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

CNT[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 CNT[31:16]: High counter value (on TIM2).
Bits 15:0 CNT[15:0]: Low counter value

18.4.11

TIM2 and TIM3 prescaler (TIM2_PSC and TIM3_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

PSC[15:0]
rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency CK_CNT is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded in the active prescaler register at each update event.

18.4.12

TIM2 and TIM3 auto-reload register (TIM2_ARR and TIM3_ARR)
Address offset: 0x2C
Reset value: 0xFFFFFFFF

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

ARR[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

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RM0091

Bits 31:16 ARR[31:16]: High auto-reload value (on TIM2).
Bits 15:0 ARR[15:0]: Low Auto-reload value
ARR is the value to be loaded in the actual auto-reload register.
Refer to Section 18.3.1: Time-base unit on page 394 for more details about ARR update and
behavior.
The counter is blocked while the auto-reload value is null.

18.4.13

TIM2 and TIM3 capture/compare register 1 (TIM2_CCR1 and
TIM3_CCR1)
Address offset: 0x34
Reset value: 0x00000000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

CCR1[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

rw

rw

rw

rw

rw

rw

rw

rw

rw

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR1[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 CCR1[31:16]: High Capture/Compare 1 value (on TIM2).
Bits 15:0 CCR1[15:0]: Low Capture/Compare 1 value
If channel CC1 is configured as output:
CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit
OC1PE). Otherwise the preload value is copied in the active capture/compare 1 register when
an update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC1 output.
If channel CC1is configured as input:
CCR1 is the counter value transferred by the last input capture 1 event (IC1).

18.4.14

TIM2 and TIM3 capture/compare register 2 (TIM2_CCR2 and
TIM3_CCR2)
Address offset: 0x38
Reset value: 0x00000000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

CCR2[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

rw

rw

rw

rw

rw

rw

rw

rw

rw

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR2[15:0]
rw

452/1004

rw

rw

rw

rw

rw

rw

rw

rw

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RM0091

General-purpose timers (TIM2 and TIM3)

Bits 31:16 CCR2[31:16]: High Capture/Compare 2 value (on TIM2).
Bits 15:0 CCR2[15:0]: Low Capture/Compare 2 value
If channel CC2 is configured as output:
CCR2 is the value to be loaded in the actual capture/compare 2 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR2 register (bit
OC2PE). Else the preload value is copied in the active capture/compare 2 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC2 output.
If channel CC2 is configured as input:
CCR2 is the counter value transferred by the last input capture 2 event (IC2).

18.4.15

TIM2 and TIM3 capture/compare register 3 (TIM2_CCR3 and
TIM3_CCR3)
Address offset: 0x3C
Reset value: 0x00000000

31

30

29

28

27

26

25

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

24

23

22

21

20

19

18

17

16

CCR3[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

rw

rw

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR3[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 CCR3[31:16]: High Capture/Compare 3 value (on TIM2).
Bits 15:0 CCR3[15:0]: Low Capture/Compare 3 value
If channel CC3 is configured as output:
CCR3 is the value to be loaded in the actual capture/compare 3 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR3 register (bit
OC3PE). Else the preload value is copied in the active capture/compare 3 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC3 output.
If channel CC3is configured as input:
CCR3 is the counter value transferred by the last input capture 3 event (IC3).

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18.4.16

RM0091

TIM2 and TIM3 capture/compare register 4 (TIM2_CCR4 and
TIM3_CCR4)
Address offset: 0x40
Reset value: 0x00000000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

CCR4[31:16] (TIM2 only)
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR4[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 CCR4[31:16]: High Capture/Compare 4 value (on TIM2)
Bits 15:0 CCR4[15:0]: Low Capture/Compare 4 value
1.
If CC4 channel is configured as output (CC4S bits):
CCR4 is the value to be loaded in the actual capture/compare 4 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR4
register (bit OC4PE). Otherwise, the preload value is copied in the active
capture/compare 4 register when an update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC4 output.
2.
If CC4 channel is configured as input (CC4S bits in TIMx_CCMR4 register):
CCR4 is the counter value transferred by the last input capture 4 event (IC4).

18.4.17

TIM2 and TIM3 DMA control register (TIM2_DCR and TIM3_DCR)
Address offset: 0x48
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

8

DBL[4:0]
rw

rw

rw

rw

7

6

5

Res.

Res.

Res.

rw

Bits 15:13 Reserved, always read as 0.

454/1004

DocID018940 Rev 9

4

3

2

1

0

rw

rw

DBA[4:0]
rw

rw

rw

RM0091

General-purpose timers (TIM2 and TIM3)

Bits 12:8 DBL[4:0]: DMA burst length
This 5-bit vector defines the number of DMA transfers (the timer recognizes a burst transfer
when a read or a write access is done to the TIMx_DMAR address).
00000: 1 transfer,
00001: 2 transfers,
00010: 3 transfers,
...
10001: 18 transfers.
Bits 7:5 Reserved, always read as 0.
Bits 4:0 DBA[4:0]: DMA base address
This 5-bit vector defines the base-address for DMA transfers (when read/write access are done
through the TIMx_DMAR address). DBA is defined as an offset starting from the address of the
TIMx_CR1 register.
Example:
00000: TIMx_CR1,
00001: TIMx_CR2,
00010: TIMx_SMCR,
...
Example: Let us consider the following transfer: DBL = 7 transfers & DBA = TIMx_CR1. In this
case the transfer is done to/from 7 registers starting from the TIMx_CR1 address.

18.4.18

TIM2 and TIM3 DMA address for full transfer (TIM2_DMAR and
TIM3_DMAR)
Address offset: 0x4C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

DMAB[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 DMAB[15:0]: DMA register for burst accesses
A read or write operation to the DMAR register accesses the register located at the address
(TIMx_CR1 address) + (DBA + DMA index) x 4
where TIMx_CR1 address is the address of the control register 1, DBA is the DMA base
address configured in TIMx_DCR register, DMA index is automatically controlled by the DMA
transfer, and ranges from 0 to DBL (DBL configured in TIMx_DCR).

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RM0091

Example of how to use the DMA burst feature
In this example the timer DMA burst feature is used to update the contents of the CCRx
registers (x = 2, 3, 4) with the DMA transferring half words into the CCRx registers.
This is done in the following steps:
1.

Configure the corresponding DMA channel as follows:
–

DMA channel peripheral address is the DMAR register address

–

DMA channel memory address is the address of the buffer in the RAM containing
the data to be transferred by DMA into CCRx registers.

–

Number of data to transfer = 3 (See note below).

–

Circular mode disabled.

2.

Configure the DCR register by configuring the DBA and DBL bit fields as follows:
DBL = 3 transfers, DBA = 0xE.

3.

Enable the TIMx update DMA request (set the UDE bit in the DIER register).

4.

Enable TIMx

5.

Enable the DMA channel

For code example refer to the Appendix section A.9.20: Two timers synchronized by an
external trigger code example.
Note:

456/1004

This example is for the case where every CCRx register to be updated once. If every CCRx
register is to be updated twice for example, the number of data to transfer should be 6. Let
us take the example of a buffer in the RAM containing data1, data2, data3, data4, data5 and
data6. The data is transferred to the CCRx registers as follows: on the first update DMA
request, data1 is transferred to CCR2, data2 is transferred to CCR3, data3 is transferred to
CCR4 and on the second update DMA request, data4 is transferred to CCR2, data5 is
transferred to CCR3 and data6 is transferred to CCR4.

DocID018940 Rev 9

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

TIM2_PSC and
TIM3_PSC

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0x28

Reset value

Res.

0x24

Res.

0x20

TIM2_CCER and
TIM3_CCER

TIM2_CNT and
TIM3_CNT

Reset value

Reset value

DocID018940 Rev 9
0
0
0
0
0
0
0
0
0

Res.

CC3P

CC3E

CC2NP

Res.

0

0
0

0

0

0

0

0
0

OC4M
[2:0]

0
0

IC4F[3:0]

0

0
0

0
0

0
0

CNT[31:16]
(TIM2 only)

0

0

0

0

CC2S
[1:0]

0

0

0

0

0
0

0

0

0
0

IC2
CC2S
PSC
[1:0]
[1:0]

0
0

CC4S
[1:0]

0

IC4
CC4S
PSC
[1:0]
[1:0]

0

0

0

0

0

0

0

CC2G
CC1G
UG

0

0
0
0
0
0

OC1FE

OC1M
[2:0]

CC3G

0
OC1PE

0
0
0
0

0
0
0
0
0
0

Res.
0

Res.

UIE

UIF

TG

CC1IE

CC1IF
0

CC2IE

CC2IF
0

CC3IE

CC3IF
0

CC4IE

CC4IF
0

Res.
0

0

TIF
0
CC4G

TIE

0

Res.

Res.

UDE

0
Res.

0

Res.

0

MSM

0

TS[2:0]

0

IC1F[3:0]

0
0

OC3M
[2:0]

0
0

IC3F[3:0]

OCCS

0

0
0

OC3FE

IC2F[3:0]
0

Res.

Res.
0

OC1CE

0

CC1DE

CC1OF

0
Res.

0

CC2DE

CC2OF

0
Res.

0

CC3DE

CC3OF

0
Res.

0
0

OC3PE

0

OC3CE

0
OC2FE

OC2M
[2:0]
OC2PE

0

Res.
TI1S

Res.

Res.

Res.

Res.

0

CC4DE

CC4OF

Reset value

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

ARPE

DIR
OPM
URS
UDIS
CEN

0
0
0
0
0

MMS[2:0]
CCDS
Res.
Res.
Res.

0

0

0

0

0

0

0

CNT[15:0]

PSC[15:0]

0

0

0

0

0

0

0

0

0
0
0
0

CC1E

0

Res.

0

ETF[3:0]

0

Res.

0
0
Res.

Res.

ECE
0

TDE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

ETP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

CMS
[1:0]

CC1P

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

OC4FE

0
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

OC4PE

OC2CE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

ETPS
[1:0]

0

CC1NP

0

CC3NP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

CC2E

0

CC4E

O24CE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value
CKD
[1:0]

CC2P

0

CC4P

0
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

CC4NP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value
TIM2_CCMR1
and
TIM3_CCMR1
Output compare
mode
Reset value
TIM2_CCMR1
and
TIM3_CCMR1
Input capture
mode
Reset value
TIM2_CCMR2
and
TIM3_CCMR2
Output compare
mode
Reset value
TIM2_CCMR2
and
TIM3_CCMR2
Input capture
mode
Reset value
Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

0x14
TIM2_EGR and
TIM3_EGR

Res.

0x10
TIM2_SR and
TIM3_SR

Res.

0x0C
TIM2_DIER and
TIM3_DIER

Res.

0x08
TIM2_SMCR and
TIM3_SMCR

Res.

0x04
TIM2_CR2 and
TIM3_CR2

Res.

TIM2_CR1 and
TIM3_CR1

Res.

0x00

Res.

Register

Res.

Offset

Res.

18.4.19

Res.

0x1C

Res.

0x18

Res.

RM0091
General-purpose timers (TIM2 and TIM3)

TIM2 and TIM3 register map
TIM2 and TIM3 registers are mapped as described in the table below:
Table 68. TIM2 and TIM3 register map and reset values

0
SMS[2:0]

0
0

0
0

CC1S
[1:0]
0

0

0

0

IC1
CC1S
PSC
[1:0]
[1:0]
0

CC3S
[1:0]

0

IC3
CC3S
PSC
[1:0]
[1:0]

0

0

0

0

0

0

0

0

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RM0091

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

Reserved

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

1

Res.

1

Res.

1

Res.

1

Res.

1

Res.

Reset value

Res.

ARR[15:0]

Res.

0x30

ARR[31:16]
(TIM2 only)

Res.

TIM2_ARR and
TIM3_ARR

Res.

0x2C

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 68. TIM2 and TIM3 register map and reset values (continued)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Reset value
TIM2_CCR1 and
TIM3_CCR1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

CCR2[31:16]
(TIM2 only)
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

CCR3[31:16]
(TIM2 only)
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0
Res.

0

Res.

0

Res.

0

Res.

0

0

CCR4[15:0]

Res.

0

0

CCR3[15:0]

CCR4[31:16]
(TIM2 only)
0

0

CCR2[15:0]

Res.

Reserved

0x44

0

Res.

Reset value

0

Res.

Reset value

0

Res.

0x40

TIM2_CCR4 and
TIM3_CCR4

Reset value

0

Res.

0x3C

TIM2_CCR3 and
TIM3_CCR3

0

Res.

TIM2_CCR2 and
TIM3_CCR2

0

Res.

0x38

0

CCR1[15:0]

Res.

Reset value

CCR1[31:16]
(TIM2 only)

Res.

0x34

Reset value
0x48

TIM2_DCR and
TIM3_DCR

0x4C

TIM2_DMAR and
TIM3_DMAR

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0
Res.

Reset value

DBL[4:0]

Reset value

0

0

0

DocID018940 Rev 9

0

0

0

0

0

0

0

0

0

0

DMAB[15:0]
0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

458/1004

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0

0

0

RM0091

General-purpose timer (TIM14)

19

General-purpose timer (TIM14)

19.1

TIM14 introduction
The TIM14 general-purpose timer consists of a 16-bit auto-reload counter driven by a
programmable prescaler.
It may be used for a variety of purposes, including measuring the pulse lengths of input
signals (input capture) or generating output waveforms (output compare, PWM).
Pulse lengths and waveform periods can be modulated from a few microseconds to several
milliseconds using the timer prescaler and the RCC clock controller prescalers.
The TIM14 timer is completely independent, and does not share any resources. It can be
synchronized together as described in Section 18.3.15.

19.2

TIM14 main features
•

16-bit auto-reload upcounter

•

16-bit programmable prescaler used to divide the counter clock frequency by any factor
between 1 and 65535 (can be changed “on the fly”)

•

independent channel for:

•

–

Input capture

–

Output compare

–

PWM generation (edge-aligned mode)

Interrupt generation on the following events:
–

Update: counter overflow, counter initialization (by software)

–

Input capture

–

Output compare

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General-purpose timer (TIM14)

RM0091

Figure 153. General-purpose timer block diagram (TIM14)

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19.3

TIM14 functional description

19.3.1

Time-base unit
The main block of the programmable advanced-control timer is a 16-bit counter with its
related auto-reload register. The counter can count up. The counter clock can be divided by
a prescaler.
The counter, the auto-reload register and the prescaler register can be written or read by
software. This is true even when the counter is running.
The time-base unit includes:
•

Counter register (TIMx_CNT)

•

Prescaler register (TIMx_PSC)

•

Auto-reload register (TIMx_ARR)

The auto-reload register is preloaded. Writing to or reading from the auto-reload register
accesses the preload register. The content of the preload register are transferred into the
shadow register permanently or at each update event (UEV), depending on the auto-reload
preload enable bit (ARPE) in TIMx_CR1 register. The update event is sent when the counter
reaches the overflow and if the UDIS bit equals 0 in the TIMx_CR1 register. It can also be
generated by software. The generation of the update event is described in detailed for each
configuration.
The counter is clocked by the prescaler output CK_CNT, which is enabled only when the
counter enable bit (CEN) in TIMx_CR1 register is set (refer also to the slave mode controller
description to get more details on counter enabling).

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RM0091

General-purpose timer (TIM14)
Note that the counter starts counting 1 clock cycle after setting the CEN bit in the TIMx_CR1
register.

Prescaler description
The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It
is based on a 16-bit counter controlled through a 16-bit register (in the TIMx_PSC register).
It can be changed on the fly as this control register is buffered. The new prescaler ratio is
taken into account at the next update event.
Figure 155 and Figure 156 give some examples of the counter behavior when the prescaler
ratio is changed on the fly.
Figure 154. Counter timing diagram with prescaler division change from 1 to 2
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.47

Figure 155. Counter timing diagram with prescaler division change from 1 to 4

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.47

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546

General-purpose timer (TIM14)

19.3.2

RM0091

Counter modes
Upcounting mode
In upcounting mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register), then restarts from 0 and generates a counter overflow event.
Setting the UG bit in the TIMx_EGR register also generates an update event.
The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until the UDIS bit has been written to 0.
However, the counter restarts from 0, as well as the counter of the prescaler (but the
prescale rate does not change). In addition, if the URS bit (update request selection) in
TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without
setting the UIF flag (thus no interrupt is sent). This is to avoid generating both update and
capture interrupts when clearing the counter on the capture event.
When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The auto-reload shadow register is updated with the preload value (TIMx_ARR),

•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register).

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.
Figure 156. Counter timing diagram, internal clock divided by 1
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.47

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RM0091

General-purpose timer (TIM14)
Figure 157. Counter timing diagram, internal clock divided by 2
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.47

Figure 158. Counter timing diagram, internal clock divided by 4
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Figure 159. Counter timing diagram, internal clock divided by N
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546

General-purpose timer (TIM14)

RM0091

Figure 160. Counter timing diagram, update event when ARPE=0
(TIMx_ARR not preloaded)
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.47

Figure 161. Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded)
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19.3.3

.47

Clock source
The counter clock is provided by the Internal clock (CK_INT) source.
The CEN (in the TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual
control bits and can be changed only by software (except for UG that remains cleared
automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal
clock CK_INT.
Figure 162 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.

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RM0091

General-purpose timer (TIM14)
Figure 162. Control circuit in normal mode, internal clock divided by 1
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.47

19.3.4

Capture/compare channels
Each Capture/Compare channel is built around a capture/compare register (including a
shadow register), a input stage for capture (with digital filter, multiplexing and prescaler) and
an output stage (with comparator and output control).
Figure 163 to Figure 165 give an overview of one capture/compare channel.
The input stage samples the corresponding TIx input to generate a filtered signal TIxF.
Then, an edge detector with polarity selection generates a signal (TIxFPx) which can be
used as trigger input by the slave mode controller or as the capture command. It is
prescaled before the capture register (ICxPS).
Figure 163. Capture/compare channel (example: channel 1 input stage)
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The output stage generates an intermediate waveform which is then used for reference:
OCxRef (active high). The polarity acts at the end of the chain.

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546

General-purpose timer (TIM14)

RM0091

Figure 164. Capture/compare channel 1 main circuit
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Figure 165. Output stage of capture/compare channel (channel 1)
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The capture/compare block is made of one preload register and one shadow register. Write
and read always access the preload register.
In capture mode, captures are actually done in the shadow register, which is copied into the
preload register.
In compare mode, the content of the preload register is copied into the shadow register
which is compared to the counter.

19.3.5

Input capture mode
In Input capture mode, the Capture/Compare Registers (TIMx_CCRx) are used to latch the
value of the counter after a transition detected by the corresponding ICx signal. When a
capture occurs, the corresponding CCXIF flag (TIMx_SR register) is set and an interrupt or
a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was
already high, then the over-capture flag CCxOF (TIMx_SR register) is set. CCxIF can be

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RM0091

General-purpose timer (TIM14)
cleared by software by writing it to ‘0’ or by reading the captured data stored in the
TIMx_CCRx register. CCxOF is cleared when you write it to ‘0’.
The following example shows how to capture the counter value in TIMx_CCR1 when TI1
input rises. To do this, use the following procedure:
1.

Select the active input: TIMx_CCR1 must be linked to the TI1 input, so write the CC1S
bits to ‘01’ in the TIMx_CCMR1 register. As soon as CC1S becomes different from ‘00’,
the channel is configured in input mode and the TIMx_CCR1 register becomes readonly.

2.

Program the input filter duration you need with respect to the signal you connect to the
timer (when the input is one of the TIx (ICxF bits in the TIMx_CCMRx register). Let us
imagine that, when toggling, the input signal is not stable during at must 5 internal clock
cycles. We must program a filter duration longer than these 5 clock cycles. We can
validate a transition on TI1 when 8 consecutive samples with the new level have been
detected (sampled at fDTS frequency). Then write IC1F bits to ‘0011’ in the
TIMx_CCMR1 register.

3.

Select the edge of the active transition on the TI1 channel by programming CC1P and
CC1NP bits to ‘00’ in the TIMx_CCER register (rising edge in this case).

4.

Program the input prescaler. In our example, we wish the capture to be performed at
each valid transition, so the prescaler is disabled (write IC1PS bits to ‘00’ in the
TIMx_CCMR1 register).

5.

Enable capture from the counter into the capture register by setting the CC1E bit in the
TIMx_CCER register.

6.

If needed, enable the related interrupt request by setting the CC1IE bit in the
TIMx_DIER register.

For code example refer to the Appendix section A.9.3: Input capture configuration code
example.
When an input capture occurs:
•

The TIMx_CCR1 register gets the value of the counter on the active transition.

•

CC1IF flag is set (interrupt flag). CC1OF is also set if at least two consecutive captures
occurred whereas the flag was not cleared.

•

An interrupt is generated depending on the CC1IE bit.

For code example refer to the Appendix section A.9.4: Input capture data management
code example.
In order to handle the overcapture, it is recommended to read the data before the
overcapture flag. This is to avoid missing an overcapture which could happen after reading
the flag and before reading the data.
Note:

IC interrupt requests can be generated by software by setting the corresponding CCxG bit in
the TIMx_EGR register.

19.3.6

Forced output mode
In output mode (CCxS bits = ‘00’ in the TIMx_CCMRx register), each output compare signal
(OCxREF and then OCx) can be forced to active or inactive level directly by software,
independently of any comparison between the output compare register and the counter.
To force an output compare signal (OCXREF/OCx) to its active level, you just need to write
‘101’ in the OCxM bits in the corresponding TIMx_CCMRx register. Thus OCXREF is forced
high (OCxREF is always active high) and OCx get opposite value to CCxP polarity bit.
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General-purpose timer (TIM14)

RM0091

For example: CCxP=’0’ (OCx active high) => OCx is forced to high level.
The OCxREF signal can be forced low by writing the OCxM bits to ‘100’ in the
TIMx_CCMRx register.
The comparison between the TIMx_CCRx shadow register and the counter is still performed
and allows the flag to be set. Interrupt requests can be sent accordingly. This is described in
the output compare mode section below.

19.3.7

Output compare mode
This function is used to control an output waveform or to indicate when a period of time has
elapsed.
When a match is found between the capture/compare register and the counter, the output
compare function:
1.

Assigns the corresponding output pin to a programmable value defined by the output
compare mode (OCxM bits in the TIMx_CCMRx register) and the output polarity (CCxP
bit in the TIMx_CCER register). The output pin can keep its level (OCXM=’000’), be set
active (OCxM=’001’), be set inactive (OCxM=’010’) or can toggle (OCxM=’011’) on
match.

2.

Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).

3.

Generates an interrupt if the corresponding interrupt mask is set (CCXIE bit in the
TIMx_DIER register).

The TIMx_CCRx registers can be programmed with or without preload registers using the
OCxPE bit in the TIMx_CCMRx register.
In output compare mode, the update event UEV has no effect on OCxREF and OCx output.
The timing resolution is one count of the counter. Output compare mode can also be used to
output a single pulse (in One-pulse mode).
Procedure:
1.

Select the counter clock (internal, external, prescaler).

2.

Write the desired data in the TIMx_ARR and TIMx_CCRx registers.

3.

Set the CCxIE bit if an interrupt request is to be generated.

4.

Select the output mode. For example:

5.

–

Write OCxM = ‘011’ to toggle OCx output pin when CNT matches CCRx

–

Write OCxPE = ‘0’ to disable preload register

–

Write CCxP = ‘0’ to select active high polarity

–

Write CCxE = ‘1’ to enable the output

Enable the counter by setting the CEN bit in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.7: Output compare configuration code
example.
The TIMx_CCRx register can be updated at any time by software to control the output
waveform, provided that the preload register is not enabled (OCxPE=’0’, else TIMx_CCRx
shadow register is updated only at the next update event UEV). An example is given in
Figure 166.

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General-purpose timer (TIM14)
Figure 166. Output compare mode, toggle on OC1
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19.3.8

PWM mode
Pulse Width Modulation mode allows you to generate a signal with a frequency determined
by the value of the TIMx_ARR register and a duty cycle determined by the value of the
TIMx_CCRx register.
The PWM mode can be selected independently on each channel (one PWM per OCx
output) by writing ‘110’ (PWM mode 1) or ‘111’ (PWM mode 2) in the OCxM bits in the
TIMx_CCMRx register. You must enable the corresponding preload register by setting the
OCxPE bit in the TIMx_CCMRx register, and eventually the auto-reload preload register (in
upcounting or center-aligned modes) by setting the ARPE bit in the TIMx_CR1 register.
As the preload registers are transferred to the shadow registers only when an update event
occurs, before starting the counter, you have to initialize all the registers by setting the UG
bit in the TIMx_EGR register.
The OCx polarity is software programmable using the CCxP bit in the TIMx_CCER register.
It can be programmed as active high or active low. The OCx output is enabled by the CCxE
bit in the TIMx_CCER register. Refer to the TIMx_CCERx register description for more
details.
In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine
whether TIMx_CNT ≤ TIMx_CCRx.
The timer is able to generate PWM in edge-aligned mode only since the counter is
upcounting.

PWM edge-aligned mode
In the following example, we consider PWM mode 1. The reference PWM signal OCxREF is
high as long as TIMx_CNT < TIMx_CCRx else it becomes low. If the compare value in
TIMx_CCRx is greater than the auto-reload value (in TIMx_ARR) then OCxREF is held at
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RM0091

‘1’. If the compare value is 0 then OCxRef is held at ‘0’. Figure 167 shows some edgealigned PWM waveforms in an example where TIMx_ARR=8.
Figure 167. Edge-aligned PWM waveforms (ARR=8)



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&&5[ 





















2&;5()
&&[,)

2&;5()
&&5[ 
&&[,)

2&;5()

µ¶

&&5[!
&&[,)

2&;5()

µ¶

&&5[ 
&&[,)

069

For code example refer to the Appendix section A.9.8: Edge-aligned PWM configuration
example.

19.3.9

Debug mode
When the microcontroller enters debug mode (Cortex™-M0 core halted), the TIMx counter
either continues to work normally or stops, depending on DBG_TIMx_STOP configuration
bit in DBG module.

19.4

TIM14 registers

19.4.1

TIM14 control register 1 (TIM14_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

CKD[1:0]
rw

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7

6

5

4

3

2

1

0

ARPE

Res.

Res.

Res.

Res.

URS

UDIS

CEN

rw

rw

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General-purpose timer (TIM14)

Bits 15:10 Reserved, must be kept at reset value.
Bits 9:8 CKD: Clock division
This bit-field indicates the division ratio between the timer clock (CK_INT) frequency and
sampling clock used by the digital filters (ETR, TIx),
00: tDTS = tCK_INT
01: tDTS = 2 × tCK_INT
10: tDTS = 4 × tCK_INT
11: Reserved
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered
Bits 6:3 Reserved, must be kept at reset value.
Bit 2 URS: Update request source
This bit is set and cleared by software to select the update interrupt (UEV) sources.
0: Any of the following events generate an UEV if enabled:
–
Counter overflow
–
Setting the UG bit
1: Only counter overflow generates an UEV if enabled.
Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable update interrupt (UEV) event
generation.
0: UEV enabled. An UEV is generated by one of the following events:
–
Counter overflow
–
Setting the UG bit.
Buffered registers are then loaded with their preload values.
1: UEV disabled. No UEV is generated, shadow registers keep their value (ARR, PSC,
CCRx). The counter and the prescaler are reinitialized if the UG bit is set.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled

19.4.2

TIM14 interrupt enable register (TIM14_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1IE

UIE

rw

rw

Bits 15:2

Reserved, must be kept at reset value.

Bit 1 CC1IE: Capture/Compare 1 interrupt enable
0: CC1 interrupt disabled
1: CC1 interrupt enabled
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled
1: Update interrupt enabled

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19.4.3

RM0091

TIM14 status register (TIM14_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

CC1OF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1IF

UIF

rc_w0

rc_w0

rc_w0

Bit 15:10 Reserved, must be kept at reset value.
Bit 9 CC1OF: Capture/Compare 1 overcapture flag
This flag is set by hardware only when the corresponding channel is configured in input
capture mode. It is cleared by software by writing it to ‘0’.
0: No overcapture has been detected.
1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was
already set
Bits 8:2 Reserved, must be kept at reset value.
Bit 1 CC1IF: Capture/compare 1 interrupt flag
If channel CC1 is configured as output:
This flag is set by hardware when the counter matches the compare value. It is cleared by
software.
0: No match.
1: The content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register.
When the contents of TIMx_CCR1 are greater than the contents of TIMx_ARR, the CC1IF bit
goes high on the counter overflow.
If channel CC1 is configured as input:
This bit is set by hardware on a capture. It is cleared by software or by reading the TIMx_CCR1
register.
0: No input capture occurred.
1: The counter value has been captured in TIMx_CCR1 register (an edge has been detected
on IC1 which matches the selected polarity).
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending. This bit is set by hardware when the registers are updated:
–
At overflow and if UDIS=’0’ in the TIMx_CR1 register.
–
When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if
URS=’0’ and UDIS=’0’ in the TIMx_CR1 register.

19.4.4

TIM14 event generation register (TIM14_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1G

UG

w

w

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General-purpose timer (TIM14)

Bits 15:2 Reserved, must be kept at reset value.
Bit 1 CC1G: Capture/compare 1 generation
This bit is set by software in order to generate an event, it is automatically cleared by hardware.
0: No action
1: A capture/compare event is generated on channel 1:
If channel CC1 is configured as output:
CC1IF flag is set, Corresponding interrupt or is sent if enabled.
If channel CC1 is configured as input:
The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set,
the corresponding interrupt is sent if enabled. The CC1OF flag is set if the CC1IF flag was
already high.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action
1: Re-initialize the counter and generates an update of the registers. Note that the prescaler
counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared.

19.4.5

TIM14 capture/compare mode register 1 (TIM14_CCMR1)
Address offset: 0x18
Reset value: 0x0000
The channels can be used in input (capture mode) or in output (compare mode). The
direction of a channel is defined by configuring the corresponding CCxS bits. All the other
bits of this register have a different function in input and in output mode. For a given bit,
OCxx describes its function when the channel is configured in output, ICxx describes its
function when the channel is configured in input. So you must take care that the same bit
can have a different meaning for the input stage and for the output stage.

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

6

5

4

OC1M[2:0]
IC1F[3:0]

rw

rw

rw

3

2

OC1PE OC1FE
IC1PSC[1:0]
rw

rw

rw

1

0

CC1S[1:0]
rw

rw

Output compare mode:
Bits 15:7 Reserved

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Bits 6:4 OC1M: Output compare 1 mode
These bits define the behavior of the output reference signal OC1REF from which OC1 is
derived. OC1REF is active high whereas OC1 active level depends on CC1P bit.
000: Frozen. The comparison between the output compare register TIMx_CCR1 and the
counter TIMx_CNT has no effect on the outputs.
001: Set channel 1 to active level on match. OC1REF signal is forced high when the counter
TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
010: Set channel 1 to inactive level on match. OC1REF signal is forced low when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
011: Toggle - OC1REF toggles when TIMx_CNT = TIMx_CCR1.
100: Force inactive level - OC1REF is forced low.
101: Force active level - OC1REF is forced high.
110: PWM mode 1 - Channel 1 is active as long as TIMx_CNT < TIMx_CCR1 else inactive.
111: PWM mode 2 - Channel 1 is inactive as long as TIMx_CNT < TIMx_CCR1 else active.
Note: In PWM mode 1 or 2, the OCREF level changes when the result of the comparison
changes or when the output compare mode switches from frozen to PWM mode.
Bit 3 OC1PE: Output compare 1 preload enable
0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the new
value is taken in account immediately.
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded in the active register at each update event.
Note: The PWM mode can be used without validating the preload register only in one pulse
mode (OPM bit set in TIMx_CR1 register). Else the behavior is not guaranteed.
Bit 2 OC1FE: Output compare 1 fast enable
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is
ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is
5 clock cycles.
1: An active edge on the trigger input acts like a compare match on CC1 output. OC is then
set to the compare level independently of the result of the comparison. Delay to sample the
trigger input and to activate CC1 output is reduced to 3 clock cycles. OC1FE acts only if the
channel is configured in PWM1 or PWM2 mode.
Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output.
01: CC1 channel is configured as input, IC1 is mapped on TI1.
10: Reserved
11: Reserved
Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

Input capture mode:
Bits 15:8 Reserved

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General-purpose timer (TIM14)

Bits 7:4 IC1F: Input capture 1 filter
This bit-field defines the frequency used to sample TI1 input and the length of the digital filter
applied to TI1. The digital filter is made of an event counter in which N events are needed to
validate a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ICxF[3:0] = 1,
2 or 3.
Bits 3:2 IC1PSC: Input capture 1 prescaler
This bit-field defines the ratio of the prescaler acting on CC1 input (IC1).
The prescaler is reset as soon as CC1E=’0’ (TIMx_CCER register).
00: no prescaler, capture is done each time an edge is detected on the capture input
01: capture is done once every 2 events
10: capture is done once every 4 events
11: capture is done once every 8 events
Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
0: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10:
11:
Note: CC1S bits are writable only when the channel is OFF (CC1E = 0 in TIMx_CCER).

19.4.6

TIM14 capture/compare enable register (TIM14_CCER)
Address offset: 0x20
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1NP

Res.

CC1P

CC1E

rw

rw

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RM0091

Bits 15:4 Reserved, must be kept at reset value.
Bit 3 CC1NP: Capture/Compare 1 complementary output Polarity.
CC1 channel configured as output: CC1NP must be kept cleared.
CC1 channel configured as input: CC1NP bit is used in conjunction with CC1P to define
TI1FP1 polarity (refer to CC1P description).
Bit 2 Reserved, must be kept at reset value.
Bit 1 CC1P: Capture/Compare 1 output Polarity.
CC1 channel configured as output:
0: OC1 active high
1: OC1 active low
CC1 channel configured as input:
The CC1P bit selects TI1FP1 and TI2FP1 polarity for trigger or capture operations.
00: noninverted/rising edge
Circuit is sensitive to TI1FP1 rising edge (capture mode), TI1FP1 is not inverted.
01: inverted/falling edge
Circuit is sensitive to TI1FP1 falling edge (capture mode), TI1FP1 is inverted.
10: reserved, do not use this configuration.
11: noninverted/both edges
Circuit is sensitive to both TI1FP1 rising and falling edges (capture mode), TI1FP1 is not
inverted.
Bit 0 CC1E: Capture/Compare 1 output enable.
CC1 channel configured as output:
0: Off - OC1 is not active
1: On - OC1 signal is output on the corresponding output pin
CC1 channel configured as input:
This bit determines if a capture of the counter value can actually be done into the input
capture/compare register 1 (TIMx_CCR1) or not.
0: Capture disabled
1: Capture enabled

Table 69. Output control bit for standard OCx channels
CCxE bit

OCx output state

0

Output Disabled (OCx=’0’, OCx_EN=’0’)

1

OCx=OCxREF + Polarity, OCx_EN=’1’

Note:

The state of the external I/O pins connected to the standard OCx channels depends on the
OCx channel state and the GPIO registers.

19.4.7

TIM14 counter (TIM14_CNT)
Address offset: 0x24
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]
rw

Bits 15:0 CNT[15:0]: Counter value

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General-purpose timer (TIM14)

19.4.8

TIM14 prescaler (TIM14_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

PSC[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency CK_CNT is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded in the active prescaler register at each update event.

19.4.9

TIM14 auto-reload register (TIM14_ARR)
Address offset: 0x2C
Reset value: 0xFFFF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 ARR[15:0]: Auto-reload value
ARR is the value to be loaded in the actual auto-reload register.
Refer to the Section 19.3.1: Time-base unit on page 460 for more details about ARR update
and behavior.
The counter is blocked while the auto-reload value is null.

19.4.10

TIM14 capture/compare register 1 (TIM14_CCR1)
Address offset: 0x34
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR1[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 CCR1[15:0]: Capture/Compare 1 value
If channel CC1 is configured as output:
CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit
OC1PE). Else the preload value is copied in the active capture/compare 1 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC1 output.
If channel CC1is configured as input:
CCR1 is the counter value transferred by the last input capture 1 event (IC1).

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19.4.11

RM0091

TIM14 option register (TIM14_OR)
Address offset: 0x50
Reset value: 0x0000

15
Res.

14
Res.

13
Res.

12

11

Res.

10

Res.

9

Res.

8

Res.

7

Res.

6

Res.

5

Res.

4

Res.

3

Res.

2

Res.

1

0
TI1_
RMP

Res.
rw

rw

Bits 15:2 Reserved, must be kept at reset value.
Bit 1:0 TI1_RMP [1:0]: Timer Input 1 remap
Set and cleared by software.
00: TIM14 Channel1 is connected to the GPIO. Refer to the alternate function mapping in the
device datasheets.
01: TIM14 Channel1 is connected to the RTCCLK.
10: TIM14 Channel1 is connected to the HSE/32 Clock.
11: TIM14 Channel1 is connected to the microcontroller clock output (MCO), this selection is
controlled by the MCO[2:0] bits of the Clock configuration register (RCC_CFGR) (see
Section 6.4.2: Clock configuration register (RCC_CFGR)).

19.4.12

TIM14 register map
TIM14 registers are mapped as 16-bit addressable registers as described in the table
below:

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1IE

UIE

CEN

Res.
Res.

UDIS

Res.

Res.

URS

Res.

Res.

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Reserved

0x08

0

Res.

Reset value

CKD
[1:0]

ARPE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM14_CR1

0x00

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 70. TIM14 register map and reset values

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Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

Res.

CC1G

UG

0

0

OC1FE

0

Res.

0

OC1PE

Res.

0

IC1F[3:0]
0

DocID018940 Rev 9

Res.

Res.

Res.

Res.
Res.

Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.

Res.
Res.

Res.

Res.
Res.

Res.

OC1M
[2:0]
0

Res.

0x18

Reset value
TIM14_CCMR1
Output compare
mode
Reset value
TIM14_CCMR1
Input capture
mode
Reset value

Res.

TIM14_EGR

0x14

0
Res.

Reset value

CC1OF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM14_SR

0x10

Res.

Reset value

UIF

TIM14_DIER

0x0C

CC1IF

Reset value

CC1S
[1:0]

0 0 0 0
IC1
CC1S
PSC
[1:0]
[1:0]
0 0 0 0

0x38 to
0x4C

0x50
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Reset value

Reset value

DocID018940 Rev 9
1
1
1
1
1
1
1
1

Res.
Res.
Res.
Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

Res.

Res.

1

Res.

0

1

Res.

Res.

Res.

Reset value
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0
0

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

CCR1[15:0]
0

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0
0
0
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

TI1_RMP

Res.

Res.

Res.

Res.

Res.

Reset value
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

TIM14_OR
Res.

Reset value
Res.

Reserved
Res.

Reset value
Res.

TIM14_CCR1

Res.

0x34
Reserved

Res.

0x30
TIM14_ARR

Res.

0x2C
TIM14_PSC

Res.

0x28
TIM14_CNT

Res.

0x24
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
CC1NP
Res.
CC1P
CC1E

Reset value

Res.

TIM14_CCER

Res.

0x20
Reserved

Res.

0x1C

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

RM0091
General-purpose timer (TIM14)

Table 70. TIM14 register map and reset values (continued)

0
0

CNT[15:0]

PSC[15:0]

0
0
0
0
0
0

0
0
0
0
0
0

ARR[15:0]

0
0

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General-purpose timers (TIM15/16/17)

20

RM0091

General-purpose timers (TIM15/16/17)
TIM15 is not available on STM32F03x devices.

20.1

TIM15/16/17 introduction
The TIM15/16/17 timers consist of a 16-bit auto-reload counter driven by a programmable
prescaler.
They may be used for a variety of purposes, including measuring the pulse lengths of input
signals (input capture) or generating output waveforms (output compare, PWM,
complementary PWM with dead-time insertion).
Pulse lengths and waveform periods can be modulated from a few microseconds to several
milliseconds using the timer prescaler and the RCC clock controller prescalers.
The TIM15/16/17 timers are completely independent, and do not share any resources. The
TIM15 can be synchronized with other timers.

20.2

TIM15 main features
TIM15 includes the following features:

480/1004

•

16-bit auto-reload upcounter

•

16-bit programmable prescaler used to divide (also “on the fly”) the counter clock
frequency by any factor between 1 and 65535

•

Up to 2 independent channels for:
–

Input capture

–

Output compare

–

PWM generation (Edge-aligned mode)

–

One-pulse mode output

•

Complementary outputs with programmable dead-time (for channel 1 only)

•

Synchronization circuit to control the timer with external signals and to interconnect
several timers together

•

Repetition counter to update the timer registers only after a given number of cycles of
the counter

•

Break input to put the timer’s output signals in the reset state or a known state

•

Interrupt/DMA generation on the following events:
–

Update: counter overflow, counter initialization (by software or internal/external
trigger)

–

Trigger event (counter start, stop, initialization or count by internal/external trigger)

–

Input capture

–

Output compare

–

Break input (interrupt request)

DocID018940 Rev 9

RM0091

General-purpose timers (TIM15/16/17)
Figure 168. TIM15 block diagram

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20.3

RM0091

TIM16 and TIM17 main features
The TIM16 and TIM17 timers include the following features:

482/1004

•

16-bit auto-reload upcounter

•

16-bit programmable prescaler used to divide (also “on the fly”) the counter clock
frequency by any factor between 1 and 65535

•

One channel for:
–

Input capture

–

Output compare

–

PWM generation (Edge-aligned mode)

–

One-pulse mode output

•

Complementary outputs with programmable dead-time

•

Repetition counter to update the timer registers only after a given number of cycles of
the counter

•

Break input to put the timer’s output signals in the reset state or a known state

•

Interrupt/DMA generation on the following events:
–

Update: counter overflow

–

Input capture

–

Output compare

–

Break input

DocID018940 Rev 9

RM0091

General-purpose timers (TIM15/16/17)
Figure 169. TIM16 and TIM17 block diagram

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20.4

TIM15/16/17 functional description

20.4.1

Time-base unit
The main block of the programmable advanced-control timer is a 16-bit counter with its
related auto-reload register. The counter can count up, down or both up and down. The
counter clock can be divided by a prescaler.
The counter, the auto-reload register and the prescaler register can be written or read by
software. This is true even when the counter is running.
The time-base unit includes:
•

Counter register (TIMx_CNT)

•

Prescaler register (TIMx_PSC)

•

Auto-reload register (TIMx_ARR)

•

Repetition counter register (TIMx_RCR)

The auto-reload register is preloaded. Writing to or reading from the auto-reload register
accesses the preload register. The content of the preload register are transferred into the
shadow register permanently or at each update event (UEV), depending on the auto-reload
preload enable bit (ARPE) in TIMx_CR1 register. The update event is sent when the counter
reaches the overflow (or underflow when downcounting) and if the UDIS bit equals 0 in the

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RM0091

TIMx_CR1 register. It can also be generated by software. The generation of the update
event is described in detailed for each configuration.
The counter is clocked by the prescaler output CK_CNT, which is enabled only when the
counter enable bit (CEN) in TIMx_CR1 register is set (refer also to the slave mode controller
description to get more details on counter enabling).
Note that the counter starts counting 1 clock cycle after setting the CEN bit in the TIMx_CR1
register.

Prescaler description
The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It
is based on a 16-bit counter controlled through a 16-bit register (in the TIMx_PSC register).
It can be changed on the fly as this control register is buffered. The new prescaler ratio is
taken into account at the next update event.
Figure 155 and Figure 156 give some examples of the counter behavior when the prescaler
ratio is changed on the fly:
Figure 170. Counter timing diagram with prescaler division change from 1 to 2

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069

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General-purpose timers (TIM15/16/17)
Figure 171. Counter timing diagram with prescaler division change from 1 to 4

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069

20.4.2

Counter modes
Upcounting mode
In upcounting mode, the counter counts from 0 to the auto-reload value (content of the
TIMx_ARR register), then restarts from 0 and generates a counter overflow event.
If the repetition counter is used, the update event (UEV) is generated after upcounting is
repeated for the number of times programmed in the repetition counter register
(TIMx_RCR). Else the update event is generated at each counter overflow.
Setting the UG bit in the TIMx_EGR register (by software or by using the slave mode
controller) also generates an update event.
The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This is to avoid updating the shadow registers while writing new values in the
preload registers. Then no update event occurs until the UDIS bit has been written to 0.
However, the counter restarts from 0, as well as the counter of the prescaler (but the
prescale rate does not change). In addition, if the URS bit (update request selection) in
TIMx_CR1 register is set, setting the UG bit generates an update event UEV but without
setting the UIF flag (thus no interrupt or DMA request is sent). This is to avoid generating
both update and capture interrupts when clearing the counter on the capture event.

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RM0091

When an update event occurs, all the registers are updated and the update flag (UIF bit in
TIMx_SR register) is set (depending on the URS bit):
•

The repetition counter is reloaded with the content of TIMx_RCR register,

•

The auto-reload shadow register is updated with the preload value (TIMx_ARR),

•

The buffer of the prescaler is reloaded with the preload value (content of the TIMx_PSC
register).

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR=0x36.
Figure 172. Counter timing diagram, internal clock divided by 1

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General-purpose timers (TIM15/16/17)
Figure 173. Counter timing diagram, internal clock divided by 2

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Figure 174. Counter timing diagram, internal clock divided by 4

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General-purpose timers (TIM15/16/17)

RM0091

Figure 175. Counter timing diagram, internal clock divided by N

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Figure 176. Counter timing diagram, update event when ARPE=0
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General-purpose timers (TIM15/16/17)
Figure 177. Counter timing diagram, update event when ARPE=1
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20.4.3



069

Repetition counter
Section 19.3.1: Time-base unit describes how the update event (UEV) is generated with
respect to the counter overflows/underflows. It is actually generated only when the repetition
counter has reached zero. This can be useful when generating PWM signals.
This means that data are transferred from the preload registers to the shadow registers
(TIMx_ARR auto-reload register, TIMx_PSC prescaler register, but also TIMx_CCRx
capture/compare registers in compare mode) every N counter overflows or underflows,
where N is the value in the TIMx_RCR repetition counter register.
The repetition counter is decremented at each counter overflow in upcounting mode.
The repetition counter is an auto-reload type; the repetition rate is maintained as defined by
the TIMx_RCR register value (refer to Figure 178). When the update event is generated by
software (by setting the UG bit in TIMx_EGR register) or by hardware through the slave
mode controller, it occurs immediately whatever the value of the repetition counter is and the
repetition counter is reloaded with the content of the TIMx_RCR register.

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General-purpose timers (TIM15/16/17)

RM0091

Figure 178. Update rate examples depending on mode and TIMx_RCR register
settings
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Clock sources
The counter clock can be provided by the following clock sources:
•

Internal clock (CK_INT)

•

External clock mode1: external input pin (only for TIM15)

•

Internal trigger inputs (ITRx) (only for TIM15): using one timer as the prescaler for
another timer, for example, you can configure TIM1 to act as a prescaler for TIM15.
Refer to Using one timer as prescaler for another for more details.

Internal clock source (CK_INT)
For TIM5 if the slave mode controller is disabled (SMS=000), then the CEN, DIR (in the
TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual control bits and can
be changed only by software (except UG which remains cleared automatically). As soon as
the CEN bit is written to 1, the prescaler is clocked by the internal clock CK_INT.

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General-purpose timers (TIM15/16/17)
Figure 19.3.4 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 179. Control circuit in normal mode, internal clock divided by 1

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External clock source mode 1
This mode is selected when SMS=111 in the TIMx_SMCR register. The counter can count at
each rising or falling edge on a selected input.
Figure 180. TI2 external clock connection example
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For example, to configure the upcounter to count in response to a rising edge on the TI2
input, use the following procedure:

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General-purpose timers (TIM15/16/17)

Note:

RM0091

1.

Configure channel 2 to detect rising edges on the TI2 input by writing CC2S = ‘01’ in
the TIMx_CCMR1 register.

2.

Configure the input filter duration by writing the IC2F[3:0] bits in the TIMx_CCMR1
register (if no filter is needed, keep IC2F=0000).

3.

Select rising edge polarity by writing CC2P=0 in the TIMx_CCER register.

4.

Configure the timer in external clock mode 1 by writing SMS=111 in the TIMx_SMCR
register.

5.

Select TI2 as the trigger input source by writing TS=110 in the TIMx_SMCR register.

6.

Enable the counter by writing CEN=1 in the TIMx_CR1 register.

The capture prescaler is not used for triggering, so you don’t need to configure it.
For code example refer to the Appendix section A.9.1: Upcounter on TI2 rising edge code
example.
When a rising edge occurs on TI2, the counter counts once and the TIF flag is set.
The delay between the rising edge on TI2 and the actual clock of the counter is due to the
resynchronization circuit on TI2 input.
Figure 181. Control circuit in external clock mode 1

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20.4.5

Capture/compare channels
Each Capture/Compare channel is built around a capture/compare register (including a
shadow register), a input stage for capture (with digital filter, multiplexing and prescaler) and
an output stage (with comparator and output control).
Figure 163 to Figure 185 give an overview of one Capture/Compare channel.
The input stage samples the corresponding TIx input to generate a filtered signal TIxF.
Then, an edge detector with polarity selection generates a signal (TIxFPx) which can be
used as trigger input by the slave mode controller or as the capture command. It is
prescaled before the capture register (ICxPS).

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General-purpose timers (TIM15/16/17)
Figure 182. Capture/compare channel (example: channel 1 input stage)
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The output stage generates an intermediate waveform which is then used for reference:
OCxRef (active high). The polarity acts at the end of the chain.
Figure 183. Capture/compare channel 1 main circuit

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Figure 184. Output stage of capture/compare channel (channel 1)


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The capture/compare block is made of one preload register and one shadow register. Write
and read always access the preload register.
In capture mode, captures are actually done in the shadow register, which is copied into the
preload register.
In compare mode, the content of the preload register is copied into the shadow register
which is compared to the counter.

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20.4.6

General-purpose timers (TIM15/16/17)

Input capture mode
In Input capture mode, the Capture/Compare Registers (TIMx_CCRx) are used to latch the
value of the counter after a transition detected by the corresponding ICx signal. When a
capture occurs, the corresponding CCXIF flag (TIMx_SR register) is set and an interrupt or
a DMA request can be sent if they are enabled. If a capture occurs while the CCxIF flag was
already high, then the over-capture flag CCxOF (TIMx_SR register) is set. CCxIF can be
cleared by software by writing it to ‘0’ or by reading the captured data stored in the
TIMx_CCRx register. CCxOF is cleared when you write it to ‘0’.
The following example shows how to capture the counter value in TIMx_CCR1 when TI1
input rises. To do this, use the following procedure:
•

Select the active input: TIMx_CCR1 must be linked to the TI1 input, so write the CC1S
bits to 01 in the TIMx_CCMR1 register. As soon as CC1S becomes different from 00,
the channel is configured in input and the TIMx_CCR1 register becomes read-only.

•

Program the input filter duration you need with respect to the signal you connect to the
timer (when the input is one of the TIx (ICxF bits in the TIMx_CCMRx register). Let’s
imagine that, when toggling, the input signal is not stable during at must 5 internal clock
cycles. We must program a filter duration longer than these 5 clock cycles. We can
validate a transition on TI1 when 8 consecutive samples with the new level have been
detected (sampled at fDTS frequency). Then write IC1F bits to 0011 in the
TIMx_CCMR1 register.

•

Select the edge of the active transition on the TI1 channel by writing CC1P bit to 0 in
the TIMx_CCER register (rising edge in this case).

•

Program the input prescaler. In our example, we wish the capture to be performed at
each valid transition, so the prescaler is disabled (write IC1PS bits to ‘00’ in the
TIMx_CCMR1 register).

•

Enable capture from the counter into the capture register by setting the CC1E bit in the
TIMx_CCER register.

•

If needed, enable the related interrupt request by setting the CC1IE bit in the
TIMx_DIER register, and/or the DMA request by setting the CC1DE bit in the
TIMx_DIER register.

For code example refer to the Appendix section A.9.3: Input capture configuration code
example.
When an input capture occurs:
•

The TIMx_CCR1 register gets the value of the counter on the active transition.

•

CC1IF flag is set (interrupt flag). CC1OF is also set if at least two consecutive captures
occurred whereas the flag was not cleared.

•

An interrupt is generated depending on the CC1IE bit.

•

A DMA request is generated depending on the CC1DE bit.

For code example refer to the Appendix section A.9.4: Input capture data management
code example.
In order to handle the overcapture, it is recommended to read the data before the
overcapture flag. This is to avoid missing an overcapture which could happen after reading
the flag and before reading the data.
Note:

IC interrupt and/or DMA requests can be generated by software by setting the
corresponding CCxG bit in the TIMx_EGR register.

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20.4.7

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PWM input mode (only for TIM15)
This mode is a particular case of input capture mode. The procedure is the same except:
•

Two ICx signals are mapped on the same TIx input.

•

These 2 ICx signals are active on edges with opposite polarity.

•

One of the two TIxFP signals is selected as trigger input and the slave mode controller
is configured in reset mode.

For example, you can measure the period (in TIMx_CCR1 register) and the duty cycle (in
TIMx_CCR2 register) of the PWM applied on TI1 using the following procedure (depending
on CK_INT frequency and prescaler value):
•

Select the active input for TIMx_CCR1: write the CC1S bits to 01 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP1 (used both for capture in TIMx_CCR1 and counter
clear): write the CC1P bit to ‘0’ (active on rising edge).

•

Select the active input for TIMx_CCR2: write the CC2S bits to 10 in the TIMx_CCMR1
register (TI1 selected).

•

Select the active polarity for TI1FP2 (used for capture in TIMx_CCR2): write the CC2P
bit to ‘1’ (active on falling edge).

•

Select the valid trigger input: write the TS bits to 101 in the TIMx_SMCR register
(TI1FP1 selected).

•

Configure the slave mode controller in reset mode: write the SMS bits to 100 in the
TIMx_SMCR register.

•

Enable the captures: write the CC1E and CC2E bits to ‘1’ in the TIMx_CCER register.

For code example refer to the Appendix section A.9.5: PWM input configuration code
example.
Figure 186. PWM input mode timing
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TI1FP1 and TI2FP2 are connected to the slave mode controller.

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General-purpose timers (TIM15/16/17)

Forced output mode
In output mode (CCxS bits = 00 in the TIMx_CCMRx register), each output compare signal
(OCxREF and then OCx/OCxN) can be forced to active or inactive level directly by software,
independently of any comparison between the output compare register and the counter.
To force an output compare signal (OCXREF/OCx) to its active level, you just need to write
101 in the OCxM bits in the corresponding TIMx_CCMRx register. Thus OCXREF is forced
high (OCxREF is always active high) and OCx get opposite value to CCxP polarity bit.
For example: CCxP=0 (OCx active high) => OCx is forced to high level.
The OCxREF signal can be forced low by writing the OCxM bits to 100 in the TIMx_CCMRx
register.
Anyway, the comparison between the TIMx_CCRx shadow register and the counter is still
performed and allows the flag to be set. Interrupt and DMA requests can be sent
accordingly. This is described in the output compare mode section below.

20.4.9

Output compare mode
This function is used to control an output waveform or indicating when a period of time has
elapsed.
When a match is found between the capture/compare register and the counter, the output
compare function:
•

Assigns the corresponding output pin to a programmable value defined by the output
compare mode (OCxM bits in the TIMx_CCMRx register) and the output polarity (CCxP
bit in the TIMx_CCER register). The output pin can keep its level (OCXM=000), be set
active (OCxM=001), be set inactive (OCxM=010) or can toggle (OCxM=011) on match.

•

Sets a flag in the interrupt status register (CCxIF bit in the TIMx_SR register).

•

Generates an interrupt if the corresponding interrupt mask is set (CCXIE bit in the
TIMx_DIER register).

•

Sends a DMA request if the corresponding enable bit is set (CCxDE bit in the
TIMx_DIER register, CCDS bit in the TIMx_CR2 register for the DMA request
selection).

The TIMx_CCRx registers can be programmed with or without preload registers using the
OCxPE bit in the TIMx_CCMRx register.
In output compare mode, the update event UEV has no effect on OCxREF and OCx output.
The timing resolution is one count of the counter. Output compare mode can also be used to
output a single pulse (in One-pulse mode).

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Procedure:
1.

Select the counter clock (internal, external, prescaler).

2.

Write the desired data in the TIMx_ARR and TIMx_CCRx registers.

3.

Set the CCxIE bit if an interrupt request is to be generated.

4.

Select the output mode. For example:

5.

–

Write OCxM = 011 to toggle OCx output pin when CNT matches CCRx

–

Write OCxPE = 0 to disable preload register

–

Write CCxP = 0 to select active high polarity

–

Write CCxE = 1 to enable the output

Enable the counter by setting the CEN bit in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.2: Up counter on each 2 ETR rising
edges code example.
The TIMx_CCRx register can be updated at any time by software to control the output
waveform, provided that the preload register is not enabled (OCxPE=’0’, else TIMx_CCRx
shadow register is updated only at the next update event UEV). An example is given in
Figure 166.
Figure 187. Output compare mode, toggle on OC1
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20.4.10

PWM mode
Pulse Width Modulation mode allows you to generate a signal with a frequency determined
by the value of the TIMx_ARR register and a duty cycle determined by the value of the
TIMx_CCRx register.
The PWM mode can be selected independently on each channel (one PWM per OCx
output) by writing ‘110’ (PWM mode 1) or ‘111’ (PWM mode 2) in the OCxM bits in the
TIMx_CCMRx register. You must enable the corresponding preload register by setting the

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OCxPE bit in the TIMx_CCMRx register, and eventually the auto-reload preload register (in
upcounting or center-aligned modes) by setting the ARPE bit in the TIMx_CR1 register.
As the preload registers are transferred to the shadow registers only when an update event
occurs, before starting the counter, you have to initialize all the registers by setting the UG
bit in the TIMx_EGR register.
OCx polarity is software programmable using the CCxP bit in the TIMx_CCER register. It
can be programmed as active high or active low. OCx output is enabled by a combination of
the CCxE, CCxNE, MOE, OSSI and OSSR bits (TIMx_CCER and TIMx_BDTR registers).
Refer to the TIMx_CCER register description for more details.
In PWM mode (1 or 2), TIMx_CNT and TIMx_CCRx are always compared to determine
whether TIMx_CCRx ≤ TIMx_CNT or TIMx_CNT ≤ TIMx_CCRx (depending on the direction
of the counter).
The timer is able to generate PWM in edge-aligned mode or center-aligned mode
depending on the CMS bits in the TIMx_CR1 register.

PWM edge-aligned mode
•

Upcounting configuration
Upcounting is active when the DIR bit in the TIMx_CR1 register is low. Refer to the
Upcounting mode on page 462.
In the following example, we consider PWM mode 1. The reference PWM signal
OCxREF is high as long as TIMx_CNT < TIMx_CCRx else it becomes low. If the
compare value in TIMx_CCRx is greater than the auto-reload value (in TIMx_ARR)
then OCxREF is held at ‘1’. If the compare value is 0 then OCxRef is held at ‘0’.
Figure 167 shows some edge-aligned PWM waveforms in an example where
TIMx_ARR=8.

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Figure 188. Edge-aligned PWM waveforms (ARR=8)



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For code example refer to the Appendix section A.9.9: Center-aligned PWM configuration
example.
•

Downcounting configuration
Downcounting is active when DIR bit in TIMx_CR1 register is high. Refer to the
Repetition counter on page 489
In PWM mode 1, the reference signal OCxRef is low as long as
TIMx_CNT > TIMx_CCRx else it becomes high. If the compare value in TIMx_CCRx is
greater than the auto-reload value in TIMx_ARR, then OCxREF is held at ‘1’. 0% PWM
is not possible in this mode.

20.4.11

Complementary outputs and dead-time insertion
The TIM15/16/17 general-purpose timers can output one complementary signal and
manage the switching-off and switching-on of the outputs.
This time is generally known as dead-time and you have to adjust it depending on the
devices you have connected to the outputs and their characteristics (intrinsic delays of levelshifters, delays due to power switches...)
You can select the polarity of the outputs (main output OCx or complementary OCxN)
independently for each output. This is done by writing to the CCxP and CCxNP bits in the
TIMx_CCER register.
The complementary signals OCx and OCxN are activated by a combination of several
control bits: the CCxE and CCxNE bits in the TIMx_CCER register and the MOE, OISx,
OISxN, OSSI and OSSR bits in the TIMx_BDTR and TIMx_CR2 registers. Refer to
Table 72: Output control bits for complementary OCx and OCxN channels with break feature

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on page 522 for more details. In particular, the dead-time is activated when switching to the
IDLE state (MOE falling down to 0).
Dead-time insertion is enabled by setting both CCxE and CCxNE bits, and the MOE bit if the
break circuit is present. There is one 10-bit dead-time generator for each channel. From a
reference waveform OCxREF, it generates 2 outputs OCx and OCxN. If OCx and OCxN are
active high:
•

The OCx output signal is the same as the reference signal except for the rising edge,
which is delayed relative to the reference rising edge.

•

The OCxN output signal is the opposite of the reference signal except for the rising
edge, which is delayed relative to the reference falling edge.

If the delay is greater than the width of the active output (OCx or OCxN) then the
corresponding pulse is not generated.
The following figures show the relationships between the output signals of the dead-time
generator and the reference signal OCxREF. (we suppose CCxP=0, CCxNP=0, MOE=1,
CCxE=1 and CCxNE=1 in these examples)
Figure 189. Complementary output with dead-time insertion

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Figure 190. Dead-time waveforms with delay greater than the negative pulse

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Figure 191. Dead-time waveforms with delay greater than the positive pulse

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The dead-time delay is the same for each of the channels and is programmable with the
DTG bits in the TIMx_BDTR register. Refer to Section 20.5.15: TIM15 break and dead-time
register (TIM15_BDTR) on page 525 for delay calculation.

Re-directing OCxREF to OCx or OCxN
In output mode (forced, output compare or PWM), OCxREF can be re-directed to the OCx
output or to OCxN output by configuring the CCxE and CCxNE bits in the TIMx_CCER
register.
This allows you to send a specific waveform (such as PWM or static active level) on one
output while the complementary remains at its inactive level. Other alternative possibilities
are to have both outputs at inactive level or both outputs active and complementary with
dead-time.
Note:

When only OCxN is enabled (CCxE=0, CCxNE=1), it is not complemented and becomes
active as soon as OCxREF is high. For example, if CCxNP=0 then OCxN=OCxRef. On the
other hand, when both OCx and OCxN are enabled (CCxE=CCxNE=1) OCx becomes
active when OCxREF is high whereas OCxN is complemented and becomes active when
OCxREF is low.

20.4.12

Using the break function
When using the break function, the output enable signals and inactive levels are modified
according to additional control bits (MOE, OSSI and OSSR bits in the TIMx_BDTR register,
OISx and OISxN bits in the TIMx_CR2 register). In any case, the OCx and OCxN outputs
cannot be set both to active level at a given time. Refer to Table 72: Output control bits for
complementary OCx and OCxN channels with break feature on page 522 for more details.
The source for break (BRK) channel can be an external source connected to the BKIN pin or
one of the following internal sources:
•

the core LOCKUP output

•

the PVD output

•

the SRAM parity error signal

•

a clock failure event generated by the CSS detector

When exiting from reset, the break circuit is disabled and the MOE bit is low. You can enable
the break function by setting the BKE bit in the TIMx_BDTR register. The break input
polarity can be selected by configuring the BKP bit in the same register. BKE and BKP can

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General-purpose timers (TIM15/16/17)
be modified at the same time. When the BKE and BKP bits are written, a delay of 1 APB
clock cycle is applied before the writing is effective. Consequently, it is necessary to wait 1
APB clock period to correctly read back the bit after the write operation.
Because MOE falling edge can be asynchronous, a resynchronization circuit has been
inserted between the actual signal (acting on the outputs) and the synchronous control bit
(accessed in the TIMx_BDTR register). It results in some delays between the asynchronous
and the synchronous signals. In particular, if you write MOE to 1 whereas it was low, you
must insert a delay (dummy instruction) before reading it correctly. This is because you write
the asynchronous signal and read the synchronous signal.
When a break occurs (selected level on the break input):

Note:

•

The MOE bit is cleared asynchronously, putting the outputs in inactive state, idle state
or in reset state (selected by the OSSI bit). This feature functions even if the MCU
oscillator is off.

•

Each output channel is driven with the level programmed in the OISx bit in the
TIMx_CR2 register as soon as MOE=0. If OSSI=0 then the timer releases the enable
output else the enable output remains high.

•

When complementary outputs are used:
–

The outputs are first put in reset state inactive state (depending on the polarity).
This is done asynchronously so that it works even if no clock is provided to the
timer.

–

If the timer clock is still present, then the dead-time generator is reactivated in
order to drive the outputs with the level programmed in the OISx and OISxN bits
after a dead-time. Even in this case, OCx and OCxN cannot be driven to their
active level together. Note that because of the resynchronization on MOE, the
dead-time duration is a bit longer than usual (around 2 ck_tim clock cycles).

–

If OSSI=0 then the timer releases the enable outputs else the enable outputs
remain or become high as soon as one of the CCxE or CCxNE bits is high.

•

The break status flag (BIF bit in the TIMx_SR register) is set. An interrupt can be
generated if the BIE bit in the TIMx_DIER register is set.

•

If the AOE bit in the TIMx_BDTR register is set, the MOE bit is automatically set again
at the next update event UEV. This can be used to perform a regulation, for instance.
Else, MOE remains low until you write it to ‘1’ again. In this case, it can be used for
security and you can connect the break input to an alarm from power drivers, thermal
sensors or any security components.

The break inputs is acting on level. Thus, the MOE cannot be set while the break input is
active (neither automatically nor by software). In the meantime, the status flag BIF cannot
be cleared.
The break can be generated by the BRK input which has a programmable polarity and an
enable bit BKE in the TIMx_BDTR Register.
In addition to the break input and the output management, a write protection has been
implemented inside the break circuit to safeguard the application. It allows you to freeze the
configuration of several parameters (dead-time duration, OCx/OCxN polarities and state
when disabled, OCxM configurations, break enable and polarity). You can choose from 3
levels of protection selected by the LOCK bits in the TIMx_BDTR register. Refer to
Section 20.5.15: TIM15 break and dead-time register (TIM15_BDTR) on page 525. The
LOCK bits can be written only once after an MCU reset.
The Figure 192 shows an example of behavior of the outputs in response to a break.

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Figure 192. Output behavior in response to a break

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One-pulse mode
One-pulse mode (OPM) is a particular case of the previous modes. It allows the counter to
be started in response to a stimulus and to generate a pulse with a programmable length
after a programmable delay.
Starting the counter can be controlled through the slave mode controller. Generating the
waveform can be done in output compare mode or PWM mode. You select One-pulse mode
by setting the OPM bit in the TIMx_CR1 register. This makes the counter stop automatically
at the next update event UEV.
A pulse can be correctly generated only if the compare value is different from the counter
initial value. Before starting (when the timer is waiting for the trigger), the configuration must
be:
•

In upcounting: CNT < CCRx ≤ ARR (in particular, 0 < CCRx)

•

In downcounting: CNT > CCRx
Figure 193. Example of One-pulse mode
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For example you may want to generate a positive pulse on OC1 with a length of tPULSE and
after a delay of tDELAY as soon as a positive edge is detected on the TI2 input pin.
Let’s use TI2FP2 as trigger 1:
•

Map TI2FP2 to TI2 by writing CC2S=’01’ in the TIMx_CCMR1 register.

•

TI2FP2 must detect a rising edge, write CC2P=’0’ in the TIMx_CCER register.

•

Configure TI2FP2 as trigger for the slave mode controller (TRGI) by writing TS=’110’ in
the TIMx_SMCR register.

•

TI2FP2 is used to start the counter by writing SMS to ‘110’ in the TIMx_SMCR register
(trigger mode).

For code example refer to the Appendix section A.9.16: One-Pulse mode code example.

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The OPM waveform is defined by writing the compare registers (taking into account the
clock frequency and the counter prescaler).
•

The tDELAY is defined by the value written in the TIMx_CCR1 register.

•

The tPULSE is defined by the difference between the auto-reload value and the compare
value (TIMx_ARR - TIMx_CCR1).

•

Let’s say you want to build a waveform with a transition from ‘0’ to ‘1’ when a compare
match occurs and a transition from ‘1’ to ‘0’ when the counter reaches the auto-reload
value. To do this you enable PWM mode 2 by writing OC1M=111 in the TIMx_CCMR1
register. You can optionally enable the preload registers by writing OC1PE=’1’ in the
TIMx_CCMR1 register and ARPE in the TIMx_CR1 register. In this case you have to
write the compare value in the TIMx_CCR1 register, the auto-reload value in the
TIMx_ARR register, generate an update by setting the UG bit and wait for external
trigger event on TI2. CC1P is written to ‘0’ in this example.

In our example, the DIR and CMS bits in the TIMx_CR1 register should be low.
You only want 1 pulse, so you write ‘1’ in the OPM bit in the TIMx_CR1 register to stop the
counter at the next update event (when the counter rolls over from the auto-reload value
back to 0).

Particular case: OCx fast enable
In One-pulse mode, the edge detection on TIx input set the CEN bit which enables the
counter. Then the comparison between the counter and the compare value makes the
output toggle. But several clock cycles are needed for these operations and it limits the
minimum delay tDELAY min we can get.
If you want to output a waveform with the minimum delay, you can set the OCxFE bit in the
TIMx_CCMRx register. Then OCxRef (and OCx) are forced in response to the stimulus,
without taking in account the comparison. Its new level is the same as if a compare match
had occurred. OCxFE acts only if the channel is configured in PWM1 or PWM2 mode.
For code example refer to the part of code conditioned by PULSE_WITHOUT_DELAY > 0 in
the Appendix section A.9.16: One-Pulse mode code example.

20.4.14

TIM15 external trigger synchronization
This section applies to STM32F05x, STM32F07x and STM32F09x devices only.
The TIM15 timer can be synchronized with an external trigger in several modes: Reset
mode, Gated mode and Trigger mode.

Slave mode: Reset mode
The counter and its prescaler can be reinitialized in response to an event on a trigger input.
Moreover, if the URS bit from the TIMx_CR1 register is low, an update event UEV is
generated. Then all the preloaded registers (TIMx_ARR, TIMx_CCRx) are updated.
In the following example, the upcounter is cleared in response to a rising edge on TI1 input:
•

506/1004

Configure the channel 1 to detect rising edges on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits

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General-purpose timers (TIM15/16/17)
select the input capture source only, CC1S = 01 in the TIMx_CCMR1 register. Write
CC1P=0 in TIMx_CCER register to validate the polarity (and detect rising edges only).
•

Configure the timer in reset mode by writing SMS=100 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Start the counter by writing CEN=1 in the TIMx_CR1 register.

For code example refer to the Appendix section A.9.12: Reset mode code example.
The counter starts counting on the internal clock, then behaves normally until TI1 rising
edge. When TI1 rises, the counter is cleared and restarts from 0. In the meantime, the
trigger flag is set (TIF bit in the TIMx_SR register) and an interrupt request, or a DMA
request can be sent if enabled (depending on the TIE and TDE bits in TIMx_DIER register).
The following figure shows this behavior when the auto-reload register TIMx_ARR=0x36.
The delay between the rising edge on TI1 and the actual reset of the counter is due to the
resynchronization circuit on TI1 input.
Figure 194. Control circuit in reset mode

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Slave mode: Gated mode
The counter can be enabled depending on the level of a selected input.
In the following example, the upcounter counts only when TI1 input is low:
•

Configure the channel 1 to detect low levels on TI1. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC1F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC1S bits
select the input capture source only, CC1S=01 in TIMx_CCMR1 register. Write
CC1P=1 in TIMx_CCER register to validate the polarity (and detect low level only).

•

Configure the timer in gated mode by writing SMS=101 in TIMx_SMCR register. Select
TI1 as the input source by writing TS=101 in TIMx_SMCR register.

•

Enable the counter by writing CEN=1 in the TIMx_CR1 register (in gated mode, the
counter doesn’t start if CEN=0, whatever is the trigger input level).

For code example refer to the Appendix section A.9.13: Gated mode code example.
The counter starts counting on the internal clock as long as TI1 is low and stops as soon as
TI1 becomes high. The TIF flag in the TIMx_SR register is set both when the counter starts
or stops.
The delay between the rising edge on TI1 and the actual stop of the counter is due to the
resynchronization circuit on TI1 input.
Figure 195. Control circuit in gated mode

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Slave mode: Trigger mode
The counter can start in response to an event on a selected input.
In the following example, the upcounter starts in response to a rising edge on TI2 input:
•

508/1004

Configure the channel 2 to detect rising edges on TI2. Configure the input filter duration
(in this example, we don’t need any filter, so we keep IC2F=0000). The capture
prescaler is not used for triggering, so you don’t need to configure it. The CC2S bits are
configured to select the input capture source only, CC2S=01 in TIMx_CCMR1 register.

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Write CC2P=1 in TIMx_CCER register to validate the polarity (and detect low level
only).
•

Configure the timer in trigger mode by writing SMS=110 in TIMx_SMCR register. Select
TI2 as the input source by writing TS=110 in TIMx_SMCR register.

For code example refer to the Appendix section A.9.14: Trigger mode code example.
When a rising edge occurs on TI2, the counter starts counting on the internal clock and the
TIF flag is set.
The delay between the rising edge on TI2 and the actual start of the counter is due to the
resynchronization circuit on TI2 input.
Figure 196. Control circuit in trigger mode
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069

The TIM timers are linked together internally for timer synchronization or chaining. Refer to
Section 18.3.15: Timer synchronization on page 428 for details.

20.4.15

Timer synchronization (TIM15)
This section applies to STM32F05x, STM32F07x and STM32F09x devices only.
The TIM timers are linked together internally for timer synchronization or chaining. Refer to
Section 18.3.15: Timer synchronization on page 428 for details.

20.4.16

Debug mode
When the microcontroller enters debug mode (Cortex™-M0 core halted), the TIMx counter
either continues to work normally or stops, depending on DBG_TIMx_STOP configuration
bit in DBG module.

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RM0091

TIM15 registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

20.5.1

TIM15 control register 1 (TIM15_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

CKD[1:0]
rw

7

6

5

4

3

2

1

0

ARPE

Res.

Res.

Res.

OPM

URS

UDIS

CEN

rw

rw

rw

rw

rw

rw

Bits 15:10 Reserved, always read as 0.
Bits 9:8 CKD[1:0]: Clock division
This bit field indicates the division ratio between the timer clock (CK_INT) frequency and the
dead-time and sampling clock (tDTS) used by the dead-time generators and the digital filters
(TIx)
00: tDTS = tCK_INT
01: tDTS = 2*tCK_INT
10: tDTS = 4*tCK_INT
11: Reserved, do not program this value
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered
Bits 6:4 Reserved, always read as 0.
Bit 3 OPM: One-pulse mode
0: Counter is not stopped at update event
1: Counter stops counting at the next update event (clearing the bit CEN)
Bit 2 URS: Update request source
This bit is set and cleared by software to select the UEV event sources.
0: Any of the following events generate an update interrupt if enabled. These events can be:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
1: Only counter overflow/underflow generates an update interrupt if enabled

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Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable UEV event generation.
0: UEV enabled. The Update (UEV) event is generated by one of the following events:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
Buffered registers are then loaded with their preload values.
1: UEV disabled. The Update event is not generated, shadow registers keep their value
(ARR, PSC, CCRx). However the counter and the prescaler are reinitialized if the UG bit is
set or if a hardware reset is received from the slave mode controller.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled
Note: External clock and gated mode can work only if the CEN bit has been previously set by
software. However trigger mode can set the CEN bit automatically by hardware.

20.5.2

TIM15 control register 2 (TIM15_CR2)
Address offset: 0x04
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

OIS2

OIS1N

OIS1

Res.

rw

rw

rw

Bit 15:11

6

5

4

MMS[2:0]
rw

rw

rw

3

2

1

0

CCDS

CCUS

Res.

CCPC

rw

rw

rw

Reserved, always read as 0.

Bit 10 OIS2: Output idle state 2 (OC2 output)
0: OC2=0 when MOE=0
1: OC2=1 when MOE=0
Note: This bit cannot be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in the TIMx_BKR register).
Bit 9 OIS1N: Output Idle state 1 (OC1N output)
0: OC1N=0 after a dead-time when MOE=0
1: OC1N=1 after a dead-time when MOE=0
Note: This bit can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BKR register).
Bit 8 OIS1: Output Idle state 1 (OC1 output)
0: OC1=0 (after a dead-time if OC1N is implemented) when MOE=0
1: OC1=1 (after a dead-time if OC1N is implemented) when MOE=0
Note: This bit can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BKR register).
Bit 7

Reserved, always read as 0.

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Bits 6:4 MMS[1:0]: Master mode selection
These bits allow to select the information to be sent in master mode to slave timers for
synchronization (TRGO). The combination is as follows:
000: Reset - the UG bit from the TIMx_EGR register is used as trigger output (TRGO). If the
reset is generated by the trigger input (slave mode controller configured in reset mode) then
the signal on TRGO is delayed compared to the actual reset.
001: Enable - the Counter Enable signal CNT_EN is used as trigger output (TRGO). It is
useful to start several timers at the same time or to control a window in which a slave timer is
enable. The Counter Enable signal is generated by a logic OR between CEN control bit and
the trigger input when configured in gated mode. When the Counter Enable signal is
controlled by the trigger input, there is a delay on TRGO, except if the master/slave mode is
selected (see the MSM bit description in TIMx_SMCR register).
010: Update - The update event is selected as trigger output (TRGO). For instance a master
timer can then be used as a prescaler for a slave timer.
011: Compare Pulse - The trigger output send a positive pulse when the CC1IF flag is to be
set (even if it was already high), as soon as a capture or a compare match occurred.
(TRGO).
100: Compare - OC1REF signal is used as trigger output (TRGO).
101: Compare - OC2REF signal is used as trigger output (TRGO).
Bit 3 CCDS: Capture/compare DMA selection
0: CCx DMA request sent when CCx event occurs
1: CCx DMA requests sent when update event occurs
Bit 2 CCUS: Capture/compare control update selection
0: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit only.
1: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit or when an rising edge occurs on TRGI.
Note: This bit acts only on channels that have a complementary output.
Bit 1 Reserved, always read as 0.
Bit 0 CCPC: Capture/compare preloaded control
0: CCxE, CCxNE and OCxM bits are not preloaded
1: CCxE, CCxNE and OCxM bits are preloaded, after having been written, they are updated
only when COM bit is set.
Note: This bit acts only on channels that have a complementary output.

20.5.3

TIM15 slave mode control register (TIM15_SMCR)
Address offset: 0x08
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

MSM
rw

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6

5

4

TS[2:0]
rw

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2

Res.
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1

0

SMS[2:0]
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Bits 15:8

Reserved, always read as 0.

Bit 7 MSM: Master/slave mode
0: No action
1: The effect of an event on the trigger input (TRGI) is delayed to allow a perfect
synchronization between the current timer and its slaves (through TRGO). It is useful if we
want to synchronize several timers on a single external event.
Bits 6:4 TS[2:0]: Trigger selection
This bit field selects the trigger input to be used to synchronize the counter.
000: Internal Trigger 0 (ITR0)
001: Internal Trigger 1 (ITR1)
010: Internal Trigger 2 (ITR2)
011: Internal Trigger 3 (ITR3)
100: TI1 Edge Detector (TI1F_ED)
101: Filtered Timer Input 1 (TI1FP1)
110: Filtered Timer Input 2 (TI2FP2)
See Table 71: TIMx Internal trigger connection on page 513 for more details on ITRx meaning
for each Timer.
Note: These bits must be changed only when they are not used (e.g. when SMS=000) to
avoid wrong edge detections at the transition.
Bit 3

Reserved, always read as 0.

Bits 2:0 SMS: Slave mode selection
When external signals are selected the active edge of the trigger signal (TRGI) is linked to the
polarity selected on the external input (see Input Control register and Control Register
description.
000: Slave mode disabled - if CEN = ‘1’ then the prescaler is clocked directly by the internal
clock.
100: Reset Mode - Rising edge of the selected trigger input (TRGI) reinitializes the counter
and generates an update of the registers.
101: Gated Mode - The counter clock is enabled when the trigger input (TRGI) is high. The
counter stops (but is not reset) as soon as the trigger becomes low. Both start and stop of
the counter are controlled.
110: Trigger Mode - The counter starts at a rising edge of the trigger TRGI (but it is not
reset). Only the start of the counter is controlled.
111: External Clock Mode 1 - Rising edges of the selected trigger (TRGI) clock the counter.
Note: The gated mode must not be used if TI1F_ED is selected as the trigger input
(TS=’100’). Indeed, TI1F_ED outputs 1 pulse for each transition on TI1F, whereas the
gated mode checks the level of the trigger signal.

Table 71. TIMx Internal trigger connection
Slave TIM

ITR0 (TS = 000)

ITR1 (TS = 001)

ITR2 (TS = 010)

ITR3 (TS = 011)

TIM15

TIM2

TIM3

TIM16_OC

TIM17_OC

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20.5.4

RM0091

TIM15 DMA/interrupt enable register (TIM15_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

12

11

Res.

TDE

Res.

Res.

Res.

rw

10

rw

Bit 15

9

CC2DE CC1DE
rw

8

7

6

5

4

3

2

1

0

UDE

BIE

TIE

COMIE

Res.

Res.

CC2IE

CC1IE

UIE

rw

rw

rw

rw

rw

rw

rw

Reserved, always read as 0.

Bit 14 TDE: Trigger DMA request enable
0: Trigger DMA request disabled
1: Trigger DMA request enabled
Bits 13:11 Reserved, always read as 0.
Bit 10 CC2DE: Capture/Compare 2 DMA request enable
0: CC2 DMA request disabled
1: CC2 DMA request enabled
Bit 9 CC1DE: Capture/Compare 1 DMA request enable
0: CC1 DMA request disabled
1: CC1 DMA request enabled
Bit 8 UDE: Update DMA request enable
0: Update DMA request disabled
1: Update DMA request enabled
Bit 7 BIE: Break interrupt enable
0: Break interrupt disabled
1: Break interrupt enabled
Bit 6 TIE: Trigger interrupt enable
0: Trigger interrupt disabled
1: Trigger interrupt enabled
Bit 5 COMIE: COM interrupt enable
0: COM interrupt disabled
1: COM interrupt enabled
Bits 4:3

Reserved, always read as 0.

Bit 2 CC2IE: Capture/Compare 2 interrupt enable
0: CC2 interrupt disabled
1: CC2 interrupt enabled
Bit 1 CC1IE: Capture/Compare 1 interrupt enable
0: CC1 interrupt disabled
1: CC1 interrupt enabled
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled
1: Update interrupt enabled

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20.5.5

TIM15 status register (TIM15_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

12

11

Res.

Res.

Res.

Res.

Res.

10

rc_w0

Bits 15:11

9

CC2OF CC1OF
rc_w0

8

7

6

5

4

3

2

1

0

Res.

BIF

TIF

COMIF

Res.

Res.

CC2IF

CC1IF

UIF

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

Reserved, always read as 0.

Bit 10 CC2OF: Capture/Compare 2 overcapture flag
refer to CC1OF description
Bit 9 CC1OF: Capture/Compare 1 overcapture flag
This flag is set by hardware only when the corresponding channel is configured in input
capture mode. It is cleared by software by writing it to ‘0’.
0: No overcapture has been detected
1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was
already set
Bit 8

Reserved, always read as 0.

Bit 7 BIF: Break interrupt flag
This flag is set by hardware as soon as the break input goes active. It can be cleared by
software if the break input is not active.
0: No break event occurred
1: An active level has been detected on the break input
Bit 6 TIF: Trigger interrupt flag
This flag is set by hardware on trigger event (active edge detected on TRGI input when the
slave mode controller is enabled in all modes but gated mode, both edges in case gated mode
is selected). It is cleared by software.
0: No trigger event occurred
1: Trigger interrupt pending
Bit 5 COMIF: COM interrupt flag
This flag is set by hardware on a COM event (once the capture/compare control bits –CCxE,
CCxNE, OCxM– have been updated). It is cleared by software by writing it to ‘0’.
0: No COM event occurred
1: COM interrupt pending
Bits 5:3 Reserved, always read as 0.

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Bit 2 CC2IF: Capture/Compare 2 interrupt flag
refer to CC1IF description
Bit 1 CC1IF: Capture/Compare 1 interrupt flag
If channel CC1 is configured as output:
This flag is set by hardware when the counter matches the compare value, with some
exception in center-aligned mode (refer to the CMS bits in the TIMx_CR1 register description).
It is cleared by software.
0: No match.
1: The content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register.
When the contents of TIMx_CCR1 are greater than the contents of TIMx_ARR, the CC1IF
bit goes high on the counter overflow (in upcounting and up/down-counting modes) or
underflow (in downcounting mode)
If channel CC1 is configured as input:
This bit is set by hardware on a capture. It is cleared by software or by reading the
TIMx_CCR1 register.
0: No input capture occurred
1: The counter value has been captured in TIMx_CCR1 register (An edge has been
detected on IC1 which matches the selected polarity)
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending. This bit is set by hardware when the registers are updated:
–At overflow regarding the repetition counter value (update if repetition counter = 0) and if
the UDIS=0 in the TIMx_CR1 register.
–When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if URS=0
and UDIS=0 in the TIMx_CR1 register.
–When CNT is reinitialized by a trigger event (refer to Section 20.5.3: TIM15 slave mode
control register (TIM15_SMCR)), if URS=0 and UDIS=0 in the TIMx_CR1 register.

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20.5.6

TIM15 event generation register (TIM15_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

BG

TG

COMG

Res.

Res.

CC2G

CC1G

UG

w

w

rw

w

w

w

Bits 15:8

Reserved, always read as 0.

Bit 7 BG: Break generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: A break event is generated. MOE bit is cleared and BIF flag is set. Related interrupt or
DMA transfer can occur if enabled.
Bit 6 TG: Trigger generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: The TIF flag is set in TIMx_SR register. Related interrupt or DMA transfer can occur if
enabled
Bit 5 COMG: Capture/Compare control update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action
1: When the CCPC bit is set, it is possible to update the CCxE, CCxNE and OCxM bits
Note: This bit acts only on channels that have a complementary output.
Bits 4:3 Reserved, always read as 0.
Bit 2 CC2G: Capture/Compare 2 generation
Refer to CC1G description
Bit 1 CC1G: Capture/Compare 1 generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action
1: A capture/compare event is generated on channel 1:
If channel CC1 is configured as output:
CC1IF flag is set, Corresponding interrupt or DMA request is sent if enabled.
If channel CC1 is configured as input:
The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set, the
corresponding interrupt or DMA request is sent if enabled. The CC1OF flag is set if the CC1IF
flag was already high.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action.
1: Reinitialize the counter and generates an update of the registers. Note that the prescaler
counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared if
the center-aligned mode is selected or if DIR=0 (upcounting), else it takes the auto-reload
value (TIMx_ARR) if DIR=1 (downcounting).

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20.5.7

RM0091

TIM15 capture/compare mode register 1 (TIM15_CCMR1)
Address offset: 0x18
Reset value: 0x0000
The channels can be used in input (capture mode) or in output (compare mode). The
direction of a channel is defined by configuring the corresponding CCxS bits. All the other
bits of this register have a different function in input and in output mode. For a given bit,
OCxx describes its function when the channel is configured in output, ICxx describes its
function when the channel is configured in input. So you must take care that the same bit
can have a different meaning for the input stage and for the output stage.

15

14

Res.

13

12

OC2M[2:0]
IC2F[3:0]

rw

rw

rw

11

10

OC2
PE

OC2
FE

9

8

CC2S[1:0]

7

6

Res.

rw

rw

4

OC1M[2:0]

IC2PSC[1:0]
rw

5

IC1F[3:0]
rw

rw

rw

rw

rw

3

2

OC1
PE

OC1
FE

1

0

CC1S[1:0]

IC1PSC[1:0]
rw

rw

rw

rw

rw

Output compare mode:
Bit 15

Reserved, always read as 0.

Bits 14:12 OC2M[2:0]: Output Compare 2 mode
Bit 11 OC2PE: Output Compare 2 preload enable
Bit 10 OC2FE: Output Compare 2 fast enable
Bits 9:8 CC2S[1:0]: Capture/Compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output.
01: CC2 channel is configured as input, IC2 is mapped on TI2.
10: CC2 channel is configured as input, IC2 is mapped on TI1.
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if
an internal trigger input is selected through the TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = ‘0’ in TIMx_CCER).
Bit 7

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Bits 6:4 OC1M: Output Compare 1 mode
These bits define the behavior of the output reference signal OC1REF from which OC1 and
OC1N are derived. OC1REF is active high whereas OC1 and OC1N active level depends on
CC1P and CC1NP bits.
000: Frozen - The comparison between the output compare register TIMx_CCR1 and the
counter TIMx_CNT has no effect on the outputs.
001: Set channel 1 to active level on match. OC1REF signal is forced high when the counter
TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
010: Set channel 1 to inactive level on match. OC1REF signal is forced low when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
011: Toggle - OC1REF toggles when TIMx_CNT=TIMx_CCR1.
100: Force inactive level - OC1REF is forced low.
101: Force active level - OC1REF is forced high.
110: PWM mode 1 - In upcounting, channel 1 is active as long as TIMx_CNTTIMx_CCR1 else active (OC1REF=’1’).
111: PWM mode 2 - In upcounting, channel 1 is inactive as long as TIMx_CNTTIMx_CCR1 else
inactive.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: In PWM mode 1 or 2, the OCREF level changes only when the result of the
comparison changes or when the output compare mode switches from “frozen” mode
to “PWM” mode.
Bit 3 OC1PE: Output Compare 1 preload enable
0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the
new value is taken in account immediately.
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded in the active register at each update event.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: The PWM mode can be used without validating the preload register only in one
pulse mode (OPM bit set in TIMx_CR1 register). Else the behavior is not guaranteed.
Bit 2 OC1FE: Output Compare 1 fast enable
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is
ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is
5 clock cycles.
1: An active edge on the trigger input acts like a compare match on CC1 output. Then, OC is
set to the compare level independently of the result of the comparison. Delay to sample the
trigger input and to activate CC1 output is reduced to 3 clock cycles. OCFE acts only if the
channel is configured in PWM1 or PWM2 mode.
Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output.
01: CC1 channel is configured as input, IC1 is mapped on TI1.
10: CC1 channel is configured as input, IC1 is mapped on TI2.
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if
an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

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Input capture mode
Bits 15:12 IC2F: Input capture 2 filter
Bits 11:10 IC2PSC[1:0]: Input capture 2 prescaler
Bits 9:8 CC2S: Capture/Compare 2 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC2 channel is configured as output
01: CC2 channel is configured as input, IC2 is mapped on TI2
10: CC2 channel is configured as input, IC2 is mapped on TI1
11: CC2 channel is configured as input, IC2 is mapped on TRC. This mode is working only if an
internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC2S bits are writable only when the channel is OFF (CC2E = ‘0’ in TIMx_CCER).
Bits 7:4 IC1F[3:0]: Input capture 1 filter
This bit-field defines the frequency used to sample TI1 input and the length of the digital filter applied to
TI1. The digital filter is made of an event counter in which N consecutive events are needed to validate
a transition on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ICxF[3:0] = 1, 2 or 3.
Bits 3:2 IC1PSC: Input capture 1 prescaler
This bit-field defines the ratio of the prescaler acting on CC1 input (IC1).
The prescaler is reset as soon as CC1E=’0’ (TIMx_CCER register).
00: no prescaler, capture is done each time an edge is detected on the capture input
01: capture is done once every 2 events
10: capture is done once every 4 events
11: capture is done once every 8 events
Bits 1:0 CC1S: Capture/Compare 1 Selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if an
internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

520/1004

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RM0091

General-purpose timers (TIM15/16/17)

20.5.8

TIM15 capture/compare enable register (TIM15_CCER)
Address offset: 0x20
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC1NP

Res.

CC2P

CC2E

rw

rw

rw

Bits 15:8

3

2

CC1NP CC1NE
rw

rw

1

0

CC1P

CC1E

rw

rw

Reserved, always read as 0.

Bit 7 CC2NP: Capture/Compare 2 complementary output polarity
refer to CC1NP description
Bit 6 Reserved, always read as 0.
Bit 5 CC2P: Capture/Compare 2 output polarity
Refer to CC1P description
Bit 4 CC2E: Capture/Compare 2 output enable
Refer to CC1E description
Bit 3 CC1NP: Capture/Compare 1 complementary output polarity
0: OC1N active high
1: OC1N active low
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register) and CC1S=”00” (the channel is configured in output).
Bit 2 CC1NE: Capture/Compare 1 complementary output enable
0: Off - OC1N is not active. OC1N level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1E bits.
1: On - OC1N signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1E bits.
Bit 1 CC1P: Capture/Compare 1 output polarity
CC1 channel configured as output:
0: OC1 active high
1: OC1 active low
CC1 channel configured as input:
The CC1NP/CC1P bits select the polarity of TI1FP1 and TI2FP1 for trigger or capture
operations.
00: noninverted/rising edge: circuit is sensitive to TIxFP1's rising edge (capture, trigger in
reset or trigger mode), TIxFP1 is not inverted (trigger in gated mode).
01: inverted/falling edge: circuit is sensitive to TIxFP1's falling edge (capture, trigger in reset,
or trigger mode), TIxFP1 is inverted (trigger in gated mode).
10: reserved, do not use this configuration.
11: noninverted/both edges: circuit is sensitive to both the rising and falling edges of TIxFP1
(capture, trigger in reset or trigger mode), TIxFP1 is not inverted (trigger in gated mode).
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register).

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Bit 0 CC1E: Capture/Compare 1 output enable
CC1 channel configured as output:
0: Off - OC1 is not active. OC1 level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1NE bits.
1: On - OC1 signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1NE bits.
CC1 channel configured as input:
This bit determines if a capture of the counter value can actually be done into the input
capture/compare register 1 (TIMx_CCR1) or not.
0: Capture disabled
1: Capture enabled

Table 72. Output control bits for complementary OCx and OCxN channels with break feature
Output states(1)

Control bits
MOE bit OSSI bit OSSR bit CCxE bit CCxNE bit OCx output state

1

522/1004

OCxN output state

0

0

0

Output Disabled (not driven Output Disabled (not driven by
by the timer)
the timer)
OCx=0, OCx_EN=0
OCxN=0, OCxN_EN=0

0

0

1

Output Disabled (not driven OCxREF + Polarity
by the timer)
OCxN=OCxREF xor CCxNP,
OCxN_EN=1
OCx=0, OCx_EN=0
Output Disabled (not driven by
the timer)
OCxN=0, OCxN_EN=0
Complementary to OCREF (not
OCREF) + Polarity + dead-time
OCxN_EN=1

0

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

0

1

1

OCREF + Polarity + deadtime
OCx_EN=1

1

0

0

Output Disabled (not driven Output Disabled (not driven by
by the timer)
the timer)
OCx=CCxP, OCx_EN=0
OCxN=CCxNP, OCxN_EN=0

1

0

1

Off-State (output enabled
with inactive state)
OCx=CCxP, OCx_EN=1

OCxREF + Polarity
OCxN=OCxREF xor CCxNP,
OCxN_EN=1

1

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

Off-State (output enabled with
inactive state)
OCxN=CCxNP, OCxN_EN=1

1

1

1

OCREF + Polarity + deadtime
OCx_EN=1

Complementary to OCREF (not
OCREF) + Polarity + dead-time
OCxN_EN=1

X

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RM0091

General-purpose timers (TIM15/16/17)

Table 72. Output control bits for complementary OCx and OCxN channels with break feature
Output states(1)

Control bits
MOE bit OSSI bit OSSR bit CCxE bit CCxNE bit OCx output state
0

0

0

0

0

1

0

1

0

0

1

1

0

0

1

0

1

1

1

0

1

1

1

1

0

X

OCxN output state

Output Disabled (not driven by the timer)
Asynchronously: OCx=CCxP, OCx_EN=0, OCxN=CCxNP,
OCxN_EN=0
Then if the clock is present: OCx=OISx and OCxN=OISxN
after a dead-time, assuming that OISx and OISxN do not
correspond to OCX and OCxN both in active state.
Off-State (output enabled with inactive state)
Asynchronously: OCx=CCxP, OCx_EN=1, OCxN=CCxNP,
OCxN_EN=1
Then if the clock is present: OCx=OISx and OCxN=OISxN
after a dead-time, assuming that OISx and OISxN do not
correspond to OCX and OCxN both in active state

1. When both outputs of a channel are not used (CCxE = CCxNE = 0), the OISx, OISxN, CCxP and CCxNP bits must be kept
cleared.

Note:

The state of the external I/O pins connected to the complementary OCx and OCxN channels
depends on the OCx and OCxN channel state and the GPIO and AFIO registers.

20.5.9

TIM15 counter (TIM15_CNT)
Address offset: 0x24
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]
rw

rw

rw

Bits 15:0

20.5.10

rw

rw

rw

rw

rw

CNT[15:0]: Counter value

TIM15 prescaler (TIM15_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

PSC[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency (CK_CNT) is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded in the active prescaler register at each update event
(including when the counter is cleared through UG bit of TIMx_EGR register or through trigger
controller when configured in “reset mode”).

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20.5.11

RM0091

TIM15 auto-reload register (TIM15_ARR)
Address offset: 0x2C
Reset value: 0xFFFF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 ARR[15:0]: Auto-reload value
ARR is the value to be loaded in the actual auto-reload register.
Refer to the Section 19.3.1: Time-base unit on page 460 for more details about ARR update
and behavior.
The counter is blocked while the auto-reload value is null.

20.5.12

TIM15 repetition counter register (TIM15_RCR)
Address offset: 0x30
Reset value: 0x0000

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

3

2

1

0

rw

rw

rw

REP[7:0]
rw

rw

rw

rw

rw

Bits 15:8 Reserved, always read as 0.
Bits 7:0 REP[7:0]: Repetition counter value
These bits allow the user to set-up the update rate of the compare registers (i.e. periodic
transfers from preload to active registers) when preload registers are enable, as well as the
update interrupt generation rate, if this interrupt is enable.
Each time the REP_CNT related downcounter reaches zero, an update event is generated
and it restarts counting from REP value. As REP_CNT is reloaded with REP value only at the
repetition update event U_RC, any write to the TIMx_RCR register is not taken in account until
the next repetition update event.
It means in PWM mode (REP+1) corresponds to the number of PWM periods in edge-aligned
mode.

20.5.13

TIM15 capture/compare register 1 (TIM15_CCR1)
Address offset: 0x34
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR1[15:0]
rw

524/1004

rw

rw

rw

rw

rw

rw

rw

rw

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RM0091

General-purpose timers (TIM15/16/17)

Bits 15:0 CCR1[15:0]: Capture/Compare 1 value
If channel CC1 is configured as output:
CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit
OC1PE). Else the preload value is copied in the active capture/compare 1 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC1 output.
If channel CC1 is configured as input:
CCR1 is the counter value transferred by the last input capture 1 event (IC1).

20.5.14

TIM15 capture/compare register 2 (TIM15_CCR2)
Address offset: 0x38
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR2[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 CCR2[15:0]: Capture/Compare 2 value
If channel CC2 is configured as output:
CCR2 is the value to be loaded in the actual capture/compare 2 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR2 register (bit
OC2PE). Else the preload value is copied in the active capture/compare 2 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signalled on OC2 output.
If channel CC2 is configured as input:
CCR2 is the counter value transferred by the last input capture 2 event (IC2).

20.5.15

TIM15 break and dead-time register (TIM15_BDTR)
Address offset: 0x44
Reset value: 0x0000

15

14

13

12

11

10

MOE

AOE

BKP

BKE

OSSR

OSSI

rw

rw

rw

rw

rw

rw

Note:

9

8

7

6

5

4

rw

rw

rw

rw

LOCK[1:0]
rw

rw

3

2

1

0

rw

rw

rw

DTG[7:0]
rw

As the bits AOE, BKP, BKE, OSSI, OSSR and DTG[7:0] can be write-locked depending on
the LOCK configuration, it can be necessary to configure all of them during the first write
access to the TIMx_BDTR register.

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RM0091

Bit 15 MOE: Main output enable
This bit is cleared asynchronously by hardware as soon as the break input is active. It is set by
software or automatically depending on the AOE bit. It is acting only on the channels which are
configured in output.
0: OC and OCN outputs are disabled or forced to idle state
1: OC and OCN outputs are enabled if their respective enable bits are set (CCxE, CCxNE in
TIMx_CCER register)
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
Bit 14 AOE: Automatic output enable
0: MOE can be set only by software
1: MOE can be set by software or automatically at the next update event (if the break input is
not be active)
Note: This bit can not be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Bit 13 BKP: Break polarity
0: Break input BRK is active low
1: Break input BRK is active high
Note: This bit can not be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 12 BKE: Break enable
0: Break inputs (BRK and CCS clock failure event) disabled
1; Break inputs (BRK and CCS clock failure event) enabled
Note: This bit cannot be modified when LOCK level 1 has been programmed (LOCK bits in
TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 11 OSSR: Off-state selection for Run mode
This bit is used when MOE=1 on channels having a complementary output which are
configured as outputs. OSSR is not implemented if no complementary output is implemented
in the timer.
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0)
1: When inactive, OC/OCN outputs are enabled with their inactive level as soon as CCxE=1
or CCxNE=1. Then, OC/OCN enable output signal=1
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).
Bit 10 OSSI: Off-state selection for Idle mode
This bit is used when MOE=0 on channels configured as outputs.
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0)
1: When inactive, OC/OCN outputs are forced first with their idle level as soon as CCxE=1 or
CCxNE=1. OC/OCN enable output signal=1)
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).

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General-purpose timers (TIM15/16/17)

Bits 9:8 LOCK[1:0]: Lock configuration
These bits offer a write protection against software errors.
00: LOCK OFF - No bit is write protected
01: LOCK Level 1 = DTG bits in TIMx_BDTR register, OISx and OISxN bits in TIMx_CR2
register and BKE/BKP/AOE bits in TIMx_BDTR register can no longer be written
10: LOCK Level 2 = LOCK Level 1 + CC Polarity bits (CCxP/CCxNP bits in TIMx_CCER
register, as long as the related channel is configured in output through the CCxS bits) as well
as OSSR and OSSI bits can no longer be written.
11: LOCK Level 3 = LOCK Level 2 + CC Control bits (OCxM and OCxPE bits in
TIMx_CCMRx registers, as long as the related channel is configured in output through the
CCxS bits) can no longer be written.
Note: The LOCK bits can be written only once after the reset. Once the TIMx_BDTR register
has been written, their content is frozen until the next reset.
Bits 7:0 DTG[7:0]: Dead-time generator setup
This bit-field defines the duration of the dead-time inserted between the complementary
outputs. DT correspond to this duration.
DTG[7:5]=0xx => DT=DTG[7:0]x tdtg with tdtg=tDTS
DTG[7:5]=10x => DT=(64+DTG[5:0])xtdtg with Tdtg=2xtDTS
DTG[7:5]=110 => DT=(32+DTG[4:0])xtdtg with Tdtg=8xtDTS
DTG[7:5]=111 => DT=(32+DTG[4:0])xtdtg with Tdtg=16xtDTS
Example if TDTS=125ns (8MHz), dead-time possible values are:
0 to 15875 ns by 125 ns steps,
16 µs to 31750 ns by 250 ns steps,
32 µs to 63 µs by 1 µs steps,
64 µs to 126 µs by 2 µs steps
Note: This bit-field can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BDTR register).

20.5.16

TIM15 DMA control register (TIM15_DCR)
Address offset: 0x48
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

8

DBL[4:0]
rw

rw

rw

rw

7

6

5

Res.

Res.

Res.

rw

4

3

2

1

0

rw

rw

DBA[4:0]
rw

rw

rw

Bits 15:13 Reserved, always read as 0.

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RM0091

Bits 12:8 DBL[4:0]: DMA burst length
This 5-bit vector defines the length of DMA transfers (the timer recognizes a burst transfer
when a read or a write access is done to the TIMx_DMAR address).
00000: 1 transfer,
00001: 2 transfers,
00010: 3 transfers,
...
10001: 18 transfers.
Bits 7:5 Reserved, always read as 0.
Bits 4:0 DBA[4:0]: DMA base address
This 5-bits vector defines the base-address for DMA transfers (when read/write access are
done through the TIMx_DMAR address). DBA is defined as an offset starting from the
address of the TIMx_CR1 register.
Example:
00000: TIMx_CR1,
00001: TIMx_CR2,
00010: TIMx_SMCR,
...

20.5.17

TIM15 DMA address for full transfer (TIM15_DMAR)
Address offset: 0x4C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

DMAB[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 DMAB[15:0]: DMA register for burst accesses
A read or write operation to the DMAR register accesses the register located at the address
(TIMx_CR1 address) + (DBA + DMA index) x 4
where TIMx_CR1 address is the address of the control register 1, DBA is the DMA base
address configured in TIMx_DCR register, DMA index is automatically controlled by the
DMA transfer, and ranges from 0 to DBL (DBL configured in TIMx_DCR).

20.5.18

TIM15 register map
TIM15 registers are mapped as 16-bit addressable registers as described in the table
below:

528/1004

DocID018940 Rev 9

CEN
0
CCPC

0

URS

0

UDIS

Res.

Res.

Res.
0

0
Res.

0

0
CCUS

0

OPM

0

MMS[2:0]

0
CCDS

0
Res.

ARPE

0
OIS1

Res.

Res.
Res.

Res.

Res.

Res.

0
OIS1N

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM15_CR2

Res.

0x04

Res.

Reset value

CKD
[1:0]

OIS2

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM15_CR1

Res.

0x00

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 73. TIM15 register map and reset values

0

0

0

0x4C

TIM15_DMAR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM15_DCR

Reset value

DocID018940 Rev 9

BKE

OSSR

OSSI

Reset value

BKP
1
1
1
1
1
1

Res.
Res.
Res.
Res.
Res.
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

0

0
0
0

Res.
Res.
Res.

0

0

0

0

0
0

0

0

0

Reset value

0

Reset value

0

0

0

0

0
0

0

0

0
0

0

0
0

0

0

0

0

0

0

0

0

0

0

0
0

0

0

0

0

0

0

0

0

Reset value

0

0

0

DBL[4:0]

0

0

0

1

0

0

0

0
0

ARR[15:0]

1

0

0

0

0

CC1E

PSC[15:0]

CC1P

0

CC1NE

CNT[15:0]

CC2E

0

CC1NP

Res.

