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"""Implements a HD44780 character LCD connected via MCP23008 on I2C.
This was tested with: https://www.adafruit.com/product/292"""
from lcd_api import LcdApi
from pyb import I2C
from pyb import delay
# The MCP23008 has a jumper selectable address: 0x20 - 0x27
DEFAULT_I2C_ADDR = 0x20
# MCP23008 Registers
IODIR = 0x00
IPOL = 0x01
GPINTEN = 0x02
DEFVAL = 0x03
INTCON = 0x04
IOCON = 0x05
GPPU = 0x06
INTF = 0x07
INTCAP = 0x08
GPIO = 0x09
OLAT = 0x0A
# Defines shifts or masks for the various LCD line attached to the MCP23008
# GP0 - NC
# GP1 - RS
# GP2 - E
# GP3 - DB4
# GP4 - DB5
# GP5 - DB6
# GP6 - DB7
# GP7 - LITE
MASK_RS = 0x02
MASK_E = 0x04
SHIFT_DATA = 3
SHIFT_BACKLIGHT = 7
class I2cLcd(LcdApi):
"""Implements a HD44780 character LCD connected via MCP23008 on I2C."""
def __init__(self, i2c, i2c_addr, num_lines, num_columns):
self.i2c = i2c
self.i2c_addr = i2c_addr
# Send IODIR address, set IODIR to all inputs, init all other registers 0
self.i2c.send(b'\x00\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00', self.i2c_addr)
# Set pins GP1 through GP7 to output, leave GP0 as input
self.i2c.mem_write(0x01, self.i2c_addr, IODIR)
# Send reset 3 times
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
delay(5) # need to delay at least 4.1 msec
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
delay(1)
self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
delay(1)
# Put LCD into 4 bit mode
self.hal_write_init_nibble(self.LCD_FUNCTION)
delay(1)
LcdApi.__init__(self, num_lines, num_columns)
cmd = self.LCD_FUNCTION
if num_lines > 1:
cmd |= self.LCD_FUNCTION_2LINES
self.hal_write_command(cmd)
def hal_write_init_nibble(self, nibble):
"""Writes an initialization nibble to the LCD.
This particular function is only used during initialization.
"""
byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
self.i2c.mem_write(byte | MASK_E, self.i2c_addr, GPIO)
self.i2c.mem_write(byte, self.i2c_addr, GPIO)
def hal_backlight_on(self):
"""Allows the hal layer to turn the backlight on."""
self.i2c.mem_write(1 << SHIFT_BACKLIGHT, self.i2c_addr, GPIO)
def hal_backlight_off(self):
"""Allows the hal layer to turn the backlight off."""
self.i2c.mem_write(0, self.i2c_addr, GPIO)
def hal_write_command(self, cmd):
"""Writes a command to the LCD.
Data is latched on the falling edge of E.
"""
byte = ((self.backlight << SHIFT_BACKLIGHT) |
(((cmd >> 4) & 0x0f) << SHIFT_DATA))
self.i2c.mem_write(byte | MASK_E, self.i2c_addr, GPIO)
self.i2c.mem_write(byte, self.i2c_addr, GPIO)
byte = ((self.backlight << SHIFT_BACKLIGHT) |
((cmd & 0x0f) << SHIFT_DATA))
self.i2c.mem_write(byte | MASK_E, self.i2c_addr, GPIO)
self.i2c.mem_write(byte, self.i2c_addr, GPIO)
if cmd <= 3:
# The home and clear commands require a worst
# case delay of 4.1 msec
delay(5)
def hal_write_data(self, data):
"""Write data to the LCD."""
byte = (MASK_RS |
(self.backlight << SHIFT_BACKLIGHT) |
(((data >> 4) & 0x0f) << SHIFT_DATA))
self.i2c.mem_write(byte | MASK_E, self.i2c_addr, GPIO)
self.i2c.mem_write(byte, self.i2c_addr, GPIO)
byte = (MASK_RS |
(self.backlight << SHIFT_BACKLIGHT) |
((data & 0x0f) << SHIFT_DATA))
self.i2c.mem_write(byte | MASK_E, self.i2c_addr, GPIO)
self.i2c.mem_write(byte, self.i2c_addr, GPIO)
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