IBM cash register displays

OK, somewhat off-topic (maybe) and slightly less than the ten year mark (these things are dated '92) but anyway... I've just been given a couple of IBM cash register displays, IBM part 4863. They're dual height, 20-character dot-matrix displays. I was going to pull them apart and just use the display units themselves, but as these things have all sorts of built-in decoding logic in them I thought I'd ask here first... So, has anyone come across these before? I've found the pin connections for the 4-pin connector which they use for comms from the host system (12V, GND, 2 serial I/O lines - I assume one per line on the display) What I don't have is any information on the protocol that the host system uses to talk to these things. IBM defined a 12-bit device protocol which could be used for other devices, but I have no idea if that's what these things use (actually, they may have a character generator on-board, in which case they perhaps can't generate arbritary dot-patterns and so I'm better off just keeping the display units anyway) Long shot, I know, but I thought I'd ask here first... :) cheers Jules