IC2F[3:0]

OC2FE

OC2PE

Res.

CC2S
[1:0]

CC2P

0

0

0
0
0

OC1M
[2:0]

0 0 0 0
0 0 0
IC2
CC2S
PSC
IC1F[3:0]
[1:0]
[1:0]
0 0 0 0 0 0 0 0

LOCK
[1:0]

0

0

0

CCR1[15:0]

CCR2[15:0]

DT[7:0]

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

0

0

0

0

0

0

0

OC1FE

0

CC2IF
CC1IF
UIF

0
0

CC1G
UG

Res.
0

CC2G

Res.

Res.

0
Res.

0
0
0
0
0
0

CC2IE
CC1IE
UIE

Res.

0
Res.

Res.

MSM

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TS[2:0]

OC1PE

TIE
COMIE
0

TIF

0
COMIF

0

TG

0

COMG

BIE

0
BIF

UDE

0

BG

Res.

CC1DE

CC1OF

Res.

Res.

Res.

Res.

TDE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CC2DE

CC2OF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

CC2NP

0

0

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

OC2M
[2:0]

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Reset value

Res.

Reset value

AOE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

MOE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM15_BDTR

Res.

0x48
TIM15_CCR2

Res.

0x44
TIM15_CCR1

Res.

0x38
TIM15_RCR

Res.

0x34
TIM15_ARR

Res.

0x30
TIM15_PSC

Res.

0x2C
TIM15_CNT

Res.

0x28
TIM15_CCER

Res.

0x24

Res.

0x20
Reset value
TIM15_CCMR1
Input capture
mode
Reset value

Res.

Reset value
TIM15_CCMR1
Output compare
mode

Res.

0x18
TIM15_EGR

Res.

0x14
TIM15_SR

Res.

0x10
TIM15_DIER

Res.

0x0C
TIM15_SMCR

Res.

0x08

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

RM0091
General-purpose timers (TIM15/16/17)

Table 73. TIM15 register map and reset values (continued)

SMS[2:0]

0
0
0

0
0
0

CC1S
[1:0]

0 0 0 0
IC1
CC1S
PSC
[1:0]
[1:0]
0 0 0 0

0
0
0
0
0
0

0
0
0
0
0
0

0
0
0
0
0
0

1
1
1
1
1
1

REP[7:0]

DBA[4:0]

DMAB[15:0]

0

0

0

0

0

0

0

0

0

0

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Refer to Section 2.2.2 on page 46 for the register boundary addresses.

20.6

TIM16 and TIM17 registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

20.6.1

TIM16 and TIM17 control register 1 (TIM16_CR1 and TIM17_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

CKD[1:0]
rw

7

6

5

4

3

2

1

0

ARPE

Res.

Res.

Res.

OPM

URS

UDIS

CEN

rw

rw

rw

rw

rw

rw

Bits 15:10 Reserved, always read as 0.
Bits 9:8 CKD[1:0]: Clock division
This bit-field indicates the division ratio between the timer clock (CK_INT) frequency and the
dead-time and sampling clock (tDTS)used by the dead-time generators and the digital filters
(TIx),
00: tDTS=tCK_INT
01: tDTS=2*tCK_INT
10: tDTS=4*tCK_INT
11: Reserved, do not program this value
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered
1: TIMx_ARR register is buffered
Bits 6:4 Reserved, always read as 0.
Bit 3 OPM: One pulse mode
0: Counter is not stopped at update event
1: Counter stops counting at the next update event (clearing the bit CEN)

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General-purpose timers (TIM15/16/17)

Bit 2 URS: Update request source
This bit is set and cleared by software to select the UEV event sources.
0: Any of the following events generate an update interrupt or DMA request if enabled.
These events can be:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
1: Only counter overflow/underflow generates an update interrupt or DMA request if
enabled.
Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable UEV event generation.
0: UEV enabled. The Update (UEV) event is generated by one of the following events:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
Buffered registers are then loaded with their preload values.
1: UEV disabled. The Update event is not generated, shadow registers keep their value
(ARR, PSC, CCRx). However the counter and the prescaler are reinitialized if the UG bit is
set or if a hardware reset is received from the slave mode controller.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled

20.6.2

TIM16 and TIM17 control register 2 (TIM16_CR2 and TIM17_CR2)
Address offset: 0x04
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

OIS1N

OIS1

Res.

Res.

Res.

Res.

CCDS

CCUS

Res.

CCPC

rw

rw

rw

rw

rw

Bits 15:10 Reserved, always read as 0.
Bit 9 OIS1N: Output Idle state 1 (OC1N output)
0: OC1N=0 after a dead-time when MOE=0
1: OC1N=1 after a dead-time when MOE=0
Note: This bit can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BKR register).
Bit 8 OIS1: Output Idle state 1 (OC1 output)
0: OC1=0 (after a dead-time if OC1N is implemented) when MOE=0
1: OC1=1 (after a dead-time if OC1N is implemented) when MOE=0
Note: This bit can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BKR register).
Bits 7:4 Reserved, always read as 0.
Bit 3 CCDS: Capture/compare DMA selection
0: CCx DMA request sent when CCx event occurs
1: CCx DMA requests sent when update event occurs

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Bit 2 CCUS: Capture/compare control update selection
0: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit only.
1: When capture/compare control bits are preloaded (CCPC=1), they are updated by setting
the COMG bit or when an rising edge occurs on TRGI.
Note: This bit acts only on channels that have a complementary output.
Bit 1 Reserved, always read as 0.
Bit 0 CCPC: Capture/compare preloaded control
0: CCxE, CCxNE and OCxM bits are not preloaded
1: CCxE, CCxNE and OCxM bits are preloaded, after having been written, they are updated
only when COM bit is set.
Note: This bit acts only on channels that have a complementary output.

20.6.3

TIM16 and TIM17 DMA/interrupt enable register (TIM16_DIER and
TIM17_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

CC1DE

UDE

BIE

Res.

COMIE

Res.

Res.

Res.

CC1IE

UIE

rw

rw

rw

rw

rw

Bit 15 Reserved, always read as 0.
Bit 14 Reserved, always read as 0.
Bits 13:10 Reserved, always read as 0.
Bit 9 CC1DE: Capture/Compare 1 DMA request enable
0: CC1 DMA request disabled
1: CC1 DMA request enabled
Bit 8 UDE: Update DMA request enable
0: Update DMA request disabled
1: Update DMA request enabled
Bit 7 BIE: Break interrupt enable
0: Break interrupt disabled
1: Break interrupt enabled
Bit 6 Reserved, always read as 0.
Bit 5 COMIE: COM interrupt enable
0: COM interrupt disabled
1: COM interrupt enabled
Bits 4:2 Reserved, always read as 0.
Bit 1 CC1IE: Capture/Compare 1 interrupt enable
0: CC1 interrupt disabled
1: CC1 interrupt enabled
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled
1: Update interrupt enabled

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RM0091

General-purpose timers (TIM15/16/17)

20.6.4

TIM16 and TIM17 status register (TIM16_SR and TIM17_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

CC1OF

Res.

BIF

Res.

COMIF

Res.

Res.

Res.

CC1IF

UIF

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

Bits 15:10 Reserved, always read as 0.
Bit 9 CC1OF: Capture/Compare 1 overcapture flag
This flag is set by hardware only when the corresponding channel is configured in input
capture mode. It is cleared by software by writing it to ‘0’.
0: No overcapture has been detected
1: The counter value has been captured in TIMx_CCR1 register while CC1IF flag was
already set
Bit 8 Reserved, always read as 0.
Bit 7 BIF: Break interrupt flag
This flag is set by hardware as soon as the break input goes active. It can be cleared by
software if the break input is not active.
0: No break event occurred
1: An active level has been detected on the break input
Bit 6 Reserved, always read as 0.
Bit 5 COMIF: COM interrupt flag
This flag is set by hardware on a COM event (once the capture/compare control bits –CCxE,
CCxNE, OCxM– have been updated). It is cleared by software by writing it to ‘0’.
0: No COM event occurred
1: COM interrupt pending

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Bits 4:2 Reserved, always read as 0.
Bit 1 CC1IF: Capture/Compare 1 interrupt flag
If channel CC1 is configured as output:
This flag is set by hardware when the counter matches the compare value, with some
exception in center-aligned mode (refer to the CMS bits in the TIMx_CR1 register description).
It is cleared by software.
0: No match.
1: The content of the counter TIMx_CNT matches the content of the TIMx_CCR1 register.
When the contents of TIMx_CCR1 are greater than the contents of TIMx_ARR, the CC1IF
bit goes high on the counter overflow (in upcounting and up/down-counting modes) or
underflow (in downcounting mode)
If channel CC1 is configured as input:
This bit is set by hardware on a capture. It is cleared by software or by reading the
TIMx_CCR1 register.
0: No input capture occurred
1: The counter value has been captured in TIMx_CCR1 register (An edge has been
detected on IC1 which matches the selected polarity)
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending. This bit is set by hardware when the registers are updated:
–
At overflow regarding the repetition counter value (update if repetition counter = 0)
and if the UDIS=0 in the TIMx_CR1 register.
–
When CNT is reinitialized by software using the UG bit in TIMx_EGR register, if
URS=0 and UDIS=0 in the TIMx_CR1 register.

20.6.5

TIM16 and TIM17 event generation register (TIM16_EGR and
TIM17_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

BG

Res.

COMG

Res.

Res.

Res.

CC1G

UG

w

w

w

w

Bits 15:8 Reserved, always read as 0.
Bit 7 BG: Break generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action.
1: A break event is generated. MOE bit is cleared and BIF flag is set. Related interrupt or
DMA transfer can occur if enabled.
Bit 6 Reserved, always read as 0.
Bit 5 COMG: Capture/Compare control update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action
1: When the CCPC bit is set, it is possible to update the CCxE, CCxNE and OCxM bits
Note: This bit acts only on channels that have a complementary output.

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General-purpose timers (TIM15/16/17)

Bits 4:2 Reserved, always read as 0.
Bit 1 CC1G: Capture/Compare 1 generation
This bit is set by software in order to generate an event, it is automatically cleared by
hardware.
0: No action.
1: A capture/compare event is generated on channel 1:
If channel CC1 is configured as output:
CC1IF flag is set, Corresponding interrupt or DMA request is sent if enabled.
If channel CC1 is configured as input:
The current value of the counter is captured in TIMx_CCR1 register. The CC1IF flag is set, the
corresponding interrupt or DMA request is sent if enabled. The CC1OF flag is set if the CC1IF
flag was already high.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action.
1: Reinitialize the counter and generates an update of the registers. Note that the prescaler
counter is cleared too (anyway the prescaler ratio is not affected). The counter is cleared if
the center-aligned mode is selected or if DIR=0 (upcounting), else it takes the auto-reload
value (TIMx_ARR) if DIR=1 (downcounting).

20.6.6

TIM16 and TIM17 capture/compare mode register 1 (TIM16_CCMR1
and TIM17_CCMR1)
Address offset: 0x18
Reset value: 0x0000
The channels can be used in input (capture mode) or in output (compare mode). The
direction of a channel is defined by configuring the corresponding CCxS bits. All the other
bits of this register have a different function in input and in output mode. For a given bit,
OCxx describes its function when the channel is configured in output, ICxx describes its
function when the channel is configured in input. So you must take care that the same bit
can have a different meaning for the input stage and for the output stage.

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

6

5

4

OC1M[2:0]
IC1F[3:0]

rw

rw

DocID018940 Rev 9

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3

2

OC1PE OC1FE
IC1PSC[1:0]
rw

rw

rw

1

0

CC1S[1:0]
rw

rw

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Output compare mode:
Bits 15:7 Reserved, always read as 0.
Bits 6:4 OC1M: Output Compare 1 mode
These bits define the behavior of the output reference signal OC1REF from which OC1 and
OC1N are derived. OC1REF is active high whereas OC1 and OC1N active level depends on
CC1P and CC1NP bits.
000: Frozen - The comparison between the output compare register TIMx_CCR1 and the
counter TIMx_CNT has no effect on the outputs.
001: Set channel 1 to active level on match. OC1REF signal is forced high when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
010: Set channel 1 to inactive level on match. OC1REF signal is forced low when the
counter TIMx_CNT matches the capture/compare register 1 (TIMx_CCR1).
011: Toggle - OC1REF toggles when TIMx_CNT=TIMx_CCR1.
100: Force inactive level - OC1REF is forced low.
101: Force active level - OC1REF is forced high.
110: PWM mode 1 - In upcounting, channel 1 is active as long as TIMx_CNTTIMx_CCR1 else active (OC1REF=’1’).
111: PWM mode 2 - In upcounting, channel 1 is inactive as long as
TIMx_CNTTIMx_CCR1 else inactive.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: In PWM mode 1 or 2, the OCREF level changes only when the result of the
comparison changes or when the output compare mode switches from “frozen” mode
to “PWM” mode.
Bit 3 OC1PE: Output Compare 1 preload enable
0: Preload register on TIMx_CCR1 disabled. TIMx_CCR1 can be written at anytime, the
new value is taken in account immediately.
1: Preload register on TIMx_CCR1 enabled. Read/Write operations access the preload
register. TIMx_CCR1 preload value is loaded in the active register at each update event.
Note: 1: These bits can not be modified as long as LOCK level 3 has been programmed
(LOCK bits in TIMx_BDTR register) and CC1S=’00’ (the channel is configured in
output).
2: The PWM mode can be used without validating the preload register only in one
pulse mode (OPM bit set in TIMx_CR1 register). Else the behavior is not guaranteed.
Bit 2 OC1FE: Output Compare 1 fast enable
This bit is used to accelerate the effect of an event on the trigger in input on the CC output.
0: CC1 behaves normally depending on counter and CCR1 values even when the trigger is
ON. The minimum delay to activate CC1 output when an edge occurs on the trigger input is
5 clock cycles.
1: An active edge on the trigger input acts like a compare match on CC1 output. Then, OC
is set to the compare level independently of the result of the comparison. Delay to sample
the trigger input and to activate CC1 output is reduced to 3 clock cycles. OC1FE acts only if
the channel is configured in PWM1 or PWM2 mode.

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General-purpose timers (TIM15/16/17)

Bits 1:0 CC1S: Capture/Compare 1 selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only
if an internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

Input capture mode:
Bits 15:8 Reserved, always read as 0.
Bits 7:4 IC1F[3:0]: Input capture 1 filter
This bit-field defines the frequency used to sample TI1 input and the length of the digital filter applied to
TI1. The digital filter is made of an event counter in which N events are needed to validate a transition
on the output:
0000: No filter, sampling is done at fDTS
0001: fSAMPLING = fCK_INT, N = 2
0010: fSAMPLING = fCK_INT, N = 4
0011: fSAMPLING = fCK_INT, N = 8
0100: fSAMPLING = fDTS / 2, N = 6
0101: fSAMPLING = fDTS / 2, N = 8
0110: fSAMPLING = fDTS / 4, N = 6
0111: fSAMPLING = fDTS / 4, N = 8
1000: fSAMPLING = fDTS / 8, N = 6
1001: fSAMPLING = fDTS / 8, N = 8
1010: fSAMPLING = fDTS / 16, N = 5
1011: fSAMPLING = fDTS / 16, N = 6
1100: fSAMPLING = fDTS / 16, N = 8
1101: fSAMPLING = fDTS / 32, N = 5
1110: fSAMPLING = fDTS / 32, N = 6
1111: fSAMPLING = fDTS / 32, N = 8
Note: Care must be taken that fDTS is replaced in the formula by CK_INT when ICxF[3:0] = 1, 2 or 3.
Bits 3:2 IC1PSC: Input capture 1 prescaler
This bit-field defines the ratio of the prescaler acting on CC1 input (IC1).
The prescaler is reset as soon as CC1E=’0’ (TIMx_CCER register).
00: no prescaler, capture is done each time an edge is detected on the capture input.
01: capture is done once every 2 events
10: capture is done once every 4 events
11: capture is done once every 8 events
Bits 1:0 CC1S: Capture/Compare 1 Selection
This bit-field defines the direction of the channel (input/output) as well as the used input.
00: CC1 channel is configured as output
01: CC1 channel is configured as input, IC1 is mapped on TI1
10: CC1 channel is configured as input, IC1 is mapped on TI2
11: CC1 channel is configured as input, IC1 is mapped on TRC. This mode is working only if an
internal trigger input is selected through TS bit (TIMx_SMCR register)
Note: CC1S bits are writable only when the channel is OFF (CC1E = ‘0’ in TIMx_CCER).

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General-purpose timers (TIM15/16/17)

20.6.7

RM0091

TIM16 and TIM17 capture/compare enable register (TIM16_CCER
and TIM17_CCER)
Address offset: 0x20
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

3

2

CC1NP CC1NE
rw

rw

1

0

CC1P

CC1E

rw

rw

Bits 15:4 Reserved, always read as 0.
Bit 3 CC1NP: Capture/Compare 1 complementary output polarity
0: OC1N active high
1: OC1N active low
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register) and CC1S=”00” (the channel is configured in output).
Bit 2 CC1NE: Capture/Compare 1 complementary output enable
0: Off - OC1N is not active. OC1N level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1E bits.
1: On - OC1N signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1E bits.
Bit 1 CC1P: Capture/Compare 1 output polarity
CC1 channel configured as output:
0: OC1 active high
1: OC1 active low
CC1 channel configured as input:
The CC1NP/CC1P bits select the polarity of TI1FP1 and TI2FP1 for capture operation.
00: Non-inverted/rising edge: circuit is sensitive to TIxFP1's rising edge TIxFP1 is not
inverted.
01: Inverted/falling edge: circuit is sensitive to TIxFP1's falling edge, TIxFP1 is inverted.
10: Reserved, do not use this configuration.
11: Non-inverted/both edges: circuit is sensitive to both the rising and falling edges of
TIxFP1, TIxFP1 is not inverted.
Note: This bit is not writable as soon as LOCK level 2 or 3 has been programmed (LOCK bits
in TIMx_BDTR register)
Bit 0 CC1E: Capture/Compare 1 output enable
CC1 channel configured as output:
0: Off - OC1 is not active. OC1 level is then function of MOE, OSSI, OSSR, OIS1, OIS1N
and CC1NE bits.
1: On - OC1 signal is output on the corresponding output pin depending on MOE, OSSI,
OSSR, OIS1, OIS1N and CC1NE bits.
CC1 channel configured as input:
This bit determines if a capture of the counter value can actually be done into the input
capture/compare register 1 (TIMx_CCR1) or not.
0: Capture disabled
1: Capture enabled

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General-purpose timers (TIM15/16/17)
Table 74. Output control bits for complementary OCx and OCxN channels with break
feature
Output states(1)

Control bits
MOE OSSI OSSR CCxE CCxNE
OCx output state
bit
bit
bit
bit
bit

1

0

0

0

0

Output Disabled (not
driven by the timer)
OCx=0, OCx_EN=0

Output Disabled (not driven by
the timer)
OCxN=0, OCxN_EN=0

0

0

1

Output Disabled (not
driven by the timer)
OCx=0, OCx_EN=0

OCxREF + Polarity
OCxN=OCxREF xor CCxNP,
OCxN_EN=1

0

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

Output Disabled (not driven by
the timer)
OCxN=0, OCxN_EN=0

0

1

1

OCREF + Polarity + deadtime
OCx_EN=1

Complementary to OCREF (not
OCREF) + Polarity + dead-time
OCxN_EN=1

1

0

0

Output Disabled (not
driven by the timer)
OCx=CCxP, OCx_EN=0

Output Disabled (not driven by
the timer)
OCxN=CCxNP, OCxN_EN=0

1

0

1

Off-State (output enabled
with inactive state)
OCx=CCxP, OCx_EN=1

OCxREF + Polarity
OCxN=OCxREF xor CCxNP,
OCxN_EN=1
Off-State (output enabled with
inactive state)
OCxN=CCxNP, OCxN_EN=1
Complementary to OCREF (not
OCREF) + Polarity + dead-time
OCxN_EN=1

X

1

1

0

OCxREF + Polarity
OCx=OCxREF xor CCxP,
OCx_EN=1

1

1

1

OCREF + Polarity + deadtime
OCx_EN=1

0

0

0

0

0

1

0

1

0

0

1

1

0

0

1

0

1

1

1

0

1

1

1

1

OCxN output state

X

Output Disabled (not driven by the timer)
Asynchronously: OCx=CCxP, OCx_EN=0, OCxN=CCxNP,
OCxN_EN=0
Then if the clock is present: OCx=OISx and OCxN=OISxN
after a dead-time, assuming that OISx and OISxN do not
correspond to OCX and OCxN both in active state.
Off-State (output enabled with inactive state)
Asynchronously: OCx=CCxP, OCx_EN=1, OCxN=CCxNP,
OCxN_EN=1
Then if the clock is present: OCx=OISx and OCxN=OISxN
after a dead-time, assuming that OISx and OISxN do not
correspond to OCX and OCxN both in active state

1. When both outputs of a channel are not used (CCxE = CCxNE = 0), the OISx, OISxN, CCxP and CCxNP
bits must be kept cleared.

Note:

The state of the external I/O pins connected to the complementary OCx and OCxN channels
depends on the OCx and OCxN channel state and the GPIO and AFIO registers.
DocID018940 Rev 9

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546

General-purpose timers (TIM15/16/17)

20.6.8

RM0091

TIM16 and TIM17 counter (TIM16_CNT and TIM17_CNT)
Address offset: 0x24
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]
rw

rw

rw

Bits 15:0

20.6.9

rw

rw

rw

rw

rw

rw

CNT[15:0]: Counter value

TIM16 and TIM17 prescaler (TIM16_PSC and TIM17_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

PSC[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency (CK_CNT) is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded in the active prescaler register at each update event
(including when the counter is cleared through UG bit of TIMx_EGR register or through trigger
controller when configured in “reset mode”).

20.6.10

TIM16 and TIM17 auto-reload register (TIM16_ARR and
TIM17_ARR)
Address offset: 0x2C
Reset value: 0xFFFF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 ARR[15:0]: Auto-reload value
ARR is the value to be loaded in the actual auto-reload register.
Refer to the Section 19.3.1: Time-base unit on page 460 for more details about ARR update
and behavior.
The counter is blocked while the auto-reload value is null.

20.6.11

TIM16 and TIM17 repetition counter register (TIM16_RCR and
TIM17_RCR)
Address offset: 0x30
Reset value: 0x0000

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

5

4

3

2

1

0

rw

rw

rw

REP[7:0]
rw

540/1004

6

rw

DocID018940 Rev 9

rw

rw

rw

RM0091

General-purpose timers (TIM15/16/17)

Bits 15:8 Reserved, always read as 0.
Bits 7:0 REP[7:0]: Repetition counter value
These bits allow the user to set-up the update rate of the compare registers (i.e. periodic
transfers from preload to active registers) when preload registers are enable, as well as the
update interrupt generation rate, if this interrupt is enable.
Each time the REP_CNT related downcounter reaches zero, an update event is generated
and it restarts counting from REP value. As REP_CNT is reloaded with REP value only at the
repetition update event U_RC, any write to the TIMx_RCR register is not taken in account until
the next repetition update event.
It means in PWM mode (REP+1) corresponds to the number of PWM periods in edge-aligned
mode.

20.6.12

TIM16 and TIM17 capture/compare register 1 (TIM16_CCR1 and
TIM17_CCR1)
Address offset: 0x34
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CCR1[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 CCR1[15:0]: Capture/Compare 1 value
If channel CC1 is configured as output:
CCR1 is the value to be loaded in the actual capture/compare 1 register (preload value).
It is loaded permanently if the preload feature is not selected in the TIMx_CCMR1 register (bit
OC1PE). Else the preload value is copied in the active capture/compare 1 register when an
update event occurs.
The active capture/compare register contains the value to be compared to the counter
TIMx_CNT and signaled on OC1 output.
If channel CC1 is configured as input:
CCR1 is the counter value transferred by the last input capture 1 event (IC1).

20.6.13

TIM16 and TIM17 break and dead-time register (TIM16_BDTR and
TIM17_BDTR)
Address offset: 0x44
Reset value: 0x0000

15

14

13

12

11

10

MOE

AOE

BKP

BKE

OSSR

OSSI

rw

rw

rw

rw

rw

rw

Note:

9

8

7

6

5

LOCK[1:0]
rw

rw

4

3

2

1

0

rw

rw

rw

DTG[7:0]
rw

rw

rw

rw

rw

As the bits AOE, BKP, BKE, OSSI, OSSR and DTG[7:0] can be write-locked depending on
the LOCK configuration, it can be necessary to configure all of them during the first write
access to the TIMx_BDTR register.

DocID018940 Rev 9

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General-purpose timers (TIM15/16/17)

RM0091

Bit 15 MOE: Main output enable
This bit is cleared asynchronously by hardware as soon as the break input is active. It is set by
software or automatically depending on the AOE bit. It is acting only on the channels which are
configured in output.
0: OC and OCN outputs are disabled or forced to idle state
1: OC and OCN outputs are enabled if their respective enable bits are set (CCxE, CCxNE in
TIMx_CCER register)
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
Bit 14 AOE: Automatic output enable
0: MOE can be set only by software
1: MOE can be set by software or automatically at the next update event (if the break input is
not be active)
Note: This bit can not be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Bit 13 BKP: Break polarity
0: Break input BRK is active low
1: Break input BRK is active high
Note: This bit can not be modified as long as LOCK level 1 has been programmed (LOCK bits
in TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 12 BKE: Break enable
0: Break inputs (BRK and CCS clock failure event) disabled
1; Break inputs (BRK and CCS clock failure event) enabled
Note: This bit cannot be modified when LOCK level 1 has been programmed (LOCK bits in
TIMx_BDTR register).
Note: Any write operation to this bit takes a delay of 1 APB clock cycle to become effective.
Bit 11 OSSR: Off-state selection for Run mode
This bit is used when MOE=1 on channels having a complementary output which are
configured as outputs. OSSR is not implemented if no complementary output is implemented in
the timer.
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0)
1: When inactive, OC/OCN outputs are enabled with their inactive level as soon as CCxE=1
or CCxNE=1. Then, OC/OCN enable output signal=1
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).
Bit 10 OSSI: Off-state selection for Idle mode
This bit is used when MOE=0 on channels configured as outputs.
See OC/OCN enable description for more details (Section 20.5.8: TIM15 capture/compare
enable register (TIM15_CCER) on page 521).
0: When inactive, OC/OCN outputs are disabled (OC/OCN enable output signal=0)
1: When inactive, OC/OCN outputs are forced first with their idle level as soon as CCxE=1 or
CCxNE=1. OC/OCN enable output signal=1)
Note: This bit can not be modified as soon as the LOCK level 2 has been programmed (LOCK
bits in TIMx_BDTR register).

542/1004

DocID018940 Rev 9

RM0091

General-purpose timers (TIM15/16/17)

Bits 9:8 LOCK[1:0]: Lock configuration
These bits offer a write protection against software errors.
00: LOCK OFF - No bit is write protected
01: LOCK Level 1 = DTG bits in TIMx_BDTR register, OISx and OISxN bits in TIMx_CR2
register and BKE/BKP/AOE bits in TIMx_BDTR register can no longer be written.
10: LOCK Level 2 = LOCK Level 1 + CC Polarity bits (CCxP/CCxNP bits in TIMx_CCER
register, as long as the related channel is configured in output through the CCxS bits) as well
as OSSR and OSSI bits can no longer be written.
11: LOCK Level 3 = LOCK Level 2 + CC Control bits (OCxM and OCxPE bits in
TIMx_CCMRx registers, as long as the related channel is configured in output through the
CCxS bits) can no longer be written.
Note: The LOCK bits can be written only once after the reset. Once the TIMx_BDTR register
has been written, their content is frozen until the next reset.
Bits 7:0 DTG[7:0]: Dead-time generator setup
This bit-field defines the duration of the dead-time inserted between the complementary
outputs. DT correspond to this duration.
DTG[7:5]=0xx => DT=DTG[7:0]x tdtg with tdtg=tDTS
DTG[7:5]=10x => DT=(64+DTG[5:0])xtdtg with Tdtg=2xtDTS
DTG[7:5]=110 => DT=(32+DTG[4:0])xtdtg with Tdtg=8xtDTS
DTG[7:5]=111 => DT=(32+DTG[4:0])xtdtg with Tdtg=16xtDTS
Example if TDTS=125ns (8MHz), dead-time possible values are:
0 to 15875 ns by 125 ns steps,
16 µs to 31750 ns by 250 ns steps,
32 µs to 63 µs by 1 µs steps,
64 µs to 126 µs by 2 µs steps
Note: This bit-field can not be modified as long as LOCK level 1, 2 or 3 has been programmed
(LOCK bits in TIMx_BDTR register).

20.6.14

TIM16 and TIM17 DMA control register (TIM16_DCR and
TIM17_DCR)
Address offset: 0x48
Reset value: 0x0000

15

14

13

Res.

Res.

Res.

12

11

10

9

8

DBL[4:0]
rw

rw

rw

rw

7

6

5

Res.

Res.

Res.

rw

4

3

2

1

0

rw

rw

DBA[4:0]
rw

rw

rw

Bits 15:13 Reserved, always read as 0.
Bits 12:8 DBL[4:0]: DMA burst length
This 5-bit vector defines the length of DMA transfers (the timer recognizes a burst transfer
when a read or a write access is done to the TIMx_DMAR address), i.e. the number of
transfers. Transfers can be in half-words or in bytes (see example below).
00000: 1 transfer,
00001: 2 transfers,
00010: 3 transfers,
...
10001: 18 transfers.
Bits 7:5 Reserved, always read as 0.

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543/1004
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General-purpose timers (TIM15/16/17)

RM0091

Bits 4:0 DBA[4:0]: DMA base address
This 5-bits vector defines the base-address for DMA transfers (when read/write access are
done through the TIMx_DMAR address). DBA is defined as an offset starting from the address
of the TIMx_CR1 register.
Example:
00000: TIMx_CR1,
00001: TIMx_CR2,
00010: TIMx_SMCR,
...
Example: Let us consider the following transfer: DBL = 7 transfers and DBA = TIMx_CR1. In
this case the transfer is done to/from 7 registers starting from the TIMx_CR1 address.

20.6.15

TIM16 and TIM17 DMA address for full transfer (TIM16_DMAR and
TIM17_DMAR)
Address offset: 0x4C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

DMAB[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 DMAB[15:0]: DMA register for burst accesses
A read or write access to the DMAR register accesses the register located at the address:
“(TIMx_CR1 address) + DBA + (DMA index)” in which:
TIMx_CR1 address is the address of the control register 1, DBA is the DMA base address
configured in TIMx_DCR register, DMA index is the offset automatically controlled by the
DMA transfer, depending on the length of the transfer DBL in the TIMx_DCR register.

Example of how to use the DMA burst feature
In this example the timer DMA burst feature is used to update the contents of the CCRx
registers (x = 2, 3, 4) with the DMA transferring half words into the CCRx registers.
This is done in the following steps:
1.

Note:

544/1004

Configure the corresponding DMA channel as follows:
–

DMA channel peripheral address is the DMAR register address

–

DMA channel memory address is the address of the buffer in the RAM containing
the data to be transferred by DMA into CCRx registers.

–

Number of data to transfer = 3 (See note below).

–

Circular mode disabled.

2.

Configure the DCR register by configuring the DBA and DBL bit fields as follows:
DBL = 3 transfers, DBA = 0xE.

3.

Enable the TIMx update DMA request (set the UDE bit in the DIER register).

4.

Enable TIMx

5.

Enable the DMA channel

This example is for the case where every CCRx register to be updated once. If every CCRx
register is to be updated twice for example, the number of data to transfer should be 6. Let
us take the example of a buffer in the RAM containing data1, data2, data3, data4, data5 and
data6. The data is transferred to the CCRx registers as follows: on the first update DMA
DocID018940 Rev 9

0x2C

TIM16_ARR and
TIM17_ARR

0x30

TIM16_RCR and
TIM17_RCR

Reset value

DocID018940 Rev 9

1

1

1

1

1

1

1

1

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIM16_PSC and
TIM17_PSC

Res.

0x28
TIM16_CNT and
TIM17_CNT

Res.

0x24

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0x20

Res.

0x18

0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0
0

0

1

0
0

0

0

1

0
0

PSC[15:0]

ARR[15:0]

REP[7:0]

0
0
0
0
0
0

0

0

0

0

0

0

1

1

1

1

1

1

0

0

0

0

0

IC1F[3:0]

0
0
0
0
0
0
0

Reset value

0
CC1E

OC1M
[2:0]
OC1FE

0

CC1P

0

CC1NE

0

OC1PE

0

0

0
0

CC1IF
UIF
0

UG

Res.

Res.

0

CC1G

Res.

Res.

Res.

0
Res.

CC1IE
UIE

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

OPM
URS
UDIS
CEN

0
0
0

CCUS
Res.
CCPC

Res.

Res.

Res.

ARPE

0

CCDS

Res.

Res.

Res.

0
Res.

OIS1

0

CC1NP

0

Res.

COMIE

COMIF

Res.
0
COMG

0

Res.

Res.
0

Res.

BIE
0

Res.

UDE
0

BIF

0

BG

Res.

0

Res.

Res.

OIS1N

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

CC1DE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

CC1OF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CKD
[1:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value
TIM16_CCMR1
and
TIM17_CCMR1
Output compare
mode
Reset value
TIM16_CCMR1
and
TIM17_CCMR1
Input capture
mode
Reset value
TIM16_CCER
and
TIM17_CCER
Res.

0x14
TIM16_EGR and
TIM17_EGR

Res.

0x10
TIM16_SR and
TIM17_SR

Res.

0x0C
Reset value
TIM16_DIER
and
TIM17_DIER

Res.

TIM16_CR2 and
TIM17_CR2

Res.

0x04

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

TIM16_CR1 and
TIM17_CR1

Res.

0x00

Res.

Register

Res.

Offset

Res.

20.6.16

Res.

RM0091
General-purpose timers (TIM15/16/17)

request, data1 is transferred to CCR2, data2 is transferred to CCR3, data3 is transferred to
CCR4 and on the second update DMA request, data4 is transferred to CCR2, data5 is
transferred to CCR3 and data6 is transferred to CCR4.

TIM16 and TIM17 register map
TIM16 and TIM17 registers are mapped as 16-bit addressable registers as described in the
table below:
Table 75. TIM16 and TIM17 register map and reset values

0
0
0

0
0

0
0

CC1S
[1:0]
0
0

IC1
CC1S
PSC
[1:0]
[1:0]

0
0
0
0

CNT[15:0]

545/1004

546

General-purpose timers (TIM15/16/17)

RM0091

Res.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

DBA[4:0]
0

0

0

0

0

0

0

0

0

0

DMAB[15:0]
0

DocID018940 Rev 9

0

DT[7:0]

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

546/1004

0

LOCK
[1:0]

DBL[4:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

BKE

OSSR

0

0

Res.

BKP
0

0

Res.

AOE
0

Res.

0

0

Res.

0

MOE

0

Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.
Res.

Res.

Res.
Res.

Res.

0

OSSI

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

0

0
Res.

Reset value
TIM16_DMAR
and
TIM17_DMAR
Reset value

Res.

0x4C

TIM16_DCR and
TIM17_DCR

Res.

0x48

CCR1[15:0]
0

Res.

0x44

TIM16_CCR1
and
TIM17_CCR1
Reset value
TIM16_BDTR
and
TIM17_BDTR
Reset value

Res.

0x34

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 75. TIM16 and TIM17 register map and reset values (continued)

0

0

0

RM0091

21

Basic timer (TIM6/TIM7)

Basic timer (TIM6/TIM7)
This section applies to STM32F05x, STM32F07x and STM32F09x devices only. TIM7 is
available only on STM32F07x and STM32F09x devices.

21.1

TIM6/TIM7 introduction
The basic timer TIM6 consists of a 16-bit auto-reload counter driven by a programmable
prescaler.
It may be used as a generic timer for time-base generation but it is also specifically used to
drive the digital-to-analog converter (DAC). In fact, TIM6 is internally connected to the DAC
and is able to drive it through its trigger outputs.

21.2

TIM6/TIM7 main features
•

16-bit auto-reload upcounter

•

16-bit programmable prescaler used to divide (also “on the fly”) the counter clock
frequency by any factor between 1 and 65535

•

Synchronization circuit to trigger the DAC

•

Interrupt/DMA generation on the update event: counter overflow
Figure 197. Basic timer block diagram

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Basic timer (TIM6/TIM7)

RM0091

21.3

TIM6/TIM7 functional description

21.3.1

Time-base unit
The main block of the programmable timer is a 16-bit upcounter with its related auto-reload
register. The counter clock can be divided by a prescaler.
The counter, the auto-reload register and the prescaler register can be written or read by
software. This is true even when the counter is running.
The time-base unit includes:
•

Counter Register (TIMx_CNT)

•

Prescaler Register (TIMx_PSC)

•

Auto-Reload Register (TIMx_ARR)

The auto-reload register is preloaded. The preload register is accessed each time an
attempt is made to write or read the auto-reload register. The contents of the preload
register are transferred into the shadow register permanently or at each update event UEV,
depending on the auto-reload preload enable bit (ARPE) in the TIMx_CR1 register. The
update event is sent when the counter reaches the overflow value and if the UDIS bit equals
0 in the TIMx_CR1 register. It can also be generated by software. The generation of the
update event is described in detail for each configuration.
The counter is clocked by the prescaler output CK_CNT, which is enabled only when the
counter enable bit (CEN) in the TIMx_CR1 register is set.
Note that the actual counter enable signal CNT_EN is set 1 clock cycle after CEN.

Prescaler description
The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It
is based on a 16-bit counter controlled through a 16-bit register (in the TIMx_PSC register).
It can be changed on the fly as the TIMx_PSC control register is buffered. The new
prescaler ratio is taken into account at the next update event.
Figure 198 and Figure 199 give some examples of the counter behavior when the prescaler
ratio is changed on the fly.

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Basic timer (TIM6/TIM7)
Figure 198. Counter timing diagram with prescaler division change from 1 to 2

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Figure 199. Counter timing diagram with prescaler division change from 1 to 4

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Basic timer (TIM6/TIM7)

21.3.2

RM0091

Counter modes
The counter counts from 0 to the auto-reload value (contents of the TIMx_ARR register),
then restarts from 0 and generates a counter overflow event.
An update event can be generate at each counter overflow or by setting the UG bit in the
TIMx_EGR register (by software or by using the slave mode controller).
The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1
register. This avoids updating the shadow registers while writing new values into the preload
registers. In this way, no update event occurs until the UDIS bit has been written to 0,
however, the counter and the prescaler counter both restart from 0 (but the prescale rate
does not change). In addition, if the URS (update request selection) bit in the TIMx_CR1
register is set, setting the UG bit generates an update event UEV, but the UIF flag is not set
(so no interrupt or DMA request is sent).
When an update event occurs, all the registers are updated and the update flag (UIF bit in
the TIMx_SR register) is set (depending on the URS bit):
•

The buffer of the prescaler is reloaded with the preload value (contents of the
TIMx_PSC register)

•

The auto-reload shadow register is updated with the preload value (TIMx_ARR)

The following figures show some examples of the counter behavior for different clock
frequencies when TIMx_ARR = 0x36.
Figure 200. Counter timing diagram, internal clock divided by 1

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Basic timer (TIM6/TIM7)
Figure 201. Counter timing diagram, internal clock divided by 2

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Figure 202. Counter timing diagram, internal clock divided by 4

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Basic timer (TIM6/TIM7)

RM0091

Figure 203. Counter timing diagram, internal clock divided by N

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Figure 204. Counter timing diagram, update event when ARPE = 0
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Basic timer (TIM6/TIM7)
Figure 205. Counter timing diagram, update event when ARPE=1
(TIMx_ARR preloaded)
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21.3.3

RM0091

Clock source
The counter clock is provided by the Internal clock (CK_INT) source.
The CEN (in the TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual
control bits and can be changed only by software (except for UG that remains cleared
automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal
clock CK_INT.
Figure 206 shows the behavior of the control circuit and the upcounter in normal mode,
without prescaler.
Figure 206. Control circuit in normal mode, internal clock divided by 1

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21.3.4

Debug mode
When the microcontroller enters the debug mode (Cortex™-M0 core - halted), the TIMx
counter either continues to work normally or stops, depending on the DBG_TIMx_STOP
configuration bit in the DBG module.

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Basic timer (TIM6/TIM7)

TIM6/TIM7 registers

21.4

Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

21.4.1

TIM6/TIM7 control register 1 (TIMx_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

ARPE

Res.

Res.

Res.

OPM

URS

UDIS

CEN

rw

rw

rw

rw

rw

Bits 15:8 Reserved, always read as 0.
Bit 7 ARPE: Auto-reload preload enable
0: TIMx_ARR register is not buffered.
1: TIMx_ARR register is buffered.
Bits 6:4 Reserved, always read as 0.
Bit 3 OPM: One-pulse mode
0: Counter is not stopped at update event
1: Counter stops counting at the next update event (clearing the CEN bit).
Bit 2 URS: Update request source
This bit is set and cleared by software to select the UEV event sources.
0: Any of the following events generates an update interrupt or DMA request if enabled.
These events can be:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
1: Only counter overflow/underflow generates an update interrupt or DMA request if
enabled.
Bit 1 UDIS: Update disable
This bit is set and cleared by software to enable/disable UEV event generation.
0: UEV enabled. The Update (UEV) event is generated by one of the following events:
–
Counter overflow/underflow
–
Setting the UG bit
–
Update generation through the slave mode controller
Buffered registers are then loaded with their preload values.
1: UEV disabled. The Update event is not generated, shadow registers keep their value
(ARR, PSC). However the counter and the prescaler are reinitialized if the UG bit is set or if
a hardware reset is received from the slave mode controller.
Bit 0 CEN: Counter enable
0: Counter disabled
1: Counter enabled
Note: Gated mode can work only if the CEN bit has been previously set by software.
However trigger mode can set the CEN bit automatically by hardware.
CEN is cleared automatically in one-pulse mode, when an update event occurs.

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21.4.2

RM0091

TIM6/TIM7 control register 2 (TIMx_CR2)
Address offset: 0x04
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

6

5

4

MMS[2:0]
rw

rw

3

2

1

0

Res.

Res.

Res.

Res.

rw

Bits 15:7 Reserved, must be kept at reset value.
Bits 6:4 MMS: Master mode selection
These bits are used to select the information to be sent in master mode to slave timers for
synchronization (TRGO). The combination is as follows:
000: Reset - the UG bit from the TIMx_EGR register is used as a trigger output (TRGO). If
reset is generated by the trigger input (slave mode controller configured in reset mode) then
the signal on TRGO is delayed compared to the actual reset.
001: Enable - the Counter enable signal, CNT_EN, is used as a trigger output (TRGO). It is
useful to start several timers at the same time or to control a window in which a slave timer
is enabled. The Counter Enable signal is generated by a logic OR between CEN control bit
and the trigger input when configured in gated mode.
When the Counter Enable signal is controlled by the trigger input, there is a delay on TRGO,
except if the master/slave mode is selected (see the MSM bit description in the TIMx_SMCR
register).
010: Update - The update event is selected as a trigger output (TRGO). For instance a
master timer can then be used as a prescaler for a slave timer.
Bits 3:0 Reserved, always read as 0.

21.4.3

TIM6/TIM7 DMA/Interrupt enable register (TIMx_DIER)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

UDE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

UIE

rw

Bit 15:9 Reserved, must be kept at reset value.
Bit 8 UDE: Update DMA request enable
0: Update DMA request disabled.
1: Update DMA request enabled.
Bits 7:1 Reserved, must be kept at reset value.
Bit 0 UIE: Update interrupt enable
0: Update interrupt disabled.
1: Update interrupt enabled.

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Basic timer (TIM6/TIM7)

21.4.4

TIM6/TIM7 status register (TIMx_SR)
Address offset: 0x10
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

UIF
rc_w0

Bits 15:1 Reserved, must be kept at reset value.
Bit 0 UIF: Update interrupt flag
This bit is set by hardware on an update event. It is cleared by software.
0: No update occurred.
1: Update interrupt pending. This bit is set by hardware when the registers are updated:
–At overflow or underflow regarding the repetition counter value and if UDIS = 0 in the
TIMx_CR1 register.
–When CNT is reinitialized by software using the UG bit in the TIMx_EGR register, if
URS = 0 and UDIS = 0 in the TIMx_CR1 register.

21.4.5

TIM6/TIM7 event generation register (TIMx_EGR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

UG
w

Bits 15:1 Reserved, must be kept at reset value.
Bit 0 UG: Update generation
This bit can be set by software, it is automatically cleared by hardware.
0: No action.
1: Re-initializes the timer counter and generates an update of the registers. Note that the
prescaler counter is cleared too (but the prescaler ratio is not affected).

21.4.6

TIM6/TIM7 counter (TIMx_CNT)
Address offset: 0x24
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]
rw

rw

Bits 15:0

rw

rw

rw

rw

rw

rw

rw

CNT[15:0]: Counter value

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21.4.7

RM0091

TIM6/TIM7 prescaler (TIMx_PSC)
Address offset: 0x28
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

PSC[15:0]
rw

Bits 15:0 PSC[15:0]: Prescaler value
The counter clock frequency CK_CNT is equal to fCK_PSC / (PSC[15:0] + 1).
PSC contains the value to be loaded into the active prescaler register at each update event.

21.4.8

TIM6/TIM7 auto-reload register (TIMx_ARR)
Address offset: 0x2C
Reset value: 0xFFFF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

ARR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:0 ARR[15:0]: Auto-reload value
ARR is the value to be loaded into the actual auto-reload register.
Refer to Section 21.3.1: Time-base unit on page 548 for more details about ARR update and
behavior.
The counter is blocked while the auto-reload value is null.

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0x2C
TIMx_ARR
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIMx_PSC

Res.

0x28
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIMx_CNT

Res.

0x24
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIMx_EGR

Res.

0x14

Reset value

Reset value

Reset value

DocID018940 Rev 9
0

0

1
0

0

1
0

0

1
0

0

1

0

0

1

0

0

1

0

0

1

0

0

1

0

0

1

0

0

1

Reset value

Reset value
UIF

Res.

Res.

0

UG

Res.

Res.
Res.
Res.

Res.
Res.
UIE

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

TIMx_CR1
Res.

URS
UDIS
CEN

OPM

Res.

Res.

Res.

ARPE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Register

0

Res.

Res.

Res.

0
Res.

0

Res.

MMS[2:0]

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

UDE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TIMx_SR

Res.

0x10
TIMx_DIER

Res.

0x0C
TIMx_CR2

Res.

0x04

Res.

0x00

Res.

Offset

Res.

21.4.9

Res.

RM0091
Basic timer (TIM6/TIM7)

TIM6/TIM7 register map
TIMx registers are mapped as 16-bit addressable registers as described in the table below:
Table 76. TIM6/TIM7 register map and reset values

0
0
0

0

0

0

CNT[15:0]

PSC[15:0]

ARR[15:0]

0
0
0
0
0
0

0
0
0
0
0
0

1
1
1
1
1
1

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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Infrared interface (IRTIM)

22

RM0091

Infrared interface (IRTIM)
An infrared interface (IRTIM) for remote control is available on the device. It can be used
with an infrared LED to perform remote control functions.
It uses internal connections with USART1, USART4, TIM16 and TIM17 as shown in
Figure 207.
To generate the infrared remote control signals, the IR interface must be enabled and TIM16
channel 1 (TIM16_OC1) and TIM17 channel 1 (TIM17_OC1) must be properly configured to
generate correct waveforms.
The infrared receiver can be implemented easily through a basic input capture mode.
Figure 207. IR internal hardware connections with TIM16 and TIM17
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1. USART1 and USART4 can be linked to IRTIM on STM32F09x devices only.

All standard IR pulse modulation modes can be obtained by programming the two timer
output compare channels.
TIM17 is used to generate the high frequency carrier signal, while TIM16 generates the
modulation envelope.
On STM32F09x devices, the modulation envelope can also be created from USART1 or
USART4 transmitter line, upon setting appropriately the IR_MOD[1:0] bits in
SYSCFG_CFGR1 register.
The infrared function is output on the IR_OUT pin. The activation of this function is done
through the GPIOx_AFRx register by enabling the related alternate function bit.
The high sink LED driver capability (only available on the PB9 pin) can be activated through
the I2C_PB9_FMP bit in the SYSCFG_CFGR1 register and used to sink the high current
needed to directly control an infrared LED.
For code example refer to the Appendix section A.10.1: TIM16 and TIM17 configuration
code example.

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RM0091

Independent watchdog (IWDG)

23

Independent watchdog (IWDG)

23.1

Introduction
The devices feature an embedded watchdog peripheral that offers a combination of high
safety level, timing accuracy and flexibility of use. The Independent watchdog peripheral
detects and solves malfunctions due to software failure, and triggers system reset when the
counter reaches a given timeout value.
The independent watchdog (IWDG) is clocked by its own dedicated low-speed clock (LSI)
and thus stays active even if the main clock fails.
The IWDG is best suited for applications that require the watchdog to run as a totally
independent process outside the main application, but have lower timing accuracy
constraints. For further information on the window watchdog, refer to Section 24 on page
570.

23.2

IWDG main features
•

Free-running downcounter

•

Clocked from an independent RC oscillator (can operate in Standby and Stop modes)

•

Conditional Reset
–

Reset (if watchdog activated) when the downcounter value becomes lower than
0x000

–

Reset (if watchdog activated) if the downcounter is reloaded outside the window

23.3

IWDG functional description

23.3.1

IWDG block diagram
Figure 208 shows the functional blocks of the independent watchdog module.
Figure 208. Independent watchdog block diagram
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1. The watchdog function is implemented in the CORE voltage domain that is still functional in Stop and
Standby modes.

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Independent watchdog (IWDG)

RM0091

When the independent watchdog is started by writing the value 0x0000 CCCC in the Key
register (IWDG_KR), the counter starts counting down from the reset value of 0xFFF. When
it reaches the end of count value (0x000) a reset signal is generated (IWDG reset).
Whenever the key value 0x0000 AAAA is written in the IWDG_KR register, the IWDG_RLR
value is reloaded in the counter and the watchdog reset is prevented.

23.3.2

Window option
The IWDG can also work as a window watchdog by setting the appropriate window in the
IWDG_WINR register.
If the reload operation is performed while the counter is greater than the value stored in the
window register (IWDG_WINR), then a reset is provided.
The default value of the IWDG_WINR is 0x0000 0FFF, so if it is not updated, the window
option is disabled.
As soon as the window value is changed, a reload operation is performed in order to reset
the downcounter to the IWDG_RLR value and ease the cycle number calculation to
generate the next reload.

Configuring the IWDG when the window option is enabled

Note:

1.

Enable the IWDG by writing 0x0000 CCCC in the IWDG_KR register.

2.

Enable register access by writing 0x0000 5555 in the IWDG_KR register.

3.

Write the IWDG prescaler by programming IWDG_PR from 0 to 7.

4.

Write the reload register (IWDG_RLR).

5.

Wait for the registers to be updated (IWDG_SR = 0x0000 0000).

6.

Write to the window register IWDG_WINR. This automatically refreshes the counter
value IWDG_RLR.

Writing the window value allows to refresh the Counter value by the RLR when IWDG_SR is
set to 0x0000 0000.
For code example refer to the Appendix section A.15.2: IWDG configuration with window
code example.

Configuring the IWDG when the window option is disabled
When the window option it is not used, the IWDG can be configured as follows:
1.

Enable the IWDG by writing 0x0000 CCCC in the IWDG_KR register.

2.

Enable register access by writing 0x0000 5555 in the IWDG_KR register.

3.

Write the IWDG prescaler by programming IWDG_PR from 0 to 7.

4.

Write the reload register (IWDG_RLR).

5.

Wait for the registers to be updated (IWDG_SR = 0x0000 0000).

6.

Refresh the counter value with IWDG_RLR (IWDG_KR = 0x0000 AAAA)

For code example refer to the Appendix section A.15.1: IWDG configuration code example.

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23.3.3

Independent watchdog (IWDG)

Hardware watchdog
If the “Hardware watchdog” feature is enabled through the device option bits, the watchdog
is automatically enabled at power-on, and generates a reset unless the Key register is
written by the software before the counter reaches end of count or if the downcounter is
reloaded inside the window.

23.3.4

Behavior in Stop and Standby modes
Once running, the IWDG cannot be stopped.

23.3.5

Register access protection
Write access to the IWDG_PR, IWDG_RLR and IWDG_WINR registers is protected. To
modify them, you must first write the code 0x0000 5555 in the IWDG_KR register. A write
access to this register with a different value will break the sequence and register access will
be protected again. This implies that it is the case of the reload operation
(writing 0x0000 AAAA).
A status register is available to indicate that an update of the prescaler or the down-counter
reload value or the window value is on going.
For code example refer to the Appendix section A.15.1: IWDG configuration code example.

23.3.6

Debug mode
When the microcontroller enters debug mode (core halted), the IWDG counter either
continues to work normally or stops, depending on DBG_IWDG_STOP configuration bit in
DBG module.

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23.4

RM0091

IWDG registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

23.4.1

Key register (IWDG_KR)
Address offset: 0x00
Reset value: 0x0000 0000 (reset by Standby mode)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

w

w

w

w

w

w

w

KEY[15:0]
w

w

w

w

w

w

w

w

w

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:0 KEY[15:0]: Key value (write only, read 0x0000)
These bits must be written by software at regular intervals with the key value 0xAAAA,
otherwise the watchdog generates a reset when the counter reaches 0.
Writing the key value 0x5555 to enable access to the IWDG_PR, IWDG_RLR and
IWDG_WINR registers (see Section 23.3.5: Register access protection)
Writing the key value 0xCCCC starts the watchdog (except if the hardware watchdog option is
selected)

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Independent watchdog (IWDG)

23.4.2

Prescaler register (IWDG_PR)
Address offset: 0x04
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

2

1

0

15

14

13

12

11

10

9

8

7

6

5

4

3

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PR[2:0]
rw

rw

rw

Bits 31:3 Reserved, must be kept at reset value.
Bits 2:0 PR[2:0]: Prescaler divider
These bits are write access protected see Section 23.3.5: Register access protection. They are
written by software to select the prescaler divider feeding the counter clock. PVU bit of
IWDG_SR must be reset in order to be able to change the prescaler divider.
000: divider /4
001: divider /8
010: divider /16
011: divider /32
100: divider /64
101: divider /128
110: divider /256
111: divider /256
Note: Reading this register returns the prescaler value from the VDD voltage domain. This
value may not be up to date/valid if a write operation to this register is ongoing. For this
reason the value read from this register is valid only when the PVU bit in the IWDG_SR
register is reset.

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23.4.3

RM0091

Reload register (IWDG_RLR)
Address offset: 0x08
Reset value: 0x0000 0FFF (reset by Standby mode)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

15

14

13

12

Res.

Res.

Res.

Res.

RL[11:0]
rw

rw

rw

rw

rw

rw

rw

Bits 31:12 Reserved, must be kept at reset value.
Bits11:0 RL[11:0]: Watchdog counter reload value
These bits are write access protected see Section 23.3.5. They are written by software to
define the value to be loaded in the watchdog counter each time the value 0xAAAA is written in
the IWDG_KR register. The watchdog counter counts down from this value. The timeout period
is a function of this value and the clock prescaler. Refer to the datasheet for the timeout
information.
The RVU bit in the IWDG_SR register must be reset in order to be able to change the reload
value.
Note: Reading this register returns the reload value from the VDD voltage domain. This value
may not be up to date/valid if a write operation to this register is ongoing on this
register. For this reason the value read from this register is valid only when the RVU bit
in the IWDG_SR register is reset.

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Independent watchdog (IWDG)

23.4.4

Status register (IWDG_SR)
Address offset: 0x0C
Reset value: 0x0000 0000 (not reset by Standby mode)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WVU

RVU

PVU

r

r

r

Bits 31:3 Reserved, must be kept at reset value.
Bit 2 WVU: Watchdog counter window value update
This bit is set by hardware to indicate that an update of the window value is ongoing. It is reset
by hardware when the reload value update operation is completed in the VDD voltage domain
(takes up to 5 RC 40 kHz cycles).
Window value can be updated only when WVU bit is reset.
Bit 1 RVU: Watchdog counter reload value update
This bit is set by hardware to indicate that an update of the reload value is ongoing. It is reset
by hardware when the reload value update operation is completed in the VDD voltage domain
(takes up to 5 RC 40 kHz cycles).
Reload value can be updated only when RVU bit is reset.
Bit 0 PVU: Watchdog prescaler value update
This bit is set by hardware to indicate that an update of the prescaler value is ongoing. It is
reset by hardware when the prescaler update operation is completed in the VDD voltage
domain (takes up to 5 RC 40 kHz cycles).
Prescaler value can be updated only when PVU bit is reset.

Note:

If several reload, prescaler, or window values are used by the application, it is mandatory to
wait until RVU bit is reset before changing the reload value, to wait until PVU bit is reset
before changing the prescaler value, and to wait until WVU bit is reset before changing the
window value. However, after updating the prescaler and/or the reload/window value it is not
necessary to wait until RVU or PVU or WVU is reset before continuing code execution
except in case of low-power mode entry.

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23.4.5

RM0091

Window register (IWDG_WINR)
Address offset: 0x10
Reset value: 0x0000 0FFF (reset by Standby mode)

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

15

14

13

12

Res.

Res.

Res.

Res.

WIN[11:0]
rw

rw

rw

rw

rw

rw

rw

Bits 31:12 Reserved, must be kept at reset value.
Bits11:0 WIN[11:0]: Watchdog counter window value
These bits are write access protected see Section 23.3.5. These bits contain the high limit of
the window value to be compared to the downcounter.
To prevent a reset, the downcounter must be reloaded when its value is lower than the
window register value and greater than 0x0
The WVU bit in the IWDG_SR register must be reset in order to be able to change the reload
value.
Note: Reading this register returns the reload value from the VDD voltage domain. This value
may not be valid if a write operation to this register is ongoing. For this reason the value
read from this register is valid only when the WVU bit in the IWDG_SR register is reset.

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0x0C

0x10
Reset value

DocID018940 Rev 9
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
1
1
1
1
1

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

0
0

1
1
1
1
1

WIN[11:0]
1
1
1
1

PVU

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0

RVU

1
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

Res.

0
Res.

Res.

0

WVU

1
Res.

1
Res.

1
Res.

1
Res.

Res.

Res.

1
Res.

Res.

Res.

1
Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Reset value

Res.

Res.

Res.

Reset value
Res.

IWDG_WINR
Res.

IWDG_SR

Res.

0x08
IWDG_RLR

Res.

0x04
IWDG_PR

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

IWDG_KR
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Register

Res.

0x00

Res.

Offset

Res.

23.4.6

Res.

RM0091
Independent watchdog (IWDG)

IWDG register map
The following table gives the IWDG register map and reset values.
Table 77. IWDG register map and reset values

KEY[15:0]
0
PR[2:0]

0
0

RL[11:0]
0
0
0

0
0
0

1
1
1

Refer to Section 2.2.2: Memory map and register boundary addresses for the register
boundary addresses.

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24

System window watchdog (WWDG)

24.1

Introduction
The system window watchdog (WWDG) is used to detect the occurrence of a software fault,
usually generated by external interference or by unforeseen logical conditions, which
causes the application program to abandon its normal sequence. The watchdog circuit
generates an MCU reset on expiry of a programmed time period, unless the program
refreshes the contents of the downcounter before the T6 bit becomes cleared. An MCU
reset is also generated if the 7-bit downcounter value (in the control register) is refreshed
before the downcounter has reached the window register value. This implies that the
counter must be refreshed in a limited window.
The WWDG clock is prescaled from the APB clock and has a configurable time-window that
can be programmed to detect abnormally late or early application behavior.
The WWDG is best suited for applications which require the watchdog to react within an
accurate timing window.

24.2

WWDG main features
•

Programmable free-running downcounter

•

Conditional reset

•

24.3

–

Reset (if watchdog activated) when the downcounter value becomes less than
0x40

–

Reset (if watchdog activated) if the downcounter is reloaded outside the window
(see Figure 210)

Early wakeup interrupt (EWI): triggered (if enabled and the watchdog activated) when
the downcounter is equal to 0x40.

WWDG functional description
If the watchdog is activated (the WDGA bit is set in the WWDG_CR register) and when the
7-bit downcounter (T[6:0] bits) is decremented from 0x40 to 0x3F (T6 becomes cleared), it
initiates a reset. If the software reloads the counter while the counter is greater than the
value stored in the window register, then a reset is generated.
The application program must write in the WWDG_CR register at regular intervals during
normal operation to prevent an MCU reset. This operation must occur only when the counter
value is lower than the window register value and higher than 0x3F. The value to be stored
in the WWDG_CR register must be between 0xFF and 0xC0.
Refer to Figure 209 for WWDG block diagram.

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System window watchdog (WWDG)
Figure 209. Watchdog block diagram
5(6(7

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FRPSDUDWRU
ZKHQ
7!:

: : : : : : :

:ULWH::'*B&5
:DWFKGRJFRQWUROUHJLVWHU ::'*B&5
:'*$
3&/.
IURP5&&FORFNFRQWUROOHU


7

7

7 7 7 7 7

ELWGRZQFRXQWHU &17

:'*SUHVFDOHU
:'*7%
06Y9

24.3.1

Enabling the watchdog
The watchdog is always disabled after a reset. It is enabled by setting the WDGA bit in the
WWDG_CR register, then it cannot be disabled again except by a reset.

24.3.2

Controlling the downcounter
This downcounter is free-running, counting down even if the watchdog is disabled. When
the watchdog is enabled, the T6 bit must be set to prevent generating an immediate reset.
The T[5:0] bits contain the number of increments which represents the time delay before the
watchdog produces a reset. The timing varies between a minimum and a maximum value
due to the unknown status of the prescaler when writing to the WWDG_CR register (see
Figure 210). The Configuration register (WWDG_CFR) contains the high limit of the window:
To prevent a reset, the downcounter must be reloaded when its value is lower than the
window register value and greater than 0x3F. Figure 210 describes the window watchdog
process.

Note:

The T6 bit can be used to generate a software reset (the WDGA bit is set and the T6 bit is
cleared).

24.3.3

Advanced watchdog interrupt feature
The Early Wakeup Interrupt (EWI) can be used if specific safety operations or data logging
must be performed before the actual reset is generated. The EWI interrupt is enabled by
setting the EWI bit in the WWDG_CFR register. When the downcounter reaches the value
0x40, an EWI interrupt is generated and the corresponding interrupt service routine (ISR)
can be used to trigger specific actions (such as communications or data logging), before
resetting the device.
In some applications, the EWI interrupt can be used to manage a software system check
and/or system recovery/graceful degradation, without generating a WWDG reset. In this
case, the corresponding interrupt service routine (ISR) should reload the WWDG counter to
avoid the WWDG reset, then trigger the required actions.
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RM0091

The EWI interrupt is cleared by writing '0' to the EWIF bit in the WWDG_SR register.
Note:

When the EWI interrupt cannot be served, e.g. due to a system lock in a higher priority task,
the WWDG reset will eventually be generated.

24.3.4

How to program the watchdog timeout
You can use the formula in Figure 210 to calculate the WWDG timeout.

Warning:

When writing to the WWDG_CR register, always write 1 in the
T6 bit to avoid generating an immediate reset.

Figure 210. Window watchdog timing diagram
7>@&17GRZQFRXQWHU

:>@

[)

5HIUHVKQRWDOORZHG 5HIUHVKDOORZHG

7LPH

7ELW
5(6(7
DLF

The formula to calculate the timeout value is given by:
WDGTB[1:0]
× ( T [ 5:0 ] + 1 )
t WWDG = t PCLK × 4096 × 2

( ms )

where:
tWWDG: WWDG timeout
tPCLK: APB clock period measured in ms
4096: value corresponding to internal divider
As an example, lets assume APB frequency is equal to 48 MHz, WDGTB1:0] is set to 3 and
T[5:0] is set to 63:
3
t WWDG = 1 ⁄ 48000 × 4096 × 2 × ( 63 + 1 ) = 43.69 ms

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System window watchdog (WWDG)

Refer to the datasheet for the minimum and maximum values of the tWWDG.

24.3.5

Debug mode
When the microcontroller enters debug mode (Cortex®-M0 core halted), the WWDG counter
either continues to work normally or stops, depending on DBG_WWDG_STOP
configuration bit in DBG module. For more details, refer to Section 32.9.2: Debug support
for timers, watchdog and I2C.

24.4

WWDG registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

24.4.1

Control register (WWDG_CR)
Address offset: 0x00
Reset value: 0x0000 007F

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

6

5

4

3

2

1

0

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WDGA

T[6:0]

rs

rw

Bits 31:8 Reserved, must be kept at reset value.
Bit 7 WDGA: Activation bit
This bit is set by software and only cleared by hardware after a reset. When WDGA = 1, the
watchdog can generate a reset.
0: Watchdog disabled
1: Watchdog enabled
Bits 6:0 T[6:0]: 7-bit counter (MSB to LSB)
These bits contain the value of the watchdog counter. It is decremented every (4096 x
2WDGTB1:0]) PCLK cycles. A reset is produced when it is decremented from 0x40 to 0x3F (T6
becomes cleared).

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24.4.2

RM0091

Configuration register (WWDG_CFR)
Address offset: 0x04
Reset value: 0x0000 007F

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

8

7

6

5

4

3

2

1

0

rw

rw

rw

15

14

13

12

11

10

9

Res.

Res.

Res.

Res.

Res.

Res.

EWI
rs

WDGTB[1:0]
rw

rw

W[6:0]
rw

rw

rw

rw

Bits 31:10 Reserved, must be kept at reset value.
Bit 9 EWI: Early wakeup interrupt
When set, an interrupt occurs whenever the counter reaches the value 0x40. This interrupt is
only cleared by hardware after a reset.
Bits 8:7 WDGTB[1:0]: Timer base
The time base of the prescaler can be modified as follows:
00: CK Counter Clock (PCLK div 4096) div 1
01: CK Counter Clock (PCLK div 4096) div 2
10: CK Counter Clock (PCLK div 4096) div 4
11: CK Counter Clock (PCLK div 4096) div 8
Bits 6:0 W[6:0]: 7-bit window value
These bits contain the window value to be compared to the downcounter.

24.4.3

Status register (WWDG_SR)
Address offset: 0x08
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

EWIF
rc_w0

Bits 31:1 Reserved, must be kept at reset value.
Bit 0 EWIF: Early wakeup interrupt flag
This bit is set by hardware when the counter has reached the value 0x40. It must be cleared by
software by writing ‘0’. A write of ‘1’ has no effect. This bit is also set if the interrupt is not
enabled.

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24.4.4

System window watchdog (WWDG)

WWDG register map
The following table gives the WWDG register map and reset values.

0

1

1

1

1

1

Res.

Res.

Res.

Res.

1

1

1

Res.

0

1

EWIF

Res.

0

Res.

1

WDGTB0

1

Res.

1

WDGTB1

1

Res.

1

EWI

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WWDG_
SR

Res.

0x08

Res.

Reset value

T[6:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WWDG_
CFR

Res.

0x04

0
Res.

Reset value

WDGA

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WWDG_
CR

Res.

0x00

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 78. WWDG register map and reset values

W[6:0]

Reset value

0

Refer to Section 2.2.2: Memory map and register boundary addresses for the register
boundary addresses.

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25

Real-time clock (RTC)

25.1

Introduction
The RTC provides an automatic wakeup to manage all low-power modes.
The real-time clock (RTC) is an independent BCD timer/counter. The RTC provides a timeof-day clock/calendar with programmable alarm interrupt.
The RTC includes also a periodic programmable wakeup flag with interrupt capability.
Two 32-bit registers contain the seconds, minutes, hours (12- or 24-hour format), day (day
of week), date (day of month), month, and year, expressed in binary coded decimal format
(BCD). The sub-seconds value is also available in binary format.
Compensations for 28-, 29- (leap year), 30-, and 31-day months are performed
automatically. Daylight saving time compensation can also be performed.
Additional 32-bit registers contain the programmable alarm subseconds, seconds, minutes,
hours, day, and date.
A digital calibration feature is available to compensate for any deviation in crystal oscillator
accuracy.
After RTC domain reset, all RTC registers are protected against possible parasitic write
accesses.
As long as the supply voltage remains in the operating range, the RTC never stops,
regardless of the device status (Run mode, low-power mode or under reset).

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25.2

Real-time clock (RTC)

RTC main features
The RTC unit main features are the following (see Figure 211: RTC block diagram in
STM32F03x, STM32F04x and STM32F05x devices and Figure 212: RTC block diagram for
STM32F07x and STM32F09x devices):
•

Calendar with subseconds, seconds, minutes, hours (12 or 24 format), day (day of
week), date (day of month), month, and year.

•

Daylight saving compensation programmable by software.

•

Programmable alarm with interrupt function. The alarm can be triggered by any
combination of the calendar fields.

•

Automatic wakeup unit generating a periodic flag that triggers an automatic wakeup
interrupt.

•

Reference clock detection: a more precise second source clock (50 or 60 Hz) can be
used to enhance the calendar precision.

•

Accurate synchronization with an external clock using the subsecond shift feature.

•

Digital calibration circuit (periodic counter correction): 0.95 ppm accuracy, obtained in a
calibration window of several seconds

•

Time-stamp function for event saving

•

Tamper detection event with configurable filter and internal pull-up

•

Maskable interrupts/events:

•

25.3

–

Alarm A

–

Wakeup interrupt

–

Time-stamp

–

Tamper detection

5 backup registers.

RTC implementation
Table 79. STM32F0xx RTC implementation(1)
STM32F03x
STM32F04x
STM32F05x

STM32F07x
STM32F09x

Periodic wakeup timer

-

X

RTC_TAMP1

X

X

RTC_TAMP2

X

X

RTC_TAMP3

-

X

Alarm A

X

X

RTC Features

1. X = supported, ‘-’= not supported.

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25.4

RTC functional description

25.4.1

RTC block diagram
Figure 211. RTC block diagram in STM32F03x, STM32F04x and STM32F05x devices
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Real-time clock (RTC)
Figure 212. RTC block diagram for STM32F07x and STM32F09x devices

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The RTC includes:
•

One alarm

•

Up to three tamper events from I/Os
–

One timestamp event from I/O

•

Tamper event detection can generate a timestamp event

•

5 32-bit backup registers
–

•

•

25.4.2

Tamper detection erases the backup registers.

•

The backup registers (RTC_BKPxR) are implemented in the RTC domain that
remains powered-on by VBAT when the VDD power is switched off.

Alternate function outputs: RTC_OUT which selects one of the following two outputs:
–

RTC_CALIB: 512 Hz or 1Hz clock output (with an LSE frequency of 32.768 kHz).
This output is enabled by setting the COE bit in the RTC_CR register.

–

RTC_ALARM: Alarm A. This output is selected by configuring the OSEL[1:0] bits
in the RTC_CR register.

Alternate function inputs:
–

RTC_TS: timestamp event

–

RTC_TAMP1: tamper1 event detection

–

RTC_TAMP2: tamper2 event detection

–

RTC_TAMP3: tamper3 event detection

–

RTC_REFIN: 50 or 60 Hz reference clock input

GPIOs controlled by the RTC
RTC_OUT, RTC_TS and RTC_TAMP1 are mapped on the same pin (PC13).
The selection of the RTC_ALARM output is performed through the RTC_TAFCR register as
follows: the PC13VALUE bit is used to select whether the RTC_ALARM output is configured
in push-pull or open drain mode.
When PC13 is not used as RTC alternate function, it can be forced in output push-pull mode
by setting the PC13MODE bit in the RTC_TAFCR. The output data value is then given by
the PC13VALUE bit. In this case, PC13 output push-pull state and data are preserved in
Standby mode.
The output mechanism follows the priority order shown in Table 80.
When PC14 and PC15 are not used as LSE oscillator, they can be forced in output push-pull
mode by setting the PC14MODE and PC15MODE bits in the RTC_TAFCR register
respectively. The output data values are then given by PC14VALUE and PC15VALUE. In
this case, the PC14 and PC15 output push-pull states and data values are preserved in
Standby mode.
The output mechanism follows the priority order shown in Table 81 and Table 82.

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Table 80. RTC pin PC13 configuration(1)

Pin
configuration
and function

RTC_ALARM
output
enabled

RTC_CALIB
output
enabled

RTC_TAMP1
input
enabled

RTC_TS
input
enabled

PC13MODE
bit

PC13VALUE
bit

RTC_ALARM
output OD

1

Don’t care

Don’t care

Don’t care

Don’t care

0

RTC_ALARM
output PP

1

Don’t care

Don’t care

Don’t care

Don’t care

1

RTC_CALIB
output PP

0

1

Don’t care

Don’t care

Don’t care

Don’t care

RTC_TAMP1
input floating

0

0

1

0

Don’t care

Don’t care

RTC_TS and
RTC_TAMP1
input floating

0

0

1

1

Don’t care

Don’t care

RTC_TS input
floating

0

0

0

1

Don’t care

Don’t care

Output PP
forced

0

0

0

0

1

PC13 output
data value

Wakeup pin or
Standard
GPIO

0

0

0

0

0

Don’t care

1. OD: open drain; PP: push-pull.

Table 81. LSE pin PC14 configuration (1)
Pin configuration and
function

LSEON bit in
RCC_BDCR register

LSEBYP bit in
RCC_BDCR register

PC14MODE
bit

PC14VALUE
bit

LSE oscillator

1

0

Don’t care

Don’t care

LSE bypass

1

1

Don’t care

Don’t care

Output PP forced

0

Don’t care

1

PC14 output data
value

Standard GPIO

0

Don’t care

0

Don’t care

1. OD: open drain; PP: push-pull.

Table 82. LSE pin PC15 configuration (1)
Pin configuration and
function

LSEON bit in
RCC_BDCR register

LSEBYP bit in
RCC_BDCR register

PC15MODE
bit

PC15VALUE
bit

1

0

Don’t care

Don’t care

1

1

0

Don’t care

1

PC15 output data
value

0

Don’t care

0

Don’t care

LSE oscillator
Output PP forced
Standard GPIO
1. OD: open drain; PP: push-pull.

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Clock and prescalers
The RTC clock source (RTCCLK) is selected through the clock controller among the LSE
clock, the LSI oscillator clock, and the HSE clock. For more information on the RTC clock
source configuration, refer to Section 6: Reset and clock control (RCC).
A programmable prescaler stage generates a 1 Hz clock which is used to update the
calendar. To minimize power consumption, the prescaler is split into 2 programmable
prescalers (see Figure 211: RTC block diagram in STM32F03x, STM32F04x and
STM32F05x devices and Figure 212: RTC block diagram for STM32F07x and STM32F09x
devices):

Note:

•

A 7-bit asynchronous prescaler configured through the PREDIV_A bits of the
RTC_PRER register.

•

A 15-bit synchronous prescaler configured through the PREDIV_S bits of the
RTC_PRER register.

When both prescalers are used, it is recommended to configure the asynchronous prescaler
to a high value to minimize consumption.
The asynchronous prescaler division factor is set to 128, and the synchronous division
factor to 256, to obtain an internal clock frequency of 1 Hz (ck_spre) with an LSE frequency
of 32.768 kHz.
The minimum division factor is 1 and the maximum division factor is 222.
This corresponds to a maximum input frequency of around 4 MHz.
fck_apre is given by the following formula:
f RTCCLK
f CK_APRE = --------------------------------------PREDIV_A + 1

The ck_apre clock is used to clock the binary RTC_SSR subseconds downcounter. When it
reaches 0, RTC_SSR is reloaded with the content of PREDIV_S.
fck_spre is given by the following formula:
f RTCCLK
f CK_SPRE = ----------------------------------------------------------------------------------------------( PREDIV_S + 1 ) × ( PREDIV_A + 1 )

The ck_spre clock can be used either to update the calendar or as timebase for the 16-bit
wakeup auto-reload timer. To obtain short timeout periods, the 16-bit wakeup auto-reload
timer can also run with the RTCCLK divided by the programmable 4-bit asynchronous
prescaler (see Section 25.4.6: Periodic auto-wakeup for details).

25.4.4

Real-time clock and calendar
The RTC calendar time and date registers are accessed through shadow registers which
are synchronized with PCLK (APB clock). They can also be accessed directly in order to
avoid waiting for the synchronization duration.

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•

RTC_SSR for the subseconds

•

RTC_TR for the time

•

RTC_DR for the date

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Every two RTCCLK periods, the current calendar value is copied into the shadow registers,
and the RSF bit of RTC_ISR register is set (see Section 25.7.4: RTC initialization and status
register (RTC_ISR)). The copy is not performed in Stop and Standby mode. When exiting
these modes, the shadow registers are updated after up to 2 RTCCLK periods.
When the application reads the calendar registers, it accesses the content of the shadow
registers. It is possible to make a direct access to the calendar registers by setting the
BYPSHAD control bit in the RTC_CR register. By default, this bit is cleared, and the user
accesses the shadow registers.
When reading the RTC_SSR, RTC_TR or RTC_DR registers in BYPSHAD=0 mode, the
frequency of the APB clock (fAPB) must be at least 7 times the frequency of the RTC clock
(fRTCCLK).
The shadow registers are reset by system reset.

25.4.5

Programmable alarm
The RTC unit provides programmable alarm: Alarm A.
The programmable alarm function is enabled through the ALRAE bit in the RTC_CR
register. The ALRAF is set to 1 if the calendar subseconds, seconds, minutes, hours, date
or day match the values programmed in the alarm registers RTC_ALRMASSR and
RTC_ALRMAR. Each calendar field can be independently selected through the MSKx bits
of the RTC_ALRMAR register, and through the MASKSSx bits of the RTC_ALRMASSR
register. The alarm interrupt is enabled through the ALRAIE bit in the RTC_CR register.

Caution:

If the seconds field is selected (MSK1 bit reset in RTC_ALRMAR), the synchronous
prescaler division factor set in the RTC_PRER register must be at least 3 to ensure correct
behavior.
Alarm A (if enabled by bits OSEL[1:0] in RTC_CR register) can be routed to the
RTC_ALARM output. RTC_ALARM output polarity can be configured through bit POL the
RTC_CR register.

25.4.6

Periodic auto-wakeup
The periodic wakeup flag is generated by a 16-bit programmable auto-reload down-counter.
The wakeup timer range can be extended to 17 bits.
The wakeup function is enabled through the WUTE bit in the RTC_CR register.
The wakeup timer clock input can be:
•

RTC clock (RTCCLK) divided by 2, 4, 8, or 16.
When RTCCLK is LSE(32.768kHz), this allows to configure the wakeup interrupt period
from 122 µs to 32 s, with a resolution down to 61 µs.

•

ck_spre (usually 1 Hz internal clock)
When ck_spre frequency is 1Hz, this allows to achieve a wakeup time from 1 s to
around 36 hours with one-second resolution. This large programmable time range is
divided in 2 parts:
–

from 1s to 18 hours when WUCKSEL [2:1] = 10

–

and from around 18h to 36h when WUCKSEL[2:1] = 11. In this last case 216 is
added to the 16-bit counter current value.When the initialization sequence is
complete (see Programming the wakeup timer on page 585), the timer starts
counting down.When the wakeup function is enabled, the down-counting remains

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active in low-power modes. In addition, when it reaches 0, the WUTF flag is set in
the RTC_ISR register, and the wakeup counter is automatically reloaded with its
reload value (RTC_WUTR register value).
The WUTF flag must then be cleared by software.
When the periodic wakeup interrupt is enabled by setting the WUTIE bit in the RTC_CR2
register, it can exit the device from low-power modes.
The periodic wakeup flag can be routed to the RTC_ALARM output provided it has been
enabled through bits OSEL[1:0] of RTC_CR register. RTC_ALARM output polarity can be
configured through the POL bit in the RTC_CR register.
System reset, as well as low-power modes (Sleep, Stop and Standby) have no influence on
the wakeup timer.

25.4.7

RTC initialization and configuration
RTC register access
The RTC registers are 32-bit registers. The APB interface introduces 2 wait-states in RTC
register accesses except on read accesses to calendar shadow registers when
BYPSHAD=0.

RTC register write protection
After system reset, the RTC registers are protected against parasitic write access by
clearing the DBP bit in the PWR_CR register (refer to the power control section). DBP bit
must be set in order to enable RTC registers write access.
After RTC domain reset, all the RTC registers are write-protected. Writing to the RTC
registers is enabled by writing a key into the Write Protection register, RTC_WPR.
The following steps are required to unlock the write protection on all the RTC registers
except for RTC_TAFCR, RTC_BKPxR and RTC_ISR[13:8].
1.

Write ‘0xCA’ into the RTC_WPR register.

2.

Write ‘0x53’ into the RTC_WPR register.

Writing a wrong key reactivates the write protection.
The protection mechanism is not affected by system reset.

Calendar initialization and configuration
To program the initial time and date calendar values, including the time format and the
prescaler configuration, the following sequence is required:

584/1004

1.

Set INIT bit to 1 in the RTC_ISR register to enter initialization mode. In this mode, the
calendar counter is stopped and its value can be updated.

2.

Poll INITF bit of in the RTC_ISR register. The initialization phase mode is entered when
INITF is set to 1. It takes around 2 RTCCLK clock cycles (due to clock synchronization).

3.

To generate a 1 Hz clock for the calendar counter, program both the prescaler factors in
RTC_PRER register.

4.

Load the initial time and date values in the shadow registers (RTC_TR and RTC_DR),
and configure the time format (12 or 24 hours) through the FMT bit in the RTC_CR
register.

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5.

Exit the initialization mode by clearing the INIT bit. The actual calendar counter value is
then automatically loaded and the counting restarts after 4 RTCCLK clock cycles.

When the initialization sequence is complete, the calendar starts counting.
Note:

After a system reset, the application can read the INITS flag in the RTC_ISR register to
check if the calendar has been initialized or not. If this flag equals 0, the calendar has not
been initialized since the year field is set at its RTC domain reset default value (0x00).
To read the calendar after initialization, the software must first check that the RSF flag is set
in the RTC_ISR register.
For code example refer to the Appendix section A.16.1: RTC calendar configuration code
example.

Daylight saving time
The daylight saving time management is performed through bits SUB1H, ADD1H, and BKP
of the RTC_CR register.
Using SUB1H or ADD1H, the software can subtract or add one hour to the calendar in one
single operation without going through the initialization procedure.
In addition, the software can use the BKP bit to memorize this operation.

Programming the alarm
A similar procedure must be followed to program or update the programmable alarms.

Note:

1.

Clear ALRAE in RTC_CR to disable Alarm A.

2.

Program the Alarm A registers (RTC_ALRMASSR/RTC_ALRMAR).

3.

Set ALRAE in the RTC_CR register to enable Alarm A again.

Each change of the RTC_CR register is taken into account after around 2 RTCCLK clock
cycles due to clock synchronization.
For code example refer to the Appendix section A.16.2: RTC alarm configuration code
example.

Programming the wakeup timer
The following sequence is required to configure or change the wakeup timer auto-reload
value (WUT[15:0] in RTC_WUTR):
1.

Clear WUTE in RTC_CR to disable the wakeup timer.

2.

Poll WUTWF until it is set in RTC_ISR to make sure the access to wakeup auto-reload
counter and to WUCKSEL[2:0] bits is allowed. It takes around 2 RTCCLK clock cycles
(due to clock synchronization).

3.

Program the wakeup auto-reload value WUT[15:0], and the wakeup clock selection
(WUCKSEL[2:0] bits in RTC_CR). Set WUTE in RTC_CR to enable the timer again.
The wakeup timer restarts down-counting. The WUTWF bit is cleared up to 2 RTCCLK
clock cycles after WUTE is cleared, due to clock synchronization.

For code example refer to the Appendix section A.16.3: RTC WUT configuration code
example.

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Reading the calendar
When BYPSHAD control bit is cleared in the RTC_CR register
To read the RTC calendar registers (RTC_SSR, RTC_TR and RTC_DR) properly, the APB
clock frequency (fPCLK) must be equal to or greater than seven times the RTC clock
frequency (fRTCCLK). This ensures a secure behavior of the synchronization mechanism.
If the APB clock frequency is less than seven times the RTC clock frequency, the software
must read the calendar time and date registers twice. If the second read of the RTC_TR
gives the same result as the first read, this ensures that the data is correct. Otherwise a third
read access must be done. In any case the APB clock frequency must never be lower than
the RTC clock frequency.
The RSF bit is set in RTC_ISR register each time the calendar registers are copied into the
RTC_SSR, RTC_TR and RTC_DR shadow registers. The copy is performed every two
RTCCLK cycles. To ensure consistency between the 3 values, reading either RTC_SSR or
RTC_TR locks the values in the higher-order calendar shadow registers until RTC_DR is
read. In case the software makes read accesses to the calendar in a time interval smaller
than 2 RTCCLK periods: RSF must be cleared by software after the first calendar read, and
then the software must wait until RSF is set before reading again the RTC_SSR, RTC_TR
and RTC_DR registers.
After waking up from low-power mode (Stop or Standby), RSF must be cleared by software.
The software must then wait until it is set again before reading the RTC_SSR, RTC_TR and
RTC_DR registers.
The RSF bit must be cleared after wakeup and not before entering low-power mode.
After a system reset, the software must wait until RSF is set before reading the RTC_SSR,
RTC_TR and RTC_DR registers. Indeed, a system reset resets the shadow registers to
their default values.
After an initialization (refer to Calendar initialization and configuration on page 584): the
software must wait until RSF is set before reading the RTC_SSR, RTC_TR and RTC_DR
registers.
After synchronization (refer to Section 25.4.10: RTC synchronization): the software must
wait until RSF is set before reading the RTC_SSR, RTC_TR and RTC_DR registers.
For code example refer to the Appendix section A.16.4: RTC read calendar code example.

When the BYPSHAD control bit is set in the RTC_CR register (bypass shadow
registers)
Reading the calendar registers gives the values from the calendar counters directly, thus
eliminating the need to wait for the RSF bit to be set. This is especially useful after exiting
from low-power modes (STOP or Standby), since the shadow registers are not updated
during these modes.
When the BYPSHAD bit is set to 1, the results of the different registers might not be
coherent with each other if an RTCCLK edge occurs between two read accesses to the
registers. Additionally, the value of one of the registers may be incorrect if an RTCCLK edge
occurs during the read operation. The software must read all the registers twice, and then
compare the results to confirm that the data is coherent and correct. Alternatively, the
software can just compare the two results of the least-significant calendar register.

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Note:

While BYPSHAD=1, instructions which read the calendar registers require one extra APB
cycle to complete.

25.4.9

Resetting the RTC
The calendar shadow registers (RTC_SSR, RTC_TR and RTC_DR) and some bits of the
RTC status register (RTC_ISR) are reset to their default values by all available system reset
sources.
On the contrary, the following registers are reset to their default values by a RTC domain
reset and are not affected by a system reset: the RTC current calendar registers, the RTC
control register (RTC_CR), the prescaler register (RTC_PRER), the RTC calibration register
(RTC_CALR), the RTC shift register (RTC_SHIFTR), the RTC timestamp registers
(RTC_TSSSR, RTC_TSTR and RTC_TSDR), the RTC tamper and alternate function
configuration register (RTC_TAFCR), the RTC backup registers (RTC_BKPxR), the wakeup
timer register (RTC_WUTR), the Alarm A registers (RTC_ALRMASSR/RTC_ALRMAR).
In addition, when it is clocked by the LSE, the RTC keeps on running under system reset if
the reset source is different from the RTC domain reset one (refer to the RTC clock section
of the Reset and clock controller for details on the list of RTC clock sources not affected by
system reset). When a RTC domain reset occurs, the RTC is stopped and all the RTC
registers are set to their reset values.

25.4.10

RTC synchronization
The RTC can be synchronized to a remote clock with a high degree of precision. After
reading the sub-second field (RTC_SSR or RTC_TSSSR), a calculation can be made of the
precise offset between the times being maintained by the remote clock and the RTC. The
RTC can then be adjusted to eliminate this offset by “shifting” its clock by a fraction of a
second using RTC_SHIFTR.
RTC_SSR contains the value of the synchronous prescaler counter. This allows one to
calculate the exact time being maintained by the RTC down to a resolution of
1 / (PREDIV_S + 1) seconds. As a consequence, the resolution can be improved by
increasing the synchronous prescaler value (PREDIV_S[14:0]. The maximum resolution
allowed (30.52 μs with a 32768 Hz clock) is obtained with PREDIV_S set to 0x7FFF.
However, increasing PREDIV_S means that PREDIV_A must be decreased in order to
maintain the synchronous prescaler output at 1 Hz. In this way, the frequency of the
asynchronous prescaler output increases, which may increase the RTC dynamic
consumption.
The RTC can be finely adjusted using the RTC shift control register (RTC_SHIFTR). Writing
to RTC_SHIFTR can shift (either delay or advance) the clock by up to a second with a
resolution of 1 / (PREDIV_S + 1) seconds. The shift operation consists of adding the
SUBFS[14:0] value to the synchronous prescaler counter SS[15:0]: this will delay the clock.
If at the same time the ADD1S bit is set, this results in adding one second and at the same
time subtracting a fraction of second, so this will advance the clock.

Caution:

Before initiating a shift operation, the user must check that SS[15] = 0 in order to ensure that
no overflow will occur.
As soon as a shift operation is initiated by a write to the RTC_SHIFTR register, the SHPF
flag is set by hardware to indicate that a shift operation is pending. This bit is cleared by
hardware as soon as the shift operation has completed.

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Caution:

This synchronization feature is not compatible with the reference clock detection feature:
firmware must not write to RTC_SHIFTR when REFCKON=1.

25.4.11

RTC reference clock detection
The update of the RTC calendar can be synchronized to a reference clock, RTC_REFIN,
which is usually the mains frequency (50 or 60 Hz). The precision of the RTC_REFIN
reference clock should be higher than the 32.768 kHz LSE clock. When the RTC_REFIN
detection is enabled (REFCKON bit of RTC_CR set to 1), the calendar is still clocked by the
LSE, and RTC_REFIN is used to compensate for the imprecision of the calendar update
frequency (1 Hz).
Each 1 Hz clock edge is compared to the nearest RTC_REFIN clock edge (if one is found
within a given time window). In most cases, the two clock edges are properly aligned. When
the 1 Hz clock becomes misaligned due to the imprecision of the LSE clock, the RTC shifts
the 1 Hz clock a bit so that future 1 Hz clock edges are aligned. Thanks to this mechanism,
the calendar becomes as precise as the reference clock.
The RTC detects if the reference clock source is present by using the 256 Hz clock
(ck_apre) generated from the 32.768 kHz quartz. The detection is performed during a time
window around each of the calendar updates (every 1 s). The window equals 7 ck_apre
periods when detecting the first reference clock edge. A smaller window of 3 ck_apre
periods is used for subsequent calendar updates.
Each time the reference clock is detected in the window, the asynchronous prescaler which
outputs the ck_apre clock is forced to reload. This has no effect when the reference clock
and the 1 Hz clock are aligned because the prescaler is being reloaded at the same
moment. When the clocks are not aligned, the reload shifts future 1 Hz clock edges a little
for them to be aligned with the reference clock.
If the reference clock halts (no reference clock edge occurred during the 3 ck_apre window),
the calendar is updated continuously based solely on the LSE clock. The RTC then waits for
the reference clock using a large 7 ck_apre period detection window centered on the
ck_spre edge.
When the RTC_REFIN detection is enabled, PREDIV_A and PREDIV_S must be set to their
default values:
•

PREDIV_A = 0x007F

•

PREVID_S = 0x00FF

Note:

RTC_REFIN clock detection is not available in Standby mode.

25.4.12

RTC smooth digital calibration
The RTC frequency can be digitally calibrated with a resolution of about 0.954 ppm with a
range from -487.1 ppm to +488.5 ppm. The correction of the frequency is performed using
series of small adjustments (adding and/or subtracting individual RTCCLK pulses). These
adjustments are fairly well distributed so that the RTC is well calibrated even when observed
over short durations of time.
The smooth digital calibration is performed during a cycle of about 220 RTCCLK pulses, or
32 seconds when the input frequency is 32768 Hz. This cycle is maintained by a 20-bit
counter, cal_cnt[19:0], clocked by RTCCLK.

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The smooth calibration register (RTC_CALR) specifies the number of RTCCLK clock cycles
to be masked during the 32-second cycle:
•

Setting the bit CALM[0] to 1 causes exactly one pulse to be masked during the 32-

second cycle.

Note:

•

Setting CALM[1] to 1 causes two additional cycles to be masked

•

Setting CALM[2] to 1 causes four additional cycles to be masked

•

and so on up to CALM[8] set to 1 which causes 256 clocks to be masked.

CALM[8:0] (RTC_CALR) specifies the number of RTCCLK pulses to be masked during the
32-second cycle. Setting the bit CALM[0] to ‘1’ causes exactly one pulse to be masked
during the 32-second cycle at the moment when cal_cnt[19:0] is 0x80000; CALM[1]=1
causes two other cycles to be masked (when cal_cnt is 0x40000 and 0xC0000); CALM[2]=1
causes four other cycles to be masked (cal_cnt = 0x20000/0x60000/0xA0000/ 0xE0000);
and so on up to CALM[8]=1 which causes 256 clocks to be masked (cal_cnt = 0xXX800).
While CALM allows the RTC frequency to be reduced by up to 487.1 ppm with fine
resolution, the bit CALP can be used to increase the frequency by 488.5 ppm. Setting CALP
to ‘1’ effectively inserts an extra RTCCLK pulse every 211 RTCCLK cycles, which means
that 512 clocks are added during every 32-second cycle.
Using CALM together with CALP, an offset ranging from -511 to +512 RTCCLK cycles can
be added during the 32-second cycle, which translates to a calibration range of -487.1 ppm
to +488.5 ppm with a resolution of about 0.954 ppm.
The formula to calculate the effective calibrated frequency (FCAL) given the input frequency
(FRTCCLK) is as follows:
FCAL = FRTCCLK x [1 + (CALP x 512 - CALM) / (220 + CALM - CALP x 512)]

Calibration when PREDIV_A<3
The CALP bit can not be set to 1 when the asynchronous prescaler value (PREDIV_A bits in
RTC_PRER register) is less than 3. If CALP was already set to 1 and PREDIV_A bits are
set to a value less than 3, CALP is ignored and the calibration operates as if CALP was
equal to 0.
To perform a calibration with PREDIV_A less than 3, the synchronous prescaler value
(PREDIV_S) should be reduced so that each second is accelerated by 8 RTCCLK clock
cycles, which is equivalent to adding 256 clock cycles every 32 seconds. As a result,
between 255 and 256 clock pulses (corresponding to a calibration range from 243.3 to
244.1 ppm) can effectively be added during each 32-second cycle using only the CALM bits.
With a nominal RTCCLK frequency of 32768 Hz, when PREDIV_A equals 1 (division factor
of 2), PREDIV_S should be set to 16379 rather than 16383 (4 less). The only other
interesting case is when PREDIV_A equals 0, PREDIV_S should be set to 32759 rather
than 32767 (8 less).
If PREDIV_S is reduced in this way, the formula given the effective frequency of the
calibrated input clock is as follows:
FCAL = FRTCCLK x [1 + (256 - CALM) / (220 + CALM - 256)]
In this case, CALM[7:0] equals 0x100 (the midpoint of the CALM range) is the correct
setting if RTCCLK is exactly 32768.00 Hz.

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Verifying the RTC calibration
RTC precision is ensured by measuring the precise frequency of RTCCLK and calculating
the correct CALM value and CALP values. An optional 1 Hz output is provided to allow
applications to measure and verify the RTC precision.
Measuring the precise frequency of the RTC over a limited interval can result in a
measurement error of up to 2 RTCCLK clock cycles over the measurement period,
depending on how the digital calibration cycle is aligned with the measurement period.
However, this measurement error can be eliminated if the measurement period is the same
length as the calibration cycle period. In this case, the only error observed is the error due to
the resolution of the digital calibration.
•

By default, the calibration cycle period is 32 seconds.

Using this mode and measuring the accuracy of the 1 Hz output over exactly 32 seconds
guarantees that the measure is within 0.477 ppm (0.5 RTCCLK cycles over 32 seconds, due
to the limitation of the calibration resolution).
•

CALW16 bit of the RTC_CALR register can be set to 1 to force a 16- second calibration
cycle period.

In this case, the RTC precision can be measured during 16 seconds with a maximum error
of 0.954 ppm (0.5 RTCCLK cycles over 16 seconds). However, since the calibration
resolution is reduced, the long term RTC precision is also reduced to 0.954 ppm: CALM[0]
bit is stuck at 0 when CALW16 is set to 1.
•

CALW8 bit of the RTC_CALR register can be set to 1 to force a 8- second calibration
cycle period.

In this case, the RTC precision can be measured during 8 seconds with a maximum error of
1.907 ppm (0.5 RTCCLK cycles over 8s). The long term RTC precision is also reduced to
1.907 ppm: CALM[1:0] bits are stuck at 00 when CALW8 is set to 1.

Re-calibration on-the-fly
The calibration register (RTC_CALR) can be updated on-the-fly while RTC_ISR/INITF=0, by
using the follow process:
1.

Poll the RTC_ISR/RECALPF (re-calibration pending flag).

2.

If it is set to 0, write a new value to RTC_CALR, if necessary. RECALPF is then
automatically set to 1

3.

Within three ck_apre cycles after the write operation to RTC_CALR, the new calibration
settings take effect.

For code example refer to the Appendix section A.16.5: RTC calibration code example.

25.4.13

Time-stamp function
Time-stamp is enabled by setting the TSE bit of RTC_CR register to 1.
The calendar is saved in the time-stamp registers (RTC_TSSSR, RTC_TSTR, RTC_TSDR)
when a time-stamp event is detected on the RTC_TS pin.
When a time-stamp event occurs, the time-stamp flag bit (TSF) in RTC_ISR register is set.
By setting the TSIE bit in the RTC_CR register, an interrupt is generated when a time-stamp
event occurs.

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If a new time-stamp event is detected while the time-stamp flag (TSF) is already set, the
time-stamp overflow flag (TSOVF) flag is set and the time-stamp registers (RTC_TSTR and
RTC_TSDR) maintain the results of the previous event.

Note:

TSF is set 2 ck_apre cycles after the time-stamp event occurs due to synchronization
process.
There is no delay in the setting of TSOVF. This means that if two time-stamp events are
close together, TSOVF can be seen as '1' while TSF is still '0'. As a consequence, it is
recommended to poll TSOVF only after TSF has been set.

Caution:

If a time-stamp event occurs immediately after the TSF bit is supposed to be cleared, then
both TSF and TSOVF bits are set.To avoid masking a time-stamp event occurring at the
same moment, the application must not write ‘0’ into TSF bit unless it has already read it to
‘1’.
Optionally, a tamper event can cause a time-stamp to be recorded. See the description of
the TAMPTS control bit in Section 25.7.15: RTC tamper and alternate function configuration
register (RTC_TAFCR).

25.4.14

Tamper detection
The RTC_TAMPx input events can be configured either for edge detection, or for level
detection with filtering.
The tamper detection can be configured for the following purposes:
•

erase the RTC backup registers

•

generate an interrupt, capable to wakeup from Stop and Standby modes

RTC backup registers
The backup registers (RTC_BKPxR) are not reset by system reset or when the device
wakes up from Standby mode.
The backup registers are reset when a tamper detection event occurs (see Section 25.7.17:
RTC backup registers (RTC_BKPxR) and Tamper detection initialization on page 591).

Tamper detection initialization
Each input can be enabled by setting the corresponding TAMPxE bits to 1 in the
RTC_TAFCR register.
Each RTC_TAMPx tamper detection input is associated with a flag TAMPxF in the RTC_ISR
register.
The TAMPxF flag is asserted after the tamper event on the pin, with the latency provided
below:
•

3 ck_apre cycles when TAMPFLT differs from 0x0 (Level detection with filtering)

•

3 ck_apre cycles when TAMPTS=1 (Timestamp on tamper event)

•

No latency when TAMPFLT=0x0 (Edge detection) and TAMPTS=0

A new tamper occurring on the same pin during this period and as long as TAMPxF is set
cannot be detected.
By setting the TAMPIE bit in the RTC_TAFCR register, an interrupt is generated when a
tamper detection event occurs. .

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Timestamp on tamper event
With TAMPTS set to ‘1’, any tamper event causes a timestamp to occur. In this case, either
the TSF bit or the TSOVF bit are set in RTC_ISR, in the same manner as if a normal
timestamp event occurs. The affected tamper flag register TAMPxF is set at the same time
that TSF or TSOVF is set.

Edge detection on tamper inputs
If the TAMPFLT bits are “00”, the RTC_TAMPx pins generate tamper detection events when
either a rising edge or a falling edge is observed depending on the corresponding
TAMPxTRG bit. The internal pull-up resistors on the RTC_TAMPx inputs are deactivated
when edge detection is selected.
Caution:

To avoid losing tamper detection events, the signal used for edge detection is logically
ANDed with the corresponding TAMPxE bit in order to detect a tamper detection event in
case it occurs before the RTC_TAMPx pin is enabled.
•

When TAMPxTRG = 0: if the RTC_TAMPx alternate function is already high before
tamper detection is enabled (TAMPxE bit set to 1), a tamper event is detected as soon
as the RTC_TAMPx input is enabled, even if there was no rising edge on the
RTC_TAMPx input after TAMPxE was set.

•

When TAMPxTRG = 1: if the RTC_TAMPx alternate function is already low before
tamper detection is enabled, a tamper event is detected as soon as the RTC_TAMPx
input is enabled (even if there was no falling edge on the RTC_TAMPx input after
TAMPxE was set.

After a tamper event has been detected and cleared, the RTC_TAMPx alternate function
should be disabled and then re-enabled (TAMPxE set to 1) before re-programming the
backup registers (RTC_BKPxR). This prevents the application from writing to the backup
registers while the RTC_TAMPx input value still indicates a tamper detection. This is
equivalent to a level detection on the RTC_TAMPx alternate function input.
Note:

Tamper detection is still active when VDD power is switched off. To avoid unwanted resetting
of the backup registers, the pin to which the RTC_TAMPx alternate function is mapped
should be externally tied to the correct level.

Level detection with filtering on RTC_TAMPx inputs
Level detection with filtering is performed by setting TAMPFLT to a non-zero value. A tamper
detection event is generated when either 2, 4, or 8 (depending on TAMPFLT) consecutive
samples are observed at the level designated by the TAMPxTRG bits.
The RTC_TAMPx inputs are precharged through the I/O internal pull-up resistance before
its state is sampled, unless disabled by setting TAMPPUDIS to 1,The duration of the
precharge is determined by the TAMPPRCH bits, allowing for larger capacitances on the
RTC_TAMPx inputs.
The trade-off between tamper detection latency and power consumption through the pull-up
can be optimized by using TAMPFREQ to determine the frequency of the sampling for level
detection.
Note:

Refer to the datasheets for the electrical characteristics of the pull-up resistors.
For code example refer to the Appendix sections: A.16.6: RTC tamper and time stamp
configuration code example and A.16.7: RTC tamper and time stamp code example.

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25.4.15

Real-time clock (RTC)

Calibration clock output
When the COE bit is set to 1 in the RTC_CR register, a reference clock is provided on the
RTC_CALIB device output.
If the COSEL bit in the RTC_CR register is reset and PREDIV_A = 0x7F, the RTC_CALIB
frequency is fRTCCLK/64. This corresponds to a calibration output at 512 Hz for an RTCCLK
frequency at 32.768 kHz. The RTC_CALIB duty cycle is irregular: there is a light jitter on
falling edges. It is therefore recommended to use rising edges.
When COSEL is set and “PREDIV_S+1” is a non-zero multiple of 256 (i.e: PREDIV_S[7:0] =
0xFF), the RTC_CALIB frequency is fRTCCLK/(256 * (PREDIV_A+1)). This corresponds to a
calibration output at 1 Hz for prescaler default values (PREDIV_A = Ox7F, PREDIV_S =
0xFF), with an RTCCLK frequency at 32.768 kHz. The 1 Hz output is affected when a shift
operation is on going and may toggle during the shift operation (SHPF=1).

Note:

When the RTC_CALIB or RTC_ALARM output is selected, the RTC_OUT pin is
automatically configured in output alternate function.
When COSEL bit is cleared, the RTC_CALIB output is the output of the 6th stage of the
asynchronous prescaler.
When COSEL bit is set, the RTC_CALIB output is the output of the 8th stage of the
synchronous prescaler.
For code example refer to the Appendix section A.16.8: RTC clock output code example.

25.4.16

Alarm output
The OSEL[1:0] control bits in the RTC_CR register are used to activate the alarm alternate
function output RTC_ALARM, and to select the function which is output. These functions
reflect the contents of the corresponding flags in the RTC_ISR register.
The polarity of the output is determined by the POL control bit in RTC_CR so that the
opposite of the selected flag bit is output when POL is set to 1.

Alarm alternate function output
The RTC_ALARM pin can be configured in output open drain or output push-pull using the
control bit ALARMOUTTYPE in the RTC_TAFCR register.
Note:

Once the RTC_ALARM output is enabled, it has priority over RTC_CALIB (COE bit is don't
care and must be kept cleared).
When the RTC_CALIB or RTC_ALARM output is selected, the RTC_OUT pin is
automatically configured in output alternate function.

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25.5

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RTC low-power modes
Table 83. Effect of low-power modes on RTC
Mode

Description

Sleep

No effect
RTC interrupts cause the device to exit the Sleep mode.

Stop

The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
tamper event, RTC timestamp event, and RTC Wakeup cause the device to exit the Stop
mode.

The RTC remains active when the RTC clock source is LSE or LSI. RTC alarm, RTC
Standby tamper event, RTC timestamp event, and RTC Wakeup cause the device to exit the
Standby mode.

25.6

RTC interrupts
All RTC interrupts are connected to the NVIC controller. Refer to Section 11.2: Extended
interrupts and events controller (EXTI).
To enable RTC interrupt(s), the following sequence is required:
1.

Configure and enable the NVIC line(s) corresponding to the RTC event(s) in interrupt
mode and select the rising edge sensitivity.

2.

Configure and enable the RTC IRQ channel in the NVIC.

3.

