LCD_IO 10 provides support for character LCD modules that use an I2C/TWI interface based on the PCF8574 or PCF8574A I/O expander. These expanders are commonly found on low‑cost LCD “I2C backpacks” sold under many brand names (YwRobot, Sainsmart, Joy‑It, generic blue/black adapters, and others).
Using mode 10
When using LCD_IO 10, the target PCF8574 or PCF8574A I/O expander port is configured by default as shown in the table below. Each bit of the byte variable i2c_lcd_byte is mapped to the appropriate LCD control or data line.
| Constant Name | Controls | Default |
|---|---|---|
|
I2C_LCD_E |
LCD Enable – Expander Port Bit |
|
|
I2C_LCD_RW |
LCD RW – Expander Port Bit |
|
|
I2C_LCD_RS |
LCD RS – Expander Port Bit |
|
|
I2C_LCD_BL |
LCD Backlight – Expander Port Bit |
|
|
I2C_LCD_D4 |
LCD Data Bit 4 – Expander Port Bit |
|
|
I2C_LCD_D5 |
LCD Data Bit 5 – Expander Port Bit |
|
|
I2C_LCD_D6 |
LCD Data Bit 6 – Expander Port Bit |
|
|
I2C_LCD_D7 |
LCD Data Bit 7 – Expander Port Bit |
|
If your I2C LCD adapter or PCB uses a different wiring arrangement, you can override the default configuration to match your hardware.
These overrides should be placed in your main program.
To apply an alternative configuration, define the following eight constants. Doing so replaces the default mappings shown in the table above.
#DEFINE I2C_LCD_E I2C_LCD_BYTE.1
#DEFINE I2C_LCD_RW I2C_LCD_BYTE.2
#DEFINE I2C_LCD_RS I2C_LCD_BYTE.0
#DEFINE I2C_LCD_BL I2C_LCD_BYTE.3
#DEFINE I2C_LCD_D4 I2C_LCD_BYTE.7
#DEFINE I2C_LCD_D5 I2C_LCD_BYTE.6
#DEFINE I2C_LCD_D6 I2C_LCD_BYTE.5
#DEFINE I2C_LCD_D7 I2C_LCD_BYTE.4