Controlling PCF8574 via i2c keypad

Hi folks, can anyone give me a example on controlling the pcf8574 using a pcf8574 i2c keypad? for example: if I press the "1" key, the "p01" output of the pcf will be enabled as long as the key is pressed. I've been interested in this since the discovery that a kenwood car stereo has an i2c output for controlling the cd loader. the idea would be to control a bluetooth audio module using the outputs of the pcf8574 controlled via the i2c output of the car radio.