MCP251XXFD CAN FD Controller Module Family Reference Manual 20005678B

MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B

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Page Count: 80

CAN FD Controller Module
1.0 Introduction
2.0 Modes of Operation
3.0 Configuration
4.0 Message Transmission
5.0 Transmit Event FIFO
- TABLE 5-1: Transmit Event FIFO Object
- 5.1 TEF Code Example
6.0 Message Filtering
7.0 Message Reception
8.0 FIFO Behavior
9.0 Timestamping
- 9.1 TBC Configuration Code Example
10.0 Interrupts
11.0 Error Handling
- 11.1 Recovery from Bus Off State
12.0 Appendix A: MCP25xxFD canfdspi API
13.0 Related Documents
14.0 Revision History
- Revision B (May 2018)
- Revision A (September 2017)
Worldwide Sales and Service

 2017-2018 Microchip Technology Inc. DS20005678B-page 1

HIGHLIGHTS

This section of the manual contains the following major topics:

1.0 Introduction ....................................................................................................................... 2

2.0 Modes of Operation .......................................................................................................... 8

3.0 Configuration................................................................................................................... 13

4.0 Message Transmission ................................................................................................... 26

5.0 Transmit Event FIFO....................................................................................................... 33

6.0 Message Filtering............................................................................................................36

7.0 Message Reception ........................................................................................................ 41

8.0 FIFO Behavior................................................................................................................. 45

9.0 Timestamping.................................................................................................................. 58

10.0 Interrupts......................................................................................................................... 59

11.0 Error Handling................................................................................................................. 68

12.0 Appendix A: MCP25xxFD canfdspi API .......................................................................... 70

13.0 Related Documents ........................................................................................................ 76

14.0 Revision History .............................................................................................................. 77

CAN FD Controller Module

MCP25xxFD Family Reference Manual

DS20005678B-page 2  2017-2018 Microchip Technology Inc.

1.0 INTRODUCTION

1.1 CAN FD vs. CAN 2.0

CAN FD addresses the increasing demand for bandwidth on CAN buses. The two major

enhancements over CAN 2.0 are:

• Increased data field up to 64 data bytes (from maximum 8 data bytes for CAN 2.0).

• Option to switch to faster bit rate in the data phase. The arbitration bit rate is the same as in

CAN 2.0.

Figure 1-1 shows the possible increase in effective bit rate due to the higher data bit rate and

increased data bytes per frame. The graph uses a CAN FD Base frame with 11 bit identifier and

500 kbps bit rate during the arbitration phase.

The CAN FD protocol was defined to allow CAN 2.0 messages and CAN FD messages to co-

exist on the same bus. This does not imply that non-CAN FD controllers can be mixed with CAN

FD controllers on the same bus. Non-CAN FD controllers will generate error frames while

receiving a CAN FD message.

The CAN FD protocol (Data Link Layer) is defined in ISO 11898-1:2015.

Figure 1-1: Effective CAN FD Bit Rate

(Base Frame: 11 Bit ID, Nominal Bit Rate = 500 Kbps)

Note: This family reference manual section is meant to serve as a complement to the

device data sheet. Please refer to the data sheet for the memory organization and

Device data sheets, application notes and code samples (MCP25xxFD canfdspi

API) are available for download from the Microchip web site (www.microchip.com).

All code samples in this manual use the MCP25xxFD canfdspi API. Please refer to

the API header files for the documentation of structures and function prototypes.

05

15

25

35

45

0123456789

Effective Bit Rate/Mbps

Data Bit Rate/Mbps

8 Bytes Payload 16 Bytes Payload

24 Bytes Payload 32 Bytes Payload

48 Bytes Payload 64 Bytes Payload

 2017-2018 Microchip Technology Inc. DS20005678B-page 3

CAN FD Controller Module

1.2 Features

The CAN FD Controller Module has the following features:

General

• External CAN FD Controller with SPI Interface

• Nominal (Arbitration) Bit Rate up to 1 Mbps

• Data Bit Rate up to 8 Mbps

• CAN FD Controller modes

- Mixed CAN 2.0B and CAN FD mode

- CAN 2.0B mode

• Conforms to ISO 11898-1:2015

Message FIFOs

• 31 FIFOs, Configurable as Transmit or Receive FIFOs

• One Transmit Queue (TXQ)

• Transmit Event FIFO (TEF) with 32-Bit Timestamp

Message Transmission

• Message Transmission Prioritization:

- Based on priority bit field, and/or

- Message with lowest ID gets transmitted first using the Transmit Queue (TXQ)

• Programmable Automatic Retransmission Attempts: unlimited, 3 attempts, or disabled

Message Reception

• 32 Flexible Filter and Mask Objects

• Each object can be configured to filter either:

- Standard ID + first 18 data bits, or

- Extended ID

• 32-Bit Timestamp

MCP25xxFD Family Reference Manual

DS20005678B-page 4  2017-2018 Microchip Technology Inc.

1.3 Module Block Diagram

Figure 1-2 shows the block diagram of the CAN FD Controller Module.

• The CAN FD Controller Module has multiple modes:

- Configuration,

- Normal CAN FD,

- Normal CAN 2.0,

- Sleep (normal Sleep mode and Low Power Mode),

- Listen Only,

- Restricted Operation, and

- Internal and External Loopback modes.

• The CAN FD Bit Stream Processor (BSP) implements the Medium Access Control of the

CAN FD protocol described in ISO 11898-1:2015. It serializes and deserializes the bit

stream, encodes and decodes the CAN FD frames, manages the medium access,

acknowledges frames, and detects and signals errors.

• The TX Handler prioritizes the messages that are requested for transmission by the

Transmit FIFOs. It uses the RAM Interface to fetch the transmit data from RAM and

provides it to the BSP for transmission.

• The BSP provides received messages to the RX Handler. The RX Handler uses

Acceptance Filter to filter out messages that shall be stored into Receive FIFOs. It uses the

RAM Interface to store received data into RAM.

• Each FIFO can be configured either as a Transmit or Receive FIFO. The FIFO Control

keeps track of the FIFO Head and Tail, and calculates the User Address. For a TX FIFO,

the User Address points to the address in RAM where the data for the next transmit

message shall be stored. For a RX FIFO, the User Address points to the address in RAM

where the data of the next receive message shall be read. The user notifies the FIFO that a

message was written to or read from RAM by incrementing the Head/Tail of the FIFO.

• The Transmit Queue (TXQ) is a special transmit FIFO that transmits the messages based

on the ID of the messages stored in the queue.

• The Transmit Event FIFO (TEF) stores the message IDs of the transmitted messages.

• A free-running Time Base Counter is used to timestamp received messages. Messages in

the TEF can also be timestamped.

• The CAN FD Controller Module generates interrupts when new messages are received or

when messages were transmitted successfully.

• The Special Function Registers (SFR) are used to control and to read the status of the CAN

FD Controller Module.

Figure 1-2: Module Block Diagram

CAN FD

Bit Stream

Processor

RAM

Interface

TX Handler

TX Prioritization

RX Handler

Acceptance

Filter

TXQ Control

TEF

Control

FIFO

Control

SFR

Interrupt

Control

Error

Handling

Diagnostics

Time Stamping

TBC

Mode

Control

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CAN FD Controller Module

1.4 CAN FD Message Frames

The ISO 11898-1:2015 describes the different CAN message frames in detail. Figure 1-3

through Figure 1-7 clarify and summarize the construction of the messages and fields.

There are four different CAN Data/Remote frames, see Figure 1-4:

• CAN Base frame: Classic CAN 2.0 frame using Standard ID.

• CAN FD Base frame: CAN FD frame using Standard ID.

• CAN Extended frame: Classic CAN 2.0 frame using Extended ID.

• CAN FD Extended frame: CAN FD frame using Extended ID.

There are no Remote frames in CAN FD frames, therefore, the RTR bit is replaced with the

RRS bit, see Figure 1-4. The RRS bit in the CAN FD Base frame can be used to extend the SID

to 12 bit. When enabled it is referred to as SID11, it is the LSB of SID<11:0>.

Figure 1-5 specifies the Control field of the different CAN messages. Before CAN FD was

added to the ISO 11898-1:2015, the FDF bit was a reserved bit. Now the FDF bit selects

between Classic and CAN FD formats.

The BRS bit selects if the bit rate should be switched in the data phase of CAN FD frames.

Figure 1-8 illustrates the Error and Overload frames. These special frames didn’t change. Note

that if an error is detected during the data phase of a CAN FD frame, the bit rate will be switched

back to the Nominal Bit Rate. Error frames are always transmitted at the arbitration bit rate.

1.4.1 ISO VS. NON ISO CRC

To support the system validation of Non-ISO CRC ECUs, the CAN FD Controller Module

supports both ISO CRC (according to ISO 11898-1:2015) and Non-ISO CRC, see Figure 1-6

and Figure 1-7. The CRC field is selectable using CiCON.ISOCRCEN. The ISO CRC field

contains the Stuff Count. This count wasn’t included in the original CAN FD specification. It was

added to fix a weakness in the error detection of the original specification.

CAN FD frames use two different lengths of CRC: 17 bit for up to 16 data bytes, and 21 bits for

20 or more data bytes. Technically, there are a total of six different CAN Data/Remove frames in

CAN FD.

Figure 1-3: General Data Frame

Figure 1-4: Arbitration Field

SOF

(1b) ARBITRATION(12/32b) CTRL(6/8/9b) DATA(0 to 64B) CRC(16/18/22b)

CRC(16/22/26b) ACK(2b) EOF(7b) IFS(≥3b)IFS(≥3b)

DATA FRAME

ARBITRATION(12/32b)

SID<10:0> RTR

SID<10:0> SRR IDE EID<17:0> RTR

SID<10:0> RRS

SID11

SID<10:0> SRR IDE EID<17:0> RRS

CAN BASE

CAN FD BASE

CAN EXT

CAN FD EXT

MCP25xxFD Family Reference Manual

DS20005678B-page 6  2017-2018 Microchip Technology Inc.

Figure 1-5: Control Field

Figure 1-6: ISO CRC Field

Figure 1-7: NON-ISO CRC Field

CTRL(6/8/9b)

IDE FDF DLC<3:0>

IDE res DLC<3:0>FDF BRS ES I

FDF r0 DLC<3:0>

res DLC<3:0>FDF BRS ES I

CAN BASE

CAN FD BASE

CAN EXT

CAN FD EXT

CRC(16/22/26b)

CRC(15b)

CRC(17/21b)

CRC

DEL

CRC

DEL

STUFF

CNT (4b)

CRC

DEL

STUFF

CNT (4b)

CRC

DEL

CAN BASE

CAN FD BASE

CAN EXT

CAN FD EXT

CRC(16/18/22b)

CRC(15b) CRC

DEL

CRC(15b) CRC

DEL

CRC(17/21b) CRC

DEL

CRC(17/21b) CRC

DEL

CAN BASE

CAN FD BASE

CAN EXT

CAN FD EXT

 2017-2018 Microchip Technology Inc. DS20005678B-page 7

CAN FD Controller Module

Figure 1-8: Error and Overload Frame

1.4.2 DLC ENCODING

The Data Length Code (DLC) specifies how many data bytes a message frame contains.

Table 1-1 illustrates the encoding.

Table 1-1: DLC Encoding

ERRFLAG(6b) ERRDEL(8b)ANYWHERE WITHIN DATA FRAME IFS(≥3b) or OVL

OVLFLAG(6b) OVLDEL(8b)EOF or ERRDEL or OVLDEL IFS(≥3b) or OVL

ERROR

OVERLOAD

Frame DLC Number of

data bytes

CAN 2.0 and CAN FD 0 0

CAN 2.0 9-15 8

CAN FD 9 12

10 16

11 20

12 24

13 32

14 48

15 64

MCP25xxFD Family Reference Manual

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2.0 MODES OF OPERATION

The CAN FD Controller Module has eight modes of operation:

• Configuration mode

• Normal CAN FD mode: supports mixing of CAN FD and CAN 2.0 messages

• Normal CAN 2.0 mode: will generate error frames while receiving CAN FD messages. The

FDF bit is forced to zero, and only CAN 2.0 frames are sent, even if the FDF bit is set in the

Transmit Message Object.

• Sleep mode (normal Sleep mode and Low Power Mode)

• Listen Only mode

• Restricted Operation mode

• Internal Loopback mode

• External Loopback mode

The modes of operation can be grouped into four main groups of modes: Configuration, Normal,

Sleep, and Debug, see Figure 2-1.

2.1 Mode Change

Figure 2-1 illustrates the possible mode transitions. New Modes of operation are requested by

writing to CiCON.REQOP. The modes of operation don’t change immediately. The modes will

only change when the bus is idle.

The current operating mode is indicated in CiCON.OPMOD. The application can enable an

interrupt on OPMOD change, or poll OPMOD.

2.1.1 CHANGING BETWEEN NORMAL MODES

Directly changing between Normal modes is not allowed. The Configuration Mode must be

selected first before a new Normal mode can be selected.

2.1.2 CHANGING BETWEEN DEBUG MODES

Directly changing between Debug modes is not allowed. The Configuration mode must be

selected first before a new Debug mode can be selected.

2.1.3 EXITING NORMAL MODE

The device will only transition to Configuration or Sleep mode after the message that is currently

being transmitted has finished.

2.1.4 ENTERING AND EXITING SLEEP MODE

The CAN FD Controller Module enters Sleep mode after a Sleep Mode request.

The device exits Sleep mode due to a dominant edge on RXCAN or by enabling the oscillator

(clearing OSC.OSCDIS). The module will transition automatically to Configuration mode.

2.1.5 INTEGRATING

The CAN FD Controller Module integrates to the bus according to the ISO 11898-1:2015

(eleven consecutive recessive bits) under the following conditions:

• Change from Configuration mode to Normal or Debug modes.

 2017-2018 Microchip Technology Inc. DS20005678B-page 9

CAN FD Controller Module

Figure 2-1: Modes of Operation

Normal FD

Mode

Normal 2.0

Mode

External/Internal

Loopback

Mode

Listen Only

Mode

“Normal” Modes “Debug” Modes

Restricted

Operation

Mode

REQOP=Sleep

AndOSC.LPMEN=0

WAKIF

OrAssertnCS

REQOP=Sleep

AndOSC.LPMEN=1

AndBusIdle

REQOP=Sleep

AndOSC.LPMEN=1

REQOP=Restricted

AndBusIdle

Yes

REQOP=”Normal”

REQOP=ListenOnly

AndBusIdle

REQOP=Config

(AndBusIdle)

REQOP=Restricted

AndBusIdle

Resbit=1received

AndPXEDIS=0

Waitfor

BusIdle

Waitfor

128Idleconditions

TXBO

Systemerror

REQOP=”Normal”

REQOP=Config

(AndBusIdle) REQOP=ListenOnly

AndBusIdle

REQOP=Config

AndBusIdle

REQOP=LoopbackInt/Ext

AndBusIdle

(Integrating)

WAKIF

OrOSC.OSCDIS=0

REQOP=Sleep

AndOSC.LPMEN=0

AndBusIdle

REQOP=Config

AndBusIdle

REQOP=”Normal”

AndBusIdle

(Integrating)

POR

Configuration

Mode

SleepMode

ClockOff

TXCANrecessive

“Normal”

Modes

RXandTX

Loopback

Modes

ListenOnly

Mode

RXOnly

TXpinhigh

TXREQignored

BusOff

ClearallTXREQ

(FRESETTXFIFOs/

TXQ)

Protocol

ExceptionEvent

NoTX

Restricted

Operation

Mode

TX:onlyACK

TXREQignored

cSERR2LOM==1?

LPM

DigitalLogicOff

TXCANrecessive

MCP25xxFD Family Reference Manual

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2.2 Configuration Mode

After Reset, the CAN FD Controller Module is in Configuration mode. The error counters are

cleared and all registers contain the reset values.

The CAN FD Controller Module has to be initialized before activation. This is only possible if the

module is in the Configuration mode, OPMOD = 100. The Configuration mode is requested by

setting REQOP = 100.

The CAN FD Controller Module will protect the user from accidentally violating the CAN protocol

through programming errors. The following registers and bit fields can only be programmed

during Configuration mode:

• CiCON: TXQEN, STEF, SERR2LOM, ESIGM, RTXAT, WAKFIL, PXEDIS, ISOCRCEN

• CiNBTCFG, CiDBTCFG, CiTDC

• CiTXQCON: PLSIZE, FSIZE

• CiFIFOCONm: PLSIZE, FSIZE, TXEN, RXTSEN

• CiTEFCON: FSIZE, TEFTSEN

The CAN FD Controller Module will not be allowed to enter the Configuration mode while a

transmission or reception is taking place in order to prevent the module from causing errors on

the CAN bus. The following registers are reset when exiting Configuration mode:

• CiTREC

• CiBDIAG0

• CiBDIAG1

In Configuration mode, FRESET is set in CiFIFOCONm, CiTXQCON, and CiTEFCON registers,

and all FIFOs and the Transmit Queue are reset.

2.3 Normal Modes

2.3.1 NORMAL CAN FD MODE

Once the device is configured, Normal Operation mode can be requested by setting

REQOP = 000.

In this mode, the device will be on the CAN bus. It can transmit and receive messages in CAN

FD mode: bit rate switching can be enabled, and up to 64 data bytes can be transmitted and

received.

2.3.2 NORMAL CAN 2.0 MODE

The Normal CAN 2.0 Operation mode can be requested by setting REQOP = 110.

