Interfacing a 4×4 Matrix keypad with an 8-Bit GPIO expander

An application note from Microchip: Interfacing a 4×4 Matrix keypad with an 8-Bit GPIO expander

This application note discusses interfacing a 4×4 matrix keypad with MCP23X08 8-Bit GPIO Expander. This application note references the MCP23X08/17 GPIO Expander Keypad/LCD Demo Board (GPIODM-KPLCD). 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/O’s) 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 does not detail all of the features of the MCP23X08. Refer to the MCP23008/MCP23S08 Data Sheet, “8-Bit I/O Expander with Serial Interface” (DS21919) for more information.