The EBlocks 3 expander board allows multiple EBlocks 3 boards to be connected to a single upstream EBlocks 3 port. The data pins are controlled using an MCP23S17 I/O expander IC via an SPI connection to the host microcontroller. The I/O expander provides digital input and output functionality as well as more advanced features such as interrupt on change.
The board features three DIP switches which are used to set the address of the I/O expander allowing for up to 8 expander boards to exist on the same SPI connections.