6 Sep
2016
6 Sep
'16
3:01 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of william degnan
Sent: Tuesday, September 6, 2016 2:52 PM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Subject: Re: SWTPC 6800 weirdness
Brad,
You'll need to make electrical measurements, from the system checkout in
the manual. You very possibly will have marginal components that need to
be replaced, but it's best to try to locate which is bad rather that
to
replace at random.
A000 is not the same place as 0100. In the 64K
space, they're quite
distant.
Eliminate all but the one RAM board, setting it to
0000. Test that
thoroughly, then add the next at the next RAM space beyond the
first card.
Continue until you have enough RAM for a minimal
Flex boot. It
should
tell you in the version of Flex you're using how much that is (24K?)
It's hard to do everything at ?>the same time, break it down into chunks..
Bill
Thanks Bill. I've tried working with just single RAM boards, but like
I said, the only one that will work at all is this modified board. I
have pics of it here:
https://drive.google.com/folderview?id=0B4pq0-BHd2x6WVFiZHdyMHBlNW8&us
p=
sharing
If I could understand better what it is set up to do, what address
spaces its occupying, I might be able to understand why my 16K DRC
boards don't work when I try to put them to $A000. I'd prefer to work
with one of those boards first since the chips are socketed, and then
I could test the chips individually and be sure one whole board is good.
I note in one of my pics there, the cap on that modified MP-M looks a
little tarnished on the outside...
Getting a memory map of your system is an important step. You need to know what memory
addresses each board is attempting to use, so that there is no
overlap. Also remember that the ROM board has RAM on it too. You would
not want to map both boards to the same A000 space, but why do you need this at all? What
wants free RAM there? One important rule is that you don't want to
overlap RAM.
Can you get to a monitor prompt without any RAM
installed other than that which is in the ROM board?
b
Based on what I've read, you *have* to have A000 if your CPU card has been modified
for Flex 2.0, which I've verified mine has. When mods on the older MP-A cards are
done apparently it disables the onboard RAM, and that's where A000 would be. I could
reverse the mod but I'm not sure if I want to forgo FLEX use. So yeah, according to
SWTPC.com since that mod was done, I have to have a board at $A000. However, setting
either of my configurable ram boards to that space doesn't work. The system will only
boot with that weird MP-M in. So there's more to it than that.. probably mods above
and beyond.
I suppose it wouldn't be too bad to just reverse the Flex 2.0 mods and start there.
I'm doubtful if I'd ever use it and I could always reverse again if I do..