Configure the RTC to generate RTC interrupt(s).
Table 84. Interrupt control bits
Interrupt event

Event flag

Enable
control
bit

Exit the
Sleep
mode

Exit the
Stop
mode

Exit the
Standby
mode

Alarm A

ALRAF

ALRAIE

yes

yes(1)

yes(1)

RTC_TS input (timestamp)

TSF

TSIE

yes

yes(1)

yes(1)

RTC_TAMP1 input detection

TAMP1F

TAMPIE

yes

yes(1)

yes(1)

RTC_TAMP2 input detection

TAMP2F

TAMPIE

yes

yes(1)

yes(1)

RTC_TAMP3 input detection(2)

TAMP3F

TAMPIE

yes

yes(1)

yes(1)

1. Wakeup from STOP and Standby modes is possible only when the RTC clock source is LSE or LSI.
2. On STM32F07x and STM32F09x devices.

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25.7

RTC registers
Refer to Section 1.1 on page 42 of the reference manual for a list of abbreviations used in
register descriptions.
The peripheral registers can be accessed by words (32-bit).

25.7.1

RTC time register (RTC_TR)
The RTC_TR is the calendar time shadow register. This register must be written in
initialization mode only. Refer to Calendar initialization and configuration on page 584 and
Reading the calendar on page 586.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x00
RTC domain reset value: 0x0000 0000
System reset: 0x0000 0000 when BYPSHAD = 0. Not affected when BYPSHAD = 1.

31

30

29

28

27

26

25

24

23

22

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PM

15

14

13

12

11

10

9

8

7

Res.

MNT[2:0]
rw

rw

MNU[3:0]
rw

rw

rw

rw

20

19

18

HT[1:0]

17

16

HU[3:0]

rw

rw

rw

rw

rw

rw

rw

6

5

4

3

2

1

0

rw

rw

Res.

rw

21

ST[2:0]
rw

rw

SU[3:0]
rw

rw

rw

Bits 31-23 Reserved, must be kept at reset value
Bit 22 PM: AM/PM notation
0: AM or 24-hour format
1: PM
Bits 21:20 HT[1:0]: Hour tens in BCD format
Bits 19:16 HU[3:0]: Hour units in BCD format
Bit 15 Reserved, must be kept at reset value.
Bits 14:12 MNT[2:0]: Minute tens in BCD format
Bits 11:8 MNU[3:0]: Minute units in BCD format
Bit 7 Reserved, must be kept at reset value.
Bits 6:4 ST[2:0]: Second tens in BCD format
Bits 3:0 SU[3:0]: Second units in BCD format

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RTC date register (RTC_DR)
The RTC_DR is the calendar date shadow register. This register must be written in
initialization mode only. Refer to Calendar initialization and configuration on page 584 and
Reading the calendar on page 586.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x04
RTC domain reset value: 0x0000 2101
System reset: 0x0000 2101 when BYPSHAD = 0. Not affected when BYPSHAD = 1.

31

30

29

28

27

26

25

24

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

rw

rw

rw

rw

WDU[2:0]
rw

rw

MT
rw

rw

MU[3:0]

23

22

20

19

18

17

16

YU[3:0]

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

Res.

Res.

rw

rw

rw

rw

rw

Bits 31:24 Reserved, must be kept at reset value
Bits 23:20 YT[3:0]: Year tens in BCD format
Bits 19:16 YU[3:0]: Year units in BCD format
Bits 15:13 WDU[2:0]: Week day units
000: forbidden
001: Monday
...
111: Sunday
Bit 12 MT: Month tens in BCD format
Bits 11:8 MU: Month units in BCD format
Bits 7:6 Reserved, must be kept at reset value.
Bits 5:4 DT[1:0]: Date tens in BCD format
Bits 3:0 DU[3:0]: Date units in BCD format

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25.7.3

RTC control register (RTC_CR)
Address offset: 0x08
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

COE

15

14

13

12

11

10

9

8

TSIE

WUTIE

rw

rw

Res.

ALRAIE

TSE

WUTE

rw

rw

rw

Res.

ALRAE

22

21

OSEL[1:0]

20

19

18

POL

COSEL

BKP

17

16

SUB1H ADD1H

rw

rw

rw

rw

rw

rw

w

w

7

6

5

4

3

2

1

0

Res.

rw

FMT
rw

BYPS
REFCKON TSEDGE
HAD
rw

rw

rw

WUCKSEL[2:0]
rw

rw

rw

Bits 31:24 Reserved, must be kept at reset value.
Bit 23 COE: Calibration output enable
This bit enables the RTC_CALIB output
0: Calibration output disabled
1: Calibration output enabled
Bits 22:21 OSEL[1:0]: Output selection
These bits are used to select the flag to be routed to RTC_ALARM output
00: Output disabled
01: Alarm A output enabled
10: Reserved
11: Wakeup output enabled
Bit 20 POL: Output polarity
This bit is used to configure the polarity of RTC_ALARM output
0: The pin is high when ALRAF/WUTF is asserted (depending on OSEL[1:0])
1: The pin is low when ALRAF/WUTF is asserted (depending on OSEL[1:0]).
Bit 19 COSEL: Calibration output selection
When COE=1, this bit selects which signal is output on RTC_CALIB.
0: Calibration output is 512 Hz (with default prescaler setting)
1: Calibration output is 1 Hz (with default prescaler setting)
These frequencies are valid for RTCCLK at 32.768 kHz and prescalers at their default values
(PREDIV_A=127 and PREDIV_S=255). Refer to Section 25.4.15: Calibration clock output
Bit 18 BKP: Backup
This bit can be written by the user to memorize whether the daylight saving time change has
been performed or not.
Bit 17 SUB1H: Subtract 1 hour (winter time change)
When this bit is set, 1 hour is subtracted to the calendar time if the current hour is not 0. This
bit is always read as 0.
Setting this bit has no effect when current hour is 0.
0: No effect
1: Subtracts 1 hour to the current time. This can be used for winter time change outside
initialization mode.

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Bit 16 ADD1H: Add 1 hour (summer time change)
When this bit is set, 1 hour is added to the calendar time. This bit is always read as 0.
0: No effect
1: Adds 1 hour to the current time. This can be used for summer time change outside
initialization mode.
Bit 15 TSIE: Time-stamp interrupt enable
0: Time-stamp Interrupt disable
1: Time-stamp Interrupt enable
Bit 14 WUTIE: Wakeup timer interrupt enable
0: Wakeup timer interrupt disabled
1: Wakeup timer interrupt enabled
Bit 13 Reserved, must be kept at reset value
Bit 12 ALRAIE: Alarm A interrupt enable
0: Alarm A interrupt disabled
1: Alarm A interrupt enabled
Bit 11 TSE: timestamp enable
0: timestamp disable
1: timestamp enable
Bit 10 WUTE: Wakeup timer enable
0: Wakeup timer disabled
1: Wakeup timer enabled
Bit 9 Reserved, must be kept at reset value
Bit 8 ALRAE: Alarm A enable
0: Alarm A disabled
1: Alarm A enabled
Bit 7 Reserved, must be kept at reset value.
Bit 6 FMT: Hour format
0: 24 hour/day format
1: AM/PM hour format
Bit 5 BYPSHAD: Bypass the shadow registers
0: Calendar values (when reading from RTC_SSR, RTC_TR, and RTC_DR) are taken from
the shadow registers, which are updated once every two RTCCLK cycles.
1: Calendar values (when reading from RTC_SSR, RTC_TR, and RTC_DR) are taken
directly from the calendar counters.
Note: If the frequency of the APB clock is less than seven times the frequency of RTCCLK,
BYPSHAD must be set to ‘1’.

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Bit 4 REFCKON: RTC_REFIN reference clock detection enable (50 or 60 Hz)
0: RTC_REFIN detection disabled
1: RTC_REFIN detection enabled
Note: PREDIV_S must be 0x00FF.
Bit 3 TSEDGE: Time-stamp event active edge
0: RTC_TS input rising edge generates a time-stamp event
1: RTC_TS input falling edge generates a time-stamp event
TSE must be reset when TSEDGE is changed to avoid unwanted TSF setting.
Bits 2:0 WUCKSEL[2:0]: Wakeup clock selection
000: RTC/16 clock is selected
001: RTC/8 clock is selected
010: RTC/4 clock is selected
011: RTC/2 clock is selected
10x: ck_spre (usually 1 Hz) clock is selected
11x: ck_spre (usually 1 Hz) clock is selected and 216 is added to the WUT counter value
(see note below)

Note:

Bits 7, 6 and 4 of this register can be written in initialization mode only (RTC_ISR/INITF = 1).
WUT = Wakeup unit counter value. WUT = (0x0000 to 0xFFFF) + 0x10000 added when
WUCKSEL[2:1 = 11].
Bits 2 to 0 of this register can be written only when RTC_CR WUTE bit = 0 and RTC_ISR
WUTWF bit = 1.
It is recommended not to change the hour during the calendar hour increment as it could
mask the incrementation of the calendar hour.
ADD1H and SUB1H changes are effective in the next second.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.

Caution:

TSE must be reset when TSEDGE is changed to avoid spuriously setting of TSF.

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RTC initialization and status register (RTC_ISR)
This register is write protected (except for RTC_ISR[13:8] bits). The write access procedure
is described in RTC register write protection on page 584.
Address offset: 0x0C
RTC domain reset value: 0x0000 0007
System reset: not affected except INIT, INITF, and RSF bits which are cleared to ‘0’

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RECALPF

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

TSF

WUTF

Res.

ALRAF

INIT

INITF

RSF

INITS

Res.

ALRAWF

rc_w0

rc_w0

rc_w0

rw

r

rc_w0

r

r

TAMP3F TAMP2F TAMP1F TSOVF
rc_w0

rc_w0

rc_w0

rc_w0

SHPF WUTWF
r

r

r

Bits 31:17 Reserved, must be kept at reset value
Bit 16 RECALPF: Recalibration pending Flag
The RECALPF status flag is automatically set to ‘1’ when software writes to the RTC_CALR
register, indicating that the RTC_CALR register is blocked. When the new calibration settings
are taken into account, this bit returns to ‘0’. Refer to Re-calibration on-the-fly.
Bit 15 TAMP3F: RTC_TAMP3 detection flag
This flag is set by hardware when a tamper detection event is detected on the RTC_TAMP3
input.
It is cleared by software writing 0
Bit 14 TAMP2F: RTC_TAMP2 detection flag
This flag is set by hardware when a tamper detection event is detected on the RTC_TAMP2
input.
It is cleared by software writing 0
Bit 13 TAMP1F: RTC_TAMP1 detection flag
This flag is set by hardware when a tamper detection event is detected on the RTC_TAMP1
input.
It is cleared by software writing 0
Bit 12 TSOVF: Time-stamp overflow flag
This flag is set by hardware when a time-stamp event occurs while TSF is already set.
This flag is cleared by software by writing 0. It is recommended to check and then clear
TSOVF only after clearing the TSF bit. Otherwise, an overflow might not be noticed if a timestamp event occurs immediately before the TSF bit is cleared.
Bit 11 TSF: Time-stamp flag
This flag is set by hardware when a time-stamp event occurs.
This flag is cleared by software by writing 0.
Bit 10 WUTF: Wakeup timer flag
This flag is set by hardware when the wakeup auto-reload counter reaches 0.
This flag is cleared by software by writing 0.
This flag must be cleared by software at least 1.5 RTCCLK periods before WUTF is set to 1
again.
Bit 9 Reserved, must be kept at reset value.

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Real-time clock (RTC)

Bit 8 ALRAF: Alarm A flag
This flag is set by hardware when the time/date registers (RTC_TR and RTC_DR) match the
Alarm A register (RTC_ALRMAR).
This flag is cleared by software by writing 0.
Bit 7 INIT: Initialization mode
0: Free running mode
1: Initialization mode used to program time and date register (RTC_TR and RTC_DR), and
prescaler register (RTC_PRER). Counters are stopped and start counting from the new
value when INIT is reset.
Bit 6 INITF: Initialization flag
When this bit is set to 1, the RTC is in initialization state, and the time, date and prescaler
registers can be updated.
0: Calendar registers update is not allowed
1: Calendar registers update is allowed
Bit 5 RSF: Registers synchronization flag
This bit is set by hardware each time the calendar registers are copied into the shadow
registers (RTC_SSRx, RTC_TRx and RTC_DRx). This bit is cleared by hardware in
initialization mode, while a shift operation is pending (SHPF=1), or when in bypass shadow
register mode (BYPSHAD=1). This bit can also be cleared by software.
It is cleared either by software or by hardware in initialization mode.
0: Calendar shadow registers not yet synchronized
1: Calendar shadow registers synchronized
Bit 4 INITS: Initialization status flag
This bit is set by hardware when the calendar year field is different from 0 (RTC domain reset
state).
0: Calendar has not been initialized
1: Calendar has been initialized
Bit 3 SHPF: Shift operation pending
0: No shift operation is pending
1: A shift operation is pending
This flag is set by hardware as soon as a shift operation is initiated by a write to the
RTC_SHIFTR register. It is cleared by hardware when the corresponding shift operation has
been executed. Writing to the SHPF bit has no effect.
Bit 2 WUTWF: Wakeup timer write flag
This bit is set by hardware up to 2 RTCCLK cycles after the WUTE bit has been set to 0 in
RTC_CR, and is cleared up to 2 RTCCLK cycles after the WUTE bit has been set to 1. The
wakeup timer values can be changed when WUTE bit is cleared and WUTWF is set.
0: Wakeup timer configuration update not allowed
1: Wakeup timer configuration update allowed
Bit 1 Reserved, must be kept at reset value.
Bit 0 ALRAWF: Alarm A write flag
This bit is set by hardware when Alarm A values can be changed, after the ALRAE bit has
been set to 0 in RTC_CR.
It is cleared by hardware in initialization mode.
0: Alarm A update not allowed
1: Alarm A update allowed

Note:

The bits ALRAF, WUTF and TSF are cleared 2 APB clock cycles after programming them to
0.

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RM0091

RTC prescaler register (RTC_PRER)
This register must be written in initialization mode only. The initialization must be performed
in two separate write accesses. Refer to Calendar initialization and configuration on
page 584.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x10
RTC domain reset value: 0x007F 00FF
System reset: not affected

31

30

29

28

27

26

25

24

23

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

rw

rw

rw

rw

rw

rw

rw

Res.

22

21

19

18

17

16

PREDIV_A[6:0]
rw

rw

rw

rw

rw

rw

rw

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

PREDIV_S[14:0]
rw

Bits 31:23 Reserved, must be kept at reset value
Bits 22:16 PREDIV_A[6:0]: Asynchronous prescaler factor
This is the asynchronous division factor:
ck_apre frequency = RTCCLK frequency/(PREDIV_A+1)
Bit 15 Reserved, must be kept at reset value.
Bits 14:0 PREDIV_S[14:0]: Synchronous prescaler factor
This is the synchronous division factor:
ck_spre frequency = ck_apre frequency/(PREDIV_S+1)

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RM0091

Real-time clock (RTC)

25.7.6

RTC wakeup timer register (RTC_WUTR)
This register can be written only when WUTWF is set to 1 in RTC_ISR.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x14
RTC domain reset value: 0x0000 FFFF
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

WUT[15:0]
rw

Bits 31:16 Reserved, must be kept at reset value
Bits 15:0 WUT[15:0]: Wakeup auto-reload value bits
When the wakeup timer is enabled (WUTE set to 1), the WUTF flag is set every (WUT[15:0]
+ 1) ck_wut cycles. The ck_wut period is selected through WUCKSEL[2:0] bits of the
RTC_CR register
When WUCKSEL[2] = 1, the wakeup timer becomes 17-bits and WUCKSEL[1] effectively
becomes WUT[16] the most-significant bit to be reloaded into the timer.
The first assertion of WUTF occurs (WUT+1) ck_wut cycles after WUTE is set. Setting
WUT[15:0] to 0x0000 with WUCKSEL[2:0] =011 (RTCCLK/2) is forbidden.

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RM0091

RTC alarm A register (RTC_ALRMAR)
This register can be written only when ALRAWF is set to 1 in RTC_ISR, or in initialization
mode.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x1C
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

MSK4

WDSEL

29

28

27

DT[1:0]

26

25

24

DU[3:0]

23

22

MSK3

PM

21

20

19

18

HT[1:0]

17

16

HU[3:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

MSK2
rw

MNT[2:0]
rw

rw

MNU[3:0]
rw

rw

rw

MSK1

rw

rw

rw

ST[2:0]
rw

rw

Bit 31 MSK4: Alarm A date mask
0: Alarm A set if the date/day match
1: Date/day don’t care in Alarm A comparison
Bit 30 WDSEL: Week day selection
0: DU[3:0] represents the date units
1: DU[3:0] represents the week day. DT[1:0] is don’t care.
Bits 29:28 DT[1:0]: Date tens in BCD format.
Bits 27:24 DU[3:0]: Date units or day in BCD format.
Bit 23 MSK3: Alarm A hours mask
0: Alarm A set if the hours match
1: Hours don’t care in Alarm A comparison
Bit 22 PM: AM/PM notation
0: AM or 24-hour format
1: PM
Bits 21:20 HT[1:0]: Hour tens in BCD format.
Bits 19:16 HU[3:0]: Hour units in BCD format.
Bit 15 MSK2: Alarm A minutes mask
0: Alarm A set if the minutes match
1: Minutes don’t care in Alarm A comparison
Bits 14:12 MNT[2:0]: Minute tens in BCD format.
Bits 11:8 MNU[3:0]: Minute units in BCD format.
Bit 7 MSK1: Alarm A seconds mask
0: Alarm A set if the seconds match
1: Seconds don’t care in Alarm A comparison
Bits 6:4 ST[2:0]: Second tens in BCD format.
Bits 3:0 SU[3:0]: Second units in BCD format.

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SU[3:0]
rw

rw

rw

RM0091

Real-time clock (RTC)

25.7.8

RTC write protection register (RTC_WPR)
Address offset: 0x24
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

3

2

1

0

w

w

w

w

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

KEY
w

w

w

w

Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 KEY: Write protection key
This byte is written by software.
Reading this byte always returns 0x00.
Refer to RTC register write protection for a description of how to unlock RTC register write
protection.

25.7.9

RTC sub second register (RTC_SSR)
Address offset: 0x28
RTC domain reset value: 0x0000 0000
System reset: 0x0000 0000 when BYPSHAD = 0. Not affected when BYPSHAD = 1.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

SS[15:0]
r

r

r

r

r

r

r

r

r

Bits31:16 Reserved, must be kept at reset value
Bits 15:0 SS: Sub second value
SS[15:0] is the value in the synchronous prescaler counter. The fraction of a second is given by
the formula below:
Second fraction = (PREDIV_S - SS) / (PREDIV_S + 1)
Note: SS can be larger than PREDIV_S only after a shift operation. In that case, the correct
time/date is one second less than as indicated by RTC_TR/RTC_DR.

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Real-time clock (RTC)

25.7.10

RM0091

RTC shift control register (RTC_SHIFTR)
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x2C
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

ADD1S

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

w

w

w

w

w

w

w

w
15
Res.

SUBFS[14:0]
w

w

w

w

w

w

w

w

Bit 31 ADD1S: Add one second
0: No effect
1: Add one second to the clock/calendar
This bit is write only and is always read as zero. Writing to this bit has no effect when a shift
operation is pending (when SHPF=1, in RTC_ISR).
This function is intended to be used with SUBFS (see description below) in order to effectively
add a fraction of a second to the clock in an atomic operation.
Bits 30:15 Reserved, must be kept at reset value
Bits 14:0 SUBFS: Subtract a fraction of a second
These bits are write only and is always read as zero. Writing to this bit has no effect when a
shift operation is pending (when SHPF=1, in RTC_ISR).
The value which is written to SUBFS is added to the synchronous prescaler counter. Since this
counter counts down, this operation effectively subtracts from (delays) the clock by:
Delay (seconds) = SUBFS / (PREDIV_S + 1)
A fraction of a second can effectively be added to the clock (advancing the clock) when the
ADD1S function is used in conjunction with SUBFS, effectively advancing the clock by:
Advance (seconds) = (1 - (SUBFS / (PREDIV_S + 1))).
Note: Writing to SUBFS causes RSF to be cleared. Software can then wait until RSF=1 to be
sure that the shadow registers have been updated with the shifted time.

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Real-time clock (RTC)

25.7.11

RTC timestamp time register (RTC_TSTR)
The content of this register is valid only when TSF is set to 1 in RTC_ISR. It is cleared when
TSF bit is reset.
Address offset: 0x30
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PM
r

15

14

Res.

13

12

11

MNT[2:0]
r

r

10

9

8

MNU[3:0]
r

r

r

r

7

6

Res.
r

21

20

19

18

HT[1:0]
r

r

r

r

5

4

3

2

ST[2:0]
r

r

17

16

HU[3:0]
r

r

1

0

r

r

SU[3:0]
r

r

r

Bits 31:23 Reserved, must be kept at reset value
Bit 22 PM: AM/PM notation
0: AM or 24-hour format
1: PM
Bits 21:20 HT[1:0]: Hour tens in BCD format.
Bits 19:16 HU[3:0]: Hour units in BCD format.
Bit 15 Reserved, must be kept at reset value
Bits 14:12 MNT[2:0]: Minute tens in BCD format.
Bits 11:8 MNU[3:0]: Minute units in BCD format.
Bit 7 Reserved, must be kept at reset value
Bits 6:4 ST[2:0]: Second tens in BCD format.
Bits 3:0 SU[3:0]: Second units in BCD format.

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Real-time clock (RTC)

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RM0091

RTC timestamp date register (RTC_TSDR)
The content of this register is valid only when TSF is set to 1 in RTC_ISR. It is cleared when
TSF bit is reset.
Address offset: 0x34
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

r

r

15

WDU[1:0]
r

r

MT
r

r

MU[3:0]
r

r

r

r

Bits 31:16 Reserved, must be kept at reset value
Bits 15:13 WDU[1:0]: Week day units
Bit 12 MT: Month tens in BCD format
Bits 11:8 MU[3:0]: Month units in BCD format
Bits 7:6 Reserved, must be kept at reset value
Bits 5:4 DT[1:0]: Date tens in BCD format
Bits 3:0 DU[3:0]: Date units in BCD format

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r

DU[3:0]
r

r

r

RM0091

Real-time clock (RTC)

25.7.13

RTC time-stamp sub second register (RTC_TSSSR)
The content of this register is valid only when RTC_ISR/TSF is set. It is cleared when the
RTC_ISR/TSF bit is reset.
Address offset: 0x38
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

SS[15:0]
r

r

r

r

r

r

r

r

r

Bits 31:16 Reserved, must be kept at reset value
Bits 15:0 SS: Sub second value
SS[15:0] is the value of the synchronous prescaler counter when the timestamp event
occurred.

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Real-time clock (RTC)

25.7.14

RM0091

RTC calibration register (RTC_CALR)
This register is write protected. The write access procedure is described in RTC register
write protection on page 584.
Address offset: 0x3C
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

CALP

CALW8

CALW
16

Res.

Res.

Res.

Res.

rw

rw

rw

rw

rw

rw

rw

CALM[8:0]
rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value
Bit 15 CALP: Increase frequency of RTC by 488.5 ppm
0: No RTCCLK pulses are added.
1: One RTCCLK pulse is effectively inserted every 211 pulses (frequency increased by
488.5 ppm).
This feature is intended to be used in conjunction with CALM, which lowers the frequency of
the calendar with a fine resolution. if the input frequency is 32768 Hz, the number of RTCCLK
pulses added during a 32-second window is calculated as follows: (512 * CALP) - CALM.
Refer to Section 25.4.12: RTC smooth digital calibration.
Bit 14 CALW8: Use an 8-second calibration cycle period
When CALW8 is set to ‘1’, the 8-second calibration cycle period is selected.
Note: CALM[1:0] are stuck at “00” when CALW8=’1’. Refer to Section 25.4.12: RTC smooth
digital calibration.
Bit 13 CALW16: Use a 16-second calibration cycle period
When CALW16 is set to ‘1’, the 16-second calibration cycle period is selected.This bit must
not be set to ‘1’ if CALW8=1.
Note: CALM[0] is stuck at ‘0’ when CALW16=’1’. Refer to Section 25.4.12: RTC smooth
digital calibration.
Bits 12:9 Reserved, must be kept at reset value
Bits 8:0 CALM[8:0]: Calibration minus
The frequency of the calendar is reduced by masking CALM out of 220 RTCCLK pulses (32
seconds if the input frequency is 32768 Hz). This decreases the frequency of the calendar
with a resolution of 0.9537 ppm.
To increase the frequency of the calendar, this feature should be used in conjunction with
CALP. See Section 25.4.12: RTC smooth digital calibration on page 588.

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RM0091

Real-time clock (RTC)

25.7.15

RTC tamper and alternate function configuration register
(RTC_TAFCR)
Address offset: 0x40
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

TAMPP
UDIS
rw

TAMPPRCH
[1:0]
rw

rw

TAMPFLT[1:0]
rw

rw

TAMPFREQ[2:0]
rw

rw

rw

23

22

21

20

19

PC15 PC15 PC14 PC14 PC13
MODE VALUE MODE VALUE MODE

18

17

16

PC13
VALUE

Res.

Res.

1

0

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

TAMPT TAMP3 TAMP3 TAMP2 TAMP2
S
TRG
E
TRG
E
rw

rw

rw

rw

rw

TAMPIE
rw

TAMP1 TAMP1
TRG
E
rw

rw

Bits 31:24 Reserved, must be kept at reset value.
Bit 23 PC15MODE: PC15 mode
0: PC15 is controlled by the GPIO configuration registers. Consequently PC15 is floating in
Standby mode.
1: PC15 is forced to push-pull output if LSE is disabled.
Bit 22 PC15VALUE: PC15 value
If the LSE is disabled and PC15MODE = 1, PC15VALUE configures the PC15 output data.
Bit 21 PC14MODE: PC14 mode
0: PC14 is controlled by the GPIO configuration registers. Consequently PC14 is floating in
Standby mode.
1: PC14 is forced to push-pull output if LSE is disabled.
Bit 20 PC14VALUE: PC14 value
If the LSE is disabled and PC14MODE = 1, PC14VALUE configures the PC14 output data.
Bit 19 PC13MODE: PC13 mode
0: PC13 is controlled by the GPIO configuration registers. Consequently PC13 is floating in
Standby mode.
1: PC13 is forced to push-pull output if all RTC alternate functions are disabled.
Bit 18 PC13VALUE: RTC_ALARM output type/PC13 value
If PC13 is used to output RTC_ALARM, PC13VALUE configures the output configuration:
0: RTC_ALARM is an open-drain output
1: RTC_ALARM is a push-pull output
If all RTC alternate functions are disabled and PC13MODE = 1, PC13VALUE configures the
PC13 output data.
Bits 17:16 Reserved, must be kept at reset value.
Bit 15 TAMPPUDIS: RTC_TAMPx pull-up disable
This bit determines if each of the RTC_TAMPx pins are pre-charged before each sample.
0: Precharge RTC_TAMPx pins before sampling (enable internal pull-up)
1: Disable precharge of RTC_TAMPx pins.

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Bits 14:13 TAMPPRCH[1:0]: RTC_TAMPx precharge duration
These bit determines the duration of time during which the pull-up/is activated before each
sample. TAMPPRCH is valid for each of the RTC_TAMPx inputs.
0x0: 1 RTCCLK cycle
0x1: 2 RTCCLK cycles
0x2: 4 RTCCLK cycles
0x3: 8 RTCCLK cycles
Bits 12:11 TAMPFLT[1:0]: RTC_TAMPx filter count
These bits determines the number of consecutive samples at the specified level (TAMP*TRG)
needed to activate a Tamper event. TAMPFLT is valid for each of the RTC_TAMPx inputs.
0x0: Tamper event is activated on edge of RTC_TAMPx input transitions to the active level
(no internal pull-up on RTC_TAMPx input).
0x1: Tamper event is activated after 2 consecutive samples at the active level.
0x2: Tamper event is activated after 4 consecutive samples at the active level.
0x3: Tamper event is activated after 8 consecutive samples at the active level.
Bits 10:8 TAMPFREQ[2:0]: Tamper sampling frequency
Determines the frequency at which each of the RTC_TAMPx inputs are sampled.
0x0: RTCCLK / 32768 (1 Hz when RTCCLK = 32768 Hz)
0x1: RTCCLK / 16384 (2 Hz when RTCCLK = 32768 Hz)
0x2: RTCCLK / 8192 (4 Hz when RTCCLK = 32768 Hz)
0x3: RTCCLK / 4096 (8 Hz when RTCCLK = 32768 Hz)
0x4: RTCCLK / 2048 (16 Hz when RTCCLK = 32768 Hz)
0x5: RTCCLK / 1024 (32 Hz when RTCCLK = 32768 Hz)
0x6: RTCCLK / 512 (64 Hz when RTCCLK = 32768 Hz)
0x7: RTCCLK / 256 (128 Hz when RTCCLK = 32768 Hz)
Bit 7 TAMPTS: Activate timestamp on tamper detection event
0: Tamper detection event does not cause a timestamp to be saved
1: Save timestamp on tamper detection event
TAMPTS is valid even if TSE=0 in the RTC_CR register.
Bit 6 TAMP3TRG: Active level for RTC_TAMP3 input
if TAMPFLT != 00:
0: RTC_TAMP3 input staying low triggers a tamper detection event.
1: RTC_TAMP3 input staying high triggers a tamper detection event.
if TAMPFLT = 00:
0: RTC_TAMP3 input rising edge triggers a tamper detection event.
1: RTC_TAMP3input falling edge triggers a tamper detection event.
Bit 5 TAMP3E: RTC_TAMP3 detection enable
0: RTC_TAMP3 input detection disabled
1: RTC_TAMP3 input detection enabled
Bit 4 TAMP2TRG: Active level for RTC_TAMP2 input
if TAMPFLT != 00:
0: RTC_TAMP2 input staying low triggers a tamper detection event.
1: RTC_TAMP2 input staying high triggers a tamper detection event.
if TAMPFLT = 00:
0: RTC_TAMP2 input rising edge triggers a tamper detection event.
1: RTC_TAMP2 input falling edge triggers a tamper detection event.

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RM0091

Real-time clock (RTC)

Bit 3 TAMP2E: RTC_TAMP2 input detection enable
0: RTC_TAMP2 detection disabled
1: RTC_TAMP2 detection enabled
Bit 2 TAMPIE: Tamper interrupt enable
0: Tamper interrupt disabled
1: Tamper interrupt enabled.
Bit 1 TAMP1TRG: Active level for RTC_TAMP1 input
If TAMPFLT != 00
0: RTC_TAMP1 input staying low triggers a tamper detection event.
1: RTC_TAMP1 input staying high triggers a tamper detection event.
if TAMPFLT = 00:
0: RTC_TAMP1 input rising edge triggers a tamper detection event.
1: RTC_TAMP1 input falling edge triggers a tamper detection event.
Bit 0 TAMP1E: RTC_TAMP1 input detection enable
0: RTC_TAMP1 detection disabled
1: RTC_TAMP1 detection enabled

Caution:

When TAMPFLT = 0, TAMPxE must be reset when TAMPxTRG is changed to avoid
spuriously setting TAMPxF.

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25.7.16

RM0091

RTC alarm A sub second register (RTC_ALRMASSR)
This register can be written only when ALRAE is reset in RTC_CR register, or in initialization
mode.
This register is write protected. The write access procedure is described in RTC register
write protection on page 584
Address offset: 0x44
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

Res.

Res.

Res.

Res.

27

26

25

24

rw

rw

rw

rw

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

MASKSS[3:0]

Res.

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

3

2

1

0

rw

rw

rw

rw

w

rw

rw

SS[14:0]
rw

Bits 31:28 Reserved, must be kept at reset value.
Bits 27:24 MASKSS[3:0]: Mask the most-significant bits starting at this bit
0: No comparison on sub seconds for Alarm A. The alarm is set when the seconds unit is
incremented (assuming that the rest of the fields match).
1: SS[14:1] are don’t care in Alarm A comparison. Only SS[0] is compared.
2: SS[14:2] are don’t care in Alarm A comparison. Only SS[1:0] are compared.
3: SS[14:3] are don’t care in Alarm A comparison. Only SS[2:0] are compared.
...
12: SS[14:12] are don’t care in Alarm A comparison. SS[11:0] are compared.
13: SS[14:13] are don’t care in Alarm A comparison. SS[12:0] are compared.
14: SS[14] is don’t care in Alarm A comparison. SS[13:0] are compared.
15: All 15 SS bits are compared and must match to activate alarm.
The overflow bits of the synchronous counter (bits 15) is never compared. This bit can be
different from 0 only after a shift operation.
Bits23:15 Reserved, must be kept at reset value.
Bits 14:0 SS[14:0]: Sub seconds value
This value is compared with the contents of the synchronous prescaler counter to determine if
Alarm A is to be activated. Only bits 0 up MASKSS-1 are compared.

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Real-time clock (RTC)

25.7.17

RTC backup registers (RTC_BKPxR)
Address offset: 0x50 to 0x60
RTC domain reset value: 0x0000 0000
System reset: not affected

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

BKP[31:16]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

w

rw

rw

BKP[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:0 BKP[31:0]
The application can write or read data to and from these registers.
They are powered-on by VBAT when VDD is switched off, so that they are not reset by
System reset, and their contents remain valid when the device operates in low-power mode.
This register is reset on a tamper detection event, as long as TAMPxF=1.

25.7.18

RTC register map

1

1

1

1

1

1

1

0

0

1

0

0

Res.

WUCKS
EL[2:0]

ALRAWF

Res.

Res.

Res.
INIT

0

INITF

0

ALRAF

TSEDGE

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

0

0

0

0

0

0

0

1

1

1

1

1

1

1

1

1

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

RTC_WPR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

MNT[2:0]

1
MSK1

PM

0

MSK2

MSK3

0

Res.

1

Res.

1

Res.

1

Res.

1

MSK4

1

WDSEL

1

Res.

1

0

HU[3:0]

1

MNU[3:0]

0

1

ST[2:0]
0

0

0

SU[3:0]
0

0

0

0

0

0

0

KEY
0

DocID018940 Rev 9

1

WUT[15:0]

Reset value

HT
[1:0]

0

0

0

RTC_ALRMAR

DU[3:0]

0

PREDIV_S[14:0]

1
DT
[1:0]

DU[3:0]

0

0

0

SHPF

0

0

WUT WF

0

0

BYPSHAD

0

0

REFCKON

0

0

0

DT
[1:0]

RSF

0

0

SU[3:0]

FMT

0

1

Res.

0

0

ALRAE

WUTE

0

Res.

0

0

Res.

MT

MU[3:0]

PREDIV_A[6:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0x24

0

0

WUTF

.TAMP2F
0

0

TSE

0

0

TSF

0

1
Res.

0

0

ALRAIE

TSIE

WUTIE

0

Reset value

0x1C

0

ST[2:0]

INITS

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

RTC_WUTR

Res.

Reset value
0x14

Res.
ADD1H

0

0
Res.

RTC_PRER

0

TAMP3F

0

0

RECALPF

0

0

BKP

0

0
SUB1H

POL

COSEL

0

0

WDU[2:0]

0

Reset value
0x10

0

MNU[3:0]

TSOVF

0

Res.

0

Res.

OSE
L
[1:0]

0

Res.

0

Res.

COE

0

0

MNT[2:0]

TAMP1F

0

YU[3:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_ISR

Res.

0x0C

Res.

Reset value

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0x08

RTC_CR

0

HU[3:0]

YT[3:0]
0

Res.

Reset value

HT
[1:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_DR

Res.

0x04

0
Res.

Reset value

PM

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_TR

Res.

0x00

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 85. RTC register map and reset values

0

0

0

0

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Real-time clock (RTC)

RM0091

Res.

0

Res.

Res.

Res.

Res.

WDU[1:0]

Reset value

0

0

0x50
to 0x60

Reset value

MT

0

Res.

MU[3:0]

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

ST[2:0]
0

0

0

0

SU[3:0]
0

DT
[1:0]

0

0

0

DU[3:0]

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

TAMP1E

Res.

TAMPFLT[1:0]
0

0

TAMPIE

Res.

0

TAMP1TRG

Res.

0

CALM[8:0]

TAMP2E

Res.

0

0

TAMP3E

CALW8

CALW16

0

0

TAMP2TRG

CALP
0

0

TAMPTS

0

TAMP3TRG

0

0

0

0

0

0

0

0

0

SS[14:0]
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

BKP[31:0]
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

BKP[31:0]
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

616/1004

0

0

0

TAMPPRCH[1:0]

Res.

0

Res.

Res.

Res.

PC13VALUE

Res.

Res.

PC13VALUE

Res.

Res.

PC14MODE

Res.

0

0

0

to
RTC_BKP4R
Reset value

0

0

0

RTC_BKP0R

0

0

0

0
Res.

PC14VALUE

0

0

SS[15:0]

TAMPPUDIS

Res.

Res.

Res.

Res.

Res.

PC15MODE

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.
Res.

PC15MODE

0

Res.

Res.

Res.

Res.
0

0

0

Res.

0

0

0

Res.

0

0

0

MNT[2:0]

Res.

HT[1:0]

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

Res.

MASKSS
[3:0]

Res.

Res.

RTC_
ALRMASSR

Res.

0x44

Res.

Reset value

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

PM

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.
Res.

Res.

RTC_TAFCR

0

MNU[3:0]

0

Reset value

0x40

0

0

0
Res.

RTC_ CALR

0

0

Reset value

0x3C

0

SUBFS[14:0]

0

0
Res.

RTC_TSSSR

0

Res.

Res.

Res.

Res.

Res.

HU[3:0]

Reset value
0x38

0

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

Res.

Res.

RTC_TSDR

Res.

Reset value
0x34

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_TSTR

0x30

0

0
Res.

0
Res.

ADD1S

Reset value

Res.

RTC_SHIFTR

Res.

0x2C

0

Res.

Reset value

SS[15:0]

TAMPFREQ[2:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RTC_SSR

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

0x28

Register

Res.

Offset

Res.

Table 85. RTC register map and reset values (continued)

DocID018940 Rev 9

RM0091

Inter-integrated circuit (I2C) interface

26

Inter-integrated circuit (I2C) interface

26.1

Introduction
The I2C (inter-integrated circuit) bus interface handles communications between the
microcontroller and the serial I2C bus. It provides multimaster capability, and controls all I2C
bus-specific sequencing, protocol, arbitration and timing. It supports Standard-mode (Sm),
Fast-mode (Fm) and Fast-mode Plus (Fm+).
It is also SMBus (system management bus) and PMBus (power management bus)
compatible.
DMA can be used to reduce CPU overload.

26.2

I2C main features
•

I2C bus specification rev03 compatibility:
–

Slave and master modes

–

Multimaster capability

–

Standard-mode (up to 100 kHz)

–

Fast-mode (up to 400 kHz)

–

Fast-mode Plus (up to 1 MHz)

–

7-bit and 10-bit addressing mode

–

Multiple 7-bit slave addresses (2 addresses, 1 with configurable mask)

–

All 7-bit addresses acknowledge mode

–

General call

–

Programmable setup and hold times

–

Easy to use event management

–

Optional clock stretching

–

Software reset

•

1-byte buffer with DMA capability

•

Programmable analog and digital noise filters

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RM0091

The following additional features are also available depending on the product
implementation (see Section 26.3: I2C implementation):
•

SMBus specification rev 2.0 compatibility:
–

26.3

Hardware PEC (Packet Error Checking) generation and verification with ACK
control

–

Command and data acknowledge control

–

Address resolution protocol (ARP) support

–

Host and Device support

–

SMBus alert

–

Timeouts and idle condition detection

•

PMBus rev 1.1 standard compatibility

•

Independent clock: a choice of independent clock sources allowing the I2C
communication speed to be independent from the PCLK reprogramming

•

Wakeup from Stop mode on address match.

I2C implementation
This manual describes the full set of features implemented in I2C1 I2C2 supports a smaller
set of features, but is otherwise identical to I2C1. The differences are listed below.
Table 86. STM32F0xx I2C implementation
I2C

features(1)

STM32F03x
STM32F04x

STM32F07x
STM32F09x

STM32F05x

I2C1

I2C1

I2C2

I2C1

I2C2

7-bit addressing mode

X

X

X

X

X

10-bit addressing mode

X

X

X

X

X

Standard mode (up to 100 kbit/s)

X

X

X

X

X

Fast mode (up to 400 kbit/s)

X

X

X

X

X

Independent clock

X

X

-

X

-

SMBus

X

X

-

X

-

Wakeup from Stop mode

X

X

-

X

-

Fast Mode Plus with extra output
drive I/Os (up to 1 Mbit/s)

X

X

-

X

X

1. X = supported.

26.4

I2C functional description
In addition to receiving and transmitting data, this interface converts it from serial to parallel
format and vice versa. The interrupts are enabled or disabled by software. The interface is
connected to the I2C bus by a data pin (SDA) and by a clock pin (SCL). It can be connected
with a standard (up to 100 kHz), Fast-mode (up to 400 kHz) or Fast-mode Plus (up to
1 MHz) I2C bus.

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RM0091

Inter-integrated circuit (I2C) interface
This interface can also be connected to a SMBus with the data pin (SDA) and clock pin
(SCL).
If SMBus feature is supported: the additional optional SMBus Alert pin (SMBA) is also
available.

26.4.1

I2C1 block diagram
The block diagram of the I2C1 interface is shown in Figure 213.
Figure 213. I2C1 block diagram

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The I2C1 is clocked by an independent clock source which allows to the I2C to operate
independently from the PCLK frequency.
This independent clock source can be selected for either of the following two clock sources:
•

HSI: high speed internal oscillator (default value)

•

SYSCLK: system clock

DocID018940 Rev 9

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686

Inter-integrated circuit (I2C) interface

RM0091

Refer to Section 6: Reset and clock control (RCC) for more details.
I2C1 I/Os support 20 mA output current drive for Fast-mode Plus operation. This is enabled
by setting the driving capability control bits for SCL and SDA in Section 9.1.1: SYSCFG
configuration register 1 (SYSCFG_CFGR1)

26.4.2

I2C2 block diagram
The block diagram of the I2C2 interface is shown in Figure 214.
Figure 214. I2C2 block diagram

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26.4.3

I2C clock requirements
The I2C kernel is clocked by I2CCLK.
The I2CCLK period tI2CCLK must respect the following conditions:
tI2CCLK < (tLOW - tfilters ) / 4 and tI2CCLK < tHIGH
with:
tLOW: SCL low time and tHIGH : SCL high time
tfilters: when enabled, sum of the delays brought by the analog filter and by the digital filter.
Analog filter delay is maximum 260 ns. Digital filter delay is DNF x tI2CCLK.
The PCLK clock period tPCLK must respect the following condition:
tPCLK < 4/3 tSCL

620/1004

DocID018940 Rev 9

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Inter-integrated circuit (I2C) interface
with tSCL: SCL period

Caution:

When the I2C kernel is clocked by PCLK. PCLK must respect the conditions for tI2CCLK.

26.4.4

Mode selection
The interface can operate in one of the four following modes:
•

Slave transmitter

•

Slave receiver

•

Master transmitter

•

Master receiver

By default, it operates in slave mode. The interface automatically switches from slave to
master when it generates a START condition, and from master to slave if an arbitration loss
or a STOP generation occurs, allowing multimaster capability.

Communication flow
In Master mode, the I2C interface initiates a data transfer and generates the clock signal. A
serial data transfer always begins with a START condition and ends with a STOP condition.
Both START and STOP conditions are generated in master mode by software.
In Slave mode, the interface is capable of recognizing its own addresses (7 or 10-bit), and
the General Call address. The General Call address detection can be enabled or disabled
by software. The reserved SMBus addresses can also be enabled by software.
Data and addresses are transferred as 8-bit bytes, MSB first. The first byte(s) following the
START condition contain the address (one in 7-bit mode, two in 10-bit mode). The address
is always transmitted in Master mode.
A 9th clock pulse follows the 8 clock cycles of a byte transfer, during which the receiver must
send an acknowledge bit to the transmitter. Refer to the following figure.
Figure 215. I2C bus protocol

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Acknowledge can be enabled or disabled by software. The I2C interface addresses can be
selected by software.

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26.4.5

RM0091

I2C initialization
Enabling and disabling the peripheral
The I2C peripheral clock must be configured and enabled in the clock controller (refer to
Section 6: Reset and clock control (RCC)).
Then the I2C can be enabled by setting the PE bit in the I2C_CR1 register.
When the I2C is disabled (PE=0), the I2C performs a software reset. Refer to
Section 26.4.6: Software reset for more details.

Noise filters
Before enabling the I2C peripheral by setting the PE bit in I2C_CR1 register, the user must
configure the noise filters, if needed. By default, an analog noise filter is present on the SDA
and SCL inputs. This analog filter is compliant with the I2C specification which requires the
suppression of spikes with a pulse width up to 50 ns in Fast-mode and Fast-mode Plus. The
user can disable this analog filter by setting the ANFOFF bit, and/or select a digital filter by
configuring the DNF[3:0] bit in the I2C_CR1 register.
When the digital filter is enabled, the level of the SCL or the SDA line is internally changed
only if it remains stable for more than DNF x I2CCLK periods. This allows to suppress
spikes with a programmable length of 1 to 15 I2CCLK periods.
Table 87. Comparison of analog vs. digital filters

Pulse width of
suppressed spikes
Benefits

Drawbacks

Caution:

622/1004

Analog filter

Digital filter

≥ 50 ns

Programmable length from 1 to 15 I2C peripheral
clocks

Available in Stop mode

– Programmable length: extra filtering capability
vs. standard requirements
– Stable length

Variation vs. temperature,
voltage, process

Wakeup from Stop mode on address match is not
available when digital filter is enabled

Changing the filter configuration is not allowed when the I2C is enabled.

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Inter-integrated circuit (I2C) interface

I2C timings
The timings must be configured in order to guarantee a correct data hold and setup time,
used in master and slave modes. This is done by programming the PRESC[3:0],
SCLDEL[3:0] and SDADEL[3:0] bits in the I2C_TIMINGR register.
The STM32CubeMX tool calculates and provides the I2C_TIMINGR content in the I2C
configuration window
Figure 216. Setup and hold timings
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•

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When the SCL falling edge is internally detected, a delay is inserted before sending
SDA output. This delay is tSDADEL = SDADEL x tPRESC + tI2CCLK where tPRESC = (PRESC+1)
x tI2CCLK.
TSDADEL impacts the hold time tHD;DAT.

The total SDA output delay is:
tSYNC1 + {[SDADEL x (PRESC+1) + 1] x tI2CCLK }
tSYNC1 duration depends on these parameters:

–

SCL falling slope

–

When enabled, input delay brought by the analog filter: tAF(min) < tAF < tAF(max) ns.

–

When enabled, input delay brought by the digital filter: tDNF = DNF x tI2CCLK

–

Delay due to SCL synchronization to I2CCLK clock (2 to 3 I2CCLK periods)

In order to bridge the undefined region of the SCL falling edge, the user must program
SDADEL in such a way that:
{tf (max) +tHD;DAT (min) -tAF(min) - [(DNF +3) x tI2CCLK]} / {(PRESC +1) x tI2CCLK } ≤ SDADEL
SDADEL ≤ {tHD;DAT (max) -tAF(max) - [(DNF+4) x tI2CCLK]} / {(PRESC +1) x tI2CCLK }
Note:

tAF(min) / tAF(max) are part of the equation only when the analog filter is enabled. Refer to
device datasheet for tAF values.
The maximum tHD;DAT could be 3.45 µs, 0.9 µs and 0.45 µs for Standard-mode, Fast-mode
and Fast-mode Plus, but must be less than the maximum of tVD;DAT by a transition time.
This maximum must only be met if the device does not stretch the LOW period (tLOW) of the
SCL signal. If the clock stretches the SCL, the data must be valid by the set-up time before
it releases the clock.
The SDA rising edge is usually the worst case, so in this case the previous equation
becomes:
SDADEL ≤ {tVD;DAT (max) -tr (max) -260 ns - [(DNF+4) x tI2CCLK]} / {(PRESC +1) x tI2CCLK }.

Note:

This condition can be violated when NOSTRETCH=0, because the device stretches SCL
low to guarantee the set-up time, according to the SCLDEL value.
Refer to Table 88: I2C-SMBUS specification data setup and hold times for tf, tr, tHD;DAT and
tVD;DAT standard values.
•

After tSDADEL delay, or after sending SDA output in case the slave had to stretch the
clock because the data was not yet written in I2C_TXDR register, SCL line is kept at
low level during the setup time. This setup time is tSCLDEL = (SCLDEL+1) x tPRESC where
tPRESC = (PRESC+1) x tI2CCLK.
tSCLDEL impacts the setup time tSU;DAT .

In order to bridge the undefined region of the SDA transition (rising edge usually worst
case), the user must program SCLDEL in such a way that:
{[tr (max) + tSU;DAT (min)] / [(PRESC+1)] x tI2CCLK]} - 1 <= SCLDEL
Refer to Table 88: I2C-SMBUS specification data setup and hold times for tr and tSU;DAT
standard values.
The SDA and SCL transition time values to be used are the ones in the application. Using
the maximum values from the standard increases the constraints for the SDADEL and
SCLDEL calculation, but ensures the feature whatever the application.

624/1004

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Note:

Inter-integrated circuit (I2C) interface
At every clock pulse, after SCL falling edge detection, the I2C master or slave stretches SCL
low during at least [(SDADEL+SCLDEL+1) x (PRESC+1) + 1] x tI2CCLK, in both transmission
and reception modes. In transmission mode, in case the data is not yet written in I2C_TXDR
when SDADEL counter is finished, the I2C keeps on stretching SCL low until the next data
is written. Then new data MSB is sent on SDA output, and SCLDEL counter starts,
continuing stretching SCL low to guarantee the data setup time.
If NOSTRETCH=1 in slave mode, the SCL is not stretched. Consequently the SDADEL
must be programmed in such a way to guarantee also a sufficient setup time.
Table 88. I2C-SMBUS specification data setup and hold times

Symbol

Parameter

Standard-mode
(Sm)

Fast-mode
(Fm)

Fast-mode Plus
(Fm+)

SMBUS
Unit

Min.

Max

Min.

Max

Min.

Max

Min.

Max

tHD;DAT

Data hold time

0

-

0

-

0

-

0.3

-

tVD;DAT

Data valid time

-

3.45

-

0.9

-

0.45

-

-

tSU;DAT

Data setup time

250

-

100

-

50

-

250

-

µs

tr

Rise time of both SDA
and SCL signals

-

1000

-

300

-

120

-

1000

tf

Fall time of both SDA
and SCL signals

-

300

-

300

-

120

-

300

ns

Additionally, in master mode, the SCL clock high and low levels must be configured by
programming the PRESC[3:0], SCLH[7:0] and SCLL[7:0] bits in the I2C_TIMINGR register.
•

When the SCL falling edge is internally detected, a delay is inserted before releasing
the SCL output. This delay is tSCLL = (SCLL+1) x tPRESC where tPRESC = (PRESC+1) x
tI2CCLK.
tSCLL impacts the SCL low time tLOW .

•

When the SCL rising edge is internally detected, a delay is inserted before forcing the
SCL output to low level. This delay is tSCLH = (SCLH+1) x tPRESC where tPRESC =
(PRESC+1) x tI2CCLK. tSCLH impacts the SCL high time tHIGH .

Refer to I2C master initialization for more details.
Caution:

Changing the timing configuration is not allowed when the I2C is enabled.
The I2C slave NOSTRETCH mode must also be configured before enabling the peripheral.
Refer to I2C slave initialization for more details.

Caution:

Changing the NOSTRETCH configuration is not allowed when the I2C is enabled.

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Figure 217. I2C initialization flowchart

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26.4.6

Software reset
A software reset can be performed by clearing the PE bit in the I2C_CR1 register. In that
case I2C lines SCL and SDA are released. Internal states machines are reset and
communication control bits, as well as status bits come back to their reset value. The
configuration registers are not impacted.
Here is the list of impacted register bits:
1.

I2C_CR2 register: START, STOP, NACK

2.

I2C_ISR register: BUSY, TXE, TXIS, RXNE, ADDR, NACKF, TCR, TC, STOPF, BERR,
ARLO, OVR

and in addition when the SMBus feature is supported:
1.

I2C_CR2 register: PECBYTE

2.

I2C_ISR register: PECERR, TIMEOUT, ALERT

PE must be kept low during at least 3 APB clock cycles in order to perform the software
reset. This is ensured by writing the following software sequence: - Write PE=0 - Check
PE=0 - Write PE=1.

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26.4.7

Inter-integrated circuit (I2C) interface

Data transfer
The data transfer is managed through transmit and receive data registers and a shift
register.

Reception
The SDA input fills the shift register. After the 8th SCL pulse (when the complete data byte is
received), the shift register is copied into I2C_RXDR register if it is empty (RXNE=0). If
RXNE=1, meaning that the previous received data byte has not yet been read, the SCL line
is stretched low until I2C_RXDR is read. The stretch is inserted between the 8th and 9th
SCL pulse (before the Acknowledge pulse).
Figure 218. Data reception

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Transmission
If the I2C_TXDR register is not empty (TXE=0), its content is copied into the shift register
after the 9th SCL pulse (the Acknowledge pulse). Then the shift register content is shifted
out on SDA line. If TXE=1, meaning that no data is written yet in I2C_TXDR, SCL line is
stretched low until I2C_TXDR is written. The stretch is done after the 9th SCL pulse.
Figure 219. Data transmission

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Hardware transfer management
The I2C has a byte counter embedded in hardware in order to manage byte transfer and to
close the communication in various modes such as:
–

NACK, STOP and ReSTART generation in master mode

–

ACK control in slave receiver mode

–

PEC generation/checking when SMBus feature is supported

The byte counter is always used in master mode. By default it is disabled in slave mode, but
it can be enabled by software by setting the SBC (Slave Byte Control) bit in the I2C_CR2
register.
The number of bytes to be transferred is programmed in the NBYTES[7:0] bit field in the
I2C_CR2 register. If the number of bytes to be transferred (NBYTES) is greater than 255, or
if a receiver wants to control the acknowledge value of a received data byte, the reload
mode must be selected by setting the RELOAD bit in the I2C_CR2 register. In this mode,
TCR flag is set when the number of bytes programmed in NBYTES has been transferred,
and an interrupt is generated if TCIE is set. SCL is stretched as long as TCR flag is set. TCR
is cleared by software when NBYTES is written to a non-zero value.
When the NBYTES counter is reloaded with the last number of bytes, RELOAD bit must be
cleared.

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Inter-integrated circuit (I2C) interface
When RELOAD=0 in master mode, the counter can be used in 2 modes:

Caution:

•

Automatic end mode (AUTOEND = ‘1’ in the I2C_CR2 register). In this mode, the
master automatically sends a STOP condition once the number of bytes programmed
in the NBYTES[7:0] bit field has been transferred.

•

Software end mode (AUTOEND = ‘0’ in the I2C_CR2 register). In this mode, software
action is expected once the number of bytes programmed in the NBYTES[7:0] bit field
has been transferred; the TC flag is set and an interrupt is generated if the TCIE bit is
set. The SCL signal is stretched as long as the TC flag is set. The TC flag is cleared by
software when the START or STOP bit is set in the I2C_CR2 register. This mode must
be used when the master wants to send a RESTART condition.

The AUTOEND bit has no effect when the RELOAD bit is set.
Table 89. I2C configuration table

26.4.8

Function

SBC bit

RELOAD bit

AUTOEND bit

Master Tx/Rx NBYTES + STOP

x

0

1

Master Tx/Rx + NBYTES + RESTART

x

0

0

Slave Tx/Rx
all received bytes ACKed

0

x

x

Slave Rx with ACK control

1

1

x

I2C slave mode
I2C slave initialization
In order to work in slave mode, the user must enable at least one slave address. Two
registers I2C_OAR1 and I2C_OAR2 are available in order to program the slave own
addresses OA1 and OA2.
•

OA1 can be configured either in 7-bit mode (by default) or in 10-bit addressing mode by
setting the OA1MODE bit in the I2C_OAR1 register.
OA1 is enabled by setting the OA1EN bit in the I2C_OAR1 register.

•

If additional slave addresses are required, the 2nd slave address OA2 can be
configured. Up to 7 OA2 LSB can be masked by configuring the OA2MSK[2:0] bits in
the I2C_OAR2 register. Therefore for OA2MSK configured from 1 to 6, only OA2[7:2],
OA2[7:3], OA2[7:4], OA2[7:5], OA2[7:6] or OA2[7] are compared with the received
address. As soon as OA2MSK is not equal to 0, the address comparator for OA2
excludes the I2C reserved addresses (0000 XXX and 1111 XXX), which are not
acknowledged. If OA2MSK=7, all received 7-bit addresses are acknowledged (except
reserved addresses). OA2 is always a 7-bit address.
These reserved addresses can be acknowledged if they are enabled by the specific
enable bit, if they are programmed in the I2C_OAR1 or I2C_OAR2 register with
OA2MSK=0.
OA2 is enabled by setting the OA2EN bit in the I2C_OAR2 register.

•

The General Call address is enabled by setting the GCEN bit in the I2C_CR1 register.

When the I2C is selected by one of its enabled addresses, the ADDR interrupt status flag is
set, and an interrupt is generated if the ADDRIE bit is set.

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By default, the slave uses its clock stretching capability, which means that it stretches the
SCL signal at low level when needed, in order to perform software actions. If the master
does not support clock stretching, the I2C must be configured with NOSTRETCH=1 in the
I2C_CR1 register.
After receiving an ADDR interrupt, if several addresses are enabled the user must read the
ADDCODE[6:0] bits in the I2C_ISR register in order to check which address matched. DIR
flag must also be checked in order to know the transfer direction.

Slave clock stretching (NOSTRETCH = 0)
In default mode, the I2C slave stretches the SCL clock in the following situations:
•

When the ADDR flag is set: the received address matches with one of the enabled
slave addresses. This stretch is released when the ADDR flag is cleared by software
setting the ADDRCF bit.

•

In transmission, if the previous data transmission is completed and no new data is
written in I2C_TXDR register, or if the first data byte is not written when the ADDR flag
is cleared (TXE=1). This stretch is released when the data is written to the I2C_TXDR
register.

•

In reception when the I2C_RXDR register is not read yet and a new data reception is
completed. This stretch is released when I2C_RXDR is read.

•

When TCR = 1 in Slave Byte Control mode, reload mode (SBC=1 and RELOAD=1),
meaning that the last data byte has been transferred. This stretch is released when
then TCR is cleared by writing a non-zero value in the NBYTES[7:0] field.

•

After SCL falling edge detection, the I2C stretches SCL low during
[(SDADEL+SCLDEL+1) x (PRESC+1) + 1] x tI2CCLK.

Slave without clock stretching (NOSTRETCH = 1)
When NOSTRETCH = 1 in the I2C_CR1 register, the I2C slave does not stretch the SCL
signal.

630/1004

•

The SCL clock is not stretched while the ADDR flag is set.

•

In transmission, the data must be written in the I2C_TXDR register before the first SCL
pulse corresponding to its transfer occurs. If not, an underrun occurs, the OVR flag is
set in the I2C_ISR register and an interrupt is generated if the ERRIE bit is set in the
I2C_CR1 register. The OVR flag is also set when the first data transmission starts and
the STOPF bit is still set (has not been cleared). Therefore, if the user clears the
STOPF flag of the previous transfer only after writing the first data to be transmitted in
the next transfer, he ensures that the OVR status is provided, even for the first data to
be transmitted.

•

In reception, the data must be read from the I2C_RXDR register before the 9th SCL
pulse (ACK pulse) of the next data byte occurs. If not an overrun occurs, the OVR flag
is set in the I2C_ISR register and an interrupt is generated if the ERRIE bit is set in the
I2C_CR1 register.

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Inter-integrated circuit (I2C) interface

Slave Byte Control mode
In order to allow byte ACK control in slave reception mode, Slave Byte Control mode must
be enabled by setting the SBC bit in the I2C_CR1 register. This is required to be compliant
with SMBus standards.
Reload mode must be selected in order to allow byte ACK control in slave reception mode
(RELOAD=1). To get control of each byte, NBYTES must be initialized to 0x1 in the ADDR
interrupt subroutine, and reloaded to 0x1 after each received byte. When the byte is
received, the TCR bit is set, stretching the SCL signal low between the 8th and 9th SCL
pulses. The user can read the data from the I2C_RXDR register, and then decide to
acknowledge it or not by configuring the ACK bit in the I2C_CR2 register. The SCL stretch is
released by programming NBYTES to a non-zero value: the acknowledge or notacknowledge is sent and next byte can be received.
NBYTES can be loaded with a value greater than 0x1, and in this case, the reception flow is
continuous during NBYTES data reception.
Note:

The SBC bit must be configured when the I2C is disabled, or when the slave is not
addressed, or when ADDR=1.
The RELOAD bit value can be changed when ADDR=1, or when TCR=1.

Caution:

Slave Byte Control mode is not compatible with NOSTRETCH mode. Setting SBC when
NOSTRETCH=1 is not allowed.

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Figure 220. Slave initialization flowchart

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For code example refer to the Appendix section A.14.3: I2C configured in slave mode code
example.

Slave transmitter
A transmit interrupt status (TXIS) is generated when the I2C_TXDR register becomes
empty. An interrupt is generated if the TXIE bit is set in the I2C_CR1 register.
The TXIS bit is cleared when the I2C_TXDR register is written with the next data byte to be
transmitted.
When a NACK is received, the NACKF bit is set in the I2C_ISR register and an interrupt is
generated if the NACKIE bit is set in the I2C_CR1 register. The slave automatically releases
the SCL and SDA lines in order to let the master perform a STOP or a RESTART condition.
The TXIS bit is not set when a NACK is received.
When a STOP is received and the STOPIE bit is set in the I2C_CR1 register, the STOPF
flag is set in the I2C_ISR register and an interrupt is generated. In most applications, the
SBC bit is usually programmed to ‘0’. In this case, If TXE = 0 when the slave address is
received (ADDR=1), the user can choose either to send the content of the I2C_TXDR
register as the first data byte, or to flush the I2C_TXDR register by setting the TXE bit in
order to program a new data byte.

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Inter-integrated circuit (I2C) interface
In Slave Byte Control mode (SBC=1), the number of bytes to be transmitted must be
programmed in NBYTES in the address match interrupt subroutine (ADDR=1). In this case,
the number of TXIS events during the transfer corresponds to the value programmed in
NBYTES.

Caution:

When NOSTRETCH=1, the SCL clock is not stretched while the ADDR flag is set, so the
user cannot flush the I2C_TXDR register content in the ADDR subroutine, in order to
program the first data byte. The first data byte to be sent must be previously programmed in
the I2C_TXDR register:
•

This data can be the data written in the last TXIS event of the previous transmission
message.

•

If this data byte is not the one to be sent, the I2C_TXDR register can be flushed by
setting the TXE bit in order to program a new data byte. The STOPF bit must be
cleared only after these actions, in order to guarantee that they are executed before the
first data transmission starts, following the address acknowledge.
If STOPF is still set when the first data transmission starts, an underrun error will be
generated (the OVR flag is set).
If a TXIS event is needed, (Transmit Interrupt or Transmit DMA request), the user must
set the TXIS bit in addition to the TXE bit, in order to generate a TXIS event.
Figure 221. Transfer sequence flowchart for I2C slave transmitter, NOSTRETCH=0
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1. For details on coding USARTDIV in the USART_BRR register, please refer to Section 27.5.4: USART baud
rate generation.
2. fCK can be fLSE, fHSI, fPCLK, fSYS.

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Universal synchronous asynchronous receiver transmitter (USART)

27.5.1

RM0091

USART character description
The word length can be selected as being either 7 or 8 or 9 bits by programming the M[1:0]
bits in the USART_CR1 register (see Figure 246).

Note:

•

7-bit character length: M[1:0] = 10

•

8-bit character length: M[1:0] = 00

•

9-bit character length: M[1:0] = 01

In 7-bit data length mode, the Smartcard mode, LIN master mode and Autobaudrate (0x7F
and 0x55 frames detection) are not supported. 7-bit mode is supported only on some
USARTs.
By default, the signal (TX or RX) is in low state during the start bit. It is in high state during
the stop bit.
These values can be inverted, separately for each signal, through polarity configuration
control.
An Idle character is interpreted as an entire frame of “1”s (the number of “1”s includes the
number of stop bits).
A Break character is interpreted on receiving “0”s for a frame period. At the end of the
break frame, the transmitter inserts 2 stop bits.
Transmission and reception are driven by a common baud rate generator, the clock for each
is generated when the enable bit is set respectively for the transmitter and receiver.
The details of each block is given below.

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 246. Word length programming

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Universal synchronous asynchronous receiver transmitter (USART)

27.5.2

RM0091

USART transmitter
The transmitter can send data words of either 7, 8 or 9 bits depending on the M bits status.
The Transmit Enable bit (TE) must be set in order to activate the transmitter function. The
data in the transmit shift register is output on the TX pin and the corresponding clock pulses
are output on the CK pin.

Character transmission
During an USART transmission, data shifts out least significant bit first (default
configuration) on the TX pin. In this mode, the USART_TDR register consists of a buffer
(TDR) between the internal bus and the transmit shift register (see Figure 245).
Every character is preceded by a start bit which is a logic level low for one bit period. The
character is terminated by a configurable number of stop bits.
The following stop bits are supported by USART: 0.5, 1, 1.5 and 2 stop bits.
Note:

The TE bit must be set before writing the data to be transmitted to the USART_TDR.
The TE bit should not be reset during transmission of data. Resetting the TE bit during the
transmission will corrupt the data on the TX pin as the baud rate counters will get frozen.
The current data being transmitted will be lost.
An idle frame will be sent after the TE bit is enabled.
Configurable stop bits
The number of stop bits to be transmitted with every character can be programmed in
Control register 2, bits 13,12.
•

1 stop bit: This is the default value of number of stop bits.

•

2 stop bits: This will be supported by normal USART, Single-wire and Modem modes.

•

1.5 stop bits: To be used in Smartcard mode.

•

0.5 stop bit: To be used when receiving data in Smartcard mode.

An idle frame transmission will include the stop bits.
A break transmission will be 10 low bits (when M[1:0] = 00) or 11 low bits (when M[1:0] = 01)
or 9 low bits (when M[1:0] = 10) followed by 2 stop bits (see Figure 247). It is not possible to
transmit long breaks (break of length greater than 9/10/11 low bits).

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RM0091

Universal synchronous asynchronous receiver transmitter (USART)
Figure 247. Configurable stop bits
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Character transmission procedure
1.

Program the M bits in USART_CR1 to define the word length.

2.

Select the desired baud rate using the USART_BRR register.

3.

Program the number of stop bits in USART_CR2.

4.

Enable the USART by writing the UE bit in USART_CR1 register to 1.

5.

Select DMA enable (DMAT) in USART_CR3 if multibuffer communication is to take
place. Configure the DMA register as explained in multibuffer communication.

6.

Set the TE bit in USART_CR1 to send an idle frame as first transmission.

7.

Write the data to send in the USART_TDR register (this clears the TXE bit). Repeat this
for each data to be transmitted in case of single buffer.

8.

After writing the last data into the USART_TDR register, wait until TC=1. This indicates
that the transmission of the last frame is complete. This is required for instance when
the USART is disabled or enters the Halt mode to avoid corrupting the last
transmission.

For code example refer to Appendix section A.19.1: USART transmitter configuration code
example.

Single byte communication
Clearing the TXE bit is always performed by a write to the transmit data register.
The TXE bit is set by hardware and it indicates:
•

The data has been moved from the USART_TDR register to the shift register and the
data transmission has started.

•

The USART_TDR register is empty.

•

The next data can be written in the USART_TDR register without overwriting the
previous data.

For code example refer to the Appendix section A.19.2: USART transmit byte code
example.
This flag generates an interrupt if the TXEIE bit is set.

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RM0091

When a transmission is taking place, a write instruction to the USART_TDR register stores
the data in the TDR register; next, the data is copied in the shift register at the end of the
currently ongoing transmission.
When no transmission is taking place, a write instruction to the USART_TDR register places
the data in the shift register, the data transmission starts, and the TXE bit is set.
If a frame is transmitted (after the stop bit) and the TXE bit is set, the TC bit goes high. An
interrupt is generated if the TCIE bit is set in the USART_CR1 register.
After writing the last data in the USART_TDR register, it is mandatory to wait for TC=1
before disabling the USART or causing the microcontroller to enter the low-power mode
(see Figure 248: TC/TXE behavior when transmitting).
Figure 248. TC/TXE behavior when transmitting
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For code example refer to the Appendix section A.19.3: USART transfer complete code
example.

Break characters
Setting the SBKRQ bit transmits a break character. The break frame length depends on the
M bits (see Figure 246).
If a ‘1’ is written to the SBKRQ bit, a break character is sent on the TX line after completing
the current character transmission. The SBKF bit is set by the write operation and it is reset
by hardware when the break character is completed (during the stop bits after the break
character). The USART inserts a logic 1 signal (STOP) for the duration of 2 bits at the end of
the break frame to guarantee the recognition of the start bit of the next frame.
In the case the application needs to send the break character following all previously
inserted data, including the ones not yet transmitted, the software should wait for the TXE
flag assertion before setting the SBKRQ bit.

Idle characters
Setting the TE bit drives the USART to send an idle frame before the first data frame.

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27.5.3

Universal synchronous asynchronous receiver transmitter (USART)

USART receiver
The USART can receive data words of either 7, 8 or 9 bits depending on the M bits in the
USART_CR1 register.

Start bit detection
The start bit detection sequence is the same when oversampling by 16 or by 8.
In the USART, the start bit is detected when a specific sequence of samples is recognized.
This sequence is: 1 1 1 0 X 0 X 0X 0X 0 X 0X 0.
Figure 249. Start bit detection when oversampling by 16 or 8
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If the sequence is not complete, the start bit detection aborts and the receiver returns to the
idle state (no flag is set), where it waits for a falling edge.
The start bit is confirmed (RXNE flag set, interrupt generated if RXNEIE=1) if the 3 sampled
bits are at 0 (first sampling on the 3rd, 5th and 7th bits finds the 3 bits at 0 and second
sampling on the 8th, 9th and 10th bits also finds the 3 bits at 0).
The start bit is validated (RXNE flag set, interrupt generated if RXNEIE=1) but the NF noise
flag is set if,
a)

for both samplings, 2 out of the 3 sampled bits are at 0 (sampling on the 3rd, 5th
and 7th bits and sampling on the 8th, 9th and 10th bits)

or
b)

for one of the samplings (sampling on the 3rd, 5th and 7th bits or sampling on the
8th, 9th and 10th bits), 2 out of the 3 bits are found at 0.

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Universal synchronous asynchronous receiver transmitter (USART)

RM0091

If neither conditions a. or b. are met, the start detection aborts and the receiver returns to the
idle state (no flag is set).

Character reception
During an USART reception, data shifts in least significant bit first (default configuration)
through the RX pin. In this mode, the USART_RDR register consists of a buffer (RDR)
between the internal bus and the receive shift register.
Character reception procedure
1.

Program the M bits in USART_CR1 to define the word length.

2.

Select the desired baud rate using the baud rate register USART_BRR

3.

Program the number of stop bits in USART_CR2.

4.

Enable the USART by writing the UE bit in USART_CR1 register to 1.

5.

Select DMA enable (DMAR) in USART_CR3 if multibuffer communication is to take
place. Configure the DMA register as explained in multibuffer communication.

6.

Set the RE bit USART_CR1. This enables the receiver which begins searching for a
start bit.

For code example refer to the Appendix section A.19.4: USART receiver configuration code
example.
When a character is received:
•

The RXNE bit is set to indicate that the content of the shift register is transferred to the
RDR. In other words, data has been received and can be read (as well as its
associated error flags).

•

An interrupt is generated if the RXNEIE bit is set.

•

The error flags can be set if a frame error, noise or an overrun error has been detected
during reception. PE flag can also be set with RXNE.

•

In multibuffer, RXNE is set after every byte received and is cleared by the DMA read of
the Receive data Register.

•

In single buffer mode, clearing the RXNE bit is performed by a software read to the
USART_RDR register. The RXNE flag can also be cleared by writing 1 to the RXFRQ
in the USART_RQR register. The RXNE bit must be cleared before the end of the
reception of the next character to avoid an overrun error.

For code example refer to the Appendix section A.19.5: USART receive byte code
example.Break character
When a break character is received, the USART handles it as a framing error.

Idle character
When an idle frame is detected, there is the same procedure as for a received data
character plus an interrupt if the IDLEIE bit is set.

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Universal synchronous asynchronous receiver transmitter (USART)

Overrun error
An overrun error occurs when a character is received when RXNE has not been reset. Data
can not be transferred from the shift register to the RDR register until the RXNE bit is
cleared.
The RXNE flag is set after every byte received. An overrun error occurs if RXNE flag is set
when the next data is received or the previous DMA request has not been serviced. When
an overrun error occurs:

Note:

•

The ORE bit is set.

•

The RDR content will not be lost. The previous data is available when a read to
USART_RDR is performed.

•

The shift register will be overwritten. After that point, any data received during overrun
is lost.

•

An interrupt is generated if either the RXNEIE bit is set or EIE bit is set.

•

The ORE bit is reset by setting the ORECF bit in the ICR register.

The ORE bit, when set, indicates that at least 1 data has been lost. There are two
possibilities:
- if RXNE=1, then the last valid data is stored in the receive register RDR and can be read,
- if RXNE=0, then it means that the last valid data has already been read and thus there is
nothing to be read in the RDR. This case can occur when the last valid data is read in the
RDR at the same time as the new (and lost) data is received.

Selecting the clock source and the proper oversampling method
The choice of the clock source is done through the Clock Control system (see Section Reset
and clock control (RCC))). The clock source must be chosen before enabling the USART
(by setting the UE bit).
The choice of the clock source must be done according to two criteria:
•

Possible use of the USART in low-power mode

•

Communication speed.

The clock source frequency is fCK.
When the dual clock domain with the wakeup from Stop mode is supported, the clock
source can be one of the following sources: PCLK (default), LSE, HSI or SYSCLK.
Otherwise, the USART clock source is PCLK.
Choosing LSE or HSI as clock source may allow the USART to receive data while the MCU
is in low-power mode. Depending on the received data and wakeup mode selection, the
USART wakes up the MCU, when needed, in order to transfer the received data by software
reading the USART_RDR register or by DMA.
For the other clock sources, the system must be active in order to allow USART
communication.
The communication speed range (specially the maximum communication speed) is also
determined by the clock source.
The receiver implements different user-configurable oversampling techniques for data
recovery by discriminating between valid incoming data and noise. This allows a trade-off
between the maximum communication speed and noise/clock inaccuracy immunity.

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The oversampling method can be selected by programming the OVER8 bit in the
USART_CR1 register and can be either 16 or 8 times the baud rate clock (Figure 250 and
Figure 251).
Depending on the application:
•

Select oversampling by 8 (OVER8=1) to achieve higher speed (up to fCK/8). In this
case the maximum receiver tolerance to clock deviation is reduced (refer to
Section 27.5.5: Tolerance of the USART receiver to clock deviation on page 705)

•

Select oversampling by 16 (OVER8=0) to increase the tolerance of the receiver to
clock deviations. In this case, the maximum speed is limited to maximum fCK/16 where
fCK is the clock source frequency.

Programming the ONEBIT bit in the USART_CR3 register selects the method used to
evaluate the logic level. There are two options:
•

The majority vote of the three samples in the center of the received bit. In this case,
when the 3 samples used for the majority vote are not equal, the NF bit is set

•

A single sample in the center of the received bit
Depending on the application:
–

select the three samples’ majority vote method (ONEBIT=0) when operating in a
noisy environment and reject the data when a noise is detected (refer to
Figure 103) because this indicates that a glitch occurred during the sampling.

–

select the single sample method (ONEBIT=1) when the line is noise-free to
increase the receiver’s tolerance to clock deviations (see Section 27.5.5:
Tolerance of the USART receiver to clock deviation on page 705). In this case the
NF bit will never be set.

When noise is detected in a frame:
•

The NF bit is set at the rising edge of the RXNE bit.

•

The invalid data is transferred from the Shift register to the USART_RDR register.

•

No interrupt is generated in case of single byte communication. However this bit rises
at the same time as the RXNE bit which itself generates an interrupt. In case of
multibuffer communication an interrupt will be issued if the EIE bit is set in the
USART_CR3 register.

The NF bit is reset by setting NFCF bit in ICR register.
Note:

700/1004

Oversampling by 8 is not available in LIN, Smartcard and IrDA modes. In those modes, the
OVER8 bit is forced to ‘0’ by hardware.

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 250. Data sampling when oversampling by 16

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Table 103. Noise detection from sampled data
Sampled value

NE status

Received bit value

000

0

0

001

1

0

010

1

0

011

1

1

100

1

0

101

1

1

110

1

1

111

0

1

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Framing error
A framing error is detected when the stop bit is not recognized on reception at the expected
time, following either a de-synchronization or excessive noise.
When the framing error is detected:
•

The FE bit is set by hardware

•

The invalid data is transferred from the Shift register to the USART_RDR register.

•

No interrupt is generated in case of single byte communication. However this bit rises
at the same time as the RXNE bit which itself generates an interrupt. In case of
multibuffer communication an interrupt will be issued if the EIE bit is set in the
USART_CR3 register.

The FE bit is reset by writing 1 to the FECF in the USART_ICR register.

Configurable stop bits during reception
The number of stop bits to be received can be configured through the control bits of Control
Register 2 - it can be either 1 or 2 in normal mode and 0.5 or 1.5 in Smartcard mode.

702/1004

•

0.5 stop bit (reception in Smartcard mode): No sampling is done for 0.5 stop bit. As
a consequence, no framing error and no break frame can be detected when 0.5 stop bit
is selected.

•

1 stop bit: Sampling for 1 stop Bit is done on the 8th, 9th and 10th samples.

•

1.5 stop bits (Smartcard mode): When transmitting in Smartcard mode, the device
must check that the data is correctly sent. Thus the receiver block must be enabled (RE
=1 in the USART_CR1 register) and the stop bit is checked to test if the smartcard has
detected a parity error. In the event of a parity error, the smartcard forces the data
signal low during the sampling - NACK signal-, which is flagged as a framing error.
Then, the FE flag is set with the RXNE at the end of the 1.5 stop bits. Sampling for 1.5
stop bits is done on the 16th, 17th and 18th samples (1 baud clock period after the
beginning of the stop bit). The 1.5 stop bits can be decomposed into 2 parts: one 0.5
baud clock period during which nothing happens, followed by 1 normal stop bit period
during which sampling occurs halfway through. Refer to Section 27.5.13: USART
Smartcard mode on page 716 for more details.

•

2 stop bits: Sampling for 2 stop bits is done on the 8th, 9th and 10th samples of the
first stop bit. If a framing error is detected during the first stop bit the framing error flag
will be set. The second stop bit is not checked for framing error. The RXNE flag will be
set at the end of the first stop bit.

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27.5.4

Universal synchronous asynchronous receiver transmitter (USART)

USART baud rate generation
The baud rate for the receiver and transmitter (Rx and Tx) are both set to the same value as
programmed in the USART_BRR register.
Equation 1: Baud rate for standard USART (SPI mode included) (OVER8 = 0 or 1)
In case of oversampling by 16, the equation is:
f CK
Tx/Rx baud = -------------------------------USARTDIV

In case of oversampling by 8, the equation is:
2 × f CK
Tx/Rx baud = -------------------------------USARTDIV

Equation 2: Baud rate in Smartcard, LIN and IrDA modes (OVER8 = 0)
In Smartcard, LIN and IrDA modes, only Oversampling by 16 is supported:
f CK
Tx/Rx baud = -------------------------------USARTDIV

USARTDIV is an unsigned fixed point number that is coded on the USART_BRR register.

Note:

•

When OVER8 = 0, BRR = USARTDIV.

•

When OVER8 = 1
–

BRR[2:0] = USARTDIV[3:0] shifted 1 bit to the right.

–

BRR[3] must be kept cleared.

–

BRR[15:4] = USARTDIV[15:4]

The baud counters are updated to the new value in the baud registers after a write operation
to USART_BRR. Hence the baud rate register value should not be changed during
communication.
In case of oversampling by 16 or 8, USARTDIV must be greater than or equal to 0d16.

How to derive USARTDIV from USART_BRR register values
Example 1
To obtain 9600 baud with fCK = 8 MHz.
•

In case of oversampling by 16:
USARTDIV = 8 000 000/9600
BRR = USARTDIV = 833d = 0341h

•

In case of oversampling by 8:
USARTDIV = 2 * 8 000 000/9600
USARTDIV = 1666,66 (1667d = 683h)
BRR[3:0] = 3h << 1 = 1h
BRR = 0x681

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Example 2
To obtain 921.6 Kbaud with fCK = 48 MHz.
•

In case of oversampling by 16:
USARTDIV = 48 000 000/921 600
BRR = USARTDIV = 52d = 34h

•

In case of oversampling by 8:
USARTDIV = 2 * 48 000 000/921 600
USARTDIV = 104 (104d = 68h)
BRR[3:0] = USARTDIV[3:0] >> 1 = 8h >> 1 = 4h
BRR = 0x64

Table 104. Error calculation for programmed baud rates at fCK = 48 MHz in both cases of
oversampling by 16 or by 8(1)
Baud rate

Oversampling by 16 (OVER8 = 0)

Oversampling by 8 (OVER8 = 1)

S.No

Desired

Actual

BRR

% Error =
(Calculated Desired)B.Rate /
Desired B.Rate

2

2.4 KBps

2.4 KBps

0x4E20

0

2.4 KBps

0x9C40

0

3

9.6 KBps

9.6 KBps

0x1388

0

9.6 KBps

0x2710

0

4

19.2 KBps

19.2 KBps

0x9C4

0

19.2 KBps

0x1384

0

5

38.4 KBps

38.4 KBps

0x4E2

0

38.4 KBps

0x9C2

0

6

57.6 KBps

57.62 KBps

0x341

0.03

57.59 KBps

0x681

0.02

7

115.2 KBps

115.11 KBps

0x1A1

0.08

115.25 KBps

0x340

0.04

8

230.4 KBps

230.76KBps

0xD0

0.16

230.21 KBps

0x1A0

0.08

9

460.8 KBps

461.54KBps

0x68

0.16

461.54KBps

0xD0

0.16

10

921.6KBps

923.07KBps

0x34

0.16

923.07KBps

0x64

0.16

11

2 MBps

2 MBps

0x18

0

2 MBps

0x30

0

12

3 MBps

3 MBps

0x10

0

3 MBps

0x20

0

13

4MBps

N.A

N.A

N.A

4MBps

0x14

0

14

5MBps

N.A

N.A

N.A

5052.63KBps

0x11

1.05

15

6MBps

N.A

N.A

N.A

6MBps

0x10

0

Actual

BRR

% Error

1. The lower the CPU clock the lower the accuracy for a particular baud rate. The upper limit of the achievable baud rate can
be fixed with these data.

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27.5.5

Universal synchronous asynchronous receiver transmitter (USART)

Tolerance of the USART receiver to clock deviation
The asynchronous receiver of the USART works correctly only if the total clock system
deviation is less than the tolerance of the USART receiver. The causes which contribute to
the total deviation are:
•

DTRA: Deviation due to the transmitter error (which also includes the deviation of the
transmitter’s local oscillator)

•

DQUANT: Error due to the baud rate quantization of the receiver

•

DREC: Deviation of the receiver’s local oscillator

•

DTCL: Deviation due to the transmission line (generally due to the transceivers which
can introduce an asymmetry between the low-to-high transition timing and the high-tolow transition timing)
DTRA + DQUANT + DREC + DTCL + DWU < USART receiver′ s tolerance

where
DWU is the error due to sampling point deviation when the wakeup from Stop mode is
used.
when M[1:0] = 01:
t WUUSART
DWU = --------------------------11 × Tbit

when M[1:0] = 00:
t WUUSART
DWU = --------------------------10 × Tbit

when M[1:0] = 10:
t WUUSART
DWU = --------------------------9 × Tbit

tWUUSART is the time between detection of the wakeup event and the instant when
clock (requested by the peripheral) and regulator are ready. In STM32F0xx, tWUUSART
corresponds to tWUSTOP value provided in the datasheet.
The USART receiver can receive data correctly at up to the maximum tolerated deviation
specified in Table 105 and Table 105 depending on the following choices:
•

9-, 10- or 11-bit character length defined by the M bits in the USART_CR1 register

•

Oversampling by 8 or 16 defined by the OVER8 bit in the USART_CR1 register

•

Bits BRR[3:0] of USART_BRR register are equal to or different from 0000.

•

Use of 1 bit or 3 bits to sample the data, depending on the value of the ONEBIT bit in
the USART_CR3 register.

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Table 105. Tolerance of the USART receiver when BRR [3:0] = 0000
OVER8 bit = 0

OVER8 bit = 1

M bits
ONEBIT=0

ONEBIT=1

ONEBIT=0

ONEBIT=1

00

3.75%

4.375%

2.50%

3.75%

01

3.41%

3.97%

2.27%

3.41%

10

4.16%

4.86%

2.77%

4.16%

Table 106. Tolerance of the USART receiver when BRR [3:0] is different from 0000
OVER8 bit = 0

OVER8 bit = 1

M bits
ONEBIT=0

ONEBIT=1

ONEBIT=0

ONEBIT=1

00

3.33%

3.88%

2%

3%

01

3.03%

3.53%

1.82%

2.73%

10

3.7%

4.31%

2.22%

3.33%

Note:

The data specified in Table 105 and Table 106 may slightly differ in the special case when
the received frames contain some Idle frames of exactly 10-bit durations when M bits = 00
(11-bit durations when M bits =01 or 9- bit durations when M bits = 10).

27.5.6

USART auto baud rate detection
The USART is able to detect and automatically set the USART_BRR register value based
on the reception of one character. Automatic baud rate detection is useful under two
circumstances:
•

The communication speed of the system is not known in advance

•

The system is using a relatively low accuracy clock source and this mechanism allows
the correct baud rate to be obtained without measuring the clock deviation.

The clock source frequency must be compatible with the expected communication speed (in
case only modes 0 and 1 are supported, oversampling by 16 must be selected and baudrate
between fCK/65535 and fCK/16. Otherwise, in case of 4 modes are supported: when
oversampling by 16, the baud rate is between fCK/65535 and fCK/16; when oversampling by
8, the baudrate is between fCK/65535 and fCK/8).
Before activating the auto baud rate detection, the auto baud rate detection mode must be
chosen. There are various modes based on different character patterns.
They can be chosen through the ABRMOD[1:0] field in the USART_CR2 register. In these
auto baud rate modes, the baud rate is measured several times during the synchronization
data reception and each measurement is compared to the previous one.

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These modes are:
•

Mode 0: Any character starting with a bit at 1. In this case the USART measures the
duration of the Start bit (falling edge to rising edge).

•

Mode 1: Any character starting with a 10xx bit pattern. In this case, the USART
measures the duration of the Start and of the 1st data bit. The measurement is done
falling edge to falling edge, ensuring better accuracy in the case of slow signal slopes.

•

Mode 2: A 0x7F character frame (it may be a 0x7F character in LSB first mode or a
0xFE in MSB first mode). In this case, the baudrate is updated first at the end of the
start bit (BRs), then at the end of bit 6 (based on the measurement done from falling
edge to falling edge: BR6). Bit 0 to bit 6 are sampled at BRs while further bits of the
character are sampled at BR6.

•

Mode 3: A 0x55 character frame. In this case, the baudrate is updated first at the end
of the start bit (BRs), then at the end of bit 0 (based on the measurement done from
falling edge to falling edge: BR0), and finally at the end of bit 6 (BR6). Bit 0 is sampled
at BRs, bit 1 to bit 6 are sampled at BR0, and further bits of the character are sampled
at BR6.
In parallel, another check is performed for each intermediate transition of RX line. An
error is generated if the transitions on RX are not sufficiently synchronized with the
receiver (the receiver being based on the baud rate calculated on bit 0).

Prior to activating auto baud rate detection, the USART_BRR register must be initialized by
writing a non-zero baud rate value.
The automatic baud rate detection is activated by setting the ABREN bit in the USART_CR2
register. The USART will then wait for the first character on the RX line. The auto baud rate
operation completion is indicated by the setting of the ABRF flag in the USART_ISR
register. If the line is noisy, the correct baud rate detection cannot be guaranteed. In this
case the BRR value may be corrupted and the ABRE error flag will be set. This also
happens if the communication speed is not compatible with the automatic baud rate
detection range (bit duration not between 16 and 65536 clock periods (oversampling by 16)
and not between 8 and 65536 clock periods (oversampling by 8)).
The RXNE interrupt will signal the end of the operation.
At any later time, the auto baud rate detection may be relaunched by resetting the ABRF
flag (by writing a 0).
Note:

If the USART is disabled (UE=0) during an auto baud rate operation, the BRR value may be
corrupted.

27.5.7

Multiprocessor communication using USART
In multiprocessor communication, the following bits are to be kept cleared:
•

LINEN bit in the USART_CR2 register,

•

HDSEL, IREN and SCEN bits in the USART_CR3 register.

It is possible to perform multiprocessor communication with the USART (with several
USARTs connected in a network). For instance one of the USARTs can be the master, its TX
output connected to the RX inputs of the other USARTs. The others are slaves, their
respective TX outputs are logically ANDed together and connected to the RX input of the
master.

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In multiprocessor configurations it is often desirable that only the intended message
recipient should actively receive the full message contents, thus reducing redundant USART
service overhead for all non addressed receivers.
The non addressed devices may be placed in mute mode by means of the muting function.
In order to use the mute mode feature, the MME bit must be set in the USART_CR1
register.
In mute mode:
•

None of the reception status bits can be set.

•

All the receive interrupts are inhibited.

•

The RWU bit in USART_ISR register is set to 1. RWU can be controlled automatically
by hardware or by software, through the MMRQ bit in the USART_RQR register, under
certain conditions.

The USART can enter or exit from mute mode using one of two methods, depending on the
WAKE bit in the USART_CR1 register:
•

Idle Line detection if the WAKE bit is reset,

•

Address Mark detection if the WAKE bit is set.

Idle line detection (WAKE=0)
The USART enters mute mode when the MMRQ bit is written to 1 and the RWU is
automatically set.
It wakes up when an Idle frame is detected. Then the RWU bit is cleared by hardware but
the IDLE bit is not set in the USART_ISR register. An example of mute mode behavior using
Idle line detection is given in Figure 252.
Figure 252. Mute mode using Idle line detection

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Note:

If the MMRQ is set while the IDLE character has already elapsed, mute mode will not be
entered (RWU is not set).
If the USART is activated while the line is IDLE, the idle state is detected after the duration
of one IDLE frame (not only after the reception of one character frame).

4-bit/7-bit address mark detection (WAKE=1)
In this mode, bytes are recognized as addresses if their MSB is a ‘1’ otherwise they are
considered as data. In an address byte, the address of the targeted receiver is put in the 4
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Universal synchronous asynchronous receiver transmitter (USART)
or 7 LSBs. The choice of 7 or 4-bit address detection is done using the ADDM7 bit. This 4bit/7-bit word is compared by the receiver with its own address which is programmed in the
ADD bits in the USART_CR2 register.

Note:

In 7-bit and 9-bit data modes, address detection is done on 6-bit and 8-bit addresses
(ADD[5:0] and ADD[7:0]) respectively.
The USART enters mute mode when an address character is received which does not
match its programmed address. In this case, the RWU bit is set by hardware. The RXNE
flag is not set for this address byte and no interrupt or DMA request is issued when the
USART enters mute mode.
The USART also enters mute mode when the MMRQ bit is written to 1. The RWU bit is also
automatically set in this case.
The USART exits from mute mode when an address character is received which matches
the programmed address. Then the RWU bit is cleared and subsequent bytes are received
normally. The RXNE bit is set for the address character since the RWU bit has been
cleared.
An example of mute mode behavior using address mark detection is given in Figure 253.
Figure 253. Mute mode using address mark detection
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27.5.8

Modbus communication using USART
The USART offers basic support for the implementation of Modbus/RTU and Modbus/ASCII
protocols. Modbus/RTU is a half duplex, block transfer protocol. The control part of the
protocol (address recognition, block integrity control and command interpretation) must be
implemented in software.
The USART offers basic support for the end of the block detection, without software
overhead or other resources.

Modbus/RTU
In this mode, the end of one block is recognized by a “silence” (idle line) for more than 2
character times. This function is implemented through the programmable timeout function.
The timeout function and interrupt must be activated, through the RTOEN bit in the
USART_CR2 register and the RTOIE in the USART_CR1 register. The value corresponding
to a timeout of 2 character times (for example 22 x bit duration) must be programmed in the

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RTO register. when the receive line is idle for this duration, after the last stop bit is received,
an interrupt is generated, informing the software that the current block reception is
completed.

Modbus/ASCII
In this mode, the end of a block is recognized by a specific (CR/LF) character sequence.
The USART manages this mechanism using the character match function.
By programming the LF ASCII code in the ADD[7:0] field and by activating the character
match interrupt (CMIE=1), the software is informed when a LF has been received and can
check the CR/LF in the DMA buffer.

27.5.9

USART parity control
Parity control (generation of parity bit in transmission and parity checking in reception) can
be enabled by setting the PCE bit in the USART_CR1 register. Depending on the frame
length defined by the M bits, the possible USART frame formats are as listed in Table 107.
Table 107. Frame formats
M bits

PCE bit

USART frame(1)

00

0

| SB | 8-bit data | STB |

00

1

| SB | 7-bit data | PB | STB |

01

0

| SB | 9-bit data | STB |

01

1

| SB | 8-bit data | PB | STB |

10

0

| SB | 7-bit data | STB |

10

1

| SB | 6-bit data | PB | STB |

1. Legends: SB: start bit, STB: stop bit, PB: parity bit. In the data register, the PB is always taking the MSB
position (9th, 8th or 7th, depending on the M bits value).

Even parity
The parity bit is calculated to obtain an even number of “1s” inside the frame of the 6, 7 or 8
LSB bits (depending on M bits values) and the parity bit.
As an example, if data=00110101, and 4 bits are set, then the parity bit will be 0 if even
parity is selected (PS bit in USART_CR1 = 0).

Odd parity
The parity bit is calculated to obtain an odd number of “1s” inside the frame made of the 6, 7
or 8 LSB bits (depending on M bits values) and the parity bit.
As an example, if data=00110101 and 4 bits set, then the parity bit will be 1 if odd parity is
selected (PS bit in USART_CR1 = 1).

Parity checking in reception
If the parity check fails, the PE flag is set in the USART_ISR register and an interrupt is
generated if PEIE is set in the USART_CR1 register. The PE flag is cleared by software
writing 1 to the PECF in the USART_ICR register.

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Parity generation in transmission
If the PCE bit is set in USART_CR1, then the MSB bit of the data written in the data register
is transmitted but is changed by the parity bit (even number of “1s” if even parity is selected
(PS=0) or an odd number of “1s” if odd parity is selected (PS=1)).

27.5.10

USART LIN (local interconnection network) mode
This section is relevant only when LIN mode is supported. Please refer to Section 27.4:
USART implementation on page 689.
The LIN mode is selected by setting the LINEN bit in the USART_CR2 register. In LIN
mode, the following bits must be kept cleared:
•

STOP[1:0] and CLKEN in the USART_CR2 register,

•

SCEN, HDSEL and IREN in the USART_CR3 register.

For code example refer to the Appendix section A.19.6: USART LIN mode code example.

LIN transmission
The procedure explained in Section 27.5.2: USART transmitter has to be applied for LIN
Master transmission. It must be the same as for normal USART transmission with the
following differences:
•

Clear the M bits to configure 8-bit word length.

•

Set the LINEN bit to enter LIN mode. In this case, setting the SBKRQ bit sends 13 ‘0’
bits as a break character. Then 2 bits of value ‘1’ are sent to allow the next start
detection.

LIN reception
When LIN mode is enabled, the break detection circuit is activated. The detection is totally
independent from the normal USART receiver. A break can be detected whenever it occurs,
during Idle state or during a frame.
When the receiver is enabled (RE=1 in USART_CR1), the circuit looks at the RX input for a
start signal. The method for detecting start bits is the same when searching break
characters or data. After a start bit has been detected, the circuit samples the next bits
exactly like for the data (on the 8th, 9th and 10th samples). If 10 (when the LBDL = 0 in
USART_CR2) or 11 (when LBDL=1 in USART_CR2) consecutive bits are detected as ‘0,
and are followed by a delimiter character, the LBDF flag is set in USART_ISR. If the LBDIE
bit=1, an interrupt is generated. Before validating the break, the delimiter is checked for as it
signifies that the RX line has returned to a high level.
If a ‘1’ is sampled before the 10 or 11 have occurred, the break detection circuit cancels the
current detection and searches for a start bit again.
If the LIN mode is disabled (LINEN=0), the receiver continues working as normal USART,
without taking into account the break detection.
If the LIN mode is enabled (LINEN=1), as soon as a framing error occurs (i.e. stop bit
detected at ‘0’, which will be the case for any break frame), the receiver stops until the break
detection circuit receives either a ‘1’, if the break word was not complete, or a delimiter
character if a break has been detected.
The behavior of the break detector state machine and the break flag is shown on the
Figure 254: Break detection in LIN mode (11-bit break length - LBDL bit is set) on page 712.

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Examples of break frames are given on Figure 255: Break detection in LIN mode vs.
Framing error detection on page 713.
Figure 254. Break detection in LIN mode (11-bit break length - LBDL bit is set)

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 255. Break detection in LIN mode vs. Framing error detection
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27.5.11

USART synchronous mode
The synchronous mode is selected by writing the CLKEN bit in the USART_CR2 register to
1. In synchronous mode, the following bits must be kept cleared:
•

LINEN bit in the USART_CR2 register,

•

SCEN, HDSEL and IREN bits in the USART_CR3 register.

In this mode, the USART can be used to control bidirectional synchronous serial
communications in master mode. The CK pin is the output of the USART transmitter clock.
No clock pulses are sent to the CK pin during start bit and stop bit. Depending on the state
of the LBCL bit in the USART_CR2 register, clock pulses are, or are not, generated during
the last valid data bit (address mark). The CPOL bit in the USART_CR2 register is used to
select the clock polarity, and the CPHA bit in the USART_CR2 register is used to select the
phase of the external clock (see Figure 256, Figure 257 and Figure 258).
During the Idle state, preamble and send break, the external CK clock is not activated.
In synchronous mode the USART transmitter works exactly like in asynchronous mode. But
as CK is synchronized with TX (according to CPOL and CPHA), the data on TX is
synchronous.
In this mode the USART receiver works in a different manner compared to the
asynchronous mode. If RE=1, the data is sampled on CK (rising or falling edge, depending
on CPOL and CPHA), without any oversampling. A setup and a hold time must be
respected (which depends on the baud rate: 1/16 bit duration).

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Note:

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The CK pin works in conjunction with the TX pin. Thus, the clock is provided only if the
transmitter is enabled (TE=1) and data is being transmitted (the data register USART_TDR
written). This means that it is not possible to receive synchronous data without transmitting
data.
The LBCL, CPOL and CPHA bits have to be selected when the USART is disabled (UE=0)
to ensure that the clock pulses function correctly.

Note:

For code example refer to the Appendix A.19.7: USART synchronous mode code example
Figure 256. USART example of synchronous transmission

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 258. USART data clock timing diagram (M bits = 01)
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Note:

The function of CK is different in Smartcard mode. Refer to Section 27.5.13: USART
Smartcard mode for more details.

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27.5.12

RM0091

USART Single-wire Half-duplex communication
Single-wire Half-duplex mode is selected by setting the HDSEL bit in the USART_CR3
register. In this mode, the following bits must be kept cleared:
•

LINEN and CLKEN bits in the USART_CR2 register,

•

SCEN and IREN bits in the USART_CR3 register.

The USART can be configured to follow a Single-wire Half-duplex protocol where the TX
and RX lines are internally connected. The selection between half- and Full-duplex
communication is made with a control bit HDSEL in USART_CR3.
As soon as HDSEL is written to 1:
•

The TX and RX lines are internally connected

•

The RX pin is no longer used

•

The TX pin is always released when no data is transmitted. Thus, it acts as a standard
I/O in idle or in reception. It means that the I/O must be configured so that TX is
configured as alternate function open-drain with an external pull-up.

Apart from this, the communication protocol is similar to normal USART mode. Any conflicts
on the line must be managed by software (by the use of a centralized arbiter, for instance).
In particular, the transmission is never blocked by hardware and continues as soon as data
is written in the data register while the TE bit is set.
For code example refer to the Appendix section A.19.8: USART single-wire half-duplex
code example.

27.5.13

USART Smartcard mode
This section is relevant only when Smartcard mode is supported. Please refer to
Section 27.4: USART implementation on page 689.
Smartcard mode is selected by setting the SCEN bit in the USART_CR3 register. In
Smartcard mode, the following bits must be kept cleared:
•

LINEN bit in the USART_CR2 register,

•

HDSEL and IREN bits in the USART_CR3 register.

Moreover, the CLKEN bit may be set in order to provide a clock to the smartcard.
The smartcard interface is designed to support asynchronous protocol for smartcards as
defined in the ISO 7816-3 standard. Both T=0 (character mode) and T=1 (block mode) are
supported.
The USART should be configured as:
•

8 bits plus parity: where word length is set to 8 bits and PCE=1 in the USART_CR1
register

•

1.5 stop bits: where STOP=11 in the USART_CR2 register. It is also possible to choose
0.5 stop bit for receiving.

In T=0 (character) mode, the parity error is indicated at the end of each character during the
guard time period.
Figure 260 shows examples of what can be seen on the data line with and without parity
error.

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Figure 260. ISO 7816-3 asynchronous protocol
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When connected to a smartcard, the TX output of the USART drives a bidirectional line that
is also driven by the smartcard. The TX pin must be configured as open drain.
Smartcard mode implements a single wire half duplex communication protocol.
•

Transmission of data from the transmit shift register is guaranteed to be delayed by a
minimum of 1/2 baud clock. In normal operation a full transmit shift register starts
shifting on the next baud clock edge. In Smartcard mode this transmission is further
delayed by a guaranteed 1/2 baud clock.

•

In transmission, if the smartcard detects a parity error, it signals this condition to the
USART by driving the line low (NACK). This NACK signal (pulling transmit line low for 1
baud clock) causes a framing error on the transmitter side (configured with 1.5 stop
bits). The USART can handle automatic re-sending of data according to the protocol.
The number of retries is programmed in the SCARCNT bit field. If the USART
continues receiving the NACK after the programmed number of retries, it stops
transmitting and signals the error as a framing error. The TXE bit can be set using the
TXFRQ bit in the USART_RQR register.

•

Smartcard auto-retry in transmission: a delay of 2.5 baud periods is inserted between
the NACK detection by the USART and the start bit of the repeated character. The TC
bit is set immediately at the end of reception of the last repeated character (no guardtime). If the software wants to repeat it again, it must insure the minimum 2 baud
periods required by the standard.

•

If a parity error is detected during reception of a frame programmed with a 1.5 stop bits
period, the transmit line is pulled low for a baud clock period after the completion of the
receive frame. This is to indicate to the smartcard that the data transmitted to the
USART has not been correctly received. A parity error is NACKed by the receiver if the
NACK control bit is set, otherwise a NACK is not transmitted (to be used in T=1 mode).
If the received character is erroneous, the RXNE/receive DMA request is not activated.
According to the protocol specification, the smartcard must resend the same character.
If the received character is still erroneous after the maximum number of retries
specified in the SCARCNT bit field, the USART stops transmitting the NACK and
signals the error as a parity error.

•

Smartcard auto-retry in reception: the BUSY flag remains set if the USART NACKs the
card but the card doesn’t repeat the character.

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Note:

RM0091

•

In transmission, the USART inserts the Guard Time (as programmed in the Guard Time
register) between two successive characters. As the Guard Time is measured after the
stop bit of the previous character, the GT[7:0] register must be programmed to the
desired CGT (Character Guard Time, as defined by the 7816-3 specification) minus 12
(the duration of one character).

•

The assertion of the TC flag can be delayed by programming the Guard Time register.
In normal operation, TC is asserted when the transmit shift register is empty and no
further transmit requests are outstanding. In Smartcard mode an empty transmit shift
register triggers the Guard Time counter to count up to the programmed value in the
Guard Time register. TC is forced low during this time. When the Guard Time counter
reaches the programmed value TC is asserted high.

•

The de-assertion of TC flag is unaffected by Smartcard mode.

•

If a framing error is detected on the transmitter end (due to a NACK from the receiver),
the NACK is not detected as a start bit by the receive block of the transmitter.
According to the ISO protocol, the duration of the received NACK can be 1 or 2 baud
clock periods.

•

On the receiver side, if a parity error is detected and a NACK is transmitted the receiver
does not detect the NACK as a start bit.

A break character is not significant in Smartcard mode. A 0x00 data with a framing error is
treated as data and not as a break.
No Idle frame is transmitted when toggling the TE bit. The Idle frame (as defined for the
other configurations) is not defined by the ISO protocol.
Figure 261 details how the NACK signal is sampled by the USART. In this example the
USART is transmitting data and is configured with 1.5 stop bits. The receiver part of the
USART is enabled in order to check the integrity of the data and the NACK signal.
Figure 261. Parity error detection using the 1.5 stop bits
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The USART can provide a clock to the smartcard through the CK output. In Smartcard
mode, CK is not associated to the communication but is simply derived from the internal
peripheral input clock through a 5-bit prescaler. The division ratio is configured in the
prescaler register USART_GTPR. CK frequency can be programmed from fCK/2 to fCK/62,
where fCK is the peripheral input clock.

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Universal synchronous asynchronous receiver transmitter (USART)

Block mode (T=1)
In T=1 (block) mode, the parity error transmission is deactivated, by clearing the NACK bit in
the UART_CR3 register.
When requesting a read from the smartcard, in block mode, the software must enable the
receiver Timeout feature by setting the RTOEN bit in the USART_CR2 register and program
the RTO bits field in the RTOR register to the BWT (block wait time) - 11 value. If no answer
is received from the card before the expiration of this period, the RTOF flag will be set and a
timeout interrupt will be generated (if RTOIE bit in the USART_CR1 register is set). If the
first character is received before the expiration of the period, it is signaled by the RXNE
interrupt.
Note:

The RXNE interrupt must be enabled even when using the USART in DMA mode to read
from the smartcard in block mode. In parallel, the DMA must be enabled only after the first
received byte.
After the reception of the first character (RXNE interrupt), the RTO bit fields in the RTOR
register must be programmed to the CWT (character wait time) - 11 value, in order to allow
the automatic check of the maximum wait time between two consecutive characters. This
time is expressed in baudtime units. If the smartcard does not send a new character in less
than the CWT period after the end of the previous character, the USART signals this to the
software through the RTOF flag and interrupt (when RTOIE bit is set).

