In several documents including the book Spacecraft Attitude Determination and Control, reference was made to a NASA document by A. Merwarth. I've been unable to locate this document online. If anyone knows the process to request documents from NASA, this one would be good to ask for:

Merwarth, A., Multimission Modular Spacecraft (MMS) Onboard Computer (OBC) Flight Executive Definition, NASA S-700–55, March 1976.