I2C 8-bit I/O expander. Adds 8 GPIO pins over I2C, used in LCD I2C backpacks.
| Pin | Name | Function | Type |
|---|---|---|---|
| 1 | A0 | I2C address bit 0 | I/O |
| 2 | A1 | I2C address bit 1 | I/O |
| 3 | A2 | I2C address bit 2 | I/O |
| 4 | P0 | I/O port 0 | I/O |
| 5 | P1 | I/O port 1 | I/O |
| 6 | P2 | I/O port 2 | I/O |
| 7 | P3 | I/O port 3 | I/O |
| 8 | GND | Ground | GND |
| 9 | P4 | I/O port 4 | I/O |
| 10 | P5 | I/O port 5 | I/O |
| 11 | P6 | I/O port 6 | I/O |
| 12 | P7 | I/O port 7 | I/O |
| 13 | INT | Interrupt output, active low | I/O |
| 14 | SCL | I2C clock | BUS |
| 15 | SDA | I2C data | BUS |
| 16 | VCC | Supply voltage | PWR |
The PCF8574 is an I2C 8-bit I/O port expander. It adds 8 general-purpose I/O pins via the I2C bus, using only 2 microcontroller pins. Up to 8 chips can share the same bus. Commonly used as the LCD I2C backpack controller.