More info.
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.
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).
Any clues in there?
Roger
--
You received this message because you are subscribed to the Google Groups
"N8VEM-S100" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
