pico_i2c_lcd.py

   1 import utime
   2
   3 from lcd_api import LcdApi
   4 from machine import I2C
   5
   6 # PCF8574 pin definitions
   7 MASK_RS = 0x01       # P0
   8 MASK_RW = 0x02       # P1
   9 MASK_E  = 0x04       # P2
  10
  11 SHIFT_BACKLIGHT = 3  # P3
  12 SHIFT_DATA      = 4  # P4-P7
  13
  14 class I2cLcd(LcdApi):
  15
  16     #Implements a HD44780 character LCD connected via PCF8574 on I2C
  17
  18     def __init__(self, i2c, i2c_addr, num_lines, num_columns):
  19         self.i2c = i2c
  20         self.i2c_addr = i2c_addr
  21         self.i2c.writeto(self.i2c_addr, bytes([0]))
  22         utime.sleep_ms(20)   # Allow LCD time to powerup
  23         # Send reset 3 times
  24         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  25         utime.sleep_ms(5)    # Need to delay at least 4.1 msec
  26         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  27         utime.sleep_ms(1)
  28         self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
  29         utime.sleep_ms(1)
  30         # Put LCD into 4-bit mode
  31         self.hal_write_init_nibble(self.LCD_FUNCTION)
  32         utime.sleep_ms(1)
  33         LcdApi.__init__(self, num_lines, num_columns)
  34         cmd = self.LCD_FUNCTION
  35         if num_lines > 1:
  36             cmd |= self.LCD_FUNCTION_2LINES
  37         self.hal_write_command(cmd)
  38
  39     def hal_write_init_nibble(self, nibble):
  40         # Writes an initialization nibble to the LCD.
  41         # This particular function is only used during initialization.
  42         byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
  43         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  44         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  45
  46     def hal_backlight_on(self):
  47         # Allows the hal layer to turn the backlight on
  48         self.i2c.writeto(self.i2c_addr, bytes([1 << SHIFT_BACKLIGHT]))
  49
  50     def hal_backlight_off(self):
  51         #Allows the hal layer to turn the backlight off
  52         self.i2c.writeto(self.i2c_addr, bytes([0]))
  53
  54     def hal_write_command(self, cmd):
  55         # Write a command to the LCD. Data is latched on the falling edge of E.
  56         byte = ((self.backlight << SHIFT_BACKLIGHT) |
  57                 (((cmd >> 4) & 0x0f) << SHIFT_DATA))
  58         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  59         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  60         byte = ((self.backlight << SHIFT_BACKLIGHT) |
  61                 ((cmd & 0x0f) << SHIFT_DATA))
  62         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  63         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  64         if cmd <= 3:
  65             # The home and clear commands require a worst case delay of 4.1 msec
  66             utime.sleep_ms(5)
  67
  68     def hal_write_data(self, data):
  69         # Write data to the LCD. Data is latched on the falling edge of E.
  70         byte = (MASK_RS |
  71                 (self.backlight << SHIFT_BACKLIGHT) |
  72                 (((data >> 4) & 0x0f) << SHIFT_DATA))
  73         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  74         self.i2c.writeto(self.i2c_addr, bytes([byte]))
  75         byte = (MASK_RS |
  76                 (self.backlight << SHIFT_BACKLIGHT) |
  77                 ((data & 0x0f) << SHIFT_DATA))
  78         self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
  79         self.i2c.writeto(self.i2c_addr, bytes([byte]))