In this mode, the device will be on the CAN bus. This is a the Classic CAN 2.0 mode. The

module will not receive CAN FD frames. It might send error frames if CAN FD frames are

detected on the bus. The FDF, BRS, and ESI bits in the TX objects will be ignored and

transmitted as ‘0’.

 2017-2018 Microchip Technology Inc. DS20005678B-page 11

CAN FD Controller Module

2.4 Sleep Mode

Sleep mode is a low-power mode, where register and RAM contents are preserved, and the

clock is switched off.

Sleep mode is requested by clearing OSC.LPMEN, and setting REQOP = 001.

The CAN module will not enter Sleep mode while a transmission or reception is taking place to

prevent causing errors on the CAN bus. The module will enter Sleep mode when the current

message completes.

The OPMOD bits indicate Configuration mode (OPMOD = 100), and OSC.OSCDIS will read

‘1’. The application software should use these bit fields as a handshake indication for the Sleep

mode request. The TXCAN pin will stay in the recessive state while the module is in Sleep

mode to prevent inadvertent CAN bus errors.

2.4.1 EXITING SLEEP MODE

There are two ways to exit Sleep mode:

• Clearing OSC.OSCDIS.

• Wake-up interrupt due to CAN bus activity.

Both ways will reenable the clock and the CAN FD Controller Module will transition to

Configuration mode.

The module will monitor the RXCAN pin for activity while the module is in Sleep mode. The

device will generate a wake-up interrupt on the falling edges of RXCAN, if WAKIE is enabled.

2.5 Low-Power Mode (LPM)(Note 3)

LPM is an ultra-low-power mode, where the majority of the chip is powered down. Only the logic

required for wake-up is powered. This significantly reduces the leakage of the device at high

temperature.

LPM is requested by setting OSC.LPMEN, and setting REQOP = 001.

The CAN module will not enter LPM while a transmission or reception is taking place to prevent

causing errors on the CAN bus. The module will enter LPM when the current message

completes.

2.5.1 EXITING LPM

There are two ways to exit LPM:

• Asserting nCS

• Wake-up interrupt due to CAN bus activity

Exiting LPM is similar to a POR. The CAN FD Controller Module will transition to Configuration

mode. All registers will be reset, and RAM data will be lost. The device has to be reconfigured.

The module will monitor the RXCAN pin for activity while the module is in LPM. The device will

generate a wake-up interrupt on the falling edges of RXCAN, if WAKIE is enabled.

Note 1: If the module is in Sleep mode or LPM, the module generates an interrupt if the WAKIE

bit in the CiINT register is set and bus activity is detected. The oscillator starts up.

Messages that caused the wake-up will be lost until the oscillator is stable and the

device was switched to Normal mode.

2: The module can be programmed to apply a low-pass filter to the RXCAN pin while in

Sleep mode and LPM. This feature can be used to protect the module from wake-up

due to short glitches on the RXCAN pin. The WAKFIL bit in the CiCON register

enables or disables the filter while the module is in Sleep mode and LPM. The filter

time is programmable using the WFT bits in the CiCON register.

3: LPM is NOT implemented in the MCP2517FD.

MCP25xxFD Family Reference Manual

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2.6 Debug Modes

2.6.1 LISTEN ONLY MODE

Listen Only mode is a variant of Normal CAN FD Operation mode. If the Listen Only mode is

activated, the module on the CAN bus is passive. It will receive messages, but it will not transmit

any bits. TXREQ bits will be ignored. No error flags or acknowledge signals are sent. The error

counters are deactivated in this state. The Listen Only mode can be used for detecting the baud

rate on the CAN bus. It is necessary that there are at least two further nodes that communicate

with each other. The baud rate can be detected empirically by testing different values, until a

message is received successfully. This mode is also useful for monitoring the CAN bus without

influencing it.

2.6.2 RESTRICTED OPERATION MODE

In Restricted Operation mode, the node is able to receive data and Remote frames, and to

acknowledge valid frames, but it does not send Data frames, Remote frames, Error frames or

Overload frames. In case of an error condition or overload condition, it does not send dominant

bits; instead it waits for the occurrence of the bus Idle condition to resynchronize itself to the

CAN communication. The error counters are not incremented.

2.6.3 LOOPBACK MODE

Loopback mode is a variant of Normal CAN FD Operation mode. This mode will allow internal

transmission of messages from the transmit FIFOs to the receive FIFOs. The module does not

require an external acknowledge from the bus. No messages can be received from the bus,

because the RXCAN pin is disconnected.

2.6.3.1 Internal Loopback Mode

The transmit signal is internally connected to receive, and TXCAN is driven high.

2.6.3.2 External Loopback Mode

The transmit signal is internally connected to receive, and transmit messages can be monitored

on the TXCAN pin.

 2017-2018 Microchip Technology Inc. DS20005678B-page 13

CAN FD Controller Module

3.0 CONFIGURATION

The MCP25xxFD should be reset and must be in Configuration mode before starting

configuration. The oscillator, FIFOs and bit time can only be configured in Configuration mode.

This prevents the device from accidentally disturbing the CAN bus.

3.1 Oscillator Configuration

Figure 3-1 shows the block diagram of the oscillator. The oscillator generates the SYSCLK that

is used by the CAN FD Controller Module. CAN FD requires that the sample point in every node

is setup identically. Therefore, a 40 MHz or 20 MHz SYSCLK is recommended. The oscillator

uses a crystal or ceramic resonator, or an external clock as the clock reference.

The OSC register is used to configure the oscillator. A PLL can be enabled to multiply a 4 MHz

clock by 10 by setting the PLLEN bit. Setting the SCLKDIV bit divides the SYSCLK by 2. The

clock is available on the CLKO pin and can be divided using the CLKODIV bits.

The oscillator will be disabled after requesting Sleep mode. OSCDIS can only be cleared by the

application. It will be set automatically after the module enters Sleep mode. Reading

OSCDIS = ‘1’ indicates that the module has entered Sleep mode.

3.1.1 CRYSTAL/RESONATOR SELECTION

Selecting the correct crystal oscillator or ceramic resonator components depends on multiple

factors that are application dependent. Please review section 6.7 of the “PIC32 Family Reference

Manual (DS611112)” and refer to the application notes listed in Section 13.0 “Related

Documents”.

The following crystals, together with 18 pF load capacitors, were successfully used in one of our

evaluation boards: ABM8G-40.000MHZ-18-D2Y-T and ABM8G-20.000MHZ-18-D2Y-T.

Figure 3-1: MCP251xFD Oscillator Block Diagram

3.2 Input/Output Pin Configuration

The IOCON register configures the I/O of the MCP25xxFD. The INT0/GPIO0/XSTBY and INT1/

GPIO1 pins can be configured as interrupt pins or as GPIO pins using the PM0 and PM1 bits. In

case the pins are configured as GPIO pins the direction of the pin is selected using the TRIS0

and TRIS1 bits.

INT, INT0 and INT1 (when configured as interrupts) can be configured as push/pull or open drain

outputs using the INTOD bit. The TXCAN pin can also be configured as open drain by setting the

TXCANOD bit.

Setting the XSTBYEN bit configures the INT0/GPIO0/XSTBY pin to automatically control the

stand-by pin of an external CAN transceiver. The pin is driven high when the MCP25xxFD enters

Sleep mode, and driven low when it exits Sleep mode. Stand-by pin control is not available in

LPM. IOCON is reset in LPM and GPIO0 will be configured as an input.

OSC1

OSC2

4, 40 or 20 MHz

CLKIN,

Crystal or

Ceramic Res.

40/20 MHz

PLLEN

OSCDIS

Divide

By 1, 2

SCLKDIV

SYSCLK

Divide

By 1, 2, 4, 10

CLKO

CLKODIV

PLL

x10

MCP25xxFD Family Reference Manual

DS20005678B-page 14  2017-2018 Microchip Technology Inc.

Setting the SOF bit will output a pulse on the CLKO/SOF pin every time a start bit of a CAN

message is transmitted or received.

3.3 CAN Configuration

The CiCON register contains several bits that can only be configured in Configuration mode.

3.3.1 ISO CRC ENABLE

The module supports ISO CRC (according to ISO 11898-1:2015) and non-ISO CRC, see

Section 1.4.1 “ISO vs. NON ISO CRC”. ISO CRC is enabled by setting the ISOCRCEN bit.

3.3.2 PROTOCOL EXCEPTION DISABLE

The negative edge between the FDF bit and the “res bit” in CAN FD frames is important for the

calculation of the transceiver delay, and for hard-synchronization. Therefore, if the “res bit”

following the FDF bit is detected recessive, the CAN FD Controller Module will treat this as a

form error. This is called “Protocol Exception Event Detection Disabled”, and is configured by

setting the PXEDIS bit.

The Protocol Exception Event Detection can be enabled by clearing the PXEDIS bit. As a

reaction to the protocol exception event, the error counters are not changed, hard

synchronization is enabled, the module sends recessive bits and enters the bus integration

state.

3.3.3 WAKE-UP FILTER

The WAKFIL bit is used to enable/disable the low-pass filter on the RXCAN pin. The filter is only

active during Sleep mode. The WFT bits allow the configuration of different filter times.

3.3.4 RESTRICTION OF TRANSMISSION ATTEMPTS

ISO 11898-1:2015 requires that frames that lost arbitration, were not acknowledged or were

destroyed by errors are automatically retransmitted. Optionally, the number of retransmission

attempts can be limited.

When the RTXAT bit is set, retransmission attempts can be limited using the TXAT bits in the

FIFO control registers. If the RTXAT bit is clear, then TXAT in the FIFO control register is

ignored and the retransmission attempts are unlimited.

3.3.5 ERROR STATE INDICATOR (ESI) IN GATEWAY MODE

Normally the ESI bit in a transmitted message reflects the error status of the CAN FD Controller

Module. ESI is transmitted recessive when the module is error passive. In case the module is

used in a Gateway application, there are situations were the ESI bit in the message should be

transmitted recessive, even though the Gateway module is error active. This can be configured

by setting the ESIGM bit.

3.3.6 MODE SELECTION IN CASE OF SYSTEM ERROR

The SERR2LOM bit selects to which mode the module will transition in case of a System Error.

The module can either transition to Restricted Operation mode or Listen Only mode.

3.3.7 RESERVING MESSAGE MEMORY FOR TX QUEUE AND TRANSMIT

EVENT FIFO

Setting the TXQEN bit will reserve RAM for the TXQ. If the TXQEN bit is cleared then the TXQ

can’t be used.

Setting the STEF bit will reserve RAM for the TEF, and all transmitted messages will be stored

in the TEF.

 2017-2018 Microchip Technology Inc. DS20005678B-page 15

CAN FD Controller Module

3.4 CAN FD Bit Time Configuration

In order to achieve higher bandwidth, bits inside a CAN FD frame are transmitted with two

different bit rates:

• Nominal Bit Rate (NBR): used during arbitration until the sample point of the BRS bit, and

from the sample point of the CRC delimiter until the EOF.

• Data Bit Rate (DBR): used during the data and CRC field.

NBR is limited by the propagation delay of the CAN network, see Section 3.4.2 “Propagation

Delay”. In the data phase, only one transmitter remains, therefore, the bit rate can be increased.

The transmitting node always compares the intended transmitted bits with the actual bits on the

CAN bus. The propagation delay in the data phase can be longer than the bit time. In this case,

the data bits are sampled at a Secondary Sample Point (SSP), see Section 3.4.3 “Transmitter

Delay Compensation (TDC)”.

NBR is the number of bits per second during the arbitration phase. It is the inverse of the Nominal

Bit Time (NBT), see Equation 3-1.

Equation 3-1: Nominal Bit Rate/Time

DBR is the number of bits per second during the data phase. It is the inverse of the Data Bit Time

(DBT), see Equation 3-1.

Equation 3-2: Data Bit Rate/Time

The Baud Rate Prescaler (BRP) is used to divide the SYSCLK. The divided SYSCLK is used to

generate the bit times.

There are two prescaler: NBRP for the nominal bit rate, and DBRP for the data bit rate. The

Time Quanta (NTQ and DTQ) are selected as shown in Equation 3-3 and Equation 3-4:

Equation 3-3: Nominal Time Quanta

Equation 3-4: Data Time Quanta

CAN bit times are made up of four segments as specified in ISO 11898-1:2015, see Figure 3-2.

Synchronization Segment (SYNC) – Synchronizes the different nodes connected on the CAN

bus. A bit edge is expected to be within this segment. The Synchronization Segment is always 1

TQ.

Propagation Segment (PRSEG) – Compensates for the propagation delay on the bus. PRSEG

has to be longer than the maximum propagation delay.

Phase Segment 1 (PHSEG1) – This time segment compensates for errors that may occur due

to phase shifts in the edges. The time segment may be automatically lengthened during

resynchronization to compensate for the phase shift.

Phase Segment 2 (PHSEG2) – This time segment compensates for errors that may occur due

to phase shifts in the edges. The time segment may be automatically shortened during

resynchronization to compensate for the phase shift.

NBR 1

NBT

-----------=

DBR 1

DBT

------------=

NTQ NBRP TSYSCLK

NBRP

FSYSCLK

--------------------------==

DTQ DBRP TSYSCLK

DBRP

FSYSCLK

--------------------------==

MCP25xxFD Family Reference Manual

DS20005678B-page 16  2017-2018 Microchip Technology Inc.

In the bit time registers, PRSEG and PHSEG1 are combined to TSEG1. PHSEG2 is called

TSEG2. Each segment is made up of multiple Time Quanta (TQ). The sample point lies between

TSEG1 and TSEG2.

Table 3-1 and Tabl e 3 -2 show the ranges for the bit time configuration parameters.

Figure 3-2: Partition of Bit Time

The total number of TQ in a bit time is programmable and can be calculated using Equation 3-5

and Equation 3-6.

Equation 3-5: Number of NTQ in a NBT

Equation 3-6: Number of DTQ in a DBT

Table 3-1: Nominal Bit Rate Configuration Ranges

Table 3-2: Data Bit Rate Configuration Ranges

3.4.1 SAMPLE POINT

The sample point is the point in the bit time at which the logic level of the bit is read and

interpreted. The sample point in percent can be calculated using Equation 3-7 and Equation 3-8.

Equation 3-7: Nominal Sample Point (%)

Segment Min. Max.

NSYNC 1 1

NTSEG1 2 256

NTSEG2 1 128

NSJW 1 128

NTQ per Bit 4 385

Segment Min. Max.

DSYNC 1 1

DTSEG1 1 32

DTSEG2 1 16

DSJW 1 16

DTQ per Bit 3 49

SY NC PRSE G PHSE G1 PHSE G2

SY NC TSEG1 TSEG2

Sample point

NBT

NTQ

------------ NSYNC NTSEG1 NTSEG2++=

DBT

DTQ

------------ D S Y N C D T S E G 1 D T S E G 2++=

NSP 1NTSEG1+

NBT

NTQ

------------

---------------------------------100=

 2017-2018 Microchip Technology Inc. DS20005678B-page 17

CAN FD Controller Module

Equation 3-8: Data Sample Point (%)

3.4.2 PROPAGATION DELAY

Figure 3-3 illustrates the propagation delay between two CAN Nodes on the bus, assuming Node

A is transmitting a CAN message. The transmitted bit will propagate from the transmitting CAN

Node A, through the transmitting CAN transceiver, over the CAN bus, through the receiving CAN

transceiver, into the receiving CAN Node B.

During the arbitration phase of a CAN message, the transmitter samples the CAN bus and

checks if the transmitted bit matches the received bit. The transmitting node has to place the

sample point after the maximum propagation delay.

Equation 3-9 describes the maximum propagation delay; where tTXD-RXD is the propagation

delay of the transceiver, maximum 255 ns according to ISO 11898-1:2015; TBUS is the delay on

the CAN bus, approximately 5 ns/m. The factor two comes from the worst case, when Node B

starts transmitting exactly when the bit from Node A arrives.

Equation 3-9: Max. Prop. Delay

Figure 3-3: Propagation Delay

DSP 1DTSEG1+

DBT

DTQ

------------

--------------------------------- 100=

TPROP 2t

TXD RXD–TBUS

+=

TPROP TPROPAB TPROPBA

+2tTXD RXD–TBUS

+==

Node A

TXCAN

RXCAN

CANH

CANL

Node B

RXCAN

TXCAN

CANH

CANL

Delay: Node A to B (TPROPAB)

CAN bus (T

BUS

)

Transceiver Propagation

Delay (t

TXD-RXD

)

Delay: Node B to A (T

PROPBA

)

Transceiver Propagation

Delay (t

TXD-RXD

)

MCP25xxFD Family Reference Manual

DS20005678B-page 18  2017-2018 Microchip Technology Inc.

3.4.3 TRANSMITTER DELAY COMPENSATION (TDC)

During the data phase of a CAN FD transmission, only one node is transmitting; all others are

receiving. Therefore, the propagation delay does not limit the maximum data rate.

When transmitting via pin TXCAN, the CAN FD Controller Module receives the transmitted data

from its local CAN transceiver via pin RXCAN. The received data is delayed by the CAN

transceiver’s loop delay. In case this delay is greater than 1+DTSEG1, a bit error would be

detected.

In order to enable a data phase bit time that is shorter than the transceiver loop delay, the

Transmitter Delay Compensation (TDC) is implemented. Instead of sampling after DTSEG1, a

Secondary Sample Point (SSP) is calculated and used for sampling during the data phase of a

CAN FD message.

Figure 3-4 illustrates how the transceiver loop delay is measured and Equation 3-10 shows how

the SSP is calculated.

