The CAT9555 is a CMOS device that provides 16-bit parallel input/output port expansion for I²C and SMBus compatible applications. These I/O expanders provide a simple solution in applications where additional I/Os are needed: sensors, power switches, LEDs, pushbuttons, and fans.The CAT9555 consists of two 8-bit Configuration ports (input or output), Input, Output and Polarity inversion registers, and an I²C/SMBus-compatible serial interface.Any of the sixteen I/Os can be configured as an input or output by writing to the configuration register. The system master can invert the CAT9555 input data by writing to the active-high polarity inversion register.The CAT9555 features an active low interrupt output which indicates to the system master that an input state has changed.The three address input pins provide the device's extended addressing capability and allow up to eight devices to share the same bus. The fixed part of the I²C slave address is the same as the CAT9554, allowing up to eight of these devices in any combination to be connected on the same bus.