2 Mar
2005
2 Mar
'05
10:12 p.m.
Tony wrote...
Ah, but your memory is core, right? In which case, a
'read' is actually a
write followed by a restore. Since you can read the same location and
keep on getting the same data from it (you can do that, right?), the
memory is basically working (for both read and write).
Correct, I'm aware core
does the write after read. I'm suspecting unibus
trouble but see below...
You could try writing to something else (perhaps the
data register on
your conosle termial card) to see if you can write to anything on the
Unibus. Or if you have a logic probe, you could see if the data lines
pulse low when you try writing 1's to a memory location.
I'll have to
figure out what address my console card is. I'll see if there's
any docs on bitsavers for the M7800. If I'm reading some of the paperwork
correctly, whatever memory address the card is set for corresponds to a real
core location and I'd just read/write to that specific address (DEC has a
rather odd definition of the word "register" to me) to see if the problem
changes. However, if I have a unibus problem, isn't the M7800 which is in an
SPC slot still going across the unibus? I haven't had my logic probe out in
years... I thought it blipped on pulse high not pulse low. Surely that's
settable. I'll check :) More germane info below...
One thing I noticed I'm not sure I mentioned. When I turn on both power
supplies, 9 out of 10 times the system will come up with the pause and
master lights lit. No switches on the front panel will do anything at all.
Even setting the halt switch and hitting start (the lights change while
start is depressed, but when releasing start the lights go back just the way
they were and no switches change anything). The only way I found to turn on
the system and have the front panel come up active is to move the halt
switch to halt and then power up. Then I can read core, etc. I'm not sure
what this behaviour means, but reading some docs I have it sounds like this
indicates a problem with unibus getting to the memory.
Thanks for all the advice!
Jay West