This is the original starter module, it used to be required for all AE Modular setups, but there is now also a smaller alternate power module that can be used. A 9 volt power supply (wall wart) is provided with the starter kit, and it plugs directly into the top of this module. This module includes patch wire inputs for the bus signals (also derived from MIDI input) which are shared through the ribbon cable underneath to other modules, as well as 3.5mm mini jacks for MIDI in, two audio in/out and two control voltage in/out.
There are 2 LEDs to indicate incoming gate and clock MIDI signals. The MIDI options are for either "omni" or specific channel choices. By default the MIDI channel is 1, but 14, 15, or 16 can be used instead. I haven't tested it, so I'm not sure what the legato mode does.