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8b67270 May 13, 2018
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1. Driver for character-based LCD displays

This driver is for displays based on the Hitachi HD44780 driver: these are widely available, typically in 16 character x 2 rows format.


2. Files

  • Driver, includes connection details.
  • Test/demo script.

3. Typical wiring

The driver uses 4-bit mode to economise on pins and wiring. Pins are arbitrary but this configuration was used in testing:

LCD Board
Rs Y1
E Y2
D7 Y3
D6 Y4
D5 Y5
D4 Y6

4. LCD Class

4.1 Constructor

This takes the following positional args:

  • pinlist A tuple of 6 strings, being the Pyboard pins used for signals Rs, E, D4, D5, D6, D7 e.g. ('Y1','Y2','Y6','Y5','Y4','Y3').
  • cols The number of horizontal characters in the display (typically 16).
  • rows Default 2. Number of rows in the display.

4.2 Display updates

The class has no public properties or methods. The display is represented as an array of strings indexed by row. The row contents is replaced in its entirety, replacing all previous contents regardless of length. This is illustrated by the test program:

import uasyncio as asyncio
import utime as time
from alcd import LCD, PINLIST

lcd = LCD(PINLIST, cols = 16)

async def lcd_task():
    for secs in range(20, -1, -1):
        lcd[0] = 'MicroPython {}'.format(secs)
        lcd[1] = "{:11d}uS".format(time.ticks_us())
        await asyncio.sleep(1)

loop = asyncio.get_event_loop()

The row contents may be read back by issuing

row0 = lcd[0]

5. Display Formatting

The driver represents an LCD display as an array indexed by row. Assigning a string to a row causes that row to be updated. To write text to a specific column of the display it is recommended to use the Python string format method.

For example this function formats a string such that it is left-padded with spaces to a given column and right-padded to the specified width (typically the width of the display). Right padding is not necessary but is included to illustrate how right-justified formatting can be achieved:

def print_at(st, col, width=16):
    return '{:>{col}s}{:{t}s}'.format(st,'', col=col+len(st), t = width-(col+len(st)))
>>> print_at('cat', 2)
'  cat           '
>>> len(_)

This use of the format method may be extended to achieve more complex tabulated data layouts.