The IBM RT mouse I have (Part No. OOF2383) is
definitly a protocol
mouse, as it has a HD63A01XOF processor for two encoders and two buttons
(
http://electrickery.xs4all.nl/tmp/rt_mouse.JPG).
I can check out the wiring and protocol (if not propietary) later.
Interesting how BIG is the processor used! :oO I'm amazed!