GPIO Expanders provide easy I/O expansion using standard serial interfaces such as I2C and SPI. They are especially useful in applications where pin count is limited on the microcontroller unit (MCU) or if remote inputs/outputs (I/Os) are needed. It is best to think of an 8-bit GPIO Expander like adding another 8-bit wide digital port to the MCU.

This application note discusses interfacing a 4×4 matrix keypad with MCP23X08 8-Bit GPIO Expander.