S3esk_startup_rev2 S3esk Startup Rev2

User Manual: s3esk_startup_rev2

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Initial Design

for

Spartan-3E Starter Kit

(LCD Display Control)

Ken Chapman

Xilinx Ltd

February 2006

Rev.2

PicoBlaze Spartan-3E Starter Kit Initial Design 2

Limited Warranty and Disclaimer. These designs are provided to you “as is”. Xilinx and its licensors make and you receive no

warranties or conditions, express, implied, statutory or otherwise, and Xilinx specifically disclaims any implied warranties of

merchantability, non-infringement, or fitness for a particular purpose. Xilinx does not warrant that the functions contained in these

designs will meet your requirements, or that the operation of these designs will be uninterrupted or error free, or that defects in

the Designs will be corrected. Furthermore, Xilinx does not warrant or make any representations regarding use or the results of

the use of the designs in terms of correctness, accuracy, reliability, or otherwise.

Limitation of Liability. In no event will Xilinx or its licensors be liable for any loss of data, lost profits, cost or procurement of

substitute goods or services, or for any special, incidental, consequential, or indirect damages arising from the use or operation

of the designs or accompanying documentation, however caused and on any theory of liability. This limitation will apply even if

Xilinx has been advised of the possibility of such damage. This limitation shall apply not-withstanding the failure of the essential

purpose of any limited remedies herein.

This design module is not supported by general Xilinx Technical support as an official Xilinx Product.

Please refer any issues initially to the provider of the module.

Any problems or items felt of value in the continued improvement of KCPSM3 or this reference design would be gratefully

received by the author.

Ken Chapman

Senior Staff Engineer – Spartan Applications Specialist

email: chapman@xilinx.com

Limitations

The author would also be pleased to hear from anyone using KCPSM3 or the UART macros with information about your

application and how these macros have been useful.

PicoBlaze Spartan-3E Starter Kit Initial Design 3

Design Overview

This design is provided on the Spartan-3E Starter Kit when it is dispatched from the factory. It confirms that the board is operational by scrolling a simple

message across the LCD display and allowing the LED’s to be controlled by the rotary knob, press buttons and slide switches.

The principle purpose of this document is to illustrate how PicoBlaze can be used to control the LCD display. It is hoped that the design may form the basis

for future PicoBlaze designs as well as provide a general introduction to the board. Some exercises are suggested to encourage further self study.

If your board has be reprogrammed since it arrived, you can still try the design quickly.

As well as the source design files, a compiled configuration bit file is provided which

you can immediately download into the Spartan XC3S500E device on your board. To

make this task really easy the first time, unzip all the files provided into a directory and

then….

double click on ‘install_s3esk_startup.bat’.

Assuming you have the Xilinx software installed, your board connected with the USB

cable and the board powered (don’t forget the switch), then this should open a DOS

window and run iMPACT in batch mode to configure the Spartan-3E with the design.

Try it now – it only takes 30 seconds!

It is recommended that you try this to become familiar with what the design does

before continuing to read. If your board is ‘fresh out of the box’, then simply connect

the power supply, switch on and see the design come to life. If it doesn’t work (XC-

DONE LED remains unlit), check that all 3 jumpers are installed in J30 and press the

PROG button again.

Scrolling message

Rotate knob to control position

of the illuminated LED

4 slide

switches

8 LEDs

4 press

buttonsPress and release knob to

toggle between control modes

SW0

SW1

SW2

SW3

East

South

North

West

Operate buttons and switches

to illuminated each LED

PicoBlaze Spartan-3E Starter Kit Initial Design 4

PicoBlaze Design Size

The images and statistics on this page show that the design occupies just 113 slices and 1 BRAM. This is only 2.5% of the slices and 5% of the BRAMs

available in an XC3S500E device and would still be less than 12% of the slices in the smallest XC3S100E device.

