PCA9555BSHP is a I²C-bus and SMBus I/O port with interrupt. It is a 24-pin CMOS device that provides 16 bits of general purpose parallel input/output expansion for I²C-bus/SMBus applications and was 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 smaller packaging. I/O expanders provide a simple solution when additional I/O is needed for ACPI power switches, sensors, push buttons, LEDs, fans, etc. It consists of two 8bit Configuration (input or output selection), Input, Output and Polarity Inversion (active HIGH or active LOW operation) registers. The data for each Input or output is kept in the corresponding input or output register. The polarity of the read register can be inverted with the Polarity Inversion register.