Equation 3-10: Secondary Sample Point

Figure 3-4: Measurement of Transceiver Delay (TDCV)

3.4.4 SYNCHRONIZATION

To compensate for phase shifts between the oscillator frequencies of the nodes on the CAN bus,

each CAN controller must be able to synchronize to the relevant edge of the incoming signal.

The CAN controller expects an edge in the received signal to occur within the SYNC segment.

Only recessive-to-dominant edges are used for synchronization.

There are two mechanisms used for synchronization:

•Hard synchronization - forces the edge that has occurred to lie within the SYNC segment.

The bit time counter is restarted with SYNC.

•Resynchronization - if the edge falls outside the SYNC segment, PHSEG1 or PHSEG2

will be adjusted.

SSP TDCV TDCO+=

TXCAN

FDF res BRS ESI DLC

Arbitration Phase Data Phase

RXCAN Arbitration Phase Data Phase

Transmitter Delay

Start Stop

Transmitter Delay

Measurement

TDCO

Secondary Sample Point (SSP)

FDF

 2017-2018 Microchip Technology Inc. DS20005678B-page 19

CAN FD Controller Module

For a more detailed description of the CAN synchronization, please refer to ISO 11898-1:2015.

3.4.5 SYNCHRONIZATION JUMP WIDTH

The Synchronization Jump Width (SJW) is the maximum amount PHSEG1 and PHSEG2 can be

adjusted during resynchronization. SJW is programmable, see Tabl e 3-1 and Table 3-2.

3.4.6 OSCILLATOR TOLERANCE

The oscillator tolerance, df, around the nominal frequency of the oscillator, fnom, is defined in

Equation 3-11.

Equation 3-12 through Equation 3-16 describe the conditions for the maximum tolerance of the

oscillator.

Equation 3-11: Oscillator Tolerance

Equation 3-12: Condition 1

Equation 3-13: Condition 2

Equation 3-14: Condition 3

Equation 3-15: Condition 4

Equation 3-16: Condition 5

1df–fnomFSYSCLK 1df+fnom

df NSJW

210NBT

NTQ

------------



----------------------------------



df min NPHSEG1 NPHSEG2,

213

NBT

NTQ

------------

NPHSEG2–







-------------------------------------------------------------------------



df DSJW

210DBT

DTQ

------------



----------------------------------



df min NPHSEG1 NPHSEG2,

DBT

DTQ

------------

DPHSEG2–





DBRP

NBRP

----------------7NBT

NTQ

------------

+







--------------------------------------------------------------------------------------------------------------------------------



DSJW max 0 NBRP

DBRP

----------------1–









–

NBT

NTQ

------------

HNSEGP2





NBRP

DBRP

----------------DPHSEG2 4 DBT

DTQ

------------

++







-------------------------------------------------------------------------------------------------------------------------------------------------------------------



MCP25xxFD Family Reference Manual

DS20005678B-page 20  2017-2018 Microchip Technology Inc.

3.4.7 RECOMMENDATIONS FOR BIT TIME CONFIGURATION

The following recommendations should be considered when configuring the bit time:

• Select the highest available CAN clock frequency

- Short TQ lead to high resolution for selecting the sample point.

- Use 20 or 40 MHz for SYSCLK.

• Select the lowest NBRP and DBRP

- Low BRP lead to short TQ.

- NSYNC and DSYNC will be short and reduce the quantization error.

- The receiving node can synchronize more accurately to the transmitting node.

• Set NBRP equal to DBRP

- Identical TQ in both phases prevent quantization errors during bit rate switching.

• Use the same Nominal Sample Point (NSP) in all nodes on the CAN FD network

Use the same Data Sample Point (DSP) in all nodes on the CAN FD network

- Different sample points in the different nodes lead to different length of the BRS and

CRC delimiter bits and introduce phase errors when switching the bit rate.

- NSP doesn’t have to be equal to DSP.

- The SSP can be different in different CAN FD nodes.

• Select the largest possible NSJW and DSJW

- Maximizes the oscillator tolerance.

- Allows the receiving nodes to quickly resynchronize to the transmitting nodes.

• Enable automatic TDC for DBR of 1Mbps and higher

- Automatic TDC measurement compensations for transmitter delay variations.

3.4.8 BIT TIME CONFIGURATION EXAMPLE

The following example illustrates the configuration of the CAN FD bit time registers, assuming a

CAN FD network in an automobile with the following parameters:

• 500 kbps NBR; sample point at 80%.

• 2 Mbps DBR; sample point at 80%.

• 40m minimum bus length

Table 3-3 and Ta ble 3 - 4 illustrate how the bit time parameters are calculated. Since the

parameters depend on multiple constraints and equations, and are calculated using an iterative

process, it is recommended to enter the equations into a spread sheet.

Table 3-5 translates the calculated values into register values. It is recommended to let the CAN

FD Controller Module measure the Transmitter Delay Compensation Value (TDCV). This is

accomplished by setting CiTDC.TDCMOD = 10 (automatic mode). In order to set the SSP to

80%, TDCO is set to (DBRP*DTSEG1).

 2017-2018 Microchip Technology Inc. DS20005678B-page 21

CAN FD Controller Module

Table 3-3: Step-by-Step Nominal Bit Rate Configuration

Table 3-4: Step-by-Step Data Bit Rate Configuration

Table 3-5: Bit Time Register Initialization (500k/2M)

Parameter Constraint Val. Unit Equations and Comments

NBT NBT ≥ 1 µs 2 µs Equation 3-1.

FSYSCLK FSYSCLK ≤ 40 MHz 40 MHz Select crystal or resonator frequency, usually 40 or

20 MHz.

NBRP 1 to 256 1 Select smallest possible BRP value to maximize

resolution.

NTQ NBT, FSYSCLK 25 ns Equation 3-3.

NBT/NTQ 4 to 385 80 Equation 3-5.

NSYNC Fixed 1 NTQ Defined in ISO 11898-1:2015.

NPRSEG NPRSEG > TPROP 47 NTQ Equation 3-9: TPROP = 910 ns,

minimum NPRSEG = TPROP/NTQ = 36.4 NTQ.

Selecting 47 will allow up to 60m bus length.

NTSEG1 2 to 256 NTQ 63 NTQ Equation 3-7. Select NTSEG1 to achieve 80% NSP.

NTSEG2 1 to 128 NTQ 16 NTQ There are 16 NTQ left to reach NBT/NTQ = 80.

NSJW 1 to 128 NTQ;

SJW ≤ min(NPHSEG1, NPHSEG2)

16 NTQ Maximizing NSJW lessens the requirement for the

oscillator tolerance.

Parameter Constraint Val. Unit Equations and Comments

DBT DBT ≥ 125 ns 500 ns Equation 3-2.

DBRP 1 to 256 1 Selecting the same prescaler as for NBT makes

sure that the TQ resolution doesn’t change during

the bit rate switching.

DTQ DBT, FSYSCLK 25 ns Equation 3-4.

DBT/DTQ 3 to 49 20 Equation 3-6.

DSYNC Fixed 1 DTQ Defined in ISO 11898-1:2015.

DTSEG1 1 to 32 DTQ 15 DTQ Equation 3-7. Select DTSEG1 to achieve 80% DSP.

DTSEG2 1 to 16 DTQ 4 DTQ There are 4 DTQ left to reach DBT/DTQ = 20.

DSJW 1 to 16 DTQ;

SJW ≤ min(DPHSEG1, DPHSEG2)

4 DTQ Maximizing DSJW lessens the requirement for the

oscillator tolerance.

Oscillator Tolerance

Condition 1-5

Minimum of Condition 1-5 0.78 % Equation 3-11 through Equation 3-16.

CiNBTCFG Value CiDBTCFG Value CiTDC Value

BRP 0 BRP 0 TDCMOD 2

TSEG1 62 TSEG1 14 TDCO 15

TSEG2 15 TSEG2 3 TDCV 0

SJW 15 SJW 3

MCP25xxFD Family Reference Manual

DS20005678B-page 22  2017-2018 Microchip Technology Inc.

3.5 Message Memory Configuration

The message objects of the Transmit Event FIFO, Transmit Queue and Transmit/Receive FIFOs

are located in RAM; see Figure 3-5. The application must configure the number of message

objects inside a FIFO between one message object and 32 message objects. Additionally, the

application must configure the payload size of the message objects inside each FIFO. This

configuration determines where message objects are located in RAM. The RAM allocation can

only be configured in Configuration mode.

In order to optimize RAM usage, the application should start configuring the RAM with the TEF,

followed by the TXQ, and continue with FIFO 1, FIFO 2, FIFO 3 and so on. In case a user

application requires TEF, TXQ, and 16 additional FIFOs, it should configure TEF, TXQ, followed

by FIFO 1 through FIFO 16. It is not necessary to configure the unused FIFOs 17 through 31.

Figure 3-5: Message Memory Organization

3.5.1 TRANSMIT EVENT FIFO CONFIGURATION

In order to reserve space in RAM for the TEF, CiCON.STEF has to be set. The number of

message objects inside the TEF is configured using CiTEFCON.FSIZE. Transmitted messages

can be timestamped by setting CiTEFCON.TEFTSEN.

3.5.2 TRANSMIT QUEUE CONFIGURATION

In order to reserve space in RAM for the TXQ, CiCON.TXQEN has to be set. The number of

message objects inside the TXQ is configured using CiTXQCON.FSIZE. All objects inside the

TXQ use the same payload size (number of data bytes), which is configured using

CiTXQCON.PLSIZE.

3.5.3 TRANSMIT FIFO CONFIGURATION

FIFO 1 through FIFO 31 can be configured as Transmit FIFOs by setting TXEN in the

CiFIFOCONm register. The number of message objects inside each Transmit FIFO is configured

using CiFIFOCONm.FSIZE. All objects inside one Transmit FIFO use the same payload size

(number of data bytes), which is determined by CiFIFOCONm.PLSIZE.

3.5.4 RECEIVE FIFO CONFIGURATION

FIFO 1 through FIFO 31 can be configured as Receive FIFOs by clearing TXEN in the

CiFIFOCONm register. The number of message objects inside each Receive FIFO is configured

using CiFIFOCONm.FSIZE. All objects inside one Receive FIFO use the same payload size

(number of data bytes), which is determined by CiFIFOCONm.PLSIZE. Received messages can

be timestamped by setting CiFIFOCONm.RXTSEN.

TEF

TX Queue

FIFO 1

FIFO 3

FIFO 2: Message Object 0

FIFO 2: Message Object 1

FIFO 2: Message Object n

FIFO 31

 2017-2018 Microchip Technology Inc. DS20005678B-page 23

CAN FD Controller Module

3.5.5 CALCULATION OF REQUIRED MESSAGE MEMORY

The size of required RAM depends on the configuration of each individual FIFO. Equation 3-17

through Equation 3-19 specify the sizes of the TEF, TXQ and the FIFOs in bytes. If the TEF or

TXQ is not used, their size is zero.

Since the size of the integrated RAM is limited, the user must check that the memory

configuration fits into RAM. The MCP25xxFD will not check that the configuration fits. Equation 3-

20 can be used to calculate the total RAM usage in bytes.

The size of the TEF objects depend on the enabling of timestamping. If TEFTSEN is set, then

tefts = 4, else tefts = 0.

The PayLoad(i) is defined in data bytes.

The size of a message object of a RX FIFO varies dependent on the enabling of timestamping.

If RXTSEN = 1 and TXEN = 0 for FIFO(i), then rxts(i) = 4, else rxts(i) = 0.

N is defined as the number of FIFOs used in addition to the TEF and the TXQ.

Equation 3-17: Size of TEF

Equation 3-18: Size of TXQ

Equation 3-19: Size of FIFOs

Equation 3-20: Total RAM Usage

STEF NElements TEFtefts 8+=

STXQ NElements TXQ8 PayLoad TXQ+=

SFIFO i NElements i rxts i 8 PayLoad i++=

SRAM STEF STXQ SFIFO i

i1=









MCP25xxFD Family Reference Manual

DS20005678B-page 24  2017-2018 Microchip Technology Inc.

3.6 Configuration Code Example

Example 3-1 shows a code example of how to configure the MCP25xxFD:

• Reset the MCP25xxFD

• Configure the Oscillator and CLKO pin

• Configure the I/O pins

• Configure the CAN Control register

• Configure the Bit Time registers

• Configure the TEF, TXQ, TX and RX FIFOs

Example 3-1: Basic Configuration

 2017-2018 Microchip Technology Inc. DS20005678B-page 25

CAN FD Controller Module

Now the device is ready to transition to Normal mode. Example 3-2 shows a code example of

how to enable ECC, initialize RAM, and select Normal mode.

Always calculate the actual RAM usage and make sure it fits into RAM.

Example 3-2: Initialize RAM, Select Normal Mode

MCP25xxFD Family Reference Manual

DS20005678B-page 26  2017-2018 Microchip Technology Inc.

4.0 MESSAGE TRANSMISSION

The application has to configure the FIFO or TXQ before it can be used for transmission,

see Section 3.5.3 “Transmit FIFO Configuration” and Section 3.5.2 “Transmit Queue

Configuration”.

4.1 Transmit Message Object

Table 4-1 specifies the Transmit Message Object used by the TXQ and the Transmit FIFOs. The

transmit objects contain the message ID, Control bits, and the payload:

•SID: Standard ID or Base ID.

•EID: ID Extension.

•DLC: Data Length Code; specifies the number of data bytes to transmit, see Section 1.4.2

“DLC Encoding”.

•IDE: ID extension selection; clearing this bit will transmit a Base frame, setting this bit will

transmit an Extended frame.

•RTR: Remote Transmit Request; this bit is only specified in CAN 2.0 frames. Setting this bit

will request a transmission of a receiving node.

•FDF: FD Format selection; if this bit is set, a CAN FD frame will be transmitted, otherwise,

a CAN 2.0 frame. If Normal CAN 2.0 mode is selected, this bit is ignored and only CAN 2.0

frames are transmitted.

•BRS: Bit Rate Switch; the data phase of a CAN FD frame will be transmitted using DBR if

this bit is set. If the bit is clear, the whole frame will be transmitted using NBR.

•ESI: Error State Indicator; normally, the ESI bit reflects the error status of the transmitting

node. A recessive ESI bit inside a CAN FD frame indicates that the transmitting node is

error passive, a dominant bit shows that the transmitting node is error active. If

CiCON.ESIGM=0, this bit inside the object is ignored. If CiCON.ESIGM=1, the ESI bit

inside the transmitted message will be transmitted recessive, if the CAN FD Controller

Module is error passive, or if the ESI bit in the message object is set. A Gateway

application would use it to signal that the ESI bit of the transmitting node was set.

•SEQ: Sequence number; SEQ is not transmitted on the CAN bus. It is used to keep track of

transmitted messages. SEQ is stored in the TEF message object.

•Transmit Buffer Data: Contains the payload of the message. Only the number of data

bytes specified by the DLC are transmitted. Byte 0 is transmitted first, followed by 1, 2, and

so on.

4.2 Loading Messages into a Transmit FIFO

Before loading a message into the FIFO, the application must verify that the FIFO is not full.

There is room in the FIFO if CiFIFOSTAm.TFNRFNIF is set. Loading a message into a full FIFO

can corrupt a message that is being transmitted.

The FIFO User Address points to the address in RAM of the next Transmit Message Object,

where the application should store the message. The actual address in RAM is calculated using

Equation 4-1. T0 of the Transmit Message Object is loaded first, followed by T1, T2 and so on.

The maximum number of data bytes is limited by the configured payload. Only the number of data

bytes specified by the DLC have to be loaded.

Equation 4-1: Address of next Message Object

After the message object was loaded into RAM, the FIFO needs to be incremented by setting

CiFIFOCONm.UINC. This will cause the CAN FD Controller Module to increment the Head of the

FIFO, and update CiFIFOUAm.

Now the message is ready for transmission, and the next message can be loaded at the new

address.

A 0x400 CiFIFOUAm+=

 2017-2018 Microchip Technology Inc. DS20005678B-page 27

CAN FD Controller Module

4.3 Loading Messages into the Transmit Queue

Loading Transmit Message Objects into the TXQ works the same ways as loading message

objects into a Transmit FIFO. The application must check CiTXQSTA if there is room in the TXQ,

use CiTXQUA instead of CiFIFOUAm to calculate the address to load the message, and set

CiTXQCON.UINC to increment the Head of the TXQ.

TABLE 4-1: TRANSMIT MESSAGE OBJECT (TXQ AND TX FIFO)

Word Bit

31/2315/7

Bit

30/22/14/6

Bit

29/21/13/5

Bit

28/20/12/4

Bit

27/19/11/3

Bit

26/18/10/2

Bit

25/17/9/1

Bit

24/16/8/0

T0 31:24 -— -— SID11 EID<17:6>

23:16 EID<12:5>

15:8 EID<4:0> SID<10:8>

7:0 SID<7:0>

T1 31:24 SEQ<22:15>

23:16 SEQ<14:7>

15:8 SEQ<6:0> ESI

7:0 FDF BRS RTR IDE DLC<3:0>

T2 (1) 31:24 Transmit Data Byte 3

23:16 Transmit Data Byte 2

15:8 Transmit Data Byte 1

7:0 Transmit Data Byte 0

T3 31:24 Transmit Data Byte 7

23:16 Transmit Data Byte 6

15:8 Transmit Data Byte 5

7:0 Transmit Data Byte 4

Ti 31:24 Transmit Data Byte n

23:16 Transmit Data Byte n-1

15:8 Transmit Data Byte n-2

7:0 Transmit Data Byte n-3

bit T0.31-30 Unimplemented: Read as ‘x’

bit T0.29 SID11: In FD mode the standard ID can be extended to 12 bit using r1

bit T0.28-11 EID<17:0>: Extended Identifier

bit T0.10-0 SID<10:0>: Standard Identifier

bit T1.31-9 SEQ<22:0>: Sequence to keep track of transmitted messages in Transmit Event FIFO (2)

bit T1.8 ESI: Error Status Indicator

In CAN to CAN gateway mode (CiCON.ESIGM=1), the transmitted ESI flag is a “logical OR” of T1.ESI

and error passive state of the CAN controller;

In normal mode ESI indicates the error status

1 = Transmitting node is error passive

0 = Transmitting node is error active

bit T1.7 FDF: FD Frame; distinguishes between CAN and CAN FD formats

bit T1.6 BRS: Bit Rate Switch; selects if data bit rate is switched

bit T1.5 RTR: Remote Transmission Request; not used in CAN FD

bit T1.4 IDE: Identifier Extension Flag; distinguishes between base and extended format

bit T1.3-0 DLC<3:0>: Data Length Code

Note 1: Data Bytes 0-n: payload size is configured individually in control register (CiFIFOCONm.PLSIZE<2:0>).