Number of occupied Slices: 113 out of 4,656 2%

Number of Block RAMs: 1 out of 20 5%

Total equivalent gate count for design: 75,945

PicoBlaze makes extensive use of the distributed memory features of the

Spartan-3E device leading to very high design efficiency. If this design

was replicated to fill the XC3S500E device, it would represent the

equivalent of over 1.5 million gates. Not bad for a device even marketing

claims to be 500 thousand gates 

MAP report

FPGA Editor view Floorplanner view

XC3S500E

PicoBlaze Spartan-3E Starter Kit Initial Design 5

Design Files

The source files provided for the reference design are…..

s3esk_startup.vhd

Top level file and main description of hardware.

Contains I/O required to disable other StrataFLASH memory device on the board which may

otherwise interfere with the LCD display.

PicoBlaze program source assembler code

kcpsm3.vhd PicoBlaze processor for Spartan-3E devices.

control.vhd

s3esk_startup.ucf I/O constraints file for Spartan-3E Starter Kit

and timing specifications for 50MHz clock.

control.psm

Assembled program for PicoBlaze (stored in a Block memory)

Note: The file shown in green is not included with the reference design as it is provided with PicoBlaze download. Please visit the PicoBlaze Web site

for your free copy of PicoBlaze, assembler, JTAG_loader and documentation.

www.xilinx.com/picoblaze

Hint - If you only want to write new programs for PicoBlaze using the existing hardware design, then simply use the JTAG_Loader utility supplied with

PicoBlaze. The design supplied is already equipped with the JTAG loading circuit (see schematic on next page).

s3esk_startup_rev2.mcs PROM programming file for this design for use with any of the FLASH storage devices

PicoBlaze Spartan-3E Starter Kit Initial Design 6

PicoBlaze Circuit Diagram

strataflash_oe

strataflash_ce

strataflash_we

Vcc

* StrataFLASH memory must be

disabled to prevent interference

with the LCD display.

interrupt_control

‘JTAG_loader’ allows rapid

PicoBlaze code development.

port_id

kcpsm3 processor

instruction

write_strobe

clk

out_port

read_strobe

address

reset

interrupt_ackinterrupt

in_port

instruction

address

control

program_rom

instruction

address

clk

port_id

write_strobe

out_port

read_strobe

interrupt_ack

interrupt

in_port

JTAG

proc_reset

clk

kcpsm3_reset

input_ports

led(6)

led(5)

led(4)

led(3)

led(2)

led(1)

led(0)

led(7)

output_ports

switch(0)

switch(1)

switch(2)

switch(3)

Pull-down resistors added

to switch and press

button inputs in UCF file.

rotary_a

rotary_press

rotary_b

lcd_rs

lcd_e

lcd_rw

lcd(7)

lcd(6)

lcd(5)

lcd(4)

lcd(7)

lcd(6)

lcd(5)

lcd(4)

bidirectional

LCD data

rotary_press_in

See reference

design called

‘Rotary Encoder

Interface for

Spartan-3E Starter

Kit’ for details of

this section.

rotary_event

rotary_left

rotary_filter & direction

btn_north

btn_east

btn_south

btn_west

clk

50MHz Synchronous design

PicoBlaze Spartan-3E Starter Kit Initial Design 7

LCD Display Connections

The board is set up to use the 4-wire data interface to the LCD character module. The data connections are shared with the StrataFLASH memory which

must be disabled to prevent interference. This diagram shows the pin connections to the Spartan-3E device.

IC22

StrataFLASH

SF-WE

SF-OE

C18

D17

390Ω

+5v

LCD

Display

SF-D8

LCD_RS

M15

L18

LCD_E

LCD_RW

L17

M18

lcd_rs

lcd_e

lcd_rw

lcd(7)

strataflash_oe

Hint - The signals can be easily monitored at

the edge of the display if desired.

+5vGND RS RW E D7D6D5D4

SF-D9

SF-D10

SF-D11

P17 lcd(6)

R16 lcd(5)

R15 lcd(4)

SF-CE0

D16

strataflash_ce

strataflash_we

OE#

WE#

CE0

D11

D10

+3.3v

390Ω

Holding all three controls High ensures that the StrataFLASH

memory does not interfere with the LCD display and also prevents

inadvertent modifications to the memory contents.

