BOAC posted an intressant link;
Fly-By-Wire A Primer for Aviation Accident Investigators
I have enjoyed reading the short description of how FBW systems operate and about C, C*, and G*U. In principle it looks almost like normal PI controllers and not PID ones. What strikes me is that all is written with the assumption that the controllers are analog and not digital. From my own experience - writing well performing digital controllers and their real-time performance is a very different story.
Regards