LCD programming Design and implementation details on the way to a valid SPI-LCD interface driver

LCD programming

Design and implementation details on the way to a valid

SPI-LCD interface driver

04/18/23 SPI and LCD , Copyright M. Smith, ECE, University of Calgary, Canada

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To be tackled today

How do you send commands from the Blackfin to a LCD device?

What commands are necessary to control the LCD device -- HD44780?

How do we get the timing correct?


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Functions we have now developed for Lab. 5 void Write_SPI_TDBR_ASM(ushort transmit_value);

• Write the value “transmit_value” to SPI TDBR register void ControlFLG5_ASM(ushort low_or_high)

• Activates FLS5 (select flag 5 bit)

• Sets FLG5 bit high or low as requested void WaitWhileSPIF_ASM(ushort low_or_high);

• Waits will SPI_STAT SPIF flag is low or high void Set_SPIregisters_ASM(ushort BAUD_SCALE) void Set_SIC_IMASK_ASM(ulong bit_to_set); void WriteSPI(ushort value) All we will need today


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Master / Slave conceptMaster to Slave data movement Master sends out

information to slave on MOSI wire

Slave receives information from the master on MOSI wire

SLAVE IGNORES INFORMATION UNLESS SLAVE SELECT LINE IS ACTIVE

Information (bits) is clocked by SCLK signal. • 1-bit, 1 clock tick

MOSI --MASTER OUT – SLAVE IN


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Now at the stage where we can do some experimenting with the hardware

We know that the following pins are “key” to the operation of the interface. • Place scope probes on these lines

MOSI – this will show the data being transmitted from the SPI interface

PF5 – chip select line• When this is pulled low, then the slave will accept any

data being transmitted, otherwise data is ignored• When this goes – low to high – then the serial data

transmitted to the slave is “latched” (converted into a parallel signal that is then sent to LCD as a data or a command request.


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Known facts -- MOSI data is transmitted from Blackfin the moment that data is written to SPI_TDBR

Blackfin Processor

LCD SCREEN SWITCHES (LOGIC LAB)

SLAVE INPUT INTERFACE SLAVE OUTPUT INTERFACE

MOSI MISO

SLAVE SELECTPF5 used (PF0 to PF7)

DATACONTROL

SPICLOCK

LOADSlave toLCD


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Known facts -- MOSI data is accepted by the SLAVE if slave-select is active low – PF5 is low – Master/Slave

Blackfin Processor



MOSI MISO


DATACONTROL

SPICLOCK

LOADSlave toLCD


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Known facts – The SLAVE only sends the data to the LCD when the PF5 line goes from low to high – interface design

Blackfin Processor



MOSI MISO


DATACONTROL

SPICLOCK

LOADSlave toLCD


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Current Solutions and Problems

Change to C++ programs as no longer taking directly to the hardware

ClearScreen( ) { WriteSPI(0x0001); }WriteLetter(char letter) {WriteSPI(0x0200 | letter); Call CursorMoveASM}

CursorMove ( ) { WriteSPI( 0x????); } etc

•How do we stop the LCD device from accepting too many commands?•How do we know when the LCD device is ready for the next command?


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ENABLE Signal


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Enable signal Enable signal works on the high-to-low

transition Send required signal to interface means

• Required signal + enable signal high• Wait long enough for voltages to “settle” (stabilize)• Required signal + enable signal low

• This strobes the information into the LCD screen

• Wait long enough for LCD command to work• How long is “long enough”?