The LCD display is powered by a +5v supply. This

means that if the display is read it will potentially

drive the data signal lines above the maximum level

(VCCO+0.5v) allowed for the Spartan-3E and

StrataFLASH pins which are both powered by 3.3v.

Therefore the display data pins have been

connected via 390Ωseries resistors to limit the

current and voltage during read operations.

Hint – This design provides all the mechanisms to enable

the display to be read but does not actually need to use it.

Most applications only require write operations.

PicoBlaze Spartan-3E Starter Kit Initial Design 8

LCD Display Timing

Once mastered, the LCD display is a practical way to display a variety of information using standard ASCII characters and even allows you to create some of

your own. However, these displays are not fast. This design scrolls the display at ½ second intervals and that really is the practical limit for clarity. This low

performance rate also relates to the signals used for communication. Compared with a Spartan-3E operating at 50MHz, the display can appear extremely

slow. This is where PicoBlaze can be used to efficiently implement timing delays as well as control the actual content of the display.

Exercise – Implement a hardware based state machine which obeys the timing requirements for an 8-bit write of data including the 40µs delay. Modify the

PicoBlaze interface and code to use your hardware circuit to write to the display. Under what circumstances would this approach be useful?

50MHz

4-bit Write Operation

This timing diagram shows a single write operation being performed. The

diagram is approximately to scale showing the minimum times allowed for

setup, hold and enable pulse length relative to a 50MHz clock (20ns period).

The data D[7:4], Register Select (RS) and write control (RW) must be set up at

least 40ns before the enable E goes High. Enable must be High for at least

230ns which is almost 12 clock cycles at 50MHz.

Hint – In a write only system, the R/W signal can be tied Low permanently.

230ns

D[7:4]

R/W

40ns 10ns

8-bit Write Operation

After initial display communication is established, all data transfers are 8-bit ASCII character

codes, data bytes or 8-bit addresses. Each 8-bit transfer obviously has to be decomposed

into two 4-bit transfers which must be spaced by at least 1µs. Following an 8-bit write

operation, there must be an interval of at least 40µs before the next communication. This

delay must be increased to 1.64ms following a clear display command.

Valid Data

0=command 1=data

D[7:4]

R/W

40µs1µs

Upper

4-bits Lower

4-bits

PicoBlaze Spartan-3E Starter Kit Initial Design 9

In this design, PicoBlaze is used to implement the LCD communication 100% in software. The fact that a processor is sequential in nature means that the

required delays can be formed simply by executing the appropriate number of instructions. PicoBlaze simplifies the task of writing code because all

instructions execute in two clock cycles under all conditions.

PicoBlaze Timing

CONSTANT delay_1us_constant, 0B

delay_1us: LOAD s0, delay_1us_constant

wait_1us: SUB s0, 01

JUMP NZ, wait_1us

RETURN

delay_40us: LOAD s1, 28

wait_40us: CALL delay_1us

SUB s1, 01

JUMP NZ, wait_40us

RETURN

The PicoBlaze program supplied implements a 1µs delay in software which it then uses as

the base for all operations. This subroutine is invoked with a ‘CALL delay_1us’ which then

LOADs register s0 with 11 (0B hex). This in turn causes the SUB and JUMPNZ instructions

to execute 11 times before RETURN completes the routine. This means that a delay of

exactly 1µs is formed by the 25 instructions each taking two clock cycles at 50MHz.

Creating other delays such as the 40µs required between 8-bit transfers is then a simple

case of calling the ‘delay_1us’ the appropriate number of times. In this case 40 (28 hex)

times results in slightly more than 40µs due to the executions of instructions within the

routine itself.

Exercise – Calculate the exact number of instructions, clock cycles and delay provided by

the ‘delay_40us’ subroutine. Prove your result either by simulation or preferably by

running a test design on the Starter Kit and making measurements.