2: SEQ<22:7> are NOT implemented in the MCP2517FD.

MCP25xxFD Family Reference Manual

DS20005678B-page 28  2017-2018 Microchip Technology Inc.

4.4 Requesting Transmission of a Message in a Transmit FIFO

After a message was loaded into a Transmit FIFO. The message is ready for transmission. The

application initiates the transmission of all messages inside a FIFO by setting

CiFIFOCONm.TXREQ or by setting the corresponding bit inside the CiTXREQ register. When all

messages have been transmitted, TXREQ will be cleared. The application can request transmis-

sion of multiple FIFOs and the TXQ simultaneously. The FIFO or TXQ with the highest priority

will start transmitting first. Messages inside a FIFO will be transmitted First In First Out.

Messages can be loaded into a FIFO while the FIFO is transmitting messages. Since TXREQ is

cleared by the FIFO automatically after the FIFO empties, UINC and TXREQ of the

CiFIFOCONm register must be set at the same time after appending a message. This makes

sure that all messages inside the FIFO are transmitted, including the appended messages.

4.5 Requesting Transmission of a Message in the Transmit Queue

After a message was loaded into the TXQ. The message is ready for transmission. The applica-

tion initiates the transmission of all messages inside the queue by setting CiTXQCON.TXREQ.

When all messages have been transmitted, TXREQ will be cleared. The application can request

transmission of the TXQ and multiple FIFOs simultaneously. The TXQ or FIFO of the CiTXQCON

will be transmitted based on their ID. The message with the highest priority ID, lowest ID value

will be transmitted first.

Messages can be loaded into the TXQ while the TXQ is transmitting messages. Since TXREQ

is cleared by the TXQ automatically after the TXQ empties, UINC and TXREQ of the CiTXQCON

messages inside the TXQ are transmitted, including the appended messages.

4.6 CiTXREQ Register

The CiTXREQ register contains the TXREQ bits of the TXQ and of all the TX FIFOs. It has the

following two purposes:

• The user application can request transmission of the TXQ, and/or one or more TX FIFOs

using only one SPI instruction, by setting the corresponding bits in the CiTXREQ register.

Clearing a bit does NOT abort any transmissions.

• Reading the CiTXREQ register gives information about which transmit FIFOs have

transmissions pending.

CiTXREQ<0> is mapped to the TXQ, CiTXREQ<1> is mapped to TX FIFO 1, CiTXREQ<2> is

mapped to TX FIFO 2, and so on, CiTXREQ<31> is mapped to TX FIFO 31.

4.7 Transmit Priority

The transmit priority of the FIFOs and TXQ needs to be configured using CiFIFOCONm.TXPRI

and CiTXQCON.TXPRI.

Before transmitting a message, the priorities of the TXQ and the TX FIFOs queued for

transmission are compared. The FIFO/TXQ with the highest priority will be transmitted first. For

example, if transmit FIFO 1 has a higher priority setting than FIFO 3, all messages in FIFO 1 will

be transmitted first. If multiple FIFOs have the same priority, the FIFO with the highest index is

transmitted. For example, if FIFO 1 and FIFO 3 have the same priority setting, all messages in

FIFO 3 will be transmitted first. If the TXQ and one or more FIFOs have the same priority, all

messages in the TXQ will be transmitted first.

The transmit priority will be recalculated after every successful transmission of a single

message.

4.7.1 TRANSMIT PRIORITY OF MESSAGES INSIDE A FIFO

As the name suggests, messages inside a FIFO are transmitted First-In-First-Out.

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CAN FD Controller Module

4.7.2 TRANSMIT PRIORITY OF MESSAGES INSIDE THE TXQ

Messages inside the Transmit Queue are transmitted based on the message ID. The message

with the lowest message ID (highest priority) is transmitted first.

4.7.3 TRANSMIT PRIORITY BASED ON ID

The goal of transmitting CAN messages based on ID is to avoid “Inner Priority Inversion”. If a

low priority message is waiting to get transmitted due to bus traffic (arbitration), a higher priority

message could be prevented from being transmitted. The TXQ helps solving that issue by

reprioritizing the messages inside the queue based on priority (ID).

4.8 Transmit Bandwidth Sharing

The bandwidth sharing feature works as follows:

• After a successful transmission of a message, the module will idle for n arbitration bit times

before it attempts to transmit the next message. It suspends the next transmission.

• After the device has received a message, it can transmit the next message as soon as the

bus is idle.

This allows other nodes on the bus to transmit their messages, even if they are lower priority.

The number of arbitration bit times between transmissions can be configured using

CiCON.TXBWS.

4.9 Retransmission Attempts

The number of retransmission attempts can be configured as follows:

• Retransmission attempts disabled

• Three retransmission attempts

• Unlimited retransmissions

The retransmission attempts can be restricted by setting CiCON.RTXAT. The number of

retransmission attempts can be configured individually for each transmit FIFO and the TXQ

using CiFIFOCONm.TXAT and CiTXQCON.TXAT, respectively.

In case CiCON.RTXAT=0, unlimited retransmission attempts will be used for all transmit FIFOs

and the TXQ, and TXAT will be ignored.

4.9.1 RETRANSMISSION ATTEMPTS DISABLED

TXREQ will be cleared after the attempt to transmit the message. If the message was not

successfully transmitted due to loss of arbitration or due to an error, TXATIF in CiFIFOSTAm or

CiTXQSTA will be set.

4.9.2 THREE RETRANSMISSION ATTEMPTS

In case an error is detected during transmission, the CAN FD Controller Module will decrement

the number of remaining attempts and try to retransmit the message the next time the bus is

idle. In case arbitration is lost, the number of remaining attempts will not change. If all

retransmission attempts are exhausted, TXREQ will be cleared, and TXATIF in CiFIFOSTAm/

CiTXQSTA will be set.

Before retransmitting the message, the transmit priority will be recalculated. The retransmission

attempts will be reinitialized if a different TX FIFO or TXQ is selected for transmission, or if a

message was received after the last transmission attempt.

4.9.3 UNLIMITED RETRANSMISSIONS

TXREQ will only be cleared after all messages inside the TX FIFO or TXQ were successfully

transmitted.

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4.10 Aborting a Transmission

A pending transmission can only be aborted before the transmission of the message starts,

before SOF.

The transmission of a specific FIFO can be aborted by clearing TXREQ in the object control

bits in the CiTXREQ register will be ignored. Bit TXABT in the FIFO control register will be set

after a successful abortion. TXREQ will remain set until the message either aborts or is

successfully transmitted.

Setting CiCON.ABAT will abort all pending messages of all FIFOs. After all TXREQ bits are

cleared, CiCON.ABAT has to be cleared in order to be able to transmit new messages.

Clearing TXREQ for a Transmit FIFO will attempt to abort all transmissions in the FIFO. If a

message is successfully transmitted, the FIFO Index will be updated as normal. If the message

is successfully aborted, the FIFO Index will not change.

The user can then use the internal index, CiFIFOSTAx.FIFOCI, to determine which messages

have already been transmitted. To reset the Transmit FIFO Index and erase all pending

messages the user can set FRESET. The FIFO can then be loaded with new messages to be

transmitted.

4.11 Remote Transmit Request

The CAN bus system has a method for allowing a master node to request data from another

node. The master sends a message with the RTR bit set. The message contains no data, only

an address to trigger a filter match.

Remote frames are only specified for CAN 2.0 frames, they are not supported in CAN FD frames.

The filter that is configured to respond to a remote transmit request will point to a FIFO that is

configured for transmission and RTREN has to be set.

Automatic remote data requests can be handled without MCU intervention. If a FIFO is properly

configured, when a filter matches and points to the FIFO, the FIFO will be queued for

transmission.

The FIFO must be configured as follows:

• Set TXEN to ‘1’.

• A filter must be enabled and loaded with a matching message identifier

• The buffer pointer for that filter must point to the TX FIFO. (Normally a filter points to an RX

FIFO)

• RTREN bit must be set to ‘1’ to enable RTR.

• The FIFO must be preloaded with at least one message to be sent.

When a remote transmit request message is received, and it matches a filter pointing to a

properly configured transmit FIFO, the TXREQ is set, queuing the object for transmission,

according to priorities.

A FIFO will only be transmitted if TXEN and RTREN are set, and if it is NOT empty. When a

request for a remote transmission occurs while the FIFO is empty, the event will be treated as an

overflow and the RXOVIF bit will be set.

4.12 Mismatch of DLC and Payload Size During Transmission

The PLSIZE reserves a certain number of bytes in the transmit FIFO. The CAN FD Controller

Module handles mismatches between DLC and payload size as follows:

• If the DLC is smaller than the reserved payload, the number of data bytes specified by the

DLC will be transmitted.

• If the DLC is bigger than the reserved payload, the module will not transmit the message,

but instead it will set the CiINT.IVMIF and CiBDIAG1.DLCMM flags and clear the TXREQ

flag. The application can use the TEF to determine which message wasn’t transmitted.

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CAN FD Controller Module

4.13 Transmit State Diagram

Figure 4-1 describes how messages are queued for transmission. It illustrates how the most

important transmit flags are set and cleared:

• Messages are queued for transmission by setting the TXREQ flag.

• Next the transmit priority will be determined. The FIFO or TXQ with the highest priority

TXPRI flag will be selected. The index of the TX message inside the FIFO or TXQ will be

calculated.

• Next the TX message is pending for transmission.

• Transmission can only start when the bus is idle.

• A pending transmission can only be aborted before SOF is transmitted.

• During the transmission of a message, the CAN FD Controller Module checks for the

following:

- Loss of arbitration, during the arbitration field.

- Transmit errors.

• In case a message of a TX FIFO or the TXQ was transmitted successfully, the TXREQ will

only be cleared after all messages of the FIFO are transmitted. After the transmission of

any message, the status flags of the FIFO or TXQ are updated. In case CiCON.STEF is

set, the message will be stored into the TEF, and a timestamp will be attached, if enabled.

• In case arbitration is lost, TXLARB of the TX FIFO or TXQ will be set, and the device will

switch over to receiving the message, see Section 7.0 “Message Reception”.

• In case an error is detected, during the transmission of a message, an Error frame will be

transmitted and the appropriate Error Flags will be set. Messages will be retransmitted

according to Section 4.9 “Retransmission Attempts”.

Figure 4-1: Transmit State Diagram

Abort: Set ABAT

Yes

Any TXREQ

IDLE

Calculate

TX Priority

Result: Idx

TX Pending[Idx]

Wait for Suspend

Time

TX In Progress

SOF

Transmit[Idx]

TX ERR

Set TXERRIF flag

TX Attempts--

TX Successful

Set TXIF[Idx]

Clr TXREQ[Idx]

cSTEF==1?

Save Msg to TEF

TX ABORT

Set TXABT[Idx]

ABORT ALL

Clr All TXREQ

Set All TXABT

Lost Arbitration

Set LARB[Idx]

Clr TXREQ[Idx]

Set TXATIF[Idx]

RX Message

cTX Attempts Exhausted?

Re-Init TX

Attempts

Based on new Idx

New TX Idx or

Received a message?

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4.14 Resetting a Transmit FIFO

A FIFO can be reset by:

• Setting CiFIFOCONm.FRESET, or

• Placing the module into Configuration Mode (OPMOD = 100)

Resetting the FIFO will reset the head and tail pointers, and the CiFIFOSTAm register. The

settings in the CiFIFOCONm register will not change.

Before resetting a TX FIFO using FRESET, ensure no transmissions are pending.

4.15 Resetting the Transmit Queue (TXQ)

The Transmit Queue can be reset by:

• Setting CiTXQCON.FRESET, or

• Placing the module into Configuration Mode (OPMOD = 100)

Resetting the TXQ will reset the head and tail pointers, and the CiTXQSTA register. The

settings in the CiTXQCON register will not change.

Before resetting the TXQ using FRESET, ensure no transmissions are pending.

4.16 Message Transmission Code Example

Example 4-1 shows a code example of how to transmit a message using the following steps:

• Check that the FIFO is not full.

• Load the message into the FIFO

• Increment and flush the FIFO. UINC and TXREQ are set at the same time. This makes

sure that all messages from the FIFO are transmitted in case a message is appended to a

FIFO while it is already transmitting.

Example 4-1: Transmit Message from TX FIFO

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CAN FD Controller Module

5.0 TRANSMIT EVENT FIFO

The Transmit Event FIFO (TEF) allows the application to keep track of the order and time the

messages were transmitted. The TEF works similar to a receive FIFO. Instead of storing

received messages, it stores transmitted messages. Messages are only saved if CiCON.STEF

is set. The sequence number (SEQ) of the transmitted message is copied into the TEF Object.

The payload data is not stored. Transmitted messages are timestamped if TEFTSEN is set.

Table 5-1 specifies the TEF Object. The first two words of the TEF Object are a copy of the

Transmit Message Object. Optionally, the TEF Object contains the timestamp when the

message was transmitted.

5.0.1 READING A TEF OBJECT

Before reading a TEF Object, the application must check that the TEF is not empty, by reading

the CiTEFSTA register. The TEF is not empty if TEFNEIF is set.

The TEF User Address points to the address in RAM of the next TEF Object to read. The actual

address in RAM is calculated using Equation 5-1. TE0 of the TEF Object is read first, followed

by TE1, and TE2.

Equation 5-1: Address of next TEF Object

After the TEF Object was read from RAM, the TEF needs to be incremented by setting

CiTEFCON.UINC. This will cause the CAN FD Controller Module to increment the Tail, and

update CiTEFUA.

Now the next message can be read from the TEF.

5.0.2 RESETTING THE TRANSMIT EVENT FIFO (TEF)

TEF can be reset by:

• Setting CiTEFCON.FRESET, or

• Placing the module into Configuration Mode (OPMOD = 100)

Resetting the FIFO will reset the head and tail pointers, and the CiTEFSTA register. The

settings in the CiTEFCON register will not change.

A 0x400 CiTEFUA+=

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TABLE 5-1: TRANSMIT EVENT FIFO OBJECT

Word Bit

31/2315/7

Bit

30/22/14/6

Bit

29/21/13/5

Bit

28/20/12/4

Bit

27/19/11/3

Bit

26/18/10/2

Bit

25/17/9/1

Bit

24/16/8/0

TE0 31:24 -— -— SID11 EID<17:6>

23:16 EID<12:5>

15:8 EID<4:0> SID<10:8>

7:0 SID<7:0>

TE1 31:24 SEQ<22:15>

23:16 SEQ<14:7>

15:8 SEQ<6:0> ESI

7:0 FDF BRS RTR IDE DLC<3:0>

TE2 (1) 31:24 TXMSGTS<31:24>

23:16 TXMSGTS<23:16>

15:8 TXMSGTS<15:8>

7:0 TXMSGTS<7:0>

bit TE0.31-30 Unimplemented: Read as ‘x’

bit TE0.29 SID11: In FD mode the standard ID can be extended to 12 bit using r1

bit TE0.28-11 EID<17:0>: Extended Identifier

bit TE0.10-0 SID<10:0>: Standard Identifier

bit TE1.31-9 SEQ<22:0>: Sequence to keep track of transmitted messages (2)

bit TE1.8 ESI: Error Status Indicator

1 = Transmitting node is error passive

0 = Transmitting node is error active

bit TE1.7 FDF: FD Frame; distinguishes between CAN and CAN FD formats

bit TE1.6 BRS: Bit Rate Switch; selects if data bit rate is switched

bit TE1.5 RTR: Remote Transmission Request; not used in CAN FD

bit TE1.4 IDE: Identifier Extension Flag; distinguishes between base and extended format

bit TE1.3-0 DLC<3:0>: Data Length Code

bit TE2.31-0 TXMSGTS<31:0>: Transmit Message Timestamp

Note 1: TE2 (TXMSGTS) only exits in objects where CiTEFCON.TEFTSEN is set.

2: SEQ<22:7> are NOT implemented in the MCP2517FD.

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CAN FD Controller Module

5.1 TEF Code Example

Example 5-1 shows a code example of how to read a message from the TEF:

• Check that the TEF is not empty.

• Read the message from the TEF.

• Increment the TEF by setting UINC.

• Process the TEF message.

Example 5-1: Reading a Message from the TEF

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6.0 MESSAGE FILTERING

All messages on a CAN network will be received by all nodes. In order to process only messages

of interest, a hardware filtering mechanism is implemented. The CAN FD Controller Module can

be configured to receive only messages of interest. The module contains 32 acceptance filters.

Each acceptance filter contains a Filter Object and Mask Object. The user application configures

the specific filter to receive a message with a given identifier by setting the Filter Object and Mask

Object to match the identifier of the message to be received.

