Wholy crap, I didnt know that was out there. There was a thread by dennis nedry that was discussing the HD20 and reverse engineering it. Maybe thats his site? info? I dunno.

Regardless, looking over the docs the protocol is actually really simple. Yea it was extremely complex back in the day though. I noticed it takes FULL Advantage of the state machine of the IWM, and it uses a dedicated PAL to break down the states into a workable addressing for the on board microcontroller.