LCD_pulse_E: XOR s4, LCD_E

OUTPUT s4, LCD_output_port

CALL delay_1us

XOR s4, LCD_E

OUTPUT s4, LCD_output_port

RETURN

The enable E pulse is formed by setting the E signal High on the output

port, waiting for 1µs and then driving E Low again. This oscilloscope screen

shot shows a single enable pulse observed at the LCD display pin. Data bit

D7 is also shown (see code on next page for more details).

1.08µs

Exercise – 1µs is greater than the 230ns minimum requirement for the enable

pulse width. Modify the code to generate an enable pulse which is 250ns.

PicoBlaze Spartan-3E Starter Kit Initial Design 10

The writing of 8-bit data is

achieved using the delays

and enable pulse routines

together with appropriate

setting the D[7:4] data bits,

RW=0 and RS=1.

Writing command

instructions to the display is

very similar but requires that

RS=0.

PicoBlaze Timing

LCD_write_data: LOAD s4, s5

AND s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0

OR s4, 0C ;Enable=1 RS=1 Data, RW=0 Write, E=0

OUTPUT s4, LCD_output_port ;set up RS and RW >40ns before enable pulse

CALL LCD_pulse_E ;write upper nibble

CALL delay_1us ;wait >1us

LOAD s4, s5 ;select lower nibble with

SL1 s4 ;Enable=1

SL1 s4 ;RS=1 Data

SL0 s4 ;RW=0 Write

SL0 s4 ;E=0

OUTPUT s4, LCD_output_port ;set up RS and RW >40ns before enable pulse

CALL LCD_pulse_E ;write lower nibble

CALL delay_40us ;wait >40us

LOAD s4, F0 ;Enable=0 RS=0 Instruction, RW=0 Write, E=0

OUTPUT s4, LCD_output_port ;Release master enable

RETURN

>1µs between E pulses writing upper and then lower nibbles 8-bit writes. >1µs between E pulses

1µs/div

44µs

PicoBlaze Spartan-3E Starter Kit Initial Design 11

Display Setup

Before the display can be used for the first time, there is an initialisation sequence which must be followed to allow communication to take place. These

sequences are ideally suited to an 8-bit processor such as PicoBlaze. Besides the relative complexity of the sequence, the process is only executed once

and then the processor is available to perform other tasks including the control on the display itself.

Hint - The PicoBlaze code provided includes a subroutine called ‘LCD_reset’ which performs this initialisation sequence.

Power

on Wait

15ms 4-bit write

= 3 hex Wait

4.1ms 4-bit write

= 3 hex Wait

100µs 4-bit write

= 3 hex 4-bit write

= 2 hex

Wait

40µs Wait

40µs

Exercise – Implement a hardware state machine which can perform the LCD initialisation sequence. Compare the size of your implementation with the 96

slices required to implement a PicoBlaze processor. Does the claim of the first paragraph hold true?

The 4-wire interface is now established which means that all subsequent communication is formed of the 8-bit writes described previously. Note that

these writes are all commands and therefore RS must be Low. The next part of the sequence is used to establish how the display should operate.

Function Set

28 hex Entry Mode

06 hex Display Control

0C hex Display Clear

01 hex Wait

1.64ms

Function Set = 28 hex : This code describes the display type as being 2 lines, 5×7 dots per character and using 4-wire communication (again).

Entry Mode = 06 hex

000001

Increment cursor position when writing a character

Do not shift display left or right when writing a character

10000011

Cursor (line under character) is off

Display is ON

Display Control = 0C hex

Cursor blinking off (character flashes)

The first part of this sequence is to establish that the 4-wire data interface is being used. Note that some of these delays are in milliseconds.

PicoBlaze Spartan-3E Starter Kit Initial Design 12

Display Control

The most common operation is simply to write ASCII characters to be displayed. These are considered to be data and hence RS will be High.

With the display set up as described previously, writing a series of characters will automatically result in their display on the top line of the display.

