The I/O expansion board allows multiple downstream boards to be connected to a single upstream port.

The data pins are controlled using an MCP23S17 I/O expansion IC via an SPI connection to the host controller.

The I/O expansion provides digital input and output functionality as well as more advanced features such as interrupt on change.

The board also features three DIP switches which are used to set the address of the I/O expansion allowing for up to 8 expansion boards to exist on the same SPI connections.

The auto ID functionality is forwarded onto the connected boards. Please note that only one board should be connected to ports labelled 1 and ports labelled 2 to allow the expansion pins to be unique and auto ID to function correctly.