Anyone have any idea how the XE-1 AP controller for the Genesis sent analog data over serial?

[RH 3,300]

As the name states, the Genesis had an analog controller and supposedly, it was legit.

I’ve done some brief searching and I’ve found some high-level, technical details on how the Genesis controllers worked, but I can’t figure out how an analog signal was sent across the line and how it was processed.  Also, what was the resolution?

If anyone knows how this device works, or how to send analog data over the controller port and how it’s implemented on a ROM? How can this be utilized in a homebrew project?

I’m thinking on taking on a personal project and I might try to build an analog interface to the Genesis for processing.

Anyone have any data, information or links that might help me figure this out, I’d appreciate.