Both MIKBUG and SWTBUG need RAM at $a000. Originally this was provided by a 6810, 128-byte SRAM on the MP-A CPU board. To run Flex and other stuff that wanted larger stack and workspace, people modified a 4K MP-M to reside at $a000 (instead of somewhere below $8000) and then removed the 6810 from the CPU board. This results in 4K of RAM at $a000 instead of 128 bytes but you need one or the other-- but not both and not neither 😉 else the monitor won't run and without 4K, Flex won't run either.
Chris On September 6, 2016 5:01:53 PM CDT, Brad H <vintagecompu...@bettercomputing.net> wrote: > > >-----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.. -- Chris Elmquist