Note:

The RTO counter starts counting:
- From the end of the stop bit in case STOP = 00.
- From the end of the second stop bit in case of STOP = 10.
- 1 bit duration after the beginning of the STOP bit in case STOP = 11.
- From the beginning of the STOP bit in case STOP = 01.
As in the Smartcard protocol definition, the BWT/CWT values are defined from the
beginning (start bit) of the last character. The RTO register must be programmed to BWT 11 or CWT -11, respectively, taking into account the length of the last character itself.
A block length counter is used to count all the characters received by the USART. This
counter is reset when the USART is transmitting (TXE=0). The length of the block is
communicated by the smartcard in the third byte of the block (prologue field). This value
must be programmed to the BLEN field in the USART_RTOR register. when using DMA
mode, before the start of the block, this register field must be programmed to the minimum
value (0x0). with this value, an interrupt is generated after the 4th received character. The
software must read the LEN field (third byte), its value must be read from the receive buffer.
In interrupt driven receive mode, the length of the block may be checked by software or by
programming the BLEN value. However, before the start of the block, the maximum value of
BLEN (0xFF) may be programmed. The real value will be programmed after the reception of
the third character.
If the block is using the LRC longitudinal redundancy check (1 epilogue byte), the
BLEN=LEN. If the block is using the CRC mechanism (2 epilogue bytes), BLEN=LEN+1
must be programmed. The total block length (including prologue, epilogue and information
fields) equals BLEN+4. The end of the block is signaled to the software through the EOBF
flag and interrupt (when EOBIE bit is set).
In case of an error in the block length, the end of the block is signaled by the RTO interrupt
(Character wait Time overflow).

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Note:

RM0091

The error checking code (LRC/CRC) must be computed/verified by software.

Direct and inverse convention
The Smartcard protocol defines two conventions: direct and inverse.
The direct convention is defined as: LSB first, logical bit value of 1 corresponds to a H state
of the line and parity is even. In order to use this convention, the following control bits must
be programmed: MSBFIRST=0, DATAINV=0 (default values).
The inverse convention is defined as: MSB first, logical bit value 1 corresponds to an L state
on the signal line and parity is even. In order to use this convention, the following control bits
must be programmed: MSBFIRST=1, DATAINV=1.
Note:

When logical data values are inverted (0=H, 1=L), the parity bit is also inverted in the same
way.
In order to recognize the card convention, the card sends the initial character, TS, as the
first character of the ATR (Answer To Reset) frame. The two possible patterns for the TS
are: LHHL LLL LLH and LHHL HHH LLH.
•

(H) LHHL LLL LLH sets up the inverse convention: state L encodes value 1 and
moment 2 conveys the most significant bit (MSB first). when decoded by inverse
convention, the conveyed byte is equal to '3F'.

•

(H) LHHL HHH LLH sets up the direct convention: state H encodes value 1 and
moment 2 conveys the least significant bit (LSB first). when decoded by direct
convention, the conveyed byte is equal to '3B'.

Character parity is correct when there is an even number of bits set to 1 in the nine
moments 2 to 10.
As the USART does not know which convention is used by the card, it needs to be able to
recognize either pattern and act accordingly. The pattern recognition is not done in
hardware, but through a software sequence. Moreover, supposing that the USART is
configured in direct convention (default) and the card answers with the inverse convention,
TS = LHHL LLL LLH => the USART received character will be ‘03’ and the parity will be odd.
Therefore, two methods are available for TS pattern recognition:
Method 1
The USART is programmed in standard Smartcard mode/direct convention. In this case, the
TS pattern reception generates a parity error interrupt and error signal to the card.
•

The parity error interrupt informs the software that the card didn’t answer correctly in
direct convention. Software then reprograms the USART for inverse convention

•

In response to the error signal, the card retries the same TS character, and it will be
correctly received this time, by the reprogrammed USART

Alternatively, in answer to the parity error interrupt, the software may decide to reprogram
the USART and to also generate a new reset command to the card, then wait again for the
TS.

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Universal synchronous asynchronous receiver transmitter (USART)
Method 2
The USART is programmed in 9-bit/no-parity mode, no bit inversion. In this mode it receives
any of the two TS patterns as:
(H) LHHL LLL LLH = 0x103 -> inverse convention to be chosen
(H) LHHL HHH LLH = 0x13B -> direct convention to be chosen
The software checks the received character against these two patterns and, if any of them
match, then programs the USART accordingly for the next character reception.
If none of the two is recognized, a card reset may be generated in order to restart the
negotiation.

27.5.14

USART IrDA SIR ENDEC block
This section is relevant only when IrDA mode is supported. Please refer to Section 27.4:
USART implementation on page 689.
IrDA mode is selected by setting the IREN bit in the USART_CR3 register. In IrDA mode,
the following bits must be kept cleared:
•

LINEN, STOP and CLKEN bits in the USART_CR2 register,

•

SCEN and HDSEL bits in the USART_CR3 register.

The IrDA SIR physical layer specifies use of a Return to Zero, Inverted (RZI) modulation
scheme that represents logic 0 as an infrared light pulse (see Figure 262).
The SIR Transmit encoder modulates the Non Return to Zero (NRZ) transmit bit stream
output from USART. The output pulse stream is transmitted to an external output driver and
infrared LED. USART supports only bit rates up to 115.2 Kbps for the SIR ENDEC. In
normal mode the transmitted pulse width is specified as 3/16 of a bit period.
The SIR receive decoder demodulates the return-to-zero bit stream from the infrared
detector and outputs the received NRZ serial bit stream to the USART. The decoder input is
normally high (marking state) in the Idle state. The transmit encoder output has the opposite
polarity to the decoder input. A start bit is detected when the decoder input is low.
•

IrDA is a half duplex communication protocol. If the Transmitter is busy (when the
USART is sending data to the IrDA encoder), any data on the IrDA receive line is
ignored by the IrDA decoder and if the Receiver is busy (when the USART is receiving
decoded data from the IrDA decoder), data on the TX from the USART to IrDA is not
encoded. while receiving data, transmission should be avoided as the data to be
transmitted could be corrupted.

•

A 0 is transmitted as a high pulse and a 1 is transmitted as a 0. The width of the pulse
is specified as 3/16th of the selected bit period in normal mode (see Figure 263).

•

The SIR decoder converts the IrDA compliant receive signal into a bit stream for
USART.

•

The SIR receive logic interprets a high state as a logic one and low pulses as logic
zeros.

•

The transmit encoder output has the opposite polarity to the decoder input. The SIR
output is in low state when Idle.

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RM0091

•

The IrDA specification requires the acceptance of pulses greater than 1.41 µs. The
acceptable pulse width is programmable. Glitch detection logic on the receiver end
filters out pulses of width less than 2 PSC periods (PSC is the prescaler value
programmed in the USART_GTPR). Pulses of width less than 1 PSC period are always
rejected, but those of width greater than one and less than two periods may be
accepted or rejected, those greater than 2 periods will be accepted as a pulse. The
IrDA encoder/decoder doesn’t work when PSC=0.

•

The receiver can communicate with a low-power transmitter.

•

In IrDA mode, the STOP bits in the USART_CR2 register must be configured to “1 stop
bit”.

IrDA low-power mode
Transmitter
In low-power mode the pulse width is not maintained at 3/16 of the bit period. Instead, the
width of the pulse is 3 times the low-power baud rate which can be a minimum of 1.42 MHz.
Generally, this value is 1.8432 MHz (1.42 MHz < PSC< 2.12 MHz). A low-power mode
programmable divisor divides the system clock to achieve this value.
Receiver
Receiving in low-power mode is similar to receiving in normal mode. For glitch detection the
USART should discard pulses of duration shorter than 1 PSC period. A valid low is accepted
only if its duration is greater than 2 periods of the IrDA low-power Baud clock (PSC value in
the USART_GTPR).
Note:

A pulse of width less than two and greater than one PSC period(s) may or may not be
rejected.
The receiver set up time should be managed by software. The IrDA physical layer
specification specifies a minimum of 10 ms delay between transmission and reception (IrDA
is a half duplex protocol).
Figure 262. IrDA SIR ENDEC- block diagram

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 263. IrDA data modulation (3/16) -Normal Mode

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27.5.15

USART continuous communication in DMA mode
The USART is capable of performing continuous communication using the DMA. The DMA
requests for Rx buffer and Tx buffer are generated independently.

Note:

Please refer to Section 27.4: USART implementation on page 689 to determine if the DMA
mode is supported. If DMA is not supported, use the USART as explained in Section 27.5.2:
USART transmitter or Section 27.5.3: USART receiver. To perform continuous
communication, the user can clear the TXE/ RXNE flags In the USART_ISR register.
For code example refer to the Appendix section A.19.11: USART DMA code example.

Transmission using DMA
DMA mode can be enabled for transmission by setting DMAT bit in the USART_CR3
register. Data is loaded from a SRAM area configured using the DMA peripheral (refer to
Section 10: Direct memory access controller (DMA) on page 188) to the USART_TDR
register whenever the TXE bit is set. To map a DMA channel for USART transmission, use
the following procedure (x denotes the channel number):
1.

Write the USART_TDR register address in the DMA control register to configure it as
the destination of the transfer. The data is moved to this address from memory after
each TXE event.

2.

Write the memory address in the DMA control register to configure it as the source of
the transfer. The data is loaded into the USART_TDR register from this memory area
after each TXE event.

3.

Configure the total number of bytes to be transferred to the DMA control register.

4.

Configure the channel priority in the DMA register

5.

Configure DMA interrupt generation after half/ full transfer as required by the
application.

6.

Clear the TC flag in the USART_ISR register by setting the TCCF bit in the
USART_ICR register.

7.

Activate the channel in the DMA register.

When the number of data transfers programmed in the DMA Controller is reached, the DMA
controller generates an interrupt on the DMA channel interrupt vector.

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RM0091

In transmission mode, once the DMA has written all the data to be transmitted (the TCIF flag
is set in the DMA_ISR register), the TC flag can be monitored to make sure that the USART
communication is complete. This is required to avoid corrupting the last transmission before
disabling the USART or entering Stop mode. Software must wait until TC=1. The TC flag
remains cleared during all data transfers and it is set by hardware at the end of transmission
of the last frame.
Figure 264. Transmission using DMA
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Reception using DMA
DMA mode can be enabled for reception by setting the DMAR bit in USART_CR3 register.
Data is loaded from the USART_RDR register to a SRAM area configured using the DMA
peripheral (refer to Section 10: Direct memory access controller (DMA) on page 188)
whenever a data byte is received. To map a DMA channel for USART reception, use the
following procedure:
1.

Write the USART_RDR register address in the DMA control register to configure it as
the source of the transfer. The data is moved from this address to the memory after
each RXNE event.

2.

Write the memory address in the DMA control register to configure it as the destination
of the transfer. The data is loaded from USART_RDR to this memory area after each
RXNE event.

3.

Configure the total number of bytes to be transferred to the DMA control register.

4.

Configure the channel priority in the DMA control register

5.

Configure interrupt generation after half/ full transfer as required by the application.

6.

Activate the channel in the DMA control register.

When the number of data transfers programmed in the DMA Controller is reached, the DMA
controller generates an interrupt on the DMA channel interrupt vector.
724/1004

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 265. Reception using DMA
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Error flagging and interrupt generation in multibuffer communication
In multibuffer communication if any error occurs during the transaction the error flag is
asserted after the current byte. An interrupt is generated if the interrupt enable flag is set.
For framing error, overrun error and noise flag which are asserted with RXNE in single byte
reception, there is a separate error flag interrupt enable bit (EIE bit in the USART_CR3
register), which, if set, enables an interrupt after the current byte if any of these errors occur.

27.5.16

RS232 hardware flow control and RS485 driver enable
using USART
It is possible to control the serial data flow between 2 devices by using the CTS input and
the RTS output. The Figure 266 shows how to connect 2 devices in this mode:
Figure 266. Hardware flow control between 2 USARTs

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RM0091

RS232 RTS and CTS flow control can be enabled independently by writing the RTSE and
CTSE bits respectively to 1 (in the USART_CR3 register).

RS232 RTS flow control
If the RTS flow control is enabled (RTSE=1), then RTS is asserted (tied low) as long as the
USART receiver is ready to receive a new data. When the receive register is full, RTS is deasserted, indicating that the transmission is expected to stop at the end of the current frame.
Figure 267 shows an example of communication with RTS flow control enabled.
Figure 267. RS232 RTS flow control

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RS232 CTS flow control
If the CTS flow control is enabled (CTSE=1), then the transmitter checks the CTS input
before transmitting the next frame. If CTS is asserted (tied low), then the next data is
transmitted (assuming that data is to be transmitted, in other words, if TXE=0), else the
transmission does not occur. when CTS is de-asserted during a transmission, the current
transmission is completed before the transmitter stops.
When CTSE=1, the CTSIF status bit is automatically set by hardware as soon as the CTS
input toggles. It indicates when the receiver becomes ready or not ready for communication.
An interrupt is generated if the CTSIE bit in the USART_CR3 register is set. Figure 268
shows an example of communication with CTS flow control enabled.

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Universal synchronous asynchronous receiver transmitter (USART)
Figure 268. RS232 CTS flow control
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Note:

For correct behavior, CTS must be asserted at least 3 USART clock source periods before
the end of the current character. In addition it should be noted that the CTSCF flag may not
be set for pulses shorter than 2 x PCLK periods.
For code example refer to the Appendix section A.19.12: USART hardware flow control
code example.

RS485 Driver Enable
The driver enable feature is enabled by setting bit DEM in the USART_CR3 control register.
This allows the user to activate the external transceiver control, through the DE (Driver
Enable) signal. The assertion time is the time between the activation of the DE signal and
the beginning of the START bit. It is programmed using the DEAT [4:0] bit fields in the
USART_CR1 control register. The de-assertion time is the time between the end of the last
stop bit, in a transmitted message, and the de-activation of the DE signal. It is programmed
using the DEDT [4:0] bit fields in the USART_CR1 control register. The polarity of the DE
signal can be configured using the DEP bit in the USART_CR3 control register.
In USART, the DEAT and DEDT are expressed in sample time units (1/8 or 1/16 bit duration,
depending on the oversampling rate).

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27.5.17

RM0091

Wakeup from Stop mode using USART
The USART is able to wake up the MCU from Stopmode when the UESM bit is set and the
USART clock is set to HSI or LSE (refer to Section Reset and clock control (RCC)).
•

USART source clock is HSI
If during stop mode the HSI clock is switched OFF, when a falling edge on the USART
receive line is detected, the USART interface requests the HSI clock to be switched
ON. The HSI clock is then used for the frame reception.

•

–

If the wakeup event is verified, the MCU wakes up from low-power mode and data
reception goes on normally.

–

If the wakeup event is not verified, the HSI clock is switched OFF again, the MCU
is not waken up and stays in low-power mode and the clock request is released.

USART source clock is LSE
Same principle as described in case of USART source clock is HSI with the difference
that the LSE is ON in stop mode, but the LSE clock is not propagated to USART if the
USART is not requesting it. The LSE clock is not OFF but there is a clock gating to
avoid useless consumption.

The MCU wakeup from Stop mode can be done using the standard RXNE interrupt. In this
case, the RXNEIE bit must be set before entering Stop mode.
Alternatively, a specific interrupt may be selected through the WUS bit fields.
In order to be able to wake up the MCU from Stop mode, the UESM bit in the USART_CR1
control register must be set prior to entering Stop mode.
When the wakeup event is detected, the WUF flag is set by hardware and a wakeup
interrupt is generated if the WUFIE bit is set.
Note:

Before entering Stop mode, the user must ensure that the USART is not performing a
transfer. BUSY flag cannot ensure that Stop mode is never entered during a running
reception.
The WUF flag is set when a wakeup event is detected, independently of whether the MCU is
in Stop or in an active mode.
When entering Stop mode just after having initialized and enabled the receiver, the REACK
bit must be checked to ensure the USART is actually enabled.
When DMA is used for reception, it must be disabled before entering Stop mode and reenabled upon exit from Stop mode.
The wakeup from Stop mode feature is not available for all modes. For example it doesn’t
work in SPI mode because the SPI operates in master mode only.

Using Mute mode with Stop mode
If the USART is put into Mute mode before entering Stop mode:

728/1004

•

Wakeup from Mute mode on idle detection must not be used, because idle detection
cannot work in Stop mode.

•

If the wakeup from Mute mode on address match is used, then the source of wake-up
from Stop mode must also be the address match. If the RXNE flag is set when entering
the Stop mode, the interface will remain in mute mode upon address match and wake
up from Stop.

•

If the USART is configured to wake up the MCU from Stop mode on START bit
detection, the WUF flag is set, but the RXNE flag is not set.

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Universal synchronous asynchronous receiver transmitter (USART)

Determining the maximum USART baudrate allowing to wakeup correctly
from Stop mode when the USART clock source is the HSI clock
The maximum baudrate allowing to wakeup correctly from stop mode depends on:
•

the parameter tWUUSART provided in the device datasheet

•

the USART receiver tolerance provided in the Section 27.5.5: Tolerance of the USART
receiver to clock deviation.

Let us take this example: OVER8 = 0, M bits = 01, ONEBIT = 0, BRR [3:0] = 0000.
In these conditions, according to Table 105: Tolerance of the USART receiver when BRR
[3:0] = 0000, the USART receiver tolerance is 3.41 %.
DTRA + DQUANT + DREC + DTCL + DWU < USART receiver's tolerance
DWU max = tWUUSART / (11 x Tbit Min)
Tbit Min = tWUUSART / (11 x DWU max)
If we consider an ideal case where the parameters DTRA, DQUANT, DREC and DTCL are
at 0%, the DWU max is 3.41 %. In reality, we need to consider at least the HSI inaccuracy.
Let us consider HSI inaccuracy = 1 %, tWUUSART = 3 μs (values provided as example, for
correct values, please refer to the device datasheet):
DWU max = 3.41 % - 1 % = 2.41 %
Tbit min = 3 μs / (11 ₓ 2.41 %) = 11.32 μs
In these conditions, the maximum baudrate allowing to wakeup correctly from Stop mode is
1/11.32 μs = 88.36 Kbaud.

27.6

USART low-power modes
Table 108. Effect of low-power modes on the USART
Mode

27.7

Description

Sleep

No effect. USART interrupt causes the device to exit Sleep mode.

Stop

The USART is able to wake up the MCU from Stop mode when the UESM
bit is set and the USART clock is set to HSI or LSE.
The MCU wakeup from Stop mode can be done using either a standard
RXNE or a WUF interrupt.

Standby

The USART is powered down and must be reinitialized when the device
has exited from Standby mode.

USART interrupts
Table 109. USART interrupt requests
Interrupt event
Transmit data register empty
CTS interrupt

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Event flag

Enable Control
bit

TXE

TXEIE

CTSIF

CTSIE

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Table 109. USART interrupt requests (continued)
Interrupt event
Transmission Complete
Receive data register not empty (data ready to be read)

Event flag

Enable Control
bit

TC

TCIE

RXNE

RXNEIE

Overrun error detected

ORE

Idle line detected

IDLE

IDLEIE

PE

PEIE

LBDF

LBDIE

NF or ORE or FE

EIE

Character match

CMF

CMIE

Receiver timeout

RTOF

RTOIE

End of Block

EOBF

EOBIE

Parity error
LIN break
Noise Flag, Overrun error and Framing Error in multibuffer
communication.

(1)

Wakeup from Stop mode

WUF

WUFIE

1. The WUF interrupt is active only in Stop mode.

The USART interrupt events are connected to the same interrupt vector (see Figure 269).
•

During transmission: Transmission Complete, Clear to Send, Transmit data Register
empty or Framing error (in Smartcard mode) interrupt.

•

During reception: Idle Line detection, Overrun error, Receive data register not empty,
Parity error, LIN break detection, Noise Flag, Framing Error, Character match, etc.

These events generate an interrupt if the corresponding Enable Control Bit is set.

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Figure 269. USART interrupt mapping diagram
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27.8

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USART registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

27.8.1

Control register 1 (USART_CR1)
Address offset: 0x00
Reset value: 0x0000

31

30

29

28

27

26

Res.

Res.

Res.

M1

EOBIE

RTOIE

rw

rw

rw

25

24

23

22

21

20

19

DEAT[4:0]
rw

rw

rw

18

17

16

rw

rw

DEDT[4:0]
rw

15

14

13

12

11

10

9

8

7

6

OVER8

CMIE

MME

M0

WAKE

PCE

PS

PEIE

TXEIE

TCIE

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

5

4

RXNEIE IDLEIE
rw

rw

rw

rw

3

2

1

0

TE

RE

UESM

UE

rw

rw

rw

rw

Bits 31:29 Reserved, must be kept at reset value
Bit 28 M1: Word length
This bit, with bit 12 (M0), determines the word length. It is set or cleared by software.
M[1:0] = 00: 1 Start bit, 8 data bits, n stop bits
M[1:0] = 01: 1 Start bit, 9 data bits, n stop bits
M[1:0] = 10: 1 Start bit, 7 data bits, n stop bits
This bit can only be written when the USART is disabled (UE=0).
Note: In 7-bit data length mode, the Smartcard mode, LIN master mode and Autobaudrate
(0x7F and 0x55 frames detection) are not supported.
Bit 27 EOBIE: End of Block interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated when the EOBF flag is set in the USART_ISR register
Note: If the USART does not support Smartcard mode, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 26 RTOIE: Receiver timeout interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: An USART interrupt is generated when the RTOF bit is set in the USART_ISR register.
Note: If the USART does not support the Receiver timeout feature, this bit is reserved and
forced by hardware to ‘0’. Section 27.4: USART implementation on page 689.
Bits 25:21 DEAT[4:0]: Driver Enable assertion time
This 5-bit value defines the time between the activation of the DE (Driver Enable) signal and
the beginning of the start bit. It is expressed in sample time units (1/8 or 1/16 bit duration,
depending on the oversampling rate).
This bit field can only be written when the USART is disabled (UE=0).
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
cleared. Please refer to Section 27.4: USART implementation on page 689.

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Bits 20:16 DEDT[4:0]: Driver Enable de-assertion time
This 5-bit value defines the time between the end of the last stop bit, in a transmitted
message, and the de-activation of the DE (Driver Enable) signal. It is expressed in sample
time units (1/8 or 1/16 bit duration, depending on the oversampling rate).
If the USART_TDR register is written during the DEDT time, the new data is transmitted only
when the DEDT and DEAT times have both elapsed.
This bit field can only be written when the USART is disabled (UE=0).
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
cleared. Please refer to Section 27.4: USART implementation on page 689.
Bit 15 OVER8: Oversampling mode
0: Oversampling by 16
1: Oversampling by 8
This bit can only be written when the USART is disabled (UE=0).
Note: In LIN, IrDA and modes, this bit must be kept cleared.
Bit 14 CMIE: Character match interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated when the CMF bit is set in the USART_ISR register.
Bit 13 MME: Mute mode enable
This bit activates the mute mode function of the USART. when set, the USART can switch
between the active and mute modes, as defined by the WAKE bit. It is set and cleared by
software.
0: Receiver in active mode permanently
1: Receiver can switch between mute mode and active mode.
Bit 12 M0: Word length
This bit, with bit 28 (M1), determines the word length. It is set or cleared by software. See Bit
28 (M1) description.
This bit can only be written when the USART is disabled (UE=0).
Bit 11 WAKE: Receiver wakeup method
This bit determines the USART wakeup method from Mute mode. It is set or cleared by
software.
0: Idle line
1: Address mark
This bit field can only be written when the USART is disabled (UE=0).
Bit 10 PCE: Parity control enable
This bit selects the hardware parity control (generation and detection). When the parity
control is enabled, the computed parity is inserted at the MSB position (9th bit if M=1; 8th bit
if M=0) and parity is checked on the received data. This bit is set and cleared by software.
Once it is set, PCE is active after the current byte (in reception and in transmission).
0: Parity control disabled
1: Parity control enabled
This bit field can only be written when the USART is disabled (UE=0).
Bit 9 PS: Parity selection
This bit selects the odd or even parity when the parity generation/detection is enabled (PCE
bit set). It is set and cleared by software. The parity will be selected after the current byte.
0: Even parity
1: Odd parity
This bit field can only be written when the USART is disabled (UE=0).

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Bit 8 PEIE: PE interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated whenever PE=1 in the USART_ISR register
Bit 7 TXEIE: interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated whenever TXE=1 in the USART_ISR register
Bit 6 TCIE: Transmission complete interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated whenever TC=1 in the USART_ISR register
Bit 5 RXNEIE: RXNE interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated whenever ORE=1 or RXNE=1 in the USART_ISR
register
Bit 4 IDLEIE: IDLE interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: A USART interrupt is generated whenever IDLE=1 in the USART_ISR register
Bit 3 TE: Transmitter enable
This bit enables the transmitter. It is set and cleared by software.
0: Transmitter is disabled
1: Transmitter is enabled
Note: During transmission, a “0” pulse on the TE bit (“0” followed by “1”) sends a preamble
(idle line) after the current word, except in Smartcard mode. In order to generate an idle
character, the TE must not be immediately written to 1. In order to ensure the required
duration, the software can poll the TEACK bit in the USART_ISR register.
In Smartcard mode, when TE is set there is a 1 bit-time delay before the transmission
starts.

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Bit 2 RE: Receiver enable
This bit enables the receiver. It is set and cleared by software.
0: Receiver is disabled
1: Receiver is enabled and begins searching for a start bit
Bit 1 UESM: USART enable in Stop mode
When this bit is cleared, the USART is not able to wake up the MCU from Stop mode.
When this bit is set, the USART is able to wake up the MCU from Stop mode, provided that
the USART clock selection is HSI or LSE in the RCC.
This bit is set and cleared by software.
0: USART not able to wake up the MCU from Stop mode.
1: USART able to wake up the MCU from Stop mode. When this function is active, the clock
source for the USART must be HSI or LSE (see Section Reset and clock control (RCC).
Note: It is recommended to set the UESM bit just before entering Stop mode and clear it on
exit from Stop mode.
If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’. Please refer to Section 27.4: USART implementation on
page 689.
Bit 0 UE: USART enable
When this bit is cleared, the USART prescalers and outputs are stopped immediately, and
current operations are discarded. The configuration of the USART is kept, but all the status
flags, in the USART_ISR are set to their default values. This bit is set and cleared by
software.
0: USART prescaler and outputs disabled, low-power mode
1: USART enabled
Note: In order to go into low-power mode without generating errors on the line, the TE bit
must be reset before and the software must wait for the TC bit in the USART_ISR to be
set before resetting the UE bit.
The DMA requests are also reset when UE = 0 so the DMA channel must be disabled
before resetting the UE bit.

27.8.2

Control register 2 (USART_CR2)
Address offset: 0x04
Reset value: 0x0000

31

30

29

28

27

ADD[7:4]

26

25

24

ADD[3:0]

23
RTOEN

22

21

ABRMOD[1:0]

20

19

18

17

MSBFI
ABREN
DATAINV TXINV
RST

16
RXINV

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

SWAP

LINEN

CLKEN

CPOL

CPHA

LBCL

Res.

LBDIE

LBDL

ADDM7

Res.

Res.

Res.

Res.

rw

rw

rw

rw

rw

rw

rw

rw

rw

STOP[1:0]
rw

rw

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Bits 31:28 ADD[7:4]: Address of the USART node
This bit-field gives the address of the USART node or a character code to be recognized.
This is used in multiprocessor communication during Mute mode or Stop mode, for wakeup with 7bit address mark detection. The MSB of the character sent by the transmitter should be equal to 1.
It may also be used for character detection during normal reception, Mute mode inactive (for
example, end of block detection in ModBus protocol). In this case, the whole received character (8bit) is compared to the ADD[7:0] value and CMF flag is set on match.
This bit field can only be written when reception is disabled (RE = 0) or the USART is disabled
(UE=0)
Bits 27:24 ADD[3:0]: Address of the USART node
This bit-field gives the address of the USART node or a character code to be recognized.
This is used in multiprocessor communication during Mute mode or Stop mode, for wakeup with
address mark detection.
This bit field can only be written when reception is disabled (RE = 0) or the USART is disabled
(UE=0)
Bit 23 RTOEN: Receiver timeout enable
This bit is set and cleared by software.
0: Receiver timeout feature disabled.
1: Receiver timeout feature enabled.
When this feature is enabled, the RTOF flag in the USART_ISR register is set if the RX line is idle
(no reception) for the duration programmed in the RTOR (receiver timeout register).
Note: If the USART does not support the Receiver timeout feature, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bits 22:21 ABRMOD[1:0]: Auto baud rate mode
These bits are set and cleared by software.
00: Measurement of the start bit is used to detect the baud rate.
01: Falling edge to falling edge measurement. (the received frame must start with a single bit = 1 ->
Frame = Start10xxxxxx)
10: 0x7F frame detection.
11: 0x55 frame detection
This bit field can only be written when ABREN = 0 or the USART is disabled (UE=0).
Note: If DATAINV=1 and/or MSBFIRST=1 the patterns must be the same on the line, for example
0xAA for MSBFIRST)
If the USART does not support the auto baud rate feature, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 20 ABREN: Auto baud rate enable
This bit is set and cleared by software.
0: Auto baud rate detection is disabled.
1: Auto baud rate detection is enabled.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 19 MSBFIRST: Most significant bit first
This bit is set and cleared by software.
0: data is transmitted/received with data bit 0 first, following the start bit.
1: data is transmitted/received with the MSB (bit 7/8/9) first, following the start bit.
This bit field can only be written when the USART is disabled (UE=0).

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Bit 18 DATAINV: Binary data inversion
This bit is set and cleared by software.
0: Logical data from the data register are send/received in positive/direct logic. (1=H, 0=L)
1: Logical data from the data register are send/received in negative/inverse logic. (1=L, 0=H). The
parity bit is also inverted.
This bit field can only be written when the USART is disabled (UE=0).
Bit 17 TXINV: TX pin active level inversion
This bit is set and cleared by software.
0: TX pin signal works using the standard logic levels (VDD =1/idle, Gnd=0/mark)
1: TX pin signal values are inverted. (VDD =0/mark, Gnd=1/idle).
This allows the use of an external inverter on the TX line.
This bit field can only be written when the USART is disabled (UE=0).
Bit 16 RXINV: RX pin active level inversion
This bit is set and cleared by software.
0: RX pin signal works using the standard logic levels (VDD =1/idle, Gnd=0/mark)
1: RX pin signal values are inverted. (VDD =0/mark, Gnd=1/idle).
This allows the use of an external inverter on the RX line.
This bit field can only be written when the USART is disabled (UE=0).
Bit 15 SWAP: Swap TX/RX pins
This bit is set and cleared by software.
0: TX/RX pins are used as defined in standard pinout
1: The TX and RX pins functions are swapped. This allows to work in the case of a cross-wired
connection to another USART.
This bit field can only be written when the USART is disabled (UE=0).
Bit 14 LINEN: LIN mode enable
This bit is set and cleared by software.
0: LIN mode disabled
1: LIN mode enabled
The LIN mode enables the capability to send LIN Sync Breaks (13 low bits) using the SBKRQ bit in
the USART_RQR register, and to detect LIN Sync breaks.
This bit field can only be written when the USART is disabled (UE=0).
Note: If the USART does not support LIN mode, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bits 13:12 STOP[1:0]: STOP bits
These bits are used for programming the stop bits.
00: 1 stop bit
01: 0.5 stop bit
10: 2 stop bits
11: 1.5 stop bits
This bit field can only be written when the USART is disabled (UE=0).
Bit 11 CLKEN: Clock enable
This bit allows the user to enable the CK pin.
0: CK pin disabled
1: CK pin enabled
This bit can only be written when the USART is disabled (UE=0).
Note: If neither synchronous mode nor Smartcard mode is supported, this bit is reserved and forced
by hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.

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Note: In order to provide correctly the CK clock to the Smartcard when CK is always available When
CLKEN = 1, regardless of the UE bit value, the steps below must be respected:
- UE = 0
- SCEN = 1
- GTPR configuration (If PSC needs to be configured, it is recommended to configure PSC and
GT in a single access to USART_ GTPR register).
- CLKEN= 1
- UE = 1
Bit 10 CPOL: Clock polarity
This bit allows the user to select the polarity of the clock output on the CK pin in synchronous mode.
It works in conjunction with the CPHA bit to produce the desired clock/data relationship
0: Steady low value on CK pin outside transmission window
1: Steady high value on CK pin outside transmission window
This bit can only be written when the USART is disabled (UE=0).
Note: If synchronous mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bit 9 CPHA: Clock phase
This bit is used to select the phase of the clock output on the CK pin in synchronous mode. It works
in conjunction with the CPOL bit to produce the desired clock/data relationship (see Figure 257 and
Figure 258)
0: The first clock transition is the first data capture edge
1: The second clock transition is the first data capture edge
This bit can only be written when the USART is disabled (UE=0).
Note: If synchronous mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bit 8 LBCL: Last bit clock pulse
This bit is used to select whether the clock pulse associated with the last data bit transmitted (MSB)
has to be output on the CK pin in synchronous mode.
0: The clock pulse of the last data bit is not output to the CK pin
1: The clock pulse of the last data bit is output to the CK pin
Caution: The last bit is the 7th or 8th or 9th data bit transmitted depending on the 7 or 8 or 9 bit
format selected by the M bits in the USART_CR1 register.
This bit can only be written when the USART is disabled (UE=0).
Note: If synchronous mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bit 7 Reserved, must be kept at reset value.
Bit 6 LBDIE: LIN break detection interrupt enable
Break interrupt mask (break detection using break delimiter).
0: Interrupt is inhibited
1: An interrupt is generated whenever LBDF=1 in the USART_ISR register
Note: If LIN mode is not supported, this bit is reserved and forced by hardware to ‘0’. Please refer to
Section 27.4: USART implementation on page 689.

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Bit 5 LBDL: LIN break detection length
This bit is for selection between 11 bit or 10 bit break detection.
0: 10-bit break detection
1: 11-bit break detection
This bit can only be written when the USART is disabled (UE=0).
Note: If LIN mode is not supported, this bit is reserved and forced by hardware to ‘0’. Please refer to
Section 27.4: USART implementation on page 689.
Bit 4 ADDM7:7-bit Address Detection/4-bit Address Detection
This bit is for selection between 4-bit address detection or 7-bit address detection.
0: 4-bit address detection
1: 7-bit address detection (in 8-bit data mode)
This bit can only be written when the USART is disabled (UE=0)
Note: In 7-bit and 9-bit data modes, the address detection is done on 6-bit and 8-bit address
(ADD[5:0] and ADD[7:0]) respectively.
Bits 3:0 Reserved, must be kept at reset value.

Note:

The 3 bits (CPOL, CPHA, LBCL) should not be written while the transmitter is enabled.

27.8.3

Control register 3 (USART_CR3)
Address offset: 0x08
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WUFIE

15

14

21

20

19

WUS

18

17

16

SCARCNT2:0]

Res.

rw

rw

rw

rw

rw

rw

13

12

11

10

9

8

7

6

5

4

3

2

1

0

ONE
BIT

CTSIE

CTSE

RTSE

DMAT

DMAR

SCEN

NACK

HDSEL

IRLP

IREN

EIE

rw

rw

rw

rw

rw

rw

v

v

rw

rw

rw

rw

DEP

DEM

DDRE

OVR
DIS

rw

rw

rw

rw

Bits 31:25 Reserved, must be kept at reset value.
Bit 24 Reserved, must be kept at reset value.
Bit 23 Reserved, must be kept at reset value.
Bit 22 WUFIE: Wakeup from Stop mode interrupt enable
This bit is set and cleared by software.
0: Interrupt is inhibited
1: An USART interrupt is generated whenever WUF=1 in the USART_ISR register
Note: WUFIE must be set before entering in Stop mode.
The WUF interrupt is active only in Stop mode.
If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.

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Bits 21:20 WUS[1:0]: Wakeup from Stop mode interrupt flag selection
This bit-field specify the event which activates the WUF (wakeup from Stop mode flag).
00: WUF active on address match (as defined by ADD[7:0] and ADDM7)
01:Reserved.
10: WuF active on Start bit detection
11: WUF active on RXNE.
This bit field can only be written when the USART is disabled (UE=0).
Note: If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.
Bits 19:17 SCARCNT[2:0]: Smartcard auto-retry count
This bit-field specifies the number of retries in transmit and receive, in Smartcard mode.
In transmission mode, it specifies the number of automatic retransmission retries, before
generating a transmission error (FE bit set).
In reception mode, it specifies the number or erroneous reception trials, before generating a
reception error (RXNE and PE bits set).
This bit field must be programmed only when the USART is disabled (UE=0).
When the USART is enabled (UE=1), this bit field may only be written to 0x0, in order to stop
retransmission.
0x0: retransmission disabled - No automatic retransmission in transmit mode.
0x1 to 0x7: number of automatic retransmission attempts (before signaling error)
Note: If Smartcard mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bit16 Reserved, must be kept at reset value.
Bit 15 DEP: Driver enable polarity selection
0: DE signal is active high.
1: DE signal is active low.
This bit can only be written when the USART is disabled (UE=0).
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
cleared. Please refer to Section 27.4: USART implementation on page 689.
Bit 14 DEM: Driver enable mode
This bit allows the user to activate the external transceiver control, through the DE signal.
0: DE function is disabled.
1: DE function is enabled. The DE signal is output on the RTS pin.
This bit can only be written when the USART is disabled (UE=0).
Note: If the Driver Enable feature is not supported, this bit is reserved and must be kept
cleared. Section 27.4: USART implementation on page 689.
Bit 13 DDRE: DMA Disable on Reception Error
0: DMA is not disabled in case of reception error. The corresponding error flag is set but
RXNE is kept 0 preventing from overrun. As a consequence, the DMA request is not
asserted, so the erroneous data is not transferred (no DMA request), but next correct
received data will be transferred (used for Smartcard mode).
1: DMA is disabled following a reception error. The corresponding error flag is set, as well as
RXNE. The DMA request is masked until the error flag is cleared. This means that the
software must first disable the DMA request (DMAR = 0) or clear RXNE before clearing the
error flag.
This bit can only be written when the USART is disabled (UE=0).
Note: The reception errors are: parity error, framing error or noise error.

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Bit 12 OVRDIS: Overrun Disable
This bit is used to disable the receive overrun detection.
0: Overrun Error Flag, ORE, is set when received data is not read before receiving new data.
1: Overrun functionality is disabled. If new data is received while the RXNE flag is still set
the ORE flag is not set and the new received data overwrites the previous content of the
USART_RDR register.
This bit can only be written when the USART is disabled (UE=0).
Note: This control bit allows checking the communication flow without reading the data.
Bit 11 ONEBIT: One sample bit method enable
This bit allows the user to select the sample method. When the one sample bit method is
selected the noise detection flag (NF) is disabled.
0: Three sample bit method
1: One sample bit method
This bit can only be written when the USART is disabled (UE=0).
Note: ONEBIT feature applies only to data bits, It does not apply to Start bit.
Bit 10 CTSIE: CTS interrupt enable
0: Interrupt is inhibited
1: An interrupt is generated whenever CTSIF=1 in the USART_ISR register
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 9 CTSE: CTS enable
0: CTS hardware flow control disabled
1: CTS mode enabled, data is only transmitted when the CTS input is asserted (tied to 0). If
the CTS input is de-asserted while data is being transmitted, then the transmission is
completed before stopping. If data is written into the data register while CTS is de-asserted,
the transmission is postponed until CTS is asserted.
This bit can only be written when the USART is disabled (UE=0)
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 8 RTSE: RTS enable
0: RTS hardware flow control disabled
1: RTS output enabled, data is only requested when there is space in the receive buffer. The
transmission of data is expected to cease after the current character has been transmitted.
The RTS output is asserted (pulled to 0) when data can be received.
This bit can only be written when the USART is disabled (UE=0).
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 7 DMAT: DMA enable transmitter
This bit is set/reset by software
1: DMA mode is enabled for transmission
0: DMA mode is disabled for transmission
Bit 6 DMAR: DMA enable receiver
This bit is set/reset by software
1: DMA mode is enabled for reception
0: DMA mode is disabled for reception

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Bit 5 SCEN: Smartcard mode enable
This bit is used for enabling Smartcard mode.
0: Smartcard Mode disabled
1: Smartcard Mode enabled
This bit field can only be written when the USART is disabled (UE=0).
Note: If the USART does not support Smartcard mode, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 4 NACK: Smartcard NACK enable
0: NACK transmission in case of parity error is disabled
1: NACK transmission during parity error is enabled
This bit field can only be written when the USART is disabled (UE=0).
Note: If the USART does not support Smartcard mode, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 3 HDSEL: Half-duplex selection
Selection of Single-wire Half-duplex mode
0: Half duplex mode is not selected
1: Half duplex mode is selected
This bit can only be written when the USART is disabled (UE=0).
Bit 2 IRLP: IrDA low-power
This bit is used for selecting between normal and low-power IrDA modes
0: Normal mode
1: Low-power mode
This bit can only be written when the USART is disabled (UE=0).
Note: If IrDA mode is not supported, this bit is reserved and forced by hardware to ‘0’. Please
refer to Section 27.4: USART implementation on page 689.
Bit 1 IREN: IrDA mode enable
This bit is set and cleared by software.
0: IrDA disabled
1: IrDA enabled
This bit can only be written when the USART is disabled (UE=0).
Note: If IrDA mode is not supported, this bit is reserved and forced by hardware to ‘0’. Please
refer to Section 27.4: USART implementation on page 689.
Bit 0 EIE: Error interrupt enable
Error Interrupt Enable Bit is required to enable interrupt generation in case of a framing
error, overrun error or noise flag (FE=1 or ORE=1 or NF=1 in the USART_ISR register).
0: Interrupt is inhibited
1: An interrupt is generated when FE=1 or ORE=1 or NF=1 in the USART_ISR register.

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27.8.4

Baud rate register (USART_BRR)
This register can only be written when the USART is disabled (UE=0). It may be
automatically updated by hardware in auto baud rate detection mode.
Address offset: 0x0C
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

BRR[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:16 Reserved, must be kept at reset value.
Bits 15:4 BRR[15:4]
BRR[15:4] = USARTDIV[15:4]
Bits 3:0 BRR[3:0]
When OVER8 = 0, BRR[3:0] = USARTDIV[3:0].
When OVER8 = 1:
BRR[2:0] = USARTDIV[3:0] shifted 1 bit to the right.
BRR[3] must be kept cleared.

27.8.5

Guard time and prescaler register (USART_GTPR)
Address offset: 0x10
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

GT[7:0]

PSC[7:0]

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Bits 31:16 Reserved, must be kept at reset value
Bits 15:8 GT[7:0]: Guard time value
This bit-field is used to program the Guard time value in terms of number of baud clock
periods.
This is used in Smartcard mode. The Transmission Complete flag is set after this guard time
value.
This bit field can only be written when the USART is disabled (UE=0).
Note: If Smartcard mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bits 7:0 PSC[7:0]: Prescaler value
In IrDA Low-power and normal IrDA mode:
PSC[7:0] = IrDA Normal and Low-Power Baud Rate
Used for programming the prescaler for dividing the USART source clock to achieve the lowpower frequency:
The source clock is divided by the value given in the register (8 significant bits):
00000000: Reserved - do not program this value
00000001: divides the source clock by 1
00000010: divides the source clock by 2
...
In Smartcard mode:
PSC[4:0]: Prescaler value
Used for programming the prescaler for dividing the USART source clock to provide the
Smartcard clock.
The value given in the register (5 significant bits) is multiplied by 2 to give the division factor
of the source clock frequency:
00000: Reserved - do not program this value
00001: divides the source clock by 2
00010: divides the source clock by 4
00011: divides the source clock by 6
...
This bit field can only be written when the USART is disabled (UE=0).
Note: Bits [7:5] must be kept cleared if Smartcard mode is used.
This bit field is reserved and forced by hardware to ‘0’ when the Smartcard and IrDA
modes are not supported. Please refer to Section 27.4: USART implementation on
page 689.

27.8.6

Receiver timeout register (USART_RTOR)
Address offset: 0x14
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

BLEN[7:0]

20

19

18

17

16

RTO[23:16]

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rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

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Bits 31:24 BLEN[7:0]: Block Length
This bit-field gives the Block length in Smartcard T=1 Reception. Its value equals the number
of information characters + the length of the Epilogue Field (1-LEC/2-CRC) - 1.
Examples:
BLEN = 0 -> 0 information characters + LEC
BLEN = 1 -> 0 information characters + CRC
BLEN = 255 -> 254 information characters + CRC (total 256 characters))
In Smartcard mode, the Block length counter is reset when TXE=0.
This bit-field can be used also in other modes. In this case, the Block length counter is reset
when RE=0 (receiver disabled) and/or when the EOBCF bit is written to 1.
Note: This value can be programmed after the start of the block reception (using the data
from the LEN character in the Prologue Field). It must be programmed only once per
received block.
Bits 23:0 RTO[23:0]: Receiver timeout value
This bit-field gives the Receiver timeout value in terms of number of bit duration.
In standard mode, the RTOF flag is set if, after the last received character, no new start bit is
detected for more than the RTO value.
In Smartcard mode, this value is used to implement the CWT and BWT. See Smartcard
section for more details.
In this case, the timeout measurement is done starting from the Start Bit of the last received
character.
Note: This value must only be programmed once per received character.

Note:

RTOR can be written on the fly. If the new value is lower than or equal to the counter, the
RTOF flag is set.
This register is reserved and forced by hardware to “0x00000000” when the Receiver
timeout feature is not supported. Please refer to Section 27.4: USART implementation on
page 689.

27.8.7

Request register (USART_RQR)
Address offset: 0x18
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

4

3

2

1

0

15

14

13

12

11

10

9

8

7

6

5

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TXFRQ RXFRQ MMRQ SBKRQ ABRRQ
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Bits 31:5 Reserved, must be kept at reset value
Bit 4 TXFRQ: Transmit data flush request
Writing 1 to this bit sets the TXE flag.
This allows to discard the transmit data. This bit must be used only in Smartcard mode,
when data has not been sent due to errors (NACK) and the FE flag is active in the
USART_ISR register.
If the USART does not support Smartcard mode, this bit is reserved and forced by hardware
to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 3 RXFRQ: Receive data flush request
Writing 1 to this bit clears the RXNE flag.
This allows to discard the received data without reading it, and avoid an overrun condition.
Bit 2 MMRQ: Mute mode request
Writing 1 to this bit puts the USART in mute mode and sets the RWU flag.
Bit 1 SBKRQ: Send break request
Writing 1 to this bit sets the SBKF flag and request to send a BREAK on the line, as soon as
the transmit machine is available.
Note: In the case the application needs to send the break character following all previously
inserted data, including the ones not yet transmitted, the software should wait for the
TXE flag assertion before setting the SBKRQ bit.
Bit 0 ABRRQ: Auto baud rate request
Writing 1 to this bit resets the ABRF flag in the USART_ISR and request an automatic baud
rate measurement on the next received data frame.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and
forced by hardware to ‘0’. Please refer to Section 27.4: USART implementation on
page 689.

27.8.8

Interrupt and status register (USART_ISR)
Address offset: 0x1C
Reset value: 0x0200 00C0

31

30

29

28

27

26

25

24

23

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

22

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

ABRF

ABRE

Res.

EOBF

RTOF

CTS

CTSIF

LBDF

TXE

TC

RXNE

IDLE

ORE

NF

FE

PE

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

Bits 31:25 Reserved, must be kept at reset value.
Bits 24:23 Reserved, must be kept at reset value.

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16

WUF

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Bit 22 REACK: Receive enable acknowledge flag
This bit is set/reset by hardware, when the Receive Enable value is taken into account by
the USART.
When the wakeup from Stop mode is supported, the REACK flag can be used to verify that
the USART is ready for reception before entering Stop mode.
Bit 21 TEACK: Transmit enable acknowledge flag
This bit is set/reset by hardware, when the Transmit Enable value is taken into account by
the USART.
It can be used when an idle frame request is generated by writing TE=0, followed by TE=1
in the USART_CR1 register, in order to respect the TE=0 minimum period.
Bit 20 WUF: Wakeup from Stop mode flag
This bit is set by hardware, when a wakeup event is detected. The event is defined by the
WUS bit field. It is cleared by software, writing a 1 to the WUCF in the USART_ICR register.
An interrupt is generated if WUFIE=1 in the USART_CR3 register.
Note: When UESM is cleared, WUF flag is also cleared.
The WUF interrupt is active only in Stop mode.
If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 19 RWU: Receiver wakeup from Mute mode
This bit indicates if the USART is in mute mode. It is cleared/set by hardware when a
wakeup/mute sequence is recognized. The mute mode control sequence (address or IDLE)
is selected by the WAKE bit in the USART_CR1 register.
When wakeup on IDLE mode is selected, this bit can only be set by software, writing 1 to the
MMRQ bit in the USART_RQR register.
0: Receiver in active mode
1: Receiver in mute mode
Bit 18 SBKF: Send break flag
This bit indicates that a send break character was requested. It is set by software, by writing
1 to the SBKRQ bit in the USART_RQR register. It is automatically reset by hardware during
the stop bit of break transmission.
0: No break character is transmitted
1: Break character will be transmitted
Bit 17 CMF: Character match flag
This bit is set by hardware, when the character defined by ADD[7:0] is received. It is cleared
by software, writing 1 to the CMCF in the USART_ICR register.
An interrupt is generated if CMIE=1in the USART_CR1 register.
0: No Character match detected
1: Character Match detected
Bit 16 BUSY: Busy flag
This bit is set and reset by hardware. It is active when a communication is ongoing on the
RX line (successful start bit detected). It is reset at the end of the reception (successful or
not).
0: USART is idle (no reception)
1: Reception on going

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Bit 15 ABRF: Auto baud rate flag
This bit is set by hardware when the automatic baud rate has been set (RXNE will also be
set, generating an interrupt if RXNEIE = 1) or when the auto baud rate operation was
completed without success (ABRE=1) (ABRE, RXNE and FE are also set in this case)
It is cleared by software, in order to request a new auto baud rate detection, by writing 1 to
the ABRRQ in the USART_RQR register.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 14 ABRE: Auto baud rate error
This bit is set by hardware if the baud rate measurement failed (baud rate out of range or
character comparison failed)
It is cleared by software, by writing 1 to the ABRRQ bit in the USART_CR3 register.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 13 Reserved, must be kept at reset value.
Bit 12 EOBF: End of block flag
This bit is set by hardware when a complete block has been received (for example T=1
Smartcard mode). The detection is done when the number of received bytes (from the start
of the block, including the prologue) is equal or greater than BLEN + 4.
An interrupt is generated if the EOBIE=1 in the USART_CR2 register.
It is cleared by software, writing 1 to the EOBCF in the USART_ICR register.
0: End of Block not reached
1: End of Block (number of characters) reached
Note: If Smartcard mode is not supported, this bit is reserved and forced by hardware to ‘0’.
Please refer to Section 27.4: USART implementation on page 689.
Bit 11 RTOF: Receiver timeout
This bit is set by hardware when the timeout value, programmed in the RTOR register has
lapsed, without any communication. It is cleared by software, writing 1 to the RTOCF bit in
the USART_ICR register.
An interrupt is generated if RTOIE=1 in the USART_CR1 register.
In Smartcard mode, the timeout corresponds to the CWT or BWT timings.
0: Timeout value not reached
1: Timeout value reached without any data reception
Note: If a time equal to the value programmed in RTOR register separates 2 characters,
RTOF is not set. If this time exceeds this value + 2 sample times (2/16 or 2/8,
depending on the oversampling method), RTOF flag is set.
The counter counts even if RE = 0 but RTOF is set only when RE = 1. If the timeout has
already elapsed when RE is set, then RTOF will be set.
If the USART does not support the Receiver timeout feature, this bit is reserved and
forced by hardware to ‘0’.
Bit 10 CTS: CTS flag
This bit is set/reset by hardware. It is an inverted copy of the status of the CTS input pin.
0: CTS line set
1: CTS line reset
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
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Bit 9 CTSIF: CTS interrupt flag
This bit is set by hardware when the CTS input toggles, if the CTSE bit is set. It is cleared by
software, by writing 1 to the CTSCF bit in the USART_ICR register.
An interrupt is generated if CTSIE=1 in the USART_CR3 register.
0: No change occurred on the CTS status line
1: A change occurred on the CTS status line
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’.
Bit 8 LBDF: LIN break detection flag
This bit is set by hardware when the LIN break is detected. It is cleared by software, by
writing 1 to the LBDCF in the USART_ICR.
An interrupt is generated if LBDIE = 1 in the USART_CR2 register.
0: LIN Break not detected
1: LIN break detected
Note: If the USART does not support LIN mode, this bit is reserved and forced by hardware
to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 7 TXE: Transmit data register empty
This bit is set by hardware when the content of the USART_TDR register has been
transferred into the shift register. It is cleared by a write to the USART_TDR register.
The TXE flag can also be cleared by writing 1 to the TXFRQ in the USART_RQR register, in
order to discard the data (only in Smartcard T=0 mode, in case of transmission failure).
An interrupt is generated if the TXEIE bit =1 in the USART_CR1 register.
0: data is not transferred to the shift register
1: data is transferred to the shift register)
Note: This bit is used during single buffer transmission.
Bit 6 TC: Transmission complete
This bit is set by hardware if the transmission of a frame containing data is complete and if
TXE is set. An interrupt is generated if TCIE=1 in the USART_CR1 register. It is cleared by
software, writing 1 to the TCCF in the USART_ICR register or by a write to the USART_TDR
register.
An interrupt is generated if TCIE=1 in the USART_CR1 register.
0: Transmission is not complete
1: Transmission is complete
Note: If TE bit is reset and no transmission is on going, the TC bit will be set immediately.
Bit 5 RXNE: Read data register not empty
This bit is set by hardware when the content of the RDR shift register has been transferred
to the USART_RDR register. It is cleared by a read to the USART_RDR register. The RXNE
flag can also be cleared by writing 1 to the RXFRQ in the USART_RQR register.
An interrupt is generated if RXNEIE=1 in the USART_CR1 register.
0: data is not received
1: Received data is ready to be read.

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Bit 4 IDLE: Idle line detected
This bit is set by hardware when an Idle Line is detected. An interrupt is generated if
IDLEIE=1 in the USART_CR1 register. It is cleared by software, writing 1 to the IDLECF in
the USART_ICR register.
0: No Idle line is detected
1: Idle line is detected
Note: The IDLE bit will not be set again until the RXNE bit has been set (i.e. a new idle line
occurs).
If mute mode is enabled (MME=1), IDLE is set if the USART is not mute (RWU=0),
whatever the mute mode selected by the WAKE bit. If RWU=1, IDLE is not set.
Bit 3 ORE: Overrun error
This bit is set by hardware when the data currently being received in the shift register is
ready to be transferred into the RDR register while RXNE=1. It is cleared by a software,
writing 1 to the ORECF, in the USART_ICR register.
An interrupt is generated if RXNEIE=1 or EIE = 1 in the USART_CR1 register.
0: No overrun error
1: Overrun error is detected
Note: When this bit is set, the RDR register content is not lost but the shift register is
overwritten. An interrupt is generated if the ORE flag is set during multibuffer
communication if the EIE bit is set.
This bit is permanently forced to 0 (no overrun detection) when the OVRDIS bit is set in
the USART_CR3 register.
Bit 2 NF: START bit Noise detection flag
This bit is set by hardware when noise is detected on a received frame. It is cleared by
software, writing 1 to the NFCF bit in the USART_ICR register.
0: No noise is detected
1: Noise is detected
Note: This bit does not generate an interrupt as it appears at the same time as the RXNE bit
which itself generates an interrupt. An interrupt is generated when the NF flag is set
during multibuffer communication if the EIE bit is set.
Note: When the line is noise-free, the NF flag can be disabled by programming the ONEBIT
bit to 1 to increase the USART tolerance to deviations (Refer to Section 27.5.5:
Tolerance of the USART receiver to clock deviation on page 705).
Bit 1 FE: Framing error
This bit is set by hardware when a de-synchronization, excessive noise or a break character
is detected. It is cleared by software, writing 1 to the FECF bit in the USART_ICR register.
In Smartcard mode, in transmission, this bit is set when the maximum number of transmit
attempts is reached without success (the card NACKs the data frame).
An interrupt is generated if EIE = 1 in the USART_CR1 register.
0: No Framing error is detected
1: Framing error or break character is detected
Bit 0 PE: Parity error
This bit is set by hardware when a parity error occurs in receiver mode. It is cleared by
software, writing 1 to the PECF in the USART_ICR register.
An interrupt is generated if PEIE = 1 in the USART_CR1 register.
0: No parity error
1: Parity error

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27.8.9

Interrupt flag clear register (USART_ICR)
Address offset: 0x20
Reset value: 0x0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WUCF

Res.

Res.

CMCF

Res.

15

14

13

12

11

10

9

8

7

6

5

3

2

Res.

Res.

Res.

TCCF

Res.

rc_w1

EOBCF RTOCF
rc_w1

rc_w1

Res.

CTSCF LBDCF
rc_w1

Res.

rc_w1

rc_w1

rc_w1

4

IDLECF ORECF
rc_w1

rc_w1

1

0

NCF

FECF

PECF

rc_w1

rc_w1

rc_w1

Bits 31:21 Reserved, must be kept at reset value.
Bit 20 WUCF: Wakeup from Stop mode clear flag
Writing 1 to this bit clears the WUF flag in the USART_ISR register.
Note: If the USART does not support the wakeup from Stop feature, this bit is reserved and
forced by hardware to ‘0’.
Bits 19:18 Reserved, must be kept at reset value.
Bit 17 CMCF: Character match clear flag
Writing 1 to this bit clears the CMF flag in the USART_ISR register.
Bits 16:13 Reserved, must be kept at reset value.
Bit 12 EOBCF: End of block clear flag
Writing 1 to this bit clears the EOBF flag in the USART_ISR register.
Note: If the USART does not support Smartcard mode, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 11 RTOCF: Receiver timeout clear flag
Writing 1 to this bit clears the RTOF flag in the USART_ISR register.
Note: If the USART does not support the Receiver timeout feature, this bit is reserved and
forced by hardware to ‘0’. Please refer to Section 27.4: USART implementation on
page 689.
Bit 10 Reserved, must be kept at reset value.
Bit 9 CTSCF: CTS clear flag
Writing 1 to this bit clears the CTSIF flag in the USART_ISR register.
Note: If the hardware flow control feature is not supported, this bit is reserved and forced by
hardware to ‘0’. Please refer to Section 27.4: USART implementation on page 689.
Bit 8 LBDCF: LIN break detection clear flag
Writing 1 to this bit clears the LBDF flag in the USART_ISR register.
Note: If LIN mode is not supported, this bit is reserved and forced by hardware to ‘0’. Please
refer to Section 27.4: USART implementation on page 689.
Bit 7 Reserved, must be kept at reset value.
Bit 6 TCCF: Transmission complete clear flag
Writing 1 to this bit clears the TC flag in the USART_ISR register.
Bit 5 Reserved, must be kept at reset value.
Bit 4 IDLECF: Idle line detected clear flag
Writing 1 to this bit clears the IDLE flag in the USART_ISR register.

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Bit 3 ORECF: Overrun error clear flag
Writing 1 to this bit clears the ORE flag in the USART_ISR register.
Bit 2 NCF: Noise detected clear flag
Writing 1 to this bit clears the NF flag in the USART_ISR register.
Bit 1 FECF: Framing error clear flag
Writing 1 to this bit clears the FE flag in the USART_ISR register.
Bit 0 PECF: Parity error clear flag
Writing 1 to this bit clears the PE flag in the USART_ISR register.

27.8.10

Receive data register (USART_RDR)
Address offset: 0x24
Reset value: Undefined

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

8

7

6

5

4

3

2

1

0

r

r

r

r

15

14

13

12

11

10

9

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RDR[8:0]
r

r

r

r

r

Bits 31:9 Reserved, must be kept at reset value.
Bits 8:0 RDR[8:0]: Receive data value
Contains the received data character.
The RDR register provides the parallel interface between the input shift register and the
internal bus (see Figure 245).
When receiving with the parity enabled, the value read in the MSB bit is the received parity
bit.

27.8.11

Transmit data register (USART_TDR)
Address offset: 0x28
Reset value: Undefined

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

15

14

13

12

11

10

9

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TDR[8:0]
rw

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Universal synchronous asynchronous receiver transmitter (USART)

Bits 31:9 Reserved, must be kept at reset value.
Bits 8:0 TDR[8:0]: Transmit data value
Contains the data character to be transmitted.
The TDR register provides the parallel interface between the internal bus and the output
shift register (see Figure 245).
When transmitting with the parity enabled (PCE bit set to 1 in the USART_CR1 register),
the value written in the MSB (bit 7 or bit 8 depending on the data length) has no effect
because it is replaced by the parity.
Note: This register must be written only when TXE=1.

27.8.12

USART register map
The table below gives the USART register map and reset values.

UE
Res.
EIE

UESM
Res.
IREN

TE

Res.
IRLP

RE

IDLEIE

Res.

NACK

HDSEL

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

BRR[15:0]
0

0

0

Res.

Res.

ADDM7

TCIE

RXNEIE

0

0

0

SCEN

0

LBDL

TXEIE
Res.

0

LBDIE

0

0

0

DMAT

0

0

0

0

DMAR

RTSE

PS
CTSE

0

0

Res.

PEIE
LBCL

CTSIE

0

0

Res.

PCE
CPOL

CPHA

ONEBIT

0

0

Res.

M0

0

0

Res.

WAKE
CLKEN

0

OVRDIS

MME

0

DEM

CMIE
LINEN

0

DDRE

DEDT0

OVER8
SWAP

0

DEP

DEDT1

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

0

0

0

0

0

0

0

GT[7:0]
0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Reset value

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

USART_RQR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TXFRQ

RXFRQ

MMRQ

SBKRQ

ABRRQ

RTO[23:0]

Res.

BLEN[7:0]

0

PSC[7:0]

Res.

USART_RTOR

0

0

Reset value

0x14

0

0

0
Res.

USART_GTPR

0

0

Reset value

0x10

0

RXINV

0

0

Res.

DEDT2

0

0

TXINV

DEDT3

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

USART_BRR
0x0C

Res.

Reset value

0

Res.

USART_CR3
0x08

DATAINV

0

SCARCNT2:0]

0

Res.

0

0

STOP
[1:0]

Res.

0

0

MSBFIRST

DEAT0

DEDT4

0

0

WUS

0

0

Res.

0

0

ABREN

DEAT1

0

ADD[3:0]

0

Res.

0

ADD[7:4]

0

ABRMOD0

DEAT2

ABRMOD1

0

USART_CR2
0x04

0

Res.

Reset value

WUFIE

DEAT3

RTOEN

0

Res.

0

Res.

RTOIE

DEAT4

0

Res.

0

Res.

M1

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

Reset value

EOBIE

Res.

USART_CR1
0x00

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 110. USART register map and reset values

0

0

0

0

0

0x18
Reset value

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USART_TDR

Reset value

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CTS
CTSIF
LBDF
TXE
TC
RXNE
IDLE
ORE
NF
FE
PE

0
0
0
0
0
0
0
1
1
0
0
0
0
0
0

Res.
CMCF
Res.
Res.
Res.

Res.
CTSCF
LBDCF
Res.
TCCF
Res.
IDLECF

0
0
0

RTOCF

Res.
Res.

Res.

EOBCF
0

Res.

RTOF

0

0

Res.

Res.

EOBF

0

Reset value

Refer to Section 2.2 on page 45 for the register boundary addresses.
TDR[8:0]

X X X X X X

PECF

X X X X X X

FECF

RDR[8:0]

NCF

0

ORECF

Res.

ABRF
ABRE

0
Res.

CMF
BUSY

0

Res.

Res.

Res.

Res.

Res.

SBKF

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

WUF

Res.

RWU

0

Res.

Res.

TEACK
0
WUCF

Res.

Res.

Res.

Res.

Res.

Res.

Res.

REACK

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

USART_RDR

Res.

0x24

Res.

USART_ICR

Res.

0x20
Res.

USART_ISR

Res.

0x1C

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

Universal synchronous asynchronous receiver transmitter (USART)
RM0091

Table 110. USART register map and reset values (continued)

0
0
0
0

X
X
X

X
X
X

RM0091

Serial peripheral interface / inter-IC sound (SPI/I2S)

28

Serial peripheral interface / inter-IC sound (SPI/I2S)

28.1

Introduction
The SPI/I²S interface can be used to communicate with external devices using the SPI
protocol or the I2S audio protocol. SPI or I2S mode is selectable by software. SPI Motorola
mode is selected by default after a device reset.
The serial peripheral interface (SPI) protocol supports half-duplex, full-duplex and simplex
synchronous, serial communication with external devices. The interface can be configured
as master and in this case it provides the communication clock (SCK) to the external slave
device. The interface is also capable of operating in multimaster configuration.
The Inter-IC sound (I2S) protocol is also a synchronous serial communication interface.It
can operate in slave or master mode with half-duplex communication. Full-duplex
operations are possible by combining two I2S blocks. It can address four different audio
standards including the Philips I2S standard, the MSB- and LSB-justified standards and the
PCM standard.

28.2

SPI main features
•

Master or slave operation

•

Full-duplex synchronous transfers on three lines

•

Half-duplex synchronous transfer on two lines (with bidirectional data line)

•

Simplex synchronous transfers on two lines (with unidirectional data line)

•

4-bit to 16-bit data size selection

•

Multimaster mode capability

•

8 master mode baud rate prescalers up to fPCLK/2.

•

Slave mode frequency up to fPCLK/2.

•

NSS management by hardware or software for both master and slave: dynamic change
of master/slave operations

•

Programmable clock polarity and phase

•

Programmable data order with MSB-first or LSB-first shifting

•

Dedicated transmission and reception flags with interrupt capability

•

SPI bus busy status flag

•

SPI Motorola support

•

Hardware CRC feature for reliable communication:
–

CRC value can be transmitted as last byte in Tx mode

–

Automatic CRC error checking for last received byte

•

Master mode fault, overrun flags with interrupt capability

•

CRC Error flag

•

Two 32-bit embedded Rx and Tx FIFOs with DMA capability

•

SPI TI mode support

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I2S main features
•

Half-duplex communication (only transmitter or receiver)

•

Master or slave operations

•

8-bit programmable linear prescaler to reach accurate audio sample frequencies (from
8 kHz to 192 kHz)

•

Data format may be 16-bit, 24-bit or 32-bit

•

Packet frame is fixed to 16-bit (16-bit data frame) or 32-bit (16-bit, 24-bit, 32-bit data
frame) by audio channel

•

Programmable clock polarity (steady state)

•

Underrun flag in slave transmission mode, overrun flag in reception mode (master and
slave) and Frame Error Flag in reception and transmitter mode (slave only)

•

16-bit register for transmission and reception with one data register for both channel
sides

•

Supported I2S protocols:
–

•

28.4

I2S Philips standard

–

MSB-justified standard (left-justified)

–

LSB-justified standard (right-justified)

–

PCM standard (with short and long frame synchronization on 16-bit channel frame
or 16-bit data frame extended to 32-bit channel frame)

Data direction is always MSB first

•

DMA capability for transmission and reception (16-bit wide)

•

Master clock can be output to drive an external audio component. Ratio is fixed at
256 × FS (where FS is the audio sampling frequency)

SPI/I2S implementation
Table 111 describes the SPI/I2S implementation in STM32F0xx devices.
Table 111. STM32F0xx SPI implementation(1)
SPI Features

STM32F04x
STM32F05x

STM32F03x

STM32F07x
STM32F09x

SPI1

SPI1

SPI2

SPI1

SPI2

Hardware CRC calculation

X

X

X

X

X

Rx/Tx FIFO

X

X

X

X

X

NSS pulse mode

X

X

X

X

X

I2S mode

X

X

-

X

X

TI mode

X

X

X

X

X

1. X = supported.

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Serial peripheral interface / inter-IC sound (SPI/I2S)

28.5

SPI functional description

28.5.1

General description
The SPI allows synchronous, serial communication between the MCU and external devices.
Application software can manage the communication by polling the status flag or using
dedicated SPI interrupt. The main elements of SPI and their interactions are shown in the
following block diagram Figure 270.
Figure 270. SPI block diagram
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Four I/O pins are dedicated to SPI communication with external devices.
•

MISO: Master In / Slave Out data. In the general case, this pin is used to transmit data
in slave mode and receive data in master mode.

•

MOSI: Master Out / Slave In data. In the general case, this pin is used to transmit data
in master mode and receive data in slave mode.

•

SCK: Serial Clock output pin for SPI masters and input pin for SPI slaves.

•

NSS: Slave select pin. Depending on the SPI and NSS settings, this pin can be used to
either:
–

select an individual slave device for communication

–

synchronize the data frame or

–

detect a conflict between multiple masters

See Section 28.5.5: Slave select (NSS) pin management for details.
The SPI bus allows the communication between one master device and one or more slave
devices. The bus consists of at least two wires - one for the clock signal and the other for
synchronous data transfer. Other signals can be added depending on the data exchange
between SPI nodes and their slave select signal management.

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Communications between one master and one slave
The SPI allows the MCU to communicate using different configurations, depending on the
device targeted and the application requirements. These configurations use 2 or 3 wires
(with software NSS management) or 3 or 4 wires (with hardware NSS management).
Communication is always initiated by the master.

Full-duplex communication
By default, the SPI is configured for full-duplex communication. In this configuration, the
shift registers of the master and slave are linked using two unidirectional lines between the
MOSI and the MISO pins. During SPI communication, data is shifted synchronously on the
SCK clock edges provided by the master. The master transmits the data to be sent to the
slave via the MOSI line and receives data from the slave via the MISO line. When the data
frame transfer is complete (all the bits are shifted) the information between the master and
slave is exchanged.
Figure 271. Full-duplex single master/ single slave application

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1. The NSS pins can be used to provide a hardware control flow between master and slave. Optionally, the
pins can be left unused by the peripheral. Then the flow has to be handled internally for both master and
slave. For more details see Section 28.5.5: Slave select (NSS) pin management.

Half-duplex communication
The SPI can communicate in half-duplex mode by setting the BIDIMODE bit in the
SPIx_CR1 register. In this configuration, one single cross connection line is used to link the
shift registers of the master and slave together. During this communication, the data is
synchronously shifted between the shift registers on the SCK clock edge in the transfer
direction selected reciprocally by both master and slave with the BDIOE bit in their
SPIx_CR1 registers. In this configuration, the master’s MISO pin and the slave’s MOSI pin
are free for other application uses and act as GPIOs.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
Figure 272. Half-duplex single master/ single slave application

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1. The NSS pins can be used to provide a hardware control flow between master and slave. Optionally, the
pins can be left unused by the peripheral. Then the flow has to be handled internally for both master and
slave. For more details see Section 28.5.5: Slave select (NSS) pin management.
2. In this configuration, the master’s MISO pin and the slave’s MOSI pin can be used as GPIOs.
3. A critical situation can happen when communication direction is changed not synchronously between two
nodes working at bidirectionnal mode and new transmitter accesses the common data line while former
transmitter still keeps an opposite value on the line (the value depends on SPI configuration and
communication data). Both nodes then fight while providing opposite output levels on the common line
temporary till next node changes its direction settings correspondingly, too. It is suggested to insert a serial
resistance between MISO and MOSI pins at this mode to protect the outputs and limit the current blowing
between them at this situation.

Simplex communications
The SPI can communicate in simplex mode by setting the SPI in transmit-only or in receiveonly using the RXONLY bit in the SPIx_CR2 register. In this configuration, only one line is
used for the transfer between the shift registers of the master and slave. The remaining
MISO and MOSI pins pair is not used for communication and can be used as standard
GPIOs.
•

Transmit-only mode (RXONLY=0): The configuration settings are the same as for fullduplex. The application has to ignore the information captured on the unused input pin.
This pin can be used as a standard GPIO.

•

Receive-only mode (RXONLY=1): The application can disable the SPI output function
by setting the RXONLY bit. In slave configuration, the MISO output is disabled and the
pin can be used as a GPIO. The slave continues to receive data from the MOSI pin
while its slave select signal is active (see 28.5.5: Slave select (NSS) pin management).
Received data events appear depending on the data buffer configuration. In the master
configuration, the MOSI output is disabled and the pin can be used as a GPIO. The
clock signal is generated continuously as long as the SPI is enabled. The only way to
stop the clock is to clear the RXONLY bit or the SPE bit and wait until the incoming
pattern from the MISO pin is finished and fills the data buffer structure, depending on its
configuration.

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Figure 273. Simplex single master/single slave application (master in transmit-only/
slave in receive-only mode)

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1. The NSS pins can be used to provide a hardware control flow between master and slave. Optionally, the
pins can be left unused by the peripheral. Then the flow has to be handled internally for both master and
slave. For more details see Section 28.5.5: Slave select (NSS) pin management.
2. An accidental input information is captured at the input of transmitter Rx shift register. All the events
associated with the transmitter receive flow must be ignored in standard transmit only mode (e.g. OVF
flag).
3. In this configuration, both the MISO pins can be used as GPIOs.

Note:

Any simplex communication can be alternatively replaced by a variant of the half-duplex
communication with a constant setting of the transaction direction (bidirectional mode is
enabled while BDIO bit is not changed).

28.5.3

Standard multi-slave communication
In a configuration with two or more independent slaves, the master uses GPIO pins to
manage the chip select lines for each slave (see Figure 274.). The master must select one
of the slaves individually by pulling low the GPIO connected to the slave NSS input. When
this is done, a standard master and dedicated slave communication is established.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
Figure 274. Master and three independent slaves

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1. NSS pin is not used on master side at this configuration. It has to be managed internally (SSM=1, SSI=1) to
prevent any MODF error.
2. As MISO pins of the slaves are connected together, all slaves must have the GPIO configuration of their
MISO pin set as alternate function open-drain (see Section 8.3.7: I/O alternate function input/output on
page 152.

28.5.4

Multi-master communication
Unless SPI bus is not designed for a multi-master capability primarily, the user can use build
in feature which detects a potential conflict between two nodes trying to master the bus at
the same time. For this detection, NSS pin is used configured at hardware input mode.
The connection of more than two SPI nodes working at this mode is impossible as only one
node can apply its output on a common data line at time.
When nodes are non active, both stay at slave mode by default. Once one node wants to
overtake control on the bus, it switches itself into master mode and applies active level on
the slave select input of the other node via dedicated GPIO pin. After the session is

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RM0091

completed, the active slave select signal is released and the node mastering the bus
temporary returns back to passive slave mode waiting for next session start.
If potentially both nodes raised their mastering request at the same time a bus conflict event
appears (see mode fault MODF event). Then the user can apply some simple arbitration
process (e.g. to postpone next attempt by predefined different time-outs applied at both
nodes).

Figure 275. Multi-master application

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1. The NSS pin is configured at hardware input mode at both nodes. Its active level enables the MISO line
output control as the passive node is configured as a slave.

28.5.5

Slave select (NSS) pin management
In slave mode, the NSS works as a standard “chip select” input and lets the slave
communicate with the master. In master mode, NSS can be used either as output or input.
As an input it can prevent multimaster bus collision, and as an output it can drive a slave
select signal of a single slave.
Hardware or software slave select management can be set using the SSM bit in the
SPIx_CR1 register:

762/1004

•

Software NSS management (SSM = 1): in this configuration, slave select information
is driven internally by the SSI bit value in register SPIx_CR1. The external NSS pin is
free for other application uses.

•

Hardware NSS management (SSM = 0): in this case, there are two possible
configurations. The configuration used depends on the NSS output configuration
(SSOE bit in register SPIx_CR1).
–

NSS output enable (SSM=0,SSOE = 1): this configuration is only used when the
MCU is set as master. The NSS pin is managed by the hardware. The NSS signal
is driven low as soon as the SPI is enabled in master mode (SPE=1), and is kept
low until the SPI is disabled (SPE =0). A pulse can be generated between
continuous communications if NSS pulse mode is activated (NSSP=1). The SPI
cannot work in multimaster configuration with this NSS setting.

–

NSS output disable (SSM=0, SSOE = 0): if the microcontroller is acting as the
master on the bus, this configuration allows multimaster capability. If the NSS pin
is pulled low in this mode, the SPI enters master mode fault state and the device is
automatically reconfigured in slave mode. In slave mode, the NSS pin works as a
standard “chip select” input and the slave is selected while NSS line is at low level.

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Figure 276. Hardware/software slave select management
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28.5.6

Communication formats
During SPI communication, receive and transmit operations are performed simultaneously.
The serial clock (SCK) synchronizes the shifting and sampling of the information on the data
lines. The communication format depends on the clock phase, the clock polarity and the
data frame format. To be able to communicate together, the master and slaves devices must
follow the same communication format.

Clock phase and polarity controls
Four possible timing relationships may be chosen by software, using the CPOL and CPHA
bits in the SPIx_CR1 register. The CPOL (clock polarity) bit controls the idle state value of
the clock when no data is being transferred. This bit affects both master and slave modes. If
CPOL is reset, the SCK pin has a low-level idle state. If CPOL is set, the SCK pin has a
high-level idle state.
If the CPHA bit is set, the second edge on the SCK pin captures the first data bit transacted
(falling edge if the CPOL bit is reset, rising edge if the CPOL bit is set). Data are latched on
each occurrence of this clock transition type. If the CPHA bit is reset, the first edge on the
SCK pin captures the first data bit transacted (falling edge if the CPOL bit is set, rising edge
if the CPOL bit is reset). Data are latched on each occurrence of this clock transition type.
The combination of CPOL (clock polarity) and CPHA (clock phase) bits selects the data
capture clock edge.

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Figure 277, shows an SPI full-duplex transfer with the four combinations of the CPHA and
CPOL bits.
Note:

Prior to changing the CPOL/CPHA bits the SPI must be disabled by resetting the SPE bit.
The idle state of SCK must correspond to the polarity selected in the SPIx_CR1 register (by
pulling up SCK if CPOL=1 or pulling down SCK if CPOL=0).
Figure 277. Data clock timing diagram
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1. The order of data bits depends on LSBFIRST bit setting.

Data frame format
The SPI shift register can be set up to shift out MSB-first or LSB-first, depending on the
value of the LSBFIRST bit. The data frame size is chosen by using the DS bits. It can be set
from 4-bit up to 16-bit length and the setting applies for both transmission and reception.
Whatever the selected data frame size, read access to the FIFO must be aligned with the
FRXTH level. When the SPIx_DR register is accessed, data frames are always right-aligned
into either a byte (if the data fits into a byte) or a half-word (see Figure 278). During
communication, only bits within the data frame are clocked and transferred.

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Figure 278. Data alignment when data length is not equal to 8-bit or 16-bit
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The minimum data length is 4 bits. If a data length of less than 4 bits is selected, it is forced
to an 8-bit data frame size.

28.5.7

Configuration of SPI
The configuration procedure is almost the same for master and slave. For specific mode
setups, follow the dedicated sections. When a standard communication is to be initialized,
perform these steps:
1.
2.

3.

Write proper GPIO registers: Configure GPIO for MOSI, MISO and SCK pins.
Write to the SPI_CR1 register:
a)

Configure the serial clock baud rate using the BR[2:0] bits (Note: 4).

b)

Configure the CPOL and CPHA bits combination to define one of the four
relationships between the data transfer and the serial clock (CPHA must be
cleared in NSSP mode). (Note: 2 - except the case when CRC is enabled at TI
mode).

c)

Select simplex or half-duplex mode by configuring RXONLY or BIDIMODE and
BIDIOE (RXONLY and BIDIMODE can't be set at the same time).

d)

Configure the LSBFIRST bit to define the frame format (Note: 2).

e)

Configure the CRCL and CRCEN bits if CRC is needed (while SCK clock signal is
at idle state).

f)

Configure SSM and SSI (Notes: 2 & 3).

g)

Configure the MSTR bit (in multimaster NSS configuration, avoid conflict state on
NSS if master is configured to prevent MODF error).

Write to SPI_CR2 register:
a)

Configure the DS[3:0] bits to select the data length for the transfer.

b)

Configure SSOE (Notes: 1 & 2 & 3).

c)

Set the FRF bit if the TI protocol is required (keep NSSP bit cleared in TI mode).

d)

Set the NSSP bit if the NSS pulse mode between two data units is required (keep
CHPA and TI bits cleared in NSSP mode).

e)

Configure the FRXTH bit. The RXFIFO threshold must be aligned to the read
access size for the SPIx_DR register.

f)

Initialize LDMA_TX and LDMA_RX bits if DMA is used in packed mode.

4.

Write to SPI_CRCPR register: Configure the CRC polynomial if needed.

5.

Write proper DMA registers: Configure DMA streams dedicated for SPI Tx and Rx in
DMA registers if the DMA streams are used.

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Note:

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(1) Step is not required in slave mode.
(2) Step is not required in TI mode.
(3) Step is not required in NSSP mode.
(4) The step is not required in slave mode except slave working at TI mode
For code example refer to the Appendix sections A.17.1: SPI master configuration code
example and A.17.2: SPI slave configuration code example.

28.5.8

Procedure for enabling SPI
It is recommended to enable the SPI slave before the master sends the clock. If not,
undesired data transmission might occur. The data register of the slave must already
contain data to be sent before starting communication with the master (either on the first
edge of the communication clock, or before the end of the ongoing communication if the
clock signal is continuous). The SCK signal must be settled at an idle state level
corresponding to the selected polarity before the SPI slave is enabled.
The master at full-duplex (or in any transmit-only mode) starts to communicate when the
SPI is enabled and TXFIFO is not empty, or with the next write to TXFIFO.
In any master receive only mode (RXONLY=1 or BIDIMODE=1 & BIDIOE=0), master starts
to communicate and the clock starts running immediately after SPI is enabled.
For handling DMA, follow the dedicated section.

28.5.9

Data transmission and reception procedures
RXFIFO and TXFIFO
All SPI data transactions pass through the 32-bit embedded FIFOs. This enables the SPI to
work in a continuous flow, and prevents overruns when the data frame size is short. Each
direction has its own FIFO called TXFIFO and RXFIFO. These FIFOs are used in all SPI
modes except for receiver-only mode (slave or master) with CRC calculation enabled (see
Section 28.5.14: CRC calculation).
The handling of FIFOs depends on the data exchange mode (duplex, simplex), data frame
format (number of bits in the frame), access size performed on the FIFO data registers (8-bit
or 16-bit), and whether or not data packing is used when accessing the FIFOs (see
Section 28.5.13: TI mode).
A read access to the SPIx_DR register returns the oldest value stored in RXFIFO that has
not been read yet. A write access to the SPIx_DR stores the written data in the TXFIFO at
the end of a send queue. The read access must be always aligned with the RXFIFO
threshold configured by the FRXTH bit in SPIx_CR2 register. FTLVL[1:0] and FRLVL[1:0]
bits indicate the current occupancy level of both FIFOs.
A read access to the SPIx_DR register must be managed by the RXNE event. This event is
triggered when data is stored in RXFIFO and the threshold (defined by FRXTH bit) is
reached. When RXNE is cleared, RXFIFO is considered to be empty. In a similar way, write
access of a data frame to be transmitted is managed by the TXE event. This event is
triggered when the TXFIFO level is less than or equal to half of its capacity. Otherwise TXE
is cleared and the TXFIFO is considered as full. In this way, RXFIFO can store up to four
data frames, whereas TXFIFO can only store up to three when the data frame format is not
greater than 8 bits. This difference prevents possible corruption of 3x 8-bit data frames
already stored in the TXFIFO when software tries to write more data in 16-bit mode into

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TXFIFO. Both TXE and RXNE events can be polled or handled by interrupts. See
Figure 280 through Figure 283.
Another way to manage the data exchange is to use DMA (see ).
If the next data is received when the RXFIFO is full, an overrun event occurs (see
description of OVR flag at Section 28.5.10: SPI status flags). An overrun event can be
polled or handled by an interrupt.
The BSY bit being set indicates ongoing transaction of a current data frame. When the clock
signal runs continuously, the BSY flag stays set between data frames at master but
becomes low for a minimum duration of one SPI clock at slave between each data frame
transfer.

Sequence handling
A few data frames can be passed at single sequence to complete a message. When
transmission is enabled, a sequence begins and continues while any data is present in the
TXFIFO of the master. The clock signal is provided continuously by the master until TXFIFO
becomes empty, then it stops waiting for additional data.
In receive-only modes, half-duplex (BIDIMODE=1, BIDIOE=0) or simplex (BIDIMODE=0,
RXONLY=1) the master starts the sequence immediately when both SPI is enabled and
receive-only mode is activated. The clock signal is provided by the master and it does not
stop until either SPI or receive-only mode is disabled by the master. The master receives
data frames continuously up to this moment.
While the master can provide all the transactions in continuous mode (SCK signal is
continuous) it has to respect slave capability to handle data flow and its content at anytime.
When necessary, the master must slow down the communication and provide either a
slower clock or separate frames or data sessions with sufficient delays. Be aware there is no
underflow error signal for master or slave in SPI mode, and data from the slave is always
transacted and processed by the master even if the slave could not prepare it correctly in
time. It is preferable for the slave to use DMA, especially when data frames are shorter and
bus rate is high.
Each sequence must be encased by the NSS pulse in parallel with the multislave system to
select just one of the slaves for communication. In a single slave system it is not necessary
to control the slave with NSS, but it is often better to provide the pulse here too, to
synchronize the slave with the beginning of each data sequence. NSS can be managed by
both software and hardware (see Section 28.5.5: Slave select (NSS) pin management).
When the BSY bit is set it signifies an ongoing data frame transaction. When the dedicated
frame transaction is finished, the RXNE flag is raised. The last bit is just sampled and the
complete data frame is stored in the RXFIFO.

Procedure for disabling the SPI
When SPI is disabled, it is mandatory to follow the disable procedures described in this
paragraph. It is important to do this before the system enters a low-power mode when the
peripheral clock is stopped. Ongoing transactions can be corrupted in this case. In some
modes the disable procedure is the only way to stop continuous communication running.
Master in full-duplex or transmit only mode can finish any transaction when it stops
providing data for transmission. In this case, the clock stops after the last data transaction.
Special care must be taken in packing mode when an odd number of data frames are
transacted to prevent some dummy byte exchange (refer to Data packing section). Before

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the SPI is disabled in these modes, the user must follow standard disable procedure. When
the SPI is disabled at the master transmitter while a frame transaction is ongoing or next
data frame is stored in TXFIFO, the SPI behavior is not guaranteed.
When the master is in any receive only mode, the only way to stop the continuous clock is to
disable the peripheral by SPE=0. This must occur in specific time window within last data
frame transaction just between the sampling time of its first bit and before its last bit transfer
starts (in order to receive a complete number of expected data frames and to prevent any
additional “dummy” data reading after the last valid data frame). Specific procedure must be
followed when disabling SPI in this mode.
Data received but not read remains stored in RXFIFO when the SPI is disabled, and must
be processed the next time the SPI is enabled, before starting a new sequence. To prevent
having unread data, ensure that RXFIFO is empty when disabling the SPI, by using the
correct disabling procedure, or by initializing all the SPI registers with a software reset via
the control of a specific register dedicated to peripheral reset (see the SPIiRST bits in the
RCC_APBiRSTR registers).
Standard disable procedure is based on pulling BSY status together with FTLVL[1:0] to
check if a transmission session is fully completed. This check can be done in specific cases,
too, when it is necessary to identify the end of ongoing transactions, for example:
•

When NSS signal is managed by software and master has to provide proper end of
NSS pulse for slave, or

•

When transactions’ streams from DMA or FIFO are completed while the last data frame
or CRC frame transaction is still ongoing in the peripheral bus.

The correct disable procedure is (except when receive only mode is used):
1.

Wait until FTLVL[1:0] = 00 (no more data to transmit).

2.

Wait until BSY=0 (the last data frame is processed).

3.

Disable the SPI (SPE=0).

4.

Read data until FRLVL[1:0] = 00 (read all the received data).

The correct disable procedure for certain receive only modes is:

Note:

1.

Interrupt the receive flow by disabling SPI (SPE=0) in the specific time window while
the last data frame is ongoing.

2.

Wait until BSY=0 (the last data frame is processed).

3.

Read data until FRLVL[1:0] = 00 (read all the received data).

If packing mode is used and an odd number of data frames with a format less than or equal
to 8 bits (fitting into one byte) has to be received, FRXTH must be set when FRLVL[1:0] =
01, in order to generate the RXNE event to read the last odd data frame and to keep good
FIFO pointer alignment.

Data packing
When the data frame size fits into one byte (less than or equal to 8 bits), data packing is
used automatically when any read or write 16-bit access is performed on the SPIx_DR
register. The double data frame pattern is handled in parallel in this case. At first, the SPI
operates using the pattern stored in the LSB of the accessed word, then with the other half
stored in the MSB. Figure 279 provides an example of data packing mode sequence
handling. Two data frames are sent after the single 16-bit access the SPIx_DR register of
the transmitter. This sequence can generate just one RXNE event in the receiver if the
RXFIFO threshold is set to 16 bits (FRXTH=0). The receiver then has to access both data

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frames by a single 16-bit read of SPIx_DR as a response to this single RXNE event. The
RxFIFO threshold setting and the following read access must be always kept aligned at the
receiver side, as data can be lost if it is not in line.
A specific problem appears if an odd number of such “fit into one byte” data frames must be
handled. On the transmitter side, writing the last data frame of any odd sequence with an 8bit access to SPIx_DR is enough. The receiver has to change the Rx_FIFO threshold level
for the last data frame received in the odd sequence of frames in order to generate the
RXNE event.
Figure 279. Packing data in FIFO for transmission and reception
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Communication using DMA (direct memory addressing)
To operate at its maximum speed and to facilitate the data register read/write process
required to avoid overrun, the SPI features a DMA capability, which implements a simple
request/acknowledge protocol.
A DMA access is requested when the TXE or RXNE enable bit in the SPIx_CR2 register is
set. Separate requests must be issued to the Tx and Rx buffers.
•

In transmission, a DMA request is issued each time TXE is set to 1. The DMA then
writes to the SPIx_DR register.

•

In reception, a DMA request is issued each time RXNE is set to 1. The DMA then reads
the SPIx_DR register.

See Figure 280 through Figure 283.
When the SPI is used only to transmit data, it is possible to enable only the SPI Tx DMA
channel. In this case, the OVR flag is set because the data received is not read. When the
SPI is used only to receive data, it is possible to enable only the SPI Rx DMA channel.
In transmission mode, when the DMA has written all the data to be transmitted (the TCIF
flag is set in the DMA_ISR register), the BSY flag can be monitored to ensure that the SPI
communication is complete. This is required to avoid corrupting the last transmission before
disabling the SPI or entering the Stop mode. The software must first wait until
FTLVL[1:0]=00 and then until BSY=0.
When starting communication using DMA, to prevent DMA channel management raising
error events, these steps must be followed in order:

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1.

Enable DMA Rx buffer in the RXDMAEN bit in the SPI_CR2 register, if DMA Rx is
used.

2.

Enable DMA streams for Tx and Rx in DMA registers, if the streams are used.

3.

Enable DMA Tx buffer in the TXDMAEN bit in the SPI_CR2 register, if DMA Tx is used.

4.

Enable the SPI by setting the SPE bit.

For code example refer to the Appendix sections A.17.5: SPI master configuration with DMA
code example and A.17.6: SPI slave configuration with DMA code example.
To close communication it is mandatory to follow these steps in order:
1.

Disable DMA streams for Tx and Rx in the DMA registers, if the streams are used.

2.

Disable the SPI by following the SPI disable procedure.

3.

Disable DMA Tx and Rx buffers by clearing the TXDMAEN and RXDMAEN bits in the
SPI_CR2 register, if DMA Tx and/or DMA Rx are used.

Packing with DMA
If the transfers are managed by DMA (TXDMAEN and RXDMAEN set in the SPIx_CR2
register) packing mode is enabled/disabled automatically depending on the PSIZE value
configured for SPI TX and the SPI RX DMA channel. If the DMA channel PSIZE value is
equal to 16-bit and SPI data size is less than or equal to 8-bit, then packing mode is
enabled. The DMA then automatically manages the write operations to the SPIx_DR
register.
If data packing mode is used and the number of data to transfer is not a multiple of two, the
LDMA_TX/LDMA_RX bits must be set. The SPI then considers only one data for the
transmission or reception to serve the last DMA transfer (for more details refer to Data
packing on page 768.)

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Communication diagrams
Some typical timing schemes are explained in this section. These schemes are valid no
matter if the SPI events are handled by polling, interrupts or DMA. For simplicity, the
LSBFIRST=0, CPOL=0 and CPHA=1 setting is used as a common assumption here. No
complete configuration of DMA streams is provided.
The following numbered notes are common for Figure 280 on page 772 through Figure 283
on page 775.
1.

The slave starts to control MISO line as NSS is active and SPI is enabled, and is
disconnected from the line when one of them is released. Sufficient time must be
provided for the slave to prepare data dedicated to the master in advance before its
transaction starts.
At the master, the SPI peripheral takes control at MOSI and SCK signals (occasionally
at NSS signal as well) only if SPI is enabled. If SPI is disabled the SPI peripheral is
disconnected from GPIO logic, so the levels at these lines depends on GPIO setting
exclusively.

2.

At the master, BSY stays active between frames if the communication (clock signal) is
continuous. At the slave, BSY signal always goes down for at least one clock cycle
between data frames.

3.

The TXE signal is cleared only if TXFIFO is full.

4.

The DMA arbitration process starts just after the TXDMAEN bit is set. The TXE
interrupt is generated just after the TXEIE is set. As the TXE signal is at an active level,
data transfers to TxFIFO start, until TxFIFO becomes full or the DMA transfer
completes.

5.

If all the data to be sent can fit into TxFIFO, the DMA Tx TCIF flag can be raised even
before communication on the SPI bus starts. This flag always rises before the SPI
transaction is completed.

6.

The CRC value for a package is calculated continuously frame by frame in the
SPIx_TxCRCR and SPIx_RxCRCR registers. The CRC information is processed after
the entire data package has completed, either automatically by DMA (Tx channel must
be set to the number of data frames to be processed) or by SW (the user must handle
CRCNEXT bit during the last data frame processing).
While the CRC value calculated in SPIx_TxCRCR is simply sent out by transmitter,
received CRC information is loaded into RxFIFO and then compared with the
SPIx_RxCRCR register content (CRC error flag can be raised here if any difference).
This is why the user must take care to flush this information from the FIFO, either by
software reading out all the stored content of RxFIFO, or by DMA when the proper
number of data frames is preset for Rx channel (number of data frames + number of
CRC frames) (see the settings at the example assumption).

7.

In data packed mode, TxE and RxNE events are paired and each read/write access to
the FIFO is 16 bits wide until the number of data frames are even. If the TxFIFO is ¾
full FTLVL status stays at FIFO full level. That is why the last odd data frame cannot be
stored before the TxFIFO becomes ½ full. This frame is stored into TxFIFO with an 8bit access either by software or automatically by DMA when LDMA_TX control is set.

8.

To receive the last odd data frame in packed mode, the Rx threshold must be changed
to 8-bit when the last data frame is processed, either by software setting FRXTH=1 or
automatically by a DMA internal signal when LDMA_RX is set.

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Figure 280. Master full-duplex communication
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Assumptions for master full-duplex communication example:
•

Data size > 8 bit

If DMA is used:
•

Number of Tx frames transacted by DMA is set to 3

•

Number of Rx frames transacted by DMA is set to 3

See also : Communication diagrams on page 771 for details about common assumptions
and notes.

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Figure 281. Slave full-duplex communication
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Assumptions for slave full-duplex communication example:
•

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If DMA is used:
•

Number of Tx frames transacted by DMA is set to 3

•

Number of Rx frames transacted by DMA is set to 3

See also : Communication diagrams on page 771 for details about common assumptions
and notes.
For code example refer to the Appendix section A.17.3: SPI full duplex communication code
example.

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Figure 282. Master full-duplex communication with CRC
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Assumptions for master full-duplex communication with CRC example:
•

Data size = 16 bit

•

CRC enabled

If DMA is used:
•

Number of Tx frames transacted by DMA is set to 2

•

Number of Rx frames transacted by DMA is set to 3

See also : Communication diagrams on page 771 for details about common assumptions
and notes.

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Figure 283. Master full-duplex communication in packed mode
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Assumptions for master full-duplex communication in packed mode example:
•

Data size = 5 bit

•

Read/write FIFO is performed mostly by 16-bit access

•

FRXTH=0

If DMA is used:
•

Number of Tx frames to be transacted by DMA is set to 3

•

Number of Rx frames to be transacted by DMA is set to 3

•

PSIZE for both Tx and Rx DMA channel is set to 16-bit

•

LDMA_TX=1 and LDMA_RX=1

See also : Communication diagrams on page 771 for details about common assumptions
and notes.

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28.5.10

RM0091

SPI status flags
Three status flags are provided for the application to completely monitor the state of the SPI
bus.

Tx buffer empty flag (TXE)
The TXE flag is set when transmission TXFIFO has enough space to store data to send.
TXE flag is linked to the TXFIFO level. The flag goes high and stays high until the TXFIFO
level is lower or equal to 1/2 of the FIFO depth. An interrupt can be generated if the TXEIE
bit in the SPIx_CR2 register is set. The bit is cleared automatically when the TXFIFO level
becomes greater than 1/2.

Rx buffer not empty (RXNE)
The RXNE flag is set depending on the FRXTH bit value in the SPIx_CR2 register:
•

If FRXTH is set, RXNE goes high and stays high until the RXFIFO level is greater or
equal to 1/4 (8-bit).

•

If FRXTH is cleared, RXNE goes high and stays high until the RXFIFO level is greater
than or equal to 1/2 (16-bit).

An interrupt can be generated if the RXNEIE bit in the SPIx_CR2 register is set.
The RXNE is cleared by hardware automatically when the above conditions are no longer
true.

Busy flag (BSY)
The BSY flag is set and cleared by hardware (writing to this flag has no effect).
When BSY is set, it indicates that a data transfer is in progress on the SPI (the SPI bus is
busy).
The BSY flag can be used in certain modes to detect the end of a transfer so that the
software can disable the SPI or its peripheral clock before entering a low-power mode which
does not provide a clock for the peripheral. This avoids corrupting the last transfer.
The BSY flag is also useful for preventing write collisions in a multimaster system.
The BSY flag is cleared under any one of the following conditions:

Note:

776/1004

•

When the SPI is correctly disabled

•

When a fault is detected in Master mode (MODF bit set to 1)

•

In Master mode, when it finishes a data transmission and no new data is ready to be
sent

•

In Slave mode, when the BSY flag is set to '0' for at least one SPI clock cycle between
each data transfer.

When the next transmission can be handled immediately by the master (e.g. if the master is
in Receive-only mode or its Transmit FIFO is not empty), communication is continuous and
the BSY flag remains set to '1' between transfers on the master side. Although this is not the
case with a slave, it is recommended to use always the TXE and RXNE flags (instead of the
BSY flags) to handle data transmission or reception operations.

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28.5.11

Serial peripheral interface / inter-IC sound (SPI/I2S)

SPI error flags
An SPI interrupt is generated if one of the following error flags is set and interrupt is enabled
by setting the ERRIE bit.

Overrun flag (OVR)
An overrun condition occurs when data is received by a master or slave and the RXFIFO
has not enough space to store this received data. This can happen if the software or the
DMA did not have enough time to read the previously received data (stored in the RXFIFO)
or when space for data storage is limited e.g. the RXFIFO is not available when CRC is
enabled in receive only mode so in this case the reception buffer is limited into a single data
frame buffer (see Section 28.5.14: CRC calculation).
When an overrun condition occurs, the newly received value does not overwrite the
previous one in the RXFIFO. The newly received value is discarded and all data transmitted
subsequently is lost. Clearing the OVR bit is done by a read access to the SPI_DR register
followed by a read access to the SPI_SR register.

Mode fault (MODF)
Mode fault occurs when the master device has its internal NSS signal (NSS pin in NSS
hardware mode, or SSI bit in NSS software mode) pulled low. This automatically sets the
MODF bit. Master mode fault affects the SPI interface in the following ways:
•

The MODF bit is set and an SPI interrupt is generated if the ERRIE bit is set.

•

The SPE bit is cleared. This blocks all output from the device and disables the SPI
interface.

•

The MSTR bit is cleared, thus forcing the device into slave mode.

Use the following software sequence to clear the MODF bit:
1.

Make a read or write access to the SPIx_SR register while the MODF bit is set.

2.

Then write to the SPIx_CR1 register.

To avoid any multiple slave conflicts in a system comprising several MCUs, the NSS pin
must be pulled high during the MODF bit clearing sequence. The SPE and MSTR bits can
be restored to their original state after this clearing sequence. As a security, hardware does
not allow the SPE and MSTR bits to be set while the MODF bit is set. In a slave device the
MODF bit cannot be set except as the result of a previous multimaster conflict.

CRC error (CRCERR)
This flag is used to verify the validity of the value received when the CRCEN bit in the
SPIx_CR1 register is set. The CRCERR flag in the SPIx_SR register is set if the value
received in the shift register does not match the receiver SPIx_RXCRCR value. The flag is
cleared by the software.

TI mode frame format error (FRE)
A TI mode frame format error is detected when an NSS pulse occurs during an ongoing
communication when the SPI is operating in slave mode and configured to conform to the TI
mode protocol. When this error occurs, the FRE flag is set in the SPIx_SR register. The SPI
is not disabled when an error occurs, the NSS pulse is ignored, and the SPI waits for the
next NSS pulse before starting a new transfer. The data may be corrupted since the error
detection may result in the loss of two data bytes.

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RM0091

The FRE flag is cleared when SPIx_SR register is read. If the ERRIE bit is set, an interrupt
is generated on the NSS error detection. In this case, the SPI should be disabled because
data consistency is no longer guaranteed and communications should be reinitiated by the
master when the slave SPI is enabled again.

28.5.12

NSS pulse mode
This mode is activated by the NSSP bit in the SPIx_CR2 register and it takes effect only if
the SPI interface is configured as Motorola SPI master (FRF=0) with capture on the first
edge (SPIx_CR1 CPHA = 0, CPOL setting is ignored). When activated, an NSS pulse is
generated between two consecutive data frame transfers when NSS stays at high level for
the duration of one clock period at least. This mode allows the slave to latch data. NSSP
pulse mode is designed for applications with a single master-slave pair.
Figure 284 illustrates NSS pin management when NSSP pulse mode is enabled.
Figure 284. NSSP pulse generation in Motorola SPI master mode
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Similar behavior is encountered when CPOL = 0. In this case the sampling edge is the rising
edge of SCK, and NSS assertion and deassertion refer to this sampling edge.

28.5.13

TI mode
TI protocol in master mode
The SPI interface is compatible with the TI protocol. The FRF bit of the SPIx_CR2 register
can be used to configure the SPI to be compliant with this protocol.
The clock polarity and phase are forced to conform to the TI protocol requirements whatever
the values set in the SPIx_CR1 register. NSS management is also specific to the TI protocol
which makes the configuration of NSS management through the SPIx_CR1 and SPIx_CR2
registers (SSM, SSI, SSOE) impossible in this case.
In slave mode, the SPI baud rate prescaler is used to control the moment when the MISO
pin state changes to HiZ when the current transaction finishes (see Figure 285). Any baud
rate can be used, making it possible to determine this moment with optimal flexibility.
However, the baud rate is generally set to the external master clock baud rate. The delay for
the MISO signal to become HiZ (trelease) depends on internal resynchronization and on the

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Serial peripheral interface / inter-IC sound (SPI/I2S)
baud rate value set in through the BR[2:0] bits in the SPIx_CR1 register. It is given by the
formula:

t baud_rate
t baud_rate
--------------------- + 4 × t pclk < t release < --------------------- + 6 × t pclk
2
2
If the slave detects a misplaced NSS pulse during a data frame transaction the TIFRE flag is
set.
If the data size is equal to 4-bits or 5-bits, the master in full-duplex mode or transmit-only
mode uses a protocol with one more dummy data bit added after LSB. TI NSS pulse is
generated above this dummy bit clock cycle instead of the LSB in each period.
This feature is not available for Motorola SPI communications (FRF bit set to 0).
Figure 285: TI mode transfer shows the SPI communication waveforms when TI mode is
selected.
Figure 285. TI mode transfer

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28.5.14

CRC calculation
Two separate CRC calculators are implemented in order to check the reliability of
transmitted and received data. The SPI offers CRC8 or CRC16 calculation independently of
the frame data length, which can be fixed to 8-bit or 16-bit. For all the other data frame
lengths, no CRC is available.

CRC principle
CRC calculation is enabled by setting the CRCEN bit in the SPIx_CR1 register before the
SPI is enabled (SPE = 1). The CRC value is calculated using an odd programmable
polynomial on each bit. The calculation is processed on the sampling clock edge defined by
the CPHA and CPOL bits in the SPIx_CR1 register. The calculated CRC value is checked
automatically at the end of the data block as well as for transfer managed by CPU or by the
DMA. When a mismatch is detected between the CRC calculated internally on the received
data and the CRC sent by the transmitter, a CRCERR flag is set to indicate a data corruption
error. The right procedure for handling the CRC calculation depends on the SPI
configuration and the chosen transfer management.

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Note:

RM0091

The polynomial value should only be odd. No even values are supported.

