16-bit bidirectional I/O port
5.5V tolerant
25 mA sink
400 mA total current out
Low standby current as low as 1 µA

https://www.modmypi.com/raspberry-pi/iousbanalogue-expansion-1028/gpio-expansion-boards-1029/modmypi-mcp23017-hat-32-channel-io-expansion-hat uses similar chips in a DIP package.
High-speed I²C ™ interface up to 3.4 MHz

See also the MCP23[S]17 http://ww1.microchip.com/downloads/en/DeviceDoc/20001952C.pdf which is used in the PiDP-10