Rohm GPIO expander series are useful especially for the application that is in short of IO ports. We have mainly two kinds of GPIO expander.
One is equipped with GPIO ports that you can widely use such as control signals.The other is exclusively for Qwerty key encoding. This series can communicate with CPU through a few lines and expand IO ports to 8, 16 (corresponding to Qwerty keyboard), and 20 ports.
GPIO expander series are also equipped with some practical functions, such as interrupt output, built-in power on reset, 3V tolerant input, and NMOS open-drain output.