6.1 Filter Configuration

The filters are controlled by the CiFLTCONm registers. The filter must be disabled by clearing

the FLTEN bit, before changing the Filter or Mask Object. The module doesn’t have to be in

Configuration mode. After the Filter Object is updated, the Buffer Pointer, FnBP, has to be

initialized, and the filter can be enabled by setting the FLTEN bit. The Buffer Pointer points to

the FIFO where the matching receive message will be stored.

6.2 Filtering a Received Message

The CAN FD Controller Module starts acceptance filtering after the arbitration field and the first

3 data bytes of a message were received. Figure 6-1 describes the flow of message filtering.

The module loops through all the filters, starting with filter 0, which is the highest priority filter.

The message in the Receive Message Assembly Buffer (RXMAB) is compared to the filter and

mask. In case the message matches the filter, and it was received without any errors, the

message will be stored to the RX FIFO pointed to by the FnBP. Acceptance filtering is stopped,

and the associated RFIF is set.

In case a Remote Transmit Request (RTR) was received, the TXREQ bit of the TX FIFO

pointed to by FnBP will be set.

Filtering will continue with the next filter, and RXOVIF will be set, if one of the following happens:

• A filter matches, but the RX FIFO is full.

• When multiple filters match the same message, and all matching RX FIFOs are full, only

the RXOVIF of the FIFO pointed to by the highest priority filter will be set.

• The RXOVIF will be set, if the TX FIFO is empty during a RTR (TXEN = 1, RTREN = 1)

If none of the filters match, the received message will be discarded.

Note: If the module receives a message that matches a filter, but the corresponding FIFO is a

TX FIFO (TXEN = 1, RTREN = 0), the module will discard the received message.

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CAN FD Controller Module

Figure 6-1: Message Filtering Flow

6.2.1 FILTERING STANDARD OR EXTENDED FRAMES

Figure 6-2 illustrates the flow of matching a single Filter Object to the received message in the

RXMAB.

The Filter Object can be configured to accept either Standard, Extended or both frames. If MIDE

is clear, both Standard and Extended frames will be accepted.

If the filter should only accept Standard frames, then MIDE must be set, and EXIDE must be

cleared. If the filter should only accept Extended frames, then both MIDE and EXIDE must be

set.

6.2.2 MASK BITS

The Mask Object is used to ignore selected bits of the received identifier. The masked-out bits

(mask bits with value ‘0’) of the RXMAB will not be compared with the bits in the Filter Object.

For example, if the user would like to receive all messages with identifiers 0, 1, 2 and 3, the user

would mask-out the lower two bits of the identifier by clearing the corresponding bits of the Mask

Object.

Match Filter Objec t 0

Match Filter Objec t 1

FIFO Not Full?

Idx = F0BP

Yes and Not RTR

Accept Message:

Receiv e rest of Message

Store in FIFO [Idx]

Yes

FIFO Not Full?

Idx = F1BP

Yes and Not RTR

Yes

Match Filter Object 31

FIFO Not Full?

Idx = F31BP

Yes and Not RTR

Yes

Match Filter Objec t 2-30

Do the same

Discard Message

Done

Yes and RTR

FIFO Not Empty And

TXEN==1 and RTREN==1?

Idx = F0BP

Set TXREQ[Idx]

Yes

Yes and RTR

FIFO Not Empty And

TXEN==1 and RTREN==1?

Idx = F1BP

Yes and RTR

FIFO Not Empty And

TXEN==1 and RTREN==1?

Idx = F31BP

Yes

Arbitration Done and

Required Data Bytes

Received

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Figure 6-2: Filter Match

Start Matching

CiMASKm.MIDE

Set?

Check IDE:

CiFLTOBJm.EXIDE == RXMAB.IDE?

Yes

NO Match

Match

RXMAB.IDE == 0?

Base Format:

CiFLTOBJm.SID == RXMAB.SID,

CiMASKm.MSID[i] = 0 are Don’t

Care

Yes

Extended Form at:

CiFLTOBJm.SID == RXMAB.SID,

CiMASKm.MSID[i] = 0 are Don’t

Care

Yes

NO Match NO MatchNo No

CiFLTOBJm.EID == RXMAB.EID,

CiMASKm.MEID[i] = 0 are Don’t

Care

Yes

NO MatchNo

SID11:

CiTDC.SID11EN and

CiMASKm.MSID11

Check SID11:

CiFLTOBJ.SID11 ==

RXMAB.SID11?

Yes

Data Bytes:

CiCON.DNCNT > 0 ?

Yes NO MatchNo

Calculate number of bits to compare:

N = DNCNT

Calculate index:

M = 18-N

Assemble Receive Data Bytes:

RXDB = {RXMAB.DB0, RXMAB.DB1, RXMAB.DB2<7:6>}

Compare:

CiFLTOBJm.EID<0:N> == RXDB<17:M> ?

CiMASKm.MEID[i] = 0 are Don’t Care

Yes

NO MatchNo

Match

Yes

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CAN FD Controller Module

6.2.3 FILTERING ON DATA BYTES

When the filter is set up for receiving Standard frames, the EID part of the Filter and Mask

Object can be selected to filter on data bytes. DNCNT in the CiCON is used to select how many

bits in the data bytes are compared. Table 6-1 explains how many data bits are compared, and

which filter bits and data bits are compared.

If DNCNT is ‘0’, then data byte filtering is disabled.

If DNCNT is non-zero, the filtering will commence on as many data bits as specified in DNCNT.

A filter hit will require matching of the SID bits and a match of n data bits with the filter’s

EID<0:17> bits. Data Byte 0<7> is always compared to EID<0>, Data Byte 0<6> to EID<1>,

Data Byte 2<6> to EID<17>.

If DNCNT is greater than 18, indicating that the user selected a number of bits greater than the

total number of EID bits, the filter comparison will terminate with the 18th bit of the data.

If DNCNT is greater than 16, and the received message has DLC = 2, indicating a payload of

two data bytes, the filter comparison will terminate with the 16th bit of the data.

If DNCNT is greater than 8, and the received message has DLC = 1, indicating a payload of one

data byte, the filter comparison will terminate with the 8th bit of the data.

If DNCNT is greater than 0, and the received message has DLC = 0, indicating no data payload,

the filter comparison will terminate with the identifier.

6.2.4 12 BIT STANDARD ID

Setting CiTDC.SID11EN allows the use of RRS as bit 12 of the SID (LSB). 12-bit SID mode is

only available for CAN FD Base frames. The filter is extended by SID11 and MSID11. Data

bytes can also be filtered in this mode.

Table 6-1: Data Byte Filter Configuration

DNCNT<4:0> Received Message Data Bits to be

Compared Byte <bits>

EID Bits Used for

Acceptance Filter

00000 No comparison No comparison

00001 Data Byte 0<7> EID<0>

00010 Data Byte 0<7:6> EID<0:1>

00011 Data Byte 0<7:5> EID<0:2>

00100 Data Byte 0<7:4> EID<0:3>

00101 Data Byte 0<7:3> EID<0:4>

00110 Data Byte 0<7:2> EID<0:5>

00111 Data Byte 0<7:1> EID<0:6>

01000 Data Byte 0<7:0> EID<0:7>

01001 Data Byte 0<7:0> and Data Byte 1<7> EID<0:8>

01010 Data Byte 0<7:0> and Data Byte 1<7:6> EID<0:9>

01011 Data Byte 0<7:0> and Data Byte 1<7:5> EID<0:10>

01100 Data Byte 0<7:0> and Data Byte 1<7:4> EID<0:11>

01101 Data Byte 0<7:0> and Data Byte 1<7:3> EID<0:12>

01110 Data Byte 0<7:0> and Data Byte 1<7:2> EID<0:13>

01111 Data Byte 0<7:0> and Data Byte 1<7:1> EID<0:14>

10000 Data Byte 0<7:0> and Data Byte 1<7:0> EID<0:15>

10001 Byte 0<7:0> and Byte 1<7:0> and Byte 2<7> EID<0:16>

10010 to 11111 Byte 0<7:0> and Byte 1<7:0> and Byte 2<7:6> EID<0:17>

MCP25xxFD Family Reference Manual

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Figure 6-3 illustrates how the first 18 data bits of the received message data payload are

compared with the corresponding EID bits of the message acceptance filter (CiFLTOBJm.EID).

The IDE bit of the received message must be ‘0’.

Figure 6-3: CAN Operation with DeviceNet™ Filtering

6.3 Filter Configuration Code Example

Example 6-1 shows a code example of how to configure a filter to match Standard frames with

SID=0x300-0x30F using the following steps:

• Disable the Filter.

• Configure the Filter Object: assign SID, clear EXIDE.

• Configure the Mask Object: assign MSID, set MIDE to filter only Standard frames.

• Link the filter to an RX FIFO and enable the filter.

Example 6-1: Filter Configuration to Match a Standard Frame Range

SID10 SID9

IDENTIFIER

11 Bits

EOF

7 Bits 3 Bits

SID0

Accept/Reject Message

IFS

DATA BYTE 0 DATA BYTE 1 DATA BYTE 2

7654321 0 76543210 76543210

Data Byte 0 Data Byte 1 Data Byte 2MESSAGE SID<10:0>

SID10 SID9 SID0

EID0 EID1 EID7

EID8 EID9 EID15 EID1

EID17

STANDARD MESSAGE DATA FRAME

MESSAGE ACCEPTANCE FILTER

SID<10:0>

MESSAGE ACCEPTANCE FILTER

EID<0:17>

Note: The DeviceNet™ filtering configuration shown for EID bits is DNCNT<4:0> = 10010.

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CAN FD Controller Module

7.0 MESSAGE RECEPTION

The application has to configure the RX FIFO before it can be used for reception, see

Section 3.5.4 “Receive FIFO Configuration”. In addition, the application has to configure and

enable at least one filter, see Section 6.1 “Filter Configuration”.

The CAN FD Controller Module continuously monitors the CAN bus. Messages that match a filter

are stored into the RX FIFO pointed to by the filter, see Section 6.2 “Filtering a Received

Message”. The message data is stored into Receive Message Objects.

7.1 Receive Message Object

Table 7-1 specifies the Receive Message Object used by the RX FIFOs. The receive objects

contain the message ID, Control bits, payload and timestamp:

•SID: Standard ID or Base ID

•EID: ID Extension

•DLC: Data Length Code; specifies the number of data bytes in the frame, see

Section 1.4.2 “DLC Encoding”.

•IDE: ID extension selection; IDE = 0 means a Base frame was received, IDE = 1 means an

Extended frame was received.

•RTR: Remote Transmit Request; this bit is only specified in CAN 2.0 frames. If this bit is

set, the module is requested to respond with a frame transmission.

•FDF: FD Format selection; if this bit is set, a CAN FD frame was received, otherwise, a

CAN 2.0 frame.

•BRS: Bit Rate Switch; the data phase of a CAN FD frame was received using DBR, if this

bit is set. If the bit is clear, the whole frame was received using NBR.

•ESI: Error State Indicator; the ESI bit reflects the error status of the transmitting node. A

recessive ESI bit inside a CAN FD frame indicates that the transmitting node is error

passive, a dominant bit shows that the transmitting node is error active.

•FILHIT: Indicates the number of the filter that matched the received message.

•RXMSGTS: Timestamp of the received message. Timestamping can be enabled for each

RX FIFO individually using CiFIFOCONm.RXTSEN. The Receive Message Object will not

contain RXMSGTS, if timestamping is disabled.

•Receive Buffer Data: contains the payload of the message. The maximum payload is

configured in CiFIFOCONm.PLSIZE.

7.1.1 READING A RECEIVE MESSAGE OBJECT

Before reading a Receive Message Object, the application must check that the RX FIFO is not

empty, by reading the CiFIFOSTAm register. The RX FIFO is not empty if TFNRFNIF is set.

The RX FIFO User Address points to the address in RAM of the next Receive Message Object

to read. The actual address in RAM is calculated using Equation 7-1. R0 of the Receive Message

Object is read first, followed by R1, R2, and so on.

Equation 7-1: Address of next Message Object

After the Receive Message Object was read from RAM, the RX FIFO needs to be incremented

by setting CiFIFOCONm.UINC. This will cause the CAN FD Controller Module to increment the

Tail of the FIFO, and update CiFIFOUAm.

Now the application can read the next message from the RX FIFO.

A 0x400 CiFIFOUAm+=

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TABLE 7-1: RECEIVE MESSAGE OBJECT

Word Bit

31/2315/7

Bit

30/22/14/6

Bit

29/21/13/5

Bit

28/20/12/4

Bit

27/19/11/3

Bit

26/18/10/2

Bit

25/17/9/1

Bit

24/16/8/0

R0 31:24 -— -— SID11 EID<17:6>

23:16 EID<12:5>

15:8 EID<4:0> SID<10:8>

7:0 SID<7:0>

R1 31:24 -— -— -— -— -— -— -— -—

23:16 -— -— -— -— -— -— -— -—

15:8 FILHIT<4:0> -— -— ESI

7:0 FDF BRS RTR IDE DLC<3:0>

R2 (2) 31:24 RXMSGTS<31:24>

23:16 RXMSGTS<23:16>

15:8 RXMSGTS<15:8>

7:0 RXMSGTS<7:0>

R3 (1) 31:24 Receive Data Byte 3

23:16 Receive Data Byte 2

15:8 Receive Data Byte 1

7:0 Receive Data Byte 0

R4 31:24 Receive Data Byte 7

23:16 Receive Data Byte 6

15:8 Receive Data Byte 5

7:0 Receive Data Byte 4

Ri 31:24 Receive Data Byte n

23:16 Receive Data Byte n-1

15:8 Receive Data Byte n-2

7:0 Receive Data Byte n-3

bit R0.31-30 Unimplemented: Read as ‘x’

bit R0.29 SID11: In FD mode the standard ID can be extended to 12 bit using r1

bit R0.28-11 EID<17:0>: Extended Identifier

bit R0.10-0 SID<10:0>: Standard Identifier

bit R1.31-16 Unimplemented: Read as ‘x’

bit R1.15-11 FILTHIT<4:0>: Filter Hit, number of filter that matched

bit R1.10-9 Unimplemented: Read as ‘x’

bit R1.8 ESI: Error Status Indicator

1 = Transmitting node is error passive

0 = Transmitting node is error active

bit R1.7 FDF: FD Frame; distinguishes between CAN and CAN FD formats

bit R1.6 BRS: Bit Rate Switch; indicates if data bit rate was switched

bit R1.5 RTR: Remote Transmission Request; not used in CAN FD

bit R1.4 IDE: Identifier Extension Flag; distinguishes between base and extended format

bit R1.3-0 DLC<3:0>: Data Length Code

bit R2.31-0 RXMSGTS<31:0>: Receive Message Timestamp

Note 1: RXMOBJ: Data Bytes 0-n: payload size is configured individually in the FIFO control register

(CiFIFOCONm.PLSIZE<2:0>).

2: R2 (RXMSGTS) only exits in objects where CiFIFOCONm.RXTSEN is set.

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CAN FD Controller Module

7.2 Receive State Diagram

Figure 7-1 illustrates how messages are received. It illustrates how the most important receive

flags are set and cleared:

• The CAN FD Controller Module remains IDLE until a SOF is detected.

• After a SOF was detected, the module will receive the Arbitration and Control fields.

• Based on the DNCNT and the received DLC, acceptance filtering will start. See Figure 6-1

for more details.

• If none of the filters match, the message will still be received, but it will not be stored.

• If a filter matches, the device checks, if the receive object, the filter points to, is full.

• If the receive object is full, the RXOVIF will be set.

• If the receive object is not full, the rest of the data bytes are received and stored to the

receive object.

• If a complete message was received, the message will be stored, a timestamp will be

attached, and the receive flags will be set: the FIFO status flags will be updated, and the

FIFO head will be incremented.

• In case an error is detected, during the reception of a message, an Error frame will be

transmitted and the appropriate Error Flags will be set.

Figure 7-1: Receive State Diagram

Error

Yes

IDLE

Receive

ARBITRATION

and CTRL field

Transmit Error

Frame

Set Error Flags

Filter Match?

Store Message to

Object

Set FIFO status

flags

Object Full?

Set RXOVIF

DNCNT>0 and DLC>0?

Receive

DATA B YTE 0-3

Receive

remaining

DATA B YTES

And Store them

Receive Rest of

Message

Receive Rest of

Message

MCP25xxFD Family Reference Manual

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7.3 Resetting a RX FIFO

A FIFO can be reset by:

• Setting CiFIFOCONm.FRESET, or

• Placing the module into Configuration Mode (OPMOD = 100)

Resetting the FIFO will reset the head and tail pointers, and the CiFIFOSTAm register. The

settings in the CiFIFOCONm register will not change.

Before resetting a RXFIFO using FRESET, ensure that no enabled filter is pointing to the FIFO.

7.4 Mismatch of DLC and Payload Size During Reception

The PLSIZE reserves a certain number of bytes in the Receive Message Object. The module

handles mismatches between DLC and payload size as follows:

• If the number of bytes specified by the DLC is smaller than the number of bytes specified

by the PLSIZE, the received message bytes will be stored in the message object, without

any padding.

• If the number of bytes specified by the DLC is bigger than the number of bytes specified by

the PLSIZE, the data bytes that fit in the Receive Message Object will be stored. The data

bytes that don’t fit into the Receive Message Object will be discarded. The module makes

sure that the next message object in RAM doesn’t get overwritten. The module will store

the message in the receive object and the RX FIFO status flags will be updated. In addition,

the CiINT.IVMIF and CiBDIAG1.DLCMM flags will be set.

