> Imagine our chagrin when days of trying to correct the > problem led to the conclusion that the diagnostic was incorrect.
I may have a situation like this in working on my FPGA PDP-10. The Processor Reference Manuals seem quite clear that the rotate instructions take E mod 256. One of the manuals I've found even adds that they never move more than 255 positions. And yet the diagnostics I have clearly want ROT AC,-256 to move 256 positions to the right, not 0. Not having a real PDP-10 to compare against, I don't know which is right. Doing it mod 256 would be easier; I had to add an extra rotor to my barrel shifter to handle the -256 case to make the diagnostic pass.
