The story so far: I'm trying to reverse engineer a certain much- maligned gaming peripheral from circa 1990. I've already interfaced with it the way microcontroller-God intended and worked out the basic functionality, but I've reached the limits of trial-and-error. There are hidden features that never saw the light of day, embedded deep in the firmware. I can't blackbox them. So I did the only reasonable thing left to do and tore this thing's brain out!
This leaves me with a 44-pin PLCC-flavored COP888CL
Trouble is, those two documents refer to COP400 family devices, so I assume it's invalid for my COP888. Also, some closer inspection of the COP888 datasheet reveals that "Care must be exercised with the D2 pin operation. At RESET, the external loads on this pin must ensure that the output voltages stay above 0.8 Vcc to prevent the chip from entering special modes." Ok, that might be the way to access a "test mode" similar to the COP400... But there's no further mention anywhere of what these modes may be, or how to interact with them. Argh.
So it seems to me that there must be some way, somehow, of dumping this chip's onboard ROM. I mean they had to verify it at least once at the factory, right? And there are references to special modes on this chip, and even explicit instructions for doing what I want to do only with an ancestor chip. And that's where I am right now. I'm about to solder on an additional 8 lines to the D port so I can blindly try various combinations of these instructions in the hopes that I'll hit some dumb luck. But this is going to take a while even if I don't make any mistakes.
I get the feeling that this is the kind of thing I could spend a couple weeks on, yet maybe someone out there worked extensively with this line many years ago and knows exactly what to do off the top of their head or something. Or maybe there are faster/easier ways to pursue this.
Any thoughts? :)