also have a look at Ardiono shield information/git incorrect for directions towards the hardware details. pay attention that the port that looks like an ethernet port is actually not an ethernet port but is used for the control chain protocol.
if you buy an arduino shield from mod devices (or make one yourself), you can interact with the various mod devices. unfortunately, currently, the hardware git can’t be successfully cloned but it should be updated soon.
there are some howtos from mod devices on how to use the arduino shield, e.g.,