7.5 Message Reception Code Example

Example 7-1 shows a code example of how to receive a message using the following steps:

• Check that the FIFO is not empty.

• Read the message from the FIFO.

• Increment the FIFO by setting UINC.

• Process the received message.

Example 7-1: Receiving a Message

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CAN FD Controller Module

8.0 FIFO BEHAVIOR

This section explains the FIFO behavior based on the configuration used in Section 3.6,

Configuration Code Example. The MCP25xxFD was configured as shown in Table 8-1. TEF, and

TXQ were enabled. FIFO1 was configured as a TX FIFO, and FIFO2 as an RX FIFO. All other

FIFOs were not configured.

The start addresses are calculated based on the number of objects in the FIFO and the payload

size. TEF always starts at address 0x400.

Table 8-1: Example FIFO Configuration

8.1 FIFO Status Flags

FIFO 1 through 31 can be configured as transmit or receive FIFOs. The same status flags in

CiFIFOSTAm are used for transmit and receive. The status flags behave differently based on the

selected configuration.

8.1.1 TX FIFO STATUS FLAGS

There are three transmit status flags:

•TFEIF (TFERFFIF): Transmit FIFO Empty IF; set when the FIFO is empty.

• TFHIF (TFHRFHIF): Transmit FIFO Half Empty IF; set when FIFO is less than half full.

• TFNIF (TFNRFNIF): Transmit FIFO Not Full IF; set when FIFO is not full.

The status flags of a transmit FIFO are set, when there is room to load a new message object

into the FIFO. Before the first message object is loaded (after the FIFO was reset), all status flags

are set. When the FIFO is fully loaded, all flags are clear.

8.1.2 RX FIFO STATUS FLAGS

There are three receive status flags:

• RFFIF (TFERFFIF): Receive FIFO Full IF; set when the FIFO is full.

•RFHIF (TFHRFHIF): Receive FIFO Half Full IF; set when the FIFO is at least half full.

•RFNIF (TFNRFNIF): Receive FIFO Not Empty IF; set when there is at least one message

in the FIFO.

The status flags of the receive FIFO are set, when there are received messages in the FIFO.

Before the first message is received (after the FIFO was reset), all status flags are clear. When

the FIFO is full, all flags are set.

FIFO Objects

in FIFO

Payload

per Object Timestamp Bytes in

Object

Bytes in

FIFO Start Address

TEF 12 N/A Yes 12 144 0x400

TXQ 8 32 N/A 40 320 0x490

FIFO1 5 64 N/A 72 360 0x5D0

FIFO2 16 64 Yes 76 1216 0x738

FIFO3 N/A 0xBF8

MCP25xxFD Family Reference Manual

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8.1.3 TXQ STATUS FLAGS

There are two TXQ status flags:

• TXQEIF: TXQ Empty IF; set when the TXQ is empty.

• TXQNIF: TXQ Not Full IF; set when TXQ is not full.

The status flags of the TXQ are set, when there is room to load a new message object into the

TXQ. Before the first message object is loaded (after the TXQ was reset), all status flags are set.

When the TXQ is fully loaded, all flags are clear.

8.1.4 TEF STATUS FLAGS

There are four TEF status flags:

• TEFFIF: TEF Full IF; set when the TEF is full.

• TEFHIF: TEF Half Full IF; set when the TEF is at least half full.

• TEFNEIF: TEF Not Empty IF; set when there is at least one message in the TEF.

The status flags of the TEF are set, when there are transmitted messages in the FIFO. Before

the first message is stored (after the TEF was reset), all status flags are clear. When the TEF is

full, all flags are set.

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CAN FD Controller Module

8.2 Transmit FIFO Behavior

FIFO 1 is configured as a TX FIFO. C1FIFOCON1 is used to control the FIFO. C1FIFOSTA1

contains the status flags, and the FIFO index (FIFOCI). C1FIFOUA1 contains the user address

of the next transmit message object to be loaded.

Remember that the actual RAM address is calculated using Equation 4-1.

Figure 8-1 through Figure 8-6 illustrate how the status flags, user address, and FIFO index are

updated.

Figure 8-1 shows the status of FIFO 1 after reset. Message Objects MO0 to MO4 are empty. All

status flags are set. The user address and the FIFO index point to MO0.

Figure 8-1: FIFO 1 - Initial State

Figure 8-2 illustrates the status of FIFO 1 after the first message (MSG0) was loaded. MO0

contains now MSG0. The user application sets C1FIFOCON1.UINC, which causes the FIFO

head to advance. The user address points now to MO1. TFEIF is cleared, since the FIFO is no

longer empty. The user application now sets TXREQ to request the transmission of MSG0.

Figure 8-2: FIFO 1 - First Message Loaded

Figure 8-3 illustrates the status of FIFO 1 after MSG0 was transmitted. The FIFO is empty again.

TFEIF is set, and TXREQ is cleared. FIFOCI now points to MO1 with user address 0x218.

Figure 8-3: FIFO 1 - First Message Transmitted

MO0

MO1

MO2

MO3

MO4

C1FIFOUA1 = 0x1D0

C1FIFOSTA1:

FIFOCI = 0

TFEIF = 1

TFHIF = 1

TFNIF = 1

C1FIFOCON1:

TXREQ = 0

MO0 / MSG0

MO1

MO2

MO3

MO4

C1FIFOUA1 = 0x218

C1FIFOSTA1:

FIFOCI = 0

TFEIF = 0

TFHIF = 1

TFNIF = 1

C1FIFOCON1:

TXREQ = 1

MO1

MO2

MO3

MO4

C1FIFOUA1 = 0x218

C1FIFOSTA1:

FIFOCI = 1

TFEIF = 1

TFHIF = 1

TFNIF = 1

C1FIFOCON1:

TXREQ = 0

MO0

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Figure 8-4 illustrates the status of FIFO 1 after three more messages were loaded: MSG1-MSG3.

The user address points now to MO4. TFHIF was cleared, because the FIFO is now less than

half empty.

Figure 8-4: FIFO 1 - Three More Messages Loaded

Figure 8-5 illustrates the status of FIFO 1 after two more messages were loaded: MSG4-MSG5.

C1FIFOUA1 points now to MO1. All status flags are now cleared, because the FIFO is full. The

user address and the FIFO index point now to MO1. The user application now sets TXREQ to

request the transmission of MSG1-MSG5.

Figure 8-5: FIFO 1 - FIFO Fully Loaded

Figure 8-6 illustrates the status of FIFO 1 after MSG1-MSG5 were transmitted. The FIFO is

empty again. all status flags are set, and TXREQ is cleared. The user address and the FIFO

index point to MO1 again.

Figure 8-6: FIFO 1 - FIFO Fully Transmitted

MO1 / MSG1

MO2 /MSG2

MO3 / MSG3

MO4

C1FIFOUA1 = 0x2F0

C1FIFOSTA1:

FIFOCI = 1

TFEIF = 0

TFHIF = 0

TFNIF = 1

C1FIFOCON1:

TXREQ = 0

MO0

MO1 / MSG1

MO2 / MSG2

MO3 / MSG3

MO4 / MSG4

C1FIFOUA1 = 0x218

C1FIFOSTA1:

FIFOCI = 1

TFEIF = 0

TFHIF = 0

TFNIF = 0

C1FIFOCON1:

TXREQ = 1

MO0 / MSG5

MO1

MO2

MO3

MO4

C1FIFOUA1 = 0x218

C1FIFOSTA1:

FIFOCI = 1

TFEIF = 1

TFHIF = 1

TFNIF = 1

C1FIFOCON1:

TXREQ = 0

MO0

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CAN FD Controller Module

8.3 Receive FIFO Behavior

FIFO 2 is configured as a RX FIFO. C1FIFOCON2 is used to control the FIFO. C1FIFOSTA2

contains the status flags, and the FIFO index (FIFOCI). C1FIFOUA2 contains the user address

of the next message object to read.

Remember that the actual RAM address is calculated using Equation 7-1.

Figure 8-7 through Figure 8-14 illustrate how the status flags, user address, and FIFO index are

updated.

Figure 8-7 shows the status of FIFO 2 after reset. Message Objects MO0 to MO15 are empty. All

status flags are clear. The user address and the FIFO index point to MO0.

Figure 8-7: FIFO 2 - Initial State

Figure 8-8 illustrates the status of FIFO 2 after the first message (MSG0) was received. MO0

contains now MSG0. The FIFO index points now to MO1. RFNIF is set, since the FIFO is not

empty anymore.

Figure 8-8: FIFO 2 - First Message Received

Figure 8-9 illustrates the status of FIFO 2 after MSG0 was read. The user application reads the

message from RAM and sets C1FIFOCON2.UINC. The user address increments and points to

MO1. The FIFO index is unchanged. The FIFO is empty again. All flags are clear.

Figure 8-9: FIFO 2 - First Message Read

MO0

MO1

MO2

MO15

C1FIFOUA2 = 0x338

C1FIFOSTA2:

FIFOCI = 0

RFFIF = 0

RFHIF = 0

RFNIF = 0

RXOVIF = 0

MO0 / MSG0

MO1

MO2

MO15

C1FIFOUA2 = 0x338

C1FIFOSTA2:

FIFOCI = 1

RFFIF = 0

RFHIF = 0

RFNIF = 1

RXOVIF = 0

MO1

MO2

MO15

C1FIFOUA2 = 0x384

C1FIFOSTA2:

FIFOCI = 1

RFFIF = 0

RFHIF = 0

RFNIF = 0

RXOVIF = 0

MO0

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Figure 8-10 illustrates the status of FIFO 2 after eight more messages were received: MSG1-

MSG8. The user address still points to MO1. RFNIF and RFHIF are set, because the FIFO is now

half full. The FIFO index points to MO9.

Figure 8-10: FIFO 2 - Half Full

Figure 8-11 illustrates the status of FIFO 2 after seven more messages were received: MSG5-

MSG15. The user address still points to MO1. The FIFO index points to MO0. RFNIF and RFHIF

are set.

Figure 8-11: FIFO 2 - FIFO Almost Full

Figure 8-12 illustrates the status of FIFO 2 after one more message was received: MSG16. All

status flags are set, because the FIFO is full. The user address and the FIFO index point to MO1.

Figure 8-12: FIFO 2 - FIFO Full

MO1 / MSG1

MO2 / MSG2

MO9

C1FIFOUA2 = 0x384

C1FIFOSTA2:

FIFOCI = 9

RFFIF = 0

RFHIF = 1

RFNIF = 1

RXOVIF = 0

MO0

MO8 / MSG8

MO15

MO10

MO1 / MSG1

MO2 / MSG2

C1FIFOUA2 = 0x384

C1FIFOSTA2:

FIFOCI = 0

RFFIF = 0

RFHIF = 1

RFNIF = 1

RXOVIF = 0

MO0

MO15 / MSG15

MO1 / MSG1

MO2 / MSG2

C1FIFOUA2 = 0x384

C1FIFOSTA2:

FIFOCI = 1

RFFIF = 1

RFHIF = 1

RFNIF = 1

RXOVIF = 0

MO0 / MSG16

MO15 / MSG15

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CAN FD Controller Module

Figure 8-13 illustrates the status of FIFO 2 after one more message was received. Since FIFO 2

was already full, an overflow occurred. The message is discarded, and RXOVIF is set. The user

address and FIFO index didn’t change.

Figure 8-13: FIFO 2 - FIFO Overflow

Figure 8-14 illustrates the status of FIFO 2 after the application cleared RXOVIF and read two

more messages. RFFIF is clear, because the FIFO isn’t full anymore. The user address points to

MO3. The FIFO index didn’t change.

Figure 8-14: FIFO 2 - Two More Messages Read

MO1 / MSG1

MO2 / MSG2

C1FIFOUA2 = 0x384

C1FIFOSTA2:

FIFOCI = 1

RFFIF = 1

RFHIF = 1

RFNIF = 1

RXOVIF = 1

MO0 / MSG16

MO15 / MSG15

MO3 / MSG3

MO4 / MSG4

C1FIFOUA2 = 0x41C

C1FIFOSTA2:

FIFOCI = 1

RFFIF = 0

RFHIF = 1

RFNIF = 1

RXOVIF = 0

MO0 / MSG16

MO15 / MSG15

MO1

MO2

MCP25xxFD Family Reference Manual

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8.4 Transmit Queue Behavior

C1TXQCON is used to control the TXQ. C1TXQSTA contains the status flags, and the TXQ index

(TXQCI). C1TXQUA contains the user address of the next transmit message object to be loaded.

The TXQCI is used by the CAN FD Controller Module to calculate the next message to transmit.

TXQCI is not incremented linearly. It is recalculated every time a message gets transmitted, or

TXREQ gets set.

Remember that the actual RAM address is calculated using Equation 4-1.

Figure 8-15 through Figure 8-20 illustrate how the status flags, and user address are updated.

There is no need for the user application to use TXQCI, therefore, it is not shown in the figures.

Figure 8-15 shows the status of the TXQ after reset. Message Objects MO0 to MO7 are empty.

All status flags are set. The user address points to MO0.

Figure 8-15: TXQ - Initial State

Figure 8-16 illustrates the status of the TXQ after the first message (MSG0) was loaded. MO0

contains now MSG0. The user application sets C1TXQCON.UINC, which causes the FIFO head

to advance. The user address points now to MO1. TXQEIF is cleared, since the queue isn’t

empty anymore. The user application now sets TXREQ to request the transmission of MSG0.

Figure 8-16: TXQ - First Message Loaded

MO0

MO1

MO2

MO7

C1TXQUA = 0x090

C1TXQSTA:

TXQEIF = 1

TXQNIF = 1

C1TXQCON:

TXREQ = 0

MO0 / MSG0

MO1

MO2

MO7

C1TXQUA = 0x0B8

C1TXQSTA:

TXQEIF = 0

TXQNIF = 1

C1TXQCON:

TXREQ = 1

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CAN FD Controller Module

Figure 8-17 illustrates the status of the TXQ after MSG0 was transmitted. The TXQ is empty

again. TFEIF is set, and TXREQ is cleared. The user address still points at MO1, because UINC

wasn’t set.

Figure 8-17: TXQ - First Message Transmitted

Figure 8-18 illustrates the status of the TXQ after MSG1 was loaded, and UINC was set. The user

address now points to the next free message object: MO0.

Figure 8-18: TXQ - Next Message Loaded

Figure 8-19 illustrates the status of the TXQ after six more messages were loaded: MSG2-

MSG7. The user address now points to the last free message object: MO7.

Figure 8-19: TXQ - Next Six Messages Loaded

MO0

MO1

MO2

MO7

C1TXQUA = 0x0B8

C1TXQSTA:

TXQEIF = 1

TXQNIF = 1

C1TXQCON:

TXREQ = 0

MO0

MO1 / MSG1

MO2

MO7

C1TXQUA = 0x090

C1TXQSTA:

TXQEIF = 0

TXQNIF = 1

C1TXQCON:

TXREQ = 0

MO0 / MSG2

MO1 / MSG1

MO2 / MSG3

C1TXQUA = 0x1A8

C1TXQSTA:

TXQEIF = 0

TXQNIF = 1

C1TXQCON:

TXREQ = 0

MO7

MO3 / MSG4

MO4 / MSG5

MO5 / MSG6

MO6 / MSG7

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Figure 8-20 illustrates the status of the TXQ after MSG8 was loaded, and UINC was set. The

TXQ is now full, all flags are clear. The user address now points to MO0. The user application

now sets TXREQ. The messages will be transmitted based on the priority of their IDs.

Figure 8-20: TXQ - Full

MO0 / MSG2

MO1 / MSG1

MO2 / MSG3

C1TXQUA = 0x090

C1TXQSTA:

TXQEIF = 0

TXQNIF = 0

C1TXQCON:

TXREQ = 1

MO7 / MSG8

MO3 / MSG4

MO4 / MSG5

MO5 / MSG6

MO6 / MSG7

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CAN FD Controller Module

8.5 Transmit Event FIFO Behavior

C1TEFCON is used to control the TEF. C1TEFSTA contains the status flags. C1TEFUA contains

the user address of the next message object to read.

Remember that the actual RAM address is calculated using Equation 5-1.

Figure 8-21 through Figure 8-28 illustrate how the status flags and user address are updated.

The TEF stores transmitted messages. Therefore, the flags behaves similar to a RX FIFO.

Figure 8-21 shows the status of the TEF after reset. Message Objects MO0 to MO11 are empty.

All status flags are clear. The user address points to MO0.

Figure 8-21: TEF - Initial State

Figure 8-22 shows the status of the TEF after the first transmit message was stored. MO0

contains ID0, the ID of MSG0. TEFNEIF is set, since the TEF is not empty. The user address

points to MO0.

Figure 8-22: TEF - First Transmit Message Was Stored

Figure 8-23 illustrates the status of the TEF after ID0 was read. The user application reads the

ID from RAM and sets C1TEFCON.UINC. The user address increments and points to MO1. The

TEF is empty again. All flags are clear.

Figure 8-23: TEF - First ID Read

MO0

MO1

MO2

MO11

C1TEFUA = 0x000

C1TEFSTA:

TEFFIF = 0

TEFHIF = 0

TEFNEIF = 0

TEFOVIF = 0

MO1

MO2

MO11

C1TEFUA = 0x000

C1TEFSTA:

TEFFIF = 0

TEFHIF = 0

TEFNEIF = 1

TEFOVIF = 0

MO0 / ID0

MO0

MO1

MO2

MO11

C1TEFUA = 0x00C

C1TEFSTA:

TEFFIF = 0

TEFHIF = 0

TEFNEIF = 0

TEFOVIF = 0

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Figure 8-24 illustrates the status of the TEF after six more messages were transmitted: MSG1-

MSG6. The user address points to MO1. TEFNEIF and TEFHIF are set, because the TEF is now

half full.

