PCA9539RPW,118 is a 16bit I²C-bus and SMBus low power I/O port with interrupt and reset. It is a 24-pin CMOS device that provides 16 bits of general purpose parallel input/output (GPIO) expansion with interrupt and reset for I²C-bus/SMBus applications and was developed to enhance the NXP Semiconductors family of I²C-bus I/O expanders. 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.