SWTPC 6800 weirdness

william degnan billdegnan at gmail.com
Tue Sep 6 16:52:08 CDT 2016

> >
> >
> >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&usp=
> 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?


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