Micropython - Driving an LCM4004A LCD with dual HD44780 (clone) driver chips

 

This is the display I'm using:

https://www.aliexpress.us/item/2251832722412443.html

There are a few vendors for these 40 column x 4 row displays, all using clones of the Hitachi HD44780 controller:

https://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller

These have a character pallet built in and have memory for 8 custom characters when needed.  And they have memory/wiring to support 80 characters on a display, so this 4004 display with 160 characters uses two drivers.  They share the same Data, RS, RW pins, but each have a separate enable pin to instruct them separately when writing to different lines of the display.

I didn't find any libraries specifically for this display, most of them are for 2004 or 4002 displays with a but this one from Adafruit gets pretty close - it's for the correct driver chip, but needed to be adapted to support two driver chips.  I ended up completely gutting this to get stuff working without the extra code, but adapted the setup sequence and write8 functions from here:

https://github.com/adafruit/Adafruit_Python_CharLCD/blob/master/Adafruit_CharLCD/Adafruit_CharLCD.py

I'm using an Arduino Nano Connect RP2040 here, so the pins will be a little different for a PI Pico or other chip. 

Generally, the way this works is we:

• Define our pins
• Initialize some globals with the values for specific instructions that the contorller understands
• Call the initialize function to turn the display on
• Subsequently use the "write8" function to write characters to the display.

What's left to do?

• Figure out how to control the cursor and write to specific locations on the display.
• Figure out how to turn on the backlight.
• Get contrast control working.  I tried to do this with a 10k pot, but the display isn't responding.
• Adapt this module to work with the fbconsole library for a fun terminal.

import time

from machine import Pin

D4 = Pin(26, Pin.OUT)

D5 = Pin(27, Pin.OUT)

D6 = Pin(28, Pin.OUT)

D7 = Pin(29, Pin.OUT)

E1 = Pin(12, Pin.OUT)

E2 = Pin(13, Pin.OUT)

RS = Pin(5, Pin.OUT)

# Commands

LCD_CLEARDISPLAY = 0x01

LCD_RETURNHOME = 0x02

LCD_ENTRYMODESET = 0x04

LCD_DISPLAYCONTROL = 0x08

LCD_CURSORSHIFT = 0x10

LCD_FUNCTIONSET = 0x20

LCD_SETCGRAMADDR = 0x40

LCD_SETDDRAMADDR = 0x80

# Entry flags

LCD_ENTRYRIGHT = 0x00

LCD_ENTRYLEFT = 0x02

LCD_ENTRYSHIFTINCREMENT = 0x01

LCD_ENTRYSHIFTDECREMENT = 0x00

# Control flags

LCD_DISPLAYON = 0x04

LCD_DISPLAYOFF = 0x00

LCD_CURSORON = 0x02

LCD_CURSOROFF = 0x00

LCD_BLINKON = 0x01

LCD_BLINKOFF = 0x00

# Move flags

LCD_DISPLAYMOVE = 0x08

LCD_CURSORMOVE = 0x00

LCD_MOVERIGHT = 0x04

LCD_MOVELEFT = 0x00

# Function set flags

LCD_8BITMODE = 0x10

LCD_4BITMODE = 0x00

LCD_2LINE = 0x08

LCD_1LINE = 0x00

LCD_5x10DOTS = 0x04

LCD_5x8DOTS = 0x00

def delay_microseconds(microseconds):

# Busy wait in loop because delays are generally very short (few microseconds).

end = time.time() + (microseconds/1000000.0)

while time.time() < end:

pass

def write8(value, enable_pin, char_mode=False):

"""Write 8-bit value in character or data mode. Value should be an int

value from 0-255, and char_mode is True if character data or False if

non-character data (default).

"""

print('write8', f'{value:#010b}', enable_pin, char_mode)

# One millisecond delay to prevent writing too quickly.

delay_microseconds(1000)

# Set the character/data bit

RS.value(1 if char_mode else 0)

# Write the Upper 4 bits

D4.value(((value >> 4) & 1) > 0)

D5.value(((value >> 5) & 1) > 0)

D6.value(((value >> 6) & 1) > 0)

D7.value(((value >> 7) & 1) > 0)

enable_pin.off()

delay_microseconds(1)

enable_pin.on()

delay_microseconds(1)

enable_pin.off()

delay_microseconds(1)

# Write the Lower 4 bits

D4.value((value & 1) > 0)

D5.value(((value >> 1) & 1) > 0)

D6.value(((value >> 2) & 1) > 0)

D7.value(((value >> 3) & 1) > 0)

enable_pin.off()

delay_microseconds(1)

enable_pin.on()

delay_microseconds(1)

enable_pin.off()

delay_microseconds(1)

def clear():

print('Clear')

write8(LCD_CLEARDISPLAY, E1) # command to clear display

delay_microseconds(3000) # 3000 microsecond sleep, clearing the display takes a long time

write8(LCD_CLEARDISPLAY, E2)

def initialize():

print('Initializing')

# Initialize display control, function, and mode registers.

displaycontrol = LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF

displayfunction = LCD_4BITMODE | LCD_1LINE | LCD_2LINE | LCD_5x8DOTS

displaymode = LCD_ENTRYLEFT | LCD_ENTRYSHIFTDECREMENT

for enable_pin in E1, E2:

write8(0x33, enable_pin)

write8(0x32, enable_pin)

# Write registers.

write8(LCD_DISPLAYCONTROL | displaycontrol, enable_pin)

write8(LCD_FUNCTIONSET | displayfunction, enable_pin)

write8(LCD_ENTRYMODESET | displaymode, enable_pin) # set the entry mode

clear()

if __name__ == '__main__':

initialize()

# Initialize the display.

for char in 'Hello World':

write8(ord(char), E1, True)

for char in 'Foo Bar! +~!123':

write8(ord(char), E2, True)