This library provides support for using PCA953X/5X chips. It provides two interfaces:

1. A class that supports all the functionality of the chip directly, including changing polarity of pins. This class is named PCA95XX.

2. An interface that is compatible with RPi.GPIO. This class is named PCA95XX_GPIO

The RPi.GPIO compatible interface allows you to simply plug the I2C class into existing libraries that expect RPi.GPIO. It does not support edge events or reading from output pins.

An example is AdaFruit's CharLCD library (which supports HD44780 compatible LCD's).

The following code will work with an LCD hooked up to a PCA9555:

from PCA95XX import PCA95XX_GPIO
from Adafruit_CharLCD import Adafruit_CharLCD

# Assumes a PCA9555 with 16 GPIO's at address 0x20
chip = PCA95XX_GPIO(0, 0x20, 16) 
# Assumes we are hooked up to pins 8, 9, 10, 11, 12, and 13 on the I2C chip
lcd = Adafruit_CharLCD(8,9, [10, 11, 12, 13], chip)

From this point, the lcd object will function as it does normally.

Note that this library requires python-smbus, and as a result, currently requires root permissions.

Support for the PCA957X series could be added, but the registers used are slighty different.

There is also a 24 GPIO version of these chips (TCA6424), which is not supported right now.