import utime from lcd_api import LcdApi from machine import I2C # PCF8574 pin definitions MASK_RS = 0x01 # P0 MASK_RW = 0x02 # P1 MASK_E = 0x04 # P2 SHIFT_BACKLIGHT = 3 # P3 SHIFT_DATA = 4 # P4-P7 class I2cLcd(LcdApi): #Implements a HD44780 character LCD connected via PCF8574 on I2C def __init__(self, i2c, i2c_addr, num_lines, num_columns): self.i2c = i2c self.i2c_addr = i2c_addr self.i2c.writeto(self.i2c_addr, bytes([0])) utime.sleep_ms(20) # Allow LCD time to powerup # Send reset 3 times self.hal_write_init_nibble(self.LCD_FUNCTION_RESET) utime.sleep_ms(5) # Need to delay at least 4.1 msec self.hal_write_init_nibble(self.LCD_FUNCTION_RESET) utime.sleep_ms(1) self.hal_write_init_nibble(self.LCD_FUNCTION_RESET) utime.sleep_ms(1) # Put LCD into 4-bit mode self.hal_write_init_nibble(self.LCD_FUNCTION) utime.sleep_ms(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.writeto(self.i2c_addr, bytes([byte | MASK_E])) self.i2c.writeto(self.i2c_addr, bytes([byte])) def hal_backlight_on(self): # Allows the hal layer to turn the backlight on self.i2c.writeto(self.i2c_addr, bytes([1 << SHIFT_BACKLIGHT])) def hal_backlight_off(self): #Allows the hal layer to turn the backlight off self.i2c.writeto(self.i2c_addr, bytes([0])) def hal_write_command(self, cmd): # Write 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.writeto(self.i2c_addr, bytes([byte | MASK_E])) self.i2c.writeto(self.i2c_addr, bytes([byte])) byte = ((self.backlight << SHIFT_BACKLIGHT) | ((cmd & 0x0f) << SHIFT_DATA)) self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E])) self.i2c.writeto(self.i2c_addr, bytes([byte])) if cmd <= 3: # The home and clear commands require a worst case delay of 4.1 msec utime.sleep_ms(5) def hal_write_data(self, data): # Write data to the LCD. Data is latched on the falling edge of E. byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | (((data >> 4) & 0x0f) << SHIFT_DATA)) self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E])) self.i2c.writeto(self.i2c_addr, bytes([byte])) byte = (MASK_RS | (self.backlight << SHIFT_BACKLIGHT) | ((data & 0x0f) << SHIFT_DATA)) self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E])) self.i2c.writeto(self.i2c_addr, bytes([byte]))