Driving an Hitachi 44780 based LCD module

To learn more about how to control a 44780 based LCD, go here first so that you get an understanding of how to control this module.

In the meantime, here are three solutions for controlling a 44780 based module with a Parallax BS2.

Each program displays the message "Lennard Electronics www.lennard.net.nz" on the LCD.

Notes: I have used a 2 x 20 LCD. If you are using a 2 x 16 LCD, you will need to make a few minor changes to the code. Also, regarding the contrast pin (pin 3). The easiest thing to do, is to ground pin 3. Of course, you will not have control over contrast (you'll get full contrast), but it will get you started quicker. Details on contrast adjustment can be found on the page linked to above.

To save Microcontroller pins:

• SIPO - 6 or 7 pins (depending on if you need R/W or not)
• I2C - 4 or 5 pins (depending on if you need R/W or not)

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• Parallel connection

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• USB connection (links to another page)

SIPO solution:

'{$stamp BS2} '[DECLARE VARIABLES] StartScreen DATA "Lennard Electronics www.lennard.net.nz" 'Writes this to EEPROM 'at compile time Clock CON 0 ' Port 0 of the stamp = Clock to 4094. DataPack CON 1 ' Port 1 of the stamp = Data pin to 4094 Strobe CON 2 ' Port 2 of the stamp = Strobe pin on the 4094 Outputenable CON 3 ' Port 3 of the stamp = Outputenable on the 4094 RS CON 4 ' Port 4, Low = Instruction to the LCD, High = Data to the LCD RW CON 5 ' Port 5, Low = Write to the LCD, High = Read from the LCD EnableLCD CON 6 ' Port 6, Enable LCD character VAR BYTE cursorposition VAR BYTE i VAR BYTE 'Just a for loop variable '[MAIN CODE BEGINS] LOW EnableLCD LOW outputenable GOSUB resetcmos GOSUB setuplcd GOSUB DisplayStartupMessage END '[END MAIN CODE] '[ROUTINES] resetcmos: 'Reset the 4094 SHIFTOUT datapack, clock, msbfirst, [0] 'clear the 4094's registers PULSOUT Strobe,1 HIGH outputenable RETURN setuplcd: 'Now, setup the LCD HIGH EnableLCD LOW RS 'sending an Instruction to the LCD LOW RW 'Writing to the LCD SHIFTOUT datapack, clock, msbfirst, [56] 'LCD = 8 bits, 2 lines, 5x7 font PULSOUT Strobe,1 LOW EnableLCD PAUSE 100 'Turn the display off HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [8] PULSOUT Strobe,1 LOW EnableLCD PAUSE 100 'Turn the display on, without a cursor HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [12] PULSOUT Strobe,1 LOW EnableLCD PAUSE 100 'Clear the display HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [1] PULSOUT Strobe,1 LOW EnableLCD HIGH RS PAUSE 1 RETURN DisplayStartupMessage: FOR i = 0 to 37 READ i, character GOSUB sendtoLCD NEXT RETURN newline: 'Start on next line LOW RS HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [192] PULSOUT Strobe,1 LOW EnableLCD HIGH RS PAUSE 1 RETURN sendtoLCD: HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [character] PULSOUT Strobe,1 LOW EnableLCD PAUSE 1 GOSUB cursor RETURN ClearDisplay: LOW RS HIGH EnableLCD SHIFTOUT DataPack,Clock,MSBFIRST,[1] PULSOUT Strobe, 1 LOW EnableLCD PAUSE 100 'Turn the display on, with a cursor HIGH EnableLCD SHIFTOUT datapack, clock, msbfirst, [13] PULSOUT Strobe,1 LOW EnableLCD PAUSE 100 HIGH RS cursorposition = 0 RETURN cursor: cursorposition=cursorposition+1 IF NOT cursorposition = 20 then carryon GOSUB newline carryon: RETURN '[END OF ROUTINES]

I2C solution:

For more information on how to implement I2C, go here.

Click here for an example of how to drive a Matrix Orbital LCD display with built in I2C support.

Notes: the resistors are needed. The outputs of all I2C devices are open drain, so the 10k resistors are needed as pull up resistors. As the Stamp has totem pole outputs, there is a slight chance that a bus short could occur when being used with I2C, so the two 220 ohm resistors limit the current if that were to happen (example, if the I2C device pulled SDA low when the Stamp was outputing a High.

