27 Apr
2008
27 Apr
'08
9:58 a.m.
On Sun, 2008-04-27 at 09:24 -0700, dwight elvey wrote:
-- snip --
TIN:
IN 1
ANI 2
JZ TIN
IN 0
RET
-- snip --
One thing I found invaluable on my 8080 was the console LED port at
0FFh. I'd stick an OUT 0FFH after IN 1 to see what's going on in real
time. Do you have anything like that on your system? Or at least some
way to watch port 1? It's clear that the system isn't seeing bit 2 of
port 1 activate the second time around.
If you can, try and swap it with another 8251, just in case. Like you
say, I doubt it would be the 8251 because it works once, but it's a
simple thing to do and it gets it out of the way, just in case it
happens to be the problem.
What system is this by the way?