CRC transfer managed by CPU
Communication starts and continues normally until the last data frame has to be sent or
received in the SPIx_DR register. Then CRCNEXT bit has to be set in the SPIx_CR1
register to indicate that the CRC frame transaction will follow after the transaction of the
currently processed data frame. The CRCNEXT bit must be set before the end of the last
data frame transaction. CRC calculation is frozen during CRC transaction.
The received CRC is stored in the RXFIFO like a data byte or word. That is why in CRC
mode only, the reception buffer has to be considered as a single 16-bit buffer used to
receive only one data frame at a time.
A CRC-format transaction usually takes one more data frame to communicate at the end of
data sequence. However, when setting an 8-bit data frame checked by 16-bit CRC, two
more frames are necessary to send the complete CRC.
When the last CRC data is received, an automatic check is performed comparing the
received value and the value in the SPIx_RXCRC register. Software has to check the
CRCERR flag in the SPIx_SR register to determine if the data transfers were corrupted or
not. Software clears the CRCERR flag by writing '0' to it.
After the CRC reception, the CRC value is stored in the RXFIFO and must be read in the
SPIx_DR register in order to clear the RXNE flag.

CRC transfer managed by DMA
When SPI communication is enabled with CRC communication and DMA mode, the
transmission and reception of the CRC at the end of communication is automatic (with the
exception of reading CRC data in receive only mode). The CRCNEXT bit does not have to
be handled by the software. The counter for the SPI transmission DMA channel has to be
set to the number of data frames to transmit excluding the CRC frame. On the receiver side,
the received CRC value is handled automatically by DMA at the end of the transaction but
user must take care to flush out received CRC information from RXFIFO as it is always
loaded into it. In full-duplex mode, the counter of the reception DMA channel can be set to
the number of data frames to receive including the CRC, which means, for example, in the
specific case of an 8-bit data frame checked by 16-bit CRC:
DMA_RX = Numb_of_data + 2
In receive only mode, the DMA reception channel counter should contain only the amount of
data transferred, excluding the CRC calculation. Then based on the complete transfer from
DMA, all the CRC values must be read back by software from FIFO as it works as a single
buffer in this mode.
At the end of the data and CRC transfers, the CRCERR flag in the SPIx_SR register is set if
corruption occurred during the transfer.
If packing mode is used, the LDMA_RX bit needs managing if the number of data is odd.

Resetting the SPIx_TXCRC and SPIx_RXCRC values
The SPIx_TXCRC and SPIx_RXCRC values are cleared automatically when new data is
sampled after a CRC phase. This allows the use of DMA circular mode (not available in
receive-only mode) in order to transfer data without any interruption, (several data blocks
covered by intermediate CRC checking phases).

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Serial peripheral interface / inter-IC sound (SPI/I2S)
If the SPI is disabled during a communication the following sequence must be followed:

Note:

1.

Disable the SPI

2.

Clear the CRCEN bit

3.

Enable the CRCEN bit

4.

Enable the SPI

When the SPI is in slave mode, the CRC calculator is sensitive to the SCK slave input clock
as soon as the CRCEN bit is set, and this is the case whatever the value of the SPE bit. In
order to avoid any wrong CRC calculation, the software must enable CRC calculation only
when the clock is stable (in steady state).
When the SPI interface is configured as a slave, the NSS internal signal needs to be kept
low during transaction of the CRC phase once the CRCNEXT signal is released. That is why
the CRC calculation can’t be used at NSS Pulse mode when NSS hardware mode should
be applied at slave normally (see more details at the product errata sheet).
At TI mode, despite the fact that clock phase and clock polarity setting is fixed and
independent on SPIx_CR1 register, the corresponding setting CPOL=0 CPHA=1 has to be
kept at the SPIx_CR1 register anyway if CRC is applied. In addition, the CRC calculation
has to be reset between sessions by SPI disable sequence with re-enable the CRCEN bit
described above at both master and slave side, else CRC calculation can be corrupted at
this specific mode.

28.6

SPI interrupts
During SPI communication an interrupts can be generated by the following events:
•

Transmit TXFIFO ready to be loaded

•

Data received in Receive RXFIFO

•

Master mode fault

•

Overrun error

•

TI frame format error

•

CRC protocol error

Interrupts can be enabled and disabled separately.
Table 112. SPI interrupt requests
Interrupt event

Event flag

Enable Control bit

TXE

TXEIE

Data received in RXFIFO

RXNE

RXNEIE

Master Mode fault event

MODF

Transmit TXFIFO ready to be loaded

Overrun error

OVR

TI frame format error

FRE

CRC protocol error

ERRIE

CRCERR

For code example refer to the Appendix section A.17.4: SPI interrupt code example.

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28.7

I2S functional description

28.7.1

I2S general description

RM0091

The block diagram of the I2S is shown in Figure 286.
Figure 286. I2S block diagram

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1. MCK is mapped on the MISO pin.

The SPI can function as an audio I2S interface when the I2S capability is enabled (by setting
the I2SMOD bit in the SPIx_I2SCFGR register). This interface mainly uses the same pins,
flags and interrupts as the SPI.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
The I2S shares three common pins with the SPI:
•

SD: Serial Data (mapped on the MOSI pin) to transmit or receive the two timemultiplexed data channels (in half-duplex mode only).

•

WS: Word Select (mapped on the NSS pin) is the data control signal output in master
mode and input in slave mode.

•

CK: Serial Clock (mapped on the SCK pin) is the serial clock output in master mode
and serial clock input in slave mode.

An additional pin can be used when a master clock output is needed for some external
audio devices:
•

MCK: Master Clock (mapped separately) is used, when the I2S is configured in master
mode (and when the MCKOE bit in the SPIx_I2SPR register is set), to output this
additional clock generated at a preconfigured frequency rate equal to 256 × fS, where
fS is the audio sampling frequency.

The I2S uses its own clock generator to produce the communication clock when it is set in
master mode. This clock generator is also the source of the master clock output. Two
additional registers are available in I2S mode. One is linked to the clock generator
configuration SPIx_I2SPR and the other one is a generic I2S configuration register
SPIx_I2SCFGR (audio standard, slave/master mode, data format, packet frame, clock
polarity, etc.).
The SPIx_CR1 register and all CRC registers are not used in the I2S mode. Likewise, the
SSOE bit in the SPIx_CR2 register and the MODF and CRCERR bits in the SPIx_SR are
not used.
The I2S uses the same SPI register for data transfer (SPIx_DR) in 16-bit wide mode.

28.7.2

I2S full duplex
Figure 287 shows how to perform full-duplex communications using two SPI/I2S instances.
In this case, the WS and CK IOs of both SPI/I2S must be connected together.
For the master full-duplex mode, one of the SPI/I2S block must be programmed in master
(I2SCFG = ‘10’ or ‘11’), and the other SPI/I2S block must be programmed in slave (I2SCFG
= ‘00’ or ‘01’). The MCK can be generated or not, depending on the application needs.
For the slave full-duplex mode, both SPI/I2S blocks must be programmed in slave. One of
them in the slave receiver (I2SCFG = ‘01’), and the other in the slave transmitter (I2SCFG =
‘00’). The master external device then provides the bit clock (CK) and the frame
synchronization (WS).
Note that the full-duplex mode can be used for all the supported standards: I2S Philips,
MSB-justified, LSB-justified and PCM.
For the full-duplex mode, both SPI/I2S instances must use the same standard, with the
same parameters: I2SMOD, I2SSTD, CKPOL, PCMSYNC, DATLEN and CHLEN must
contain the same value on both instances.

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Figure 287. Full-duplex communication
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28.7.3

Supported audio protocols
The three-line bus has to handle only audio data generally time-multiplexed on two
channels: the right channel and the left channel. However there is only one 16-bit register
for transmission or reception. So, it is up to the software to write into the data register the
appropriate value corresponding to each channel side, or to read the data from the data
register and to identify the corresponding channel by checking the CHSIDE bit in the
SPIx_SR register. Channel left is always sent first followed by the channel right (CHSIDE
has no meaning for the PCM protocol).
Four data and packet frames are available. Data may be sent with a format of:
•

16-bit data packed in a 16-bit frame

•

16-bit data packed in a 32-bit frame

•

24-bit data packed in a 32-bit frame

•

32-bit data packed in a 32-bit frame

When using 16-bit data extended on 32-bit packet, the first 16 bits (MSB) are the significant
bits, the 16-bit LSB is forced to 0 without any need for software action or DMA request (only
one read/write operation).
The 24-bit and 32-bit data frames need two CPU read or write operations to/from the
SPIx_DR register or two DMA operations if the DMA is preferred for the application. For 24bit data frame specifically, the 8 non-significant bits are extended to 32 bits with 0-bits (by
hardware).
For all data formats and communication standards, the most significant bit is always sent
first (MSB first).

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Serial peripheral interface / inter-IC sound (SPI/I2S)
The I2S interface supports four audio standards, configurable using the I2SSTD[1:0] and
PCMSYNC bits in the SPIx_I2SCFGR register.

I2S Philips standard
For this standard, the WS signal is used to indicate which channel is being transmitted. It is
activated one CK clock cycle before the first bit (MSB) is available.
Figure 288. I2S Philips protocol waveforms (16/32-bit full accuracy)
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Data are latched on the falling edge of CK (for the transmitter) and are read on the rising
edge (for the receiver). The WS signal is also latched on the falling edge of CK.
Figure 289. I2S Philips standard waveforms (24-bit frame)
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This mode needs two write or read operations to/from the SPIx_DR register.
•

In transmission mode:
If 0x8EAA33 has to be sent (24-bit):

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Figure 290. Transmitting 0x8EAA33

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In reception mode:
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Figure 292. I2S Philips standard (16-bit extended to 32-bit packet frame)
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When 16-bit data frame extended to 32-bit channel frame is selected during the I2S
configuration phase, only one access to the SPIx_DR register is required. The 16 remaining
bits are forced by hardware to 0x0000 to extend the data to 32-bit format.
If the data to transmit or the received data are 0x76A3 (0x76A30000 extended to 32-bit), the
operation shown in Figure 293 is required.
Figure 293. Example of 16-bit data frame extended to 32-bit channel frame
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Serial peripheral interface / inter-IC sound (SPI/I2S)
For transmission, each time an MSB is written to SPIx_DR, the TXE flag is set and its
interrupt, if allowed, is generated to load the SPIx_DR register with the new value to send.
This takes place even if 0x0000 have not yet been sent because it is done by hardware.
For reception, the RXNE flag is set and its interrupt, if allowed, is generated when the first
16 MSB half-word is received.
In this way, more time is provided between two write or read operations, which prevents
underrun or overrun conditions (depending on the direction of the data transfer).

MSB justified standard
For this standard, the WS signal is generated at the same time as the first data bit, which is
the MSBit.
Figure 294. MSB Justified 16-bit or 32-bit full-accuracy length
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Data are latched on the falling edge of CK (for transmitter) and are read on the rising edge
(for the receiver).
Figure 295. MSB justified 24-bit frame length
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Figure 296. MSB justified 16-bit extended to 32-bit packet frame
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LSB justified standard
This standard is similar to the MSB justified standard (no difference for the 16-bit and 32-bit
full-accuracy frame formats).
The sampling of the input and output signals is the same as for the I2S Philips standard.
Figure 297. LSB justified 16-bit or 32-bit full-accuracy
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Figure 298. LSB justified 24-bit frame length
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•

In transmission mode:
If data 0x3478AE have to be transmitted, two write operations to the SPIx_DR register
are required by software or by DMA. The operations are shown below.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
Figure 299. Operations required to transmit 0x3478AE
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In reception mode:
If data 0x3478AE are received, two successive read operations from the SPIx_DR
register are required on each RXNE event.
Figure 300. Operations required to receive 0x3478AE
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Figure 301. LSB justified 16-bit extended to 32-bit packet frame
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When 16-bit data frame extended to 32-bit channel frame is selected during the I2S
configuration phase, Only one access to the SPIx_DR register is required. The 16 remaining
bits are forced by hardware to 0x0000 to extend the data to 32-bit format. In this case it
corresponds to the half-word MSB.
If the data to transmit or the received data are 0x76A3 (0x0000 76A3 extended to 32-bit),
the operation shown in Figure 302 is required.

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Figure 302. Example of 16-bit data frame extended to 32-bit channel frame
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069

In transmission mode, when a TXE event occurs, the application has to write the data to be
transmitted (in this case 0x76A3). The 0x000 field is transmitted first (extension on 32-bit).
The TXE flag is set again as soon as the effective data (0x76A3) is sent on SD.
In reception mode, RXNE is asserted as soon as the significant half-word is received (and
not the 0x0000 field).
In this way, more time is provided between two write or read operations to prevent underrun
or overrun conditions.

PCM standard
For the PCM standard, there is no need to use channel-side information. The two PCM
modes (short and long frame) are available and configurable using the PCMSYNC bit in
SPIx_I2SCFGR register.
In PCM mode, the output signals (WS, SD) are sampled on the rising edge of CK signal.
The input signals (WS, SD) are captured on the falling edge of CK.
Note that CK and WS are configured as output in MASTER mode.
Figure 303. PCM standard waveforms (16-bit)

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For long frame synchronization, the WS signal assertion time is fixed to 13 bits in master
mode.
For short frame synchronization, the WS synchronization signal is only one cycle long.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
Figure 304. PCM standard waveforms (16-bit extended to 32-bit packet frame)
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Note:

For both modes (master and slave) and for both synchronizations (short and long), the
number of bits between two consecutive pieces of data (and so two synchronization signals)
needs to be specified (DATLEN and CHLEN bits in the SPIx_I2SCFGR register) even in
slave mode.

28.7.4

Start-up description
The Figure 305 shows how the serial interface is handled in MASTER mode, when the
SPI/I2S is enabled (via I2SE bit). It shows as well the effect of CKPOL on the generated
signals.

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Figure 305. Start sequence in master mode

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In slave mode, the user has to enable the audio interface before the WS becomes active.
This means that the I2SE bit must be set to 1 when WS = 1 for I2S Philips standard, or when
WS = 0 for other standards.

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Clock generator
The I2S bit rate determines the data flow on the I2S data line and the I2S clock signal
frequency.
I2S bit rate = number of bits per channel × number of channels × sampling audio frequency
For a 16-bit audio, left and right channel, the I2S bit rate is calculated as follows:
I2S bit rate = 16 × 2 × fS
It will be: I2S bit rate = 32 x 2 x fS if the packet length is 32-bit wide.
Figure 306. Audio sampling frequency definition

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When the master mode is configured, a specific action needs to be taken to properly
program the linear divider in order to communicate with the desired audio frequency.
Figure 307. I2S clock generator architecture

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28.7.5

Serial peripheral interface / inter-IC sound (SPI/I2S)

069

1. Where x can be 2 or 3.

Figure 307 presents the communication clock architecture. The I2Sx clock is always the
system clock.
The audio sampling frequency may be 192 kHz, 96 kHz, 48 kHz, 44.1 kHz, 32 kHz,
22.05 kHz, 16 kHz, 11.025 kHz or 8 kHz (or any other value within this range). In order to
reach the desired frequency, the linear divider needs to be programmed according to the
formulas below:

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When the master clock is generated (MCKOE in the SPIx_I2SPR register is set):
fS = I2SxCLK / [(16*2)*((2*I2SDIV)+ODD)*8)] when the channel frame is 16-bit wide
fS = I2SxCLK / [(32*2)*((2*I2SDIV)+ODD)*4)] when the channel frame is 32-bit wide
When the master clock is disabled (MCKOE bit cleared):
fS = I2SxCLK / [(16*2)*((2*I2SDIV)+ODD))] when the channel frame is 16-bit wide
fS = I2SxCLK / [(32*2)*((2*I2SDIV)+ODD))] when the channel frame is 32-bit wide
Table 113 provides example precision values for different clock configurations.
Note:

Other configurations are possible that allow optimum clock precision.
Table 113. Audio-frequency precision using standard 8 MHz HSE(1)
SYSCLK

794/1004

(MHz)

Data
length

I2SDIV

I2SODD

MCLK

48

16

8

0

No

96000

93750

2.3438%

48

32

4

0

No

96000

93750

2.3438%

48

16

15

1

No

48000

48387.0968

0.8065%

48

32

8

0

No

48000

46875

2.3438%

48

16

17

0

No

44100

44117.647

0.0400%

48

32

8

1

No

44100

44117.647

0.0400%

48

16

23

1

No

32000

31914.8936

0.2660%

48

32

11

1

No

32000

32608.696

1.9022%

48

16

34

0

No

22050

22058.8235

0.0400%

48

32

17

0

No

22050

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0.0400%

48

16

47

0

No

16000

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48

32

23

1

No

16000

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48

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68

0

No

11025

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48

32

34

0

No

11025

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48

16

94

0

No

8000

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0.2660%

48

32

47

0

No

8000

7978.7234

0.2660%

48

16

2

0

Yes

48000

46875

2.3430%

48

32

2

0

Yes

48000

46875

2.3430%

48

16

2

0

Yes

44100

46875

6.2925%

48

32

2

0

Yes

44100

46875

6.2925%

48

16

3

0

Yes

32000

31250

2.3438%

48

32

3

0

Yes

32000

31250

2.3438%

48

16

4

1

Yes

22050

20833.333

5.5178%

48

32

4

1

Yes

22050

20833.333

5.5178%

48

16

6

0

Yes

16000

15625

2.3438%

48

32

6

0

Yes

16000

15625

2.3438%

DocID018940 Rev 9

Target fs
(Hz)

Real fs (kHz)

Error

RM0091

Serial peripheral interface / inter-IC sound (SPI/I2S)
Table 113. Audio-frequency precision using standard 8 MHz HSE(1) (continued)
SYSCLK
(MHz)

Data
length

I2SDIV

I2SODD

MCLK

Target fs
(Hz)

48

16

8

1

Yes

11025

11029.4118

0.0400%

48

32

8

1

Yes

11025

11029.4118

0.0400%

48

16

11

1

Yes

8000

8152.17391

1.9022%

48

32

11

1

Yes

8000

8152.17391

1.9022%

Real fs (kHz)

Error

1. This table gives only example values for different clock configurations. Other configurations allowing
optimum clock precision are possible.

28.7.6

I2S master mode
The I2S can be configured in master mode. This means that the serial clock is generated on
the CK pin as well as the Word Select signal WS. Master clock (MCK) may be output or not,
controlled by the MCKOE bit in the SPIx_I2SPR register.

Procedure
1.

Select the I2SDIV[7:0] bits in the SPIx_I2SPR register to define the serial clock baud
rate to reach the proper audio sample frequency. The ODD bit in the SPIx_I2SPR
register also has to be defined.

2.

Select the CKPOL bit to define the steady level for the communication clock. Set the
MCKOE bit in the SPIx_I2SPR register if the master clock MCK needs to be provided
to the external DAC/ADC audio component (the I2SDIV and ODD values should be
computed depending on the state of the MCK output, for more details refer to
Section 28.7.5: Clock generator).

3.

Set the I2SMOD bit in the SPIx_I2SCFGR register to activate the I2S functions and
choose the I2S standard through the I2SSTD[1:0] and PCMSYNC bits, the data length
through the DATLEN[1:0] bits and the number of bits per channel by configuring the
CHLEN bit. Select also the I2S master mode and direction (Transmitter or Receiver)
through the I2SCFG[1:0] bits in the SPIx_I2SCFGR register.

4.

If needed, select all the potential interrupt sources and the DMA capabilities by writing
the SPIx_CR2 register.

5.

The I2SE bit in SPIx_I2SCFGR register must be set.

WS and CK are configured in output mode. MCK is also an output, if the MCKOE bit in
SPIx_I2SPR is set.

Transmission sequence
The transmission sequence begins when a half-word is written into the Tx buffer.
Lets assume the first data written into the Tx buffer corresponds to the left channel data.
When data are transferred from the Tx buffer to the shift register, TXE is set and data
corresponding to the right channel have to be written into the Tx buffer. The CHSIDE flag
indicates which channel is to be transmitted. It has a meaning when the TXE flag is set
because the CHSIDE flag is updated when TXE goes high.
A full frame has to be considered as a left channel data transmission followed by a right
channel data transmission. It is not possible to have a partial frame where only the left
channel is sent.
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The data half-word is parallel loaded into the 16-bit shift register during the first bit
transmission, and then shifted out, serially, to the MOSI/SD pin, MSB first. The TXE flag is
set after each transfer from the Tx buffer to the shift register and an interrupt is generated if
the TXEIE bit in the SPIx_CR2 register is set.
For more details about the write operations depending on the I2S standard mode selected,
refer to Section 28.7.3: Supported audio protocols).
To ensure a continuous audio data transmission, it is mandatory to write the SPIx_DR
register with the next data to transmit before the end of the current transmission.
To switch off the I2S, by clearing I2SE, it is mandatory to wait for TXE = 1 and BSY = 0.

Reception sequence
The operating mode is the same as for transmission mode except for the point 3 (refer to the
procedure described in Section 28.7.6: I2S master mode), where the configuration should
set the master reception mode through the I2SCFG[1:0] bits.
Whatever the data or channel length, the audio data are received by 16-bit packets. This
means that each time the Rx buffer is full, the RXNE flag is set and an interrupt is generated
if the RXNEIE bit is set in SPIx_CR2 register. Depending on the data and channel length
configuration, the audio value received for a right or left channel may result from one or two
receptions into the Rx buffer.
Clearing the RXNE bit is performed by reading the SPIx_DR register.
CHSIDE is updated after each reception. It is sensitive to the WS signal generated by the
I2S cell.
For more details about the read operations depending on the I2S standard mode selected,
refer to Section 28.7.3: Supported audio protocols.
If data are received while the previously received data have not been read yet, an overrun is
generated and the OVR flag is set. If the ERRIE bit is set in the SPIx_CR2 register, an
interrupt is generated to indicate the error.
To switch off the I2S, specific actions are required to ensure that the I2S completes the
transfer cycle properly without initiating a new data transfer. The sequence depends on the
configuration of the data and channel lengths, and on the audio protocol mode selected. In
the case of:
•

•

•

16-bit data length extended on 32-bit channel length (DATLEN = 00 and CHLEN = 1)
using the LSB justified mode (I2SSTD = 10)
a)

Wait for the second to last RXNE = 1 (n – 1)

b)

Then wait 17 I2S clock cycles (using a software loop)

c)

Disable the I2S (I2SE = 0)

16-bit data length extended on 32-bit channel length (DATLEN = 00 and CHLEN = 1) in
MSB justified, I2S or PCM modes (I2SSTD = 00, I2SSTD = 01 or I2SSTD = 11,
respectively)
a)

Wait for the last RXNE

b)

Then wait 1 I2S clock cycle (using a software loop)

c)

Disable the I2S (I2SE = 0)

For all other combinations of DATLEN and CHLEN, whatever the audio mode selected
through the I2SSTD bits, carry out the following sequence to switch off the I2S:
a)

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Serial peripheral interface / inter-IC sound (SPI/I2S)
b)

Then wait one I2S clock cycle (using a software loop)

c)

Disable the I2S (I2SE = 0)

Note:

The BSY flag is kept low during transfers.

28.7.7

I2S slave mode
For the slave configuration, the I2S can be configured in transmission or reception mode.
The operating mode is following mainly the same rules as described for the I2S master
configuration. In slave mode, there is no clock to be generated by the I2S interface. The
clock and WS signals are input from the external master connected to the I2S interface.
There is then no need, for the user, to configure the clock.
The configuration steps to follow are listed below:
1.

Set the I2SMOD bit in the SPIx_I2SCFGR register to select I2S mode and choose the
I2S standard through the I2SSTD[1:0] bits, the data length through the DATLEN[1:0]
bits and the number of bits per channel for the frame configuring the CHLEN bit. Select
also the mode (transmission or reception) for the slave through the I2SCFG[1:0] bits in
SPIx_I2SCFGR register.

2.

If needed, select all the potential interrupt sources and the DMA capabilities by writing
the SPIx_CR2 register.

3.

The I2SE bit in SPIx_I2SCFGR register must be set.

Transmission sequence
The transmission sequence begins when the external master device sends the clock and
when the NSS_WS signal requests the transfer of data. The slave has to be enabled before
the external master starts the communication. The I2S data register has to be loaded before
the master initiates the communication.
For the I2S, MSB justified and LSB justified modes, the first data item to be written into the
data register corresponds to the data for the left channel. When the communication starts,
the data are transferred from the Tx buffer to the shift register. The TXE flag is then set in
order to request the right channel data to be written into the I2S data register.
The CHSIDE flag indicates which channel is to be transmitted. Compared to the master
transmission mode, in slave mode, CHSIDE is sensitive to the WS signal coming from the
external master. This means that the slave needs to be ready to transmit the first data
before the clock is generated by the master. WS assertion corresponds to left channel
transmitted first.
Note:

The I2SE has to be written at least two PCLK cycles before the first clock of the master
comes on the CK line.
The data half-word is parallel-loaded into the 16-bit shift register (from the internal bus)
during the first bit transmission, and then shifted out serially to the MOSI/SD pin MSB first.
The TXE flag is set after each transfer from the Tx buffer to the shift register and an interrupt
is generated if the TXEIE bit in the SPIx_CR2 register is set.
Note that the TXE flag should be checked to be at 1 before attempting to write the Tx buffer.
For more details about the write operations depending on the I2S standard mode selected,
refer to Section 28.7.3: Supported audio protocols.
To secure a continuous audio data transmission, it is mandatory to write the SPIx_DR
register with the next data to transmit before the end of the current transmission. An

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underrun flag is set and an interrupt may be generated if the data are not written into the
SPIx_DR register before the first clock edge of the next data communication. This indicates
to the software that the transferred data are wrong. If the ERRIE bit is set into the SPIx_CR2
register, an interrupt is generated when the UDR flag in the SPIx_SR register goes high. In
this case, it is mandatory to switch off the I2S and to restart a data transfer starting from the
left channel.
To switch off the I2S, by clearing the I2SE bit, it is mandatory to wait for TXE = 1 and
BSY = 0.

Reception sequence
The operating mode is the same as for the transmission mode except for the point 1 (refer to
the procedure described in Section 28.7.7: I2S slave mode), where the configuration should
set the master reception mode using the I2SCFG[1:0] bits in the SPIx_I2SCFGR register.
Whatever the data length or the channel length, the audio data are received by 16-bit
packets. This means that each time the RX buffer is full, the RXNE flag in the SPIx_SR
register is set and an interrupt is generated if the RXNEIE bit is set in the SPIx_CR2
register. Depending on the data length and channel length configuration, the audio value
received for a right or left channel may result from one or two receptions into the RX buffer.
The CHSIDE flag is updated each time data are received to be read from the SPIx_DR
register. It is sensitive to the external WS line managed by the external master component.
Clearing the RXNE bit is performed by reading the SPIx_DR register.
For more details about the read operations depending the I2S standard mode selected, refer
to Section 28.7.3: Supported audio protocols.
If data are received while the preceding received data have not yet been read, an overrun is
generated and the OVR flag is set. If the bit ERRIE is set in the SPIx_CR2 register, an
interrupt is generated to indicate the error.
To switch off the I2S in reception mode, I2SE has to be cleared immediately after receiving
the last RXNE = 1.
Note:

The external master components should have the capability of sending/receiving data in 16bit or 32-bit packets via an audio channel.

28.7.8

I2S status flags
Three status flags are provided for the application to fully monitor the state of the I2S bus.

Busy flag (BSY)
The BSY flag is set and cleared by hardware (writing to this flag has no effect). It indicates
the state of the communication layer of the I2S.
When BSY is set, it indicates that the I2S is busy communicating. There is one exception in
master receive mode (I2SCFG = 11) where the BSY flag is kept low during reception.
The BSY flag is useful to detect the end of a transfer if the software needs to disable the I2S.
This avoids corrupting the last transfer. For this, the procedure described below must be
strictly respected.
The BSY flag is set when a transfer starts, except when the I2S is in master receiver mode.

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Serial peripheral interface / inter-IC sound (SPI/I2S)
The BSY flag is cleared:
•

When a transfer completes (except in master transmit mode, in which the
communication is supposed to be continuous)

•

When the I2S is disabled

When communication is continuous:

Note:

•

In master transmit mode, the BSY flag is kept high during all the transfers

•

In slave mode, the BSY flag goes low for one I2S clock cycle between each transfer

Do not use the BSY flag to handle each data transmission or reception. It is better to use the
TXE and RXNE flags instead.

Tx buffer empty flag (TXE)
When set, this flag indicates that the Tx buffer is empty and the next data to be transmitted
can then be loaded into it. The TXE flag is reset when the Tx buffer already contains data to
be transmitted. It is also reset when the I2S is disabled (I2SE bit is reset).

RX buffer not empty (RXNE)
When set, this flag indicates that there are valid received data in the RX Buffer. It is reset
when SPIx_DR register is read.

Channel Side flag (CHSIDE)
In transmission mode, this flag is refreshed when TXE goes high. It indicates the channel
side to which the data to transfer on SD has to belong. In case of an underrun error event in
slave transmission mode, this flag is not reliable and I2S needs to be switched off and
switched on before resuming the communication.
In reception mode, this flag is refreshed when data are received into SPIx_DR. It indicates
from which channel side data have been received. Note that in case of error (like OVR) this
flag becomes meaningless and the I2S should be reset by disabling and then enabling it
(with configuration if it needs changing).
This flag has no meaning in the PCM standard (for both Short and Long frame modes).
When the OVR or UDR flag in the SPIx_SR is set and the ERRIE bit in SPIx_CR2 is also
set, an interrupt is generated. This interrupt can be cleared by reading the SPIx_SR status
register (once the interrupt source has been cleared).

28.7.9

I2S error flags
There are three error flags for the I2S cell.

Underrun flag (UDR)
In slave transmission mode this flag is set when the first clock for data transmission appears
while the software has not yet loaded any value into SPIx_DR. It is available when the
I2SMOD bit in the SPIx_I2SCFGR register is set. An interrupt may be generated if the
ERRIE bit in the SPIx_CR2 register is set.
The UDR bit is cleared by a read operation on the SPIx_SR register.

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Overrun flag (OVR)
This flag is set when data are received and the previous data have not yet been read from
the SPIx_DR register. As a result, the incoming data are lost. An interrupt may be generated
if the ERRIE bit is set in the SPIx_CR2 register.
In this case, the receive buffer contents are not updated with the newly received data from
the transmitter device. A read operation to the SPIx_DR register returns the previous
correctly received data. All other subsequently transmitted half-words are lost.
Clearing the OVR bit is done by a read operation on the SPIx_DR register followed by a
read access to the SPIx_SR register.

Frame error flag (FRE)
This flag can be set by hardware only if the I2S is configured in Slave mode. It is set if the
external master is changing the WS line while the slave is not expecting this change. If the
synchronization is lost, the following steps are required to recover from this state and
resynchronize the external master device with the I2S slave device:
1.

Disable the I2S.

2.

Enable it again when the correct level is detected on the WS line (WS line is high in I2S
mode or low for MSB- or LSB-justified or PCM modes.

Desynchronization between master and slave devices may be due to noisy environment on
the CK communication clock or on the WS frame synchronization line. An error interrupt can
be generated if the ERRIE bit is set. The desynchronization flag (FRE) is cleared by
software when the status register is read.

28.7.10

DMA features
In I2S mode, the DMA works in exactly the same way as it does in SPI mode. There is no
difference except that the CRC feature is not available in I2S mode since there is no data
transfer protection system.

28.8

I2S interrupts
Table 114 provides the list of I2S interrupts.
Table 114. I2S interrupt requests
Interrupt event

800/1004

Event flag

Enable control bit

Transmit buffer empty flag

TXE

TXEIE

Receive buffer not empty flag

RXNE

RXNEIE

Overrun error

OVR

Underrun error

UDR

Frame error flag

FRE

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SPI and I2S registers

28.9

The peripheral registers can be accessed by half-words (16-bit) or words (32-bit). SPI_DR
in addition by can be accessed by 8-bit access.

28.9.1

SPI control register 1 (SPIx_CR1)
Address offset: 0x00
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

BIDI
MODE

BIDI
OE

CRC
EN

CRC
NEXT

CRCL

RX
ONLY

SSM

SSI

LSB
FIRST

SPE

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

5

4

3

BR [2:0]
rw

rw

rw

2

1

0

MSTR

CPOL

CPHA

rw

rw

rw

Bit 15 BIDIMODE: Bidirectional data mode enable. This bit enables half-duplex communication using
common single bidirectional data line. Keep RXONLY bit clear when bidirectional mode is
active.
0: 2-line unidirectional data mode selected
1: 1-line bidirectional data mode selected
Note: This bit is not used in I2S mode.
Bit 14 BIDIOE: Output enable in bidirectional mode
This bit combined with the BIDIMODE bit selects the direction of transfer in bidirectional mode
0: Output disabled (receive-only mode)
1: Output enabled (transmit-only mode)
Note: In master mode, the MOSI pin is used and in slave mode, the MISO pin is used.
This bit is not used in I2S mode.
Bit 13 CRCEN: Hardware CRC calculation enable
0: CRC calculation disabled
1: CRC calculation Enabled
Note: This bit should be written only when SPI is disabled (SPE = ‘0’) for correct operation.
This bit is not used in I2S mode.
Bit 12 CRCNEXT: Transmit CRC next
0: Next transmit value is from Tx buffer
1: Next transmit value is from Tx CRC register
Note: This bit has to be written as soon as the last data is written in the SPIx_DR register.
This bit is not used in I2S mode.
Bit 11 CRCL: CRC length
This bit is set and cleared by software to select the CRC length.
0: 8-bit CRC length
1: 16-bit CRC length
Note: This bit should be written only when SPI is disabled (SPE = ‘0’) for correct operation.
This bit is not used in I2S mode.

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Bit 10 RXONLY: Receive only mode enabled.
This bit enables simplex communication using a single unidirectional line to receive data
exclusively. Keep BIDIMODE bit clear when receive only mode is active.This bit is also useful
in a multislave system in which this particular slave is not accessed, the output from the
accessed slave is not corrupted.
0: Full-duplex (Transmit and receive)
1: Output disabled (Receive-only mode)
Note: This bit is not used in I2S mode.
Bit 9 SSM: Software slave management
When the SSM bit is set, the NSS pin input is replaced with the value from the SSI bit.
0: Software slave management disabled
1: Software slave management enabled
Note: This bit is not used in I2S mode and SPI TI mode.
Bit 8 SSI: Internal slave select
This bit has an effect only when the SSM bit is set. The value of this bit is forced onto the NSS
pin and the I/O value of the NSS pin is ignored.
Note: This bit is not used in I2S mode and SPI TI mode.
Bit 7 LSBFIRST: Frame format
0: data is transmitted / received with the MSB first
1: data is transmitted / received with the LSB first
Note: 1. This bit should not be changed when communication is ongoing.
2. This bit is not used in I2S mode and SPI TI mode.
Bit 6 SPE: SPI enable
0: Peripheral disabled
1: Peripheral enabled
Note: When disabling the SPI, follow the procedure described in Procedure for disabling the
SPI on page 767.
This bit is not used in I2S mode.
Bits 5:3 BR[2:0]: Baud rate control
000: fPCLK/2
001: fPCLK/4
010: fPCLK/8
011: fPCLK/16
100: fPCLK/32
101: fPCLK/64
110: fPCLK/128
111: fPCLK/256
Note: These bits should not be changed when communication is ongoing.
This bit is not used in I2S mode.

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Bit 2 MSTR: Master selection
0: Slave configuration
1: Master configuration
Note: This bit should not be changed when communication is ongoing.
This bit is not used in I2S mode.
Bit1 CPOL: Clock polarity
0: CK to 0 when idle
1: CK to 1 when idle
Note: This bit should not be changed when communication is ongoing.
This bit is not used in I2S mode and SPI TI mode except the case when CRC is applied
at TI mode.
Bit 0 CPHA: Clock phase
0: The first clock transition is the first data capture edge
1: The second clock transition is the first data capture edge
Note: This bit should not be changed when communication is ongoing.
This bit is not used in I2S mode and SPI TI mode except the case when CRC is applied
at TI mode.

28.9.2

SPI control register 2 (SPIx_CR2)
Address offset: 0x04
Reset value: 0x0700

15

14

13

12

Res.

LDMA
_TX

LDMA
_RX

FRXT
H

rw

rw

rw

11

10

9

8

DS [3:0]
rw

rw

rw

7

6

5

TXEIE RXNEIE ERRIE
rw

rw

rw

rw

4

3

2

FRF

NSSP

SSOE

rw

rw

rw

1

0

TXDMAEN RXDMAEN
rw

rw

Bit 15 Reserved, must be kept at reset value.
Bit 14 LDMA_TX: Last DMA transfer for transmission
This bit is used in data packing mode, to define if the total number of data to transmit by DMA
is odd or even. It has significance only if the TXDMAEN bit in the SPIx_CR2 register is set and
if packing mode is used (data length =< 8-bit and write access to SPIx_DR is 16-bit wide). It
has to be written when the SPI is disabled (SPE = 0 in the SPIx_CR1 register).
0: Number of data to transfer is even
1: Number of data to transfer is odd
Note: Refer to Procedure for disabling the SPI on page 767 if the CRCEN bit is set.
This bit is not used in I²S mode.
Bit 13 LDMA_RX: Last DMA transfer for reception
This bit is used in data packing mode, to define if the total number of data to receive by DMA is
odd or even. It has significance only if the RXDMAEN bit in the SPIx_CR2 register is set and if
packing mode is used (data length =< 8-bit and write access to SPIx_DR is 16-bit wide). It has
to be written when the SPI is disabled (SPE = 0 in the SPIx_CR1 register).
0: Number of data to transfer is even
1: Number of data to transfer is odd
Note: Refer to Procedure for disabling the SPI on page 767 if the CRCEN bit is set.
This bit is not used in I²S mode.

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Bit 12 FRXTH: FIFO reception threshold
This bit is used to set the threshold of the RXFIFO that triggers an RXNE event
0: RXNE event is generated if the FIFO level is greater than or equal to 1/2 (16-bit)
1: RXNE event is generated if the FIFO level is greater than or equal to 1/4 (8-bit)
Note: This bit is not used in I²S mode.
Bits 11:8 DS [3:0]: Data size
These bits configure the data length for SPI transfers:
0000: Not used
0001: Not used
0010: Not used
0011: 4-bit
0100: 5-bit
0101: 6-bit
0110: 7-bit
0111: 8-bit
1000: 9-bit
1001: 10-bit
1010: 11-bit
1011: 12-bit
1100: 13-bit
1101: 14-bit
1110: 15-bit
1111: 16-bit
If software attempts to write one of the “Not used” values, they are forced to the value “0111”(8bit).
Note: This bit is not used in I²S mode.
Bit 7 TXEIE: Tx buffer empty interrupt enable
0: TXE interrupt masked
1: TXE interrupt not masked. Used to generate an interrupt request when the TXE flag is set.
Bit 6 RXNEIE: RX buffer not empty interrupt enable
0: RXNE interrupt masked
1: RXNE interrupt not masked. Used to generate an interrupt request when the RXNE flag is
set.
Bit 5 ERRIE: Error interrupt enable
This bit controls the generation of an interrupt when an error condition occurs (CRCERR,
OVR, MODF in SPI mode, FRE at TI mode and UDR, OVR, and FRE in I2S mode).
0: Error interrupt is masked
1: Error interrupt is enabled
Bit 4 FRF: Frame format
0: SPI Motorola mode
1 SPI TI mode
Note: This bit must be written only when the SPI is disabled (SPE=0).
This bit is not used in I2S mode.

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Bit 3 NSSP: NSS pulse management
This bit is used in master mode only. it allow the SPI to generate an NSS pulse between two
consecutive data when doing continuous transfers. In the case of a single data transfer, it
forces the NSS pin high level after the transfer.
It has no meaning if CPHA = ’1’, or FRF = ’1’.
0: No NSS pulse
1: NSS pulse generated
Note: 1. This bit must be written only when the SPI is disabled (SPE=0).
2. This bit is not used in I2S mode and SPI TI mode.
Bit 2 SSOE: SS output enable
0: SS output is disabled in master mode and the SPI interface can work in multimaster
configuration
1: SS output is enabled in master mode and when the SPI interface is enabled. The SPI
interface cannot work in a multimaster environment.
Note: This bit is not used in I2S mode and SPI TI mode.
Bit 1 TXDMAEN: Tx buffer DMA enable
When this bit is set, a DMA request is generated whenever the TXE flag is set.
0: Tx buffer DMA disabled
1: Tx buffer DMA enabled
Bit 0 RXDMAEN: Rx buffer DMA enable
When this bit is set, a DMA request is generated whenever the RXNE flag is set.
0: Rx buffer DMA disabled
1: Rx buffer DMA enabled

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28.9.3

RM0091

SPI status register (SPIx_SR)
Address offset: 0x08
Reset value: 0x0002

15
Res.

14
Res.

13
Res.

12

11

10

9

FTLVL[1:0]

FRLVL[2:0]

r

r

r

r

8

7

6

5

4

3

2

1

0

UDR

CHSIDE

TXE

RXNE

r

r

r

r

FRE

BSY

OVR

MODF

CRC
ERR

r

r

r

r

rc_w0

Bits 15:13 Reserved, must be kept at reset value.
Bits 12:11 FTLVL[1:0]: FIFO Transmission Level
These bits are set and cleared by hardware.
00: FIFO empty
01: 1/4 FIFO
10: 1/2 FIFO
11: FIFO full (considered as FULL when the FIFO threshold is greater than 1/2)
Note: These bits are not used in I²S mode.
Bits 10:9 FRLVL[1:0]: FIFO reception level
These bits are set and cleared by hardware.
00: FIFO empty
01: 1/4 FIFO
10: 1/2 FIFO
11: FIFO full
Note: These bits are not used in I²S mode and in SPI receive-only mode while CRC
calculation is enabled.
Bit 8 FRE: Frame format error
This flag is used for SPI in TI slave mode and I2S slave mode. Refer to Section 28.5.11: SPI
error flags and Section 28.7.9: I2S error flags.
This flag is set by hardware and reset when SPIx_SR is read by software.
0: No frame format error
1: A frame format error occurred
Bit 7 BSY: Busy flag
0: SPI (or I2S) not busy
1: SPI (or I2S) is busy in communication or Tx buffer is not empty
This flag is set and cleared by hardware.
Note: The BSY flag must be used with caution: refer to Section 28.5.10: SPI status flags and
Procedure for disabling the SPI on page 767.
Bit 6 OVR: Overrun flag
0: No overrun occurred
1: Overrun occurred
This flag is set by hardware and reset by a software sequence. Refer to I2S error flags on
page 799 for the software sequence.
Bit 5 MODF: Mode fault
0: No mode fault occurred
1: Mode fault occurred
This flag is set by hardware and reset by a software sequence. Refer to Section : Mode fault
(MODF) on page 777 for the software sequence.
Note: This bit is not used in I2S mode.

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Bit 4 CRCERR: CRC error flag
0: CRC value received matches the SPIx_RXCRCR value
1: CRC value received does not match the SPIx_RXCRCR value
This flag is set by hardware and cleared by software writing 0.
Note: This bit is not used in I2S mode.
Bit 3 UDR: Underrun flag
0: No underrun occurred
1: Underrun occurred
This flag is set by hardware and reset by a software sequence. Refer to I2S error flags on
page 799 for the software sequence.
Note: This bit is not used in SPI mode.
Bit 2 CHSIDE: Channel side
0: Channel Left has to be transmitted or has been received
1: Channel Right has to be transmitted or has been received
Note: This bit is not used in SPI mode. It has no significance in PCM mode.
Bit 1 TXE: Transmit buffer empty
0: Tx buffer not empty
1: Tx buffer empty
Bit 0 RXNE: Receive buffer not empty
0: Rx buffer empty
1: Rx buffer not empty

28.9.4

SPI data register (SPIx_DR)
Address offset: 0x0C
Reset value: 0x0000

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

DR[15:0]
rw

Bits 15:0 DR[15:0]: Data register
Data received or to be transmitted
The data register serves as an interface between the Rx and Tx FIFOs. When the data
register is read, RxFIFO is accessed while the write to data register accesses TxFIFO (See
Section 28.5.9: Data transmission and reception procedures).
Note: Data is always right-aligned. Unused bits are ignored when writing to the register, and
read as zero when the register is read. The Rx threshold setting must always
correspond with the read access currently used.

28.9.5

SPI CRC polynomial register (SPIx_CRCPR)
Address offset: 0x10
Reset value: 0x0007

15

14

13

12

11

10

9

8

rw

rw

rw

rw

rw

rw

rw

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

CRCPOLY[15:0]
rw

rw

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Bits 15:0 CRCPOLY[15:0]: CRC polynomial register
This register contains the polynomial for the CRC calculation.
The CRC polynomial (0007h) is the reset value of this register. Another polynomial can be
configured as required.
Note: The polynomial value should be odd only. No even value is supported.

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28.9.6

SPI Rx CRC register (SPIx_RXCRCR)
Address offset: 0x14
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

RxCRC[15:0]
r

r

r

r

r

r

r

r

r

Bits 15:0 RXCRC[15:0]: Rx CRC register
When CRC calculation is enabled, the RxCRC[15:0] bits contain the computed CRC value of
the subsequently received bytes. This register is reset when the CRCEN bit in SPIx_CR1
register is written to 1. The CRC is calculated serially using the polynomial programmed in the
SPIx_CRCPR register.
Only the 8 LSB bits are considered when the CRC frame format is set to be 8-bit length (CRCL
bit in the SPIx_CR1 is cleared). CRC calculation is done based on any CRC8 standard.
The entire 16-bits of this register are considered when a 16-bit CRC frame format is selected
(CRCL bit in the SPIx_CR1 register is set). CRC calculation is done based on any CRC16
standard.
Note: A read to this register when the BSY Flag is set could return an incorrect value.
These bits are not used in I2S mode.

28.9.7

SPI Tx CRC register (SPIx_TXCRCR)
Address offset: 0x18
Reset value: 0x0000

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

TxCRC[15:0]
r

r

r

r

r

r

r

r

r

Bits 15:0 TxCRC[15:0]: Tx CRC register
When CRC calculation is enabled, the TxCRC[7:0] bits contain the computed CRC value of
the subsequently transmitted bytes. This register is reset when the CRCEN bit of SPIx_CR1 is
written to 1. The CRC is calculated serially using the polynomial programmed in the
SPIx_CRCPR register.
Only the 8 LSB bits are considered when the CRC frame format is set to be 8-bit length
(CRCL bit in the SPIx_CR1 is cleared). CRC calculation is done based on any CRC8
standard.
The entire 16-bits of this register are considered when a 16-bit CRC frame format is selected
(CRCL bit in the SPIx_CR1 register is set). CRC calculation is done based on any CRC16
standard.
Note: A read to this register when the BSY flag is set could return an incorrect value.
These bits are not used in I2S mode.

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SPIx_I2S configuration register (SPIx_I2SCFGR)

28.9.8

Address offset: 0x1C
Reset value: 0x0000
15

14

13

12

11

10

Res.

Res.

Res.

Res.

I2SMOD

I2SE

rw

rw

9

8

I2SCFG
rw

rw

7

6

PCMSYNC

Res.

rw

5

4

I2SSTD
rw

rw

3
CKPOL
rw

2

DATLEN
rw

Bits 15:12 Reserved: Forced to 0 by hardware
Bit 11 I2SMOD: I2S mode selection
0: SPI mode is selected
1: I2S mode is selected
Note: This bit should be configured when the SPI or I2S is disabled.
Bit 10 I2SE: I2S enable
0: I2S peripheral is disabled
1: I2S peripheral is enabled
Note: This bit is not used in SPI mode.
Bits 9:8 I2SCFG: I2S configuration mode
00: Slave - transmit
01: Slave - receive
10: Master - transmit
11: Master - receive
Note: These bits should be configured when the I2S is disabled.
They are not used in SPI mode.
Bit 7 PCMSYNC: PCM frame synchronization
0: Short frame synchronization
1: Long frame synchronization
Note: This bit has a meaning only if I2SSTD = 11 (PCM standard is used).
It is not used in SPI mode.
Bit 6 Reserved: forced at 0 by hardware
Bits 5:4 I2SSTD: I2S standard selection
00: I2S Philips standard.
01: MSB justified standard (left justified)
10: LSB justified standard (right justified)
11: PCM standard
For more details on I2S standards, refer to Section 28.7.3 on page 784
Note: For correct operation, these bits should be configured when the I2S is disabled.
They are not used in SPI mode.

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Serial peripheral interface / inter-IC sound (SPI/I2S)

Bit 3 CKPOL: Inactive state clock polarity
0: I2S clock inactive state is low level
1: I2S clock inactive state is high level
Note: For correct operation, this bit should be configured when the I2S is disabled.
It is not used in SPI mode.
The bit CKPOL does not affect the CK edge sensitivity used to receive or transmit the SD and
WS signals.
Bits 2:1 DATLEN: Data length to be transferred
00: 16-bit data length
01: 24-bit data length
10: 32-bit data length
11: Not allowed
Note: For correct operation, these bits should be configured when the I2S is disabled.
They are not used in SPI mode.
Bit 0 CHLEN: Channel length (number of bits per audio channel)
0: 16-bit wide
1: 32-bit wide
The bit write operation has a meaning only if DATLEN = 00 otherwise the channel length is fixed to
32-bit by hardware whatever the value filled in.
Note: For correct operation, this bit should be configured when the I2S is disabled.
It is not used in SPI mode.

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SPIx_I2S prescaler register (SPIx_I2SPR)

28.9.9

Address offset: 0x20
Reset value: 0x0002

15

14

13

12

11

10

9

8

7

6

5

4

3

Res.

Res.

Res.

Res.

Res.

Res.

MCKOE

ODD

I2SDIV[7:0]

rw

rw

rw

2

1

0

Bits 15:10 Reserved: Forced to 0 by hardware
Bit 9 MCKOE: Master clock output enable
0: Master clock output is disabled
1: Master clock output is enabled
Note: This bit should be configured when the I2S is disabled. It is used only when the I2S is in master
mode.
It is not used in SPI mode.
Bit 8 ODD: Odd factor for the prescaler
0: Real divider value is = I2SDIV *2
1: Real divider value is = (I2SDIV * 2)+1
Refer to Section 28.7.4 on page 791
Note: This bit should be configured when the I2S is disabled. It is used only when the I2S is in master
mode.
It is not used in SPI mode.
Bits 7:0 I2SDIV[7:0]: I2S linear prescaler
I2SDIV [7:0] = 0 or I2SDIV [7:0] = 1 are forbidden values.
Refer to Section 28.7.4 on page 791
Note: These bits should be configured when the I2S is disabled. They are used only when the I2S is
in master mode.
They are not used in SPI mode.

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SPIx_I2SPR
Reset value

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0
0
0

Reset value
0

0

0

0

0

0
0
0

RXDMAEN

0
0

0

DR[15:0]

0
0

CRCPOLY[15:0]
0
0

RxCRC[15:0]
0
0

TxCRC[15:0]

0
0

0
0
0
0

0
0

RXNE

SSOE
TXDMAEN

0

TXE

0
CHSIDE

FRF
NSSP

0
UDR

ERRIE
0
CRCERR

RXNEIE
0

OVR

0
MODF

0

0

0

0

0

0
0

0
0
0
0
0
0
1
0

0
0
0
0
0
0
0

0
0
0
1
1
1

0
0
0
0
0
0

0
0
0
0
0
0

0

0

0
0

0
0

0
0
0

0
0

0

CPOL

0

CPHA

0

MSTR

SPE

SSI
LSBFIRST

0

CHLEN

0

0

TXEIE

0

BR [2:0]

DATLEN

0

1

BSY

SSM

0

CKPOL

0

1

FRE

CRCNEXT
CRCL

BIDIOE
CRCEN
0

I2SSTD

FRLVL[1:0]

1

Res.

0

DS[3:0]

PCMSYNC

0
0

ODD

0
0

0

0

I2SCFG

0
0

MCKOE

0

RXONLY

BIDIMODE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

I2SE

FRXTH
0
FTLVL[1:0]

LDMA_TX
LDMA_RX
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0
0

Res.

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

I2SMOD

Reset value
0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Reset value

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SPIx_I2SCFGR

Res.

0x1C
SPIx_TXCRCR

Res.

0x18
SPIx_RXCRCR

Res.

0x14
SPIx_CRCPR

Res.

0x10
SPIx_DR

Res.

0x0C
SPIx_SR

Res.

0x08
SPIx_CR2

Res.

0x04
SPIx_CR1

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

28.9.10

Res.

RM0091
Serial peripheral interface / inter-IC sound (SPI/I2S)

SPI/I2S register map
Table 115 shows the SPI/I2S register map and reset values.
Table 115. SPI register map and reset values

0
0
0

I2SDIV
0
0
0

0
1
0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

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Controller area network (bxCAN)

29

RM0091

Controller area network (bxCAN)
This section applies to STM32F042, STM32F072 and STM32F09x devices only.

29.1

Introduction
The Basic Extended CAN peripheral, named bxCAN, interfaces the CAN network. It
supports the CAN protocols version 2.0A and B. It has been designed to manage a high
number of incoming messages efficiently with a minimum CPU load. It also meets the
priority requirements for transmit messages.
For safety-critical applications, the CAN controller provides all hardware functions for
supporting the CAN Time Triggered Communication option.

29.2

bxCAN main features
•

Supports CAN protocol version 2.0 A, B Active

•

Bit rates up to 1 Mbit/s

•

Supports the Time Triggered Communication option

Transmission
•

Three transmit mailboxes

•

Configurable transmit priority

•

Time Stamp on SOF transmission

Reception
•

Two receive FIFOs with three stages

•

Scalable filter banks:
–

14 filter banks

•

Identifier list feature

•

Configurable FIFO overrun

•

Time Stamp on SOF reception

Time-triggered communication option
•

Disable automatic retransmission mode

•

16-bit free running timer

•

Time Stamp sent in last two data bytes

Management

814/1004

•

Maskable interrupts

•

Software-efficient mailbox mapping at a unique address space

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29.3

Controller area network (bxCAN)

bxCAN general description
In today’s CAN applications, the number of nodes in a network is increasing and often
several networks are linked together via gateways. Typically the number of messages in the
system (and thus to be handled by each node) has significantly increased. In addition to the
application messages, Network Management and Diagnostic messages have been
introduced.
•

An enhanced filtering mechanism is required to handle each type of message.

Furthermore, application tasks require more CPU time, therefore real-time constraints
caused by message reception have to be reduced.
•

A receive FIFO scheme allows the CPU to be dedicated to application tasks for a long
time period without losing messages.

The standard HLP (Higher Layer Protocol) based on standard CAN drivers requires an
efficient interface to the CAN controller.

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29.3.1

CAN 2.0B active core
The bxCAN module handles the transmission and the reception of CAN messages fully
autonomously. Standard identifiers (11-bit) and extended identifiers (29-bit) are fully
supported by hardware.

29.3.2

Control, status and configuration registers
The application uses these registers to:

29.3.3

•

Configure CAN parameters, e.g. baud rate

•

Request transmissions

•

Handle receptions

•

Manage interrupts

•

Get diagnostic information

Tx mailboxes
Three transmit mailboxes are provided to the software for setting up messages. The
transmission Scheduler decides which mailbox has to be transmitted first.

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Acceptance filters
The bxCAN provides up to 14 scalable/configurable identifier filter banks, for selecting the
incoming messages, that the software needs and discarding the others.

Receive FIFO
Two receive FIFOs are used by hardware to store the incoming messages. Three complete
messages can be stored in each FIFO. The FIFOs are managed completely by hardware.

29.4

bxCAN operating modes
bxCAN has three main operating modes: initialization, normal and Sleep. After a
hardware reset, bxCAN is in Sleep mode to reduce power consumption and an internal pullup is active on CANTX. The software requests bxCAN to enter initialization or Sleep mode
by setting the INRQ or SLEEP bits in the CAN_MCR register. Once the mode has been
entered, bxCAN confirms it by setting the INAK or SLAK bits in the CAN_MSR register and
the internal pull-up is disabled. When neither INAK nor SLAK are set, bxCAN is in normal
mode. Before entering normal mode bxCAN always has to synchronize on the CAN bus.
To synchronize, bxCAN waits until the CAN bus is idle, this means 11 consecutive recessive
bits have been monitored on CANRX.

29.4.1

Initialization mode
The software initialization can be done while the hardware is in Initialization mode. To enter
this mode the software sets the INRQ bit in the CAN_MCR register and waits until the
hardware has confirmed the request by setting the INAK bit in the CAN_MSR register.
To leave Initialization mode, the software clears the INQR bit. bxCAN has left Initialization
mode once the INAK bit has been cleared by hardware.
While in Initialization Mode, all message transfers to and from the CAN bus are stopped and
the status of the CAN bus output CANTX is recessive (high).
Entering Initialization Mode does not change any of the configuration registers.
To initialize the CAN Controller, software has to set up the Bit Timing (CAN_BTR) and CAN
options (CAN_MCR) registers.
To initialize the registers associated with the CAN filter banks (mode, scale, FIFO
assignment, activation and filter values), software has to set the FINIT bit (CAN_FMR). Filter
initialization also can be done outside the initialization mode.

Note:

When FINIT=1, CAN reception is deactivated.
The filter values also can be modified by deactivating the associated filter activation bits (in
the CAN_FA1R register).
If a filter bank is not used, it is recommended to leave it non active (leave the corresponding
FACT bit cleared).
For code example refer to the Appendix section A.11.1: bxCAN initialization mode code
example.

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29.4.2

Controller area network (bxCAN)

Normal mode
Once the initialization is complete, the software must request the hardware to enter Normal
mode to be able to synchronize on the CAN bus and start reception and transmission.
The request to enter Normal mode is issued by clearing the INRQ bit in the CAN_MCR
register. The bxCAN enters Normal mode and is ready to take part in bus activities when it
has synchronized with the data transfer on the CAN bus. This is done by waiting for the
occurrence of a sequence of 11 consecutive recessive bits (Bus Idle state). The switch to
Normal mode is confirmed by the hardware by clearing the INAK bit in the CAN_MSR
register.
The initialization of the filter values is independent from Initialization Mode but must be done
while the filter is not active (corresponding FACTx bit cleared). The filter scale and mode
configuration must be configured before entering Normal Mode.

29.4.3

Sleep mode (low-power)
To reduce power consumption, bxCAN has a low-power mode called Sleep mode. This
mode is entered on software request by setting the SLEEP bit in the CAN_MCR register. In
this mode, the bxCAN clock is stopped, however software can still access the bxCAN
mailboxes.
If software requests entry to initialization mode by setting the INRQ bit while bxCAN is in
Sleep mode, it must also clear the SLEEP bit.
bxCAN can be woken up (exit Sleep mode) either by software clearing the SLEEP bit or on
detection of CAN bus activity.
On CAN bus activity detection, hardware automatically performs the wakeup sequence by
clearing the SLEEP bit if the AWUM bit in the CAN_MCR register is set. If the AWUM bit is
cleared, software has to clear the SLEEP bit when a wakeup interrupt occurs, in order to exit
from Sleep mode.

Note:

If the wakeup interrupt is enabled (WKUIE bit set in CAN_IER register) a wakeup interrupt
will be generated on detection of CAN bus activity, even if the bxCAN automatically
performs the wakeup sequence.
After the SLEEP bit has been cleared, Sleep mode is exited once bxCAN has synchronized
with the CAN bus, refer to Figure 309: bxCAN operating modes. The Sleep mode is exited
once the SLAK bit has been cleared by hardware.

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RM0091
Figure 309. bxCAN operating modes
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1. ACK = The wait state during which hardware confirms a request by setting the INAK or SLAK bits in the
CAN_MSR register
2. SYNC = The state during which bxCAN waits until the CAN bus is idle, meaning 11 consecutive recessive
bits have been monitored on CANRX

29.5

Test mode
Test mode can be selected by the SILM and LBKM bits in the CAN_BTR register. These bits
must be configured while bxCAN is in Initialization mode. Once test mode has been
selected, the INRQ bit in the CAN_MCR register must be reset to enter Normal mode.

29.5.1

Silent mode
The bxCAN can be put in Silent mode by setting the SILM bit in the CAN_BTR register.
In Silent mode, the bxCAN is able to receive valid data frames and valid remote frames, but
it sends only recessive bits on the CAN bus and it cannot start a transmission. If the bxCAN
has to send a dominant bit (ACK bit, overload flag, active error flag), the bit is rerouted
internally so that the CAN Core monitors this dominant bit, although the CAN bus may
remain in recessive state. Silent mode can be used to analyze the traffic on a CAN bus
without affecting it by the transmission of dominant bits (Acknowledge Bits, Error Frames).

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Controller area network (bxCAN)
Figure 310. bxCAN in silent mode
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29.5.2

Loop back mode
The bxCAN can be set in Loop Back Mode by setting the LBKM bit in the CAN_BTR
register. In Loop Back Mode, the bxCAN treats its own transmitted messages as received
messages and stores them (if they pass acceptance filtering) in a Receive mailbox.
Figure 311. bxCAN in loop back mode
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This mode is provided for self-test functions. To be independent of external events, the CAN
Core ignores acknowledge errors (no dominant bit sampled in the acknowledge slot of a
data / remote frame) in Loop Back Mode. In this mode, the bxCAN performs an internal
feedback from its Tx output to its Rx input. The actual value of the CANRX input pin is
disregarded by the bxCAN. The transmitted messages can be monitored on the CANTX pin.

29.5.3

Loop back combined with silent mode
It is also possible to combine Loop Back mode and Silent mode by setting the LBKM and
SILM bits in the CAN_BTR register. This mode can be used for a “Hot Selftest”, meaning the
bxCAN can be tested like in Loop Back mode but without affecting a running CAN system
connected to the CANTX and CANRX pins. In this mode, the CANRX pin is disconnected
from the bxCAN and the CANTX pin is held recessive.

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Figure 312. bxCAN in combined mode
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29.6

Behavior in debug mode
When the microcontroller enters the debug mode (Cortex®-M0 core halted), the bxCAN
continues to work normally or stops, depending on:
•

the DBG_CAN1_STOP bit for CAN1 or the DBG_CAN2_STOP bit for CAN2 in the
DBG module.

•

the DBF bit in CAN_MCR. For more details, refer to Section 29.9.2: CAN control and
status registers.

29.7

bxCAN functional description

29.7.1

Transmission handling
In order to transmit a message, the application must select one empty transmit mailbox, set
up the identifier, the data length code (DLC) and the data before requesting the transmission
by setting the corresponding TXRQ bit in the CAN_TIxR register. Once the mailbox has left
empty state, the software no longer has write access to the mailbox registers. Immediately
after the TXRQ bit has been set, the mailbox enters pending state and waits to become the
highest priority mailbox, see Transmit Priority. As soon as the mailbox has the highest
priority it will be scheduled for transmission. The transmission of the message of the
scheduled mailbox will start (enter transmit state) when the CAN bus becomes idle. Once
the mailbox has been successfully transmitted, it will become empty again. The hardware
indicates a successful transmission by setting the RQCP and TXOK bits in the CAN_TSR
register.
If the transmission fails, the cause is indicated by the ALST bit in the CAN_TSR register in
case of an Arbitration Lost, and/or the TERR bit, in case of transmission error detection.
For code example refer to the Appendix section A.11.2: bxCAN transmit code example.

Transmit priority
By identifier
When more than one transmit mailbox is pending, the transmission order is given by the
identifier of the message stored in the mailbox. The message with the lowest identifier value
has the highest priority according to the arbitration of the CAN protocol. If the identifier
values are equal, the lower mailbox number will be scheduled first.

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Controller area network (bxCAN)
By transmit request order
The transmit mailboxes can be configured as a transmit FIFO by setting the TXFP bit in the
CAN_MCR register. In this mode the priority order is given by the transmit request order.
This mode is very useful for segmented transmission.

Abort
A transmission request can be aborted by the user setting the ABRQ bit in the CAN_TSR
register. In pending or scheduled state, the mailbox is aborted immediately. An abort
request while the mailbox is in transmit state can have two results. If the mailbox is
transmitted successfully the mailbox becomes empty with the TXOK bit set in the
CAN_TSR register. If the transmission fails, the mailbox becomes scheduled, the
transmission is aborted and becomes empty with TXOK cleared. In all cases the mailbox
will become empty again at least at the end of the current transmission.

Non automatic retransmission mode
This mode has been implemented in order to fulfill the requirement of the Time Triggered
Communication option of the CAN standard. To configure the hardware in this mode the
NART bit in the CAN_MCR register must be set.
In this mode, each transmission is started only once. If the first attempt fails, due to an
arbitration loss or an error, the hardware will not automatically restart the message
transmission.
At the end of the first transmission attempt, the hardware considers the request as
completed and sets the RQCP bit in the CAN_TSR register. The result of the transmission is
indicated in the CAN_TSR register by the TXOK, ALST and TERR bits.
Figure 313. Transmit mailbox states
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Controller area network (bxCAN)

29.7.2

RM0091

Time triggered communication mode
In this mode, the internal counter of the CAN hardware is activated and used to generate the
Time Stamp value stored in the CAN_RDTxR/CAN_TDTxR registers, respectively (for Rx
and Tx mailboxes). The internal counter is incremented each CAN bit time (refer to
Section 29.7.7: Bit timing). The internal counter is captured on the sample point of the Start
Of Frame bit in both reception and transmission.

29.7.3

Reception handling
For the reception of CAN messages, three mailboxes organized as a FIFO are provided. In
order to save CPU load, simplify the software and guarantee data consistency, the FIFO is
managed completely by hardware. The application accesses the messages stored in the
FIFO through the FIFO output mailbox.

Valid message
A received message is considered as valid when it has been received correctly according to
the CAN protocol (no error until the last but one bit of the EOF field) and It passed through
the identifier filtering successfully, see Section 29.7.4: Identifier filtering.
Figure 314. Receive FIFO states
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Controller area network (bxCAN)

FIFO management
Starting from the empty state, the first valid message received is stored in the FIFO which
becomes pending_1. The hardware signals the event setting the FMP[1:0] bits in the
CAN_RFR register to the value 01b. The message is available in the FIFO output mailbox.
The software reads out the mailbox content and releases it by setting the RFOM bit in the
CAN_RFR register. The FIFO becomes empty again. If a new valid message has been
received in the meantime, the FIFO stays in pending_1 state and the new message is
available in the output mailbox.
For code example refer to the Appendix section A.11.3: bxCAN receive code example.
If the application does not release the mailbox, the next valid message will be stored in the
FIFO which enters pending_2 state (FMP[1:0] = 10b). The storage process is repeated for
the next valid message putting the FIFO into pending_3 state (FMP[1:0] = 11b). At this
point, the software must release the output mailbox by setting the RFOM bit, so that a
mailbox is free to store the next valid message. Otherwise the next valid message received
will cause a loss of message.
Refer also to Section 29.7.5: Message storage

Overrun
Once the FIFO is in pending_3 state (i.e. the three mailboxes are full) the next valid
message reception will lead to an overrun and a message will be lost. The hardware
signals the overrun condition by setting the FOVR bit in the CAN_RFR register. Which
message is lost depends on the configuration of the FIFO:
•

If the FIFO lock function is disabled (RFLM bit in the CAN_MCR register cleared) the
last message stored in the FIFO will be overwritten by the new incoming message. In
this case the latest messages will be always available to the application.

•

If the FIFO lock function is enabled (RFLM bit in the CAN_MCR register set) the most
recent message will be discarded and the software will have the three oldest messages
in the FIFO available.

Reception related interrupts
Once a message has been stored in the FIFO, the FMP[1:0] bits are updated and an
interrupt request is generated if the FMPIE bit in the CAN_IER register is set.
When the FIFO becomes full (i.e. a third message is stored) the FULL bit in the CAN_RFR
register is set and an interrupt is generated if the FFIE bit in the CAN_IER register is set.
On overrun condition, the FOVR bit is set and an interrupt is generated if the FOVIE bit in
the CAN_IER register is set.

29.7.4

Identifier filtering
In the CAN protocol the identifier of a message is not associated with the address of a node
but related to the content of the message. Consequently a transmitter broadcasts its
message to all receivers. On message reception a receiver node decides - depending on
the identifier value - whether the software needs the message or not. If the message is
needed, it is copied into the SRAM. If not, the message must be discarded without
intervention by the software.
To fulfill this requirement the bxCAN Controller provides 14 configurable and scalable filter
banks (13-0) to the application, in order to receive only the messages the software needs.

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This hardware filtering saves CPU resources which would be otherwise needed to perform
filtering by software. Each filter bank x consists of two 32-bit registers, CAN_FxR0 and
CAN_FxR1.

Scalable width
To optimize and adapt the filters to the application needs, each filter bank can be scaled
independently. Depending on the filter scale a filter bank provides:
•

One 32-bit filter for the STDID[10:0], EXTID[17:0], IDE and RTR bits.

•

Two 16-bit filters for the STDID[10:0], RTR, IDE and EXTID[17:15] bits.

Refer to Figure 315.
Furthermore, the filters can be configured in mask mode or in identifier list mode.

Mask mode
In mask mode the identifier registers are associated with mask registers specifying which
bits of the identifier are handled as “must match” or as “don’t care”.

Identifier list mode
In identifier list mode, the mask registers are used as identifier registers. Thus instead of
defining an identifier and a mask, two identifiers are specified, doubling the number of single
identifiers. All bits of the incoming identifier must match the bits specified in the filter
registers.

Filter bank scale and mode configuration
The filter banks are configured by means of the corresponding CAN_FMR register. To
configure a filter bank it must be deactivated by clearing the FACT bit in the CAN_FAR
register. The filter scale is configured by means of the corresponding FSCx bit in the
CAN_FS1R register, refer to Figure 315. The identifier list or identifier mask mode for the
corresponding Mask/Identifier registers is configured by means of the FBMx bits in the
CAN_FMR register.
To filter a group of identifiers, configure the Mask/Identifier registers in mask mode.
To select single identifiers, configure the Mask/Identifier registers in identifier list mode.
Filters not used by the application should be left deactivated.
Each filter within a filter bank is numbered (called the Filter Number) from 0 to a maximum
dependent on the mode and the scale of each of the filter banks.
Concerning the filter configuration, refer to Figure 315.

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Controller area network (bxCAN)
Figure 315. Filter bank scale configuration - register organization
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Filter match index
Once a message has been received in the FIFO it is available to the application. Typically,
application data is copied into SRAM locations. To copy the data to the right location the
application has to identify the data by means of the identifier. To avoid this, and to ease the
access to the SRAM locations, the CAN controller provides a Filter Match Index.
This index is stored in the mailbox together with the message according to the filter priority
rules. Thus each received message has its associated filter match index.
The Filter Match index can be used in two ways:
•

Compare the Filter Match index with a list of expected values.

•

Use the Filter Match Index as an index on an array to access the data destination
location.

For non masked filters, the software no longer has to compare the identifier.
If the filter is masked the software reduces the comparison to the masked bits only.
The index value of the filter number does not take into account the activation state of the
filter banks. In addition, two independent numbering schemes are used, one for each FIFO.
Refer to Figure 316 for an example.

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Figure 316. Example of filter numbering

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069

Filter priority rules
Depending on the filter combination it may occur that an identifier passes successfully
through several filters. In this case the filter match value stored in the receive mailbox is
chosen according to the following priority rules:

826/1004

•

A 32-bit filter takes priority over a 16-bit filter.

•

For filters of equal scale, priority is given to the Identifier List mode over the Identifier
Mask mode

•

For filters of equal scale and mode, priority is given by the filter number (the lower the
number, the higher the priority).

DocID018940 Rev 9

RM0091

Controller area network (bxCAN)
Figure 317. Filtering mechanism - example
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The example above shows the filtering principle of the bxCAN. On reception of a message,
the identifier is compared first with the filters configured in identifier list mode. If there is a
match, the message is stored in the associated FIFO and the index of the matching filter is
stored in the Filter Match Index. As shown in the example, the identifier matches with
Identifier #2 thus the message content and FMI 2 is stored in the FIFO.
If there is no match, the incoming identifier is then compared with the filters configured in
mask mode.
If the identifier does not match any of the identifiers configured in the filters, the message is
discarded by hardware without disturbing the software.

29.7.5

Message storage
The interface between the software and the hardware for the CAN messages is
implemented by means of mailboxes. A mailbox contains all information related to a
message; identifier, data, control, status and time stamp information.

Transmit mailbox
The software sets up the message to be transmitted in an empty transmit mailbox. The
status of the transmission is indicated by hardware in the CAN_TSR register.

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Controller area network (bxCAN)

RM0091
Table 116. Transmit mailbox mapping

Offset to transmit mailbox base address

Register name

0

CAN_TIxR

4

CAN_TDTxR

8

CAN_TDLxR

12

CAN_TDHxR

Receive mailbox
When a message has been received, it is available to the software in the FIFO output
mailbox. Once the software has handled the message (e.g. read it) the software must
release the FIFO output mailbox by means of the RFOM bit in the CAN_RFR register to
make the next incoming message available. The filter match index is stored in the MFMI
field of the CAN_RDTxR register. The 16-bit time stamp value is stored in the TIME[15:0]
field of CAN_RDTxR.
Table 117. Receive mailbox mapping
Offset to receive mailbox base
address (bytes)

Register name

0

CAN_RIxR

4

CAN_RDTxR

8

CAN_RDLxR

12

CAN_RDHxR

Figure 318. CAN error state diagram
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828/1004

DocID018940 Rev 9

RM0091

29.7.6

Controller area network (bxCAN)

Error management
The error management as described in the CAN protocol is handled entirely by hardware
using a Transmit Error Counter (TEC value, in CAN_ESR register) and a Receive Error
Counter (REC value, in the CAN_ESR register), which get incremented or decremented
according to the error condition. For detailed information about TEC and REC management,
please refer to the CAN standard.
Both of them may be read by software to determine the stability of the network.
Furthermore, the CAN hardware provides detailed information on the current error status in
CAN_ESR register. By means of the CAN_IER register (ERRIE bit, etc.), the software can
configure the interrupt generation on error detection in a very flexible way.

Bus-Off recovery
The Bus-Off state is reached when TEC is greater than 255, this state is indicated by BOFF
bit in CAN_ESR register. In Bus-Off state, the bxCAN is no longer able to transmit and
receive messages.
Depending on the ABOM bit in the CAN_MCR register bxCAN will recover from Bus-Off
(become error active again) either automatically or on software request. But in both cases
the bxCAN has to wait at least for the recovery sequence specified in the CAN standard
(128 occurrences of 11 consecutive recessive bits monitored on CANRX).
If ABOM is set, the bxCAN will start the recovering sequence automatically after it has
entered Bus-Off state.
If ABOM is cleared, the software must initiate the recovering sequence by requesting
bxCAN to enter and to leave initialization mode.
Note:

In initialization mode, bxCAN does not monitor the CANRX signal, therefore it cannot
complete the recovery sequence. To recover, bxCAN must be in normal mode.

29.7.7

Bit timing
The bit timing logic monitors the serial bus-line and performs sampling and adjustment of
the sample point by synchronizing on the start-bit edge and resynchronizing on the following
edges.
Its operation may be explained simply by splitting nominal bit time into three segments as
follows:
•

Synchronization segment (SYNC_SEG): a bit change is expected to occur within this
time segment. It has a fixed length of one time quantum (1 x tq).

•

Bit segment 1 (BS1): defines the location of the sample point. It includes the
PROP_SEG and PHASE_SEG1 of the CAN standard. Its duration is programmable
between 1 and 16 time quanta but may be automatically lengthened to compensate for
positive phase drifts due to differences in the frequency of the various nodes of the
network.

•

Bit segment 2 (BS2): defines the location of the transmit point. It represents the
PHASE_SEG2 of the CAN standard. Its duration is programmable between 1 and 8
time quanta but may also be automatically shortened to compensate for negative
phase drifts.

The resynchronization Jump Width (SJW) defines an upper bound to the amount of
lengthening or shortening of the bit segments. It is programmable between 1 and 4 time
quanta.

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Controller area network (bxCAN)

RM0091

A valid edge is defined as the first transition in a bit time from dominant to recessive bus
level provided the controller itself does not send a recessive bit.
If a valid edge is detected in BS1 instead of SYNC_SEG, BS1 is extended by up to SJW so
that the sample point is delayed.
Conversely, if a valid edge is detected in BS2 instead of SYNC_SEG, BS2 is shortened by
up to SJW so that the transmit point is moved earlier.
As a safeguard against programming errors, the configuration of the Bit Timing Register
(CAN_BTR) is only possible while the device is in Standby mode.
Note:

For a detailed description of the CAN bit timing and resynchronization mechanism, please
refer to the ISO 11898 standard.
Figure 319. Bit timing
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069

RM0091

Controller area network (bxCAN)
Figure 320. CAN frames
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Controller area network (bxCAN)

29.8

RM0091

bxCAN interrupts
Four interrupt vectors are dedicated to bxCAN. Each interrupt source can be independently
enabled or disabled by means of the CAN Interrupt Enable Register (CAN_IER).
Figure 321. Event flags and interrupt generation
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The transmit interrupt can be generated by the following events:
–

Transmit mailbox 0 becomes empty, RQCP0 bit in the CAN_TSR register set.

–

Transmit mailbox 1 becomes empty, RQCP1 bit in the CAN_TSR register set.

–

Transmit mailbox 2 becomes empty, RQCP2 bit in the CAN_TSR register set.

The FIFO 0 interrupt can be generated by the following events:
–

Reception of a new message, FMP0 bits in the CAN_RF0R register are not ‘00’.

–

FIFO0 full condition, FULL0 bit in the CAN_RF0R register set.

–

FIFO0 overrun condition, FOVR0 bit in the CAN_RF0R register set.

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RM0091

Controller area network (bxCAN)
•

The FIFO 1 interrupt can be generated by the following events:

•

29.9

–

Reception of a new message, FMP1 bits in the CAN_RF1R register are not ‘00’.

–

FIFO1 full condition, FULL1 bit in the CAN_RF1R register set.

–

FIFO1 overrun condition, FOVR1 bit in the CAN_RF1R register set.

The error and status change interrupt can be generated by the following events:
–

Error condition, for more details on error conditions please refer to the CAN Error
Status register (CAN_ESR).

–

Wakeup condition, SOF monitored on the CAN Rx signal.

–

Entry into Sleep mode.

CAN registers
The peripheral registers have to be accessed by words (32 bits).

29.9.1

Register access protection
Erroneous access to certain configuration registers can cause the hardware to temporarily
disturb the whole CAN network. Therefore the CAN_BTR register can be modified by
software only while the CAN hardware is in initialization mode.
Although the transmission of incorrect data will not cause problems at the CAN network
level, it can severely disturb the application. A transmit mailbox can be only modified by
software while it is in empty state, refer to Figure 313: Transmit mailbox states.
The filter values can be modified either deactivating the associated filter banks or by setting
the FINIT bit. Moreover, the modification of the filter configuration (scale, mode and FIFO
assignment) in CAN_FMxR, CAN_FSxR and CAN_FFAR registers can only be done when
the filter initialization mode is set (FINIT=1) in the CAN_FMR register.

29.9.2

CAN control and status registers
Refer to Section 1.1 for a list of abbreviations used in register descriptions.

CAN master control register (CAN_MCR)
Address offset: 0x00
Reset value: 0x0001 0002
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DBF
rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

RESET

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TTCM

ABOM

AWUM

NART

RFLM

TXFP

SLEEP

INRQ

rw

rw

rw

rw

rw

rw

rw

rw

rs

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Controller area network (bxCAN)

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Bits 31:17 Reserved, must be kept at reset value.
Bit 16 DBF: Debug freeze
0: CAN working during debug
1: CAN reception/transmission frozen during debug. Reception FIFOs can still be
accessed/controlled normally.
Bit 15 RESET: bxCAN software master reset
0: Normal operation.
1: Force a master reset of the bxCAN -> Sleep mode activated after reset (FMP bits and
CAN_MCR register are initialized to the reset values). This bit is automatically reset to 0.
Bits 14:8 Reserved, must be kept at reset value.
Bit 7 TTCM: Time triggered communication mode
0: Time Triggered Communication mode disabled.
1: Time Triggered Communication mode enabled
Note: For more information on Time Triggered Communication mode, please refer to
Section 29.7.2: Time triggered communication mode.
Bit 6 ABOM: Automatic bus-off management
This bit controls the behavior of the CAN hardware on leaving the Bus-Off state.
0: The Bus-Off state is left on software request, once 128 occurrences of 11 recessive bits
have been monitored and the software has first set and cleared the INRQ bit of the
CAN_MCR register.
1: The Bus-Off state is left automatically by hardware once 128 occurrences of 11 recessive
bits have been monitored.
For detailed information on the Bus-Off state please refer to Section 29.7.6: Error
management.
Bit 5 AWUM: Automatic wakeup mode
This bit controls the behavior of the CAN hardware on message reception during Sleep
mode.
0: The Sleep mode is left on software request by clearing the SLEEP bit of the CAN_MCR
register.
1: The Sleep mode is left automatically by hardware on CAN message detection.
The SLEEP bit of the CAN_MCR register and the SLAK bit of the CAN_MSR register are
cleared by hardware.
Bit 4 NART: No automatic retransmission
0: The CAN hardware will automatically retransmit the message until it has been
successfully transmitted according to the CAN standard.
1: A message will be transmitted only once, independently of the transmission result
(successful, error or arbitration lost).
Bit 3 RFLM: Receive FIFO locked mode
0: Receive FIFO not locked on overrun. Once a receive FIFO is full the next incoming
message will overwrite the previous one.
1: Receive FIFO locked against overrun. Once a receive FIFO is full the next incoming
message will be discarded.

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Controller area network (bxCAN)

Bit 2 TXFP: Transmit FIFO priority
This bit controls the transmission order when several mailboxes are pending at the same
time.
0: Priority driven by the identifier of the message
1: Priority driven by the request order (chronologically)
Bit 1 SLEEP: Sleep mode request
This bit is set by software to request the CAN hardware to enter the Sleep mode. Sleep
mode will be entered as soon as the current CAN activity (transmission or reception of a
CAN frame) has been completed.
This bit is cleared by software to exit Sleep mode.
This bit is cleared by hardware when the AWUM bit is set and a SOF bit is detected on the
CAN Rx signal.
This bit is set after reset - CAN starts in Sleep mode.
Bit 0 INRQ: Initialization request
The software clears this bit to switch the hardware into normal mode. Once 11 consecutive
recessive bits have been monitored on the Rx signal the CAN hardware is synchronized and
ready for transmission and reception. Hardware signals this event by clearing the INAK bit in
the CAN_MSR register.
Software sets this bit to request the CAN hardware to enter initialization mode. Once
software has set the INRQ bit, the CAN hardware waits until the current CAN activity
(transmission or reception) is completed before entering the initialization mode. Hardware
signals this event by setting the INAK bit in the CAN_MSR register.

CAN master status register (CAN_MSR)
Address offset: 0x04
Reset value: 0x0000 0C02

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

RX

SAMP

RXM

TXM

Res.

Res.

Res.

SLAKI

WKUI

ERRI

SLAK

INAK

r

r

r

r

rc_w1

rc_w1

rc_w1

r

r

Bits 31:12 Reserved, must be kept at reset value.
Bit 11 RX: CAN Rx signal
Monitors the actual value of the CAN_RX Pin.
Bit 10 SAMP: Last sample point
The value of RX on the last sample point (current received bit value).
Bit 9 RXM: Receive mode
The CAN hardware is currently receiver.
Bit 8 TXM: Transmit mode
The CAN hardware is currently transmitter.
Bits 7:5 Reserved, must be kept at reset value.

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Bit 4 SLAKI: Sleep acknowledge interrupt
When SLKIE=1, this bit is set by hardware to signal that the bxCAN has entered Sleep
Mode. When set, this bit generates a status change interrupt if the SLKIE bit in the
CAN_IER register is set.
This bit is cleared by software or by hardware, when SLAK is cleared.
Note: When SLKIE=0, no polling on SLAKI is possible. In this case the SLAK bit can be
polled.
Bit 3 WKUI: Wakeup interrupt
This bit is set by hardware to signal that a SOF bit has been detected while the CAN
hardware was in Sleep mode. Setting this bit generates a status change interrupt if the
WKUIE bit in the CAN_IER register is set.
This bit is cleared by software.
Bit 2 ERRI: Error interrupt
This bit is set by hardware when a bit of the CAN_ESR has been set on error detection and
the corresponding interrupt in the CAN_IER is enabled. Setting this bit generates a status
change interrupt if the ERRIE bit in the CAN_IER register is set.
This bit is cleared by software.
Bit 1 SLAK: Sleep acknowledge
This bit is set by hardware and indicates to the software that the CAN hardware is now in
Sleep mode. This bit acknowledges the Sleep mode request from the software (set SLEEP
bit in CAN_MCR register).
This bit is cleared by hardware when the CAN hardware has left Sleep mode (to be
synchronized on the CAN bus). To be synchronized the hardware has to monitor a
sequence of 11 consecutive recessive bits on the CAN RX signal.
Note: The process of leaving Sleep mode is triggered when the SLEEP bit in the CAN_MCR
register is cleared. Please refer to the AWUM bit of the CAN_MCR register description
for detailed information for clearing SLEEP bit
Bit 0 INAK: Initialization acknowledge
This bit is set by hardware and indicates to the software that the CAN hardware is now in
initialization mode. This bit acknowledges the initialization request from the software (set
INRQ bit in CAN_MCR register).
This bit is cleared by hardware when the CAN hardware has left the initialization mode (to
be synchronized on the CAN bus). To be synchronized the hardware has to monitor a
sequence of 11 consecutive recessive bits on the CAN RX signal.

CAN transmit status register (CAN_TSR)
Address offset: 0x08
Reset value: 0x1C00 0000
31

30

29

28

27

26

LOW2

LOW1

LOW0

TME2

TME1

TME0

r

r

r

r

r

r

25

CODE[1:0]
r

15

14

13

12

11

10

9

ABRQ1

Res.

Res.

Res.

TERR1

ALST1

TXOK1

rc_w1

rc_w1

rc_w1

rs

836/1004

24

23

22

21

20

19

18

17

16

ABRQ2

Res.

Res.

Res.

TERR2

ALST2

TXOK2

RQCP2

rc_w1

rc_w1

rc_w1

rc_w1

r

rs

8

7

RQCP1 ABRQ0
rc_w1

rs

DocID018940 Rev 9

6

5

4

3

2

1

0

Res.

Res.

Res.

TERR0

ALST0

TXOK0

RQCP0

rc_w1

rc_w1

rc_w1

rc_w1

RM0091

Controller area network (bxCAN)

Bit 31 LOW2: Lowest priority flag for mailbox 2
This bit is set by hardware when more than one mailbox are pending for transmission and
mailbox 2 has the lowest priority.
Bit 30 LOW1: Lowest priority flag for mailbox 1
This bit is set by hardware when more than one mailbox are pending for transmission and
mailbox 1 has the lowest priority.
Bit 29 LOW0: Lowest priority flag for mailbox 0
This bit is set by hardware when more than one mailbox are pending for transmission and
mailbox 0 has the lowest priority.
Note: The LOW[2:0] bits are set to zero when only one mailbox is pending.
Bit 28 TME2: Transmit mailbox 2 empty
This bit is set by hardware when no transmit request is pending for mailbox 2.
Bit 27 TME1: Transmit mailbox 1 empty
This bit is set by hardware when no transmit request is pending for mailbox 1.
Bit 26 TME0: Transmit mailbox 0 empty
This bit is set by hardware when no transmit request is pending for mailbox 0.
Bits 25:24 CODE[1:0]: Mailbox code
In case at least one transmit mailbox is free, the code value is equal to the number of the
next transmit mailbox free.
In case all transmit mailboxes are pending, the code value is equal to the number of the
transmit mailbox with the lowest priority.
Bit 23 ABRQ2: Abort request for mailbox 2
Set by software to abort the transmission request for the corresponding mailbox.
Cleared by hardware when the mailbox becomes empty.
Setting this bit has no effect when the mailbox is not pending for transmission.
Bits 22:20 Reserved, must be kept at reset value.
Bit 19 TERR2: Transmission error of mailbox 2
This bit is set when the previous TX failed due to an error.
Bit 18 ALST2: Arbitration lost for mailbox 2
This bit is set when the previous TX failed due to an arbitration lost.
Bit 17 TXOK2: Transmission OK of mailbox 2
The hardware updates this bit after each transmission attempt.
0: The previous transmission failed
1: The previous transmission was successful
This bit is set by hardware when the transmission request on mailbox 2 has been completed
successfully. Please refer to Figure 313.
Bit 16 RQCP2: Request completed mailbox2
Set by hardware when the last request (transmit or abort) has been performed.
Cleared by software writing a “1” or by hardware on transmission request (TXRQ2 set in
CAN_TMID2R register).
Clearing this bit clears all the status bits (TXOK2, ALST2 and TERR2) for Mailbox 2.
Bit 15 ABRQ1: Abort request for mailbox 1
Set by software to abort the transmission request for the corresponding mailbox.
Cleared by hardware when the mailbox becomes empty.
Setting this bit has no effect when the mailbox is not pending for transmission.
Bits 14:12 Reserved, must be kept at reset value.

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Bit 11 TERR1: Transmission error of mailbox1
This bit is set when the previous TX failed due to an error.
Bit 10 ALST1: Arbitration lost for mailbox1
This bit is set when the previous TX failed due to an arbitration lost.
Bit 9 TXOK1: Transmission OK of mailbox1
The hardware updates this bit after each transmission attempt.
0: The previous transmission failed
1: The previous transmission was successful
This bit is set by hardware when the transmission request on mailbox 1 has been completed
successfully. Please refer to Figure 313
Bit 8 RQCP1: Request completed mailbox1
Set by hardware when the last request (transmit or abort) has been performed.
Cleared by software writing a “1” or by hardware on transmission request (TXRQ1 set in
CAN_TI1R register).
Clearing this bit clears all the status bits (TXOK1, ALST1 and TERR1) for Mailbox 1.
Bit 7 ABRQ0: Abort request for mailbox0
Set by software to abort the transmission request for the corresponding mailbox.
Cleared by hardware when the mailbox becomes empty.
Setting this bit has no effect when the mailbox is not pending for transmission.
Bits 6:4 Reserved, must be kept at reset value.
Bit 3 TERR0: Transmission error of mailbox0
This bit is set when the previous TX failed due to an error.
Bit 2 ALST0: Arbitration lost for mailbox0
This bit is set when the previous TX failed due to an arbitration lost.
Bit 1 TXOK0: Transmission OK of mailbox0
The hardware updates this bit after each transmission attempt.
0: The previous transmission failed
1: The previous transmission was successful
This bit is set by hardware when the transmission request on mailbox 1 has been completed
successfully. Please refer to Figure 313
Bit 0 RQCP0: Request completed mailbox0
Set by hardware when the last request (transmit or abort) has been performed.
Cleared by software writing a “1” or by hardware on transmission request (TXRQ0 set in
CAN_TI0R register).
Clearing this bit clears all the status bits (TXOK0, ALST0 and TERR0) for Mailbox 0.

CAN receive FIFO 0 register (CAN_RF0R)
Address offset: 0x0C
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FULL0

Res.

RFOM0 FOVR0
rs

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Bits 31:6 Reserved, must be kept at reset value.
Bit 5 RFOM0: Release FIFO 0 output mailbox
Set by software to release the output mailbox of the FIFO. The output mailbox can only be
released when at least one message is pending in the FIFO. Setting this bit when the FIFO
is empty has no effect. If at least two messages are pending in the FIFO, the software has to
release the output mailbox to access the next message.
Cleared by hardware when the output mailbox has been released.
Bit 4 FOVR0: FIFO 0 overrun
This bit is set by hardware when a new message has been received and passed the filter
while the FIFO was full.
This bit is cleared by software.
Bit 3 FULL0: FIFO 0 full
Set by hardware when three messages are stored in the FIFO.
This bit is cleared by software.
Bit 2 Reserved, must be kept at reset value.
Bits 1:0 FMP0[1:0]: FIFO 0 message pending
These bits indicate how many messages are pending in the receive FIFO.
FMP is increased each time the hardware stores a new message in to the FIFO. FMP is
decreased each time the software releases the output mailbox by setting the RFOM0 bit.

CAN receive FIFO 1 register (CAN_RF1R)
Address offset: 0x10
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FULL1

Res.

RFOM1 FOVR1
rs

rc_w1

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FMP1[1:0]
r

r

Bits 31:6 Reserved, must be kept at reset value.
Bit 5 RFOM1: Release FIFO 1 output mailbox
Set by software to release the output mailbox of the FIFO. The output mailbox can only be
released when at least one message is pending in the FIFO. Setting this bit when the FIFO
is empty has no effect. If at least two messages are pending in the FIFO, the software has to
release the output mailbox to access the next message.
Cleared by hardware when the output mailbox has been released.
Bit 4 FOVR1: FIFO 1 overrun
This bit is set by hardware when a new message has been received and passed the filter
while the FIFO was full.
This bit is cleared by software.

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Bit 3 FULL1: FIFO 1 full
Set by hardware when three messages are stored in the FIFO.
This bit is cleared by software.
Bit 2 Reserved, must be kept at reset value.
Bits 1:0 FMP1[1:0]: FIFO 1 message pending
These bits indicate how many messages are pending in the receive FIFO1.
FMP1 is increased each time the hardware stores a new message in to the FIFO1. FMP is
decreased each time the software releases the output mailbox by setting the RFOM1 bit.

CAN interrupt enable register (CAN_IER)
Address offset: 0x14
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SLKIE

WKUIE

rw

rw

15
ERRIE

14
Res.

rw

13
Res.

12

11

10

9

8

Res.

LEC
IE

BOF
IE

EPV
IE

EWG
IE

rw

rw

rw

rw

7

6

5

4

3

2

1

0

Res.

FOV
IE1

FF
IE1

FMP
IE1

FOV
IE0

FF
IE0

FMP
IE0

TME
IE

rw

rw

rw

rw

rw

rw

rw

Bits 31:18 Reserved, must be kept at reset value.
Bit 17 SLKIE: Sleep interrupt enable
0: No interrupt when SLAKI bit is set.
1: Interrupt generated when SLAKI bit is set.
Bit 16 WKUIE: Wakeup interrupt enable
0: No interrupt when WKUI is set.
1: Interrupt generated when WKUI bit is set.
Bit 15 ERRIE: Error interrupt enable
0: No interrupt will be generated when an error condition is pending in the CAN_ESR.
1: An interrupt will be generation when an error condition is pending in the CAN_ESR.
Bits 14:12 Reserved, must be kept at reset value.
Bit 11 LECIE: Last error code interrupt enable
0: ERRI bit will not be set when the error code in LEC[2:0] is set by hardware on error
detection.
1: ERRI bit will be set when the error code in LEC[2:0] is set by hardware on error detection.
Bit 10 BOFIE: Bus-off interrupt enable
0: ERRI bit will not be set when BOFF is set.
1: ERRI bit will be set when BOFF is set.
Bit 9 EPVIE: Error passive interrupt enable
0: ERRI bit will not be set when EPVF is set.
1: ERRI bit will be set when EPVF is set.

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Bit 8 EWGIE: Error warning interrupt enable
0: ERRI bit will not be set when EWGF is set.
1: ERRI bit will be set when EWGF is set.
Bit 7 Reserved, must be kept at reset value.
Bit 6 FOVIE1: FIFO overrun interrupt enable
0: No interrupt when FOVR is set.
1: Interrupt generation when FOVR is set.
Bit 5 FFIE1: FIFO full interrupt enable
0: No interrupt when FULL bit is set.
1: Interrupt generated when FULL bit is set.
Bit 4 FMPIE1: FIFO message pending interrupt enable
0: No interrupt generated when state of FMP[1:0] bits are not 00b.
1: Interrupt generated when state of FMP[1:0] bits are not 00b.
Bit 3 FOVIE0: FIFO overrun interrupt enable
0: No interrupt when FOVR bit is set.
1: Interrupt generated when FOVR bit is set.
Bit 2 FFIE0: FIFO full interrupt enable
0: No interrupt when FULL bit is set.
1: Interrupt generated when FULL bit is set.
Bit 1 FMPIE0: FIFO message pending interrupt enable
0: No interrupt generated when state of FMP[1:0] bits are not 00b.
1: Interrupt generated when state of FMP[1:0] bits are not 00b.
Bit 0 TMEIE: Transmit mailbox empty interrupt enable
0: No interrupt when RQCPx bit is set.
1: Interrupt generated when RQCPx bit is set.
Note: Refer to Section 29.8: bxCAN interrupts.

CAN error status register (CAN_ESR)
Address offset: 0x18
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

REC[7:0]
r

r

r

r

r

20

19

18

17

16

r

r

r

TEC[7:0]
r

r

r

r

r
6

15

14

13

12

11

10

9

8

7

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

r

r

5

4

LEC[2:0]
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3

2

1

0

Res.

BOFF

EPVF

EWGF

r

r

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Bits 31:24 REC[7:0]: Receive error counter
The implementing part of the fault confinement mechanism of the CAN protocol. In case of
an error during reception, this counter is incremented by 1 or by 8 depending on the error
condition as defined by the CAN standard. After every successful reception the counter is
decremented by 1 or reset to 120 if its value was higher than 128. When the counter value
exceeds 127, the CAN controller enters the error passive state.
Bits 23:16 TEC[7:0]: Least significant byte of the 9-bit transmit error counter
The implementing part of the fault confinement mechanism of the CAN protocol.
Bits 15:7 Reserved, must be kept at reset value.
Bits 6:4 LEC[2:0]: Last error code
This field is set by hardware and holds a code which indicates the error condition of the last
error detected on the CAN bus. If a message has been transferred (reception or
transmission) without error, this field will be cleared to ‘0’.
The LEC[2:0] bits can be set to value 0b111 by software. They are updated by hardware to
indicate the current communication status.
000: No Error
001: Stuff Error
010: Form Error
011: Acknowledgment Error
100: Bit recessive Error
101: Bit dominant Error
110: CRC Error
111: Set by software
Bit 3 Reserved, must be kept at reset value.
Bit 2 BOFF: Bus-off flag
This bit is set by hardware when it enters the bus-off state. The bus-off state is entered on
TEC overflow, greater than 255, refer to Section 29.7.6 on page 829.
Bit 1 EPVF: Error passive flag
This bit is set by hardware when the Error Passive limit has been reached (Receive Error
Counter or Transmit Error Counter>127).
Bit 0 EWGF: Error warning flag
This bit is set by hardware when the warning limit has been reached
(Receive Error Counter or Transmit Error Counter≥96).

CAN bit timing register (CAN_BTR)
Address offset: 0x1C
Reset value: 0x0123 0000
This register can only be accessed by the software when the CAN hardware is in
initialization mode.
31

30

29

28

27

26

SILM

LBKM

Res.

Res.

Res.

Res.

rw

rw

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

25

SJW[1:0]
rw

rw

9

8

23

22

Res.

7

21

20

19

18

TS2[2:0]

17

16

TS1[3:0]

rw

rw

rw

rw

rw

rw

rw

6

5

4

3

2

1

0

rw

rw

rw

rw

BRP[9:0]
rw

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Controller area network (bxCAN)

Bit 31 SILM: Silent mode (debug)
0: Normal operation
1: Silent Mode
Bit 30 LBKM: Loop back mode (debug)
0: Loop Back Mode disabled
1: Loop Back Mode enabled
Bits 29:26 Reserved, must be kept at reset value.
Bits 25:24 SJW[1:0]: Resynchronization jump width
These bits define the maximum number of time quanta the CAN hardware is allowed to
lengthen or shorten a bit to perform the resynchronization.
tRJW = tq x (SJW[1:0] + 1)
Bit 23 Reserved, must be kept at reset value.
Bits 22:20 TS2[2:0]: Time segment 2
These bits define the number of time quanta in Time Segment 2.
tBS2 = tq x (TS2[2:0] + 1)
Bits 19:16 TS1[3:0]: Time segment 1
These bits define the number of time quanta in Time Segment 1
tBS1 = tq x (TS1[3:0] + 1)
For more information on bit timing, please refer to Section 29.7.7: Bit timing on page 829.
Bits 15:10 Reserved, must be kept at reset value.
Bits 9:0 BRP[9:0]: Baud rate prescaler
These bits define the length of a time quanta.
tq = (BRP[9:0]+1) x tPCLK

29.9.3

CAN mailbox registers
This chapter describes the registers of the transmit and receive mailboxes. Refer to
Section 29.7.5: Message storage on page 827 for detailed register mapping.
Transmit and receive mailboxes have the same registers except:
•

The FMI field in the CAN_RDTxR register.

•

A receive mailbox is always write protected.

•

A transmit mailbox is write-enabled only while empty, corresponding TME bit in the
CAN_TSR register set.

There are 3 TX Mailboxes and 2 RX Mailboxes. Each RX Mailbox allows access to a 3 level
depth FIFO, the access being offered only to the oldest received message in the FIFO.
Each mailbox consist of 4 registers.

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Figure 322. Can mailbox registers

&$1B5,5

&$1B5,5

&$1B7,5

&$1B7,5

&$1B7,5

&$1B5'75

&$1B5'75

&$1B7'75

&$1B7'75

&$1B7'75

&$1B5/5

&$1B5/5

&$1B7'/5

&$1B7'/5

&$1B7'/5

&$1B5+5

&$1B5+5

&$1B7'+5

&$1B7'+5

&$1B7'+5

),)2

),)2

7KUHH7;PDLOER[HV
069

CAN TX mailbox identifier register (CAN_TIxR) (x = 0..2)
Address offsets: 0x180, 0x190, 0x1A0
Reset value: 0xXXXX XXXX (except bit 0, TXRQ = 0)
All TX registers are write protected when the mailbox is pending transmission (TMEx reset).
This register also implements the TX request control (bit 0) - reset value 0.
31

30

29

28

27

26

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

25

24

23

22

21

20

19

rw

rw

rw

rw

rw

rw

rw

9

8

7

6

5

4

3

STID[10:0]/EXID[28:18]

rw

rw

rw

rw

rw

rw

17

16

rw

rw

rw

2

1

0

IDE

RTR

TXRQ

rw

rw

rw

EXID[17:13]

EXID[12:0]
rw

18

rw

rw

rw

rw

rw

rw

Bits 31:21 STID[10:0]/EXID[28:18]: Standard identifier or extended identifier
The standard identifier or the MSBs of the extended identifier (depending on the IDE bit
value).
Bit 20:3 EXID[17:0]: Extended identifier
The LSBs of the extended identifier.
Bit 2 IDE: Identifier extension
This bit defines the identifier type of message in the mailbox.
0: Standard identifier.
1: Extended identifier.
Bit 1 RTR: Remote transmission request
0: Data frame
1: Remote frame
Bit 0 TXRQ: Transmit mailbox request
Set by software to request the transmission for the corresponding mailbox.
Cleared by hardware when the mailbox becomes empty.

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CAN mailbox data length control and time stamp register
(CAN_TDTxR) (x = 0..2)
All bits of this register are write protected when the mailbox is not in empty state.
Address offsets: 0x184, 0x194, 0x1A4
Reset value: 0xXXXX XXXX
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

TIME[15:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
rw

rw

DLC[3:0]
rw

rw

Bits 31:16 TIME[15:0]: Message time stamp
This field contains the 16-bit timer value captured at the SOF transmission.
Bits 15:9 Reserved, must be kept at reset value.
Bit 8 TGT: Transmit global time
This bit is active only when the hardware is in the Time Trigger Communication mode,
TTCM bit of the CAN_MCR register is set.
0: Time stamp TIME[15:0] is not sent.
1: Time stamp TIME[15:0] value is sent in the last two data bytes of the 8-byte message:
TIME[7:0] in data byte 7 and TIME[15:8] in data byte 6, replacing the data written in
CAN_TDHxR[31:16] register (DATA6[7:0] and DATA7[7:0]). DLC must be programmed as 8
in order these two bytes to be sent over the CAN bus.
Bits 7:4 Reserved, must be kept at reset value.
Bits 3:0 DLC[3:0]: Data length code
This field defines the number of data bytes a data frame contains or a remote frame request.
A message can contain from 0 to 8 data bytes, depending on the value in the DLC field.

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CAN mailbox data low register (CAN_TDLxR) (x = 0..2)
All bits of this register are write protected when the mailbox is not in empty state.
Address offsets: 0x188, 0x198, 0x1A8
Reset value: 0xXXXX XXXX
31

30

29

28

27

26

25

24

23

22

21

DATA3[7:0]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

DATA1[7:0]
rw

rw

rw

rw

19

18

17

16

DATA2[7:0]

rw

rw

20

rw

rw

rw

rw

rw

4

3

2

1

0

rw

rw

rw

18

17

16

DATA0[7:0]
rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:24 DATA3[7:0]: Data byte 3
Data byte 3 of the message.
Bits 23:16 DATA2[7:0]: Data byte 2
Data byte 2 of the message.
Bits 15:8 DATA1[7:0]: Data byte 1

Data byte 1 of the message.
Bits 7:0 DATA0[7:0]: Data byte 0
Data byte 0 of the message.
A message can contain from 0 to 8 data bytes and starts with byte 0.

CAN mailbox data high register (CAN_TDHxR) (x = 0..2)
All bits of this register are write protected when the mailbox is not in empty state.
Address offsets: 0x18C, 0x19C, 0x1AC
Reset value: 0xXXXX XXXX
31

30

29

28

27

26

25

24

23

22

21

DATA7[7:0]

20

19

DATA6[7:0]

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

DATA5[7:0]

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Bits 31:24 DATA7[7:0]: Data byte 7
Data byte 7 of the message.
Note: If TGT of this message and TTCM are active, DATA7 and DATA6 will be replaced by
the TIME stamp value.
Bits 23:16 DATA6[7:0]: Data byte 6
Data byte 6 of the message.
Bits 15:8 DATA5[7:0]: Data byte 5

Data byte 5 of the message.
Bits 7:0 DATA4[7:0]: Data byte 4
Data byte 4 of the message.

CAN receive FIFO mailbox identifier register (CAN_RIxR) (x = 0..1)
Address offsets: 0x1B0, 0x1C0
Reset value: 0xXXXX XXXX
All RX registers are write protected.

31

30

29

28

27

26

25

24

23

22

21

20

19

STID[10:0]/EXID[28:18]
r

r

r

r

r

r

15

14

13

12

11

10

r

r

r

r

r

r

r

r

r

r

r

r

9

8

7

6

5

4

3

r

17

16

r

r

EXID[17:13]

EXID[12:0]
r

18

r

r

r

r

r

r

r
2

1

0

IDE

RTR

Res

r

r

Bits 31:21 STID[10:0]/EXID[28:18]: Standard identifier or extended identifier
The standard identifier or the MSBs of the extended identifier (depending on the IDE bit
value).
Bits 20:3 EXID[17:0]: Extended identifier
The LSBs of the extended identifier.
Bit 2 IDE: Identifier extension
This bit defines the identifier type of message in the mailbox.
0: Standard identifier.
1: Extended identifier.
Bit 1 RTR: Remote transmission request
0: Data frame
1: Remote frame
Bit 0 Reserved, must be kept at reset value.