Figure 8-24: TEF - Half Full

Figure 8-25 illustrates the status of the TEF after five more messages were transmitted: MSG7-

MSG11. The user address still points to MO1. TEFNEIF and TEFHIF are set.

Figure 8-25: TEF - Almost Full

Figure 8-26 illustrates the status of the TEF after one more message was transmitted: MSG12.

All status flags are set, because the TEF is full. The user address points to MO1.

Figure 8-26: TEF - Full

MO1 / ID1

MO7

MO6 / ID6

MO8

MO0

MO11

C1TEFUA = 0x00C

C1TEFSTA:

TEFFIF = 0

TEFHIF = 1

TEFNEIF = 1

TEFOVIF = 0

MO2 / ID2

MO1 / ID1

MO11 / ID11

C1TEFUA = 0x00C

C1TEFSTA:

TEFFIF = 0

TEFHIF = 1

TEFNEIF = 1

TEFOVIF = 0

MO2 / ID2

MO0

MO1 / ID1

MO11 / ID11

C1TEFUA = 0x00C

C1TEFSTA:

TEFFIF = 1

TEFHIF = 1

TEFNEIF = 1

TEFOVIF = 0

MO2 / ID2

MO0 / ID12

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CAN FD Controller Module

Figure 8-27 illustrates the status of the TEF after one more message was transmitted. Since the

TEF was already full an overflow occurred. The ID is discarded, and TEFOVIF is set. The user

address didn’t change.

Figure 8-27: TEF - Overflow

Figure 8-28 illustrates the status of the TEF after the application cleared TEFOVIF and read one

more message. TEFFIF is clear, because the TEF isn’t full anymore. The user address points to

MO2.

Figure 8-28: TEF - One More ID Read

MO1 / ID1

MO11 / ID11

C1TEFUA = 0x00C

C1TEFSTA:

TEFFIF = 1

TEFHIF = 1

TEFNEIF = 1

TEFOVIF = 1

MO2 / ID2

MO0 / ID12

MO11 / ID11

C1TEFUA = 0x018

C1TEFSTA:

TEFFIF = 0

TEFHIF = 1

TEFNEIF = 1

TEFOVIF = 0

MO2 / ID2

MO0 / ID12

MO1

MO3 / ID3

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9.0 TIMESTAMPING

The CAN FD Controller Module contains a Time Base Counter (TBC). The TBC is a 32-bit free-

running counter that increments on multiples of SYSCLK and rolls over to zero.

• CiTSCON.TBCPRE is used to configure the prescaler for the TBC.

• Setting CiTSCON.TBCEN enables the TBC.

• Clearing TBCEN disables, stops and resets the TBC.

• The TBC has to be disabled, before writing to CiTBC by clearing CiTSCON.TBCEN.

• CiTEFCON.TEFTSEN has to be set to timestamp messages in the Transmit Event FIFO.

• CiFIFOCONm.RXTSEN has to be set to timestamp messages in the individual RX FIFO.

• The application can read CiTBC at any time. Like with any multi-byte counter, the

application has to consider that the counter increments, and might roll-over, between

reading the different bytes of the counter.

All timestamps are 32-bit, allowing timestamps to be used for system time synchronization with

high resolution.

A roll-over of the TBC will generate an interrupt, if TBCIE is set.

Messages can be timestamped either at the beginning of a frame or at the end, depending on

CiTSCON.TSEOF. When TSEOF = 0, CiTSCON.TSRES specifies if FD frames are

timestamped at SOF or the res bit. Tab l e 9- 1 specifies the reference points when the

timestamping occurs. At the reference point the value of the TBC (CiTBC) is captured and

stored into the message object:

• Receive Message Object: the TBC value is stored in RXMSGTS, see Table 7-1.

• TEF Object: the TBC value is stored in TXMSGTS, see Table 5-1.

Table 9-1: Reference Point

9.1 TBC Configuration Code Example

Example 9-1 shows a code example of how to configure the TBC:

• Disable the TBC

• Configure the Prescaler

• Optionally, set the TBC to a certain value

• Enable the TBC.

Example 9-1: Configuration of TBC

Frame CAN 2.0 CAN FD

Start of TX Sample point of SOF Sample point of SOF or the bit after FDF

Start of RX Sample point of SOF Sample point of SOF or the bit after FDF

Valid TX No error till end of EOF No error till end of EOF

Valid RX No error till the last but one bit of

EOF

No error till the last but one bit of EOF

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CAN FD Controller Module

10.0 INTERRUPTS

Interrupts can be classified into multiple layers. Lower layer interrupts propagate to higher

layers by multiplexing them into single interrupts. Figure 10-1 illustrates the layers of interrupts:

1. FIFO Individual Interrupts

2. FIFO Combined Interrupts

3. Main Interrupts

These interrupts are then funneled into three separate module interrupts:

1. Receive Interrupt

2. Transmit Interrupt

3. Information Interrupt

All module interrupts are persistent, meaning the condition that caused the interrupt must be

cleared within the module for the interrupt request to be removed.

In addition, the MCP25xxFD generates interrupts for the following events:

• SPI CRC errors: Format and CRC error.

• ECC errors: Single Error Corrected (SEC), Double Error Detected (DED).

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Figure 10-1: Interrupt Multiplexing

31x

RFFIE

RFFIF

RFHIE

RFHIF

RFNIE

RFNIF

31 FIFOS

31x

CiRXIF.RFIF<31:1>

CiTXQCON, CiTXQSTA

CiFIFOCONm, CiFIFOSTAm

CiINT.RXIE

CiINT.RXIF

31x

TFEIE

TFEIF

TFHIE

TFHIF

TFNIE

TFNIF

31 FIFOS

32x

CiTXIF.TFIF<31:1>

CiINT.TXIE

CiINT.TXIF

31x

RXOVIE

RXOVIF

31 FIFOS 31x

CiRXOVIF.RFOVIF<31:1>

CiINT.RXOVIE

CiINT.RXOVIF

31x

TXATIE

TXATIF

31 FIFOS 32x

CiTXATIF.TFATIF<31:1>

CiINT.TXATIE

CiINT.TXATIF

TEFFIE

TEFFIF

TEFHIE

TEFHIF

TEFNEIE

TEFNEIF

1 FIFO CiINT.TEFIE

CiINT.TEFIF

CiINT.IVMIE

CiINT.IVMIF

CiINT.WAKIE

CiINT.WAKIF

CiINT.CERRIE

CiINT.CERRIF

CiINT.MODIE

CiINT.MODIF

CiINT.TBCIE

CiINT.TBCIF

CiINT.SERRIE

CiINT.SERRIF

FIFO Individual

Interrupts

FIFO Combined

Interrupts

Main Interrupts Interrupt Pins

TEFOVIE

TEFOVIF

RX Interrupt

TX Interrupt

Info Interrupt

CiTEFCON

CiTEFSTA

CiINT.SPICRCIE

CiINT.ECCIE

CiINT.ECCIF

FERRIE

FERRIF

CRCERRIE

CRCERRIF

SECIE

SECIF

DEDIE

DEDIF

MCP25xxFD

TXQEIE

TXQEIF

TXQNIE

TXQNIF

CiTXIF.TFIF<0>

TXATIE

TXATIF

1 TXQ CiTXATIF.TFATIF<0>

1 TXQ

CiINT.SPICRCIF

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CAN FD Controller Module

10.1 FIFO Individual Interrupts

CiFIFOCONm contains the interrupt enable and CiFIFOSTAm contains the interrupt flags for

the FIFOs. There is a separate register for each individual FIFO.

10.1.1 TRANSMIT QUEUE (TXQ) INTERRUPTS

CiTXQCON contains the interrupt enable and CiTXQSTA contains the interrupt flags for the

TXQ.

The TXQ interrupt occurs when there is a change in the status of the TXQ. There are two

interrupt sources:

• TXQ Not Full Interrupt - TXQNIF

• TXQ Empty Interrupt - TXQEIF

Both interrupts can be enabled individually. The interrupts cannot be cleared by the application;

they will be cleared when the condition of the FIFO terminates.

Both interrupt sources are OR’d together and reflected in the CiTXIF.TFIF<0> flag.

10.1.2 RECEIVE FIFO INTERRUPT - RFIF

The Receive FIFO interrupt occurs when there is a change in the status of the Receive FIFO.

There are three interrupt sources:

• Receive FIFO Full Interrupt - RFFIF

• Receive FIFO Half Full Interrupt - RFHIF

• Receive FIFO Not Empty Interrupt - RFNIF

All three interrupts can be enabled individually. The interrupts can not be cleared by the

application, they will be cleared when the condition of the FIFO terminates.

The three interrupt sources are OR’d together and reflected in the CiRXIF.RFIF<m> flag.

10.1.3 TRANSMIT FIFO INTERRUPT - TFIF

The Transmit FIFO interrupt occurs when there is a change in the status of the Transmit FIFO.

There are three interrupt sources:

• Transmit FIFO Not Full Interrupt - TFNIF

• Transmit FIFO Half Empty Interrupt - TFHIF

• Transmit FIFO Empty Interrupt - TFEIF

All three interrupts can be enabled individually. The interrupts can not be cleared by the

application, they will be cleared when the condition of the FIFO terminates.

The three interrupt sources are OR’d together and reflected in the CiTXIF.TFIF<m> flag.

10.1.4 RECEIVE FIFO OVERRUN INTERRUPT - RXOVIF

When a message is successfully received, but the FIFO is full, the RXOVIF of the individual

FIFO is set. The flag must be cleared by the application.

10.1.5 TRANSMIT FIFO ATTEMPT INTERRUPT - TXATIF

When the retransmission of a message fails due to an error and all retransmission attempts are

exhausted, the TXATIF is set. The flag must be cleared by the application.

10.1.6 TRANSMIT EVENT FIFO INTERRUPT - TEFIF

The Transmit Event FIFO (TEF) interrupt occurs when there is a change in the status of the

Transmit Event FIFO. There are four interrupt sources:

• TEF Full Interrupt - TEFFIF

• TEF Half Full Interrupt - TEFHIF

• TEF Not Empty Interrupt - TEFNEIF

• TEF Overrun Interrupt - TEFOVIF

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The TEF interrupts work similar to the Receive FIFO interrupts. All four interrupts can be

enabled individually.

TEFFIF, TEFHIF and TEFNEIF can not be cleared by the application, they will be cleared when

the status of the FIFO terminates.

The TEFOVIF must be cleared by the application.

The four interrupt sources are OR’d together and reflected in the CiINT.TEFIF flag.

10.2 MCP25xxFD SPI CRC Interrupts

The CRC register contains the interrupt enable bits, FERRIE, and CRCERRIE; and the interrupt

status flags, FERRIF, and CRCERRIF.

The status flags must be cleared by the application.

10.3 MCP25xxFD RAM ECC Interrupts

The ECCCON register contains the interrupt enable bits, DEDIE, and SECIE.

The ECCSTA register contains the interrupt status flags, DEDIF, and SECIF.

The status flags must be cleared by the application.

10.4 FIFO Combined Interrupts

The following interrupts are individual FIFO interrupts:

• FIFOs/TXQ: RFIF, TFIF, RFOVIF and TFATIF

They are combined into single interrupt status registers:

• CiRXIF, CiTXIF, CiRXOVIF and CiTXATIF.

The bits inside the status registers are mapped to the FIFOs as follows: Bit 0 to TXQ, Bit 1 to

FIFO 1, Bit 2 to FIFO 2, and so on, Bit 31 to FIFO 31. Since Bit 0 corresponds to the TXQ, Bit 0

of CiRXIF and CiRXOVIF are reserved. Therefore, by reading one register the application can

check the status of all FIFOs for a particular interrupt (e.g. any RFIF pending).

The FIFO interrupts are enabled in CiFIFOCONm.

TXQ interrupts are enabled in CiTXQCON.

The clearing of the FIFO interrupts is explained in Section 10.1 “FIFO Individual Interrupts”.

10.5 Main Interrupts

The CiINT register contains all main interrupts. The following interrupts are a logical ‘or’ of all

combined FIFO interrupts: RXIF, TXIF, RXOVIF, TXATIF. These flags are read-only and must be

cleared in preceding hierarchies.

The TEFIF is generated in the Transmit Event FIFO. The flag is read-only, and must be cleared

in preceding hierarchies.

All interrupts in CiINT can be enabled individually.

10.5.1 INVALID MESSAGE INTERRUPT - IVMIF

If a CAN bus error or DLC mismatch was detected during the last message transmitted or

received, the IVMIF will be set. The CiBDIAG1 register sets a flag for each specific error. The

flag must be cleared by the application.

The following CAN bus errors will trigger the interrupt in case an error frame was transmitted:

CRC, Stuff bit, Form, Bit, ACK.

The flag will not be set if the ESI of a received message was set.

10.5.2 WAKE-UP INTERRUPT - WAKIF

Bus activity has been detected while the module is in Sleep Mode. The flag must be cleared by

the application.

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CAN FD Controller Module

10.5.3 CAN BUS ERROR INTERRUPT - CERRIF

The CiTREC register will count the errors during transmit and receive according to the ISO

11898-1:2015. The CERRIF flag will be set based on the error counter values. The flag must be

cleared by the application.

CERRIF will be set each time a threshold in the TEC/REC counter is crossed by the following

conditions:

• TEC or REC exceeds the Error Warning state threshold

• The transmitter or receiver transitions to Error Passive state

• The transmitter transitions to Bus Off state

• The transmitter or receiver transitions from Error Passive to Error Active state

• The module transitions from Bus Off to Error Active state, after the bus off recovery

sequence

When the user clears CERRIF, it will remain clear until a new counter crossing occurs.

10.5.4 CAN MODE CHANGE INTERRUPT - MODIF

When the OPMOD bits change, the MODIF flag will be set. The flag must be cleared by the

application.

10.5.5 CAN TIMER INTERRUPT - TBCIF

When the Time Base Counter rolls-over, TBCIF will be set. The flag must be cleared by the

application.

10.5.6 SYSTEM ERROR INTERRUPT - SERRIF

Bus Bandwidth Error:

Bandwidth errors can happen during receive and transmit.

Receive Message Assembly Buffer (RX MAB) overflow occurs when the module is unable to

write a received CAN message to RAM before the next message arrives.

Transmit Message Assembly Buffer (TX MAB) underflow occurs when the module can’t feed the

TX MAB fast enough to provide consistent data to the Bit Stream Processor.

The SERRIF flag will be set and CiVEC.ICODE bits will be set to 100 0101.

Handling of RX MAB Overflow Errors:

RX MAB overflows are not accepted by automotive OEM. To prevent overflows, frame filtering

and data saving starts as early as possible, the latest at the beginning of the CRC field of the

received message. Updating the FIFO status has to wait until the beginning of the 7th bit of the

EOF field, since the received frame is only valid at this point. The complete message has to be

saved and the FIFO has to be updated, until the end of the arbitration field of the next message.

In case of an RX MAB overflow, the new message that caused the RX MAB overflow will be

discarded. The module continues to store the message that was already completely received

and filtered. Afterwards, the module will be able to receive new messages on the bus. The

application will be notified using the SERRIF.

SERRIF will be cleared by writing a zero to CiINT.SERRIF. This will also clear the SERRIF

condition from the ICODE.

Handling of TX MAB Underflow Errors:

ISO 11898-1:2015 requires MAC data consistency: a transmitted message must contain

consistent data. If data errors occur due to ECC errors, or TX MAB underflow, the transmission

shall not be started. If it is already in progress, the transmission shall be stopped, and the

module shall transition to either Restricted Operation or Listen Only mode, selectable using

CiCON.SERR2LOM.

The module handles these errors by stopping the transmission and transitioning to Restricted

Operation or Listen Only mode. The TXCAN pin will be forced high. Additionally, all TXREQ are

ignored. The application will be notified using SERRIF. The module will continue receiving mes-

sages.

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10.5.7 SPI CRC INTERRUPT - SPICRCIF

The individual SPI CRC error interrupts are combined into the SPICRCIF. The flag is read-only

and must be cleared in preceding hierarchies.

10.5.8 ECC INTERRUPT - ECCIF

The individual ECC error interrupts are combined into the ECCIF. The flag is read-only and must

be cleared in preceding hierarchies.

10.6 Interrupt Handling

The CAN FD Controller Module allows the application to handle interrupts efficiently in two

different ways:

• Implementing a lookup table using the CiVEC register.

• Using the status registers and decide which interrupt to service first.

The application can also use a combination of the two.

10.6.1 INTERRUPT LOOKUP TABLE

The ICODE and FILTHIT bits in the CiVEC register enable the application to use a lookup table

to implement the interrupt service routine.

The following bit fields allow the application to make full use of the three interrupt pins:

• TXCODE: Reflects which object has a transmit interrupt pending.

• RXCODE: Reflects which object has a receive interrupt pending.

A separate lookup table can be implemented for transmit and receive interrupts.

If more than one object has an interrupt pending, the interrupt or FIFO with the highest number

will show up in RXCODE, TXCODE and ICODE. Once the interrupt with the highest priority is

cleared, the next highest priority interrupt will show up in CiVEC. RXCODE, TXCODE and

ICODE are implemented with combinatorial logic using the interrupt flags as inputs.

