I/O Expander, 4bit, 400kHz, I2C, SMBus, 2.3V, 5.5V, TSSOP - 

The PCA9536DP is a 4-bit CMOS I²C-bus and SMBus I/O Port provides 4-bit of general purpose parallel input/output (GPIO) expansion for I²C-bus/SMBus applications and was developed to enhance the 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 and fans. This consists of a 4-bit configuration register (input or output selection), 4-bit input port register, 4-bit output port register and a 4-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 or output port register. The polarity of the read register can be inverted with the polarity inversion register. All registers can be read by the system master.