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CAN receive FIFO mailbox data length control and time stamp register
(CAN_RDTxR) (x = 0..1)
Address offsets: 0x1B4, 0x1C4
Reset value: 0xXXXX XXXX
All RX registers are write protected.
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

TIME[15:0]
r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

r

r

r

r

r

r

r

r

r

FMI[7:0]
r

DLC[3:0]
r

r

Bits 31:16 TIME[15:0]: Message time stamp
This field contains the 16-bit timer value captured at the SOF detection.
Bits 15:8 FMI[7:0]: Filter match index
This register contains the index of the filter the message stored in the mailbox passed
through. For more details on identifier filtering please refer to Section 29.7.4: Identifier
filtering on page 823 - Filter Match Index paragraph.
Bits 7:4 Reserved, must be kept at reset value.
Bits 3:0 DLC[3:0]: Data length code
This field defines the number of data bytes a data frame contains (0 to 8). It is 0 in the case
of a remote frame request.

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Controller area network (bxCAN)

CAN receive FIFO mailbox data low register (CAN_RDLxR) (x = 0..1)
All bits of this register are write protected when the mailbox is not in empty state.
Address offsets: 0x1B8, 0x1C8
Reset value: 0xXXXX XXXX
All RX registers are write protected.
31

30

29

28

r

r

r

r

15

14

13

12

27

26

25

24

23

22

21

r

r

r

r

r

r

r

r

11

10

9

8

7

6

5

4

DATA3[7:0]

r

r

r

r

19

18

17

16

r

r

r

r

3

2

1

0

r

r

r

18

17

16

DATA2[7:0]

DATA1[7:0]
r

20

DATA0[7:0]
r

r

r

r

r

r

r

r

Bits 31:24 DATA3[7:0]: Data Byte 3
Data byte 3 of the message.
Bits 23:16 DATA2[7:0]: Data Byte 2
Data byte 2 of the message.
Bits 15:8 DATA1[7:0]: Data Byte 1

Data byte 1 of the message.
Bits 7:0 DATA0[7:0]: Data Byte 0
Data byte 0 of the message.
A message can contain from 0 to 8 data bytes and starts with byte 0.

CAN receive FIFO mailbox data high register (CAN_RDHxR) (x = 0..1)
Address offsets: 0x1BC, 0x1CC
Reset value: 0xXXXX XXXX
All RX registers are write protected.
31

30

29

28

r

r

r

r

15

14

13

12

27

26

25

24

23

22

21

r

r

r

r

r

r

r

r

r

r

r

r

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

DATA7[7:0]

r

r

r

r

19

DATA6[7:0]

DATA5[7:0]
r

20

DATA4[7:0]
r

r

r

r

r

r

r

r

Bits 31:24 DATA7[7:0]: Data Byte 7
Data byte 3 of the message.

DocID018940 Rev 9

849/1004

Controller area network (bxCAN)

RM0091

Bits 23:16 DATA6[7:0]: Data Byte 6
Data byte 2 of the message.
Bits 15:8 DATA5[7:0]: Data Byte 5

Data byte 1 of the message.
Bits 7:0 DATA4[7:0]: Data Byte 4
Data byte 0 of the message.

29.9.4

CAN filter registers
CAN filter master register (CAN_FMR)
Address offset: 0x200
Reset value: 0x2A1C 0E01
All bits of this register are set and cleared by software.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FINIT
rw

Bits 31:1 Reserved, must be kept at reset value.
Bit 0 FINIT: Filter initialization mode
Initialization mode for filter banks
0: Active filters mode.
1: Initialization mode for the filters.

850/1004

DocID018940 Rev 9

RM0091

Controller area network (bxCAN)

CAN filter mode register (CAN_FM1R)
Address offset: 0x204
Reset value: 0x0000 0000
This register can be written only when the filter initialization mode is set (FINIT=1) in the
CAN_FMR register.
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

13

12

11

10

15

14

Res.

Res.

FBM13 FBM12 FBM11 FBM10
rw

Note:

rw

rw

rw

9

8

7

6

5

4

3

2

1

0

FBM9

FBM8

FBM7

FBM6

FBM5

FBM4

FBM3

FBM2

FBM1

FBM0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Please refer to Figure 315: Filter bank scale configuration - register organization on
page 825
Bits 31:14 Reserved, must be kept at reset value.
Bits 13:0 FBMx: Filter mode
Mode of the registers of Filter x.
0: Two 32-bit registers of filter bank x are in Identifier Mask mode.
1: Two 32-bit registers of filter bank x are in Identifier List mode.

CAN filter scale register (CAN_FS1R)
Address offset: 0x20C
Reset value: 0x0000 0000
This register can be written only when the filter initialization mode is set (FINIT=1) in the
CAN_FMR register.
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res

Res

FSC13

FSC12

FSC11

FSC10

FSC9

FSC8

FSC7

FSC6

FSC5

FSC4

FSC3

FSC2

FSC1

FSC0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:14 Reserved, must be kept at reset value.
Bits 13:0 FSCx: Filter scale configuration
These bits define the scale configuration of Filters 13-0.
0: Dual 16-bit scale configuration
1: Single 32-bit scale configuration

Note:

Please refer to Figure 315: Filter bank scale configuration - register organization on
page 825.

DocID018940 Rev 9

851/1004

Controller area network (bxCAN)

RM0091

CAN filter FIFO assignment register (CAN_FFA1R)
Address offset: 0x214
Reset value: 0x0000 0000
This register can be written only when the filter initialization mode is set (FINIT=1) in the
CAN_FMR register.
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res

Res

FFA13

FFA12

FFA11

FFA10

FFA9

FFA8

FFA7

FFA6

FFA5

FFA4

FFA3

FFA2

FFA1

FFA0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:14 Reserved, must be kept at reset value.
Bits 13:0 FFAx: Filter FIFO assignment for filter x
The message passing through this filter will be stored in the specified FIFO.
0: Filter assigned to FIFO 0
1: Filter assigned to FIFO 1

CAN filter activation register (CAN_FA1R)
Address offset: 0x21C
Reset value: 0x0000 0000
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

Res

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res

FACT1
3

FACT1
2

FACT1
1

FACT1
0

FACT9

FACT8

FACT7

FACT6

FACT5

FACT4

FACT3

FACT2

FACT1

FACT0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

Res

Bits 31:14 Reserved, must be kept at reset value.
Bits 13:0 FACTx: Filter active
The software sets this bit to activate Filter x. To modify the Filter x registers (CAN_FxR[0:7]),
the FACTx bit must be cleared or the FINIT bit of the CAN_FMR register must be set.
0: Filter x is not active
1: Filter x is active

852/1004

DocID018940 Rev 9

RM0091

Controller area network (bxCAN)

Filter bank i register x (CAN_FiRx) (i = 0..13, x = 1, 2)
Address offsets: 0x240 to 0x2AC
Reset value: 0xXXXX XXXX
There are 14 filter banks, i= 0 to 13. Each filter bank i is composed of two 32-bit registers,
CAN_FiR[2:1].
This register can only be modified when the FACTx bit of the CAN_FAxR register is cleared
or when the FINIT bit of the CAN_FMR register is set.
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

FB31

FB30

FB29

FB28

FB27

FB26

FB25

FB24

FB23

FB22

FB21

FB20

FB19

FB18

FB17

FB16

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

FB15

FB14

FB13

FB12

FB11

FB10

FB9

FB8

FB7

FB6

FB5

FB4

FB3

FB2

FB1

FB0

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

In all configurations:
Bits 31:0 FB[31:0]: Filter bits
Identifier
Each bit of the register specifies the level of the corresponding bit of the expected identifier.
0: Dominant bit is expected
1: Recessive bit is expected
Mask
Each bit of the register specifies whether the bit of the associated identifier register must
match with the corresponding bit of the expected identifier or not.
0: Do not care, the bit is not used for the comparison
1: Must match, the bit of the incoming identifier must have the same level has specified in
the corresponding identifier register of the filter.

Note:

Depending on the scale and mode configuration of the filter the function of each register can
differ. For the filter mapping, functions description and mask registers association, refer to
Section 29.7.4: Identifier filtering on page 823.
A Mask/Identifier register in mask mode has the same bit mapping as in identifier list
mode.
For the register mapping/addresses of the filter banks please refer to the Table 118 on
page 854.

DocID018940 Rev 9

853/1004

0x180

854/1004

CAN_BTR

Reset value

0

0

- - - -

0

0

1

0

0

0

1

1

- - - - - -

0

0

0

0

0

-

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

x

x

x

x

x

x

x

x

x

x

x

x

TS2[2:0]

-

0

x

x

x

x

x

x

x
LECIE
BOFIE
EPVIE
EWGIE
Res.
FOVIE1
FFIE1

- - 0
0
0
0

0
0

TS1[3:0]

STID[10:0]/EXID[28:18]

x

DocID018940 Rev 9

x

x

Res.

x
Res.
Res.
Res.
Res.
Res.

x

- - - - - - - - -

x

BRP[9:0]

EXID[17:0]

0
0
0

0

0

0

0

0

x

x

x

0

Res.

FFIE0
FMPIE0
TMEIE

ABRQ0
Res.

TERR0
ALST0
TXOK0

0
0

- - 0
0
0
0
0

- - 0
0
0

CAN_RF0R
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
Res.

Res.
Res.
Res.
Res.
Res.
RFOM0
FOVR0
FULL0
Res.

Reset value

- - - - - - - - - - - - - - - - - - - - - - - - - 0
0
0

-

CAN_RF1R

Reset value

- - - - - - - - - - - - - - - - - - - - - - - - - FOVR1
FULL1
Res.

0
0
0

0
0

FMP1[1:0]

RFOM1

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FMP0[1:0]

Res.

Res.

Res.

Res.

DBF
RESET
Res.

Res.
Res.
Res.

INRQ

INAK

0

0
0
0
1
0

RQCP0

TXFP
SLEEP
1

ERRI

0
SLAK

NART
0

WKUI

0

SLAKI

RFLM

Res.
ABOM

Res.

Res.

AWUM

TXM

Res.

0

Res.

RXM

Res.

0

Res.

SAMP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

TTCM

RX

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

CODE[1:0]

Res.

- - -

TXRQ

EWGF

0
EPVF

x
0
BOFF

RQCP1

0

Res.

Res.

0

Res.

TXOK1

0

Res.

0

Res.

ALST1

0

Res.

Res.

1

IDE

TERR1

- - -

TME[2:0]

Res.

Res.

1

FOVIE0

Res.

0

Res.

- - - - - - - - - - - - - - - - - - - -

FMPIE1

ABRQ1

0

Res.

Res.

Reset value

Res.

RQCP2

0

Res.

CAN_MSR

Res.

TXOK2

1

Res.

- - - - - - -

Res.

ALST2

1

Res.

0

Res.

Res.

TERR2

1

Res.

1

Res.

Res.

- - - - - - - - - - - - - - Res.

Reset value

LEC[2:0]

Res.

Res.

Res.

0

Res.

ERRIE

0
Res.

0

WKUIE

Res.

0

Res.

ABRQ2

0

LOW[2:0]

0

Res.

CAN_MCR

RTR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

TEC[7:0]
0

Res.

REC[7:0]

Res.

0x018
SLKIE

- - - - - - - - - - - - - -

Res.

0

Res.

CAN_ESR

SJW[1:0]

0

Res.

Reset value

Res.

CAN_IER

Res.

0x014
Res.

0x010

Res.

0x00C
Reset value

Res.

CAN_TSR

Res.

0x008

Res.

0x004

Res.

0x000

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.
0

Res.

Reset value
0

Res.

CAN_TI0R
0

Res.

0x0200x17F
0

Res.

0x01C
0

SILM

Reset value

LBKM

Offset

Res.

29.9.5

Res.

Controller area network (bxCAN)
RM0091

bxCAN register map
Refer to Section 2.2.2 on page 46 for the register boundary addresses.
Table 118. bxCAN register map and reset values

0

0
0

0
0
0
0
0

x

x

0

RM0091

Controller area network (bxCAN)

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

0x1A8

x

x

x

x

x

x

x

0x1AC

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

DATA7[7:0]
x

x

CAN_RI0R

x

x

x

x

x

x

Res.

Res.

Res.

Res.

x

x

x

x

x

- - - -

- - - - - - -

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

- - - -

- - - - - - -

x

x

x

x

x

x

x

x

x

x

x

x

x

STID[10:0]/EXID[28:18]

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

DocID018940 Rev 9

x

x

x

x

x

x

x

x

x

x

0

x

x

x

x

x

x

x

x

x

x

0

x

x

x

x

x

x

x

x

x

x

x

-

x

DATA4[7:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

EXID[17:0]
x

x

DLC[3:0]

0x1B0
Reset value

x

DATA0[7:0]

DATA5[7:0]
x

x

x

DLC[3:0]

x

x

x

x

DATA4[7:0]

DATA1[7:0]
x

x

DATA0[7:0]

x

DATA6[7:0]
x

Res.

x

DATA2[7:0]
x

Res.

x

EXID[17:0]

DATA3[7:0]

CAN_TDH2R
Reset value

x

DATA5[7:0]

TIME[15:0]

CAN_TDL2R
Reset value

x

DATA1[7:0]

0x1A4
Reset value

x

x

Res.

x

x

Res.

CAN_TDT2R

x

x

Res.

x

x

Res.

x

x

TGT

x

x

Res.

x

x

Res.

x

x

x

x

STID[10:0]/EXID[28:18]
x

x

x

DATA6[7:0]
x

x

x

DATA2[7:0]
x

x

Res.

x

DATA7[7:0]

CAN_TI2R
Reset value

x

x

x

DATA4[7:0]

Res.

0x1A0

x

x

EXID[17:0]

DATA3[7:0]

CAN_TDH1R
Reset value

x

x

Res.

0x19C

x

Res.

DATA5[7:0]

TIME[15:0]
x

x

Res.

x

x

Res.

x

x

Res.

x

x

TGT

x

x

Res.

x

x

Res.

x

x

Res.

x

x

x

DATA0[7:0]

Res.

x

- - - -

Res.

x

CAN_TDL1R
Reset value

x

STID[10:0]/EXID[28:18]

CAN_TDT1R

0x198

x

DATA6[7:0]
x

x

DATA1[7:0]

0x194
Reset value

- - - - - - -

DATA2[7:0]

DATA7[7:0]
x

x

TXRQ

x

x

TXRQ

x

x

Res.

x

x

IDE

x

x

RTR

x

IDE

x

RTR

x

TGT

x

Res.

x

IDE

x

CAN_TI1R
Reset value

x

Res.

0x190

x

DATA3[7:0]

CAN_TDH0R
Reset value

x

DLC[3:0]

RTR

CAN_TDL0R
Reset value

0x18C

x

Res.

0x188

x

Res.

Reset value

Res.

TIME[15:0]

Res.

Res.

CAN_TDT0R
0x184

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 118. bxCAN register map and reset values (continued)

855/1004

Controller area network (bxCAN)

RM0091

x

x

x

x

x

x

x

x

x

x

x

CAN_RI1R

x

x

x

x

x

x

x

x

x

x

x

DATA2[7:0]
x

x

x

x

DATA7[7:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

- - - -

x

DATA1[7:0]
x

x

x

x

DATA6[7:0]
x

x

x

x

x

x

x

x

x

STID[10:0]/EXID[28:18]

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

CAN_RDT1R

x

x

x

x

x

x

x

x

x

x

x

x

TIME[15:0]

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

FMI[7:0]

0x1C4
Reset value
CAN_RDL1R
Reset value

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

FINIT

0

0

-

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

-

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
Res.

Res.

Res.

0

Res.

0

DocID018940 Rev 9

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.
Res.

- - - - - - - - - - - - - - - - - Res.

Reset value

Res.

Res.

FBM[13:0]

CAN_FS1R

-

Res.

1

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

Res.

0

Res.

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

- - - - - - - - - - - - - - - - - -

Res.

Reset value

Res.

CAN_FM1R

Res.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Res.

Res.

x

Res.

x

Res.

x

Res.

x

Res.

x

Res.

x

Res.

x

Res.

x

Res.

x

DATA4[7:0]

Res.

x

x

Res.

x

x

Res.

x

x

Res.

x

x

Res.

x

x

Res.

x

x

DATA0[7:0]

DATA5[7:0]
x

x

Res.

x

x

x

Res.

x

x

x

Res.

x

- - - -

x

Res.

x

x

Res.

x

x

Res.

x

x

Res.

x

x

DATA1[7:0]

DATA6[7:0]
x

x

Res.

x

x

DLC[3:0]

Res.

x

x

-

Res.

x

x

x

Res.

x

x

x

Res.

x

x

DATA2[7:0]

DATA7[7:0]
x

x

x

Reset value

0x20C

856/1004

x

x

CAN_FMR

0x204

0x210

x

x

-

0x200

0x208

x

x

Res.

0x1D00x1FF

x

CAN_RDH1R
Reset value

x

DATA3[7:0]

Res.

0x1CC

x

Res.

0x1C8

x

x

DATA4[7:0]

EXID[17:0]

x

x

x

0x1C0
Reset value

x

DATA0[7:0]

DATA5[7:0]
x

x

Res.

x

IDE

x

Res.

x

DATA3[7:0]

CAN_RDH0R
Reset value

x

Res.

CAN_RDL0R
Reset value

0x1BC

x

Res.

0x1B8

x

Res.

Reset value

DLC[3:0]

RTR

FMI[7:0]

Res.

TIME[15:0]

Res.

CAN_RDT0R
0x1B4

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 118. bxCAN register map and reset values (continued)

FSC[13:0]

RM0091

Controller area network (bxCAN)

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CAN_FA1R

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

- - - - - - - - - - - - - - - - - -

0

0

0

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

FB[31:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

FB[31:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

FB[31:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x
.
.
.
.

CAN_F27R1

FB[31:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

CAN_F27R2
Reset value

Res.

Res.

Res.

0x31C

x

.
.
.
.

Reset value

Res.

Res.

Res.

0x318

0

Res.

Res.

Res.

.
.
.
.

x

CAN_F1R2
Reset value

0

Res.

Res.

Res.

0x24C

x

CAN_F1R1
Reset value

0

Res.

Res.

Res.

0x248

0

FB[31:0]

CAN_F0R2
Reset value

0

Res.

Res.

Res.

Reset value

0

Res.

Res.

Res.

CAN_F0R1

0

Res.

Res.

-

0

Res.

Res.

0x2240x23F

0

Res.

-

FACT[13:0]

Res.

0x220

0x244

Res.

-

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

Res.

Res.

0

0x21C

0x240

FFA[13:0]

- - - - - - - - - - - - - - - - - -

Reset value
0x218

Res.

CAN_FFA1R
0x214

Res.

Register

Res.

Offset

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Table 118. bxCAN register map and reset values (continued)

x

x

FB[31:0]
x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

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30

RM0091

Universal serial bus full-speed device interface (USB)
This section applies to STM32F04x, STM32F072 and STM32F078 devices only.

30.1

Introduction
The USB peripheral implements an interface between a full-speed USB 2.0 bus and the
APB bus.
USB suspend/resume are supported which allows to stop the device clocks for low-power
consumption.

30.2

30.3

USB main features
•

USB specification version 2.0 full-speed compliant

•

Configurable number of endpoints from 1 to 8

•

Up to 1024 bytes of dedicated packet buffer memory SRAM (last 256 Bytes are
exclusively shared with CAN peripheral)

•

Cyclic redundancy check (CRC) generation/checking, Non-return-to-zero Inverted
(NRZI) encoding/decoding and bit-stuffing

•

Isochronous transfers support

•

Double-buffered bulk/isochronous endpoint support

•

USB Suspend/Resume operations

•

Frame locked clock pulse generation

•

USB 2.0 Link Power Management support

•

Battery Charging Specification Revision 1.2 support

•

USB connect / disconnect capability (controllable embedded pull-up resistor on
USB_DP line)

USB implementation
Table 119 describes the USB implementation in the devices.
Table 119. STM32F0xx USB implementation
STM32F04x, STM32F072,
USB

features(1)

STM32F078,
USB

Number of endpoints

8

Size of dedicated packet buffer memory SRAM
Dedicated packet buffer memory SRAM access scheme
USB 2.0 Link Power Management (LPM) support

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2 x 16 bits / word
X

RM0091

Universal serial bus full-speed device interface (USB)
Table 119. STM32F0xx USB implementation (continued)
STM32F04x, STM32F072,
(1)

USB features

STM32F078,
USB

Battery Charging Detection (BCD) support

X

Embedded pull-up resistor on USB_DP line

X

1. X= supported
2. When the CAN peripheral clock is enabled in the RCC_APB1ENR register, only the first
768 Bytes are available to USB while the last 256 Bytes are used by CAN.

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USB functional description
Figure 323 shows the block diagram of the USB peripheral.
Figure 323. USB peripheral block diagram

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The USB peripheral provides an USB-compliant connection between the host PC and the
function implemented by the microcontroller. Data transfer between the host PC and the
system memory occurs through a dedicated packet buffer memory accessed directly by the
USB peripheral. This dedicated memory size is up to 1024 bytes, and up to 16 monodirectional or 8 bidirectional endpoints can be used. The USB peripheral interfaces with the
USB host, detecting token packets, handling data transmission/reception, and processing
handshake packets as required by the USB standard. Transaction formatting is performed
by the hardware, including CRC generation and checking.
Each endpoint is associated with a buffer description block indicating where the endpointrelated memory area is located, how large it is or how many bytes must be transmitted.
When a token for a valid function/endpoint pair is recognized by the USB peripheral, the
related data transfer (if required and if the endpoint is configured) takes place. The data
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Universal serial bus full-speed device interface (USB)
buffered by the USB peripheral is loaded in an internal 16-bit register and memory access to
the dedicated buffer is performed. When all the data has been transferred, if needed, the
proper handshake packet over the USB is generated or expected according to the direction
of the transfer.
At the end of the transaction, an endpoint-specific interrupt is generated, reading status
registers and/or using different interrupt response routines. The microcontroller can
determine:
•

which endpoint has to be served,

•

which type of transaction took place, if errors occurred (bit stuffing, format, CRC,
protocol, missing ACK, over/underrun, etc.).

Special support is offered to isochronous transfers and high throughput bulk transfers,
implementing a double buffer usage, which allows to always have an available buffer for the
USB peripheral while the microcontroller uses the other one.
The unit can be placed in low-power mode (SUSPEND mode), by writing in the control
register, whenever required. At this time, all static power dissipation is avoided, and the USB
clock can be slowed down or stopped. The detection of activity at the USB inputs, while in
low-power mode, wakes the device up asynchronously. A special interrupt source can be
connected directly to a wakeup line to allow the system to immediately restart the normal
clock generation and/or support direct clock start/stop.

30.4.1

Description of USB blocks
The USB peripheral implements all the features related to USB interfacing, which include
the following blocks:
•

USB Physical Interface (USB PHY): This block is maintaining the electrical interface to
an external USB host. It contains the differential analog transceiver itself, controllable
embedded pull-up resistor (connected to USB_DP line) and support for Battery
Charging Detection (BCD), multiplexed on same USB_DP and USB_DM lines. The
output enable control signal of the analog transceiver (active low) is provided externally
on USB_NOE. It can be used to drive some activity LED or to provide information about
the actual communication direction to some other circuitry.

•

Serial Interface Engine (SIE): The functions of this block include: synchronization
pattern recognition, bit-stuffing, CRC generation and checking, PID
verification/generation, and handshake evaluation. It must interface with the USB
transceivers and uses the virtual buffers provided by the packet buffer interface for
local data storage. This unit also generates signals according to USB peripheral
events, such as Start of Frame (SOF), USB_Reset, Data errors etc. and to Endpoint
related events like end of transmission or correct reception of a packet; these signals
are then used to generate interrupts.

•

Timer: This block generates a start-of-frame locked clock pulse and detects a global
suspend (from the host) when no traffic has been received for 3 ms.

•

Packet Buffer Interface: This block manages the local memory implementing a set of
buffers in a flexible way, both for transmission and reception. It can choose the proper
buffer according to requests coming from the SIE and locate them in the memory
addresses pointed by the Endpoint registers. It increments the address after each
exchanged byte until the end of packet, keeping track of the number of exchanged
bytes and preventing the buffer to overrun the maximum capacity.

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Note:

RM0091

•

Endpoint-Related Registers: Each endpoint has an associated register containing the
endpoint type and its current status. For mono-directional/single-buffer endpoints, a
single register can be used to implement two distinct endpoints. The number of
registers is 8, allowing up to 16 mono-directional/single-buffer or up to 7 double-buffer
endpoints in any combination. For example the USB peripheral can be programmed to
have 4 double buffer endpoints and 8 single-buffer/mono-directional endpoints.

•

Control Registers: These are the registers containing information about the status of
the whole USB peripheral and used to force some USB events, such as resume and
power-down.

•

Interrupt Registers: These contain the Interrupt masks and a record of the events. They
can be used to inquire an interrupt reason, the interrupt status or to clear the status of a
pending interrupt.

* Endpoint 0 is always used for control transfer in single-buffer mode.
The USB peripheral is connected to the APB bus through an APB interface, containing the
following blocks:

30.5

•

Packet Memory: This is the local memory that physically contains the Packet Buffers. It
can be used by the Packet Buffer interface, which creates the data structure and can
be accessed directly by the application software. The size of the Packet Memory is up
to 1024 bytes, structured as 512 half-words by 16 bits.

•

Arbiter: This block accepts memory requests coming from the APB bus and from the
USB interface. It resolves the conflicts by giving priority to APB accesses, while always
reserving half of the memory bandwidth to complete all USB transfers. This time-duplex
scheme implements a virtual dual-port SRAM that allows memory access, while an
USB transaction is happening. Multiword APB transfers of any length are also allowed
by this scheme.

•

Register Mapper: This block collects the various byte-wide and bit-wide registers of the
USB peripheral in a structured 16-bit wide half-word set addressed by the APB.

•

APB Wrapper: This provides an interface to the APB for the memory and register. It
also maps the whole USB peripheral in the APB address space.

•

Interrupt Mapper: This block is used to select how the possible USB events can
generate interrupts and map them to the NVIC.

Programming considerations
In the following sections, the expected interactions between the USB peripheral and the
application program are described, in order to ease application software development.

30.5.1

Generic USB device programming
This part describes the main tasks required of the application software in order to obtain
USB compliant behavior. The actions related to the most general USB events are taken into
account and paragraphs are dedicated to the special cases of double-buffered endpoints
and Isochronous transfers. Apart from system reset, action is always initiated by the USB
peripheral, driven by one of the USB events described below.

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30.5.2

Universal serial bus full-speed device interface (USB)

System and power-on reset
Upon system and power-on reset, the first operation the application software should perform
is to provide all required clock signals to the USB peripheral and subsequently de-assert its
reset signal so to be able to access its registers. The whole initialization sequence is
hereafter described.
As a first step application software needs to activate register macrocell clock and de-assert
macrocell specific reset signal using related control bits provided by device clock
management logic.
After that, the analog part of the device related to the USB transceiver must be switched on
using the PDWN bit in CNTR register, which requires a special handling. This bit is intended
to switch on the internal voltage references that supply the port transceiver. This circuit has
a defined startup time (tSTARTUP specified in the datasheet) during which the behavior of the
USB transceiver is not defined. It is thus necessary to wait this time, after setting the PDWN
bit in the CNTR register, before removing the reset condition on the USB part (by clearing
the FRES bit in the CNTR register). Clearing the ISTR register then removes any spurious
pending interrupt before any other macrocell operation is enabled.
At system reset, the microcontroller must initialize all required registers and the packet
buffer description table, to make the USB peripheral able to properly generate interrupts and
data transfers. All registers not specific to any endpoint must be initialized according to the
needs of application software (choice of enabled interrupts, chosen address of packet
buffers, etc.). Then the process continues as for the USB reset case (see further
paragraph).

USB reset (RESET interrupt)
When this event occurs, the USB peripheral is put in the same conditions it is left by the
system reset after the initialization described in the previous paragraph: communication is
disabled in all endpoint registers (the USB peripheral will not respond to any packet). As a
response to the USB reset event, the USB function must be enabled, having as USB
address 0, implementing only the default control endpoint (endpoint address is 0 too). This
is accomplished by setting the Enable Function (EF) bit of the USB_DADDR register and
initializing the EP0R register and its related packet buffers accordingly. During USB
enumeration process, the host assigns a unique address to this device, which must be
written in the ADD[6:0] bits of the USB_DADDR register, and configures any other
necessary endpoint.
When a RESET interrupt is received, the application software is responsible to enable again
the default endpoint of USB function 0 within 10 ms from the end of reset sequence which
triggered the interrupt.

Structure and usage of packet buffers
Each bidirectional endpoint may receive or transmit data from/to the host. The received data
is stored in a dedicated memory buffer reserved for that endpoint, while another memory
buffer contains the data to be transmitted by the endpoint. Access to this memory is
performed by the packet buffer interface block, which delivers a memory access request
and waits for its acknowledgment. Since the packet buffer memory has to be accessed by
the microcontroller also, an arbitration logic takes care of the access conflicts, using half
APB cycle for microcontroller access and the remaining half for the USB peripheral access.
In this way, both the agents can operate as if the packet memory is a dual-port SRAM,
without being aware of any conflict even when the microcontroller is performing back-to-

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back accesses. The USB peripheral logic uses a dedicated clock. The frequency of this
dedicated clock is fixed by the requirements of the USB standard at 48 MHz, and this can be
different from the clock used for the interface to the APB bus. Different clock configurations
are possible where the APB clock frequency can be higher or lower than the USB peripheral
one.
Note:

Due to USB data rate and packet memory interface requirements, the APB clock must have
a minimum frequency of 10 MHz to avoid data overrun/underrun problems.
Each endpoint is associated with two packet buffers (usually one for transmission and the
other one for reception). Buffers can be placed anywhere inside the packet memory
because their location and size is specified in a buffer description table, which is also
located in the packet memory at the address indicated by the USB_BTABLE register. Each
table entry is associated to an endpoint register and it is composed of four 16-bit half-words
so that table start address must always be aligned to an 8-byte boundary (the lowest three
bits of USB_BTABLE register are always “000”). Buffer descriptor table entries are
described in the Section 30.6.2: Buffer descriptor table. If an endpoint is unidirectional and it
is neither an Isochronous nor a double-buffered bulk, only one packet buffer is required (the
one related to the supported transfer direction). Other table locations related to unsupported
transfer directions or unused endpoints, are available to the user. Isochronous and doublebuffered bulk endpoints have special handling of packet buffers (Refer to Section 30.5.4:
Isochronous transfers and Section 30.5.3: Double-buffered endpoints respectively). The
relationship between buffer description table entries and packet buffer areas is depicted in
Figure 324.
Figure 324. Packet buffer areas with examples of buffer description table locations

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Universal serial bus full-speed device interface (USB)
Each packet buffer is used either during reception or transmission starting from the bottom.
The USB peripheral will never change the contents of memory locations adjacent to the
allocated memory buffers; if a packet bigger than the allocated buffer length is received
(buffer overrun condition) the data will be copied to the memory only up to the last available
location.

Endpoint initialization
The first step to initialize an endpoint is to write appropriate values to the
ADDRn_TX/ADDRn_RX registers so that the USB peripheral finds the data to be
transmitted already available and the data to be received can be buffered. The EP_TYPE
bits in the USB_EPnR register must be set according to the endpoint type, eventually using
the EP_KIND bit to enable any special required feature. On the transmit side, the endpoint
must be enabled using the STAT_TX bits in the USB_EPnR register and COUNTn_TX must
be initialized. For reception, STAT_RX bits must be set to enable reception and
COUNTn_RX must be written with the allocated buffer size using the BL_SIZE and
NUM_BLOCK fields. Unidirectional endpoints, except Isochronous and double-buffered bulk
endpoints, need to initialize only bits and registers related to the supported direction. Once
the transmission and/or reception are enabled, register USB_EPnR and locations
ADDRn_TX/ADDRn_RX, COUNTn_TX/COUNTn_RX (respectively), should not be modified
by the application software, as the hardware can change their value on the fly. When the
data transfer operation is completed, notified by a CTR interrupt event, they can be
accessed again to re-enable a new operation.

IN packets (data transmission)
When receiving an IN token packet, if the received address matches a configured and valid
endpoint, the USB peripheral accesses the contents of ADDRn_TX and COUNTn_TX
locations inside the buffer descriptor table entry related to the addressed endpoint. The
content of these locations is stored in its internal 16 bit registers ADDR and COUNT (not
accessible by software). The packet memory is accessed again to read the first byte to be
transmitted (Refer to Structure and usage of packet buffers on page 863) and starts sending
a DATA0 or DATA1 PID according to USB_EPnR bit DTOG_TX. When the PID is
completed, the first byte, read from buffer memory, is loaded into the output shift register to
be transmitted on the USB bus. After the last data byte is transmitted, the computed CRC is
sent. If the addressed endpoint is not valid, a NAK or STALL handshake packet is sent
instead of the data packet, according to STAT_TX bits in the USB_EPnR register.
The ADDR internal register is used as a pointer to the current buffer memory location while
COUNT is used to count the number of remaining bytes to be transmitted. Each half-word
read from the packet buffer memory is transmitted over the USB bus starting from the least
significant byte. Transmission buffer memory is read starting from the address pointed by
ADDRn_TX for COUNTn_TX/2 half-words. If a transmitted packet is composed of an odd
number of bytes, only the lower half of the last half-word accessed will be used.
On receiving the ACK receipt by the host, the USB_EPnR register is updated in the
following way: DTOG_TX bit is toggled, the endpoint is made invalid by setting
STAT_TX=10 (NAK) and bit CTR_TX is set. The application software must first identify the
endpoint, which is requesting microcontroller attention by examining the EP_ID and DIR bits
in the USB_ISTR register. Servicing of the CTR_TX event starts clearing the interrupt bit;
the application software then prepares another buffer full of data to be sent, updates the
COUNTn_TX table location with the number of byte to be transmitted during the next
transfer, and finally sets STAT_TX to ‘11 (VALID) to re-enable transmissions. While the
STAT_TX bits are equal to ‘10 (NAK), any IN request addressed to that endpoint is NAKed,

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indicating a flow control condition: the USB host will retry the transaction until it succeeds. It
is mandatory to execute the sequence of operations in the above mentioned order to avoid
losing the notification of a second IN transaction addressed to the same endpoint
immediately following the one which triggered the CTR interrupt.

OUT and SETUP packets (data reception)
These two tokens are handled by the USB peripheral more or less in the same way; the
differences in the handling of SETUP packets are detailed in the following paragraph about
control transfers. When receiving an OUT/SETUP PID, if the address matches a valid
endpoint, the USB peripheral accesses the contents of the ADDRn_RX and COUNTn_RX
locations inside the buffer descriptor table entry related to the addressed endpoint. The
content of the ADDRn_RX is stored directly in its internal register ADDR. While COUNT is
now reset and the values of BL_SIZE and NUM_BLOCK bit fields, which are read within
COUNTn_RX content are used to initialize BUF_COUNT, an internal 16 bit counter, which is
used to check the buffer overrun condition (all these internal registers are not accessible by
software). Data bytes subsequently received by the USB peripheral are packed in halfwords (the first byte received is stored as least significant byte) and then transferred to the
packet buffer starting from the address contained in the internal ADDR register while
BUF_COUNT is decremented and COUNT is incremented at each byte transfer. When the
end of DATA packet is detected, the correctness of the received CRC is tested and only if no
errors occurred during the reception, an ACK handshake packet is sent back to the
transmitting host.
In case of wrong CRC or other kinds of errors (bit-stuff violations, frame errors, etc.), data
bytes are still copied in the packet memory buffer, at least until the error detection point, but
ACK packet is not sent and the ERR bit in USB_ISTR register is set. However, there is
usually no software action required in this case: the USB peripheral recovers from reception
errors and remains ready for the next transaction to come. If the addressed endpoint is not
valid, a NAK or STALL handshake packet is sent instead of the ACK, according to bits
STAT_RX in the USB_EPnR register and no data is written in the reception memory buffers.
Reception memory buffer locations are written starting from the address contained in the
ADDRn_RX for a number of bytes corresponding to the received data packet length, CRC
included (i.e. data payload length + 2), or up to the last allocated memory location, as
defined by BL_SIZE and NUM_BLOCK, whichever comes first. In this way, the USB
peripheral never writes beyond the end of the allocated reception memory buffer area. If the
length of the data packet payload (actual number of bytes used by the application) is greater
than the allocated buffer, the USB peripheral detects a buffer overrun condition. in this case,
a STALL handshake is sent instead of the usual ACK to notify the problem to the host, no
interrupt is generated and the transaction is considered failed.
When the transaction is completed correctly, by sending the ACK handshake packet, the
internal COUNT register is copied back in the COUNTn_RX location inside the buffer
description table entry, leaving unaffected BL_SIZE and NUM_BLOCK fields, which
normally do not require to be re-written, and the USB_EPnR register is updated in the
following way: DTOG_RX bit is toggled, the endpoint is made invalid by setting STAT_RX =
‘10 (NAK) and bit CTR_RX is set. If the transaction has failed due to errors or buffer overrun
condition, none of the previously listed actions take place. The application software must
first identify the endpoint, which is requesting microcontroller attention by examining the
EP_ID and DIR bits in the USB_ISTR register. The CTR_RX event is serviced by first
determining the transaction type (SETUP bit in the USB_EPnR register); the application
software must clear the interrupt flag bit and get the number of received bytes reading the
COUNTn_RX location inside the buffer description table entry related to the endpoint being

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processed. After the received data is processed, the application software should set the
STAT_RX bits to ‘11 (Valid) in the USB_EPnR, enabling further transactions. While the
STAT_RX bits are equal to ‘10 (NAK), any OUT request addressed to that endpoint is
NAKed, indicating a flow control condition: the USB host will retry the transaction until it
succeeds. It is mandatory to execute the sequence of operations in the above mentioned
order to avoid losing the notification of a second OUT transaction addressed to the same
endpoint following immediately the one which triggered the CTR interrupt.

Control transfers
Control transfers are made of a SETUP transaction, followed by zero or more data stages,
all of the same direction, followed by a status stage (a zero-byte transfer in the opposite
direction). SETUP transactions are handled by control endpoints only and are very similar to
OUT ones (data reception) except that the values of DTOG_TX and DTOG_RX bits of the
addressed endpoint registers are set to 1 and 0 respectively, to initialize the control transfer,
and both STAT_TX and STAT_RX are set to ‘10 (NAK) to let software decide if subsequent
transactions must be IN or OUT depending on the SETUP contents. A control endpoint must
check SETUP bit in the USB_EPnR register at each CTR_RX event to distinguish normal
OUT transactions from SETUP ones. A USB device can determine the number and
direction of data stages by interpreting the data transferred in the SETUP stage, and is
required to STALL the transaction in the case of errors. To do so, at all data stages before
the last, the unused direction should be set to STALL, so that, if the host reverses the
transfer direction too soon, it gets a STALL as a status stage.
While enabling the last data stage, the opposite direction should be set to NAK, so that, if
the host reverses the transfer direction (to perform the status stage) immediately, it is kept
waiting for the completion of the control operation. If the control operation completes
successfully, the software will change NAK to VALID, otherwise to STALL. At the same time,
if the status stage will be an OUT, the STATUS_OUT (EP_KIND in the USB_EPnR register)
bit should be set, so that an error is generated if a status transaction is performed with notzero data. When the status transaction is serviced, the application clears the STATUS_OUT
bit and sets STAT_RX to VALID (to accept a new command) and STAT_TX to NAK (to delay
a possible status stage immediately following the next setup).
Since the USB specification states that a SETUP packet cannot be answered with a
handshake different from ACK, eventually aborting a previously issued command to start
the new one, the USB logic doesn’t allow a control endpoint to answer with a NAK or STALL
packet to a SETUP token received from the host.
When the STAT_RX bits are set to ‘01 (STALL) or ‘10 (NAK) and a SETUP token is
received, the USB accepts the data, performing the required data transfers and sends back
an ACK handshake. If that endpoint has a previously issued CTR_RX request not yet
acknowledged by the application (i.e. CTR_RX bit is still set from a previously completed
reception), the USB discards the SETUP transaction and does not answer with any
handshake packet regardless of its state, simulating a reception error and forcing the host to
send the SETUP token again. This is done to avoid losing the notification of a SETUP
transaction addressed to the same endpoint immediately following the transaction, which
triggered the CTR_RX interrupt.

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Double-buffered endpoints
All different endpoint types defined by the USB standard represent different traffic models,
and describe the typical requirements of different kind of data transfer operations. When
large portions of data are to be transferred between the host PC and the USB function, the
bulk endpoint type is the most suited model. This is because the host schedules bulk
transactions so as to fill all the available bandwidth in the frame, maximizing the actual
transfer rate as long as the USB function is ready to handle a bulk transaction addressed to
it. If the USB function is still busy with the previous transaction when the next one arrives, it
will answer with a NAK handshake and the host PC will issue the same transaction again
until the USB function is ready to handle it, reducing the actual transfer rate due to the
bandwidth occupied by re-transmissions. For this reason, a dedicated feature called
‘double-buffering’ can be used with bulk endpoints.
When ‘double-buffering’ is activated, data toggle sequencing is used to select, which buffer
is to be used by the USB peripheral to perform the required data transfers, using both
‘transmission’ and ‘reception’ packet memory areas to manage buffer swapping on each
successful transaction in order to always have a complete buffer to be used by the
application, while the USB peripheral fills the other one. For example, during an OUT
transaction directed to a ‘reception’ double-buffered bulk endpoint, while one buffer is being
filled with new data coming from the USB host, the other one is available for the
microcontroller software usage (the same would happen with a ‘transmission’ doublebuffered bulk endpoint and an IN transaction).
Since the swapped buffer management requires the usage of all 4 buffer description table
locations hosting the address pointer and the length of the allocated memory buffers, the
USB_EPnR registers used to implement double-buffered bulk endpoints are forced to be
used as unidirectional ones. Therefore, only one STAT bit pair must be set at a value
different from ‘00 (Disabled): STAT_RX if the double-buffered bulk endpoint is enabled for
reception, STAT_TX if the double-buffered bulk endpoint is enabled for transmission. In
case it is required to have double-buffered bulk endpoints enabled both for reception and
transmission, two USB_EPnR registers must be used.
To exploit the double-buffering feature and reach the highest possible transfer rate, the
endpoint flow control structure, described in previous chapters, has to be modified, in order
to switch the endpoint status to NAK only when a buffer conflict occurs between the USB
peripheral and application software, instead of doing it at the end of each successful
transaction. The memory buffer which is currently being used by the USB peripheral is
defined by the DTOG bit related to the endpoint direction: DTOG_RX (bit 14 of USB_EPnR
register) for ‘reception’ double-buffered bulk endpoints or DTOG_TX (bit 6 of USB_EPnR
register) for ‘transmission’ double-buffered bulk endpoints. To implement the new flow
control scheme, the USB peripheral should know which packet buffer is currently in use by
the application software, so to be aware of any conflict. Since in the USB_EPnR register,
there are two DTOG bits but only one is used by USB peripheral for data and buffer
sequencing (due to the unidirectional constraint required by double-buffering feature) the
other one can be used by the application software to show which buffer it is currently using.
This new buffer flag is called SW_BUF. In the following table the correspondence between
USB_EPnR register bits and DTOG/SW_BUF definition is explained, for the cases of
‘transmission’ and ‘reception’ double-buffered bulk endpoints.

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Table 120. Double-buffering buffer flag definition
Buffer flag

‘Transmission’ endpoint

DTOG
SW_BUF

‘Reception’ endpoint

DTOG_TX (USB_EPnR bit 6)

DTOG_RX (USB_EPnR bit 14)

USB_EPnR bit 14

USB_EPnR bit 6

The memory buffer which is currently being used by the USB peripheral is defined by DTOG
buffer flag, while the buffer currently in use by application software is identified by SW_BUF
buffer flag. The relationship between the buffer flag value and the used packet buffer is the
same in both cases, and it is listed in the following table.
Table 121. Bulk double-buffering memory buffers usage
Endpoint
DTOG SW_BUF
Type

Packet buffer used by USB
Peripheral

Packet buffer used by
Application Software

0

1

ADDRn_TX_0 / COUNTn_TX_0 ADDRn_TX_1 / COUNTn_TX_1
Buffer description table locations. Buffer description table locations.

1

0

ADDRn_TX_1 / COUNTn_TX_1
Buffer description table locations

ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.

0

0

None (1)

ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.

1

1

None (1)

ADDRn_TX_0 / COUNTn_TX_0
Buffer description table locations.

0

1

ADDRn_RX_0 / COUNTn_RX_0 ADDRn_RX_1 / COUNTn_RX_1
Buffer description table locations. Buffer description table locations.

1

0

ADDRn_RX_1 / COUNTn_RX_1 ADDRn_RX_0 / COUNTn_RX_0
Buffer description table locations. Buffer description table locations.

0

0

None (1)

ADDRn_RX_0 / COUNTn_RX_0
Buffer description table locations.

1

1

None (1)

ADDRn_RX_1 / COUNTn_RX_1
Buffer description table locations.

IN

OUT

1. Endpoint in NAK Status.

Double-buffering feature for a bulk endpoint is activated by:
•

Writing EP_TYPE bit field at ‘00 in its USB_EPnR register, to define the endpoint as a
bulk, and

•

Setting EP_KIND bit at ‘1 (DBL_BUF), in the same register.

The application software is responsible for DTOG and SW_BUF bits initialization according
to the first buffer to be used; this has to be done considering the special toggle-only property
that these two bits have. The end of the first transaction occurring after having set
DBL_BUF, triggers the special flow control of double-buffered bulk endpoints, which is used
for all other transactions addressed to this endpoint until DBL_BUF remain set. At the end of
each transaction the CTR_RX or CTR_TX bit of the addressed endpoint USB_EPnR
register is set, depending on the enabled direction. At the same time, the affected DTOG bit
in the USB_EPnR register is hardware toggled making the USB peripheral buffer swapping
completely software independent. Unlike common transactions, and the first one after

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DBL_BUF setting, STAT bit pair is not affected by the transaction termination and its value
remains ‘11 (Valid). However, as the token packet of a new transaction is received, the
actual endpoint status will be masked as ‘10 (NAK) when a buffer conflict between the USB
peripheral and the application software is detected (this condition is identified by DTOG and
SW_BUF having the same value, see Table 121 on page 869). The application software
responds to the CTR event notification by clearing the interrupt flag and starting any
required handling of the completed transaction. When the application packet buffer usage is
over, the software toggles the SW_BUF bit, writing ‘1 to it, to notify the USB peripheral about
the availability of that buffer. In this way, the number of NAKed transactions is limited only by
the application elaboration time of a transaction data: if the elaboration time is shorter than
the time required to complete a transaction on the USB bus, no re-transmissions due to flow
control will take place and the actual transfer rate will be limited only by the host PC.
The application software can always override the special flow control implemented for
double-buffered bulk endpoints, writing an explicit status different from ‘11 (Valid) into the
STAT bit pair of the related USB_EPnR register. In this case, the USB peripheral will always
use the programmed endpoint status, regardless of the buffer usage condition.

30.5.4

Isochronous transfers
The USB standard supports full speed peripherals requiring a fixed and accurate data
production/consume frequency, defining this kind of traffic as ‘Isochronous’. Typical
examples of this data are: audio samples, compressed video streams, and in general any
sort of sampled data having strict requirements for the accuracy of delivered frequency.
When an endpoint is defined to be ‘isochronous’ during the enumeration phase, the host
allocates in the frame the required bandwidth and delivers exactly one IN or OUT packet
each frame, depending on endpoint direction. To limit the bandwidth requirements, no retransmission of failed transactions is possible for Isochronous traffic; this leads to the fact
that an isochronous transaction does not have a handshake phase and no ACK packet is
expected or sent after the data packet. For the same reason, Isochronous transfers do not
support data toggle sequencing and always use DATA0 PID to start any data packet.
The Isochronous behavior for an endpoint is selected by setting the EP_TYPE bits at ‘10 in
its USB_EPnR register; since there is no handshake phase the only legal values for the
STAT_RX/STAT_TX bit pairs are ‘00 (Disabled) and ‘11 (Valid), any other value will produce
results not compliant to USB standard. Isochronous endpoints implement double-buffering
to ease application software development, using both ‘transmission’ and ‘reception’ packet
memory areas to manage buffer swapping on each successful transaction in order to have
always a complete buffer to be used by the application, while the USB peripheral fills the
other.
The memory buffer which is currently used by the USB peripheral is defined by the DTOG
bit related to the endpoint direction (DTOG_RX for ‘reception’ isochronous endpoints,
DTOG_TX for ‘transmission’ isochronous endpoints, both in the related USB_EPnR
register) according to Table 122.

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Table 122. Isochronous memory buffers usage
Endpoint
Type

DTOG bit
value

Packet buffer used by the
USB peripheral

Packet buffer used by the
application software

0

ADDRn_TX_0 / COUNTn_TX_0
buffer description table
locations.

ADDRn_TX_1 / COUNTn_TX_1
buffer description table
locations.

1

ADDRn_TX_1 / COUNTn_TX_1
buffer description table
locations.

ADDRn_TX_0 / COUNTn_TX_0
buffer description table
locations.

0

ADDRn_RX_0 / COUNTn_RX_0
buffer description table
locations.

ADDRn_RX_1 / COUNTn_RX_1
buffer description table
locations.

1

ADDRn_RX_1 / COUNTn_RX_1
buffer description table
locations.

ADDRn_RX_0 / COUNTn_RX_0
buffer description table
locations.

IN

OUT

As it happens with double-buffered bulk endpoints, the USB_EPnR registers used to
implement Isochronous endpoints are forced to be used as unidirectional ones. In case it is
required to have Isochronous endpoints enabled both for reception and transmission, two
USB_EPnR registers must be used.
The application software is responsible for the DTOG bit initialization according to the first
buffer to be used; this has to be done considering the special toggle-only property that these
two bits have. At the end of each transaction, the CTR_RX or CTR_TX bit of the addressed
endpoint USB_EPnR register is set, depending on the enabled direction. At the same time,
the affected DTOG bit in the USB_EPnR register is hardware toggled making buffer
swapping completely software independent. STAT bit pair is not affected by transaction
completion; since no flow control is possible for Isochronous transfers due to the lack of
handshake phase, the endpoint remains always ‘11 (Valid). CRC errors or buffer-overrun
conditions occurring during Isochronous OUT transfers are anyway considered as correct
transactions and they always trigger an CTR_RX event. However, CRC errors will anyway
set the ERR bit in the USB_ISTR register to notify the software of the possible data
corruption.

30.5.5

Suspend/Resume events
The USB standard defines a special peripheral state, called SUSPEND, in which the
average current drawn from the USB bus must not be greater than 2.5 mA. This
requirement is of fundamental importance for bus-powered devices, while self-powered
devices are not required to comply to this strict power consumption constraint. In suspend
mode, the host PC sends the notification by not sending any traffic on the USB bus for more
than 3 ms: since a SOF packet must be sent every 1 ms during normal operations, the USB
peripheral detects the lack of 3 consecutive SOF packets as a suspend request from the
host PC and set the SUSP bit to ‘1 in USB_ISTR register, causing an interrupt if enabled.
Once the device is suspended, its normal operation can be restored by a so called
RESUME sequence, which can be started from the host PC or directly from the peripheral
itself, but it is always terminated by the host PC. The suspended USB peripheral must be
anyway able to detect a RESET sequence, reacting to this event as a normal USB reset
event.

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The actual procedure used to suspend the USB peripheral is device dependent since
according to the device composition, different actions may be required to reduce the total
consumption.
A brief description of a typical suspend procedure is provided below, focused on the USBrelated aspects of the application software routine responding to the SUSP notification of
the USB peripheral:

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1.

Set the FSUSP bit in the USB_CNTR register to 1. This action activates the suspend
mode within the USB peripheral. As soon as the suspend mode is activated, the check
on SOF reception is disabled to avoid any further SUSP interrupts being issued while
the USB is suspended.

2.

Remove or reduce any static power consumption in blocks different from the USB
peripheral.

3.

Set LP_MODE bit in USB_CNTR register to 1 to remove static power consumption in
the analog USB transceivers but keeping them able to detect resume activity.

4.

Optionally turn off external oscillator and device PLL to stop any activity inside the
device.

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When an USB event occurs while the device is in SUSPEND mode, the RESUME
procedure must be invoked to restore nominal clocks and regain normal USB behavior.
Particular care must be taken to insure that this process does not take more than 10 ms
when the wakening event is an USB reset sequence (See “Universal Serial Bus
Specification” for more details). The start of a resume or reset sequence, while the USB
peripheral is suspended, clears the LP_MODE bit in USB_CNTR register asynchronously.
Even if this event can trigger an WKUP interrupt if enabled, the use of an interrupt response
routine must be carefully evaluated because of the long latency due to system clock restart;
to have the shorter latency before re-activating the nominal clock it is suggested to put the
resume procedure just after the end of the suspend one, so its code is immediately
executed as soon as the system clock restarts. To prevent ESD discharges or any other kind
of noise from waking-up the system (the exit from suspend mode is an asynchronous
event), a suitable analog filter on data line status is activated during suspend; the filter width
is about 70 ns.
The following is a list of actions a resume procedure should address:
1.

Optionally turn on external oscillator and/or device PLL.

2.

Clear FSUSP bit of USB_CNTR register.

3.

If the resume triggering event has to be identified, bits RXDP and RXDM in the
USB_FNR register can be used according to Table 123, which also lists the intended
software action in all the cases. If required, the end of resume or reset sequence can
be detected monitoring the status of the above mentioned bits by checking when they
reach the “10” configuration, which represent the Idle bus state; moreover at the end of
a reset sequence the RESET bit in USB_ISTR register is set to 1, issuing an interrupt if
enabled, which should be handled as usual.
Table 123. Resume event detection
[RXDP,RXDM] status

Wakeup event

Required resume software action

“00”

Root reset

None

“10”

None (noise on bus)

Go back in Suspend mode

“01”

Root resume

None

“11”

Not allowed (noise on bus) Go back in Suspend mode

A device may require to exit from suspend mode as an answer to particular events not
directly related to the USB protocol (e.g. a mouse movement wakes up the whole system).
In this case, the resume sequence can be started by setting the RESUME bit in the
USB_CNTR register to ‘1 and resetting it to 0 after an interval between 1 ms and 15 ms (this
interval can be timed using ESOF interrupts, occurring with a 1 ms period when the system
clock is running at nominal frequency). Once the RESUME bit is clear, the resume
sequence will be completed by the host PC and its end can be monitored again using the
RXDP and RXDM bits in the USB_FNR register.
Note:

The RESUME bit must be anyway used only after the USB peripheral has been put in
suspend mode, setting the FSUSP bit in USB_CNTR register to 1.

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USB registers
The USB peripheral registers can be divided into the following groups:
•

Common Registers: Interrupt and Control registers

•

Endpoint Registers: Endpoint configuration and status

•

Buffer Descriptor Table: Location of packet memory used to locate data buffers

All register addresses are expressed as offsets with respect to the USB peripheral registers
base address 0x4000 5C00, except the buffer descriptor table locations, which starts at the
address specified by the USB_BTABLE register.
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

30.6.1

Common registers
These registers affect the general behavior of the USB peripheral defining operating mode,
interrupt handling, device address and giving access to the current frame number updated
by the host PC.

USB control register (USB_CNTR)
Address offset: 0x40
Reset value: 0x0003
15

14

13

12

11

10

9

8

CTR
M

PMAOVR
M

ERR
M

WKUP
M

SUSP
M

RESET
M

SOF
M

ESOF
M

rw

rw

rw

rw

rw

rw

rw

rw

7

6

L1REQ Res
M
.
rw

5

4

3

2

1

0

L1
RESUME

RE
SUME

F
SUSP

LP_
MODE

PDW
N

F
RES

rw

rw

rw

rw

rw

rw

Bit 15 CTRM: Correct transfer interrupt mask
0: Correct Transfer (CTR) Interrupt disabled.
1: CTR Interrupt enabled, an interrupt request is generated when the corresponding bit in the
USB_ISTR register is set.
Bit 14 PMAOVRM: Packet memory area over / underrun interrupt mask
0: PMAOVR Interrupt disabled.
1: PMAOVR Interrupt enabled, an interrupt request is generated when the corresponding bit
in the USB_ISTR register is set.
Bit 13 ERRM: Error interrupt mask
0: ERR Interrupt disabled.
1: ERR Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.
Bit 12 WKUPM: Wakeup interrupt mask
0: WKUP Interrupt disabled.
1: WKUP Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.
Bit 11 SUSPM: Suspend mode interrupt mask
0: Suspend Mode Request (SUSP) Interrupt disabled.
1: SUSP Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.

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Bit 10 RESETM: USB reset interrupt mask
0: RESET Interrupt disabled.
1: RESET Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.
Bit 9 SOFM: Start of frame interrupt mask
0: SOF Interrupt disabled.
1: SOF Interrupt enabled, an interrupt request is generated when the corresponding bit in the
USB_ISTR register is set.
Bit 8 ESOFM: Expected start of frame interrupt mask
0: Expected Start of Frame (ESOF) Interrupt disabled.
1: ESOF Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.
Bit 7 L1REQM: LPM L1 state request interrupt mask
0: LPM L1 state request (L1REQ) Interrupt disabled.
1: L1REQ Interrupt enabled, an interrupt request is generated when the corresponding bit in
the USB_ISTR register is set.
Bit 6 Reserved.
Bit 5 L1RESUME: LPM L1 Resume request
The microcontroller can set this bit to send a LPM L1 Resume signal to the host. After the
signaling ends, this bit is cleared by hardware.
Bit 4 RESUME: Resume request
The microcontroller can set this bit to send a Resume signal to the host. It must be activated,
according to USB specifications, for no less than 1 ms and no more than 15 ms after which
the Host PC is ready to drive the resume sequence up to its end.
Bit 3 FSUSP: Force suspend
Software must set this bit when the SUSP interrupt is received, which is issued when no
traffic is received by the USB peripheral for 3 ms.
0: No effect.
1: Enter suspend mode. Clocks and static power dissipation in the analog transceiver are left
unaffected. If suspend power consumption is a requirement (bus-powered device), the
application software should set the LP_MODE bit after FSUSP as explained below.

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Bit 2 LP_MODE: Low-power mode
This mode is used when the suspend-mode power constraints require that all static power
dissipation is avoided, except the one required to supply the external pull-up resistor. This
condition should be entered when the application is ready to stop all system clocks, or
reduce their frequency in order to meet the power consumption requirements of the USB
suspend condition. The USB activity during the suspend mode (WKUP event)
asynchronously resets this bit (it can also be reset by software).
0: No Low-power mode.
1: Enter Low-power mode.
Bit 1 PDWN: Power down
This bit is used to completely switch off all USB-related analog parts if it is required to
completely disable the USB peripheral for any reason. When this bit is set, the USB
peripheral is disconnected from the transceivers and it cannot be used.
0: Exit Power Down.
1: Enter Power down mode.
Bit 0 FRES: Force USB Reset
0: Clear USB reset.
1: Force a reset of the USB peripheral, exactly like a RESET signaling on the USB. The USB
peripheral is held in RESET state until software clears this bit. A “USB-RESET” interrupt is
generated, if enabled.

USB interrupt status register (USB_ISTR)
Address offset: 0x44
Reset value: 0x0000 0000
15

14

13

12

11

10

9

8

7

6

5

4

CTR

PMA
OVR

ERR

WKUP

SUSP

RESET

SOF

ESOF

L1REQ

Res.

Res.

DIR

r

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

rc_w0

r

3

2

1

0

EP_ID[3:0]
r

r

r

r

This register contains the status of all the interrupt sources allowing application software to
determine, which events caused an interrupt request.
The upper part of this register contains single bits, each of them representing a specific
event. These bits are set by the hardware when the related event occurs; if the
corresponding bit in the USB_CNTR register is set, a generic interrupt request is generated.
The interrupt routine, examining each bit, will perform all necessary actions, and finally it will
clear the serviced bits. If any of them is not cleared, the interrupt is considered to be still
pending, and the interrupt line will be kept high again. If several bits are set simultaneously,
only a single interrupt will be generated.
Endpoint transaction completion can be handled in a different way to reduce interrupt
response latency. The CTR bit is set by the hardware as soon as an endpoint successfully
completes a transaction, generating a generic interrupt request if the corresponding bit in
USB_CNTR is set. An endpoint dedicated interrupt condition is activated independently
from the CTRM bit in the USB_CNTR register. Both interrupt conditions remain active until
software clears the pending bit in the corresponding USB_EPnR register (the CTR bit is
actually a read only bit). For endpoint-related interrupts, the software can use the Direction
of Transaction (DIR) and EP_ID read-only bits to identify, which endpoint made the last
interrupt request and called the corresponding interrupt service routine.

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The user can choose the relative priority of simultaneously pending USB_ISTR events by
specifying the order in which software checks USB_ISTR bits in an interrupt service routine.
Only the bits related to events, which are serviced, are cleared. At the end of the service
routine, another interrupt will be requested, to service the remaining conditions.
To avoid spurious clearing of some bits, it is recommended to clear them with a load
instruction where all bits which must not be altered are written with 1, and all bits to be
cleared are written with ‘0 (these bits can only be cleared by software). Read-modify-write
cycles should be avoided because between the read and the write operations another bit
could be set by the hardware and the next write will clear it before the microprocessor has
the time to serve the event.
The following describes each bit in detail:
Bit 15 CTR: Correct transfer
This bit is set by the hardware to indicate that an endpoint has successfully completed a
transaction; using DIR and EP_ID bits software can determine which endpoint requested the
interrupt. This bit is read-only.
Bit 14 PMAOVR: Packet memory area over / underrun
This bit is set if the microcontroller has not been able to respond in time to an USB memory
request. The USB peripheral handles this event in the following way: During reception an
ACK handshake packet is not sent, during transmission a bit-stuff error is forced on the
transmitted stream; in both cases the host will retry the transaction. The PMAOVR interrupt
should never occur during normal operations. Since the failed transaction is retried by the
host, the application software has the chance to speed-up device operations during this
interrupt handling, to be ready for the next transaction retry; however this does not happen
during Isochronous transfers (no isochronous transaction is anyway retried) leading to a loss
of data in this case. This bit is read/write but only ‘0 can be written and writing ‘1 has no
effect.
Bit 13 ERR: Error
This flag is set whenever one of the errors listed below has occurred:
NANS: No ANSwer. The timeout for a host response has expired.
CRC: Cyclic Redundancy Check error. One of the received CRCs, either in the token or in
the data, was wrong.
BST: Bit Stuffing error. A bit stuffing error was detected anywhere in the PID, data, and/or
CRC.
FVIO: Framing format Violation. A non-standard frame was received (EOP not in the right
place, wrong token sequence, etc.).
The USB software can usually ignore errors, since the USB peripheral and the PC host
manage retransmission in case of errors in a fully transparent way. This interrupt can be
useful during the software development phase, or to monitor the quality of transmission over
the USB bus, to flag possible problems to the user (e.g. loose connector, too noisy
environment, broken conductor in the USB cable and so on). This bit is read/write but only ‘0
can be written and writing ‘1 has no effect.
Bit 12 WKUP: Wakeup
This bit is set to 1 by the hardware when, during suspend mode, activity is detected that
wakes up the USB peripheral. This event asynchronously clears the LP_MODE bit in the
CTLR register and activates the USB_WAKEUP line, which can be used to notify the rest of
the device (e.g. wakeup unit) about the start of the resume process. This bit is read/write but
only ‘0 can be written and writing ‘1 has no effect.

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Bit 11 SUSP: Suspend mode request
This bit is set by the hardware when no traffic has been received for 3 ms, indicating a
suspend mode request from the USB bus. The suspend condition check is enabled
immediately after any USB reset and it is disabled by the hardware when the suspend mode
is active (FSUSP=1) until the end of resume sequence. This bit is read/write but only ‘0 can
be written and writing ‘1 has no effect.
Bit 10 RESET: USB reset request
Set when the USB peripheral detects an active USB RESET signal at its inputs. The USB
peripheral, in response to a RESET, just resets its internal protocol state machine, generating
an interrupt if RESETM enable bit in the USB_CNTR register is set. Reception and
transmission are disabled until the RESET bit is cleared. All configuration registers do not
reset: the microcontroller must explicitly clear these registers (this is to ensure that the
RESET interrupt can be safely delivered, and any transaction immediately followed by a
RESET can be completed). The function address and endpoint registers are reset by an USB
reset event.
This bit is read/write but only ‘0 can be written and writing ‘1 has no effect.
Bit 9 SOF: Start of frame
This bit signals the beginning of a new USB frame and it is set when a SOF packet arrives
through the USB bus. The interrupt service routine may monitor the SOF events to have a
1 ms synchronization event to the USB host and to safely read the USB_FNR register which
is updated at the SOF packet reception (this could be useful for isochronous applications).
This bit is read/write but only ‘0 can be written and writing ‘1 has no effect.
Bit 8 ESOF: Expected start of frame
This bit is set by the hardware when an SOF packet is expected but not received. The host
sends an SOF packet each 1 ms, but if the hub does not receive it properly, the Suspend
Timer issues this interrupt. If three consecutive ESOF interrupts are generated (i.e. three
SOF packets are lost) without any traffic occurring in between, a SUSP interrupt is
generated. This bit is set even when the missing SOF packets occur while the Suspend
Timer is not yet locked. This bit is read/write but only ‘0 can be written and writing ‘1 has no
effect.
Bit 7 L1REQ: LPM L1 state request
This bit is set by the hardware when LPM command to enter the L1 state is successfully
received and acknowledged. This bit is read/write but only ‘0 can be written and writing ‘1 has
no effect.

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Bits 6:5 Reserved.
Bit 4 DIR: Direction of transaction
This bit is written by the hardware according to the direction of the successful transaction,
which generated the interrupt request.
If DIR bit=0, CTR_TX bit is set in the USB_EPnR register related to the interrupting endpoint.
The interrupting transaction is of IN type (data transmitted by the USB peripheral to the host
PC).
If DIR bit=1, CTR_RX bit or both CTR_TX/CTR_RX are set in the USB_EPnR register
related to the interrupting endpoint. The interrupting transaction is of OUT type (data
received by the USB peripheral from the host PC) or two pending transactions are waiting to
be processed.
This information can be used by the application software to access the USB_EPnR bits
related to the triggering transaction since it represents the direction having the interrupt
pending. This bit is read-only.
Bits 3:0 EP_ID[3:0]: Endpoint Identifier
These bits are written by the hardware according to the endpoint number, which generated
the interrupt request. If several endpoint transactions are pending, the hardware writes the
endpoint identifier related to the endpoint having the highest priority defined in the following
way: Two endpoint sets are defined, in order of priority: Isochronous and double-buffered
bulk endpoints are considered first and then the other endpoints are examined. If more than
one endpoint from the same set is requesting an interrupt, the EP_ID bits in USB_ISTR
register are assigned according to the lowest requesting endpoint register, EP0R having the
highest priority followed by EP1R and so on. The application software can assign a register
to each endpoint according to this priority scheme, so as to order the concurring endpoint
requests in a suitable way. These bits are read only.

USB frame number register (USB_FNR)
Address offset: 0x48
Reset value: 0x0XXX where X is undefined
15

14

13

RXDP

RXDM

LCK

r

r

r

12

11

10

9

8

7

6

r

r

r

r

r

LSOF[1:0]
r

r

5

4

3

2

1

0

r

r

r

r

r

FN[10:0]
r

Bit 15 RXDP: Receive data + line status
This bit can be used to observe the status of received data plus upstream port data line. It
can be used during end-of-suspend routines to help determining the wakeup event.
Bit 14 RXDM: Receive data - line status
This bit can be used to observe the status of received data minus upstream port data line. It
can be used during end-of-suspend routines to help determining the wakeup event.

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Bit 13 LCK: Locked
This bit is set by the hardware when at least two consecutive SOF packets have been
received after the end of an USB reset condition or after the end of an USB resume
sequence. Once locked, the frame timer remains in this state until an USB reset or USB
suspend event occurs.
Bits 12:11 LSOF[1:0]: Lost SOF
These bits are written by the hardware when an ESOF interrupt is generated, counting the
number of consecutive SOF packets lost. At the reception of an SOF packet, these bits are
cleared.
Bits 10:0 FN[10:0]: Frame number
This bit field contains the 11-bits frame number contained in the last received SOF packet.
The frame number is incremented for every frame sent by the host and it is useful for
Isochronous transfers. This bit field is updated on the generation of an SOF interrupt.

USB device address (USB_DADDR)
Address offset: 0x4C
Reset value: 0x0000
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

EF

ADD6

ADD5

ADD4

ADD3

ADD2

ADD1

ADD0

rw

rw

rw

rw

rw

rw

rw

rw

Bits 15:8 Reserved
Bit 7 EF: Enable function
This bit is set by the software to enable the USB device. The address of this device is
contained in the following ADD[6:0] bits. If this bit is at ‘0 no transactions are handled,
irrespective of the settings of USB_EPnR registers.
Bits 6:0 ADD[6:0]: Device address
These bits contain the USB function address assigned by the host PC during the
enumeration process. Both this field and the Endpoint Address (EA) field in the associated
USB_EPnR register must match with the information contained in a USB token in order to
handle a transaction to the required endpoint.

Buffer table address (USB_BTABLE)
Address offset: 0x50
Reset value: 0x0000
15

14

13

12

11

10

9

8

7

6

5

4

3

BTABLE[15:3]
rw

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Bits 15:3 BTABLE[15:3]: Buffer table
These bits contain the start address of the buffer allocation table inside the dedicated packet
memory. This table describes each endpoint buffer location and size and it must be aligned
to an 8 byte boundary (the 3 least significant bits are always ‘0). At the beginning of every
transaction addressed to this device, the USB peripheral reads the element of this table
related to the addressed endpoint, to get its buffer start location and the buffer size (Refer to
Structure and usage of packet buffers on page 863).
Bits 2:0 Reserved, forced by hardware to 0.

LPM control and status register (USB_LPMCSR)
Address offset: 0x54
Reset value: 0x0000
15
Res.

14
Res.

13
Res.

12
Res.

11
Res.

10
Res.

9

8

Res.

7

6

Res.

5

4

3

BESL[3:0]

REM
WAKE

r

r

2

1

0

Res.

LPM
ACK

LPM
EN

rw

rw

Bits 15:8 Reserved.
Bits 7:4 BESL[3:0]: BESL value
These bits contain the BESL value received with last ACKed LPM Token
Bit 3 REMWAKE: bRemoteWake value
This bit contains the bRemoteWake value received with last ACKed LPM Token
Bit 2 Reserved
Bit 1 LPMACK: LPM Token acknowledge enable
0: the valid LPM Token will be NYET.
1: the valid LPM Token will be ACK.
The NYET/ACK will be returned only on a successful LPM transaction:
No errors in both the EXT token and the LPM token (else ERROR)
A valid bLinkState = 0001B (L1) is received (else STALL)
Bit 0 LPMEN: LPM support enable
This bit is set by the software to enable the LPM support within the USB device. If this bit is
at ‘0 no LPM transactions are handled.

Battery charging detector (USB_BCDR)
Address offset: 0x58
Reset value: 0x0000
15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

DPPU

Res.

Res.

Res.

Res.

Res.

Res.

Res.

PS2
DET

SDET

PDET

DC
DET

SDEN

PDEN

DCD
EN

BCD
EN

r

r

r

r

rw

rw

rw

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Bit 15 DPPU: DP pull-up control
This bit is set by software to enable the embedded pull-up on the DP line. Clearing it to ‘0’
can be used to signalize disconnect to the host when needed by the user software.
Bits 14:8 Reserved.
Bit 7 PS2DET: DM pull-up detection status
This bit is active only during PD and gives the result of comparison between DM voltage
level and VLGC threshold. In normal situation, the DM level should be below this threshold. If
it is above, it means that the DM is externally pulled high. This can be caused by connection
to a PS2 port (which pulls-up both DP and DM lines) or to some proprietary charger not
following the BCD specification.
0: Normal port detected (connected to SDP, ACA, CDP or DCP).
1: PS2 port or proprietary charger detected.
Bit 6 SDET: Secondary detection (SD) status
This bit gives the result of SD.
0: CDP detected.
1: DCP detected.
Bit 5 PDET: Primary detection (PD) status
This bit gives the result of PD.
0: no BCD support detected (connected to SDP or proprietary device).
1: BCD support detected (connected to ACA, CDP or DCP).
Bit 4 DCDET: Data contact detection (DCD) status
This bit gives the result of DCD.
0: data lines contact not detected.
1: data lines contact detected.
Bit 3 SDEN: Secondary detection (SD) mode enable
This bit is set by the software to put the BCD into SD mode. Only one detection mode (DCD,
PD, SD or OFF) should be selected to work correctly.
Bit 2 PDEN: Primary detection (PD) mode enable
This bit is set by the software to put the BCD into PD mode. Only one detection mode (DCD,
PD, SD or OFF) should be selected to work correctly.
Bit 1 DCDEN: Data contact detection (DCD) mode enable
This bit is set by the software to put the BCD into DCD mode. Only one detection mode
(DCD, PD, SD or OFF) should be selected to work correctly.
Bit 0 BCDEN: Battery charging detector (BCD) enable
This bit is set by the software to enable the BCD support within the USB device. When
enabled, the USB PHY is fully controlled by BCD and cannot be used for normal
communication. Once the BCD discovery is finished, the BCD should be placed in OFF
mode by clearing this bit to ‘0 in order to allow the normal USB operation.

Endpoint-specific registers
The number of these registers varies according to the number of endpoints that the USB
peripheral is designed to handle. The USB peripheral supports up to 8 bidirectional
endpoints. Each USB device must support a control endpoint whose address (EA bits) must
be set to 0. The USB peripheral behaves in an undefined way if multiple endpoints are
enabled having the same endpoint number value. For each endpoint, an USB_EPnR
register is available to store the endpoint specific information.

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USB endpoint n register (USB_EPnR), n=[0..7]
Address offset: 0x00 to 0x1C
Reset value: 0x0000
15

14

CTR_
RX

DTOG
_RX

rc_w0

t

13

12

STAT_RX[1:0]
t

t

11
SETUP
r

10

9

EP
TYPE[1:0]
rw

rw

8

7

6

EP_
KIND

CTR_
TX

DTOG_
TX

rw

rc_w0

t

5

4

3

STAT_TX[1:0]
t

t

2

1

0

rw

rw

EA[3:0]
rw

rw

They are also reset when an USB reset is received from the USB bus or forced through bit
FRES in the CTLR register, except the CTR_RX and CTR_TX bits, which are kept
unchanged to avoid missing a correct packet notification immediately followed by an USB
reset event. Each endpoint has its USB_EPnR register where n is the endpoint identifier.
Read-modify-write cycles on these registers should be avoided because between the read
and the write operations some bits could be set by the hardware and the next write would
modify them before the CPU has the time to detect the change. For this purpose, all bits
affected by this problem have an ‘invariant’ value that must be used whenever their
modification is not required. It is recommended to modify these registers with a load
instruction where all the bits, which can be modified only by the hardware, are written with
their ‘invariant’ value.

Bit 15 CTR_RX: Correct Transfer for reception
This bit is set by the hardware when an OUT/SETUP transaction is successfully completed
on this endpoint; the software can only clear this bit. If the CTRM bit in USB_CNTR register
is set accordingly, a generic interrupt condition is generated together with the endpoint
related interrupt condition, which is always activated. The type of occurred transaction, OUT
or SETUP, can be determined from the SETUP bit described below.
A transaction ended with a NAK or STALL handshake does not set this bit, since no data is
actually transferred, as in the case of protocol errors or data toggle mismatches.
This bit is read/write but only ‘0 can be written, writing 1 has no effect.
Bit 14 DTOG_RX: Data Toggle, for reception transfers
If the endpoint is not Isochronous, this bit contains the expected value of the data toggle bit
(0=DATA0, 1=DATA1) for the next data packet to be received. Hardware toggles this bit,
when the ACK handshake is sent to the USB host, following a data packet reception having
a matching data PID value; if the endpoint is defined as a control one, hardware clears this
bit at the reception of a SETUP PID addressed to this endpoint.
If the endpoint is using the double-buffering feature this bit is used to support packet buffer
swapping too (Refer to Section 30.5.3: Double-buffered endpoints).
If the endpoint is Isochronous, this bit is used only to support packet buffer swapping since
no data toggling is used for this sort of endpoints and only DATA0 packet are transmitted
(Refer to Section 30.5.4: Isochronous transfers). Hardware toggles this bit just after the end
of data packet reception, since no handshake is used for isochronous transfers.
This bit can also be toggled by the software to initialize its value (mandatory when the
endpoint is not a control one) or to force specific data toggle/packet buffer usage. When the
application software writes ‘0, the value of DTOG_RX remains unchanged, while writing ‘1
makes the bit value toggle. This bit is read/write but it can be only toggled by writing 1.

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Bits 13:12 STAT_RX [1:0]: Status bits, for reception transfers
These bits contain information about the endpoint status, which are listed in Table 124:
Reception status encoding on page 885.These bits can be toggled by software to initialize
their value. When the application software writes ‘0, the value remains unchanged, while
writing ‘1 makes the bit value toggle. Hardware sets the STAT_RX bits to NAK when a
correct transfer has occurred (CTR_RX=1) corresponding to a OUT or SETUP (control only)
transaction addressed to this endpoint, so the software has the time to elaborate the
received data before it acknowledge a new transaction
Double-buffered bulk endpoints implement a special transaction flow control, which control
the status based upon buffer availability condition (Refer to Section 30.5.3: Double-buffered
endpoints).
If the endpoint is defined as Isochronous, its status can be only “VALID” or “DISABLED”, so
that the hardware cannot change the status of the endpoint after a successful transaction. If
the software sets the STAT_RX bits to ‘STALL’ or ‘NAK’ for an Isochronous endpoint, the
USB peripheral behavior is not defined. These bits are read/write but they can be only
toggled by writing ‘1.
Bit 11 SETUP: Setup transaction completed
This bit is read-only and it is set by the hardware when the last completed transaction is a
SETUP. This bit changes its value only for control endpoints. It must be examined, in the
case of a successful receive transaction (CTR_RX event), to determine the type of
transaction occurred. To protect the interrupt service routine from the changes in SETUP
bits due to next incoming tokens, this bit is kept frozen while CTR_RX bit is at 1; its state
changes when CTR_RX is at 0. This bit is read-only.
Bits 10:9 EP_TYPE[1:0]: Endpoint type
These bits configure the behavior of this endpoint as described in Table 125: Endpoint type
encoding on page 886. Endpoint 0 must always be a control endpoint and each USB
function must have at least one control endpoint which has address 0, but there may be
other control endpoints if required. Only control endpoints handle SETUP transactions,
which are ignored by endpoints of other kinds. SETUP transactions cannot be answered
with NAK or STALL. If a control endpoint is defined as NAK, the USB peripheral will not
answer, simulating a receive error, in the receive direction when a SETUP transaction is
received. If the control endpoint is defined as STALL in the receive direction, then the
SETUP packet will be accepted anyway, transferring data and issuing the CTR interrupt.
The reception of OUT transactions is handled in the normal way, even if the endpoint is a
control one.
Bulk and interrupt endpoints have very similar behavior and they differ only in the special
feature available using the EP_KIND configuration bit.
The usage of Isochronous endpoints is explained in Section 30.5.4: Isochronous transfers
Bit 8 EP_KIND: Endpoint kind
The meaning of this bit depends on the endpoint type configured by the EP_TYPE bits.
Table 126 summarizes the different meanings.
DBL_BUF: This bit is set by the software to enable the double-buffering feature for this bulk
endpoint. The usage of double-buffered bulk endpoints is explained in Section 30.5.3:
Double-buffered endpoints.
STATUS_OUT: This bit is set by the software to indicate that a status out transaction is
expected: in this case all OUT transactions containing more than zero data bytes are
answered ‘STALL’ instead of ‘ACK’. This bit may be used to improve the robustness of the
application to protocol errors during control transfers and its usage is intended for control
endpoints only. When STATUS_OUT is reset, OUT transactions can have any number of
bytes, as required.

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Bit 7 CTR_TX: Correct Transfer for transmission
This bit is set by the hardware when an IN transaction is successfully completed on this
endpoint; the software can only clear this bit. If the CTRM bit in the USB_CNTR register is
set accordingly, a generic interrupt condition is generated together with the endpoint related
interrupt condition, which is always activated.
A transaction ended with a NAK or STALL handshake does not set this bit, since no data is
actually transferred, as in the case of protocol errors or data toggle mismatches.
This bit is read/write but only ‘0 can be written.
Bit 6 DTOG_TX: Data Toggle, for transmission transfers
If the endpoint is non-isochronous, this bit contains the required value of the data toggle bit
(0=DATA0, 1=DATA1) for the next data packet to be transmitted. Hardware toggles this bit
when the ACK handshake is received from the USB host, following a data packet
transmission. If the endpoint is defined as a control one, hardware sets this bit to 1 at the
reception of a SETUP PID addressed to this endpoint.
If the endpoint is using the double buffer feature, this bit is used to support packet buffer
swapping too (Refer to Section 30.5.3: Double-buffered endpoints)
If the endpoint is Isochronous, this bit is used to support packet buffer swapping since no
data toggling is used for this sort of endpoints and only DATA0 packet are transmitted (Refer
to Section 30.5.4: Isochronous transfers). Hardware toggles this bit just after the end of data
packet transmission, since no handshake is used for Isochronous transfers.
This bit can also be toggled by the software to initialize its value (mandatory when the
endpoint is not a control one) or to force a specific data toggle/packet buffer usage. When
the application software writes ‘0, the value of DTOG_TX remains unchanged, while writing
‘1 makes the bit value toggle. This bit is read/write but it can only be toggled by writing 1.
Bits 5:4 STAT_TX [1:0]: Status bits, for transmission transfers
These bits contain the information about the endpoint status, listed in Table 127. These bits
can be toggled by the software to initialize their value. When the application software writes
‘0, the value remains unchanged, while writing ‘1 makes the bit value toggle. Hardware sets
the STAT_TX bits to NAK, when a correct transfer has occurred (CTR_TX=1) corresponding
to a IN or SETUP (control only) transaction addressed to this endpoint. It then waits for the
software to prepare the next set of data to be transmitted.
Double-buffered bulk endpoints implement a special transaction flow control, which controls
the status based on buffer availability condition (Refer to Section 30.5.3: Double-buffered
endpoints).
If the endpoint is defined as Isochronous, its status can only be “VALID” or “DISABLED”.
Therefore, the hardware cannot change the status of the endpoint after a successful
transaction. If the software sets the STAT_TX bits to ‘STALL’ or ‘NAK’ for an Isochronous
endpoint, the USB peripheral behavior is not defined. These bits are read/write but they can
be only toggled by writing ‘1.
Bits 3:0 EA[3:0]: Endpoint address
Software must write in this field the 4-bit address used to identify the transactions directed to
this endpoint. A value must be written before enabling the corresponding endpoint.

Table 124. Reception status encoding
STAT_RX[1:0]

Meaning

00

DISABLED: all reception requests addressed to this endpoint are ignored.

01

STALL: the endpoint is stalled and all reception requests result in a STALL
handshake.

10

NAK: the endpoint is naked and all reception requests result in a NAK handshake.

11

VALID: this endpoint is enabled for reception.

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Table 125. Endpoint type encoding
EP_TYPE[1:0]

Meaning

00

BULK

01

CONTROL

10

ISO

11

INTERRUPT

Table 126. Endpoint kind meaning
EP_TYPE[1:0]

EP_KIND meaning

00

BULK

DBL_BUF

01

CONTROL

STATUS_OUT

10

ISO

Not used

11

INTERRUPT

Not used

Table 127. Transmission status encoding
STAT_TX[1:0]

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Meaning

00

DISABLED: all transmission requests addressed to this endpoint are ignored.

01

STALL: the endpoint is stalled and all transmission requests result in a STALL
handshake.

10

NAK: the endpoint is naked and all transmission requests result in a NAK
handshake.

11

VALID: this endpoint is enabled for transmission.

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30.6.2

Buffer descriptor table
Although the buffer descriptor table is located inside the packet buffer memory, its entries
can be considered as additional registers used to configure the location and size of the
packet buffers used to exchange data between the USB macro cell and the device.
The first packet memory location is located at 0x4000 6000. The buffer descriptor table
entry associated with the USB_EPnR registers is described below. The packet memory
should be accessed only by byte (8-bit) or half-word (16-bit) accesses. Word (32-bit)
accesses are not allowed.
A thorough explanation of packet buffers and the buffer descriptor table usage can be found
in Structure and usage of packet buffers on page 863.

Transmission buffer address n (USB_ADDRn_TX)
Address offset: [USB_BTABLE] + n*8
Note:

In case of double-buffered or isochronous endpoints in the IN direction, this address location
is referred to as USB_ADDRn_TX_0.
In case of double-buffered or isochronous endpoints in the OUT direction, this address
location is used for USB_ADDRn_RX_0.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

ADDRn_TX[15:1]
rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

rw

-

Bits 15:1 ADDRn_TX[15:1]: Transmission buffer address
These bits point to the starting address of the packet buffer containing data to be transmitted
by the endpoint associated with the USB_EPnR register at the next IN token addressed to it.
Bit 0 Must always be written as ‘0 since packet memory is half-word wide and all packet buffers
must be half-word aligned.

Transmission byte count n (USB_COUNTn_TX)
Address offset: [USB_BTABLE] + n*8 + 2
Note:

In case of double-buffered or isochronous endpoints in the IN direction, this address location
is referred to as USB_COUNTn_TX_0.
In case of double-buffered or isochronous endpoints in the OUT direction, this address
location is used for USB_COUNTn_RX_0.

15

14

13

12

11

10

Res.

Res.

Res.

Res.

Res.

Res.

9

8

7

6

rw

rw

rw

rw

5

4

3

2

1

0

rw

rw

rw

rw

COUNTn_TX[9:0]

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887/1004
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Universal serial bus full-speed device interface (USB)

RM0091

Bits 15:10 These bits are not used since packet size is limited by USB specifications to 1023 bytes. Their
value is not considered by the USB peripheral.
Bits 9:0 COUNTn_TX[9:0]: Transmission byte count
These bits contain the number of bytes to be transmitted by the endpoint associated with the
USB_EPnR register at the next IN token addressed to it.

Reception buffer address n (USB_ADDRn_RX)
Address offset: [USB_BTABLE] + n*8 + 4
Note:

In case of double-buffered or isochronous endpoints in the OUT direction, this address
location is referred to as USB_ADDRn_RX_1.
In case of double-buffered or isochronous endpoints in the IN direction, this address location
is used for USB_ADDRn_TX_1.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

ADDRn_RX[15:1]
rw

rw

rw

rw

rw

rw

rw

rw

-

rw

rw

rw

rw

rw

rw

rw

-

Bits 15:1 ADDRn_RX[15:1]: Reception buffer address
These bits point to the starting address of the packet buffer, which will contain the data
received by the endpoint associated with the USB_EPnR register at the next OUT/SETUP
token addressed to it.
Bit 0 This bit must always be written as ‘0 since packet memory is half-word wide and all packet
buffers must be half-word aligned.

Reception byte count n (USB_COUNTn_RX)
Address offset: [USB_BTABLE] + n*8 + 6
Note:

In case of double-buffered or isochronous endpoints in the OUT direction, this address
location is referred to as USB_COUNTn_RX_1.
In case of double-buffered or isochronous endpoints in the IN direction, this address location
is used for USB_COUNTn_TX_1.

15

14

BLSIZE
rw

13

12

11

10

9

8

7

6

NUM_BLOCK[4:0]
rw

rw

rw

rw

5

4

3

2

1

0

r

r

r

r

COUNTn_RX[9:0]
rw

r

r

r

r

r

r

This table location is used to store two different values, both required during packet
reception. The most significant bits contains the definition of allocated buffer size, to allow
buffer overflow detection, while the least significant part of this location is written back by the
USB peripheral at the end of reception to give the actual number of received bytes. Due to
the restrictions on the number of available bits, buffer size is represented using the number
of allocated memory blocks, where block size can be selected to choose the trade-off
between fine-granularity/small-buffer and coarse-granularity/large-buffer. The size of
allocated buffer is a part of the endpoint descriptor and it is normally defined during the

888/1004

DocID018940 Rev 9

RM0091

Universal serial bus full-speed device interface (USB)
enumeration process according to its maxPacketSize parameter value (See “Universal
Serial Bus Specification”).
Bit 15 BL_SIZE: Block size
This bit selects the size of memory block used to define the allocated buffer area.
–
If BL_SIZE=0, the memory block is 2-byte large, which is the minimum block
allowed in a half-word wide memory. With this block size the allocated buffer size
ranges from 2 to 62 bytes.
–
If BL_SIZE=1, the memory block is 32-byte large, which allows to reach the
maximum packet length defined by USB specifications. With this block size the
allocated buffer size theoretically ranges from 32 to 1024 bytes, which is the longest
packet size allowed by USB standard specifications. However, the applicable size is
limited by the available buffer memory.
Bits 14:10 NUM_BLOCK[4:0]: Number of blocks
These bits define the number of memory blocks allocated to this packet buffer. The actual
amount of allocated memory depends on the BL_SIZE value as illustrated in Table 128.
Bits 9:0 COUNTn_RX[9:0]: Reception byte count
These bits contain the number of bytes received by the endpoint associated with the
USB_EPnR register during the last OUT/SETUP transaction addressed to it.

Table 128. Definition of allocated buffer memory
Value of
NUM_BLOCK[4:0]

Memory allocated
when BL_SIZE=0

Memory allocated
when BL_SIZE=1

0 (‘00000)

Not allowed

32 bytes

1 (‘00001)

2 bytes

64 bytes

2 (‘00010)

4 bytes

96 bytes

3 (‘00011)

6 bytes

128 bytes

...

...

...

14 (‘01110)

28 bytes

480 bytes

15 (‘01111)

30 bytes

512 bytes

16 (‘10000)

32 bytes

544 bytes

...

...

...

29 (‘11101)

58 bytes

960 bytes

30 (‘11110)

60 bytes

992 bytes

31 (‘11111)

62 bytes

N/A

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891

0x4C

890/1004

USB_DADDR

CTR

PMAOVR

ERR

0

0

0

USB_FNR

Reset value

DocID018940 Rev 9

RXDM

LCK

0

0

0

0

0

x

x

x

x

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value
EP_KIND
CTR_TX
DTOG_TX

0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Res.
L1RESUME
RESUME
FSUSP
LPMODE
PDWN
FRES

0

0

0

1

1

STAT_
RX
[1:0]
0
0

0

0

0

0
0

DTOG_RX

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

SETUP

EP_KIND
CTR_TX
DTOG_TX

SETUP

DTOG_TX

DTOG_TX

DTOG_TX

DTOG_TX

DTOG_TX

CTR_RX

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CTR_TX

0

EP_KIND

SETUP

CTR_TX

0

EP_KIND
CTR_TX

0

EP_KIND
CTR_TX

0

EP_KIND

CTR_TX

0
EP_KIND

DTOG_TX

0

CTR_TX

0

EP_KIND

0

0
0
0

EP
TYPE
[1:0]
0
0
0
0

EP
TYPE
[1:0]
0
0
0
0

EP
TYPE
[1:0]
0
0
0
0

EP
TYPE
[1:0]
0
0
0
0

EP
TYPE
[1:0]

0
0
0
0

EP
TYPE
[1:0]

0
0
0
0

EP
TYPE
[1:0]

0

0

0

0

EF

LSOF
[1:0]

0

0

0

0

x

0

0

0

0

0

0

0

0

x

0

DIR

STAT_
RX
[1:0]

0

0

Res.

0
0

0

0

Res.

Reserved

L1REQM

STAT_
RX
[1:0]

0

EP
TYPE
[1:0]

L1REQ

0
0

SOFM

0

0

ESOFM

STAT_
RX
[1:0]

SOF

0

0

ESOF

STAT_
RX
[1:0]
SETUP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

STAT_
RX
[1:0]

SETUP

0

0

SETUP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DTOG_RX

USB_EP3R
Res.

CTR_RX
0

STAT_
RX
[1:0]

SETUP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DTOG_RX

DTOG_RX

USB_EP4R
Res.

CTR_RX

0

Res.

USB_EP2R
0

0

SETUP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CTR_RX

USB_EP5R
Res.

0

Res.

Res.

USB_EP1R
0

SUSPM

0

SUSP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

0

Res.

0

Res.

Reset value

Res.

0

Res.

0

RESETM

WKUPM

0

WKUP

USB_EP6R
Res.

DTOG_RX

0

Res.

CTR_RX

DTOG_RX

DTOG_RX

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Reset value

Res.

Reset value

Res.

0

Res.

Reset value
STAT_
RX
[1:0]

RESET

ERRM

USB_EP7R
DTOG_RX

PMAOVRM
0

Res.

0

Res.

Reset value

Res.

CTR_RX

CTR_RX

0

Res.

Reset value

Res.

Reset value

CTR_RX

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CTRM

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

RXDP

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

Res.

Res.

Res.

Res.

Reset value

Res.

0x200x3F

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0x48

USB_ISTR

Res.

0x44
USB_CNTR

Res.

0x40

Res.

0x1C

Res.

0x18

Res.

0x14

Res.

0x10

Res.

0x0C

Res.

0x08

Res.

0x04
USB_EP0R

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

30.6.3

Res.

Universal serial bus full-speed device interface (USB)
RM0091

USB register map

The table below provides the USB register map and reset values.
Table 129. USB register map and reset values

STAT_
TX
[1:0]
0

0

0

0

0

0

0

0

x

0

EA[3:0]

0

STAT_
TX
[1:0]
0

STAT_
TX
[1:0]

STAT_
TX
[1:0]

0

STAT_
TX
[1:0]

0

0

STAT_
TX
[1:0]
0

STAT_
TX
[1:0]

STAT_
TX
[1:0]
0

FN[10:0]

ADD[6:0]

0

0

0

0

x

x

x

x

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

EA[3:0]
0

EA[3:0]
0

EA[3:0]
0

EA[3:0]
0

EA[3:0]
0

EA[3:0]
0

EA[3:0]

EP_ID[3:0]

0x58
USB_BCDR

Reset value

DocID018940 Rev 9

0
0
0

Reset value

0

Res.
Res.
Res.
Res.
Res.
Res.
Res.

0
0
0
0

BESL[3:0]

0
0
0

Res.

0

Res.

0

LPMEN

0
0
0

BCDEN

0

Res.

0

Res.

0

LPMACK

0

DCDEN

REMWAKE

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

BTABLE[15:3]

PDEN

0
SDEN

0

PDET

0

DCDET

0

SDET

0

PS2DET

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Reset value

DPPU

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

USB_LPMCSR

Res.

0x54
USB_BTABLE

Res.

0x50

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

RM0091
Universal serial bus full-speed device interface (USB)

Table 129. USB register map and reset values (continued)

0
0
0

Refer to Section 2.2.2 on page 46 for the register boundary addresses.

891/1004

891

HDMI-CEC controller (HDMI-CEC)

31

RM0091

HDMI-CEC controller (HDMI-CEC)
This applies to STM32F05x, STM32F04x, STM32F07x and STM32F09x devices only.

31.1

Introduction
Consumer Electronics Control (CEC) is part of HDMI (High-Definition Multimedia Interface)
standard as appendix supplement 1. It contains a protocol that provides high-level control
functions between various audiovisual products. CEC operates at low speeds, with
minimum processing and memory overhead.
The HDMI-CEC controller provides hardware support for this protocol.

31.2

HDMI-CEC controller main features
•

Complies with HDMI-CEC v1.4 Specification

•

32 kHz CEC kernel with 2 clock source options
–

HSI RC oscillator with fixed prescaler (HSI/244)

–

LSE oscillator

•

Works in Stop mode for ultra low-power applications

•

Configurable Signal Free Time before start of transmission
–

Automatic by hardware, according to CEC state and transmission history

–

Fixed by software (7 timing options)

•

Configurable Peripheral Address (OAR)

•

Supports Listen mode
–

•

•

•

Configurable Rx-tolerance margin
–

Standard tolerance

–

Extended tolerance

Receive-Error detection
–

Bit rising error (BRE), with optional stop of reception (BRESTP)

–

Short bit period error (SBPE)

–

Long bit period error (LBPE)

Configurable error-bit generation
–

on BRE detection (BREGEN)

–

on LBPE detection (LBPEGEN)

–

always generated on SBPE detection

•

Transmission error detection (TXERR)

•

Arbitration Lost detection (ARBLST)
–

892/1004

Enables reception of CEC messages sent to destination address different from
OAR without interfering with the CEC line

With automatic transmission retry

•

Transmission underrun detection (TXUDR)

•

Reception overrun detection (RXOVR)

DocID018940 Rev 9

RM0091

HDMI-CEC controller (HDMI-CEC)

31.3

HDMI-CEC functional description

31.3.1

HDMI-CEC pin
The CEC bus consists of a single bidirectional line that is used to transfer data in and out of
the device. It is connected to a +3.3 V supply voltage via a 27 kΩ pull-up resistor. The output
stage of the device must have an open-drain or open-collector to allow a wired-and
connection.
The HDMI-CEC controller manages the CEC bidirectional line as an alternate function of a
standard GPIO, assuming that it is configured as Alternate Function Open Drain. The 27 kΩ
pull-up must be added externally to the STM32.
To not interfere with the CEC bus when the application power is removed, it is mandatory to
isolate the CEC pin from the bus in such conditions. This could be done by using a MOS
transistor, as shown on Figure 325.
Table 130. HDMI pin
Name

CEC

31.3.2

Signal type

Remarks
two states:
1 = high impedance
0 = low impedance
A 27 kΩ must be added externally.

bidirectional

HDMI-CEC block diagram
Figure 325. HDMI-CEC block diagram
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DocID018940 Rev 9

893/1004
910

HDMI-CEC controller (HDMI-CEC)

31.3.3

RM0091

Message description
All transactions on the CEC line consist of an initiator and one or more followers. The
initiator is responsible for sending the message structure and the data. The follower is the
recipient of any data and is responsible for setting any acknowledgment bits.
A message is conveyed in a single frame which consists of a start bit followed by a header
block and optionally an opcode and a variable number of operand blocks.
All these blocks are made of a 8-bit payload - most significant bit is transmitted first followed by an end of message (EOM) bit and an acknowledge (ACK) bit.
The EOM bit is set in the last block of a message and kept reset in all others. In the event
that a message contains additional blocks after an EOM is indicated, those additional blocks
should be ignored. The EOM bit may be set in the header block to ‘ping’ other devices, to
make sure they are active.
The acknowledge bit is always set to high impedance by the initiator so that it can be driven
low either by the follower which has read its own address in the header or by the follower
which needs to reject a broadcast message.
The header consists of the source logical address field, and the destination logical address
field. Note that the special address 0xF is used for broadcast messages.
Figure 326. Message structure
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Figure 327. Blocks


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31.3.4

Bit timing
The format of the start bit is unique and identifies the start of a message. It should be
validated by its low duration and its total duration.
All remaining data bits in the message, after the start bit, have consistent timing. The high to
low transition at the end of the data bit is the start of the next data bit except for the final bit
where the CEC line remains high.

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RM0091

HDMI-CEC controller (HDMI-CEC)
Figure 328. Bit timings
PVPV
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31.4

Arbitration
All devices that have to transmit - or retransmit - a message onto the CEC line have to
ensure that it has been inactive for a number of bit periods. This signal free time is defined
as the time starting from the final bit of the previous frame and depends on the initiating
device and the current status as shown in the table below.
Figure 329. Signal free time
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069

Since only one initiator is allowed at any one time, an arbitration mechanism is provided to
avoid conflict when more than one initiator begins transmitting at the same time.
CEC line arbitration commences with the leading edge of the start bit and continues until the
end of the initiator address bits within the header block. During this period, the initiator shall
monitor the CEC line, if whilst driving the line to high impedance it reads it back to 0, it then
assumes it has lost arbitration, stops transmitting and becomes a follower.

DocID018940 Rev 9

895/1004
910

HDMI-CEC controller (HDMI-CEC)

RM0091
Figure 330. Arbitration phase

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The Figure 331 shows an example for a SFT of three nominal bit periods
Figure 331. SFT of three nominal bit periods

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069

A configurable time window is counted before starting the transmission.
In the SFT=0x0 configuration the HDMI-CEC device performs automatic SFT calculation
ensuring compliance with the HDMI-CEC Standard:
•

2.5 data bit periods if the CEC is the last bus initiator with unsuccessful transmission

•

4 data bit periods if the CEC is the new bus initiator

•

6 data bit periods if the CEC is the last bus initiator with successful transmission

This is done to guarantee the maximum priority to a failed transmission and the lowest one
to the last initiator that completed successfully its transmission.
Otherwise there is the possibility to configure the SFT bits to count a fixed timing value.
Possible values are 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5 data bit periods.

31.4.1

SFT option bit
In case of SFTOPT=0 configuration SFT starts being counted when the start-oftransmission command is set by software (TXSOM=1).
In case of SFTOPT=1, SFT starts automatically being counted by the HDMI-CEC device
when a bus-idle or line error condition is detected. If the SFT timer is completed at the time
TXSOM command is set then transmission starts immediately without latency. If the SFT

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RM0091

HDMI-CEC controller (HDMI-CEC)
timer is still running instead, the system waits until the timer elapses before transmission
can start.
In case of SFTOPT=1 a bus-event condition starting the SFT timer is detected in the
following cases:
•

In case of a regular end of transmission/reception, when TXEND/RXEND bits are set at
the minimum nominal data bit duration of the last bit in the message (ACK bit).

•

In case of a transmission error detection, SFT timer starts when the TXERR
transmission error is detected (TXERR=1).

•

In case of a missing acknowledge from the CEC follower, the SFT timer starts when the
TXACKE bit is set, that is at the nominal sampling time of the ACK bit.

•

In case of a transmission underrun error, the SFT timer starts when the TXUDR bit is
set at the end of the ACK bit.

•

In case of a receive error detection implying reception abort, the SFT timer starts at the
same time the error is detected. If an error bit is generated, then SFT starts being
counted at the end of the error bit.

•

In case of a wrong start bit or of any uncodified low impedance bus state from idle, the
SFT timer is restarted as soon as the bus comes back to hi-impedance idleness.

31.5

Error handling

31.5.1

Bit error
If a data bit - excluding the start bit - is considered invalid, the follower is expected to notify
such error by generating a low bit period on the CEC line of 1.4 to 1.6 times the nominal
data bit period, i.e. 3.6 ms nominally.
Figure 332. Error bit timing

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31.5.2

Message error
A message is considered lost and therefore may be retransmitted under the following
conditions:
•

a message is not acknowledged in a directly addressed message

•

a message is negatively acknowledged in a broadcast message

•

a low impedance is detected on the CEC line while it is not expected (line error)

Three kinds of error flag can be detected when the CEC interface is receiving a data bit:

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31.5.3

RM0091

Bit Rising Error (BRE)
BRE (bit rising error): is set when a bit rising edge is detected outside the windows where it
is expected (see Figure 333). BRE flag also generates a CEC interrupt if the BREIE=1.
In the case of a BRE detection, the message reception can be stopped according to the
BRESTP bit value and an error bit can be generated if BREGEN bit is set.
When BRE is detected in a broadcast message with BRESTP=1 an error bit is generated
even if BREGEN=0 to enforce initiator’s retry of the failed transmission. Error bit generation
can be disabled by configuring BREGEN=0, BRDNOGEN=1.

31.5.4

Short Bit Period Error (SBPE)
SBPE is set when a bit falling edge is detected earlier than expected (see Figure 333).
SBPE flag also generates a CEC interrupt if the SBPEIE=1.
An error bit is always generated on the line in case of a SBPE error detection. An Error Bit is
not generated upon SBPE detection only when Listen mode is set (LSTN=1) and the
following conditions are met:

31.5.5

•

A directly addressed message is received containing SBPE

•

A broadcast message is received containing SBPE AND BRDNOGEN=1

Long Bit Period Error (LBPE)
LBPE is set when a bit falling edge is not detected in a valid window (see Figure 333). LBPE
flag also generates a CEC interrupt if the LBPEIE=1.
LBPE always stops the reception, an error bit is generated on the line when LBPEGEN bit is
set.
When LBPE is detected in a broadcast message an error bit is generated even if
LBPEGEN=0 to enforce initiator’s retry of the failed transmission. Error bit generation can
be disabled by configuring LBPEGEN=0, BRDNOGEN=1.

Note:

898/1004

The BREGEN=1, BRESTP=0 configuration must be avoided

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RM0091

HDMI-CEC controller (HDMI-CEC)
Figure 333. Error handling
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Table 131. Error handling timing parameters
Time

RXTOL

ms

Ts

x

0

1

0.3

0

0.4

x

0.6

0

0.8

1

0.9

The latest time for a low - high transition when
indicating a logical 1.

x

1.05

Nominal sampling time.

1

1.2

0

1.3

The earliest time a device is permitted return to a
high impedance state (logical 0).

x

1.5

0

1.7

1

1.8

1

1.85

0

2.05

x

2.4

0

2.75

1

2.95

T1
Tn1
T2
Tns
T3
Tn0
T4
T5
Tnf
T6

Description
Bit start event.
The earliest time for a low - high transition when
indicating a logical 1.
The nominal time for a low - high transition when
indicating a logical 1.

The nominal time a device is permitted return to a
high impedance state (logical 0).
The latest time a device is permitted return to a high
impedance state (logical 0).
The earliest time for the start of a following bit.
The nominal data bit period.
The latest time for the start of a following bit.

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31.5.6

RM0091

Transmission Error Detection (TXERR)
The CEC initiator sets the TXERR flag if detecting low impedance on the CEC line when it is
transmitting high impedance and is not expecting a follower asserted bit. TXERR flag also
generates a CEC interrupt if the TXERRIE=1.
TXERR assertion stops the message transmission. Application is in charge to retry the
failed transmission up to 5 times.
TXERR checks are performed differently depending on the different states of the CEC line
and on the RX tolerance configuration.
Figure 334. TXERR detection
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Table 132. TXERR timing parameters
Time

RXTOL

ms

Ts

x

0

1

0.3

0

0.4

x

0.6

0

0.8

1

0.9

The latest time for a low - high transition when
indicating a logical 1.

x

1.05

Nominal sampling time.

