On 8/21/2014 12:30 PM, Tony Duell wrote:
I actually realized that late last night (and I feel like an
idiot for overlooking it). I've transcribed the ALU column over to a text
I'd better not start a thread pf the number of times I've felt like a
complete idiot. We'd all run out of disk space :-)
file and now I just need to reorder it by address
(rather than by symbol)
and convert it into a binary.
DEC (obviously) didn't wnt you to program your
own PROMs, they expected
you to buy spares from them :-). So the listings wre not designed as PROM
programmign files, there are there, esentially, to expalin the operation
of the machine. And very useful they are too.
Yes, they make debugging of the machine actually possible to
accomplish. The 11/05 manuals are very thorough, I'm finding them very
easy to follow.
Hve yuo made sure no oher microcode PROM gives all 1's? IIRC these are
open-collector outptu PROMs, so if the enable cirucitry fails, all
outputs float (And are puleld to 1's bu the external resistors).
So far, it looks like the A20A2 ROM may also be faulty. Amongst other
things, it controls the "Mode" bit for the ALU and it's always coming
out 1. So I suspect there are probably others but I figure I'll take it
one at a time. If they were socketed I'd just pull them and dump them
out but as it is I'll wait to see what else is broken first. There are
a lot of these things on these two boards!
The enable circuitry does seem to be OK, and the faulty A11A2 ROM does
have some non-zero data in it (verified while debugging by having my
logic analyzer trigger on a non-zero output and later by dumping it
after removing it from the board). I haven't examined it closely to see
if there's a pattern to the bad data or not, I suspect there probably is.