I've done a good deal more research inspired on the few hints djy gave and it seems that the RC770CDV was a universal remote that came with a laserdisc/cd/cdv player (the cdv770, I guess). Granted that's only based on correlation with the marantz cdv780 and rc780cdv laserdisc player and remote. From what I can figure out, the remote can handle ten devices including the LD player and the knobs were for frame jogging and scanrate changes.

I've figured out part of the programming routine. There's no apparent useable input/output port as the UART lines on the microcontroller are already used to decode the pushbuttons. Programming is done through plain old learning by pointing the originating remote at the rc770cdv. Seems absolutely all buttons are programmable except for the device selection keys and the knobs. The LCD shows the name of the active device (haven't figured out how to change that yet) the charge level of the battery, a transmission indicator, a graphical interface for learning/programming mode and five menu points (with associated buttons offscreen) that can be renamed. Seems the default configuration for the LD player uses the NEC infrared protocol or an extended version thereof (dedicated NEC ir transmission uC present as well and linked to the main uC, a Mitsubishi M50747 with an external SRAM chip of unknown capacity).

I'll contact Philips or Marantz tomorrow with that extra info to see if they can fish out an old manual from their archives.