The PCA9539 provides 16 bits of General Purpose Input/Output (GPIO) expansion with interrupt and reset for I2C-bus/SMBus applications. It is designed for a wide voltage range of 2.3 V to 5.5 V. 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 PCA9539 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 read register. The PCA9539 has an open-drain interrupt output which is activated when any one of the GPIO changes from its corresponding input port register state. INT can be connected to the interrupt input of a microcontroller. By sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via the I2C-bus. Thus, PCA9539 can remain a simple slave. The power on reset sets the registers to default values and initializes the device state machine. The RESET pin can be used to achieve same reset functionality without power down/up cycling by keeping active low. The state machine and the registers are in their default state until the RESET input is once again HIGH. This input requires pull up to V_CC. The PCA9539 has two address pins A0 and A1 which can be used to configure the I2C bus slave address of the device. It allows up-to four devices to share the same I2C-bus/SMBus.