• Required signal + enable signal high• Avoid “race” conditions to make sure that we don’t loose

the signal


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Hooking up the LCD

WATCH OUTDB lines are ordered L-to-R

LO to HIGHBut data bit connector lines are

labelled R-to-L


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Blackfin transmits 16 bits with THIS format

DB7, DB6, ………DB1, DB0

RS

1 – LCD data

0 – LCD instruction

R/W

1 – Read from LCD

0 – Write to LCD

E – Enable / Strobe

1 0 – When this line goes from high to the low, then the command is send to (latched into) LCD

To make LCD respond to command 0x4F0Then Blackfin must transmit 0x5F0 ( E High )0x4F0 ( E low )0x5F0 ( E high )


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LCD Instruction set


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Current Solutions -- Instruction


#define ENABLE_BIT 0x100#define R_W_BIT 0x200#define DATA_BIT 0x400

ClearScreen( ) {#define ClearDisplayCommand 0x0001;

WriteSPI(ClearDisplayCommand | ENABLE_BIT); Wait till voltages settle WriteSPI(ClearDisplayCommand); Wait for command to finish (1.64 ms – Lab 3 s, ms, us timer)

WriteSPI(ClearDisplayCommand | ENABLE_BIT); }


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Current Solutions -- Data


#define ENABLE_BIT 0x100 // Active low#define R_W_BIT 0x200#define DATA_BIT 0x400

WriteLetter( char letter) {

WriteSPI(letter | DATA_BIT | ENABLE_BIT); Wait till voltages settle WriteSPI(letter | DATA_BIT); Wait for command to finish (40 us – Lab 3 s, ms, us timer)

WriteSPI(letter | DATA_BIT | ENABLE_BIT); }


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Some commands

LCD COMMANDS

RS R/W DATA DB7 to DB0

ClearScreen( ) 0 0 0x01

CursorIncrease( ) 0 0 0x05

CursorMove( ) 0 0 0x10

DisplayOn( ) 0 0 0x0B

WriteLetter(value) 1 0 value

WriteLetter(‘a’) 1 0 0x61 (ascii ‘a’)

WriteLetter(‘A’) 1 0 0x41 (ascii ‘A’)


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SetUpDisplay( )

From the manual

Send command 0x30 – wait 4 ms Send command 0x30 – wait 4 ms Send command 0x3C – wait 4 ms Send command 0x3C – wait 4 ms

Don’t forget to send the command to “activate the screen” -- LCDDisplay(ushort On_or_OFF);


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You write the code for

LCDDisplay(ushort On_or_OFF); CursorMove(ushort left_or_right);


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This was the solution of writing “Hello” to LCD

SetUpDisplay( ); EnableDisplay( );ClearDisplay( );

UseFixedTimeASM( );CursorIncrease( ); UseFixedTimeASM( );DisplayOn( );

Use FixedTimeASM( );WriteLetter(‘H’); UseFixedTimeASM( );CursorMove( ); UseFixedTimeASM( );WriteLetter(‘e’); etc.

General concept was there,

Now fix the solution to write

“Happy Christmas” to LCD screen

Except for the wiring and demoLab. 5 is essentially done

Note: As of 24th October theSPI interface was unstable

for input to BlackfinDON’T connect input interface


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Details of what is needed


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Data to send a character Complicated or not? To cause “A” to appear on

LCD screen need bit pattern 01000001 = 0x41sent to LCD data pins

Also send the necessary LCD control signals

How do the letter bit patterns for the LCD data patterns relate to ASCII bit patterns? • standard format used to

store characters in a C++ character array?


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Now complete part of Lab. 4LCD as video screen

Now play the video game by moving the cursor on the LCD screen• Minimum requirements

• Move the cursor in response to temperature changes

• Print “player 1” wins if cursor moves all the way to the right

• Print “player 2” wins if cursor moves all the way to the left


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Information taken from Analog Devices On-line Manuals with permission http://www.analog.com/processors/resources/technicalLibrary/manuals/

Information furnished by Analog Devices is believed to be accurate and reliable. However, Analog Devices assumes no responsibility for its use or for any infringement of any patent other rights of any third party which may result from its use. No license is granted by implication or otherwise under any patent or patent right of Analog Devices. Copyright Analog Devices, Inc. All rights reserved.

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LCD programming Design and implementation details on the way to a valid SPI-LCD interface driver