LOAD s5, character_S

CALL LCD_write_data

LOAD s5, character_P

CALL LCD_write_data

LOAD s5, character_A

CALL LCD_write_data

LOAD s5, character_R

CALL LCD_write_data

LOAD s5, character_T

CALL LCD_write_data

LOAD s5, character_A

CALL LCD_write_data

LOAD s5, character_N

S P A R T A N S

SSSSSSSS

Following the execution of this code, the display will look like this.

Cursor is here waiting for the next character to be written

If you continue to write characters, they will eventually fall off the end of the first line but they will not automatically

appear on the second line. This is because the memory map of this display is not consecutive from line to line. The

diagram below shows the memory address of each character location.

80 81 82 83 84 85 86 87

C0 C1 C2 C3 C4 C5 C6 C7

88 89 8A 8B 8C 8D 8E 8F

C8 C9 CA CB CC CD CE CF

Exercise – Although this design does make use of the scrolling display feature, it really is not recommended other than for simple messages as used in

this example. Analyse the supplied PicoBlaze code and LCD display controller data sheets to determine how scrolling is achieved. Implement a design in

which the message is greater than 40 characters per line (Hint – The memory map is actually 40 locations per line. Addresses 80-A7 and C0-E7).

Hint - The PicoBlaze code provided includes a subroutine called ‘LCD_cursor’. Load register ‘s5’ with the desired position. The upper nibble (value 1 or 2)

will define the line and the lower nibble the character position on the line (0 to F). E.g. s5 = 2B will position the cursor at the 12th position on line 2.

0123456789ABCDEF

To set the cursor in the position required for subsequent characters to be

displayed, the 8-bit memory address of that position must be written to the

display as a command (RS=0). Note that this can not be confused with any

of the other commands since the MSB is always ‘1’ in these addresses.

The ability to move to any particular location and write a few characters is

ideal for the display of various information as it becomes available such as

time, date, measurements and short status messages.

PicoBlaze Spartan-3E Starter Kit Initial Design 13

Complete PicoBlaze Program

This information is intended to give a guide to the way in which the PicoBlaze assembler code is organised. It is not intended to be a lesson in how to write

assembler code or explain how PicoBlaze works. Please refer to the documentation for PicoBlaze (KCPSM3).

Interrupt Service Routine

Scratch Pad Memory (SPM)

Fetch mode from

SPM and test

Store direction

and event in SPM

Interrupts occur every time the rotary control is rotated left or right.

The interrupt service routine (ISR) reads a value set into SPM by

the main program to determine if the LED display mode is using

the rotary control or slide/press button switches to determine if the

interrupt is relevant.

If the rotary control is relevant, then the direction of rotation is read

from the input port and stored together with an ‘event pending’ flag

bit. The main program monitors the SPM to determine if the LED

pattern should change and in what direction.

The position of the walking ‘1’ used in the rotary control mode is

also remembered in scratch pad memory.

Main program

Initialise LCD display

Set mode to rotary control in SPM

There are comments contained in the ‘control.psm’ file which should help explain the finer points.

Subroutines are used for

delays and LCD display

Read direction of

rotary encoder

Set event

pending flag

Write full messages to display memory

SPARTAN-3E STARTER KIT

www.xilinx.com/s3estarter

Enable Interrupts

Set walking ‘1’ LED pattern in SPM

00001000 = 08Hex

Read switches and Buttons

Output pattern to LEDs

Fetch walking ‘1’ pattern from SPM

Fetch rotary information from SPM

Test event pending flag

Output pattern to LEDs

Store walking ‘1’ pattern in SPM

clear flag

Shift ‘1’ left or right

No event

Delay 1ms

Read rotary press switch

and test state

Decrement counter

and test for zero

Load counter with 500(ms)

Toggle mode

Fetch mode from SPM

Switch/button mode

Read rotary press switch

and test state

Fetch mode from

SPM and test

Rotary mode

Event

up down

Call appropriate routine

Shift LCD display

Store mode in SPM

Delay 1ms

Decrement counter

and test for zero

Shift LCD display

>0 0

Load counter with 500

down

Program maintains 500ms shifting of

LCD display during mode switching

even if button is held down

Switch/button

function

Rotary function

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