SWTPC 6800 weirdness

Brad H vintagecomputer at bettercomputing.net
Tue Sep 6 23:56:22 CDT 2016

Okay I think I'm starting to figure this out a bit.  Beginning with basics, I cleaned up the contacts on all the SS50 pins.  The system seems to power up more reliably now.  Next, I poked around in the monitor to figure out exactly which addresses the modified MP-M board was dealing with.  Since it has 64 chips on it (32 ICs x with 32 more piggybacked), I assumed it probably has 16K.  I figured out it went from 8000 to around BFFF.  I think.

So next I installed the DR 16K boards.  I configured one for 0000-3FFF, and the second for C000-FFFF.  So that leaves 4000-7FFF uncovered.

So now I went to the second MP-M board.  This board has 8K installed, and I assumed it followed the MP-MX specs for upgrading to that.  But, it doesn't.  There were several cut traces and jumper wires.  I have no idea why or what for.  So I went and reversed all of that, and then set the address jumper to start at 4000.  That gave me 4K more of RAM, covering 4000-4FFF.  I don't know why it didn't give me 8K, up to 5FFF.  I'm thinking it has something to do with the way it was modded.

At any rate, the machine is almost fully decked out.  I was able to load TSC Basic without any issues.  Yay!  So I think next goal is figure out how to use the RAM diags properly and then sic those on it and see how things check out.

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