Wow, that predates (even) my time at Yamaha. The CP30 (how many Hall & Oates tunes used that classic electric piano)? You can probably still download the Owner's Manual from the Official Yamaha Download site. I'm not sure if it will be of much help. I'll ask to see if anyone remains from that era who can shed some more light on exactly what Yamaha was up to with that electronic piano. It stood as an alternative to the Rhodes (which was everywhere at the time).

I have CP35, it's a great instrument with the same high quality keyboard as CS80. It has even the velocity sensitivity. Sound synthesis is explained in Service Manual since page 10. You can download it from internet, Google is your friend.