Configuration is as I said: CompuPro CPU-Z80 @ 4 MHz, Digital Research Computers 64k static RAM, N8VEM serial card (port addresses @ 0Axh), and of course, the V3 card.
Send 92h to control port (33h), and I can read bits on port B and they make sense (i.e. correct bit positions - put +5 on B3 and read 08h, put +5 on B2,B3 and read 0Ch, etc., etc.). BUT, if I send 80h to port 33h, and then output 55h to port B, *ALL* port B pins show nothing. My logic probe doesn't even show them as "high" or "low". They don't register at all (almost seems that they are tri-stated?). I've tried other ports on the 8255 with the same result. I swapped 8255s and see the same result.
Roger are you sure you are sending the right configuration codes to the 8255. I don’t want to have to spend time going back and digging into that to find the bits are wrong. How familiar are you with the 8255?
Another curious thing is that there is activity on all RD*,WR*,and CS* of the 8255 while trying to output to port B. That shouldn't be, right? Shouldn't WR* and CS* be active, and RD* high? I can trace all three signals back to the GAL(2) ... pins 15,16, and 23 (if I remember correctly) show the same activity (all pulsing). Even when *ALL* I/O to the 8255 is stopped, RD* shows activity at the 8255 and the GAL(2) (but WR* and CS* are both high).
Absolutely incorrect! RD* & WR* are the generalized bus signals pulsing all the time. They are relevant to the 8255 ONLY when CS* is low.
Roger don’t take it personally, but I’m beginning to feel you are out of your depth hardware wise. Do you want just send the darn board to me and I will check it out.
If so send personal e-mail.
John
Any clues in there?
Roger