1

1.2

0

1.3

The earliest time a device is permitted return to a
high impedance state (logical 0).

T1
Tn1
T2
Tns
T3

900/1004

Description
Bit start event.
The earliest time for a low - high transition when
indicating a logical 1.
The nominal time for a low - high transition when
indicating a logical 1.

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HDMI-CEC controller (HDMI-CEC)
Table 132. TXERR timing parameters (continued)
Time

RXTOL

ms

Tn0

x

1.5

0

1.7

1

1.8

1

1.85

0

2.05

x

2.4

0

2.75

1

2.95

T4
T5
Tnf
T6

31.6

Description
The nominal time a device is permitted return to a
high impedance state (logical 0).
The latest time a device is permitted return to a high
impedance state (logical 0).
The earliest time for the start of a following bit.
The nominal data bit period.
The latest time for the start of a following bit.

HDMI-CEC interrupts
An interrupt can be produced:
•

during reception if a Receive Block Transfer is finished or if a Receive Error occurs.

•

during transmission if a Transmit Block Transfer is finished or if a Transmit Error
occurs.
Table 133. HDMI-CEC interrupts
Interrupt event

Event flag

Enable Control bit

RXBR

RXBRIE

End of reception

RXEND

RXENDIE

Rx-Overrun

RXOVR

RXOVRIE

BRE

BREIE

Rx-Short Bit Period Error

SBPE

SBPEIE

Rx-Long Bit Period Error

LBPE

LBPEIE

Rx-Missing Acknowledge Error

RXACKE

RXACKEIE

Arbitration lost

ARBLST

ARBLSTIE

TXBR

TXBRIE

End of transmission

TXEND

TXENDIE

Tx-Buffer Underrun

TXUDR

TXUDRIE

Tx-Error

TXERR

TXERRIE

TXACKE

TXACKEIE

Rx-Byte Received

RxBit Rising Error

Tx-Byte Request

Tx-Missing Acknowledge Error

For code example refer to the Appendix sections A.13.1: HDMI-CEC configure CEC code
example, A.13.2: HDMI-CEC transmission with interrupt enabled code example and A.13.3:
HDMI-CEC interrupt management code example.

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31.7

RM0091

HDMI-CEC registers
Refer to Section 1.1 on page 42 for a list of abbreviations used in register descriptions.

31.7.1

CEC control register (CEC_CR)
Address offset: 0x00
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

TX
EOM

TX
SOM

CEC
EN

rs

rs

rw

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Bits 31:3 Reserved, must be kept at reset value.
Bit 2 TXEOM: Tx End Of Message
The TXEOM bit is set by software to command transmission of the last byte of a CEC message.
TXEOM is cleared by hardware at the same time and under the same conditions as for TXSOM.
0: TXDR data byte is transmitted with EOM=0
1: TXDR data byte is transmitted with EOM=1
Note: TXEOM must be set when CECEN=1
TXEOM must be set before writing transmission data to TXDR
If TXEOM is set when TXSOM=0, transmitted message will consist of 1 byte (HEADER) only
(PING message)
Bit 1 TXSOM: Tx Start Of Message
TXSOM is set by software to command transmission of the first byte of a CEC message. If the CEC
message consists of only one byte, TXEOM must be set before of TXSOM.
Start-Bit is effectively started on the CEC line after SFT is counted. If TXSOM is set while a message
reception is ongoing, transmission will start after the end of reception.
TXSOM is cleared by hardware after the last byte of the message is sent with a positive acknowledge
(TXEND=1), in case of transmission underrun (TXUDR=1), negative acknowledge (TXACKE=1), and
transmission error (TXERR=1). It is also cleared by CECEN=0. It is not cleared and transmission is
automatically retried in case of arbitration lost (ARBLST=1).

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HDMI-CEC controller (HDMI-CEC)

TXSOM can be also used as a status bit informing application whether any transmission request is
pending or under execution. The application can abort a transmission request at any time by clearing
the CECEN bit.
0: No CEC transmission is on-going
1: CEC transmission command
Note: TXSOM must be set when CECEN=1
TXSOM must be set when transmission data is available into TXDR
HEADER’s first four bits containing own peripheral address are taken from TXDR[7:4], not from
CEC_CFGR.OAR which is used only for reception
Bit 0 CECEN: CEC Enable
The CECEN bit is set and cleared by software. CECEN=1 starts message reception and enables the
TXSOM control. CECEN=0 disables the CEC peripheral, clears all bits of CEC_CR register and aborts
any on-going reception or transmission.
0: CEC peripheral is off
1: CEC peripheral is on

31.7.2

CEC configuration register (CEC_CFGR)
This register is used to configure the HDMI-CEC controller.
Address offset: 0x04
Reset value: 0x0000 0000

Caution: It is mandatory to write CEC_CFGR only when CECEN=0.
31

30

29

28

27

26

25

24

LSTN

Res.

22

21

20

19

18

17

16

2

1

0

OAR[14:0]

rw
15

23

rw
14
Res.

13
Res.

12
Res.

11
Res.

10
Res.

9

8

7

6

5

4

3

Res.

SFT
OPT

BRDN
OGEN

LBPE
GEN

BRE
GEN

BRE
STP

RX
TOL

SFT[2:0]

rw

rw

rw

rw

rw

rw

rw

Bit 31 LSTN: Listen mode
LSTN bit is set and cleared by software.
0: CEC peripheral receives only message addressed to its own address (OAR). Messages
addressed to different destination are ignored. Broadcast messages are always received.
1: CEC peripheral receives messages addressed to its own address (OAR) with positive
acknowledge. Messages addressed to different destination are received, but without interfering with
the CEC bus: no acknowledge sent.
Bits 30:16 OAR: Own addresses configuration
The OAR bits are set by software to select which destination logical addresses has to be considered in
receive mode. Each bit, when set, enables the CEC logical address identified by the given bit position.
At the end of HEADER reception, the received destination address is compared with the enabled
addresses. In case of matching address, the incoming message is acknowledged and received. In
case of non-matching address, the incoming message is received only in listen mode (LSTN=1), but
without acknowledge sent. Broadcast messages are always received.
Example:
OAR = 0b000 0000 0010 0001 means that CEC acknowledges addresses 0x0 and 0x5.
Consequently, each message directed to one of these addresses is received.
Bits 15:9 Reserved, must be kept at reset value.

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Bit 8 SFTOP: SFT Option Bit
The SFTOPT bit is set and cleared by software.
0: SFT timer starts when TXSOM is set by software
1: SFT timer starts automatically at the end of message transmission/reception.
Bit 7 BRDNOGEN: Avoid Error-Bit Generation in Broadcast
The BRDNOGEN bit is set and cleared by software.
0: BRE detection with BRESTP=1 and BREGEN=0 on a broadcast message generates an Error-Bit
on the CEC line. LBPE detection with LBPEGEN=0 on a broadcast message generates an Error-Bit
on the CEC line
1: Error-Bit is not generated in the same condition as above. An Error-Bit is not generated even in
case of an SBPE detection in a broadcast message if listen mode is set.
Bit 6 LBPEGEN: Generate Error-Bit on Long Bit Period Error
The LBPEGEN bit is set and cleared by software.
0: LBPE detection does not generate an Error-Bit on the CEC line
1: LBPE detection generates an Error-Bit on the CEC line
Note: If BRDNOGEN=0, an Error-bit is generated upon LBPE detection in broadcast even if
LBPEGEN=0
Bit 5 BREGEN: Generate Error-Bit on Bit Rising Error
The BREGEN bit is set and cleared by software.
0: BRE detection does not generate an Error-Bit on the CEC line
1: BRE detection generates an Error-Bit on the CEC line (if BRESTP is set)
Note: If BRDNOGEN=0, an Error-bit is generated upon BRE detection with BRESTP=1 in broadcast
even if BREGEN=0

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HDMI-CEC controller (HDMI-CEC)

Bit 4 BRESTP: Rx-Stop on Bit Rising Error
The BRESTP bit is set and cleared by software.
0: BRE detection does not stop reception of the CEC message. Data bit is sampled at 1.05 ms.
1: BRE detection stops message reception
Bit 3 RXTOL: Rx-Tolerance
The RXTOL bit is set and cleared by software.
0: Standard tolerance margin:
–
Start-Bit, +/- 200 µs rise, +/- 200 µs fall.
–
Data-Bit: +/- 200 µs rise. +/- 350 µs fall.
1: Extended Tolerance
–
Start-Bit: +/- 400 µs rise, +/- 400 µs fall
–
Data-Bit: +/-300 µs rise, +/- 500 µs fall
Bits 2:0 SFT: Signal Free Time
SFT bits are set by software. In the SFT=0x0 configuration the number of nominal data bit periods
waited before transmission is ruled by hardware according to the transmission history. In all the other
configurations the SFT number is determined by software.
″
0x0
–
2.5 Data-Bit periods if CEC is the last bus initiator with unsuccessful transmission
(ARBLST=1, TXERR=1, TXUDR=1 or TXACKE= 1)
–
4 Data-Bit periods if CEC is the new bus initiator
–
6 Data-Bit periods if CEC is the last bus initiator with successful transmission (TXEOM=1)
″
0x1: 0.5 nominal data bit periods
″
0x2: 1.5 nominal data bit periods
″
0x3: 2.5 nominal data bit periods
″
0x4: 3.5 nominal data bit periods
″
0x5: 4.5 nominal data bit periods
″
0x6: 5.5 nominal data bit periods
″
0x7: 6.5 nominal data bit periods

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31.7.3

RM0091

CEC Tx data register (CEC_TXDR)
Address offset: 0x8
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.
w

w

w

w

w

w

w

TXD[7:0]
w

Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 TXD[7:0]: Tx Data register.
TXD is a write-only register containing the data byte to be transmitted.
Note: TXD must be written when TXSTART=1

31.7.4

CEC Rx Data Register (CEC_RXDR)
Address offset: 0xC
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

7

6

5

4

3

2

1

0

r

r

r

15

14

13

12

11

10

9

8

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

RXD[7:0]
r

r

r

r

r

Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 RXD[7:0]: Rx Data register.
RXD is read-only and contains the last data byte which has been received from the CEC line.

31.7.5

CEC Interrupt and Status Register (CEC_ISR)
Address offset: 0x10
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

TX
ACKE

TX
ERR

TX
UDR

TX
END

TXBR

ARB
LST

RX
ACKE

LBPE

SBPE

BRE

RX
OVR

RX
END

RXBR

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

rc_w1

Res.

Res.

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HDMI-CEC controller (HDMI-CEC)

Bits 31:13 Reserved, must be kept at reset value.
Bit 12 TXACKE: Tx-Missing Acknowledge Error
In transmission mode, TXACKE is set by hardware to inform application that no acknowledge was
received. In case of broadcast transmission, TXACKE informs application that a negative
acknowledge was received. TXACKE aborts message transmission and clears TXSOM and TXEOM
controls.
TXACKE is cleared by software write at 1.
Bit 11 TXERR: Tx-Error
In transmission mode, TXERR is set by hardware if the CEC initiator detects low impedance on the
CEC line while it is released. TXERR aborts message transmission and clears TXSOM and TXEOM
controls.
TXERR is cleared by software write at 1.
Bit 10 TXUDR: Tx-Buffer Underrun
In transmission mode, TXUDR is set by hardware if application was not in time to load TXDR before of
next byte transmission. TXUDR aborts message transmission and clears TXSOM and TXEOM control
bits.
TXUDR is cleared by software write at 1
Bit 9 TXEND: End of Transmission
TXEND is set by hardware to inform application that the last byte of the CEC message has been
successfully transmitted. TXEND clears the TXSOM and TXEOM control bits.
TXEND is cleared by software write at 1.
Bit 8 TXBR: Tx-Byte Request
TXBR is set by hardware to inform application that the next transmission data has to be written to
TXDR. TXBR is set when the 4th bit of currently transmitted byte is sent. Application must write the
next byte to TXDR within 6 nominal data-bit periods before transmission underrun error occurs
(TXUDR).
TXBR is cleared by software write at 1.
Bit 7 ARBLST: Arbitration Lost
ARBLST is set by hardware to inform application that CEC device is switching to reception due to
arbitration lost event following the TXSOM command. ARBLST can be due either to a contending
CEC device starting earlier or starting at the same time but with higher HEADER priority. After
ARBLST assertion TXSOM bit keeps pending for next transmission attempt.
ARBLST is cleared by software write at 1.
Bit 6 RXACKE: Rx-Missing Acknowledge
In receive mode, RXACKE is set by hardware to inform application that no acknowledge was seen on
the CEC line. RXACKE applies only for broadcast messages and in listen mode also for not directly
addressed messages (destination address not enabled in OAR). RXACKE aborts message reception.
RXACKE is cleared by software write at 1.
Bit 5 LBPE: Rx-Long Bit Period Error
LBPE is set by hardware in case a Data-Bit waveform is detected with Long Bit Period Error. LBPE is
set at the end of the maximum bit-extension tolerance allowed by RXTOL, in case falling edge is still
longing. LBPE always stops reception of the CEC message. LBPE generates an Error-Bit on the CEC
line if LBPEGEN=1. In case of broadcast, Error-Bit is generated even in case of LBPEGEN=0.
LBPE is cleared by software write at 1.
Bit 4 SBPE: Rx-Short Bit Period Error
SBPE is set by hardware in case a Data-Bit waveform is detected with Short Bit Period Error. SBPE is
set at the time the anticipated falling edge occurs. SBPE generates an Error-Bit on the CEC line.
SBPE is cleared by software write at 1.

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RM0091

Bit 3 BRE: Rx-Bit Rising Error
BRE is set by hardware in case a Data-Bit waveform is detected with Bit Rising Error. BRE is set either
at the time the misplaced rising edge occurs, or at the end of the maximum BRE tolerance allowed by
RXTOL, in case rising edge is still longing. BRE stops message reception if BRESTP=1. BRE
generates an Error-Bit on the CEC line if BREGEN=1.
BRE is cleared by software write at 1.
Bit 2 RXOVR: Rx-Overrun
RXOVR is set by hardware if RXBR is not yet cleared at the time a new byte is received on the CEC
line and stored into RXD. RXOVR assertion stops message reception so that no acknowledge is sent.
In case of broadcast, a negative acknowledge is sent.
RXOVR is cleared by software write at 1.
Bit 1 RXEND: End Of Reception
RXEND is set by hardware to inform application that the last byte of a CEC message is received from
the CEC line and stored into the RXD buffer. RXEND is set at the same time of RXBR.
RXEND is cleared by software write at 1.
Bit 0 RXBR: Rx-Byte Received
The RXBR bit is set by hardware to inform application that a new byte has been received from the
CEC line and stored into the RXD buffer.
RXBR is cleared by software write at 1.

31.7.6

CEC interrupt enable register (CEC_IER)
Address offset: 0x14
Reset value: 0x0000 0000

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

3

2

1

0

Res.

Res.

Res.

TXACK TXERR
TX
TXEND
IE
IE
UDRIE
IE
rw

rw

rw

rw

8

7

6

5

4

TXBR
IE

ARBLST
IE

RXACK
IE

LBPE
IE

SBPE
IE

rw

rw

rw

rw

rw

Bits 31:13 Reserved, must be kept at reset value.
Bit 12 TXACKIE: Tx-Missing Acknowledge Error Interrupt Enable
The TXACKEIE bit is set and cleared by software.
0: TXACKE interrupt disabled
1: TXACKE interrupt enabled
Bit 11 TXERRIE: Tx-Error Interrupt Enable
The TXERRIE bit is set and cleared by software.
0: TXERR interrupt disabled
1: TXERR interrupt enabled
Bit 10 TXUDRIE: Tx-Underrun Interrupt Enable
The TXUDRIE bit is set and cleared by software.
0: TXUDR interrupt disabled
1: TXUDR interrupt enabled

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RXOVR RXEND RXBR
BREIE
IE
IE
IE
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RM0091

HDMI-CEC controller (HDMI-CEC)

Bit 9 TXENDIE: Tx-End Of Message Interrupt Enable
The TXENDIE bit is set and cleared by software.
0: TXEND interrupt disabled
1: TXEND interrupt enabled
Bit 8 TXBRIE: Tx-Byte Request Interrupt Enable
The TXBRIE bit is set and cleared by software.
0: TXBR interrupt disabled
1: TXBR interrupt enabled
Bit 7 ARBLSTIE: Arbitration Lost Interrupt Enable
The ARBLSTIE bit is set and cleared by software.
0: ARBLST interrupt disabled
1: ARBLST interrupt enabled
Bit 6 RXACKIE: Rx-Missing Acknowledge Error Interrupt Enable
The RXACKIE bit is set and cleared by software.
0: RXACKE interrupt disabled
1: RXACKE interrupt enabled
Bit 5 LBPEIE: Long Bit Period Error Interrupt Enable
The LBPEIE bit is set and cleared by software.
0: LBPE interrupt disabled
1: LBPE interrupt enabled
Bit 4 SBPEIE: Short Bit Period Error Interrupt Enable
The SBPEIE bit is set and cleared by software.
0: SBPE interrupt disabled
1: SBPE interrupt enabled
Bit 3 BREIE: Bit Rising Error Interrupt Enable
The BREIE bit is set and cleared by software.
0: BRE interrupt disabled
1: BRE interrupt enabled
Bit 2 RXOVRIE: Rx-Buffer Overrun Interrupt Enable
The RXOVRIE bit is set and cleared by software.
0: RXOVR interrupt disabled
1: RXOVR interrupt enabled
Bit 1 RXENDIE: End Of Reception Interrupt Enable
The RXENDIE bit is set and cleared by software.
0: RXEND interrupt disabled
1: RXEND interrupt enabled
Bit 0 RXBRIE: Rx-Byte Received Interrupt Enable
The RXBRIE bit is set and cleared by software.
0: RXBR interrupt disabled
1: RXBR interrupt enabled
Caution: (*) It is mandatory to write CEC_IER only when CECEN=0

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CEC_IER

DocID018940 Rev 9
TXBR
ARBLST
RXACKE
LBPE
SBPE
BRE
RXOVR
RXEND
RXBR

0
0
0
0
0
0
0
0
0
0
0
0
0

TXBRIE
ARBLSTIE
RXACKIE
LBPEIE
SBPEIE
BREIE
RXOVRIE
RXENDIE
RXBRIE

Reset value
TXEND

Reset value

TXENDIE

Res.

Res.

CEC_TXDR

Res.

0

TXUDR

0

TXUDRIE

0

Res.

0

TXERR

0

TXACKE

0

TXACKIE

0

TXERRIE

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.

0

Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.
Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

LSTN

Reset value
SFTOPT
BRDNOGEN
LBPEGEN
BREGEN
BRESTP
RXTOL

Res.

Res.

Res.

Res.

Res.

Res.

Res.

OAR[14:0]

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CEC_CFGR

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CEC_ISR

Res.

0x10
CEC_RXDR

Res.

0x0C
Res.

0x08

Res.

0x04

Reset value
0

Reset value

Refer to Section 2.2.2 on page 46 for the register boundary addresses.
0
0
0

0
0
0
0
0
0

TXSOM
CECEN

Reset value
TXEOM

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

CEC_CR

Res.

0x00

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

Offset

Res.

31.7.7

Res.

HDMI-CEC controller (HDMI-CEC)
RM0091

HDMI-CEC register map
The following table summarizes the HDMI-CEC registers.
Table 134. HDMI-CEC register map and reset values

0
0
0

SFT[2:0]

TXD[7:0]
0

0
0
0

0
0
0

RXD[7:0]

0
0
0
0
0
0
0
0

0
0
0
0
0
0
0
0
0
0
0
0
0

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Debug support (DBG)

32

Debug support (DBG)

32.1

Overview
The STM32F0xx devices are built around a Cortex®-M0 core which contains hardware
extensions for advanced debugging features. The debug extensions allow the core to be
stopped either on a given instruction fetch (breakpoint) or data access (watchpoint). When
stopped, the core’s internal state and the system’s external state may be examined. Once
examination is complete, the core and the system may be restored and program execution
resumed.
The debug features are used by the debugger host when connecting to and debugging the
STM32F0xx MCUs.
One interface for debug is available:
•

Serial wire

Figure 335. Block diagram of STM32F0xx MCU and Cortex®-M0-level debug support

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069

1. The debug features embedded in the Cortex®-M0 core are a subset of the ARM CoreSight Design Kit.
®

The ARM Cortex -M0 core provides integrated on-chip debug support. It is comprised of:
•

SW-DP: Serial wire

•

BPU: Break point unit

•

DWT: Data watchpoint trigger

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It also includes debug features dedicated to the STM32F0xx:
•

Flexible debug pinout assignment

•

MCU debug box (support for low-power modes, control over peripheral clocks, etc.)

Note:

For further information on debug functionality supported by the ARM Cortex®-M0 core, refer
to the Cortex®-M0 Technical Reference Manual (see Section 32.2: Reference ARM
documentation).

32.2

Reference ARM documentation

32.3

•

Cortex®-M0 Technical Reference Manual (TRM)
It is available from:
http://infocenter.arm.com

•

ARM Debug Interface V5

•

ARM CoreSight Design Kit revision r1p1 Technical Reference Manual

Pinout and debug port pins
The STM32F0xx MCUs are available in various packages with different numbers of
available pins.

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32.3.1

Debug support (DBG)

SWD port pins
Two pins are used as outputs for the SW-DP as alternate functions of general purpose I/Os.
These pins are available on all packages.
Table 135. SW debug port pins
SW debug port
SW-DP pin name
Type

32.3.2

SWDIO

IO

SWCLK

I

Debug assignment

Pin
assignment

Serial Wire Data Input/Output

PA13

Serial Wire Clock

PA14

SW-DP pin assignment
After reset (SYSRESETn or PORESETn), the pins used for the SW-DP are assigned as
dedicated pins which are immediately usable by the debugger host.
However, the MCU offers the possibility to disable the SWD port and can then release the
associated pins for general-purpose I/O (GPIO) usage. For more details on how to disable
SW-DP port pins, please refer to Section 8.3.2: I/O pin alternate function multiplexer and
mapping on page 150.

32.3.3

Internal pull-up & pull-down on SWD pins
Once the SW I/O is released by the user software, the GPIO controller takes control of these
pins. The reset states of the GPIO control registers put the I/Os in the equivalent states:
•

SWDIO: input pull-up

•

SWCLK: input pull-down

Having embedded pull-up and pull-down resistors removes the need to add external
resistors.

32.4

ID codes and locking mechanism
There are several ID codes inside the MCU. ST strongly recommends the tool
manufacturers (for example Keil, IAR, Raisonance) to lock their debugger using the MCU
device ID located at address 0x40015800.
Only the DEV_ID[15:0] should be used for identification by the debugger/programmer tools
(the revision ID must not be taken into account).

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32.4.1

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MCU device ID code
The STM32F0xx products integrate an MCU ID code. This ID identifies the ST MCU part
number and the die revision.
This code is accessible by the software debug port (two pins) or by the user software.
For code example refer to the Appendix section A.12.1: DBG read device ID code example.

DBGMCU_IDCODE
Address: 0x40015800
Only 32-bit access supported. Read-only
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

REV_ID
r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.
r

r

r

r

r

r

r

r

r

r

r

DEV_ID
r

Bits 31:16 REV_ID[15:0] Revision identifier
This field indicates the revision of the device. Refer to Table 136.
Bits 15:12 Reserved: read 0b0110.
Bits 11:0 DEV_ID[11:0]: Device identifier
This field indicates the device ID. Refer to Table 136.

Table 136. DEV_ID and REV_ID field values
Device

DEV_ID

Revision code

Revision number

REV_ID

STM32F03x

0x444

A or 1

1.0

0x1000

STM32F04x

0x445

A

1.0

0x1000

STM32F05x

0x440

A

1.0

0x1000

B or 1

1.1

0x1001

A

1.0

0x1000

Z

1.1

0x1001

B

2.0

0x2000

Y or 1

2.1

0x2001

A

1.0

0x1000

STM32F07x

STM32F09x

914/1004

0x448

0x442

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Debug support (DBG)

32.5

SWD port

32.5.1

SWD protocol introduction
This synchronous serial protocol uses two pins:
•

SWCLK: clock from host to target

•

SWDIO: bidirectional

The protocol allows two banks of registers (DPACC registers and APACC registers) to be
read and written to.
Bits are transferred LSB-first on the wire.
For SWDIO bidirectional management, the line must be pulled-up on the board (100 kΩ
recommended by ARM).
Each time the direction of SWDIO changes in the protocol, a turnaround time is inserted
where the line is not driven by the host nor the target. By default, this turnaround time is one
bit time, however this can be adjusted by configuring the SWCLK frequency.

32.5.2

SWD protocol sequence
Each sequence consist of three phases:
1.

Packet request (8 bits) transmitted by the host

2.

Acknowledge response (3 bits) transmitted by the target

3.

Data transfer phase (33 bits) transmitted by the host or the target
Table 137. Packet request (8-bits)
Bit

Name

Description

0

Start

Must be “1”

1

APnDP

0: DP Access
1: AP Access

2

RnW

0: Write Request
1: Read Request

4:3

A[3:2]

Address field of the DP or AP registers (refer to Table 141 on
page 918)

5

Parity

Single bit parity of preceding bits

6

Stop

0

7

Park

Not driven by the host. Must be read as “1” by the target
because of the pull-up

Refer to the Cortex®-M0 TRM for a detailed description of DPACC and APACC registers.
The packet request is always followed by the turnaround time (default 1 bit) where neither
the host nor target drive the line.

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Table 138. ACK response (3 bits)

Bit
0..2

Name

Description
001: FAULT
010: WAIT
100: OK

ACK

The ACK Response must be followed by a turnaround time only if it is a READ transaction
or if a WAIT or FAULT acknowledge has been received.
Table 139. DATA transfer (33 bits)
Bit
0..31
32

Name

Description

WDATA or
RDATA

Write or Read data

Parity

Single parity of the 32 data bits

The DATA transfer must be followed by a turnaround time only if it is a READ transaction.

32.5.3

SW-DP state machine (reset, idle states, ID code)
The State Machine of the SW-DP has an internal ID code which identifies the SW-DP. It
follows the JEP-106 standard. This ID code is the default ARM one and is set to
0x0BB11477 (corresponding to Cortex®-M0).

Note:

Note that the SW-DP state machine is inactive until the target reads this ID code.
•

The SW-DP state machine is in RESET STATE either after power-on reset, or after the
line is high for more than 50 cycles

•

The SW-DP state machine is in IDLE STATE if the line is low for at least two cycles
after RESET state.

•

After RESET state, it is mandatory to first enter into an IDLE state AND to perform a
READ access of the DP-SW ID CODE register. Otherwise, the target will issue a
FAULT acknowledge response on another transactions.

Further details of the SW-DP state machine can be found in the Cortex®-M0 TRM and the
CoreSight Design Kit r1p0 TRM.

32.5.4

916/1004

DP and AP read/write accesses
•

Read accesses to the DP are not posted: the target response can be immediate (if
ACK=OK) or can be delayed (if ACK=WAIT).

•

Read accesses to the AP are posted. This means that the result of the access is
returned on the next transfer. If the next access to be done is NOT an AP access, then
the DP-RDBUFF register must be read to obtain the result.
The READOK flag of the DP-CTRL/STAT register is updated on every AP read access
or RDBUFF read request to know if the AP read access was successful.

•

The SW-DP implements a write buffer (for both DP or AP writes), that enables it to
accept a write operation even when other transactions are still outstanding. If the write
buffer is full, the target acknowledge response is “WAIT”. With the exception of

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Debug support (DBG)
IDCODE read or CTRL/STAT read or ABORT write which are accepted even if the write
buffer is full.
•

32.5.5

Because of the asynchronous clock domains SWCLK and HCLK, two extra SWCLK
cycles are needed after a write transaction (after the parity bit) to make the write
effective internally. These cycles should be applied while driving the line low (IDLE
state)
This is particularly important when writing the CTRL/STAT for a power-up request. If the
next transaction (requiring a power-up) occurs immediately, it will fail.

SW-DP registers
Access to these registers are initiated when APnDP=0
Table 140. SW-DP registers
CTRLSEL bit
of SELECT
register

A[3:2]

R/W

Register

00

Read

IDCODE

00

Write

ABORT

Notes
The manufacturer code is set to the default
ARM code for Cortex-M0:
0x0BB11477 (identifies the SW-DP)

01

Read/Write

0

Purpose is to:
– request a system or debug power-up
– configure the transfer operation for AP
accesses
DP-CTRL/STAT
– control the pushed compare and pushed
verify operations.
– read some status flags (overrun, power-up
acknowledges)

01

Read/Write

1

WIRE
CONTROL

Purpose is to configure the physical serial
port protocol (like the duration of the
turnaround time)

10

Read

READ
RESEND

Enables recovery of the read data from a
corrupted debugger transfer, without
repeating the original AP transfer.

10

Write

SELECT

The purpose is to select the current access
port and the active 4-words register window

11

Read/Write

This read buffer is useful because AP
accesses are posted (the result of a read AP
request is available on the next AP
READ BUFFER transaction).
This read buffer captures data from the AP,
presented as the result of a previous read,
without initiating a new transaction

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32.5.6

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SW-AP registers
Access to these registers are initiated when APnDP=1
There are many AP Registers addressed as the combination of:
•

The shifted value A[3:2]

•

The current value of the DP SELECT register.
Table 141. 32-bit debug port registers addressed through the shifted value A[3:2]
Address A[3:2] value
0x0

00

Reserved, must be kept at reset value.

01

DP CTRL/STAT register. Used to:
– Request a system or debug power-up
– Configure the transfer operation for AP accesses
– Control the pushed compare and pushed verify operations.
– Read some status flags (overrun, power-up acknowledges)

0x8

10

DP SELECT register: Used to select the current access port and the
active 4-words register window.
– Bits 31:24: APSEL: select the current AP
– Bits 23:8: reserved
– Bits 7:4: APBANKSEL: select the active 4-words register window on the
current AP
– Bits 3:0: reserved

0xC

11

DP RDBUFF register: Used to allow the debugger to get the final result
after a sequence of operations (without requesting new JTAG-DP
operation)

0x4

32.6

Description

Core debug
Core debug is accessed through the core debug registers. Debug access to these registers
is by means of the debug access port. It consists of four registers:
Table 142. Core debug registers

918/1004

Register

Description

DHCSR

The 32-bit Debug Halting Control and Status Register
This provides status information about the state of the processor enable core debug
halt and step the processor

DCRSR

The 17-bit Debug Core Register Selector Register:
This selects the processor register to transfer data to or from.

DCRDR

The 32-bit Debug Core Register Data Register:
This holds data for reading and writing registers to and from the processor selected
by the DCRSR (Selector) register.

DEMCR

The 32-bit Debug Exception and Monitor Control Register:
This provides Vector Catching and Debug Monitor Control.

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Debug support (DBG)
These registers are not reset by a system reset. They are only reset by a power-on reset.
Refer to the Cortex®-M0 TRM for further details.
To Halt on reset, it is necessary to:

32.7

•

enable the bit0 (VC_CORRESET) of the Debug and Exception Monitor Control
Register

•

enable the bit0 (C_DEBUGEN) of the Debug Halting Control and Status Register

BPU (Break Point Unit)
The Cortex-M0 BPU implementation provides four breakpoint registers. The BPU is a
subset of the Flash Patch and Breakpoint (FPB) block available in ARMv7-M (Cortex-M3 &
Cortex-M4).

32.7.1

BPU functionality
The processor breakpoints implement PC based breakpoint functionality.
Refer the ARMv6-M ARM and the ARM CoreSight Components Technical Reference
Manual for more information about the BPU CoreSight identification registers, and their
addresses and access types.

32.8

DWT (Data Watchpoint)
The Cortex-M0 DWT implementation provides two watchpoint register sets.

32.8.1

DWT functionality
The processor watchpoints implement both data address and PC based watchpoint
functionality, a PC sampling register, and support comparator address masking, as
described in the ARMv6-M ARM.

32.8.2

DWT Program Counter Sample Register
A processor that implements the data watchpoint unit also implements the ARMv6-M
optional DWT Program Counter Sample Register (DWT_PCSR). This register permits a
debugger to periodically sample the PC without halting the processor. This provides coarse
grained profiling. See the ARMv6-M ARM for more information.
The Cortex-M0 DWT_PCSR records both instructions that pass their condition codes and
those that fail.

32.9

MCU debug component (DBGMCU)
The MCU debug component helps the debugger provide support for:
•

Low-power modes

•

Clock control for timers, watchdog and I2C during a breakpoint

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Debug support for low-power modes
To enter low-power mode, the instruction WFI or WFE must be executed.
The MCU implements several low-power modes which can either deactivate the CPU clock
or reduce the power of the CPU.
The core does not allow FCLK or HCLK to be turned off during a debug session. As these
are required for the debugger connection, during a debug, they must remain active. The
MCU integrates special means to allow the user to debug software in low-power modes.
For this, the debugger host must first set some debug configuration registers to change the
low-power mode behavior:
•

In Sleep mode: FCLK and HCLK are still active. Consequently, this mode does not
impose any restrictions on the standard debug features.

•

In Stop/Standby mode, the DBG_STOP bit must be previously set by the debugger.

This enables the internal RC oscillator clock to feed FCLK and HCLK in Stop mode.
For code example refer to the Appendix section A.12.2: DBG debug in Low-power mode
code example.

32.9.2

Debug support for timers, watchdog and I2C
During a breakpoint, it is necessary to choose how the counter of timers and watchdog
should behave:
•

They can continue to count inside a breakpoint. This is usually required when a PWM is
controlling a motor, for example.

•

They can stop to count inside a breakpoint. This is required for watchdog purposes.

For the I2C, the user can choose to block the SMBUS timeout during a breakpoint.

32.9.3

Debug MCU configuration register (DBGMCU_CR)
This register allows the configuration of the MCU under DEBUG. This concerns:
•

Low-power mode support

This DBGMCU_CR is mapped at address 0x4001 5804.
It is asynchronously reset by the PORESET (and not the system reset). It can be written by
the debugger under system reset.
If the debugger host does not support these features, it is still possible for the user software
to write to these registers.
Address: 0x40015804
Only 32-bit access supported
POR Reset: 0x0000 0000 (not reset by system reset)

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31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

DBG_
STAND
BY

DBG_
STOP

Res.

rw

rw

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Bits 31:3 Reserved, must be kept at reset value.
Bit 2 DBG_STANDBY: Debug Standby mode
0: (FCLK=Off, HCLK=Off) The whole digital part is unpowered.
From software point of view, exiting from Standby is identical than fetching reset vector
(except a few status bit indicated that the MCU is resuming from Standby)
1: (FCLK=On, HCLK=On) In this case, the digital part is not unpowered and FCLK and
HCLK are provided by the internal RC oscillator which remains active. In addition, the MCU
generate a system reset during Standby mode so that exiting from Standby is identical than
fetching from reset
Bit 1 DBG_STOP: Debug Stop mode
0: (FCLK=Off, HCLK=Off) In STOP mode, the clock controller disables all clocks (including
HCLK and FCLK). When exiting from STOP mode, the clock configuration is identical to the
one after RESET (CPU clocked by the 8 MHz internal RC oscillator (HSI)). Consequently,
the software must reprogram the clock controller to enable the PLL, the Xtal, etc.
1: (FCLK=On, HCLK=On) In this case, when entering STOP mode, FCLK and HCLK are
provided by the internal RC oscillator which remains active in STOP mode. When exiting
STOP mode, the software must reprogram the clock controller to enable the PLL, the Xtal,
etc. (in the same way it would do in case of DBG_STOP=0)

32.9.4

Debug MCU APB1 freeze register (DBGMCU_APB1_FZ)
The DBGMCU_APB1_FZ register is used to configure the MCU under DEBUG. It concerns
some APB peripherals:
•

Timer clock counter freeze

•

I2C SMBUS timeout freeze

•

System window watchdog and independent watchdog counter freeze support

This DBGMCU_APB1_FZ is mapped at address 0x4001 5808.
The register is asynchronously reset by the POR (and not the system reset). It can be
written by the debugger under system reset.
Address offset: 0x08
Only 32-bit access are supported.
Power on reset (POR): 0x0000 0000 (not reset by system reset)

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30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

DBG_CAN_STOP

Res.

Res.

Res.

DBG_I2C1_SMBUS_TIMEOUT

Res.

Res.

Res.

Res.

Res.

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

DBG_WWDG_STOP

DBG_RTC_STOP

Res.

DBG_TIM14_STOP

Res.

Res.

DBG_TIM7_STOP

DBG_TIM6_STOP

Res.

Res.

DBG_TIM3_STOP

DBG_TIM2_STOP

RM0091

DBG_IWDG_STOP

Debug support (DBG)

rw

rw

rw

rw

rw

rw

rw

rw

rw

Bits 31:26 Reserved, must be kept at reset value.
Bit 25 DBG_CAN_STOP: CAN stopped when core is halted
0: Same behavior as in normal mode
1: The CAN receive registers are frozen
Bits 22:24 Reserved, must be kept at reset value.
Bit 21 DBG_I2C1_SMBUS_TIMEOUT: SMBUS timeout mode stopped when core is halted
0: Same behavior as in normal mode
1: The SMBUS timeout is frozen
Bits 20:13 Reserved, must be kept at reset value.
Bit 12 DBG_IWDG_STOP: Debug independent watchdog stopped when core is halted
0: The independent watchdog counter clock continues even if the core is halted
1: The independent watchdog counter clock is stopped when the core is halted
Bit 11 DBG_WWDG_STOP: Debug window watchdog stopped when core is halted
0: The window watchdog counter clock continues even if the core is halted
1: The window watchdog counter clock is stopped when the core is halted
Bit 10 DBG_RTC_STOP: Debug RTC stopped when core is halted
0: The clock of the RTC counter is fed even if the core is halted
1: The clock of the RTC counter is stopped when the core is halted
Bit 9 Reserved, must be kept at reset value.
Bit 8 DBG_TIM14_STOP: TIM14 counter stopped when core is halted
0: The counter clock of TIM14 is fed even if the core is halted
1: The counter clock of TIM14 is stopped when the core is halted
Bits 7:6 Reserved, must be kept at reset value.
Bit 5 DBG_TIM7_STOP: TIM7 counter stopped when core is halted.
0: The counter clock of TIM7 is fed even if the core is halted
1: The counter clock of TIM7 is stopped when the core is halted

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Bit 4 DBG_TIM6_STOP: TIM6 counter stopped when core is halted
0: The counter clock of TIM6 is fed even if the core is halted
1: The counter clock of TIM6 is stopped when the core is halted
Bits 3:2 Reserved, must be kept at reset value.
Bit 1 DBG_TIM3_STOP: TIM3 counter stopped when core is halted
0: The counter clock of TIM3 is fed even if the core is halted
1: The counter clock of TIM3 is stopped when the core is halted
Bit 0 DBG_TIM2_STOP: TIM2 counter stopped when core is halted
0: The counter clock of TIM2 is fed even if the core is halted
1: The counter clock of TIM2 is stopped when the core is halted

32.9.5

Debug MCU APB2 freeze register (DBGMCU_APB2_FZ)
The DBGMCU_APB2_FZ register is used to configure the MCU under DEBUG. It concerns
some APB peripherals:
•

Timer clock counter freeze

This register is mapped at address 0x4001580C.
It is asynchronously reset by the POR (and not the system reset). It can be written by the
debugger under system reset.
Address offset: 0x0C
Only 32-bit access is supported.

31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DBG_TIM17_STOP

DBG_TIM16_STOP

DBG_TIM15_STOP

rw

rw

rw

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Res.

Res.

Res.

Res.

DBG_TIM1_STOP

POR: 0x0000 0000 (not reset by system reset)

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

rw

Bits 31:19 Reserved, must be kept at reset value.
Bit 18 DBG_TIM17_STOP: TIM17 counter stopped when core is halted
0: The counter clock of TIM17 is fed even if the core is halted
1: The counter clock of TIM17 is stopped when the core is halted
Bit 17 DBG_TIM16_STOP: TIM16 counter stopped when core is halted
0: The counter clock of TIM16 is fed even if the core is halted
1: The counter clock of TIM16 is stopped when the core is halted

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Bit 16 DBG_TIM15_STOP: TIM15 counter stopped when core is halted
0: The counter clock of TIM15 is fed even if the core is halted
1: The counter clock of TIM15 is stopped when the core is halted
Bits 15:12 Reserved, must be kept at reset value.
Bit 11 DBG_TIM1_STOP: TIM1 counter stopped when core is halted
0: The counter clock of TIM 1 is fed even if the core is halted
1: The counter clock of TIM 1 is stopped when the core is halted
Bits 0:10 Reserved, must be kept at reset value.

32.9.6

DBG register map
The following table summarizes the Debug registers.
.

Res.

Res.

1. The reset value is product dependent. For more information, refer to Section 32.4.1: MCU device ID code.

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Res.

Res.

DBG_TIM6_STOP
0

Res.

DBG_TIM7_STOP

Res.

0

0

Res.

Res.

Res.
Res.

Res.

DBG_TIM14_STOP

DBG_TIM1_STOP

0

Res.

DBG_RTC_STOP
0

Res.

DBG_WWDG_STOP
0

Res.

DBG_IWDG_STOP

Res.

0

Res.

DBG_TIM15_STOP

0

Res.

DBG_TIM16_STOP

Res.

Res.

Res.

Res.

Res.

0

0

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

Res.

DBG_I2C1_SMBUS_TIMEOUT

Res.

Res.

Res.
Res.

Res.

Res.

Res.

Res.

Res.

0
DBG_TIM17_STOP

Reset value

Res.

DBGMCU_
APB2_FZ

0

Res.

0x4001580C

Reset value

DBG_CAN_STOP

Res.

Res.

Res.

Res.

Res.

DBGMCU_
APB1_FZ

Res.

0x40015808

Reset value

0

0

X

Res.

Res.

X
DBG_STOP

Res.

X

DBG_TIM2_STOP

Res.

X

DBG_TIM3_STOP

X

0

0

Res.

X

Res.

X

Res.

X

DBG_STANDBY

X

Res.

X

Res.

X

Res.

Res.

Res.

Res.
X

Res.

Res.

X

DEV_ID

Res.

Res.

X

Res.

Res.

X

Res.

Res.

X

Res.

Res.

X

Res.

DBGMCU_CR

X X X X

Res.

X

Res.

X

Res.

X

Res.

X

Res.

X

Res.

X

Res.

X

Res.

Reset value(1)

Res.

REV_ID

Res.

DBGMCU_
IDCODE

Res.

31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0

Register

Res.

0x40015804

0x40015800

Addr.

Table 143. DBG register map and reset values

RM0091

Device electronic signature

33

Device electronic signature
The device electronic signature is stored in the System memory area of the Flash memory
module, and can be read using the debug interface or by the CPU. It contains factoryprogrammed identification and calibration data that allow the user firmware or other external
devices to automatically match to the characteristics of the STM32F0xx microcontroller.

33.1

Unique device ID register (96 bits)
The unique device identifier is ideally suited:
•

for use as serial numbers (for example USB string serial numbers or other end
applications)

•

for use as part of the security keys in order to increase the security of code in Flash
memory while using and combining this unique ID with software cryptographic
primitives and protocols before programming the internal Flash memory

•

to activate secure boot processes, etc.

The 96-bit unique device identifier provides a reference number which is unique for any
device and in any context. These bits cannot be altered by the user.
Base address: 0x1FFF F7AC
Address offset: 0x00
Read only = 0xXXXX XXXX where X is factory-programmed
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

UID[31:16]
r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

UID[15:0]
r

r

r

r

r

r

r

r

r

Bits 31:0 UID[31:0]: X and Y coordinates on the wafer expressed in BCD format

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Address offset: 0x04
Read only = 0xXXXX XXXX where X is factory-programmed
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

UID[63:48]
r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

UID[47:32]
r

r

r

r

r

r

r

r

r

Bits 31:8 UID[63:40]: LOT_NUM[23:0]
Lot number (ASCII encoded)
Bits 7:0 UID[39:32]: WAF_NUM[7:0]
Wafer number (8-bit unsigned number)

Address offset: 0x08
Read only = 0xXXXX XXXX where X is factory-programmed
31

30

29

28

27

26

25

24

23

22

21

20

19

18

17

16

UID[95:80]
r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

r

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

UID[79:64]
r

r

r

r

r

r

r

r

r

Bits 31:0 UID[95:64]: LOT_NUM[55:24]
Lot number (ASCII encoded)

33.2

Memory size data register

33.2.1

Flash size data register
Base address: 0x1FFF F7CC
Address offset: 0x00
Read only = 0xXXXX where X is factory-programmed

15

14

13

12

11

10

9

r

r

r

r

r

r

r

8

7

6

5

4

3

2

1

0

r

r

r

r

r

r

r

FLASH_SIZE
r

r

Bits 15:0 FLASH_SIZE[15:0]: Flash memory size
This bitfield indicates the size of the device Flash memory expressed in Kbytes.
As an example, 0x040 corresponds to 64 Kbytes.

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RM0091

Code examples

Appendix A
A.1

Code examples

Introduction
This appendix shows the code examples of the sequence described in this Reference
Manual.
These code examples are extracted from the STM32F0xx Snippet firmware package
STM32SnippetsF0 available on www.st.com.
These code examples used the peripheral bit and register description from the CMSIS
header file (stm32f0xx.h).
Code lines starting with // should be uncommented if the given register has been modified
before.

A.2

Flash operation code example

A.2.1

Flash memory unlocking sequence code
/* (1) Wait till no operation is on going */
/* (2) Check that the Flash is unlocked */
/* (3) Perform unlock sequence */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (1) */

{
/* For robust implementation, add here time-out management */

}
if ((FLASH->CR & FLASH_CR_LOCK) != 0) /* (2) */
{
FLASH->KEYR = FLASH_FKEY1; /* (3) */
FLASH->KEYR = FLASH_FKEY2;
}

A.2.2

Main Flash programming sequence code example
/* (1) Set the PG bit in the FLASH_CR register to enable programming */
/* (2) Perform the data write (half-word) at the desired address */
/* (3) Wait until the BSY bit is reset in the FLASH_SR register */
/* (4) Check the EOP flag in the FLASH_SR register */
/* (5) clear it by software by writing it at 1 */
/* (6) Reset the PG Bit to disable programming */
FLASH->CR |= FLASH_CR_PG; /* (1) */
*(__IO uint16_t*)(flash_addr) = data; /* (2) */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (3) */
{
/* For robust implementation, add here time-out management */
}

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if ((FLASH->SR & FLASH_SR_EOP) != 0) /* (4) */
{
FLASH->SR = FLASH_SR_EOP; /* (5) */
}
else
{
/* Manage the error cases */
}
FLASH->CR &= ~FLASH_CR_PG; /* (6) */

A.2.3

Page erase sequence code example
/* (1) Set the PER bit in the FLASH_CR register to enable page erasing */
/* (2) Program the FLASH_AR register to select a page to erase */
/* (3) Set the STRT bit in the FLASH_CR register to start the erasing */
/* (4) Wait until the BSY bit is reset in the FLASH_SR register */
/* (5) Check the EOP flag in the FLASH_SR register */
/* (6) Clear EOP flag by software by writing EOP at 1 */
/* (7) Reset the PER Bit to disable the page erase */
FLASH->CR |= FLASH_CR_PER; /* (1) */
FLASH->AR = page_addr; /* (2) */
FLASH->CR |= FLASH_CR_STRT; /* (3) */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (4) */
{
/* For robust implementation, add here time-out management */
}
if ((FLASH->SR & FLASH_SR_EOP) != 0) /* (5) */
{
FLASH->SR = FLASH_SR_EOP; /* (6)*/
}
else
{
/* Manage the error cases */
}
FLASH->CR &= ~FLASH_CR_PER; /* (7) */

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A.2.4

Code examples

Mass erase sequence code example
/* (1) Set the MER bit in the FLASH_CR register to enable mass erasing */
/* (2) Set the STRT bit in the FLASH_CR register to start the erasing */
/* (3) Wait until the BSY bit is reset in the FLASH_SR register */
/* (4) Check the EOP flag in the FLASH_SR register */
/* (5) Clear EOP flag by software by writing EOP at 1 */
/* (6) Reset the PER Bit to disable the mass erase */
FLASH->CR |= FLASH_CR_MER; /* (1) */
FLASH->CR |= FLASH_CR_STRT; /* (2) */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (3) */
{
/* For robust implementation, add here time-out management */
}
if ((FLASH->SR & FLASH_SR_EOP) != 0) /* (4)*/
{
FLASH->SR = FLASH_SR_EOP; /* (5) */
}
else
{
/* Manage the error cases */
}
FLASH->CR &= ~FLASH_CR_MER; /* (6) */

A.2.5

Option byte unlocking sequence code example
/* (1) Wait till no operation is on going */
/* (2) Check that the Flash is unlocked */
/* (3) Perform unlock sequence for Flash */
/* (4) Check that the Option Bytes are unlocked */
/* (5) Perform unlock sequence for Option Bytes */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (1) */
{
/* For robust implementation, add here time-out management */
}
if ((FLASH->CR & FLASH_CR_LOCK) != 0) /* (2) */
{
FLASH->KEYR = FLASH_FKEY1; /* (3) */
FLASH->KEYR = FLASH_FKEY2;
}
if ((FLASH->CR & FLASH_CR_OPTWRE) == 0) /* (4) */
{
FLASH->OPTKEYR = FLASH_OPTKEY1; /* (5) */
FLASH->OPTKEYR = FLASH_OPTKEY2;
}

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A.2.6

RM0091

Option byte programming sequence code example
/* (1) Set the PG bit in the FLASH_CR register to enable programming */
/* (2) Perform the data write */
/* (3) Wait until the BSY bit is reset in the FLASH_SR register */
/* (4) Check the EOP flag in the FLASH_SR register */
/* (5) Clear the EOP flag by software by writing it at 1 */
/* (6) Reset the PG Bit to disable programming */
FLASH->CR |= FLASH_CR_OPTPG; /* (1) */
*opt_addr = data; /* (2) */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (3) */
{
/* For robust implementation, add here time-out management */
}
if ((FLASH->SR & FLASH_SR_EOP) != 0) /* (4) */
{
FLASH->SR = FLASH_SR_EOP; /* (5) */
}
else
{
/* Manage the error cases */
}
FLASH->CR &= ~FLASH_CR_OPTPG; /* (6) */

A.2.7

Option byte erasing sequence code example
/* (1) Set the OPTER bit in the FLASH_CR register to enable option byte
erasing */
/* (2) Set the STRT bit in the FLASH_CR register to start the erasing */
/* (3) Wait until the BSY bit is reset in the FLASH_SR register */
/* (4) Check the EOP flag in the FLASH_SR register */
/* (5) Clear EOP flag by software by writing EOP at 1 */
/* (6) Reset the PER Bit to disable the page erase */
FLASH->CR |= FLASH_CR_OPTER; /* (1) */
FLASH->CR |= FLASH_CR_STRT; /* (2) */
while ((FLASH->SR & FLASH_SR_BSY) != 0) /* (3) */
{
/* For robust implementation, add here time-out management */
}
if ((FLASH->SR & FLASH_SR_EOP) != 0) /* (4) */
{
FLASH->SR = FLASH_SR_EOP; /* (5)*/
}
else
{
/* Manage the error cases */
}
FLASH->CR &= ~FLASH_CR_OPTER; /* (6) */

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Code examples

A.3

Clock controller

A.3.1

HSE start sequence code example
/**
* Description: This function enables the interrupt on HSE ready,
*
and start the HSE as external clock.
*/
__INLINE void StartHSE(void)
{
/* Configure NVIC for RCC */
/* (1) Enable Interrupt on RCC */
/* (2) Set priority for RCC */
NVIC_EnableIRQ(RCC_CRS_IRQn); /* (1)*/
NVIC_SetPriority(RCC_CRS_IRQn,0); /* (2) */
/* (1) Enable interrupt on HSE ready */
/* (2) Enable the CSS
Enable the HSE and set HSEBYP to use the external clock
instead of an oscillator
Enable HSE */
/* Note : the clock is switched to HSE in the RCC_CRS_IRQHandler ISR */
RCC->CIR |= RCC_CIR_HSERDYIE; /* (1) */
RCC->CR |= RCC_CR_CSSON | RCC_CR_HSEBYP | RCC_CR_HSEON; /* (2) */
}
/**
* Description: This function handles RCC interrupt request
*
and switch the system clock to HSE.
*/
void RCC_CRS_IRQHandler(void)
{
/* (1) Check the flag HSE ready */
/* (2) Clear the flag HSE ready */
/* (3) Switch the system clock to HSE */
if ((RCC->CIR & RCC_CIR_HSERDYF) != 0) /* (1) */
{
RCC->CIR |= RCC_CIR_HSERDYC; /* (2) */
RCC->CFGR = ((RCC->CFGR & (~RCC_CFGR_SW)) | RCC_CFGR_SW_0); /* (3) */
}
else
{
/* Report an error */
}
}

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A.3.2

RM0091

PLL configuration modification code example
/* (1) Test if PLL is used as System clock */
/* (2) Select HSI as system clock */
/* (3) Wait for HSI switched */
/* (4) Disable the PLL */
/* (5) Wait until PLLRDY is cleared */
/* (6) Set the PLL multiplier to 6 */
/* (7) Enable the PLL */
/* (8) Wait until PLLRDY is set */
/* (9) Select PLL as system clock */
/* (10) Wait until the PLL is switched on */
if ((RCC->CFGR & RCC_CFGR_SWS) == RCC_CFGR_SWS_PLL) /* (1) */
{
RCC->CFGR &= (uint32_t) (~RCC_CFGR_SW); /* (2) */
while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_HSI) /* (3) */
{
/* For robust implementation, add here time-out management */
}
}
RCC->CR &= (uint32_t)(~RCC_CR_PLLON);/* (4) */
while((RCC->CR & RCC_CR_PLLRDY) != 0) /* (5) */
{
/* For robust implementation, add here time-out management */
}
RCC->CFGR = RCC->CFGR & (~RCC_CFGR_PLLMUL) | (RCC_CFGR_PLLMUL6); /* (6) */
RCC->CR |= RCC_CR_PLLON; /* (7) */
while((RCC->CR & RCC_CR_PLLRDY) == 0) /* (8) */
{
/* For robust implementation, add here time-out management */
}
RCC->CFGR |= (uint32_t) (RCC_CFGR_SW_PLL); /* (9) */
while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_PLL) /* (10) */
{
/* For robust implementation, add here time-out management */
}

A.3.3

MCO selection code example
/* Select system clock to be output on the MCO without prescaler */
RCC->CFGR |= RCC_CFGR_MCO_SYSCLK;

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A.3.4

Code examples

Clock measurement configuration with TIM14 code example
/**
* Description: This function configures the TIM14 as input capture
*
and enables the interrupt on TIM14
*/
__INLINE void ConfigureTIM14asInputCapture(void)
{
/* (1) Enable the peripheral clock of Timer 14 */
/* (2) Select the active input TI1,Program the input filter, and prescaler
*/
/* (3) Enable interrupt on Capture/Compare */
RCC->APB1ENR |= RCC_APB1ENR_TIM14EN; /* (1) */
TIM14->CCMR1 |= TIM_CCMR1_IC1F_0 | TIM_CCMR1_IC1F_1 \
| TIM_CCMR1_CC1S_0 | TIM_CCMR1_IC1PSC_1; /* (2)*/
TIM14->DIER |= TIM_DIER_CC1IE; /* (3) */
/* Configure NVIC for TIM14 */
/* (4) Enable Interrupt on TIM14 */
/* (5) Set priority for TIM14 */
NVIC_EnableIRQ(TIM14_IRQn); /* (4) */
NVIC_SetPriority(TIM14_IRQn,0); /* (5) */
/* (6) Select HSE/32 as input on TI1 */
/* (7) Enable counter */
/* (8) Enable capture */
TIM14->OR |= TIM14_OR_TI1_RMP_1; /* (6) */
TIM14->CR1 |= TIM_CR1_CEN; /* (7) */
TIM14->CCER |= TIM_CCER_CC1E; /* (8) */
}

Note:

The measurement is done in the TIM14 interrupt subroutine.

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A.4

GPIO

A.4.1

Lock sequence code example
/**
* Description: This function locks the targeted pins of Port A
configuration
This function can be easily modified to lock Port B
* Parameter: lock contains the port pin mask to be locked
*/
void LockGPIOA(uint16_t lock)
{
/* (1) Write LCKK bit to 1 and set the pin bits to lock */
/* (2) Write LCKK bit to 0 and set the pin bits to lock */
/* (3) Write LCKK bit to 1 and set the pin bits to lock */
/* (4) Read the Lock register */
/* (5) Check the Lock register (optionnal) */
GPIOA->LCKR = GPIO_LCKR_LCKK + lock; /* (1) */
GPIOA->LCKR = lock; /* (2) */
GPIOA->LCKR = GPIO_LCKR_LCKK + lock; /* (3) */
GPIOA->LCKR; /* (4) */
if ((GPIOA->LCKR & GPIO_LCKR_LCKK) == 0) /* (5) */
{
/* Manage an error */
}
}

A.4.2

Alternate function selection sequence code example
/* This sequence select AF2 for GPIOA4, 8 and 9. This can be easily adapted
with another port by changing all GPIOA references by another GPIO port,
and the alternate function number can be changed by replacing 0x04 or
0x02 for
each pin by the targeted alternate function in the 2 last code lines. */
/* (1) Enable the peripheral clock of GPIOA */
/* (2) Select alternate function mode on GPIOA pin 4, 8 and 9 */
/* (3) Select AF4 on PA4 in AFRL for TIM14_CH1 */
/* (4) Select AF2 on PA8 and PA9 in AFRH for TIM1_CH1 and TIM1_CH2 */
RCC->AHBENR |= RCC_AHBENR_GPIOAEN; /* (1) */
GPIOA->MODER = (GPIOA->MODER & ~(GPIO_MODER_MODER4 | GPIO_MODER_MODER8
| GPIO_MODER_MODER9)) | GPIO_MODER_MODER4_1
| GPIO_MODER_MODER8_1 | GPIO_MODER_MODER9_1; /* (2) */
GPIOA->AFR[0] |= 0x04 << GPIO_AFRL_AFRL4_Pos; /* (3) */
GPIOA->AFR[1] |= (0x02 << GPIO_AFRL_AFRH8_Pos) | (0x02 <<
GPIO_AFRL_AFRH9_Pos); /* (4) */

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A.4.3

Code examples

Analog GPIO configuration code example
/* (1) Enable the peripheral clock of GPIOA, GPIOB and GPIOC */
/* (2) Select analog mode for PA1 */
/* (3) Select analog mode for PB1 */
/* (4) Select analog mode for PC0 */
RCC->AHBENR |= RCC_AHBENR_GPIOAEN | RCC_AHBENR_GPIOBEN
| RCC_AHBENR_GPIOCEN; /* (1) */
GPIOA->MODER |= GPIO_MODER_MODER1; /* (2) */
GPIOB->MODER |= GPIO_MODER_MODER1; /* (3) */
GPIOC->MODER |= GPIO_MODER_MODER0; /* (4) */

A.5

DMA

A.5.1

DMA Channel Configuration sequence code example
/* The following example is given for the ADC. It can be easily ported on
any peripheral supporting DMA transfer taking of the associated channel
to the peripheral, this must check in the datasheet. */
/* (1) Enable the peripheral clock on DMA */
/* (2) Enable DMA transfer on ADC */
/* (3) Configure the peripheral data register address */
/* (4) Configure the memory address */
/* (5) Configure the number of DMA tranfer to be performs on channel 1 */
/* (6) Configure increment, size and interrupts */
/* (7) Enable DMA Channel 1 */
RCC->AHBENR |= RCC_AHBENR_DMA1EN; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_DMAEN; /* (2) */
DMA1_Channel1->CPAR = (uint32_t) (&(ADC1->DR)); /* (3) */
DMA1_Channel1->CMAR = (uint32_t)(ADC_array); /* (4) */
DMA1_Channel1->CNDTR = 3; /* (5) */
DMA1_Channel1->CCR |= DMA_CCR_MINC | DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_0
| DMA_CCR_TEIE | DMA_CCR_TCIE ; /* (6) */
DMA1_Channel1->CCR |= DMA_CCR_EN; /* (7) */
/* Configure NVIC for DMA */
/* (1) Enable Interrupt on DMA Channel 1 */
/* (2) Set priority for DMA Channel 1 */
NVIC_EnableIRQ(DMA1_Channel1_IRQn); /* (1) */
NVIC_SetPriority(DMA1_Channel1_IRQn,0); /* (2) */

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Code examples

RM0091

A.6

Interrupts and event

A.6.1

NVIC initialization example
/* (1) Enable Interrupt on ADC */
/* (2) Set priority for ADC to 2*/
NVIC_EnableIRQ(ADC1_COMP_IRQn); /* (1) */
NVIC_SetPriority(ADC1_COMP_IRQn,2); /* (2) */

A.6.2

External interrupt selection code example
/* (1) Enable the peripheral clock of GPIOA */
/* (2) Select Port A for pin 0 external interrupt by writing 0000 in
EXTI0 (reset value)*/
/* (3) Configure the corresponding mask bit in the EXTI_IMR register */
/* (4) Configure the Trigger Selection bits of the Interrupt line on
rising edge*/
/* (5) Configure the Trigger Selection bits of the Interrupt line on
falling edge*/
RCC->AHBENR |= RCC_AHBENR_GPIOAEN; /* (1) */
//SYSCFG->EXTICR[1] &= (uint16_t)~SYSCFG_EXTICR1_EXTI0_PA; /* (2) */
EXTI->IMR = 0x0001; /* (3) */
EXTI->RTSR = 0x0001; /* (4) */
EXTI->FTSR = 0x0001; /* (5) */
/* Configure NVIC for External Interrupt */
/* (1) Enable Interrupt on EXTI0_1 */
/* (2) Set priority for EXTI0_1 */
NVIC_EnableIRQ(EXTI0_1_IRQn); /* (1) */
NVIC_SetPriority(EXTI0_1_IRQn,0); /* (2) */

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Code examples

A.7

ADC

A.7.1

ADC Calibration code example
/* (1) Ensure that ADEN = 0 */
/* (2) Clear ADEN by setting ADDIS*/
/* (3) Clear DMAEN */
/* (4) Launch the calibration by setting ADCAL */
/* (5) Wait until ADCAL=0 */
if ((ADC1->CR & ADC_CR_ADEN) != 0) /* (1) */
{
ADC1->CR |= ADC_CR_ADDIS; /* (2) */
}
while ((ADC1->CR & ADC_CR_ADEN) != 0)
{
/* For robust implementation, add here time-out management */
}
ADC1->CFGR1 &= ~ADC_CFGR1_DMAEN; /* (3) */
ADC1->CR |= ADC_CR_ADCAL; /* (4) */
while ((ADC1->CR & ADC_CR_ADCAL) != 0) /* (5) */
{
/* For robust implementation, add here time-out management */
}

A.7.2

ADC enable sequence code example
/* (1) Ensure that ADRDY = 0 */
/* (2) Clear ADRDY */
/* (3) Enable the ADC */
/* (4) Wait until ADC ready */
if ((ADC1->ISR & ADC_ISR_ADRDY) != 0) /* (1) */
{
ADC1->ISR |= ADC_CR_ADRDY; /* (2) */
}
ADC1->CR |= ADC_CR_ADEN; /* (3) */
while ((ADC1->ISR & ADC_ISR_ADRDY) == 0) /* (4) */
{
/* For robust implementation, add here time-out management */
}

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A.7.3

RM0091

ADC disable sequence code example
/* (1) Stop any ongoing conversion */
/* (2) Wait until ADSTP is reset by hardware i.e. conversion is stopped */
/* (3) Disable the ADC */
/* (4) Wait until the ADC is fully disabled */
ADC1->CR |= ADC_CR_ADSTP; /* (1) */
while ((ADC1->CR & ADC_CR_ADSTP) != 0) /* (2) */
{
/* For robust implementation, add here time-out management */
}
ADC1->CR |= ADC_CR_ADDIS; /* (3) */
while ((ADC1->CR & ADC_CR_ADEN) != 0) /* (4) */
{
/* For robust implementation, add here time-out management */
}

A.7.4

ADC Clock selection code example
/* This code selects the HSI14 as clock source. */
/* (1) Enable the peripheral clock of the ADC */
/* (2) Start HSI14 RC oscillator */
/* (3) Wait HSI14 is ready */
/* (4) Select HSI14 by writing 00 in CKMODE (reset value) */
RCC->APB2ENR |= RCC_APB2ENR_ADC1EN; /* (1) */
RCC->CR2 |= RCC_CR2_HSI14ON; /* (2) */
while ((RCC->CR2 & RCC_CR2_HSI14RDY) == 0) /* (3) */
{
/* For robust implementation, add here time-out management */
}
//ADC1->CFGR2 &= (~ADC_CFGR2_CKMODE); /* (4) */

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A.7.5

Code examples

Single conversion sequence code example - Software trigger
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select CHSEL0, CHSEL9, CHSEL10 andCHSEL17 for VRefInt */
/* (3) Select a sampling mode of 111 i.e. 239.5 ADC clk to be greater
than 17.1us */
/* (4) Wake-up the VREFINT (only for VBAT, Temp sensor and VRefInt) */
//ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CHSELR = ADC_CHSELR_CHSEL0 | ADC_CHSELR_CHSEL9
| ADC_CHSELR_CHSEL10 | ADC_CHSELR_CHSEL17; /* (2) */
ADC1->SMPR |= ADC_SMPR_SMP_0 | ADC_SMPR_SMP_1 | ADC_SMPR_SMP_2; /* (3) */
ADC->CCR |= ADC_CCR_VREFEN; /* (4) */
while (1)
{
/* Performs the AD conversion */
ADC1->CR |= ADC_CR_ADSTART; /* Start the ADC conversion */
for (i=0; i < 4; i++)
{
while ((ADC1->ISR & ADC_ISR_EOC) == 0) /* Wait end of conversion */
{
/* For robust implementation, add here time-out management */
}
ADC_Result[i] = ADC1->DR; /* Store the ADC conversion result */
}
ADC1->CFGR1 ^= ADC_CFGR1_SCANDIR; /* Toggle the scan direction */
}

A.7.6

Continuous conversion sequence code example - Software trigger
/* This code example configures the AD conversion in continuous mode and in
backward scan. It also enable the interrupts. */
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the continuous mode and scanning direction */
/* (3) Select CHSEL1, CHSEL9, CHSEL10 and CHSEL17 */
/* (4) Select a sampling mode of 111 i.e. 239.5 ADC clk to be greater than
17.1us */
/* (5) Enable interrupts on EOC, EOSEQ and overrrun */
/* (6) Wake-up the VREFINT (only for VBAT, Temp sensor and VRefInt) */
//ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_CONT | ADC_CFGR1_SCANDIR; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL1 | ADC_CHSELR_CHSEL9
| ADC_CHSELR_CHSEL10 | ADC_CHSELR_CHSEL17; /* (3) */
ADC1->SMPR |= ADC_SMPR_SMP_0 | ADC_SMPR_SMP_1 | ADC_SMPR_SMP_2; /* (4) */
ADC1->IER = ADC_IER_EOCIE | ADC_IER_EOSEQIE | ADC_IER_OVRIE; /* (5) */
ADC->CCR |= ADC_CCR_VREFEN; /* (6) */
/* Configure NVIC for ADC */
/* (7) Enable Interrupt on ADC */
/* (8) Set priority for ADC */
NVIC_EnableIRQ(ADC1_COMP_IRQn); /* (7) */
NVIC_SetPriority(ADC1_COMP_IRQn,0); /* (8) */

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A.7.7

RM0091

Single conversion sequence code example - Hardware trigger
/* Configure the ADC, the ADC and its clock having previously been
enabled. */
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the external trigger on falling edge and external trigger on
TIM15_TRGO */
/* (3) Select CHSEL0, 1, 2 and 3 */
//ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_EXTEN_0 | ADC_CFGR1_EXTSEL_2; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL0 | ADC_CHSELR_CHSEL1
| ADC_CHSELR_CHSEL2 | ADC_CHSELR_CHSEL3; /* (3) */

A.7.8

Continuous conversion sequence code example - Hardware trigger
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the external trigger on TIM15_TRGO (EXTSEL = 100),falling
edge (EXTEN = 10), the continuous mode (CONT = 1)*/
/* (3) Select CHSEL0/1/2/3 */
/* (4) Enable interrupts on EOC, EOSEQ and overrrun */
//ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_EXTEN_1 | ADC_CFGR1_EXTSEL_2
| ADC_CFGR1_CONT; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL0 | ADC_CHSELR_CHSEL1
| ADC_CHSELR_CHSEL2 | ADC_CHSELR_CHSEL3; /* (3)*/
ADC1->IER = ADC_IER_EOCIE | ADC_IER_EOSEQIE | ADC_IER_OVRIE; /* (4) */
/* Configure NVIC for ADC */
/* (1) Enable Interrupt on ADC */
/* (2) Set priority for ADC */
NVIC_EnableIRQ(ADC1_COMP_IRQn); /* (1) */
NVIC_SetPriority(ADC1_COMP_IRQn,0); /* (2) */

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A.7.9

Code examples

DMA one shot mode sequence code example
/* (1) Enable the peripheral clock on DMA */
/* (2) Enable DMA transfer on ADC - DMACFG is kept at 0
for one shot mode */
/* (3) Configure the peripheral data register address */
/* (4) Configure the memory address */
/* (5) Configure the number of DMA tranfer to be performs
on DMA channel 1 */
/* (6) Configure increment, size and interrupts */
/* (7) Enable DMA Channel 1 */
RCC->AHBENR |= RCC_AHBENR_DMA1EN; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_DMAEN; /* (2) */
DMA1_Channel1->CPAR = (uint32_t) (&(ADC1->DR)); /* (3) */
DMA1_Channel1->CMAR = (uint32_t)(ADC_array); /* (4) */
DMA1_Channel1->CNDTR = NUMBER_OF_ADC_CHANNEL; /* (5) */
DMA1_Channel1->CCR |= DMA_CCR_MINC | DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_0
| DMA_CCR_TEIE | DMA_CCR_TCIE ; /* (6) */
DMA1_Channel1->CCR |= DMA_CCR_EN; /* (7) */

A.7.10

DMA circular mode sequence code example
/*
/*
/*
/*
/*

Enable the peripheral clock on DMA */
Enable DMA transfer on ADC and circular mode */
Configure the peripheral data register address */
Configure the memory address */
Configure the number of DMA tranfer to be performs
on DMA channel 1 */
/* (6) Configure increment, size, interrupts and circular mode */
/* (7) Enable DMA Channel 1 */
RCC->AHBENR |= RCC_AHBENR_DMA1EN; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_DMAEN | ADC_CFGR1_DMACFG; /* (2) */
DMA1_Channel1->CPAR = (uint32_t) (&(ADC1->DR)); /* (3) */
DMA1_Channel1->CMAR = (uint32_t)(ADC_array); /* (4) */
DMA1_Channel1->CNDTR = NUMBER_OF_ADC_CHANNEL; /* (5) */
DMA1_Channel1->CCR |= DMA_CCR_MINC | DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_0
| DMA_CCR_TEIE | DMA_CCR_CIRC; /* (6) */
DMA1_Channel1->CCR |= DMA_CCR_EN; /* (7) */

A.7.11

(1)
(2)
(3)
(4)
(5)

Wait mode sequence code example
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the continuous mode and the wait mode */
/* (3) Select CHSEL1/2/3 */
ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_CONT | ADC_CFGR1_WAIT; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL1 | ADC_CHSELR_CHSEL2
| ADC_CHSELR_CHSEL3; /* (3)*/
ADC1->CR |= ADC_CR_ADSTART; /* start the ADC conversions */

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A.7.12

RM0091

Auto Off and no wait mode sequence code example
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the external trigger on TIM15_TRGO and rising edge
and auto off */
/* (3) Select CHSEL1/2/3/4 */
/* (4) Enable interrupts on EOC, EOSEQ and overrrun */
ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_EXTEN_1 | ADC_CFGR1_EXTSEL_2
| ADC_CFGR1_AUTOFF; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL1 | ADC_CHSELR_CHSEL2
| ADC_CHSELR_CHSEL3 | ADC_CHSELR_CHSEL4; /* (3) */
ADC1->IER = ADC_IER_EOCIE | ADC_IER_EOSEQIE | ADC_IER_OVRIE; /* (4) */

A.7.13

Auto Off and wait mode sequence code example
/* (1) Select HSI14 by writing 00 in CKMODE (reset value) */
/* (2) Select the external trigger on TIM15_TRGO and falling edge,
the continuous mode, scanning direction and auto off */
/* (3) Select CHSEL1, CHSEL9, CHSEL10 and CHSEL17 */
/* (4) Enable interrupts on EOC, EOSEQ and overrrun */
ADC1->CFGR2 &= ~ADC_CFGR2_CKMODE; /* (1) */
ADC1->CFGR1 |= ADC_CFGR1_EXTEN_0 | ADC_CFGR1_EXTSEL_2
| ADC_CFGR1_SCANDIR | ADC_CFGR1_AUTOFF; /* (2) */
ADC1->CHSELR = ADC_CHSELR_CHSEL1 | ADC_CHSELR_CHSEL2
| ADC_CHSELR_CHSEL3 | ADC_CHSELR_CHSEL4; /* (3) */
ADC1->IER = ADC_IER_EOCIE | ADC_IER_EOSEQIE | ADC_IER_OVRIE; /* (4) */

A.7.14

Analog watchdog code example
/* (1) Select the continuous mode
and configure the Analog watchdog to monitor only CH17 */
/* (2) Define analog watchdog range : 16b-MSW is the high limit
and 16b-LSW is the low limit */
/* (3) Enable interrupt on Analog Watchdog */
ADC1->CFGR1 |= ADC_CFGR1_CONT
| (17 << 26) | ADC_CFGR1_AWDEN | ADC_CFGR1_AWDSGL; /* (1) */
ADC1->TR = (vrefint_high << 16) + vrefint_low; /* (2)*/
ADC1->IER = ADC_IER_AWDIE; /* (3) */

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A.7.15

Code examples

Temperature configuration code example
/* (1) Select CHSEL16 for temperature sensor */
/* (2) Select a sampling mode of 111 i.e. 239.5 ADC clk to be greater than
17.1us */
/* (3) Wake-up the Temperature sensor (only for VBAT, Temp sensor and
VRefInt) */
ADC1->CHSELR = ADC_CHSELR_CHSEL16; /* (1) */
ADC1->SMPR |= ADC_SMPR_SMP_0 | ADC_SMPR_SMP_1 | ADC_SMPR_SMP_2; /* (2) */
ADC->CCR |= ADC_CCR_TSEN; /* (3) */

A.7.16

Temperature computation code example
/* Temperature sensor calibration value address */
#define TEMP110_CAL_ADDR ((uint16_t*) ((uint32_t) 0x1FFFF7C2))
#define TEMP30_CAL_ADDR ((uint16_t*) ((uint32_t) 0x1FFFF7B8))
#define VDD_CALIB ((uint16_t) (330))
#define VDD_APPLI ((uint16_t) (300))
int32_t temperature; /* will contain the temperature in degrees Celsius */
temperature = (((int32_t) ADC1->DR * VDD_APPLI / VDD_CALIB)
- (int32_t) *TEMP30_CAL_ADDR );
temperature = temperature * (int32_t)(110 - 30);
temperature = temperature / (int32_t)(*TEMP110_CAL_ADDR
- *TEMP30_CAL_ADDR);
temperature = temperature + 30;

A.8

DAC

A.8.1

Independent trigger without wave generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Enable DMA transfer on DAC ch1 and ch2,
enable interrupt on DMA underrun DAC ch1 and ch2,
enable the DAC ch1 and ch2,
select TIM6 as trigger by keeping 000 in TSEL1
select TIM7 as trigger by writing 010 in TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_TSEL2_1 | DAC_CR_DMAUDRIE2 | DAC_CR_DMAEN2
| DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_DMAUDRIE1 | DAC_CR_DMAEN1 | DAC_CR_BOFF1
| DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
DAC->DHR12R1 = DAC_OUT1_VALUE; /* Initialize the DAC value on ch1 */
DAC->DHR12R2 = DAC_OUT2_VALUE; /* Initialize the DAC value on ch2 */

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A.8.2

RM0091

Independent trigger with single LFSR generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 01 and LFSR mask amplitude (MAMPx) at 1000 for
a 511-bits amplitude,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL2,
and select TIM6 as trigger by keeping 000 in TSEL1 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_0 | DAC_CR_MAMP1_3
| DAC_CR_MAMP2_3 | DAC_CR_WAVE2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2
| DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_BOFF1 | DAC_CR_TEN1
| DAC_CR_EN1; /* (2) */
DAC->DHR12R1 = DAC_OUT1_VALUE; /* Initialize the DAC output value */
DAC->DHR12R2 = DAC_OUT2_VALUE; /* Initialize the DAC output value */

A.8.3

Independent trigger with different LFSR generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 01 and LFSR mask amplitude (MAMPx) at 1000 for a
511-bits amplitude,
LFSR mask amplitude (MAMP2) at 0111 i.e. a 255-bits amplitude for
ch2,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL2,
and select TIM6 as trigger by keeping 000 in TSEL1 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_0 | DAC_CR_WAVE2_0 | DAC_CR_MAMP1_3
| DAC_CR_MAMP2_2 | DAC_CR_MAMP2_1 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_BOFF1 | DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
DAC->DHR12R1 = DAC_OUT1_VALUE; /* Initialize DAC output value */
DAC->DHR12R2 = DAC_OUT2_VALUE; /* Initialize DAC output value */

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A.8.4

Code examples

Independent trigger with single triangle generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 10 and LFSR mask amplitude (MAMPx) at 1001 for a
1023-bits amplitude,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL2
and select TIM6 as trigger by keeping 000 in TSEL1 */
/* (3) Define the low value of the triangle on channel1 */
/* (4) Define the low value of the triangle on channel2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_1 | DAC_CR_WAVE2_1
| DAC_CR_MAMP1_3 | DAC_CR_MAMP1_0
| DAC_CR_MAMP2_3 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_BOFF1 | DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
DAC->DHR12R1 = DAC_OUT1_VALUE; /* (3) */
DAC->DHR12R2 = DAC_OUT2_VALUE; /* (4) */

A.8.5

Independent trigger with different triangle generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 10,
configure mask amplitude for ch1 (MAMP1) at 1001 for a 1023-bits
amplitude,
and mask amplitude for ch2 (MAMP1) at 1011 for a 4095-bits amplitude,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL2,
and select TIM6 as trigger by keeping 000 in TSEL1 */
/* (3) Define the low value of the triangle on channel1 */
/* (4) Define the low value of the triangle on channel2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_1 | DAC_CR_WAVE2_1
| DAC_CR_MAMP1_3 | DAC_CR_MAMP1_0
| DAC_CR_MAMP2_3 | DAC_CR_MAMP2_1 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_BOFF1 | DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
DAC->DHR12R1 = DAC_OUT1_VALUE; /* (3) */
DAC->DHR12R2 = DAC_OUT2_VALUE; /* (4) */

A.8.6

Simultaneous software start code example
/* Load the dual DAC channel data to the desired DHR register */
DAC->DHR12RD = (uint32_t)((signal1[x] << 16) + signal2[x]);

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A.8.7

RM0091

Simultaneous trigger without wave generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Enable DMA transfer on DAC ch1 for both channels,
enable the DAC ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_TSEL1_1 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL2_1 | DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
/* Initialize the dual DAC value */
DAC->DHR12RD = (uint32_t)((2048 << 16) + 2048);

A.8.8

Simultaneous trigger with single LFSR generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 01 and LFSR mask amplitude (MAMPx) at 1000 for a
511-bits amplitude,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_0 | DAC_CR_WAVE2_0
| DAC_CR_MAMP1_3 | DAC_CR_MAMP2_3
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2
| DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL1_1 | DAC_CR_BOFF1
| DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
/* Initialize the dual register */
DAC->DHR12RD = (uint32_t)((DAC_OUT2_VALUE << 16) + DAC_OUT1_VALUE);

A.8.9

Simultaneous trigger with different LFSR generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 01 and LFSR mask amplitude (MAMP1) at 1000 for a
511-bits amplitude,
set LFSR mask amplitude (MAMP2) at 0111 i.e. a 255-bits amplitude for
ch2,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_0 | DAC_CR_WAVE2_0 | DAC_CR_MAMP1_3
| DAC_CR_MAMP2_2 | DAC_CR_MAMP2_1 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2
| DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL1_1| DAC_CR_BOFF1
| DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
/* Initialize the dual register */
DAC->DHR12RD = (uint32_t)((DAC_OUT2_VALUE << 16) + DAC_OUT1_VALUE);

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A.8.10

Code examples

Simultaneous trigger with single triangle generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 10 and LFSR mask amplitude (MAMPx) at 1001 for a
1023-bits amplitude,
enable the DAC ch1 and ch2,
disable buffer on ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_1 | DAC_CR_WAVE2_1
| DAC_CR_MAMP1_3 | DAC_CR_MAMP1_0
| DAC_CR_MAMP2_3 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_BOFF2
| DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL1_1 | DAC_CR_BOFF1
| DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
/* Initialize the dual register */
DAC->DHR12RD = (uint32_t)((DAC_OUT2_VALUE << 16) + DAC_OUT1_VALUE);

A.8.11

Simultaneous trigger with different triangle generation code example
/* (1) Enable the peripheral clock of the DAC */
/* (2) Configure WAVEx at 10,
configure mask amplitude for ch1 (MAMP1) at 1001 for a 1023-bits
amplitude and mask amplitude for ch2 (MAMP1) at 1011 for a 4095-bits
amplitude,
enable the DAC ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
RCC->APB1ENR |= RCC_APB1ENR_DACEN; /* (1) */
DAC->CR |= DAC_CR_WAVE1_1 | DAC_CR_WAVE2_1
| DAC_CR_MAMP1_3 | DAC_CR_MAMP1_0
| DAC_CR_MAMP2_3 | DAC_CR_MAMP2_1 | DAC_CR_MAMP2_0
| DAC_CR_TSEL2_1 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL1_1 | DAC_CR_TEN1 | DAC_CR_EN1; /* (2) */
/* Initialize the dual register */
DAC->DHR12RD = (uint32_t)((DAC_OUT2_VALUE << 16) + DAC_OUT1_VALUE);

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A.8.12

RM0091

DMA initialization code example
/* (1) Enable DMA transfer on DAC ch1 for both channels,
enable interrupt on DMA underrun DAC,
enable the DAC ch1 and ch2,
select TIM7 as trigger by writing 010 in TSEL1 and TSEL2 */
DAC->CR |= DAC_CR_TSEL1_1 | DAC_CR_TEN2 | DAC_CR_EN2
| DAC_CR_TSEL2_1 | DAC_CR_DMAUDRIE1 | DAC_CR_DMAEN1
| DAC_CR_TEN1 | DAC_CR_EN1; /* (1) */
/* (1) Enable the peripheral clock on DMA */
/* (2) Configure the peripheral data register address */
/* (3) Configure the memory address */
/* (4) Configure the number of DMA tranfer to be performs on channel 3 */
/* (5) Configure increment, size (32-bits), interrupts, transfer from
memory to peripheral and circular mode */
/* (6) Enable DMA Channel 3 */
RCC->AHBENR |= RCC_AHBENR_DMA1EN; /* (1) */
DMA1_Channel3->CPAR = (uint32_t) (&(DAC->DHR12RD)); /* (2) */
DMA1_Channel3->CMAR = (uint32_t)signal_data; /* (3) */
DMA1_Channel3->CNDTR = SIGNAL_ARRAY_SIZE; /* (4) */
DMA1_Channel3->CCR |= DMA_CCR_MINC | DMA_CCR_MSIZE_1 | DMA_CCR_PSIZE_1
| DMA_CCR_TEIE | DMA_CCR_CIRC; /* (5) */
DMA1_Channel3->CCR |= DMA_CCR_EN; /* (6) */

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Code examples

A.9

Timers

A.9.1

Upcounter on TI2 rising edge code example
/*
/*
/*
/*

(1)
(2)
(3)
(4)

Enable the peripheral clock of Timer 1 */
Enable the peripheral clock of GPIOA */
Select Alternate function mode (10) on GPIOA pin 9 */
Select TIM1_CH2 on PA9 by enabling AF2 for pin 9 in GPIOA AFRH
register */
RCC->APB2ENR |= RCC_APB2ENR_TIM1EN; /* (1) */
RCC->AHBENR |= RCC_AHBENR_GPIOAEN; /* (2) */
GPIOA->MODER = (GPIOA->MODER & ~(GPIO_MODER_MODER9))
| (GPIO_MODER_MODER9_1); /* (3) */
GPIOA->AFR[1] |= 0x2 << ((9-8)*4); /* (4) */
/* (1) Configure channel 2 to detect rising edges on the TI2 input by
writing CC2S = ‘01’, and configure the input filter duration by
writing the IC2F[3:0] bits in the TIMx_CCMR1 register (if no filter
is needed, keep IC2F=0000).*/
/* (2) Select rising edge polarity by writing CC2P=0 in the TIMx_CCER
register (reset value). */
/* (3) Configure the timer in external clock mode 1 by writing SMS=111
Select TI2 as the trigger input source by writing TS=110
in the TIMx_SMCR register.*/
/* (4) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
TIMx->CCMR1 |= TIM_CCMR1_IC2F_0 | TIM_CCMR1_IC2F_1
| TIM_CCMR1_CC2S_0; /* (1) */
TIMx->CCER &= (uint16_t)(~TIM_CCER_CC2P); /* (2) */
TIMx->SMCR |= TIM_SMCR_SMS | TIM_SMCR_TS_2 | TIM_SMCR_TS_1; /* (3) */
TIMx->CR1 |= TIM_CR1_CEN; /* (4) */

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A.9.2

RM0091

Up counter on each 2 ETR rising edges code example
/*
/*
/*
/*

Enable the peripheral clock of Timer 1 */
Enable the peripheral clock of GPIOA */
Select Alternate function mode (10) on GPIOA pin 12 */
Select TIM1_ETR on PA12 by enabling AF2 for pin 12 in GPIOA AFRH
register */
RCC->APB2ENR |= RCC_APB2ENR_TIM1EN; /* (1) */
RCC->AHBENR |= RCC_AHBENR_GPIOAEN; /* (2) */
GPIOA->MODER = (GPIOA->MODER & ~(GPIO_MODER_MODER12))
| (GPIO_MODER_MODER12_1); /* (3) */
GPIOA->AFR[1] |= 0x2 << ((12-8)*4); /* (4) */
/* (1) As no filter is needed in this example, write ETF[3:0]=0000
in the TIMx_SMCR register. Keep the reset value.
Set the prescaler by writing ETPS[1:0]=01 in the TIMx_SMCR
register.
Select rising edge detection on the ETR pin by writing ETP=0
in the TIMx_SMCR register. Keep the reset value.
Enable external clock mode 2 by writing ECE=1 in the TIMx_SMCR
register. */
/* (2) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
TIMx->SMCR |= TIM_SMCR_ETPS_0 | TIM_SMCR_ECE; /* (1) */
TIMx->CR1 |= TIM_CR1_CEN; /* (2) */

A.9.3

(1)
(2)
(3)
(4)

Input capture configuration code example
/* (1) Select the active input TI1 (CC1S = 01),
program the input filter for 8 clock cycles (IC1F = 0011),
select the rising edge on CC1 (CC1P = 0, reset value)
and prescaler at each valid transition (IC1PS = 00, reset value) */
/* (2) Enable capture by setting CC1E */
/* (3) Enable interrupt on Capture/Compare */
/* (4) Enable counter */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0
| TIM_CCMR1_IC1F_0 | TIM_CCMR1_IC1F_1; /* (1)*/
TIMx->CCER |= TIM_CCER_CC1E; /* (2) */
TIMx->DIER |= TIM_DIER_CC1IE; /* (3) */
TIMx->CR1 |= TIM_CR1_CEN; /* (4) */

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A.9.4

Code examples

Input capture data management code example
This code must be inserted in the Timer interrupt subroutine.
if ((TIMx->SR & TIM_SR_CC1IF) != 0)
{
if ((TIMx->SR & TIM_SR_CC1OF) != 0) /* Check the overflow */
{
/* Overflow error management */
gap = 0; /* Reinitialize the laps computing */
TIMx->SR &= ~(TIM_SR_CC1OF | TIM_SR_CC1IF); /* Clear the flags */
return;
}
if (gap == 0) /* Test if it is the first rising edge */
{
counter0 = TIMx->CCR1; /* Read the capture counter which clears the
CC1ICF */
gap = 1; /* Indicate that the first rising edge has yet been detected */
}
else
{
counter1 = TIMx->CCR1; /* Read the capture counter which clears the
CC1ICF */
if (counter1 > counter0) /* Check capture counter overflow */
{
Counter = counter1 - counter0;
}
else
{
Counter = counter1 + 0xFFFF - counter0 + 1;
}
counter0 = counter1;
}
}
else
{
/* Unexpected Interrupt */
/* Manage an error for robust application */
}

Note:

This code manages only a single counter overflow. To manage many counter overflows the
update interrupt must be enabled (UIE = 1) and properly managed.

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A.9.5

RM0091

PWM input configuration code example
/* (1) Select the active input TI1 for TIMx_CCR1 (CC1S = 01),
select the active input TI1 for TIMx_CCR2 (CC2S = 10) */
/* (2) Select TI1FP1 as valid trigger input (TS = 101)
configure the slave mode in reset mode (SMS = 100) */
/* (3) Enable capture by setting CC1E and CC2E
select the rising edge on CC1 and CC1N (CC1P = 0 and CC1NP = 0, reset
value),
select the falling edge on CC2 (CC2P = 1). */
/* (4) Enable interrupt on Capture/Compare 1 */
/* (5) Enable counter */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0 | TIM_CCMR1_CC2S_1; /* (1)*/
TIMx->SMCR |= TIM_SMCR_TS_2 | TIM_SMCR_TS_0
| TIM_SMCR_SMS_2; /* (2) */
TIMx->CCER |= TIM_CCER_CC1E | TIM_CCER_CC2E | TIM_CCER_CC2P; /* (3) */
TIMx->DIER |= TIM_DIER_CC1IE; /* (4) */
TIMx->CR1 |= TIM_CR1_CEN; /* (5) */

A.9.6

PWM input with DMA configuration code example
/*
/*
/*
/*

(1)
(2)
(3)
(4)

Enable the peripheral clock on DMA */
Configure the peripheral data register address for DMA channel x */
Configure the memory address for DMA channel x */
Configure the number of DMA tranfers to be performed
on DMA channel x */
/* (5) Configure no increment (reset value), size (16-bits), interrupts,
transfer from peripheral to memory and circular mode
for DMA channel x */
/* (6) Enable DMA Channel x */
RCC->AHBENR |= RCC_AHBENR_DMA1EN; /* (1) */
DMA1_Channel2->CPAR = (uint32_t) (&(TIM1->CCR1)); /* (2) */
DMA1_Channel2->CMAR = (uint32_t)(&Period); /* (3) */
DMA1_Channel2->CNDTR = 1; /* (4) */
DMA1_Channel2->CCR |= DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_0
| DMA_CCR_TEIE | DMA_CCR_CIRC; /* (5) */
DMA1_Channel2->CCR |= DMA_CCR_EN; /* (6) */
/* repeat (2) to (6) for channel 3 */
DMA1_Channel3->CPAR = (uint32_t) (&(TIM1->CCR2)); /* (2) */
DMA1_Channel3->CMAR = (uint32_t)(&DutyCycle); /* (3) */
DMA1_Channel3->CNDTR = 1; /* (4) */
DMA1_Channel3->CCR |= DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_0
| DMA_CCR_TEIE | DMA_CCR_CIRC; /* (5) */
DMA1_Channel3->CCR |= DMA_CCR_EN; /* (6) */
/* Configure NVIC for DMA */
/* (7) Enable Interrupt on DMA Channels x */
/* (8) Set priority for DMA Channels x */
NVIC_EnableIRQ(DMA1_Channel2_3_IRQn); /* (7) */
NVIC_SetPriority(DMA1_Channel2_3_IRQn,3); /* (8) */

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A.9.7

Code examples

Output compare configuration code example
/*
/*
/*
/*

Set prescaler to 3, so APBCLK/4 i.e 12MHz */
Set ARR = 12000 -1 */
Set CCRx = ARR, as timer clock is 12MHz, an event occurs each 1 ms */
Select toggle mode on OC1 (OC1M = 011),
disable preload register on OC1 (OC1PE = 0, reset value) */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (6) Enable output (MOE = 1)*/
/* (7) Enable counter */
TIMx->PSC |= 3; /* (1) */
TIMx->ARR = 12000 - 1; /* (2) */
TIMx->CCR1 = 12000 - 1; /* (3) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_0 | TIM_CCMR1_OC1M_1; /* (4) */
TIMx->CCER |= TIM_CCER_CC1E; /* (5)*/
TIMx->BDTR |= TIM_BDTR_MOE; /* (6) */
TIMx->CR1 |= TIM_CR1_CEN; /* (7) */

A.9.8

(1)
(2)
(3)
(4)

Edge-aligned PWM configuration example
/*
/*
/*
/*

(1)
(2)
(3)
(4)

Set prescaler to 47, so APBCLK/48 i.e 1MHz */
Set ARR = 8, as timer clock is 1MHz the period is 9 us */
Set CCRx = 4, , the signal will be high during 4 us */
Select PWM mode 1 on OC1 (OC1M = 110),
enable preload register on OC1 (OC1PE = 1) */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (6) Enable output (MOE = 1)*/
/* (7) Enable counter (CEN = 1)
select edge aligned mode (CMS = 00, reset value)
select direction as upcounter (DIR = 0, reset value) */
/* (8) Force update generation (UG = 1) */
TIMx->PSC = 47; /* (1) */
TIMx->ARR = 8; /* (2) */
TIMx->CCR1 = 4; /* (3) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1
| TIM_CCMR1_OC1PE; /* (4) */
TIMx->CCER |= TIM_CCER_CC1E; /* (5) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (6) */
TIMx->CR1 |= TIM_CR1_CEN; /* (7) */
TIMx->EGR |= TIM_EGR_UG; /* (8) */

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A.9.9

RM0091

Center-aligned PWM configuration example
/* (1) Set prescaler to 47, so APBCLK/48 i.e 1MHz */
/* (2) Set ARR = 8, as timer clock is 1MHz and center-aligned counting,
the period is 16 us */
/* (3) Set CCRx = 7, the signal will be high during 14 us */
/* (4) Select PWM mode 1 on OC1 (OC1M = 110),
enable preload register on OC1 (OC1PE = 1, reset value) */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (6) Enable output (MOE = 1)*/
/* (7) Enable counter (CEN = 1)
select center-aligned mode 1 (CMS = 01) */
/* (8) Force update generation (UG = 1) */
TIMx->PSC = 47; /* (1) */
TIMx->ARR = 8; /* (2) */
TIMx->CCR1 = 7; /* (3) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1
| TIM_CCMR1_OC1PE; /* (4) */
TIMx->CCER |= TIM_CCER_CC1E; /* (5) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (6) */
TIMx->CR1 |= TIM_CR1_CMS_0 | TIM_CR1_CEN; /* (7) */
TIMx->EGR |= TIM_EGR_UG; /* (8) */

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A.9.10

Code examples

ETR configuration to clear OCxREF code example
/* This code is similar to the edge-aligned PWM configuration but it enables
the clearing on OC1 for ETRclearing (OC1CE = 1) in CCMR1 (5) and ETR is
configured in SMCR (7).*/
/* (1) Set prescaler to 47, so APBCLK/48 i.e 1MHz */
/* (2) Set ARR = 8, as timer clock is 1MHz the period is 9 us */
/* (3) Set CCRx = 4, , the signal will be high during 4 us */
/* (4) Select PWM mode 1 on OC1 (OC1M = 110),
enable preload register on OC1 (OC1PE = 1),
enable clearing on OC1 for ETR clearing (OC1CE = 1) */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (6) Enable output (MOE = 1) */
/* (7) Select ETR as OCREF clear source (OCCS = 1),
select External Trigger Prescaler off (ETPS = 00, reset value),
disable external clock mode 2 (ECE = 0, reset value),
select active at high level (ETP = 0, reset value) */
/* (8) Enable counter (CEN = 1),
select edge aligned mode (CMS = 00, reset value),
select direction as upcounter (DIR = 0, reset value) */
/* (9) Force update generation (UG = 1) */
TIMx->PSC = 47; /* (1) */
TIMx->ARR = 8; /* (2) */
TIMx->CCR1 = 4; /* (3) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1 | TIM_CCMR1_OC1PE
| TIM_CCMR1_OC1CE; /* (4) */
TIMx->CCER |= TIM_CCER_CC1E; /* (5) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (6) */
TIMx->SMCR |= TIM_SMCR_OCCS; /* (7) */
TIMx->CR1 |= TIM_CR1_CEN; /* (8) */
TIMx->EGR |= TIM_EGR_UG; /* (9) */

A.9.11

Encoder interface code example
/* (1) Configure TI1FP1 on TI1 (CC1S = 01),
configure TI1FP2 on TI2 (CC2S = 01) */
/* (2) Configure TI1FP1 and TI1FP2 non inverted (CC1P = CC2P = 0, reset
value) */
/* (3) Configure both inputs are active on both rising and falling edges
(SMS = 011) */
/* (4) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0 | TIM_CCMR1_CC2S_0; /* (1)*/
TIMx->CCER &= (uint16_t)(~(TIM_CCER_CC21 | TIM_CCER_CC2P); /* (2) */
TIMx->SMCR |= TIM_SMCR_SMS_0 | TIM_SMCR_SMS_1; /* (3) */
TIMx->CR1 |= TIM_CR1_CEN; /* (4) */

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A.9.12

RM0091

Reset mode code example
/* (1) Configure channel 1 to detect rising edges on the TI1 input
by writing CC1S = ‘01’,
and configure the input filter duration by writing the IC1F[3:0]
bits in the TIMx_CCMR1 register (if no filter is needed, keep
IC1F=0000).*/
/* (2) Select rising edge polarity by writing CC1P=0 in the TIMx_CCER
register
Not necessary as it keeps the reset value. */
/* (3) Configure the timer in reset mode by writing SMS=100
Select TI1 as the trigger input source by writing TS=101
in the TIMx_SMCR register.*/
/* (4) Set prescaler to 48000-1 in order to get an increment each 1ms */
/* (5) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0; /* (1)*/
TIMx->CCER &= (uint16_t)(~TIM_CCER_CC1P); /* (2) */
TIMx->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_TS_2 | TIM_SMCR_TS_0; /* (3) */
TIM1->PSC = 47999; /* (4) */
TIMx->CR1 |= TIM_CR1_CEN; /* (5) */

A.9.13

Gated mode code example
/* (1) Configure channel 1 to detect low level on the TI1 input
by writing CC1S = ‘01’,
and configure the input filter duration by writing the IC1F[3:0]
bits in the TIMx_CCMR1 register (if no filter is needed,
keep IC1F=0000). */
/* (2) Select polarity by writing CC1P=1 in the TIMx_CCER register */
/* (3) Configure the timer in gated mode by writing SMS=101
Select TI1 as the trigger input source by writing TS=101
in the TIMx_SMCR register. */
/* (4) Set prescaler to 12000-1 in order to get an increment each 250us */
/* (5) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0; /* (1)*/
TIMx->CCER |= TIM_CCER_CC1P; /* (2) */
TIMx->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_0
| TIM_SMCR_TS_2 | TIM_SMCR_TS_0; /* (3) */
TIMx->PSC = 11999; /* (4) */
TIMx->CR1 |= TIM_CR1_CEN; /* (5) */

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A.9.14

Code examples

Trigger mode code example
/* (1) Configure channel 2 to detect rising edge on the TI2 input
by writing CC2S = ‘01’,
and configure the input filter duration by writing the IC1F[3:0]
bits in the TIMx_CCMR1 register (if no filter is needed,
keep IC1F=0000). */
/* (2) Select polarity by writing CC2P=0 (reset value) in the TIMx_CCER
register */
/* (3) Configure the timer in trigger mode by writing SMS=110
Select TI2 as the trigger input source by writing TS=110
in the TIMx_SMCR register. */
/* (4) Set prescaler to 12000-1 in order to get an increment each 250us */
TIMx->CCMR1 |= TIM_CCMR1_CC2S_0; /* (1)*/
TIMx->CCER &= ~TIM_CCER_CC2P; /* (2) */
TIMx->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1
| TIM_SMCR_TS_2 | TIM_SMCR_TS_1; /* (3) */
TIM1->PSC = 11999; /* (4) */

A.9.15

External clock mode 2 + trigger mode code example
/* (1) Configure no input filter (ETF=0000, reset value)
configure prescaler disabled (ETPS = 0, reset value)
select detection on rising edge on ETR (ETP = 0, reset value)
enable external clock mode 2 (ECE = 1) */
/* (2) Configure no input filter (IC1F=0000, reset value)
select input capture source on TI1 (CC1S = 01) */
/* (3) Select polarity by writing CC1P=0 (reset value) in the TIMx_CCER
register */
/* (4) Configure the timer in trigger mode by writing SMS=110
Select TI1 as the trigger input source by writing TS=101
in the TIMx_SMCR register. */
TIMx->SMCR |= TIM_SMCR_ECE; /* (1) */
TIMx->CCMR1 |= TIM_CCMR1_CC1S_0; /* (2)*/
TIMx->CCER &= ~TIM_CCER_CC1P; /* (3) */
TIMx->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1
| TIM_SMCR_TS_2 | TIM_SMCR_TS_0; /* (4) */
/* Use TI2FP2 as trigger 1 */
/* (1) Map TI2FP2 on TI2 by writing CC2S=01 in the TIMx_CCMR1 register */
/* (2) TI2FP2 must detect a rising edge, write CC2P=0 and CC2NP=0
in the TIMx_CCER register (keep the reset value) */
/* (3) Configure TI2FP2 as trigger for the slave mode controller (TRGI)
by writing TS=110 in the TIMx_SMCR register,
TI2FP2 is used to start the counter by writing SMS to ‘110'
in the TIMx_SMCR register (trigger mode) */
TIMx->CCMR1 |= TIM_CCMR1_CC2S_0; /* (1) */
//TIMx->CCER &= ~(TIM_CCER_CC2P | TIM_CCER_CC2NP); /* (2) */
TIMx->SMCR |= TIM_SMCR_TS_2 | TIM_SMCR_TS_1
| TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1; /* (3) */

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A.9.16

RM0091

One-Pulse mode code example
/*
/*
/*
/*
/*

OPM waveform is defined by writing the compare registers */
Set prescaler to 47, so APBCLK/48 i.e 1MHz */
Set ARR = 7, as timer clock is 1MHz the period is 8 us */
Set CCRx = 5, the burst will be delayed for 5 us (must be > 0) */
Select PWM mode 2 on OC1 (OC1M = 111),
enable preload register on OC1 (OC1PE = 1, reset value)
enable fast enable (no delay) if PULSE_WITHOUT_DELAY is set */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (6) Enable output (MOE = 1) */
/* (7) Write '1 in the OPM bit in the TIMx_CR1 register to stop the counter
at the next update event (OPM = 1),
enable auto-reload register(ARPE = 1) */
TIMx->PSC = 47; /* (1) */
TIMx->ARR = 7; /* (2) */
TIMx->CCR1 = 5; /* (3) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1 | TIM_CCMR1_OC1M_0
| TIM_CCMR1_OC1PE
#if PULSE_WITHOUT_DELAY > 0
| TIM_CCMR1_OC1FE
#endif
; /* (4) */
TIMx->CCER |= TIM_CCER_CC1E; /* (5) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (6) */
TIMx->CR1 |= TIM_CR1_OPM | TIM_CR1_ARPE; /* (7) */

A.9.17

The
(1)
(2)
(3)
(4)

Timer prescaling another timer code example
/* TIMy is slave of TIMx */
/* (1) Select Update Event as Trigger output (TRG0) by writing MMS = 010
in TIMx_CR2. */
/* (2) Configure TIMy in slave mode using ITR1 as internal trigger
by writing TS = 000 in TIMy_SMCR (reset value)
Configure TIMy in external clock mode 1, by writing SMS=111 in the
TIMy_SMCR register. */
/* (3) Set TIMx prescaler to 47999 in order to get an increment each 1ms */
/* (4) Set TIMx Autoreload to 999 in order to get an overflow (so an UEV)
each second */
/* (5) Set TIMx Autoreload to 24*3600-1 in order to get an overflow each 24hour */
/* (6) Enable the counter by writing CEN=1 in the TIMx_CR1 register. */
/* (7) Enable the counter by writing CEN=1 in the TIMy_CR1 register. */
TIMx->CR2 |= TIM_CR2_MMS_1; /* (1) */
TIMy->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1 | TIM_SMCR_SMS_0; /* (2) */
TIMx->PSC = 47999; /* (3) */
TIMx->ARR = 999; /* (4) */
TIMy->ARR = (24 * 3600) - 1; /* (5) */
TIMx->CR1 |= TIM_CR1_CEN; /* (6) */
TIMy->CR1 |= TIM_CR1_CEN; /* (7) */

