-----Original Message----- From: cctalk [mailto:cctalk-boun...@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@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..