10.6.2 INTERRUPT STATUS REGISTERS

The CAN FD Controller Module contains 31 FIFOs and a TXQ. It could be too inflexible to use

the ICODE, since the interrupt priorities are determined by the module. Therefore, other

measures were taken to assure efficient servicing of interrupts:

• CiINT contains all main interrupt sources. The application can find out which categories of

interrupts are pending and decides which interrupts to service first (e.g., RXIF).

• All categories of interrupts for all FIFOs are combined into single registers: CiRXIF, CiTXIF,

CiRXOVIF and CiTXATIF. The application can find out which RFIFs are pending by reading

only one register. The same is true for TFIF, RXOVIF and TXATIF.

• In the register map, the interrupt status registers are arranged in a single block: CiVEC,

followed by CiINT, CiRXIF, CiTXIF, CiRXOVIF and CiTXATIF. This allows reading all status

registers with a single SPI read access.

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CAN FD Controller Module

10.7 Interrupt Flags

Table 10-1 summarizes all interrupt flags, and lists how interrupts are cleared.

Table 10-1: Interrupt Flags

Flag Register Category Cleared by

Module(1)

Cleared by

Application Read-Only(2)Description

RFFIF

RFHIF

RFNIF

CiFIFOSTAm FIFO X — — RX FIFO

TFNIF

TFHIF

TFEIF

CiFIFOSTAm FIFO X — — TX FIFO

TXQNIF

TXQEIF

CiTXQSTA TXQ X — — Transmit Queue

RXOVIF CiFIFOSTAm FIFO — X — RX Overrun

TXATIF CiFIFOSTAm

CiTXQSTA

FIFO

TXQ

— X — TX Attempt

TEFFIF

TEFHIF

TEFNEIF

CiTEFSTA FIFO X — — TEF

TEFOVIF CiTEFSTA FIFO — X — TEF Overrun

RFIF CiRXIF Combined — — X All RX FIFOs

TFIF CiTXIF Combined — — X All TX FIFOs

RFOVIF CiRXOVIF Combined — — X All RX FIFO

Overruns

TFATIF CiTXATIF Combined — — X All TX FIFO Attempts

FERRIF

CRCERRIF

CRC MCP25xxFD — X — SPI CRC Errors

SECIF

DEDIF

ECCSTA MCP25xxFD — X — ECC Errors

RXIF CiINT Main — — X RX

TXIF CiINT Main — — X TX

RXOVIF CiINT Main — — X RX Overrun

TXATIF CiINT Main — — X TX Attempt

TEFIF CiINT Main — — X TEF

IVMIF CiINT Main — X — Invalid Message

WAKIF CiINT Main — X — Wake-up

CERRIF CiINT Main — X — CAN Bus Error

MODIF CiINT Main — X — Mode Change

TBCIF CiINT Main — X — Time Base Counter

SERRIF CiINT Main — X — System Error

SPICRCIF CiINT Main — — X SPI CRC Error

ECCIF CiINT Main — — X RAM ECC Error

Note 1:The flags will be cleared, when the condition of the FIFO terminates, initiated by CiFIFOCONm.UINC.

2:The flags need to be cleared in the preceding hierarchies.

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10.8 Interrupt Configuration and Handling Code Examples

Example 10-1 shows a code example of how to configure the TX and RX interrupts:

• Clear Module Interrupts. TX and RX interrupts are cleared when the condition of the FIFO

terminates, therefore, they can’t be cleared by the application.

• Enable Transmit Queue interrupt.

• Enable Receive FIFO interrupt.

• Enable RX and TX interrupts in CiINT.

Example 10-1: Configuration of Interrupts

Example 10-2 shows a code example of how to use the TX interrupt pin (INT0) to check if the

TXQ is ready for transmission:

• Check that the TXQ is not full.

• Load the message into the TXQ.

• Increment and flush the TXQ. UINC and TXREQ are set at the same time. This makes sure

that all messages in the TXQ are transmitted in case a message is appended to the TXQ

while it is already transmitting.

Example 10-2: Using TX Interrupt Pin to Check if TXQ is Ready for Transmission

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CAN FD Controller Module

Example 10-3 shows a code example of how to use the RX interrupt pin (INT1) to check it there

is a receive message in FIFO 2:

• Check that the FIFO is not empty.

• Read the message from the FIFO.

• Increment the FIFO by setting UINC.

• Process the received message.

Example 10-3: Using RX Interrupt Pin to Check if FIFO 2 Contains a New Message

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11.0 ERROR HANDLING

Every CAN controller checks the messages on the bus for the following errors: Bit, Stuff, CRC,

Form, and ACK errors. Whenever the controller detects an error, an Error frame is transmitted

that usually destroys the message on the bus. Error frames are always signaled using the

Nominal Bit Rate.

Error Detection and Fault Confinement is described in the ISO 11898-1:2015. CiTREC contains

the error counters, TEC and REC. It also contains the Error Warning and Error State bits. TEC

and REC increment and decrement according to ISO 11898-1:2015.

Figure 11-1 illustrates the different Error states of the CAN FD Controller Module. The module

starts out in Error Active state. If the TEC or REC exceed 127, the module transitions to Error

Passive state. If the TEC exceeds 255, the module will go to Bus Off state.

The module transmits Active Error frames, when in Error Active state. It will transmit Passive

Error frames, while in Error Passive state. When the module is Bus Off, TXCAN is always driven

high, and no dominant bits are transmitted.

In order to avoid transitioning to Error Passive state, the module will warn the application if the

TEC or REC reach 96 using the CERRIF interrupt flag, see Section 10.5.3 “CAN Bus Error

Interrupt - CERRIF”. This allows the application to take action before it enters Error Passive

state.

Figure 11-1: Error States

The Bus Diagnostics registers provide additional information about the health of the CAN bus:

• CiBDIAG0 contains separate Error Counters for receive/transmit and for nominal/data bit

rates. The counters work differently than the counters in the CiTREC register. They are

simply incremented by one on every error. They are never decremented, but can be

cleared by writing zero to the register.

• CiBDIAG1 keeps track of the kind of error that occurred since the last clearing of the

counter are cleared by writing zero to the register.

The Error Free Message Counter together with the Error Counters, and the Error Flags can be

used to determine the quality of the bus.

TEC> 255

Error

Active

Error

Passive Bus Off

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CAN FD Controller Module

11.1 Recovery from Bus Off State

If the TEC exceeds 255, CiTREC.TXBO and CiINT.CERRIF will be set. The module will go Bus

Off and start the bus off recovery sequence.

The bus off recovery sequence is started automatically. The module will transition out of Bus Off

only after the detection of 128 idle conditions, see “ISO11898-1:2015: Bus Off Management”.

The module will set FRESET for all transmit FIFOs when entering Bus Off state to ensure the

module doesn't try to retransmit indefinitely. The application will be notified by CERRIF and has

the option to queue new messages for transmission.

The module signals the exit from the Bus Off state with a CERRIF, and by setting

CiBDIAG1.TXBOERR. Additionally, CiTREC will be reset.

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12.0 APPENDIX A: MCP25XXFD CANFDSPI API

12.1 Introduction

The Application Programming Interface (API) provides a firmware library for the MCP25xxFD.

The API simplifies the development of a CAN FD application by providing type definitions and

functions for the following tasks:

• Configuration: Bit Time, FIFOs, Filters and Masks

• Mode Selection

• Message Transmission

• Message Reception

• Event (Interrupt) Handling

• Error State Tracking.

The API is MCU independent by using the peripheral library or drivers for the SPI transfer. The

API calls only one hardware dependent SPI function: DRV_SPI_TransferData. The

application must implement an SPI initialization function and the DRV_SPI_TransferData on

the selected target MCU.

12.2 Abstraction Model

The API provides a hardware abstraction of the CAN FD Controller Module with a C interface to

the application, see Figure 12-1.

The API provides interface routines to interact with the CAN FD Controller Module. A channel

(FIFO) can be either a transmit channel or a receive channel. The size of the payload of a CAN

message can be configured between 8 and 64 bytes. The number of message objects of a chan-

nel (the number of messages in the FIFO) is configurable between 1 and 32 messages. The API

provides access to these channels and message objects via the library interface.

The application must enable and configure message acceptance filters to receive messages.

These filters compare the ID field of the incoming message with configured values and accepts

the messages if IDs match. The message is then stored in a selectable receive channel. At least

one message acceptance filter object and one mask object must be enabled for the CAN FD

Controller Module to receive messages. A mask allows specified filter bits to be ignored during

the comparison process. This allows the filter to accept messages with a range of IDs.

The API provides functions to configure and handle events (interrupts). Events can be generated

at the channel level and at the module level. Channel events are generated by transmit and

receive channels. Module events are generated by various sources (including channels) within

the CAN FD Controller Module. Each event can be enabled or disabled. Enabling a channel

event will cause the CAN FD Controller Module to generate a module event. An enabled module

level event will cause the MCP25xxFD to assert one or more of the interrupt pins. The interrupt

pins of the MCP25xxFD are connected to MCU input pins. The application can either poll the

input pins, or setup external interrupts on these inputs.

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CAN FD Controller Module

Figure 12-1: Hardware Abstraction Model

MCP25xxFD

DRV_SPI DMA TMRISR

SYS

CAN

XCR

TXCAN

RXCAN

INT0:2

SCK

SDI

SDO

INT0:2

XSTBY

I/O

PLIB

DRV_CANFDSPI

CANFDApplication

XSTBY

MCUFirmware

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12.3 Getting Started with the SPI Communication

The application must implement a minimum of two SPI functions on the target MCU:

• Initialization: this function initializes the SPI peripheral. Please review the “SPI Interface”

section of the device data sheet for details on the SPI configuration.

• Transfer Data: this function asserts nCS, writes/reads n data bytes, and de-asserts nCS.

In order to minimize the SPI transfer time, the application should make use of SPI FIFO buffers,

or use DMAs to feed the SPI.

12.3.1 SPI INITIALIZATION CODE EXAMPLE

Example 12-1 shows the initialization function for a PIC32MX470F512H. It was generated using

MBLAB Harmony Configurator. The SPI is setup as a Master in mode 0,0. The application takes

advantage of the Enhanced Buffering mode, which minimizes the SPI transfer time.

Example 12-1: SPI Initialization Function

Note: The frequency of SCK has to be less than or equal to half the frequency of SYSY-

CLK. This ensures that the synchronization between SCK and SYSCLK works

correctly.

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12.3.2 SPI DATA TRANSFER CODE EXAMPLE

Example 12-2 shows the data transfer function for a PIC32MX470F512H. It was generated using

MBLAB Harmony Configurator and slightly modified. The function makes use of the 16 byte SPI

FIFO buffer. It first fills the transmit buffer with up to 16 bytes, then reads back as many bytes as

were transmitted, therefore, minimizing the dead time between the SPI bytes.

The application passes the transmit data to the function using the SpiTxData pointer. The func-

tion returns the read data to the application in the array pointed to by the SpiRxData. A total of

spiTransferSize bytes are transfered.

Example 12-2: SPI Data Transfer Function

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12.3.3 SPI READ AND WRITE ACCESS FUNCTIONS

Example 12-3 lists some of the SPI access functions. The access functions use the

DRV_SPI_TransferData to send read and write commands to the MCP25xxFD. These

functions can be used for communication between the MCU and the MCP25xxFD, or for testing

the DRV_SPI_TransferData function.

Example 12-3: SPI Access Functions

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CAN FD Controller Module

12.3.4 VERIFICATION OF THE SPI COMMUNICATION

Example 12-4 shows an example of verifying that reads and writes to RAM work correctly. Since

all SPI access functions use the DRV_SPI_TransferData, only one of the access function

needs to be used to verify DRV_SPI_TransferData.

Example 12-4: Verifying SPI Communication using RAM Access

Example 12-5 shows an example of verifying that reads and writes to registers work correctly.

Example 12-5: Verifying SPI Communication using Register Access

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13.0 RELATED DOCUMENTS

This section lists documents that are related to this section of the manual. These documents may

not be written specifically for the MCP25xxFD device family, but the concepts are pertinent and

could be used with modification and possible limitations. The current documents related to the

CAN FD Controller Module include the following:

Title Document #

PIC32 Family Reference Manual - Section 34. Controller Area Network (CAN) DS61154

PIC32 Family Reference Manual - Section 6. Oscillators DS61112

Crystal Oscillator Basics and Crystal Selection for rfPIC® and PIC® MCU Devices DS00826

Basic PIC® Microcontroller Oscillator Design DS00849

Practical PIC® Microcontroller Oscillator Analysis and Design DS00943

Making Your Oscillator Work DS00949

Note: Please visit the Microchip web site (www.microchip.com) for additional application

notes and code examples for the MCP25xxFD family of devices.

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CAN FD Controller Module

14.0 REVISION HISTORY

Revision B (May 2018)

• Added MCP2518FD.

• Added LPM description.

• Increased SEQ field for Transmit Message and TEF objects.

Revision A (September 2017)

• Original release of this document.

MCP25xxFD Family Reference Manual

DS20005678B-page 78  2017-2018 Microchip Technology Inc.

NOTES:

 2017-2018 Microchip Technology Inc. DS20005678B-page 79

Information contained in this publication regarding device

applications and the like is provided only for your convenience

and may be superseded by updates. It is your responsibility to

ensure that your application meets with your specifications.

MICROCHIP MAKES NO REPRESENTATIONS OR

WARRANTIES OF ANY KIND WHETHER EXPRESS OR

IMPLIED, WRITTEN OR ORAL, STATUTORY OR

OTHERWISE, RELATED TO THE INFORMATION,

INCLUDING BUT NOT LIMITED TO ITS CONDITION,

QUALITY, PERFORMANCE, MERCHANTABILITY OR

FITNESS FOR PURPOSE. Microchip disclaims all liability

arising from this information and its use. Use of Microchip

devices in life support and/or safety applications is entirely at

the buyer’s risk, and the buyer agrees to defend, indemnify and

hold harmless Microchip from any and all damages, claims,

suits, or expenses resulting from such use. No licenses are

conveyed, implicitly or otherwise, under any Microchip

intellectual property rights unless otherwise stated.

Trademarks

The Microchip name and logo, the Microchip logo, AnyRate, AVR,

AVR logo, AVR Freaks, BeaconThings, BitCloud, CryptoMemory,

CryptoRF, dsPIC, FlashFlex, flexPWR, Heldo, JukeBlox, KEELOQ,

KEELOQ logo, Kleer, LANCheck, LINK MD, maXStylus,

maXTouch, MediaLB, megaAVR, MOST, MOST logo, MPLAB,

OptoLyzer, PIC, picoPower, PICSTART, PIC32 logo, Prochip

Designer, QTouch, RightTouch, SAM-BA, SpyNIC, SST, SST

Logo, SuperFlash, tinyAVR, UNI/O, and XMEGA are registered

trademarks of Microchip Technology Incorporated in the U.S.A.

and other countries.

ClockWorks, The Embedded Control Solutions Company,

EtherSynch, Hyper Speed Control, HyperLight Load, IntelliMOS,

mTouch, Precision Edge, and Quiet-Wire are registered

trademarks of Microchip Technology Incorporated in the U.S.A.

Adjacent Key Suppression, AKS, Analog-for-the-Digital Age, Any

Capacitor, AnyIn, AnyOut, BodyCom, chipKIT, chipKIT logo,

CodeGuard, CryptoAuthentication, CryptoCompanion,

CryptoController, dsPICDEM, dsPICDEM.net, Dynamic Average

Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial

Programming, ICSP, Inter-Chip Connectivity, JitterBlocker,

KleerNet, KleerNet logo, Mindi, MiWi, motorBench, MPASM, MPF,

MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK, NetDetach,

Omniscient Code Generation, PICDEM, PICDEM.net, PICkit,

PICtail, PureSilicon, QMatrix, RightTouch logo, REAL ICE, Ripple

Blocker, SAM-ICE, Serial Quad I/O, SMART-I.S., SQI,

SuperSwitcher, SuperSwitcher II, Total Endurance, TSHARC,

USBCheck, VariSense, ViewSpan, WiperLock, Wireless DNA, and

ZENA are trademarks of Microchip Technology Incorporated in the

U.S.A. and other countries.

SQTP is a service mark of Microchip Technology Incorporated in

the U.S.A.

Silicon Storage Technology is a registered trademark of Microchip

Technology Inc. in other countries.

GestIC is a registered trademark of Microchip Technology

Germany II GmbH & Co. KG, a subsidiary of Microchip Technology

Inc., in other countries.

All other trademarks mentioned herein are property of their

respective companies.

Reserved.

ISBN: 978-1-5224-2986-9

Note the following details of the code protection feature on Microchip devices:

• Microchip products meet the specification contained in their particular Microchip Data Sheet.

• Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the

intended manner and under normal conditions.

• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our

knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data

Sheets. Most likely, the person doing so is engaged in theft of intellectual property.

• Microchip is willing to work with the customer who is concerned about the integrity of their code.

• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not

mean that we are guaranteeing the product as “unbreakable.”

Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our

products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts

allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.

Microchip received ISO/TS-16949:2009 certification for its worldwide

headquarters, design and wafer fabrication facilities in Chandler and

Tempe, Arizona; Gresham, Oregon and design centers in California

and India. The Company’s quality system processes and procedures

are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping

devices, Serial EEPROMs, microperipherals, nonvolatile memory and

analog products. In addition, Microchip’s quality system for the design

and manufacture of development systems is ISO 9001:2000 certified.

QUALITYMANAGEMENTS

YSTEM

CERTIFIEDBYDNV

== ISO/TS16949==

DS20005678B-page 80  2017-2018 Microchip Technology Inc.

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10/25/17

MCP251XXFD CAN FD Controller Module Family Reference Manual 20005678B

MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B

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