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A.9.18

Code examples

Timer enabling another timer code example
/* TIMy is slave of TIMx */
/* (1) Configure Timer x master mode to send its Output Compare 1 Reference
(OC1REF) signal as trigger output
(MMS=100 in the TIM1_CR2 register). */
/* (2) Configure the Timer x OC1REF waveform (TIM1_CCMR1 register)
Channel 1 is in PWM mode 1 when the counter is less than the
capture/compare register (write OC1M = 110) */
/* (3) Configure TIMy in slave mode using ITR1 as internal trigger
by writing TS = 000 in TIMy_SMCR (reset value)
Configure TIMy in gated mode, by writing SMS=101 in the
TIMy_SMCR register. */
/* (4) Set TIMx prescaler to 2 */
/* (5) Set TIMy prescaler to 2 */
/* (6) Set TIMx Autoreload to 999 in order to get an overflow (so an UEV)
each 100ms */
/* (7) Set capture compare register to a value between 0 and 999 */
TIMx->CR2 |= TIM_CR2_MMS_2; /* (1) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1; /* (2) */
TIMy->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_0; /* (3) */
TIMx->PSC = 2; /* (4) */
TIMy->PSC = 2; /* (5) */
TIMx->ARR = 999; /* (6) */
TIMx-> CCR1 = 700; /* (7) */
/* Configure the slave timer to generate toggling on each count */
/* (1) Configure the TIMy in PWM mode 1 (write OC1M = 110) */
/* (2) Set TIMy Autoreload to 1 */
/* (3) Set capture compare register to 1 */
TIMy->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1; /* (1) */
TIMy->ARR = 1; /* (2) */
TIMy-> CCR1 = 1; /* (3) */
/* Enable the output of TIMx OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (2) Enable output (MOE = 1) */
TIMx->CCER |= TIM_CCER_CC1E; /* (1) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (2) */
/* Enable the output of TIMy OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (2) Enable output (MOE = 1) */
TIMy->CCER |= TIM_CCER_CC1E; /* (1) */
TIMy->BDTR |= TIM_BDTR_MOE; /* (2) */
/* (1) Enable the slave counter first by writing CEN=1
in the TIMy_CR1 register. */
/* (2) Enable the master counter by writing CEN=1
in the TIMx_CR1 register. */
TIMy->CR1 |= TIM_CR1_CEN; /* (1) */
TIMx->CR1 |= TIM_CR1_CEN; /* (2) */

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RM0091

Master and slave synchronization code example
/* (1) Configure Timer x master mode to send its enable signal
as trigger output (MMS=001 in the TIM1_CR2 register). */
/* (2) Configure the Timer x Channel 1 waveform (TIM1_CCMR1 register)
is in PWM mode 1 (write OC1M = 110) */
/* (3) Configure TIMy in slave mode using ITR1 as internal trigger
by writing TS = 000 in TIMy_SMCR (reset value)
Configure TIMy in gated mode, by writing SMS=101 in the
TIMy_SMCR register. */
/* (4) Set TIMx prescaler to 2 */
/* (5) Set TIMy prescaler to 2 */
/* (6) Set TIMx Autoreload to 99 in order to get an overflow (so an UEV)
each 10ms */
/* (7) Set capture compare register to a value between 0 and 99 */
TIMx->CR2 |= TIM_CR2_MMS_0; /* (1) */
TIMx->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1; /* (2) */
TIMy->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_0; /* (3) */
TIMx->PSC = 2; /* (4) */
TIMy->PSC = 2; /* (5) */
TIMx->ARR = 99; /* (6) */
TIMx-> CCR1 = 25; /* (7) */
/* Configure the slave timer Channel 1 as PWM as Timer
to show synchronicity */
/* (1) Configure the TIMy in PWM mode 1 (write OC1M = 110) */
/* (2) Set TIMy Autoreload to 99 */
/* (3) Set capture compare register to 25 */
TIMy->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1; /* (1) */
TIMy->ARR = 99; /* (2) */
TIMy-> CCR1 = 25; /* (3) */
/* Enable the output of TIMx OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (2) Enable output (MOE = 1) */
TIMx->CCER |= TIM_CCER_CC1E; /* (1) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (2) */
/* Enable the output of TIMy OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (2) Enable output (MOE = 1) */
TIMy->CCER |= TIM_CCER_CC1E; /* (1) */
TIMy->BDTR |= TIM_BDTR_MOE; /* (2) */
/* (1) Reset Timer x by writing ‘1 in UG bit (TIMx_EGR register) */
/* (2) Reset Timer y by writing ‘1 in UG bit (TIMy_EGR register) */
TIMx->EGR |= TIM_EGR_UG; /* (1) */
TIMy->EGR |= TIM_EGR_UG; /* (2) */
/* (1) Enable the slave counter first by writing CEN=1 in the TIMy_CR1
register.
TIMy will start synchronously with the master timer */
/* (2) Start the master counter by writing CEN=1
in the TIMx_CR1 register. */
TIMy->CR1 |= TIM_CR1_CEN; /* (1) */
TIMx->CR1 |= TIM_CR1_CEN; /* (2) */

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A.9.20

Code examples

Two timers synchronized by an external trigger code example
/* (1) Configure TIMx master mode to send its enable signal
as trigger output (MMS=001 in the TIM1_CR2 register). */
/* (2) Configure TIMx in slave mode to get the input trigger from TI1
by writing TS = 100 in TIMx_SMCR
Configure TIMx in trigger mode, by writing SMS=110 in the
TIMx_SMCR register.
Configure TIMx in Master/Slave mode by writing MSM = 1
in TIMx_SMCR */
/* (3) Configure TIMy in slave mode to get the input trigger from Timer1
by writing TS = 000 in TIMy_SMCR (reset value)
Configure TIMy in trigger mode, by writing SMS=110 in the
TIMy_SMCR register. */
/* (4) Reset Timer x counter by writing ‘1 in UG bit (TIMx_EGR register) */
/* (5) Reset Timer y counter by writing ‘1 in UG bit (TIMy_EGR register) */
TIMx->CR2 |= TIM_CR2_MMS_0; /* (1)*/
TIMx->SMCR |= TIM_SMCR_TS_2 | TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1
| TIM_SMCR_MSM; /* (2) */
TIMy->SMCR |= TIM_SMCR_SMS_2 | TIM_SMCR_SMS_1; /* (3) */
TIMx->EGR |= TIM_EGR_UG; /* (4) */
TIMy->EGR |= TIM_EGR_UG; /* (5) */
/* Configure the Timer Channel 2 as PWM */
/* (1) Configure the Timer x Channel 2 waveform (TIM1_CCMR1 register)
is in PWM mode 1 (write OC2M = 110) */
/* (2) Set TIMx prescaler to 2 */
/* (3) Set TIMx Autoreload to 99 in order to get an overflow (so an UEV)
each 10ms */
/* (4) Set capture compare register to a value between 0 and 99 */
TIMx->CCMR1 |= TIM_CCMR1_OC2M_2 | TIM_CCMR1_OC2M_1; /* (1) */
TIMx->PSC = 2; /* (2) */
TIMx->ARR = 99; /* (3) */
TIMx->CCR2 = 25; /* (4) */
/* Configure the slave timer Channel 1 as PWM as Timer
to show synchronicity */
/* (1) Configure the TIMy in PWM mode 1 (write OC1M = 110) */
/* (2) Set TIMy prescaler to 2 */
/* (3) Set TIMx Autoreload to 99 */
/* (4) Set capture compare register to 25 */
TIMy->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1; /* (1) */
TIMy->PSC = 2; /* (2) */
TIMy->ARR = 99; /* (3) */
TIMy-> CCR1 = 25; /* (4) */
/* Enable the output of TIMx OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (2) Enable output (MOE = 1)*/
TIMx->CCER |= TIM_CCER_CC2E; /* (1) */
TIMx->BDTR |= TIM_BDTR_MOE; /* (2) */
/* Enable the output of TIMy OC1 */
/* (1) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (2) Enable output (MOE = 1)*/
TIMy->CCER |= TIM_CCER_CC1E; /* (1) */
TIMy->BDTR |= TIM_BDTR_MOE; /* (2) */

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DMA burst feature code example
/* In this example TIMx has been previously configured
in PWM center-aligned */
/* Configure DMA Burst Feature */
/* Configure the corresponding DMA channel */
/* (1) Set DMA channel peripheral address is the DMAR register address */
/* (2) Set DMA channel memory address is the address of the buffer
in the RAM containing the data to be transferred by DMA
into CCRx registers */
/* (3) Set the number of data transfer to sizeof(Duty_Cycle_Table) */
/* (4) Configure DMA transfer in CCR register,
enable the circular mode by setting CIRC bit (optional),
set memory size to 16_bits MSIZE = 01,
set peripheral size to 32_bits PSIZE = 10,
enable memory increment mode by setting MINC,
set data transfer direction read from memory by setting DIR. */
/* (5) Configure TIMx_DCR register with DBL = 3 transfers
and DBA = (@TIMx->CCR2 - @TIMx->CR1) >> 2 = 0xE */
/* (6) Enable the TIMx update DMA request by setting UDE bit in DIER
register */
/* (7) Enable TIMx */
/* (8) Enable DMA channel */
DMA1_Channel2->CPAR = (uint32_t)(&(TIMx->DMAR)); /* (1) */
DMA1_Channel2->CMAR = (uint32_t)(Duty_Cycle_Table); /* (2) */
DMA1_Channel2->CNDTR = 10*3; /* (3) */
DMA1_Channel2->CCR |= DMA_CCR_CIRC | DMA_CCR_MSIZE_0 | DMA_CCR_PSIZE_1
| DMA_CCR_MINC | DMA_CCR_DIR; /* (4) */
TIMx->DCR = (3 << 8)
+ ((((uint32_t)(&TIMx->CCR2))
- ((uint32_t)(&TIMx->CR1))) >> 2); /* (5) */
TIMx->DIER |= TIM_DIER_UDE; /* (6) */
TIMx->CR1 |= TIM_CR1_CEN; /* (7) */
DMA1_Channel2->CCR |= DMA_CCR_EN; /* (8) */

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Code examples

A.10

IRTIM code example

A.10.1

TIM16 and TIM17 configuration code example
/* The following configuration is for RC5 standard */
/* TIM16 is used for the enveloppe while TIM17 is used for the carrier */
#define TIM_ENV TIM16
#define TIM_CAR TIM17
/* (1) Enable the peripheral clocks of Timer 16 and 17 and SYSCFG */
/* (2) Enable the peripheral clock of GPIOB */
/* (3) Select alternate function mode on GPIOB pin 9 */
/* (4) Select AF0 on PB9 in AFRH for IR_OUT (reset value) */
/* (5) Enable the high sink driver capability by setting I2C_PB9_FM+ bit
in SYSCFG_CFGR1 */
RCC->APB2ENR |= RCC_APB2ENR_TIM16EN | RCC_APB2ENR_TIM17EN
| RCC_APB2ENR_SYSCFGCOMPEN; /* (1) */
RCC->AHBENR |= RCC_AHBENR_GPIOBEN; /* (2) */
GPIOB->MODER = (GPIOB->MODER & ~GPIO_MODER_MODER9)
| GPIO_MODER_MODER9_1; /* (3) */
GPIOB->AFR[1] &= ~(0x0F << ((9 - 8) * 4)); /* (4) */
SYSCFG->CFGR1 |= SYSCFG_CFGR1_I2C_FMP_PB9; /* (5) */
/* Configure TIM_CAR as carrier signal */
/* (1) Set prescaler to 1, so APBCLK i.e 48MHz */
/* (2) Set ARR = 1333, as timer clock is 48MHz the frequency is 36kHz */
/* (3) Set CCRx = 1333/4, , the signal will bhave a 25% duty cycle */
/* (4) Select PWM mode 1 on OC1 (OC1M = 110),
enable preload register on OC1 (OC1PE = 1) */
/* (5) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1)*/
/* (6) Enable output (MOE = 1)*/
TIM_CAR->PSC = v; /* (1) */
TIM_CAR->ARR = 1333; /* (2) */
TIM_CAR->CCR1 = (uint16_t)(1333 / 4); /* (3) */
TIM_CAR->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1
| TIM_CCMR1_OC1PE; /* (4) */
TIM_CAR->CCER |= TIM_CCER_CC1E; /* (5) */
TIM_CAR->BDTR |= TIM_BDTR_MOE; /* (6) */
/* Configure TIM_ENV is the modulation enveloppe */
/* (1) Set prescaler to 1, so APBCLK i.e 48MHz */
/* (2) Set ARR = 42627, as timer clock is 48MHz the period is 888 us */
/* (3) Select Forced inactive on OC1 (OC1M = 100) */
/* (4) Select active high polarity on OC1 (CC1P = 0, reset value),
enable the output on OC1 (CC1E = 1) */
/* (5) Enable output (MOE = 1) */
/* (6) Enable Update interrupt (UIE = 1) */
TIM_ENV->PSC = 0; /* (1) */
TIM_ENV->ARR = 42627; /* (2) */
TIM_ENV->CCMR1 |= TIM_CCMR1_OC1M_2; /* (3) */
TIM_ENV->CCER |= TIM_CCER_CC1E; /* (4) */
TIM_ENV->BDTR |= TIM_BDTR_MOE; /* (5) */
TIM_ENV->DIER |= TIM_DIER_UIE; /* (6) */
/* Enable and reset TIM_CAR only */
/* (1) Enable counter (CEN = 1),
select edge aligned mode (CMS = 00, reset value),
select direction as upcounter (DIR = 0, reset value) */

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/* (2) Force update generation (UG = 1) */
TIM_CAR->CR1 |= TIM_CR1_CEN; /* (1) */
TIM_CAR->EGR |= TIM_EGR_UG; /* (2) */
/* Configure TIM_ENV interrupt */
/* (1) Enable Interrupt on TIM_ENV */
/* (2) Set priority for TIM_ENV */
NVIC_EnableIRQ(TIM_ENV_IRQn); /* (1) */
NVIC_SetPriority(TIM_ENV_IRQn,0); /* (2) */

A.10.2

IRQHandler for IRTIM code example
/**
* Description: This function handles TIM_16 interrupt request.
*
This interrupt subroutine computes the laps between 2
*
rising edges on T1IC.
*
This laps is stored in the "Counter" variable.
*/
void TIM16_IRQHandler(void)
{
uint8_t bit_msg = 0;
if ((SendOperationReady == 1)
&& (BitsSentCounter < (RC5_GlobalFrameLength * 2)))
{
if (BitsSentCounter < 32)
{
SendOperationCompleted = 0x00;
bit_msg = (uint8_t)((ManchesterCodedMsg >> BitsSentCounter)& 1);
if (bit_msg== 1)
{
/* Force active level - OC1REF is forced high */
TIM_ENV->CCMR1 |= TIM_CCMR1_OC1M_0;
}
else
{
/* Force inactive level - OC1REF is forced low */
TIM_ENV->CCMR1 &= (uint16_t)(~TIM_CCMR1_OC1M_0);
}
}
BitsSentCounter++;
}
else
{
SendOperationCompleted = 0x01;
SendOperationReady = 0;
BitsSentCounter = 0;
}
/* Clear TIM_ENV update interrupt */
TIM_ENV->SR &= (uint16_t)(~TIM_SR_UIF);
}

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Code examples

A.11

bxCAN code example

A.11.1

bxCAN initialization mode code example
/*
/*
/*
/*

Enter CAN init mode to write the configuration */
Wait the init mode entering */
Exit sleep mode */
Loopback mode, set timing to 1Mb/s: BS1 = 4, BS2 = 3,
prescaler = 6 */
/* (5) Leave init mode */
/* (6) Wait the init mode leaving */
/* (7) Enter filter init mode, (16-bit + mask, filter 0 for FIFO 0) */
/* (8) Acivate filter 0 */
/* (9) Set the Id and the mask (all bits of standard id care */
/* (10) Leave filter init */
/* (11) Set FIFO0 message pending IT enable */
CAN->MCR |= CAN_MCR_INRQ; /* (1) */
while ((CAN->MSR & CAN_MSR_INAK) != CAN_MSR_INAK) /* (2) */
{
/* add time out here for a robust application */
}
CAN->MCR &=~ CAN_MCR_SLEEP; /* (3) */
CAN->BTR |= CAN_BTR_LBKM | 2 << 20 | 3 << 16 | 5 << 0; /* (4) */
CAN->MCR &=~ CAN_MCR_INRQ; /* (5) */
while ((CAN->MSR & CAN_MSR_INAK) == CAN_MSR_INAK) /* (6) */
{
/* add time out here for a robust application */
}
CAN->FMR |= CAN_FMR_FINIT; /* (7) */
CAN->FA1R |= CAN_FA1R_FACT0; /* (8) */
CAN->sFilterRegister[0].FR1 = CAN_ID << 5 | 0xFF70U << 16; /* (9) */
CAN->FMR &=~ CAN_FMR_FINIT; /* (10) */
CAN->IER |= CAN_IER_FMPIE0; /* (11) */

A.11.2

(1)
(2)
(3)
(4)

bxCAN transmit code example
/* (1) check mailbox 0 is empty */
/* (2) fill data length = 1 */
/* (3) fill 8-bit data */
/* (4) fill Id field and request a transmission */
if ((CAN->TSR & CAN_TSR_TME0) == CAN_TSR_TME0) /* (1) */
{
CAN->sTxMailBox[0].TDTR = 1; /* (2) */
CAN->sTxMailBox[0].TDLR = CMD; /* (3) */
CAN->sTxMailBox[0].TIR = (uint32_t)(CAN_ID << 21
| CAN_TI0R_TXRQ); /* (4) */
}

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RM0091

bxCAN receive code example
/* check if a message is filtered and received by FIFO 0 */
if ((CAN->RF0R & CAN_RF0R_FMP0)!=0)
{
CAN_ReceiveMessage = CAN->sFIFOMailBox[0].RDLR; /* read data */
CAN->RF0R |= CAN_RF0R_RFOM0; /* release FIFO */
if ((CAN_ReceiveMessage & 0xFF) == CMD)
{
/* Process */
}
}

A.12

DBG code example

A.12.1

DBG read device ID code example
/* Read MCU Id, 32-bit access */
MCU_Id = DBGMCU->IDCODE;

A.12.2

DBG debug in Low-power mode code example
/* To be able to debug in stop mode */
DBGMCU->CR |= DBGMCU_CR_DBG_STOP;

A.13

HDMI-CEC code example

A.13.1

HDMI-CEC configure CEC code example
/* (1) OAR = 0x0001 => OA = 0x0 */
/* (2) Receive byte interrupt enable, receive end interrupt enable */
/* (3) CEC enable */
CEC->CFGR = (0x001<<16); /* (1) */
CEC->IER = CEC_IER_RXBRIEICEC_IER_RXENDIE; /* (2) */
CEC->CR = CEC_CR_CECEN; /* (3) */

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A.13.2

Code examples

HDMI-CEC transmission with interrupt enabled code example
/* (1) Set transmit IT */
/* (2) Fill transmit data register with nibbles (initiator 0x0, destination
0x1) */
/* (3) Set start of message bit */
CEC->IER |= CEC_IER_TXBRIE; /* (1) */
CEC->TXDR = (uint32_t)(ADDRESS_INITIATOR << 4
| ADDRESS_DESTINATION); /* (2) */
CEC->CR |= CEC_CR_TXSOM; /* (3) */

A.13.3

HDMI-CEC interrupt management code example
if ((CEC->ISR & CEC_ISR_RXEND) == CEC_ISR_RXEND)
{
CEC->ISR = CEC_ISR_RXBR | CEC_ISR_RXEND; /* Reset flag */
Received_Data = CEC->RXDR;
if (Received_Data == CMD)
{
/* Process */
}
}
else if ((CEC->ISR & CEC_ISR_RXBR) == CEC_ISR_RXBR)
{
CEC->ISR = CEC_ISR_RXBR; /* Reset flag */
Received_Data = CEC->RXDR;
/* Process */
}
else if ((CEC->ISR & CEC_ISR_TXBR) == CEC_ISR_TXBR)
{
CEC->IER &= ~CEC_IER_TXBRIE; /* Reset Tx IT */
CEC->CR I= CEC_CR_TXEOM; /* this is the last byte */
CEC->TXDR = CMD;
}

A.14

I2C code example

A.14.1

I2C configured in master mode to receive code example
/* (1) Timing register value is computed with the AN4235 xls file,
fast Mode @400kHz with I2CCLK = 48MHz, rise time = 140ns,
fall time = 40ns */
/* (2) Periph enable, receive interrupt enable */
/* (3) Slave address = 0x5A, read transfer, 1 byte to receive, autoend */
I2C2->TIMINGR = (uint32_t)0x00B01A4B; /* (1) */
I2C2->CR1 = I2C_CR1_PE | I2C_CR1_RXIE; /* (2) */
I2C2->CR2 = I2C_CR2_AUTOEND | (1<<16) | I2C_CR2_RD_WRN
| (I2C1_OWN_ADDRESS << 1); /* (3) */

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RM0091

I2C configured in master mode to transmit code example
/* (1) Timing register value is computed with the AN4235 xls file,
fast Mode @400kHz with I2CCLK = 48MHz, rise time = 140ns,
fall time = 40ns */
/* (2) Periph enable */
/* (3) Slave address = 0x5A, write transfer, 1 byte to transmit, autoend */
I2C2->TIMINGR = (uint32_t)0x00B01A4B; /* (1) */
I2C2->CR1 = I2C_CR1_PE; /* (2) */
I2C2->CR2 = I2C_CR2_AUTOEND | (1 << 16) | (I2C1_OWN_ADDRESS << 1); /* (3) */

A.14.3

I2C configured in slave mode code example
/* (1) Timing register value is computed with the AN4235 xls file,
fast Mode @400kHz with I2CCLK = 48MHz, rise time = 140ns,
fall time = 40ns */
/* (2) Periph enable, address match interrupt enable */
/* (3) 7-bit address = 0x5A */
/* (4) Enable own address 1 */
I2C1->TIMINGR = (uint32_t)0x00B00000; /* (1) */
I2C1->CR1 = I2C_CR1_PE | I2C_CR1_ADDRIE; /* (2) */
I2C1->OAR1 |= (uint32_t)(I2C1_OWN_ADDRESS << 1); /* (3) */
I2C1->OAR1 |= I2C_OAR1_OA1EN; /* (4) */

A.14.4

I2C master transmitter code example
/* Check Tx empty */
if ((I2C2->ISR & I2C_ISR_TXE) == I2C_ISR_TXE)
{
I2C2->TXDR = I2C_BYTE_TO_SEND; /* Byte to send */
I2C2->CR2 |= I2C_CR2_START; /* Go */
}

A.14.5

I2C master receiver code example
if ((I2C2->ISR & I2C_ISR_RXNE) == I2C_ISR_RXNE)
{
/* Read receive register, will clear RXNE flag */
if (I2C2->RXDR == I2C_BYTE_TO_SEND)
{
/* Process */
}
}

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A.14.6

Code examples

I2C slave transmitter code example
uint32_t I2C_InterruptStatus = I2C1->ISR; /* Get interrupt status */
/* Check address match */
if ((I2C_InterruptStatus & I2C_ISR_ADDR) == I2C_ISR_ADDR)
{
I2C1->ICR |= I2C_ICR_ADDRCF; /* Clear address match flag */
/* Check if transfer direction is read (slave transmitter) */
if ((I2C1->ISR & I2C_ISR_DIR) == I2C_ISR_DIR)
{
I2C1->CR1 |= I2C_CR1_TXIE; /* Set transmit IT */
}
}
else if ((I2C_InterruptStatus & I2C_ISR_TXIS) == I2C_ISR_TXIS)
{
I2C1->CR1 &=~ I2C_CR1_TXIE; /* Disable transmit IT */
I2C1->TXDR = I2C_BYTE_TO_SEND; /* Byte to send */
}

A.14.7

I2C slave receiver code example
uint32_t I2C_InterruptStatus = I2C1->ISR; /* Get interrupt status */
if ((I2C_InterruptStatus & I2C_ISR_ADDR) == I2C_ISR_ADDR)
{
I2C1->ICR |= I2C_ICR_ADDRCF; /* Address match event */
}
else if ((I2C_InterruptStatus & I2C_ISR_RXNE) == I2C_ISR_RXNE)
{
/* Read receive register, will clear RXNE flag */
if (I2C1->RXDR == I2C_BYTE_TO_SEND)
{
/* Process */
}
}

A.14.8

I2C configured in master mode to transmit with DMA code example
/* (1) Timing register value is computed with the AN4235 xls file,
fast Mode @400kHz with I2CCLK = 48MHz, rise time = 140ns,
fall time = 40ns */
/* (2) Periph enable */
/* (3) Slave address = 0x5A, write transfer, 2 bytes to transmit,
autoend */
I2C2->TIMINGR = (uint32_t)0x00B01A4B; /* (1) */
I2C2->CR1 = I2C_CR1_PE | I2C_CR1_TXDMAEN; /* (2) */
I2C2->CR2 = I2C_CR2_AUTOEND | (SIZE_OF_DATA << 16)
| (I2C1_OWN_ADDRESS << 1); /* (3) */

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RM0091

I2C configured in slave mode to receive with DMA code example
/* (1) Timing register value is computed with the AN4235 xls file,
fast Mode @400kHz with I2CCLK = 48MHz, rise time = 140ns,
fall time = 40ns */
/* (2) Periph enable, receive DMA enable */
/* (3) 7-bit address = 0x5A */
/* (4) Enable own address 1 */
I2C1->TIMINGR = (uint32_t)0x00B00000; /* (1) */
I2C1->CR1 = I2C_CR1_PE | I2C_CR1_RXDMAEN | I2C_CR1_ADDRIE; /* (2) */
I2C1->OAR1 |= (uint32_t)(I2C1_OWN_ADDRESS << 1); /* (3) */
I2C1->OAR1 |= I2C_OAR1_OA1EN; /* (4) */

A.15

IWDG code example

A.15.1

IWDG configuration code example
/* (1) Activate IWDG (not needed if done in option bytes) */
/* (2) Enable write access to IWDG registers */
/* (3) Set prescaler by 8 */
/* (4) Set reload value to have a rollover each 100ms */
/* (5) Check if flags are reset */
/* (6) Refresh counter */
IWDG->KR = IWDG_START; /* (1) */
IWDG->KR = IWDG_WRITE_ACCESS; /* (2) */
IWDG->PR = IWDG_PR_PR_0; /* (3) */
IWDG->RLR = IWDG_RELOAD; /* (4) */
while (IWDG->SR) /* (5) */
{
/* add time out here for a robust application */
}
IWDG->KR = IWDG_REFRESH; /* (6) */

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A.15.2

Code examples

IWDG configuration with window code example
/* (1) Activate IWDG (not needed if done in option bytes) */
/* (2) Enable write access to IWDG registers */
/* (3) Set prescaler by 8 */
/* (4) Set reload value to have a rollover each 100ms */
/* (5) Check if flags are reset */
/* (6) Set a 50ms window, this will refresh the IWDG */
IWDG->KR = IWDG_START; /* (1) */
IWDG->KR = IWDG_WRITE_ACCESS; /* (2) */
IWDG->PR = IWDG_PR_PR_0; /* (3) */
IWDG->RLR = IWDG_RELOAD; /* (4) */
while (IWDG->SR) /* (5) */
{
/* add time out here for a robust application */
}
IWDG->WINR = IWDG_RELOAD >> 1; /* (6) */

A.16

RTC code example

A.16.1

RTC calendar configuration code example
/* (1) Write access for RTC registers */
/* (2) Enable init phase */
/* (3) Wait until it is allow to modify RTC register values */
/* (4) set prescaler, 40kHz/128 => 312 Hz, 312Hz/312 => 1Hz */
/* (5) New time in TR */
/* (6) Disable init phase */
/* (7) Disable write access for RTC registers */
RTC->WPR = 0xCA; /* (1) */
RTC->WPR = 0x53; /* (1) */
RTC->ISR |= RTC_ISR_INIT; /* (2) */
while ((RTC->ISR & RTC_ISR_INITF) != RTC_ISR_INITF) /* (3) */
{
/* add time out here for a robust application */
}
RTC->PRER = 0x007F0137; /* (4) */
RTC->TR = RTC_TR_PM | Time; /* (5) */
RTC->ISR &=~ RTC_ISR_INIT; /* (6) */
RTC->WPR = 0xFE; /* (7) */
RTC->WPR = 0x64; /* (7) */

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RTC alarm configuration code example
/* (1) Write access for RTC registers */
/* (2) Disable alarm A to modify it */
/* (3) Wait until it is allow to modify alarm A value */
/* (4) Modify alarm A mask to have an interrupt each 1Hz */
/* (5) Enable alarm A and alarm A interrupt */
/* (6) Disable write access */
RTC->WPR = 0xCA; /* (1) */
RTC->WPR = 0x53; /* (1) */
RTC->CR &=~ RTC_CR_ALRAE; /* (2) */
while ((RTC->ISR & RTC_ISR_ALRAWF) != RTC_ISR_ALRAWF) /* (3) */
{
/* add time out here for a robust application */
}
RTC->ALRMAR = RTC_ALRMAR_MSK4 | RTC_ALRMAR_MSK3
| RTC_ALRMAR_MSK2 | RTC_ALRMAR_MSK1; /* (4) */
RTC->CR = RTC_CR_ALRAIE | RTC_CR_ALRAE; /* (5) */
RTC->WPR = 0xFE; /* (6) */
RTC->WPR = 0x64; /* (6) */

A.16.3

RTC WUT configuration code example
/* (1) Write access for RTC registers */
/* (2) Disable wake up timerto modify it */
/* (3) Wait until it is allow to modify wake up reload value */
/* (4) Modify wake upvalue reload counter to have a wake up each 1Hz */
/* (5) Enable wake up counter and wake up interrupt */
/* (6) Disable write access */
RTC->WPR = 0xCA; /* (1) */
RTC->WPR = 0x53; /* (1) */
RTC->CR &= ~RTC_CR_WUTE; /* (2) */
while ((RTC->ISR & RTC_ISR_WUTWF) != RTC_ISR_WUTWF) /* (3) */
{
/* add time out here for a robust application */
}
RTC->WUTR = 0x9C0; /* (4) */
RTC->CR = RTC_CR_WUTE | RTC_CR_WUTIE; /* (5) */
RTC->WPR = 0xFE; /* (6) */
RTC->WPR = 0x64; /* (6) */

A.16.4

RTC read calendar code example
if((RTC->ISR & RTC_ISR_RSF) == RTC_ISR_RSF)
{
TimeToCompute = RTC->TR; /* get time */
DateToCompute = RTC->DR; /* need to read date also */
}

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A.16.5

Code examples

RTC calibration code example
/* (1) Write access for RTC registers */
/* (2) Enable init phase */
/* (3) Wait until it is allow to modify RTC register values */
/* (4) set prescaler, 40kHz/125 => 320 Hz, 320Hz/320 => 1Hz */
/* (5) New time in TR */
/* (6) Disable init phase */
/* (7) Wait until it's allow to modify calibartion register */
/* (8) Set calibration to around +20ppm, which is a standard value @25°C */
/* Note: the calibration is relevant when LSE is selected for RTC clock */
/* (9) Disable write access for RTC registers */
RTC->WPR = 0xCA; /* (1) */
RTC->WPR = 0x53; /* (1) */
RTC->ISR |= RTC_ISR_INIT; /* (2) */
while ((RTC->ISR & RTC_ISR_INITF) != RTC_ISR_INITF) /* (3) */
{
/* add time out here for a robust application */
}
RTC->PRER = (124<<16) | 319; /* (4) */
RTC->TR = RTC_TR_PM | Time; /* (5) */
RTC->ISR &=~ RTC_ISR_INIT; /* (6) */
while((RTC->ISR & RTC_ISR_RECALPF) == RTC_ISR_RECALPF) /* (7) */
{
/* add time out here for a robust application */
}
RTC->CALR = RTC_CALR_CALP | 482; /* (8) */
RTC->WPR = 0xFE; /* (9) */
RTC->WPR = 0x64; /* (9) */

A.16.6

RTC tamper and time stamp configuration code example
/* Tamper configuration:
- Disable precharge (PU)
- RTCCLK/256 tamper sampling frequency
- Activate time stamp on tamper detection
- input rising edge trigger detection on RTC_TAMP2 (PA0)
- Tamper interrupt enable */
RTC->TAFCR = RTC_TAFCR_TAMPPUDIS | RTC_TAFCR_TAMPFREQ | RTC_TAFCR_TAMPTS
| RTC_TAFCR_TAMP2E | RTC_TAFCR_TAMPIE;

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RTC tamper and time stamp code example
/* Check tamper and timestamp flag */
if (((RTC->ISR & (RTC_ISR_TAMP2F)) == (RTC_ISR_TAMP2F))
&& ((RTC->ISR & (RTC_ISR_TSF)) == (RTC_ISR_TSF)))
{
RTC->ISR &= ~RTC_ISR_TAMP2F; /* clear tamper flag */
EXTI->PR = EXTI_PR_PR19; /* clear exti line 19 flag */
TimeToCompute = RTC->TSTR; /* get tamper time in timestamp register */
RTC->ISR &= ~RTC_ISR_TSF; /* clear timestamp flag */
}

A.16.8

RTC clock output code example
/*
/*
/*
/*
/*

(1)
(2)
(3)
(4)
(5)

Write access for RTC registers */
Disable alarm A to modify it */
Wait until it is allow to modify alarm A value */
Modify alarm A mask to have an interrupt each 1Hz */
Enable alarm A and alarm A interrupt,
enable calibration output (1Hz) */
/* (6) Disable write access */
RTC->WPR = 0xCA; /* (1) */
RTC->WPR = 0x53; /* (1) */
RTC->CR &=~ RTC_CR_ALRAE; /* (2) */
while ((RTC->ISR & RTC_ISR_ALRAWF) != RTC_ISR_ALRAWF) /* (3) */
{
/* add time out here for a robust application */
}
RTC->ALRMAR = RTC_ALRMAR_MSK4 | RTC_ALRMAR_MSK3
| RTC_ALRMAR_MSK2 | RTC_ALRMAR_MSK1; /* (4) */
RTC->CR = RTC_CR_ALRAIE | RTC_CR_ALRAE | RTC_CR_COE
| RTC_CR_COSEL; /* (5) */
RTC->WPR = 0xFE; /* (6) */
RTC->WPR = 0x64; /* (6) */

A.17

SPI code example

A.17.1

SPI master configuration code example
/* (1) Master selection, BR: Fpclk/256 (due to C27 on the board, SPI_CLK is
set to the minimum) CPOL and CPHA at zero (rising first edge) */
/* (2) Slave select output enabled, RXNE IT, 8-bit Rx fifo */
/* (3) Enable SPI1 */
SPI1->CR1 = SPI_CR1_MSTR | SPI_CR1_BR; /* (1) */
SPI1->CR2 = SPI_CR2_SSOE | SPI_CR2_RXNEIE | SPI_CR2_FRXTH
| SPI_CR2_DS_2 | SPI_CR2_DS_1 | SPI_CR2_DS_0; /* (2) */
SPI1->CR1 |= SPI_CR1_SPE; /* (3) */

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Code examples

SPI slave configuration code example
/* nSS hard, slave, CPOL and CPHA at zero (rising first edge) */
/* (1) RXNE IT, 8-bit Rx fifo */
/* (2) Enable SPI2 */
SPI2->CR2 = SPI_CR2_RXNEIE | SPI_CR2_FRXTH
| SPI_CR2_DS_2 | SPI_CR2_DS_1 | SPI_CR2_DS_0; /* (1) */
SPI2->CR1 |= SPI_CR1_SPE; /* (2) */

A.17.3

SPI full duplex communication code example
if ((SPI1->SR & SPI_SR_TXE) == SPI_SR_TXE) /* Test Tx empty */
{
/* Will inititiate 8-bit transmission if TXE */
*(uint8_t *)&(SPI1->DR) = SPI1_DATA;
}

A.17.4

SPI interrupt code example
if ((SPI1->SR & SPI_SR_RXNE) == SPI_SR_RXNE)
{
SPI1_Data = (uint8_t)SPI1->DR; /* receive data, clear flag */
/* Process */
}

A.17.5

SPI master configuration with DMA code example
/* (1) Master selection, BR: Fpclk/256 (due to C27 on the board, SPI_CLK is
set to the minimum)
CPOL and CPHA at zero (rising first edge) */
/* (2) TX and RX with DMA,
enable slave select output,
enable RXNE interrupt,
select 8-bit Rx fifo */
/* (3) Enable SPI1 */
SPI1->CR1 = SPI_CR1_MSTR | SPI_CR1_BR; /* (1) */
SPI1->CR2 = SPI_CR2_TXDMAEN | SPI_CR2_RXDMAEN | SPI_CR2_SSOE
| SPI_CR2_RXNEIE | SPI_CR2_FRXTH
| SPI_CR2_DS_2 | SPI_CR2_DS_1 | SPI_CR2_DS_0; /* (2) */
SPI1->CR1 |= SPI_CR1_SPE; /* (3) */

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SPI slave configuration with DMA code example
/* nSS hard, slave, CPOL and CPHA at zero (rising first edge) */
/* (1) Select TX and RX with DMA,
enable RXNE interrupt,
select 8-bit Rx fifo */
/* (2) Enable SPI2 */
SPI2->CR2 = SPI_CR2_TXDMAEN | SPI_CR2_RXDMAEN
| SPI_CR2_RXNEIE | SPI_CR2_FRXTH
| SPI_CR2_DS_2 | SPI_CR2_DS_1 | SPI_CR2_DS_0; /* (1) */
SPI2->CR1 |= SPI_CR1_SPE; /* (2) */

A.18

TSC code example

A.18.1

TSC configuration code example
/* Configure TCS */
/* With a charge transfer around 2.5 µs */
/* (1) Select fPGCLK = fHCLK/32,
Set pulse high = 2xtPGCLK,Master
Set pulse low = 2xtPGCLK
Set Max count value = 16383 pulses
Enable TSC */
/* (2) Disable hysteresis */
/* (3) Enable end of acquisition IT */
/* (4) Sampling enabled, G2IO4 */
/* (5) Channel enabled, G2IO3 */
/* (6) Enable group, G2 */
TSC->CR = TSC_CR_PGPSC_2 | TSC_CR_PGPSC_0 | TSC_CR_CTPH_0 | TSC_CR_CTPL_0
| TSC_CR_MCV_2 | TSC_CR_MCV_1 | TSC_CR_TSCE; /* (1) */
TSC->IOHCR &= (uint32_t)(~(TSC_IOHCR_G2_IO4 | TSC_IOHCR_G2_IO3)); /* (2) */
TSC->IER = TSC_IER_EOAIE; /* (3) */
TSC->IOSCR = TSC_IOSCR_G2_IO4; /* (4) */
TSC->IOCCR = TSC_IOCCR_G2_IO3; /* (5) */
TSC->IOGCSR |= TSC_IOGCSR_G2E; /* (5) */

A.18.2

TSC interrupt code example
/* End of acquisition flag */
if ((TSC->ISR & TSC_ISR_EOAF) == TSC_ISR_EOAF)
{
TSC->ICR = TSC_ICR_EOAIC; /* Clear flag */
AcquisitionValue = TSC->IOGXCR[1]; /* Get G2 counter value */
}

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Code examples

A.19

USART code example

A.19.1

USART transmitter configuration code example
/* (1) Oversampling by 16,
/* (2) 8 data bit, 1 start
USART1->BRR = 480000 / 96;
USART1->CR1 = USART_CR1_TE

A.19.2

9600 baud */
bit, 1 stop bit, no parity */
/* (1) */
| USART_CR1_UE; /* (2) */

USART transmit byte code example
/* Start USART transmission */
USART1->TDR = stringtosend[send++]; /* Will inititiate TC if TXE is set*/

A.19.3

USART transfer complete code example
if ((USART1->ISR & USART_ISR_TC) == USART_ISR_TC)
{
if (send == sizeof(stringtosend))
{
send=0;
USART1->ICR |= USART_ICR_TCCF; /* Clear transfer complete flag */
}
else
{
/* clear transfer complete flag and fill TDR with a new char */
USART1->TDR = stringtosend[send++];
}
}

A.19.4

USART receiver configuration code example
/* (1) oversampling by 16, 9600 baud */
/* (2) 8 data bit, 1 start bit, 1 stop bit, no parity, reception mode */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR1 = USART_CR1_RXNEIE | USART_CR1_RE | USART_CR1_UE; /* (2) */

A.19.5

USART receive byte code example
if ((USART1->ISR & USART_ISR_RXNE) == USART_ISR_RXNE)
{
chartoreceive = (uint8_t)(USART1->RDR); /* Receive data, clear flag */
}

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RM0091

USART LIN mode code example
/* (1) oversampling by 16, 9600 baud */
/* (2) LIN mode */
/* (3) 8 data bit, 1 start bit, 1 stop bit, no parity,
reception and transmission enabled */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR2 = USART_CR2_LINEN | USART_CR2_LBDIE; /* (2) */
USART1->CR1 = USART_CR1_TE | USART_CR1_RXNEIE
| USART_CR1_RE | USART_CR1_UE; /* (3) */
/* Polling idle frame Transmission */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

A.19.7

USART synchronous mode code example
/* (1) Oversampling by 16, 9600 baud */
/* (2) Synchronous mode
CPOL and CPHA = 0 => rising first edge
Last bit clock pulse
Most significant bit first in transmit/receive */
/* (3) 8 data bit, 1 start bit, 1 stop bit, no parity
Transmission enabled, reception enabled */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR2 = USART_CR2_MSBFIRST | USART_CR2_CLKEN
| USART_CR2_LBCL; /* (2) */
USART1->CR1 = USART_CR1_TE | USART_CR1_RXNEIE
| USART_CR1_RE | USART_CR1_UE; /* (3) */
/* Polling idle frame Transmission w/o clock */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

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A.19.8

Code examples

USART single-wire half-duplex code example
/* (1) Oversampling by 16, 9600 baud */
/* (2) Single-wire half-duplex mode */
/* (3) 8 data bit, 1 start bit, 1 stop bit, no parity, reception and
transmission enabled */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR3 = USART_CR3_HDSEL; /* (2) */
USART1->CR1 = USART_CR1_TE | USART_CR1_RXNEIE
| USART_CR1_RE | USART_CR1_UE; /* (3) */
/* Polling idle frame Transmission */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

A.19.9

USART smartcard mode code example
/* (1) Oversampling by 16, 9600 baud */
/* (2) Clock divided by 16 = 3MHz */
/* (3) Smart card mode enable */
/* (4) 1.5 stop bits, clock enbale */
/* (5) 8-data bit plus parity, 1 start bit */
USART1->BRR = 480000 / 96; /* (1) */
USART1->GTPR = 16 >> 1; /* (2) */
USART1->CR3 = USART_CR3_SCEN; /* (3) */
USART1->CR2 = USART_CR2_STOP_1 | USART_CR2_STOP_0
| USART_CR2_CLKEN; /* (4) */
USART1->CR1 = USART_CR1_M | USART_CR1_PCE
| USART_CR1_TE | USART_CR1_UE; /* (5) */
/* Polling idle frame transmission transfer complete
(this frame is not sent) */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

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USART IrDA mode code example
/* (1) Oversampling by 16, 9600 baud */
/* (2) Divide by 24 to achieve the low power frequency */
/* (3) Enable IrDA */
/* (4) 8 data bit, 1 start bit, 1 stop bit, no parity */
USART1->BRR = 480000 / 96; /* (1) */
USART1->GTPR = 24; /* (2) */
USART1->CR3 = USART_CR3_IREN; /* (3) */
USART1->CR1 = USART_CR1_TE | USART_CR1_UE; /* (4) */
/* Polling idle frame Transmission */
while((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

A.19.11

USART DMA code example
/* (1) Oversampling by 16, 9600 baud */
/* (2) Enable DMA in reception and transmission */
/* (3) 8 data bit, 1 start bit, 1 stop bit, no parity, reception and
transmission enabled */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR3 = USART_CR3_DMAT | USART_CR3_DMAR; /* (2) */
USART1->CR1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE; /* (3) */
/* Polling idle frame Transmission */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

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Code examples

USART hardware flow control code example
/* (1) oversampling by 16, 9600 baud */
/* (2) RTS and CTS enabled */
/* (3) 8 data bit, 1 start bit, 1 stop bit, no parity, reception and
transmission enabled */
USART1->BRR = 480000 / 96; /* (1) */
USART1->CR3 = USART_CR3_RTSE | USART_CR3_CTSE; /* (2) */
USART1->CR1 = USART_CR1_TE | USART_CR1_RXNEIE
| USART_CR1_RE | USART_CR1_UE; /* (3) */
/* Polling idle frame Transmission */
while ((USART1->ISR & USART_ISR_TC) != USART_ISR_TC)
{
/* add time out here for a robust application */
}
USART1->ICR |= USART_ICR_TCCF; /* Clear TC flag */
USART1->CR1 |= USART_CR1_TCIE; /* Enable TC interrupt */

A.20

WWDG code example

A.20.1

WWDG configuration code example
/* (1) Set prescaler to have a roll-over each about 5.5ms,
set window value (about 2.25ms) */
/* (2) Refresh WWDG before activate it */
/* (3) Activate WWDG */
WWDG->CFR = 0x60; /* (1) */
WWDG->CR = WWDG_REFRESH; /* (2) */
WWDG->CR |= WWDG_CR_WDGA; /* (3) */

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Revision history
Table 144. Document revision history
Date

Revision

06-Apr-2012

1

Initial release

2

Documentation conventions
– Added ‘Always read...’ in Section 1.1: List of abbreviations for registers
Memory map
– Added boot configuration link in Table 1: STM32F05xxx memory map and
peripheral register boundary addresses
– Added Footnote under Table 3: Boot modes
– Remove ‘DCode’ after ‘CPU’ in Section : DMA bus
– Replaced sentence and added Physical remap paragraph in Section 2.5:
Boot configuration
– Corrected Prefetch buffer and added paragraph in Section 1.2.2: Read
operations
– Removed sentence ‘It is set after the first...’, removed note and added
description of bit 5 in Section 1.5.1: Flash access control register
(FLASH_ACR)
CRC
– Replaced references to bits 4:3 and 2:1 in Section 6.4.3: Control register
(CRC_CR)
PWR
– Replaced ‘POR’, ‘PDR’ and ‘PVD’ by ‘VPOR’, ‘VPDR’ and ‘VPVD’ in
Figure 2 and Figure 3
– Modified “When VDDA is different from VDD...” paragraph in Section 1.1.1:
Independent A/D and D/A converter supply and reference voltage
– Moved arrow in Figure 2: Power on reset/power down reset waveform
– Corrected WKUP1 in Section 1.4.2: Power control/status register
(PWR_CSR)
RCC
– Added Power reset in Section 1.1.2: System reset
– Added paragraph ‘For more details on how to measure..’ in Section 1.2.2:
HSI clock
– Added ‘LSE’ and ‘LSI’ bullets in Section 1.2.12: Clock-out capability
– Added ‘/1’, ‘LSI’ and ‘LSE’ in Figure 2: Clock tree (STM32F03x and
STM32F05x devices)
– Added the sentence “... drive the HSI clock ...” to Section 1.2.2: HSI clock
– Added “independent” to the title of Section 1.2.11: Independent watchdog
clock
– Replaced the first sentence after Figure 5: Frequency measurement with
TIM14 in capture mode
– Added the sentence “When the system is in stop mode...” in Section : The
input capture channel of the Timer 14 can be a GPIO line or an internal clock
of the MCU. This selection is performed through the TI1_RMP [1:0] bits in
the TIM14_OR register. The possibilities available are the following ones.
– Added Section 1.2.13: Internal/external clock measurement with TIM14 and
Section 1.3: Low-power modes

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Table 144. Document revision history (continued)

Date

08-Aug-2012

Revision

Changes

2

– Modified description of Bit 19 and Bits 15:8 in Section 1.4.1: Clock control
register (RCC_CR)
– Replaced text under ‘PLLXTPRE’ and modified description of bits 26:24 in
Section 1.4.2: Clock configuration register (RCC_CFGR)
– Modified the formating in the register of Section 1.4.4 and Section 1.4.5:
APB peripheral reset register 1 (RCC_APB1RSTR)
– Modified title of Bit 0 in the registers of Section 1.4.7: APB peripheral clock
enable register 2 (RCC_APB2ENR)
– Replaced ‘IWWDGRSTF’ by ‘IWDGRSTF and added PORV18RSTDF
POR/PDR for bit 23 in Section 1.4.10: Control/status register (RCC_CSR)
– Modified Section 1.4.4: APB peripheral reset register 2 (RCC_APB2RSTR)
to Section 1.4.8: APB peripheral clock enable register 1 (RCC_APB1ENR)
title name.
GPIO
– Replaced SWDAT in Section 9.3.1: General-purpose I/O (GPIO)
– Added specific reset values in Section 9.4.3: GPIO port output speed
register (GPIOx_OSPEEDR) (x = A..F)
DMA
– Added ‘I2C1’, ‘TIM15’, ‘TIM16 and ‘TIM17’ to Figure 21: DMA block diagram
ADC
– Changed JIITOFF_D2 and JITOFF_D4 to JITOFF_DIV4 and JITOFF_DIV2
in Section 13.12.5: ADC configuration register 2 (ADC_CFGR2) and
Section 13.12.11: ADC register map
– Replaced ‘SMPR’ with ‘SMP’ in Section 13.12.11: ADC register map
DAC
– Replaced note in Section 14.2: DAC1 main features
COMP
– Replaced ‘bandgap’ with ‘VREFINT’ and added PA12 to COMP2_OUT in
Figure 92: Comparator 1 and 2 block diagrams
– Added the sentence “Reset and clock enable bits....” to Section 15.3.3:
COMP reset and clocks
– Modified COMP2MODE and COMP1MODE bit description in Section 15.6.1:
COMP control and status register (COMP_CSR)
Timers
– Added OCCS bit in Section 1.4.3: TIM2 and TIM3 slave mode control
register (TIM2_SMCR and TIM3_SMCR) and Section 1.4.3: TIM1 slave
mode control register (TIM1_SMCR)
– Mapped ‘TI1_RMP’ to bit 0 and 1 in Section 1.4.10: TIM14 capture/compare
register 1 (TIM14_CCR1)
Infrared
– Infrared function output changed to IR_OUT
RTC
– Removed VDD in Section 25.6.19: RTC backup registers (RTC_BKPxR)
– Removed Tamper3 in RTC ISR and TAFCR registers
– RTC ordered before WDG
IWDG
– Replaced ‘IWWDG’ occurrences by ‘IWDG’

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Revision

Changes

2

I2C
– Modified Section 24.4.5: I2C initialization, Section 24.4.6: Software reset
– Removed ‘SWRST’ in Section 24.7.1: Control register 1 (I2Cx_CR1) and
Section 24.7.7: Interrupt and Status register (I2Cx_ISR)
USART
– Removed “with a 12-bit mantissa and 4-bit fraction” in Section 25.5: USART
functional description
– Changed Equation in Section 25.5.5: Tolerance of the USART receiver to
clock deviation
– Changed reset values length in Section 25.7: USART registers
– Corrected reset values for ‘DEP’, ‘TC’, ‘RDR’ and ‘TDR’ in Table 90: USART
register map and reset values
Debug
– Removed ‘Control of the trace..’ bullet in Section 1.9: MCU debug
component (DBGMCU)
– Replaced IDCODE values in Section 1.5.3: SW-DP state machine (reset,
idle states, ID code) and Section 1.5.5: SW-DP registers
– Replaced “APB low” to APB1 in Section 1.9.2: Debug support for timers,
watchdog and I2C
– Corrected Figure 1: Block diagram of STM32F0xx MCU and Cortex®-M0level debug support
– Modified the title of Section 1.3.1: SWD port pins
– Modified Section 1.3.2: SW-DP pin assignment and Section 1.3.3: Internal
pull-up & pull-down on SWD pins
– Modified titles in Section 1.5: SWD port and replaced ‘SWDAT’
– Removed ‘DBG SLEEP’ in Section 1.9.3: Debug MCU configuration register
(DBGMCU_CR)
– Added ‘System’ to window watchdog in Section 1.9.4: Debug MCU APB1
freeze register (DBGMCU_APB1_FZ)
– Marked bit 0, 5, 6 and 7 as reserved in Section 1.9.6: DBG register map
Unique ID
– Removed Bold from ‘base address’ in Section 32.1: Unique device ID
register (96 bits)

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Table 144. Document revision history (continued)

Date

10-May-2013

Revision

Changes

3

– Added part numbers STM32F06x throughout the document.
– Updated document title.
Documentation conventions
– Added “(w_r0)” to Section 1.1: List of abbreviations for registers.
– Added reference to PM0215 in Related documents.
– Updated Glossary.
System and memory overview
– Modified Sections BusMatrix and AHB to APB bridge.
– Added Note: in Section 2.3: Embedded SRAM.
Embedded Flash memory
– Updated Table 4: Access status versus protection level and execution
modes.
– Modified phrasing of Level 2: no debug paragraph in Section 1.3.1: Read
protection.
– Added description of information block in Section 1.2.1: Flash memory
organization.
– Renamed “FKEYR” to “FKEY” and renamed “OPTKEYR” to “OPTKEY”.
– Renamed and modified Section 1.5.7: Flash Option byte register
(FLASH_OBR).
– Modified information about reset value in Section 1.5.2: Flash key register
(FLASH_KEYR), Section 1.5.3: Flash option key register
(FLASH_OPTKEYR), Section 1.5.7: Flash Option byte register
(FLASH_OBR) and Section 1.5.8: Write protection register
(FLASH_WRPR).
– Modified Section Unlocking the Flash memory, item 5. in Main Flash memory
programming, procedure in sections Page Erase and Mass Erase.
– Added Note: in Page Erase and Mass Erase.
– Updated Table 6: Flash interface - register map and reset values.
Option bytes
– Reworked Section 2: Option bytes.
PWR
– Modified introduction of Section 1.1: Power supplies.
– Added bullet “In STM32F06x devices...” in Section 1.1.4: Voltage regulator.
– Added section External NPOR signal.
– Added Caution: in Section 1.3: Low-power modes and in Section 1.3.5:
Standby mode.

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Revision

Changes

3

RCC
– Inverted order of sections Section 1.1.1: Power reset and Section 1.1.2:
System reset.
– Added Caution: in External crystal/ceramic resonator (HSE crystal) and
Caution: in Section 1.2.5: LSE clock
– Added bullet “The timer clock frequencies are automatically fixed by
hardware...” in Section 1.2: Clocks.
– Updated Section 1.1.1: Power reset, Section 1.1.2: System reset,
Section 1.1.3: RTC domain reset, Calibration of the HSI14, Section 1.2.12:
Clock-out capability, Section 1.2.13: Internal/external clock measurement
with TIM14, Section 1.4.2: Clock configuration register (RCC_CFGR),
Section 1.4.4: APB peripheral reset register 2 (RCC_APB2RSTR),
Section 1.4.12: Clock configuration register 2 (RCC_CFGR2),
Section 1.4.13: Clock configuration register 3 (RCC_CFGR3).
– Modified Figure 1: Simplified diagram of the reset circuit and Figure 2: Clock
tree (STM32F03x and STM32F05x devices).
– Replaced FORCE_OBL with OBL_LAUNCH in Option byte loader reset.
– Deleted Section 7.2.13: Clock-independent system clock sources for TIM14.
– Added USART3EN, UART4EN and UART5EN in Table 1: RCC register map
and reset values.
– Modified reset values of RCC_CSR register in Table 1: RCC register map
and reset values.
– Modified reset value and description of Bit 23 in Section 1.4.10:
Control/status register (RCC_CSR).
– Specified Bit 8 as obsolete in Section 1.4.13: Clock configuration register 3
(RCC_CFGR3).
GPIO
– Updated Section 9.1: Introduction.
– Removed “Analog” arrows in Figure 17: Basic structure of a five-volt tolerant
I/O port bit.
– Renamed Section 9.4.11: GPIO port bit reset register (GPIOx_BRR) (x =
A..F).
SYSCFG
– Modified values of register bits 23, 22 and 20.
Interrupts and events
– Added Priority numbers and modified description of EXTI4_15 in Table 1:
Vector table.
ADC
– Rephrased part of Section 13.4.1: Calibration (ADCAL).
– Replaced AUTDLY with WAIT in sections 13.5.5: Example timing diagrams
(single/continuous modes hardware/software triggers) and 13.12.4: ADC
configuration register 1 (ADC_CFGR1).
– Updated Figure 25: ADC block diagram.
– Replaced "0x44...0x2FC" with "0x44...0x304" in Table 44: ADC register map
and reset values.

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Date

10-May-2013

Revision

Changes

3

DAC
– Corrected name of Table 66: External triggers.
– Replaced every occurrence of “DAC1” with “DAC”.
COMP
– Replaced “COMP1SW1 : Comparator enable” with “COMP1SW1 :
Comparator 1 non inverting input DAC switch” in Section 15.6.1: COMP
control and status register (COMP_CSR).
TIM2 and TIM3
– Corrected Figure 106: Advanced-control timer block diagram.
TIM14
– Updated Figure 17: TIM16 and TIM17 block diagram.
TIM15/16/17
– Updated Section 2.1: TIM15/16/17 introduction, Section 2.3: TIM16 and
TIM17 main features and Section 2.4.4: Clock sources.
– Removed Note in Section 2.6.1: TIM16 and TIM17 control register 1
(TIM16_CR1 and TIM17_CR1).
– Marked as “reserved”: Bits 14 and 6 in Section 2.6.3: TIM16 and TIM17
DMA/interrupt enable register (TIM16_DIER and TIM17_DIER), bits 6 and 0
in Section 2.6.4: TIM16 and TIM17 status register (TIM16_SR and
TIM17_SR), and bit 6 in Section 2.6.5: TIM16 and TIM17 event generation
register (TIM16_EGR and TIM17_EGR).
– Updated Table 7: TIM16 and TIM17 register map and reset values.
RTC
– Replaced “power-on reset” with “backup domain reset” throughout
Section 25: Real-time clock (RTC).
– Removed “the backup registers are reset when a tamper detection event
occurs” in Section 25.2: RTC main features.
– Updated RTC backup registers.
– Updated RTC_ISR register reset values in Section 25.3.9: Resetting the
RTC and Section 25.6.4: RTC initialization and status register (RTC_ISR).
I2C
– Updated case of digital filter enabled and Table 81: Comparison of analog
vs. digital filters.
– Added note for WUPEN in Section 26.7.1: Control register 1 (I2Cx_CR1).
– Corrected Figure 275: Transfer sequence flowchart for I2C master
transmitter for N>255 bytes.
– Removed maximum values of parameter “Data hold time” and added row
“Data valid time” in Table 90: I2C-SMBUS specification data setup and hold
times.
– Updated sub-sections I2C timings and Slave clock stretching (NOSTRETCH
= 0).

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3

I2C (continued)
– Updated Figure 257: I2C block diagram and Figure 259: Setup and hold
timings.
– Reclassified section “I2C register map” from 2.8 to 26.7.12.
– Added Caution: “If wakeup from Stop is disabled...” in Section 26.4.14:
Wakeup from Stop mode on address match.
– Added Section 26.5: I2C low-power modes.
– Moved Section 24.7: I2C debug mode to 26.4.17 and renamed it Debug
mode.
– Updated Table 93: Examples of timings settings for fI2CCLK = 8 MHz.
USART
– Removed note on bit 19 (RWU) in Section 25.7.8: Interrupt & status register
(USART_ISR).
SPI/I2S
– Reorganized SPI initialization and sequence handling sections.
– Corrected and updated SPI disabling and DMA handling procedures.
– Updated description of NSSP and TI modes.
– Corrected DMA CRC management.
– Removed CRC interrupt capability.
– Changed RXONLY and BIDIMODE bit description.
– Modified sections : Simplex communications on page 828 and : Data frame
format on page 833, 28.5.7: Procedure for enabling SPI on page 835,
Figure 318: Hardware/software slave select management, Figure 319: Data
clock timing diagram, Figure 320: Data alignment when data length is not
equal to 8-bit or 16-bit, Figure 327: TI mode transfer.
– Modified reset value of SPIx_I2SPR in Section 28.9.9: SPIx_I2S prescaler
register (SPIx_I2SPR).
– Added Figure 322: Master full duplex communication, Figure 323: Slave full
duplex communication, Figure 324: Master full duplex communication with
CRC, Figure 325: Master full duplex communication in packed mode.
TSC
– Replaced “Power-on reset value” with “Reset value” in Section 17.6.2: TSC
interrupt enable register (TSC_IER).
Debug
– Renamed Section 1.3.2: SW-DP pin assignment.
– Changed description of Bits 11:0 in Section 1.4.1: MCU device ID code.
– Modified notes regarding IDCODE register in Table 5: SW-DP registers.

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Table 144. Document revision history (continued)

Date

21-May-2013

09-Jan-2014

Revision

Changes

4

ADC
– Added note in Section 13.5.2: Programmable resolution (RES) - fast
conversion mode: RES[1:0] can be changed only when ADEN=0.
– Added bit CKMODE.
– Rewrote Section 13.4.2: ADC on-off control (ADEN, ADDIS, ADRDY) and
Section 13.4.3: ADC clock (CKMODE).
– Added Figure 28: ADC clock scheme.
– Fixed issues concerning CKMODE & JITOFF bits. Now bits
JITOFF_DIV4/DIV2 bits are replaced with bits CKMODE[1:0] at the same
position and with same decoding as v1.
– Changed note on ADRDY in Section 13.4.2: ADC on-off control (ADEN,
ADDIS, ADRDY).
– Extended Section 13.12.8: ADC channel selection register (ADC_CHSELR)
(added channel 18).
– Removed reference to TSVREFE bit in Section 13.9: Temperature sensor
and internal reference voltage and referred to TSEN/VREFEN instead.

5

Cover page
– Changed part numbers in title and introduction on page 1
– Renamed low-density to STM32F03x
– Renamed medium-density to STM32F05x
– Renamed STM32F06x to STM32F0x8
– Added STM32F07x microcontrollers (STM32F071xB and STM32F072xx).
Expanded the Flash memory range to 128 Kbytes.
– Added Section 8: Clock recovery system (CRS), Section 29: Controller area
network (bxCAN) and Section 30: Universal serial bus full-speed device
interface (USB).
Documentation conventions
– Updated Section 1.2: Glossary.
System and memory overview
– Added ‘TIM7, USART3, USART4, CAN and USB’ and ‘7 channels DMA’ in
Figure 1: System architecture (all features).
– Added ‘CRS, TIM7, USART3, USART4, CAN and USB’ in Table 1:
STM32F0xx peripheral register boundary addresses.
– Updated Table 1: STM32F0xx peripheral register boundary addresses.
– Added Table 2: STM32F0xx memory boundary addresses
– Added 16 KB-RAM for STM32F07x devices in Section 2.3: Embedded
SRAM.
– Added USB in Embedded boot loader.
Embedded Flash memory
– Added Table 2: Flash memory organization (STM32F07x devices).
– Added ‘WRP[31:16]’ in Section 1.5.8: Write protection register
(FLASH_WRPR) and Table 6: Flash interface - register map and reset
values.
Option bytes
– Added row ‘0x1FFF F80C’ in Table 8: Option byte organization.
– Updated Section 2.1.3: Write protection option bytes.
– Updated Table 9: Option byte map and ST production values.

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Changes

5

CRC
– Introduced programmable polynomial feature in Section 6.2: CRC main
features, Section 6.4.3: Control register (CRC_CR) and Section 6.4.6: CRC
register map.
– Added Section : Polynomial programmability and Section 6.4.5: CRC
polynomial (CRC_POL).
PWR
– Added STM32F07x device features
– Updated Figure 1: Power supply overview
– Added Section 1.1.2: Independent I/O supply rail
– Added bits 10 to 15 in Section 1.4.2: Power control/status register
(PWR_CSR)
RCC
– Renamed “backup domain” to “RTC domain”.
– Added HSI48 48 MHz RC oscillator clock and USART2 features for
STM32F07x devices:
– Modified Section 1.2: Clocks and Section 1.2.2: HSI clock, Section 1.2.4:
PLL, Section 1.2.7: System clock (SYSCLK) selection, Section 1.2.12:
Clock-out capability, Section 1.3: Low-power modes.
– Added Figure 3: Clock tree (STM32F04x and STM32F07x devices) and
Section 1.2.3: HSI48 clock.
– Updated register descriptions for STM32F07x devices in Section 1.4.2:
Clock configuration register (RCC_CFGR), Section 1.4.3: Clock interrupt
register (RCC_CIR), Section 1.4.5: APB peripheral reset register 1
(RCC_APB1RSTR), Section 1.4.6: AHB peripheral clock enable register
(RCC_AHBENR), Section 1.4.8: APB peripheral clock enable register 1
(RCC_APB1ENR), Section 1.4.11: AHB peripheral reset register
(RCC_AHBRSTR), Section 1.4.13: Clock configuration register 3
(RCC_CFGR3), and Section 1.4.14: Clock control register 2 (RCC_CR2)
and updated Table 1: RCC register map and reset values.
GPIO
– Added port E in ranges of all registers except LCKR.
– Modified Section 9.1: Introduction.
– Replaced VDD with VDDIO in Figure 17: Basic structure of an I/O port bit,
Figure 18: Input floating/pull up/pull down configurations, Figure 19: Output
configuration, Figure 20: Alternate function configuration and Figure 21:
High impedance-analog configuration.
SYSCFG
– Added bits [30:24] and 21 for STM32F07x devices in Section 1.1.1:
SYSCFG configuration register 1 (SYSCFG_CFGR1).
– Added pin PE[x] for bits [15:0] in Section 1.1.2: SYSCFG external interrupt
configuration register 1 (SYSCFG_EXTICR1), pins PD[x] and PE[x] for bits
[15:0] in Section 1.1.3: SYSCFG external interrupt configuration register 2
(SYSCFG_EXTICR2), pins PD[x], PE[x] and PF[x] for bits [15:0] in
Section 1.1.4: SYSCFG external interrupt configuration register 3
(SYSCFG_EXTICR3) and Section 1.1.5: SYSCFG external interrupt
configuration register 4 (SYSCFG_EXTICR4).
– Updated Table 1: SYSCFG register map and reset values.

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Date

09-Jan-2014

Revision

Changes

5

DMA
– Change 5 channels to up to 7 channels
– Updated Figure 21: DMA block diagram
– Updated Figure 23: DMA request mapping
– Added Table 29: Summary of the DMA requests for each channel on
STM32F03x, STM32F04x and STM32F05x devices and Table 30: Summary
of the DMA requests for each channel on STM32F07x devices
– Added bits 27 to 20 in Section 11.5.1: DMA interrupt status register
(DMA_ISR) and Section 11.5.2: DMA interrupt flag clear register
(DMA_IFCR)
Interrupts and events
– Updated Table 1: Vector table
ADC
– Updated Section 13.9: Temperature sensor and internal reference voltage
DAC
– Added second channel DAC_OUT2, Noise-wave generation, Triangularwave generation and dual mode for STM32F07x devices
– Updated Section 14.2: DAC1 main features
– Added Section 14.4: Dual mode functional description (STM32F07x devices)
– Added Section 14.4: Noise generation
– Added Section 14.5: DMA request
– Added bits 29 to 16 and bits 11 to 6 in Section 14.6.1: DAC control register
(DAC_CR)
– Added bit1 ‘SWTRIG2’ in Section 14.6.2: DAC software trigger register
(DAC_SWTRIGR)
– Added Section 14.8.6: DAC channel2 12-bit right-aligned data holding
register (DAC_DHR12R2), Section 14.8.7: DAC channel2 12-bit left-aligned
data holding register (DAC_DHR12L2), Section 14.8.8: DAC channel2 8-bit
right-aligned data holding register (DAC_DHR8R2), Section 14.8.9: Dual
DAC 12-bit right-aligned data holding register (DAC_DHR12RD),
Section 14.8.10: Dual DAC 12-bit left-aligned data holding register
(DAC_DHR12LD), Section 14.8.11: Dual DAC 8-bit right-aligned data
holding register (DAC_DHR8RD), Section 14.8.13: DAC channel2 data
output register (DAC_DOR2)
– Added bit 29 in Section 14.6.7: DAC status register (DAC_SR)
Basic timer (TIM6/TIM7)
– Added TIM7 for STM32F07x devices in Section 1: Basic timer (TIM6/TIM7)
RTC
– Renamed “backup domain to “RTC domain”
– Added RTC_TAMP3 and wakeup interrupt for STM32F07x devices
– Added Table 67: STM32F0xx RTC implementation
– Added Section 25.3.6: Periodic auto-wakeup, Section : Programming the
wakeup timer
– Corrected bit SHPF read and clear parameters in Section 25.6.4: RTC
initialization and status register (RTC_ISR)
I2C
– Added Table 74: STM32F0xx I2C implementation
– Updated Table 90: I2C-SMBUS specification data setup and hold times

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5

– Replaced 50ns into tAF(min) and 260ns into tAF(max) in section I2C timings
USART
– Added number of auto baud rate detection mode in Table 90: STM32F0xx
USART implementation.
– Removed mentions of mantissa and fraction in Figure 288: USART block
diagram and Section 27.7.4: Baud rate register (USARTx_BRR).
– Sections RTS flow control and CTS flow control renamed RS232 RTS flow
control and RS232 CTS flow control. Added case of idle character in
Section 27.5.1: USART character description. Added recommendation of TE
reset during data transmission in Section : Character transmission. Updated
Section : Break characters.
– Removed note related to USART disabling procedure in Section : Single
byte communication.
– Added case of oversampling by 8 in Section 27.5.6: Auto baud rate
detection.
– Renamed Section 27.5.16 RS232 Hardware flow control and RS485 Driver
Enable.
– Added check that no transfer is ongoing before entering stop mode in
Section 27.5.17: Wakeup from Stop mode; added case of RXNE set in
Section : Using Mute mode with Stop mode.
– Updated Table 111: USART register map and reset values.
– Modified Table 90: STM32F0xx USART implementation.
– Added note related to smartcard mode in Section 27.7.1: Control register 1
(USARTx_CR1).
– Added sequence to deliver SCLK clock to smartcards, in CLKEN description
of Section 27.7.2: Control register 2 (USARTx_CR2).
– Added note related to PSC configuration in Section 27.7.5: Guard time and
prescaler register (USARTx_GTPR).
– Added support of 7-bit data word length: added 6 LSB bits in Section 27.5.1:
USART character description, Section 27.5.9: Parity control, Section : Even
parity and Section : Odd parity, Section 27.5.5: Tolerance of the USART
receiver to clock deviation, renamed M bit M0 in Section 27.7.1: Control
register 1 (USARTx_CR1).
– Added 2 auto baud rate detection modes: modes 2 and 3 in Section 27.5.5:
Tolerance of the USART receiver to clock deviation and Section 27.5.6: Auto
baud rate detection.
– Replaced in Bit 2 MMRQ Section 25.7.7: Request register (USART_RQR)
“resets the RWU flag” by “sets the RWU flag”
– Added ‘In Smartcard, LIN and IrDA modes, only Oversampling by 16 is
supported’ in Section 25.5.4: Baud rate generation
– Corrected and updated stop bits in Figure 198: Word length programming
SPI
– Modified Table 98: STM32F0xx SPI implementation
TSC
– Added Groups 7 and 8 and channels 19 to 24 in Section 17: Touch sensing
controller (TSC). Added Table 106: Capacitive sensing GPIOs

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09-Jan-2014

06-May-2014

Revision

Changes

5

DEBUG
– Added STM32F07x ID in bits DEV_IDx in Section 1.4.1: MCU device ID
code
– Added bit 5 ‘DBG_TIM7_STOP’ and bit 25 ‘DBG_CAN_STOP’ to
Section 1.9.4: Debug MCU APB1 freeze register (DBGMCU_APB1_FZ)

6

Cover page
– Updated for STingray adding STM32F042x4/x6 and STM32F048x6 devices.
MMAP
– updated Table 2: STM32F0xx memory boundary addresses
– updated Section 2.5: Boot configuration
Embedded Flash memory
– Updated Section 1.2.1: Flash memory organization, Table 4: Access status
versus protection level and execution modes and Section 1.5: Flash register
description
– Option byte : updated Section 2.1: Option byte description
RCC
– Updated with STM32F04x devices : Section 1.2: Clocks and Figure 3: Clock
tree (STM32F04x and STM32F07x devices).
CRS
– Updated adding STM32F04x devices.
GPIO
– Updated Figure 17: Basic structure of an I/O port bit
SYSCFG
– Updated SYSCFG Registers
DMA updated
IRTIM
– Updated Figure 252: IR internal hardware connections with TIM16 and
TIM17.
IWDG
– updated Section 24.3: IWDG functional description.step6 moved to step1.
– updated Section 24.4: IWDG registers.Moved Note From IWDG_WINR to
IWDG_SR register.
– Added STM32F04x
RTC
– Updated Figure 256: RTC block diagram title.
– Updated Table 67: STM32F0xx RTC implementation.
– Updated 25.3: RTC functional description.
I2C
– Added STM32F04x in Table 74: STM32F0xx I2C implementation
USART
– Changed Stingray adding STM32F04x in Table 90: STM32F0xx USART
implementation, 27.5: USART functional description and 27.7: USART
registers.
– Updated Table 109: Frame formats in USART IP
– Changed Stingray adding STM32F04x in Table 98.: STM32F0xx SPI
implementation.

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Revision

Changes

6

– Changed Stingray adding STM32F04x in Table 98.: STM32F0xx SPI
implementation.
– Updated TSC IP adding STM32F04x.
USB
– Changed USB IP Stingray by adding STM32F04x and STM32F078.
– Change Stingray and Nemo in USB main features and Description of USB
blocks.
– Updated Section 32: Device electronic signature
– Updated Section 1.3.10: One-pulse mode and Section 1.3.15: Timer
synchronization.

7

Extended the applicability to STM32F091xB/xC and STM32F098xC devices.
Updated the following sections:
– cover page
System and memory overview
– Figure 1: System architecture
– Table 1: STM32F0xx peripheral register boundary addresses
– Section 2.3: Embedded SRAM
– Section 2.5: Boot configuration
Embedded Flash memory
– Section 3.1: Flash main features
– Section 3.2: Flash memory functional description
– Section 4.1.3: Write protection option byte
Cyclic redundancy check calculation unit (CRC)
– Introduction
Power control (PWR)
– Figure footnote 1 related to the figure Power supply overview
– Section 6.1.2: Independent I/O supply rail
– Section 6.4.2: Power control/status register (PWR_CSR)
Reset and clock control (RCC)
– Section 7.2: Clocks
– Figure 12: Clock tree (STM32F04x, STM32F07x and STM32F09x devices)
– Section 7.2.3: HSI48 clock
– Section 7.2.7: System clock (SYSCLK) selection
– Section 7.2.12: Clock-out capability
– Section 7.3: Low-power modes
– Section 7.4.2: Clock configuration register (RCC_CFGR)
– Section 7.4.4: APB peripheral reset register 2 (RCC_APB2RSTR)
– Section 7.4.5: APB peripheral reset register 1 (RCC_APB1RSTR)
– Section 7.4.6: AHB peripheral clock enable register (RCC_AHBENR)
– Section 7.4.7: APB peripheral clock enable register 2 (RCC_APB2ENR)
– Section 7.4.8: APB peripheral clock enable register 1 (RCC_APB1ENR)
– Section 7.4.13: Clock configuration register 3 (RCC_CFGR3)
Clock recovery system (CRS)
– Introduction

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Table 144. Document revision history (continued)

Date

29-Oct-2014

Revision

7

Changes
General-purpose I/Os (GPIO)
– Introduction
System configuration controller (SYSCFG)
– Section 10.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1)
– Added Section 10.1.7: SYSCFG interrupt line 0 status register
(SYSCFG_ITLINE0) to Section 10.1.37: SYSCFG interrupt line 30 status
register (SYSCFG_ITLINE30)
– Added Table 28: SYSCFG register map and reset values for STM32F09x
devices
Direct memory access controller (DMA)
– Table 32: Summary of the DMA requests for each channel on STM32F07x
devices
– Table 36: DMA register map and reset values (registers available on
STM32F07x and STM32F09x devices only)
Interrupts and events
– Table 38: Vector table
– Section 12.2.5: External and internal interrupt/event line mapping
– Section 12.3.1: Interrupt mask register (EXTI_IMR)
Digital-to-analog converter (DAC)
– Introduction
– Section 14.2: DAC main features
– Section 14.5.2: DAC channel conversion
– Section 14.6: Dual-mode functional description (STM32F07x and
STM32F09x devices)
– Section 14.7: Noise generation(STM32F07x and STM32F09x devices)
– Section 14.8: Triangle-wave generation (STM32F07x and STM32F09x
devices)
– Section 14.10.14: DAC status register (DAC_SR)
Comparator (COMP)
– Introduction
– Section 15.1: Introduction
General purpose timers (TIM15/16)
– Section 19.4.14: TIM15 external trigger synchronization
– Section 19.4.15: Timer synchronization (TIM15)
Basic timer (TIM6/TIM7)
– Introduction
Infrared interface (IRTIM)
– Figure 202: IR internal hardware connections with TIM16 and TIM17
Real time clock (RTC)
– Table 71: STM32F0xx RTC implementation
– Figure 205: RTC block diagram for STM32F07x and STM32F09x devices
– Table 76: Interrupt control bits
Inter-Integrated circuit (I2C) interface
Table 79: STM32F0xx I2C implementation
Universal synchronous asynchronous receiver transmitter (USART)
– Table 95: STM32F0xx USART implementation

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Revision history

RM0091
Table 144. Document revision history (continued)

Date

29-Oct-2014

29-Jul-2015

20-Jan-2017

996/1004

Revision

Changes

7

Serial peripheral interface / inter-IC sound (SPI/I2S)
– Table 104: STM32F0xx SPI implementation
Touch sensing controller (TSC)
– Introduction
Controller area network (bxCAN)
– Introduction
HDMI-CEC controller (HDMI-CEC)
– Introduction
Debug support (DBG)
Section 32.4.1: MCU device ID code

8

System and memory overview
– Corrected the original memory space value for STM32F09x devices in
Section 2.5: Boot configuration.
CRS
– Added the note in SYNCSRC[1:0] description of CRS configuration register
(CRS_CFGR) in Section 8.6.2: CRS configuration register (CRS_CFGR).
Interrupts and events
– Corrected the definition for EXTI line 31 in Section 12.2.5: External and
internal interrupt/event line mapping
Appendix A Code examples
– Global update of Section Appendix A: Code examples: now displayed with
colors.

9

The order of functions (peripherals) changed.
Updated the following sections:
System and memory overview
– Table 1: STM32F0xx peripheral register boundary addresses
– Section 2.3: Embedded SRAM
– Section 2.5: Boot configuration
Embedded Flash memory
– Section 3.5.4: Flash status register (FLASH_SR)
– Section 3.5.7: Flash Option byte register (FLASH_OBR)
– Section 4: Option byte
Power control (PWR)
– Section 5.4.2: Power control/status register (PWR_CSR)
Reset and clock control (RCC)
– Section 6.2.10: RTC clock
– Section 6.4.9: RTC domain control register (RCC_BDCR)
– Table 19: RCC register map and reset values
– Section 6.4.14: Clock control register 2 (RCC_CR2)
General-purpose I/Os (GPIO)
– Section 8.3.2: I/O pin alternate function multiplexer and mapping
– Section 8.4.12: GPIO register map
– AFRy field names changed to AFSELy in Section 8.4.9: GPIO alternate
function low register (GPIOx_AFRL) (x = A..F), Section 8.4.10: GPIO
alternate function high register (GPIOx_AFRH) (x = A..F)

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Table 144. Document revision history (continued)

Date

20-Jan-2017

Revision

Changes

9

– Figure 17: Input floating/pull up/pull down configurations
– Figure 18: Output configuration
– Figure 19: Alternate function configuration
– Figure 20: High impedance-analog configuration
System configuration controller (SYSCFG)
– Section 9.1.1: SYSCFG configuration register 1 (SYSCFG_CFGR1)
– Section 9.1.38: SYSCFG register maps
Direct memory access controller (DMA)
– Table 30: Summary of the DMA requests for each channel on STM32F07x
devices
Interrupts and events
– Section 11.3.3: Rising trigger selection register (EXTI_RTSR)
– Section 11.3.4: Falling trigger selection register (EXTI_FTSR)
– Section 11.3.5: Software interrupt event register (EXTI_SWIER)
– Section 11.3.6: Pending register (EXTI_PR)
– Section 11.3.7: EXTI register map
Cyclic redundancy check calculation unit (CRC)
– Feature list
– Figure 25: CRC calculation unit block diagram
– Table 40: CRC register map and reset values
– Section 12.4.2: CRC internal signals
– Section 12.5.3: Control register (CRC_CR)
– Section 12.5.5: CRC polynomial (CRC_POL)
Analogl-to-digital converter (ADC)
– Figure 26: ADC block diagram
– Section 13.4.1: Calibration (ADCAL)
– Section 13.4.2: ADC on-off control (ADEN, ADDIS, ADRDY)
– Section : Reading the temperature
– Section 13.12.1: ADC interrupt and status register (ADC_ISR)
– Section 13.12.3: ADC control register (ADC_CR)
– Section 13.12.5: ADC configuration register 2 (ADC_CFGR2)
Digital-to-analog converter (DAC)
– Sections DAC output buffer enable and DAC channel enable moved outside
Single and Dual mode functional description sections
– Separation of Single mode and Dual mode functional descriptions
Comparator (COMP)
– Section 15.5.1: COMP control and status register (COMP_CSR)
All timers
– Reset value of all TIMx_ARR registers corrected to 0xFFFF
Advanced control timers (TIM1)
– Section Figure 59.: Advanced-control timer block diagram
– Section 17.3.2: Counter modes
– Section 17.3.12: Using the break function
– Section 17.4.5: TIM1 status register (TIM1_SR)
General-purpose timers (TIM2 and TIM3)
– Section 18.3.5: Input capture mode

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RM0091
Table 144. Document revision history (continued)

Date

20-Jan-2017

998/1004

Revision

Changes

9

General-purpose timers (TIM15/16/17)
– Section Figure 168.: TIM15 block diagram
– Section Figure 169.: TIM16 and TIM17 block diagram
– Section 20.4.12: Using the break function
– Section 20.4.13: One-pulse mode
– Section 20.5.3: TIM15 slave mode control register (TIM15_SMCR)
– Section 20.5.5: TIM15 status register (TIM15_SR)
– Section 20.6.4: TIM16 and TIM17 status register (TIM16_SR and
TIM17_SR)
Infrared interface (IRTIM)
– Introduction
Independent watchdog (IWDG)
Added Section 23.3.4: Behavior in Stop and Standby modesReal time clock
(RTC)
– Figure 211: RTC block diagram in STM32F03x, STM32F04x and
STM32F05x devices
– Figure 212: RTC block diagram for STM32F07x and STM32F09x devices
– Section 25.4.9: Resetting the RTC
– Section 25.7.15: RTC tamper and alternate function configuration register
(RTC_TAFCR)
– Section 25.7.18: RTC register map
– Section 25.4.15: Calibration clock output.
– Added caution at the end of Section 25.7.3: RTC control register (RTC_CR).
Inter-Integrated circuit (I2C) interface
– Table 86: STM32F0xx I2C implementation
– Figure 216: Setup and hold timings
– Section I2C timings
– Section 26.4.9: I2C master mode
– Section 26.7.3: Own address 1 register (I2C_OAR1)
– Section 26.7.4: Own address 2 register (I2C_OAR2)
– Section 26.7.5: Timing register (I2C_TIMINGR)
– Figure 220: Slave initialization flowchart
Universal synchronous asynchronous receiver transmitter (USART)
– all nCTS / nRTS / SCLK replaced with CTS / RTS / CK
– Section 27.5.5: Tolerance of the USART receiver to clock deviation
– Added description to Section 27.5.17: Wakeup from Stop mode using
USART
– Section 27.8.3: Control register 3 (USART_CR3)
– Section 27.8.9: Interrupt flag clear register (USART_ICR)
– Adding section Determining the maximum USART baudrate allowing to
wakeup correctly from Stop mode when the USART clock source is the HSI
clock

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Revision history
Table 144. Document revision history (continued)

Date

20-Jan-2017

Revision

Changes

9

Serial peripheral interface / inter-IC sound (SPI/I2S)
– Footnotes of Figure 271: Full-duplex single master/ single slave application,
Figure 272: Half-duplex single master/ single slave application and
Figure 273: Simplex single master/single slave application (master in
transmit-only/ slave in receive-only mode)
– Figure 287: Full-duplex communication
– Added Section 28.5.4: Multi-master communication
– Added Section 28.7.2: I2S full duplex
Touch sensing controller (TSC)
– Section 16.3.4: Charge transfer acquisition sequence - note added
– Section 16.6.1: TSC control register (TSC_CR) - note added
– Section 16.6.4: TSC interrupt status register (TSC_ISR)
– Removed section Capacitive sensing GPIOs
HDMI-CEC
– Section Figure 325.: HDMI-CEC block diagram
DBG
– Section 32.4.1: MCU device ID code
Appendix A - Code examples
– Section A.2.2: Main Flash programming sequence code example
– Section A.2.3: Page erase sequence code example
– Section A.2.4: Mass erase sequence code example
– Section A.2.6: Option byte programming sequence code example
– Section A.4.2: Alternate function selection sequence code example
– Section A.2.7: Option byte erasing sequence code example
– Section A.7.1: ADC Calibration code example
– Section A.7.2: ADC enable sequence code example
– Section A.7.3: ADC disable sequence code example
– Section A.16.7: RTC tamper and time stamp code example

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Index
A
ADC_CCR . . . . . . . . . . . . . . . . . . . . . . . . . . .266
ADC_CFGR1 . . . . . . . . . . . . . . . . . . . . . . . . .259
ADC_CFGR2 . . . . . . . . . . . . . . . . . . . . . . . . .263
ADC_CHSELR . . . . . . . . . . . . . . . . . . . . . . . .265
ADC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . .257
ADC_DR . . . . . . . . . . . . . . . . . . . . . . . . . . . .265
ADC_IER . . . . . . . . . . . . . . . . . . . . . . . . . . . .255
ADC_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . .254
ADC_SMPR . . . . . . . . . . . . . . . . . . . . . . . . . .263
ADC_TR . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264

C
CAN_BTR . . . . . . . . . . . . . . . . . . . . . . . . . . .842
CAN_ESR . . . . . . . . . . . . . . . . . . . . . . . . . . .841
CAN_FA1R . . . . . . . . . . . . . . . . . . . . . . . . . .852
CAN_FFA1R . . . . . . . . . . . . . . . . . . . . . . . . .852
CAN_FiRx . . . . . . . . . . . . . . . . . . . . . . . . . . .853
CAN_FM1R . . . . . . . . . . . . . . . . . . . . . . . . . .851
CAN_FMR . . . . . . . . . . . . . . . . . . . . . . . . . . .850
CAN_FS1R . . . . . . . . . . . . . . . . . . . . . . . . . .851
CAN_IER . . . . . . . . . . . . . . . . . . . . . . . . . . . .840
CAN_MCR . . . . . . . . . . . . . . . . . . . . . . . . . . .833
CAN_MSR . . . . . . . . . . . . . . . . . . . . . . . . . . .835
CAN_RDHxR . . . . . . . . . . . . . . . . . . . . . . . . .849
CAN_RDLxR . . . . . . . . . . . . . . . . . . . . . . . . .849
CAN_RDTxR . . . . . . . . . . . . . . . . . . . . . . . . .848
CAN_RF0R . . . . . . . . . . . . . . . . . . . . . . . . . .838
CAN_RF1R . . . . . . . . . . . . . . . . . . . . . . . . . .839
CAN_RIxR . . . . . . . . . . . . . . . . . . . . . . . . . . .847
CAN_TDHxR . . . . . . . . . . . . . . . . . . . . . . . . .846
CAN_TDLxR . . . . . . . . . . . . . . . . . . . . . . . . .846
CAN_TDTxR . . . . . . . . . . . . . . . . . . . . . . . . .845
CAN_TIxR . . . . . . . . . . . . . . . . . . . . . . . . . . .844
CAN_TSR . . . . . . . . . . . . . . . . . . . . . . . . . . .836
CEC_CFGR . . . . . . . . . . . . . . . . . . . . . . . . . .903
CEC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . .902
CEC_IER . . . . . . . . . . . . . . . . . . . . . . . . . . . .908
CEC_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . .906
CEC_RXDR . . . . . . . . . . . . . . . . . . . . . . . . . .906
CEC_TXDR . . . . . . . . . . . . . . . . . . . . . . . . . .906
COMP_CSR . . . . . . . . . . . . . . . . . . . . . . . . . .297
CRC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . .224
CRC_DR . . . . . . . . . . . . . . . . . . . . . . . . . . . .223
CRC_IDR . . . . . . . . . . . . . . . . . . . . . . . . . . . .223
CRC_INIT . . . . . . . . . . . . . . . . . . . . . . . . . . . .225
CRC_POL . . . . . . . . . . . . . . . . . . . . . . . . . . .225

1000/1004

CRS_CFGR . . . . . . . . . . . . . . . . . . . . . . . . . . 143
CRS_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
CRS_ICR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
CRS_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

D
DAC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
DAC_DHR12L1 . . . . . . . . . . . . . . . . . . . . . . . 286
DAC_DHR12L2 . . . . . . . . . . . . . . . . . . . . . . . 287
DAC_DHR12LD . . . . . . . . . . . . . . . . . . . . . . 288
DAC_DHR12R1 . . . . . . . . . . . . . . . . . . . . . . 285
DAC_DHR12R2 . . . . . . . . . . . . . . . . . . . . . . 286
DAC_DHR12RD . . . . . . . . . . . . . . . . . . . . . . 288
DAC_DHR8R1 . . . . . . . . . . . . . . . . . . . . . . . 286
DAC_DHR8R2 . . . . . . . . . . . . . . . . . . . . . . . 287
DAC_DHR8RD . . . . . . . . . . . . . . . . . . . . . . . 288
DAC_DOR1 . . . . . . . . . . . . . . . . . . . . . . . . . . 289
DAC_DOR2 . . . . . . . . . . . . . . . . . . . . . . . . . . 289
DAC_SR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
DAC_SWTRIGR . . . . . . . . . . . . . . . . . . . . . . 285
DBGMCU_APB1_FZ . . . . . . . . . . . . . . . . . . . 921
DBGMCU_APB2_FZ . . . . . . . . . . . . . . . . . . . 923
DBGMCU_CR . . . . . . . . . . . . . . . . . . . . . . . . 920
DBGMCU_IDCODE . . . . . . . . . . . . . . . . . . . 914
DMA_CCRx . . . . . . . . . . . . . . . . . . . . . . . . . . 201
DMA_CMARx . . . . . . . . . . . . . . . . . . . . . . . . 204
DMA_CNDTRx . . . . . . . . . . . . . . . . . . . . . . . 203
DMA_CPARx . . . . . . . . . . . . . . . . . . . . . . . . . 203
DMA_IFCR . . . . . . . . . . . . . . . . . . . . . . . . . . 200
DMA_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
DMA2_CCRx . . . . . . . . . . . . . . . . . . . . . . . . . 201
DMA2_CMARx . . . . . . . . . . . . . . . . . . . . . . . 204
DMA2_CNDTRx . . . . . . . . . . . . . . . . . . . . . . 203
DMA2_CPARx . . . . . . . . . . . . . . . . . . . . . . . . 203
DMA2_CSELR . . . . . . . . . . . . . . . . . . . . . . . 205
DMA2_IFCR . . . . . . . . . . . . . . . . . . . . . . . . . 200
DMA2_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . 199
DMAx_CSELR . . . . . . . . . . . . . . . . . . . . . . . . 205

E
EXTI_EMR . . . . . . . . . . . . . . . . . . . . . . . . . . 216
EXTI_FTSR . . . . . . . . . . . . . . . . . . . . . . . . . . 217
EXTI_IMR . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
EXTI_PR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
EXTI_RTSR . . . . . . . . . . . . . . . . . . . . . . . . . . 216
EXTI_SWIER . . . . . . . . . . . . . . . . . . . . . . . . . 217

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Index

F
FLASH_ACR . . . . . . . . . . . . . . . . . . . . . . . . . .67
FLASH_CR . . . . . . . . . . . . . . . . . . . . . . . . . . .69
FLASH_KEYR . . . . . . . . . . . . . . . . . . . . . . . . .68
FLASH_OPTKEYR . . . . . . . . . . . . . . . . . . . . .68
FLASH_SR . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
FMPI2C_ISR . . . . . . . . . . . . . . . . . . . . . . . . .680

G
GPIOx_AFRH . . . . . . . . . . . . . . . . . . . . . . . . .162
GPIOx_AFRL . . . . . . . . . . . . . . . . . . . . . . . . .161
GPIOx_BRR . . . . . . . . . . . . . . . . . . . . . . . . . .162
GPIOx_BSRR . . . . . . . . . . . . . . . . . . . . . . . .159
GPIOx_IDR . . . . . . . . . . . . . . . . . . . . . . . . . .159
GPIOx_LCKR . . . . . . . . . . . . . . . . . . . . . . . . .160
GPIOx_MODER . . . . . . . . . . . . . . . . . . . . . . .157
GPIOx_ODR . . . . . . . . . . . . . . . . . . . . . . . . .159
GPIOx_OSPEEDR . . . . . . . . . . . . . . . . . . . . .158
GPIOx_OTYPER . . . . . . . . . . . . . . . . . . . . . .157
GPIOx_PUPDR . . . . . . . . . . . . . . . . . . . . . . .158

I
I2C_CR1 . . . . . . . . . . . . . . . . . . . . . . . . . . . .670
I2C_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .673
I2C_ICR . . . . . . . . . . . . . . . . . . . . . . . . . . . . .682
I2C_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . . .680
I2C_OAR1 . . . . . . . . . . . . . . . . . . . . . . . . . . .676
I2C_OAR2 . . . . . . . . . . . . . . . . . . . . . . . . . . .677
I2C_PECR . . . . . . . . . . . . . . . . . . . . . . . . . . .683
I2C_RXDR . . . . . . . . . . . . . . . . . . . . . . . . . . .684
I2C_TIMEOUTR . . . . . . . . . . . . . . . . . . . . . . .679
I2C_TIMINGR . . . . . . . . . . . . . . . . . . . . . . . .678
I2C_TXDR . . . . . . . . . . . . . . . . . . . . . . . . . . .684
I2Cx_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . .673
IWDG_KR . . . . . . . . . . . . . . . . . . . . . . . . . . .564
IWDG_PR . . . . . . . . . . . . . . . . . . . . . . . . . . .565
IWDG_RLR . . . . . . . . . . . . . . . . . . . . . . . . . .566
IWDG_SR . . . . . . . . . . . . . . . . . . . . . . . . . . .567
IWDG_WINR . . . . . . . . . . . . . . . . . . . . . . . . .568

P
PWR_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
PWR_CSR . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

R
RCC_AHBENR . . . . . . . . . . . . . . . . . . . . . . .120
RCC_AHBRSTR . . . . . . . . . . . . . . . . . . . . . .129
RCC_APB1ENR . . . . . . . . . . . . . . . . . . . . . . .123

RCC_APB1RSTR . . . . . . . . . . . . . . . . . . . . . 117
RCC_APB2ENR . . . . . . . . . . . . . . . . . . . . . . 121
RCC_APB2RSTR . . . . . . . . . . . . . . . . . . . . . 116
RCC_BDCR . . . . . . . . . . . . . . . . . . . . . . . . . 126
RCC_CFGR . . . . . . . . . . . . . . . . . . . . . . . . . 110
RCC_CFGR2 . . . . . . . . . . . . . . . . . . . . . . . . 131
RCC_CFGR3 . . . . . . . . . . . . . . . . . . . . . . . . 132
RCC_CIR . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
RCC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
RCC_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
RCC_CSR . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
RTC_ALRMAR . . . . . . . . . . . . . . . . . . . . . . . 604
RTC_BKPxR . . . . . . . . . . . . . . . . . . . . . . . . . 615
RTC_CALR . . . . . . . . . . . . . . . . . . . . . . . . . . 610
RTC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
RTC_DR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
RTC_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600
RTC_PRER . . . . . . . . . . . . . . . . . . . . . . . . . . 602
RTC_SHIFTR . . . . . . . . . . . . . . . . . . . . . . . . 606
RTC_SSR . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
RTC_TAFCR . . . . . . . . . . . . . . . . . . . . . . . . . 611
RTC_TR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
RTC_TSDR . . . . . . . . . . . . . . . . . . . . . . . . . . 608
RTC_TSSSR . . . . . . . . . . . . . . . . . . . . . . . . . 609
RTC_TSTR . . . . . . . . . . . . . . . . . . . . . . . . . . 607
RTC_WPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
RTC_WUTR . . . . . . . . . . . . . . . . . . . . . . . . . 603

S
SPIx_CR1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 801
SPIx_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 803
SPIx_CRCPR . . . . . . . . . . . . . . . . . . . . . . . . 807
SPIx_DR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807
SPIx_I2SCFGR . . . . . . . . . . . . . . . . . . . . . . . 810
SPIx_I2SPR . . . . . . . . . . . . . . . . . . . . . . . . . 812
SPIx_RXCRCR . . . . . . . . . . . . . . . . . . . . . . . 809
SPIx_SR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 806
SPIx_TXCRCR . . . . . . . . . . . . . . . . . . . . . . . 809
SYSCFG_CFGR1 . . . . . . . . . . . . . . . . . . . . . 165
SYSCFG_CFGR2 . . . . . . . . . . . . . . . . . . . . . 172
SYSCFG_EXTICR1 . . . . . . . . . . . . . . . . . . . 169
SYSCFG_EXTICR2 . . . . . . . . . . . . . . . . . . . 169
SYSCFG_EXTICR3 . . . . . . . . . . . . . . . . . . . 170
SYSCFG_EXTICR4 . . . . . . . . . . . . . . . . . . . 171
SYSCFG_ITLINE0 . . . . . . . . . . . . . . . . . . . . 172
SYSCFG_ITLINE1 . . . . . . . . . . . . . . . . . . . . 173
SYSCFG_ITLINE10 . . . . . . . . . . . . . . . . . . . 177
SYSCFG_ITLINE11 . . . . . . . . . . . . . . . . . . . 177
SYSCFG_ITLINE12 . . . . . . . . . . . . . . . . . . . 178
SYSCFG_ITLINE13 . . . . . . . . . . . . . . . . . . . 178
SYSCFG_ITLINE14 . . . . . . . . . . . . . . . . . . . 179

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Index

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SYSCFG_ITLINE15 . . . . . . . . . . . . . . . . . . . .179
SYSCFG_ITLINE16 . . . . . . . . . . . . . . . . . . . .179
SYSCFG_ITLINE17 . . . . . . . . . . . . . . . . . . . .180
SYSCFG_ITLINE18 . . . . . . . . . . . . . . . . . . . .180
SYSCFG_ITLINE19 . . . . . . . . . . . . . . . . . . . .180
SYSCFG_ITLINE2 . . . . . . . . . . . . . . . . . . . . .173
SYSCFG_ITLINE20 . . . . . . . . . . . . . . . . . . . .181
SYSCFG_ITLINE21 . . . . . . . . . . . . . . . . . . . .181
SYSCFG_ITLINE22 . . . . . . . . . . . . . . . . . . . .181
SYSCFG_ITLINE23 . . . . . . . . . . . . . . . . . . . .182
SYSCFG_ITLINE24 . . . . . . . . . . . . . . . . . . . .182
SYSCFG_ITLINE25 . . . . . . . . . . . . . . . . . . . .182
SYSCFG_ITLINE26 . . . . . . . . . . . . . . . . . . . .183
SYSCFG_ITLINE27 . . . . . . . . . . . . . . . . . . . .183
SYSCFG_ITLINE28 . . . . . . . . . . . . . . . . . . . .183
SYSCFG_ITLINE29 . . . . . . . . . . . . . . . . . . . .184
SYSCFG_ITLINE3 . . . . . . . . . . . . . . . . . . . . .174
SYSCFG_ITLINE30 . . . . . . . . . . . . . . . . . . . .184
SYSCFG_ITLINE4 . . . . . . . . . . . . . . . . . . . . .174
SYSCFG_ITLINE5 . . . . . . . . . . . . . . . . . . . . .175
SYSCFG_ITLINE6 . . . . . . . . . . . . . . . . . . . . .175
SYSCFG_ITLINE7 . . . . . . . . . . . . . . . . . . . . .175
SYSCFG_ITLINE8 . . . . . . . . . . . . . . . . . . . . .176
SYSCFG_ITLINE9 . . . . . . . . . . . . . . . . . . . . .176

TIMx_CCR2 . . . . . . . . . . . . . . . . . . . . . . 386, 452
TIMx_CCR3 . . . . . . . . . . . . . . . . . . . . . . 387, 453
TIMx_CCR4 . . . . . . . . . . . . . . . . . . . . . . 387, 454
TIMx_CNT . . . . . . . . . . .385, 451, 476, 540, 557
TIMx_CR1 . . . . . . . . . . .367, 435, 470, 530, 555
TIMx_CR2 . . . . . . . . . . . . . . . . . . . 368, 437, 531
TIMx_DCR . . . . . . . . . . . . . . . . . . . 389, 454, 543
TIMx_DIER . . . . . . . . . .372, 441, 471, 532, 556
TIMx_DMAR . . . . . . . . . . . . . . . . . 390, 455, 544
TIMx_EGR . . . . . . . . . . .375, 444, 472, 534, 557
TIMx_PSC . . . . . . . . . . .385, 451, 477, 540, 558
TIMx_RCR . . . . . . . . . . . . . . . . . . . . . . . 385, 540
TIMx_SMCR . . . . . . . . . . . . . . . . . . . . . 370, 438
TIMx_SR . . . . . . . . . . . .373, 442, 472, 533, 557
TSC_CR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
TSC_ICR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
TSC_IER . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
TSC_IOASCR . . . . . . . . . . . . . . . . . . . . . . . . 315
TSC_IOCCR . . . . . . . . . . . . . . . . . . . . . . . . . 316
TSC_IOGCSR . . . . . . . . . . . . . . . . . . . . . . . . 316
TSC_IOGxCR . . . . . . . . . . . . . . . . . . . . . . . . 317
TSC_IOHCR . . . . . . . . . . . . . . . . . . . . . . . . . 314
TSC_IOSCR . . . . . . . . . . . . . . . . . . . . . . . . . 315
TSC_ISR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

T

U

TIM15_ARR . . . . . . . . . . . . . . . . . . . . . . . . . .524
TIM15_BDTR . . . . . . . . . . . . . . . . . . . . . . . . .525
TIM15_CCER . . . . . . . . . . . . . . . . . . . . . . . . .521
TIM15_CCMR1 . . . . . . . . . . . . . . . . . . . . . . .518
TIM15_CCR1 . . . . . . . . . . . . . . . . . . . . . . . . .524
TIM15_CCR2 . . . . . . . . . . . . . . . . . . . . . . . . .525
TIM15_CNT . . . . . . . . . . . . . . . . . . . . . . . . . .523
TIM15_CR1 . . . . . . . . . . . . . . . . . . . . . . . . . .510
TIM15_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . .511
TIM15_DCR . . . . . . . . . . . . . . . . . . . . . . . . . .527
TIM15_DIER . . . . . . . . . . . . . . . . . . . . . . . . .514
TIM15_DMAR . . . . . . . . . . . . . . . . . . . . . . . .528
TIM15_EGR . . . . . . . . . . . . . . . . . . . . . . . . . .517
TIM15_PSC . . . . . . . . . . . . . . . . . . . . . . . . . .523
TIM15_RCR . . . . . . . . . . . . . . . . . . . . . . . . . .524
TIM15_SMCR . . . . . . . . . . . . . . . . . . . . . . . .512
TIM15_SR . . . . . . . . . . . . . . . . . . . . . . . . . . .515
TIM5_OR . . . . . . . . . . . . . . . . . . . . . . . . . . . .478
TIM6_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . . .556
TIMx_ARR . . . . . . . . . . 385, 451, 477, 540, 558
TIMx_BDTR . . . . . . . . . . . . . . . . . . . . . .388, 541
TIMx_CCER . . . . . . . . . . . . . 381, 449, 475, 538
TIMx_CCMR1 . . . . . . . . . . . 376, 445, 473, 535
TIMx_CCMR2 . . . . . . . . . . . . . . . . . . . .380, 448
TIMx_CCR1 . . . . . . . . . . . . . 386, 452, 477, 541

USART_BRR . . . . . . . . . . . . . . . . . . . . . . . . . 743
USART_CR1 . . . . . . . . . . . . . . . . . . . . . . . . . 732
USART_CR2 . . . . . . . . . . . . . . . . . . . . . . . . . 735
USART_CR3 . . . . . . . . . . . . . . . . . . . . . . . . . 739
USART_GTPR . . . . . . . . . . . . . . . . . . . . . . . 743
USART_ICR . . . . . . . . . . . . . . . . . . . . . . . . . 751
USART_ISR . . . . . . . . . . . . . . . . . . . . . . . . . 746
USART_RDR . . . . . . . . . . . . . . . . . . . . . . . . 752
USART_RQR . . . . . . . . . . . . . . . . . . . . . . . . 745
USART_RTOR . . . . . . . . . . . . . . . . . . . . . . . 744
USART_TDR . . . . . . . . . . . . . . . . . . . . . . . . . 752
USB_ADDRn_RX . . . . . . . . . . . . . . . . . . . . . 888
USB_ADDRn_TX . . . . . . . . . . . . . . . . . . . . . 887
USB_BCDR . . . . . . . . . . . . . . . . . . . . . . . . . . 881
USB_BTABLE . . . . . . . . . . . . . . . . . . . . . . . . 880
USB_CNTR . . . . . . . . . . . . . . . . . . . . . . . . . . 874
USB_COUNTn_RX . . . . . . . . . . . . . . . . . . . . 888
USB_COUNTn_TX . . . . . . . . . . . . . . . . . . . . 887
USB_DADDR . . . . . . . . . . . . . . . . . . . . . . . . 880
USB_EPnR . . . . . . . . . . . . . . . . . . . . . . . . . . 883
USB_FNR . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
USB_ISTR . . . . . . . . . . . . . . . . . . . . . . . . . . . 876
USB_LPMCSR . . . . . . . . . . . . . . . . . . . . . . . 881

1002/1004

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RM0091

Index

W
WWDG_CFR . . . . . . . . . . . . . . . . . . . . . . . . .574
WWDG_CR . . . . . . . . . . . . . . . . . . . . . . . . . .573
WWDG_SR . . . . . . . . . . . . . . . . . . . . . . . . . .574

DocID018940 Rev 9

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RM0091

IMPORTANT NOTICE – PLEASE READ CAREFULLY
STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, enhancements, modifications, and
improvements to ST products and/or to this document at any time without notice. Purchasers should obtain the latest relevant information on
ST products before placing orders. ST products are sold pursuant to ST’s terms and conditions of sale in place at the time of order
acknowledgement.
Purchasers are solely responsible for the choice, selection, and use of ST products and ST assumes no liability for application assistance or
the design of Purchasers’ products.
No license, express or implied, to any intellectual property right is granted by ST herein.
Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product.
ST and the ST logo are trademarks of ST. All other product or service names are the property of their respective owners.
Information in this document supersedes and replaces information previously supplied in any prior versions of this document.
© 2017 STMicroelectronics – All rights reserved

1004/1004

DocID018940 Rev 9



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