The PCA9555 provides 16 bits of General Purpose Input/Output (GPIO) expansion for I²C-bus/SMBus applications. It is designed for a wide voltage range of 2.3 V to 5.5 V with interrupt and default pull-up resistors on GPIOs. Nexperia GPIO expanders provide an elegant solution when additional IOs are needed while keeping the interconnections to a minimum, for example, in ACPI power switches, sensors, push buttons, LEDs and fan control. The PCA9555 contains a set of 8 bit Input, Output, Configuration and Polarity Inversion registers. At power up all IOs default to inputs. Each IO can be configured as either input or output by changing the corresponding bit in the configuration register. The data for each input or output is stored in the corresponding Input or Output register. The polarity inversion register can be programmed to invert the polarity of the input register. The PCA9555 has an open-drain interrupt output which is activated when any one of the GPIO changes from its corresponding input port register state. The power on reset sets the registers to default values and initializes the device state machine. The PCA9555 has three address pins A0, A1 and A2 which can be used to configure the I²C bus slave address of the device. It allows up-to eight devices to share the same I²C-bus/SMBus.