The PCA9554PW is a 16-pin CMOS Device that provide 8 bits of general purpose parallel input/output (GPIO) expansion for I²C-bus/SMBus applications and were developed to enhance the NXP semiconductors family of I²C-bus I/O expanders. The improvements include higher drive capability, 5V I/O tolerance, lower supply current, individual I/O configuration and 400kHz clock frequency. I/O expander provides a simple solution when additional I/O is needed for ACPI power switches, push buttons, LEDs and fans. The PCA9554 consist of an 8-bit configuration register (input or output selection), 8-bit input port register, 8-bit output port register and an 8-bit polarity inversion register (active high or active low operation). The system master can enable the I/Os as either inputs or outputs by writing to the I/O configuration bits. The data for each input or output is kept in the corresponding input port or output port register.