According to Rabbit documentation, the following Rabbit revisions exist: Rabbit 2000, Rabbit 2000A, Rabbit 2000A, Rabbit 2000C, Rabbit 3000, Rabbit 3000A, Rabbit 4000, Rabbit 5000, Rabbit 6000.
However, on an RCM, I saw a processor marked as “R6000B-0-1200”, a number that looks like a Rabbit 6000B to me. So I guess, there is a Rabbit 6000A, too. Maybe there are further Rabbit revisions I don’t know about? And what was changed in these undocumented revisions vs. the documentd ones?
Looking at sysiodefs.lib, I can tell that there isn’t any code that differentiates between chips, but it is possible that there were multiple revisions.
I’m traveling but will check hardware at my office to see if I have anything marked with an earlier revision. I can also try reading GCPU and GREV from some early and recent boards to see if they report multiple revisions. I also see that the WriteIdBlock library stores the board’s GCPU and GREV register values.
It’s possible that there was a preliminary “A” revision that wasn’t used on production boards, and the “B” marking just identifies the released version of the chip.
The oldest Rabbit 6000 board I was able to find came from 2013 and it has the “R6000B” marking on the CPU. I’d say that it’s likely there was only one revision released publicly.