[Ed in SoDak]

The X-10 system ran on the TI as I recall. It sent commands to modules that could control AC lights and appliances, all monitored and operated from a TI and other supported systems. Last I saw, there was still some people using this neat software/hardware application. That probably had some form of A/D conversion at its root.

There was also a PE Box card designed for prototyping. I'm woefully ignorant what it all entails. Maybe a cruise of the Micropendium archives would reveal some stuff. They reported on all sorts of TI modifications over the years. There used to be TI newsletter pretty much dedicated to hardware hacking. Probably archived on the whtftp site.

Plenty out there on TI internals in the reference books and manuals, get ready for some deep reading.

I was curious about it back then, but my own TI systems would often lock up during long unattended sessions, making it difficult to trust them to a 24/7 type of control of a "whole-house" system like the X-10.

A lot can be done if you know TTL, driver design and how to energize relays from a data or control line or via software. Any of these suggestions might help you with how to access specific data location to feed to an external circuit. Might be a long search, but I don't have anything specific to point you directly to what you seek.
-Ed