'{$STAMP BS2} 'I2C test program. 4/9/2002 Ben Lennard 'Bit Bashing I2C on a Parallax BS2 'Write to an LCD via the 8 ports of a PCF8574A Bidirectional 8 bit I/O 'chip meaning only 5 pins needed (4 if you don't need R/W on the LCD) 'STAMP EEPROM DATA Companyname DATA "Lennard Electronics " URL DATA "www.lennard.net.nz " 'CONSTANTS SCL CON 0 'I2C Clock line SDA CON 1 'I2C Data line LCD_RS CON 2 LCD_E CON 3 PCF8574_Write CON %01110000 'VARIABLES ack VAR BIT 'Acknowledge from the I2C bus I2C_data VAR BYTE 'Data to/from the I2C bus i VAR BYTE 'just a for loop variable LCDcharacter VAR BYTE start VAR BYTE 'Starting point in Stamp's EEPROM to read from finish VAR BYTE 'Finishing point in Stamp's EEPROM to read from   DIRS=%1111111111111111 LOW LCD_RS LOW LCD_E 'MAIN CODE Main: GOSUB LCD_Init 'Set up the LCD GOSUB DisplayStartupMessage 'Display a Message at System Power On '[END MAIN CODE] END '[SUBROUTINES] '************************ LCD SOUBROUTINES ******************************** LCD_Init: PAUSE 500 ' let the LCD settle LCDcharacter = 56 ' multi-line mode GOSUB LCD_Command PAUSE 5 PULSOUT LCD_E,1 PULSOUT LCD_E,1 LCDcharacter = 6 ' inc crsr, no disp shift GOSUB LCD_Command PAUSE 5 RETURN LCD_Command: LOW LCD_E LOW LCD_RS sendtoLCD: GOSUB StartI2C I2C_data = PCF8574_Write 'The address of the IC on the I2C bus GOSUB Write_data I2C_data = LCDcharacter GOSUB Write_data GOSUB StopI2C PULSOUT LCD_E,1 HIGH LCD_RS RETURN ClearDisplay: LCDcharacter = 1 GOSUB LCD_Command LCDcharacter = 12 GOSUB LCD_Command RETURN newline: 'Start on next line LCDcharacter = 192 GOSUB LCD_command RETURN '^^^^^^^^^^^^^^^^^^^^^^^ LCD SUBROUTINES ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   '*********************** I2C SUBROUTINES ********************************** 'Start Procedure. Set start condition on bus: SDA Hi-Lo while SCL Hi StartI2C: HIGH SDA HIGH SCL LOW SDA LOW SCL RETURN 'Stop Procedure. Set stop condition on bus: SDA Lo-Hi while SCL Hi StopI2C: LOW SDA HIGH SCL HIGH SDA RETURN 'Write Address/Data Procedure Write_data: shiftout SDA, SCL, msbfirst, [I2C_data] 'Check for Receiver Acknowledge RX_ACK: HIGH SDA DIRS=%111111111111101 HIGH SCL ack = IN1 LOW SCL DIRS=%1111111111111111 'if ack = 1 then indicate_NO_ACK 'debug "Acknowledged", 13 'RETURN 'indicate_NO_ACK: ' debug "NO Acknowledge", 13 RETURN '^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I2C SUBROUTINES ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ DisplayStartupMessage: ' "Lennard Electronics " GOSUB ClearDisplay ' "www.lennard.net.nz " start = 0 finish = 18 GOSUB ReadEEPROM GOSUB newline start = 19 finish = 36 GOSUB ReadEEPROM RETURN ReadEEPROM: FOR i = start to (start + finish) READ i, LCDcharacter GOSUB sendtoLCD NEXT RETURN '[END OF SUBROUTINES]

Parallel Solution:

'{$stamp BS2} '[DECLARE VARIABLES] StartScreen DATA "Lennard Electronics www.lennard.net.nz" RS CON 8 ' Port 8, Low = Instruction to the LCD, High = Data to the LCD RW CON 9 ' Port 9, Low = Write to the LCD, High = Read from the LCD EnableLCD CON 10 ' Port 10, Enable LCD character VAR BYTE cursorposition VAR BYTE i VAR BYTE 'Just a for loop variable '[MAIN CODE BEGINS] DIRS=%0000011111111111 'Set required ports (P10 - P0) as OUTPUTS GOSUB setuplcd GOSUB DisplayStartupMessage END '[END MAIN CODE] '[ROUTINES] setuplcd: 'Now, setup the LCD HIGH EnableLCD LOW RS 'sending an Instruction to the LCD LOW RW 'Writing to the LCD OUTl = 56 '00011100 LOW EnableLCD PAUSE 100 'Turn the display off HIGH EnableLCD OUTL = 8 '00010000 LOW EnableLCD PAUSE 100 'Turn the display on, without a cursor HIGH EnableLCD OUTL = 12 '00110000 LOW EnableLCD PAUSE 100 'Clear the display HIGH EnableLCD OUTL = 1 '10000000 LOW EnableLCD HIGH RS PAUSE 1 RETURN DisplayStartupMessage: FOR i = 0 to 37 READ i, character GOSUB sendtoLCD NEXT RETURN newline: 'Start on next line LOW RS HIGH EnableLCD OUTL = 192 LOW EnableLCD HIGH RS PAUSE 1 RETURN sendtoLCD: HIGH EnableLCD OUTL = character LOW EnableLCD PAUSE 1 GOSUB cursor RETURN ClearDisplay: LOW RS HIGH EnableLCD OUTl = 1 LOW EnableLCD PAUSE 100 HIGH EnableLCD 'Turn the display on, with a cursor OUTl = 13 LOW EnableLCD PAUSE 100 HIGH RS cursorposition = 0 RETURN cursor: cursorposition=cursorposition+1 IF NOT cursorposition = 20 then carryon GOSUB newline carryon: RETURN '[END OF ROUTINES]