83 lines
3.2 KiB
Python
83 lines
3.2 KiB
Python
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"""Implements a HD44780 character LCD connected via PCF8574 on I2C.
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This was tested with: https://www.wemos.cc/product/d1-mini.html"""
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from lcd_api import LcdApi
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from time import sleep_ms
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# The PCF8574 has a jumper selectable address: 0x20 - 0x27
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DEFAULT_I2C_ADDR = 0x27
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# Defines shifts or masks for the various LCD line attached to the PCF8574
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MASK_RS = 0x01
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MASK_RW = 0x02
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MASK_E = 0x04
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SHIFT_BACKLIGHT = 3
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SHIFT_DATA = 4
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class I2cLcd(LcdApi):
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"""Implements a HD44780 character LCD connected via PCF8574 on I2C."""
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def __init__(self, i2c, i2c_addr, num_lines, num_columns):
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self.i2c = i2c
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self.i2c_addr = i2c_addr
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self.i2c.writeto(self.i2c_addr, bytearray([0]))
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sleep_ms(20) # Allow LCD time to powerup
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# Send reset 3 times
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self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
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sleep_ms(5) # need to delay at least 4.1 msec
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self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
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sleep_ms(1)
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self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
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sleep_ms(1)
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# Put LCD into 4 bit mode
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self.hal_write_init_nibble(self.LCD_FUNCTION)
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sleep_ms(1)
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LcdApi.__init__(self, num_lines, num_columns)
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cmd = self.LCD_FUNCTION
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if num_lines > 1:
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cmd |= self.LCD_FUNCTION_2LINES
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self.hal_write_command(cmd)
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def hal_write_init_nibble(self, nibble):
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"""Writes an initialization nibble to the LCD.
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This particular function is only used during initialization.
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"""
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byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
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self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
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self.i2c.writeto(self.i2c_addr, bytearray([byte]))
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def hal_backlight_on(self):
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"""Allows the hal layer to turn the backlight on."""
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self.i2c.writeto(self.i2c_addr, bytearray([1 << SHIFT_BACKLIGHT]))
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def hal_backlight_off(self):
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"""Allows the hal layer to turn the backlight off."""
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self.i2c.writeto(self.i2c_addr, bytearray([0]))
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def hal_write_command(self, cmd):
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"""Writes a command to the LCD.
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Data is latched on the falling edge of E.
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"""
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byte = ((self.backlight << SHIFT_BACKLIGHT) | (((cmd >> 4) & 0x0f) << SHIFT_DATA))
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self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
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self.i2c.writeto(self.i2c_addr, bytearray([byte]))
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byte = ((self.backlight << SHIFT_BACKLIGHT) | ((cmd & 0x0f) << SHIFT_DATA))
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self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
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self.i2c.writeto(self.i2c_addr, bytearray([byte]))
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if cmd <= 3:
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# The home and clear commands require a worst case delay of 4.1 msec
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sleep_ms(5)
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def hal_write_data(self, data):
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"""Write data to the LCD."""
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byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | (((data >> 4) & 0x0f) << SHIFT_DATA))
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self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
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self.i2c.writeto(self.i2c_addr, bytearray([byte]))
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byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | ((data & 0x0f) << SHIFT_DATA))
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self.i2c.writeto(self.i2c_addr, bytearray([byte | MASK_E]))
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self.i2c.writeto(self.i2c_addr, bytearray([byte]))
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