SWTPC 6800

Chris Elmquist chrise at pobox.com
Fri Aug 5 13:54:57 CDT 2016

On Friday (08/05/2016 at 11:23AM -0700), Brad H wrote:
> Okay thanks.  I gues where I'm getting confused is Michael Holley's guide to new 6800 users says because of the 6810 being cut you want RAM at $A000.. what you're suggesting sounds like the opposite?  Maybe I'd better reread those instructions.

MIKBUG and SWTBUG need the RAM at $A000 not $0000.  RAM at $A000 was
the original MEK6800-D1 reference design for which MIKBUG was invented
and the MP-A is likely derived.

As an aside, I have what I think is a kinda rare EXORBUS to SS-50
adapter that SWTPC may have made during development of the machine so
that an MEK6800-D1 could be used as the CPU board on SS-50 bus.  It is
an interposer with 86-pin EXORBUS socket on the top and (5) 10-pin MOLEX
on the bottom which mate to one of the SS-50 50-pin backplane locations.

It has SWTPC logo on it so I don't think it was a third-party deal.


> -------- Original message --------
> From: Brent Hilpert <hilpert at cs.ubc.ca> 
> Date: 2016-08-05  10:52 AM  (GMT-08:00) 
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> 
> Subject: Re: SWTPC 6800 
> On 2016-Aug-05, at 9:55 AM, Brad H wrote:
> > 
> > 3) Ah, this may be part of my problem.  I don't quite understand memory
> > addressing yet.  The instructions said you needed RAM at A000 if the 6810
> > chip was disabled (which it appears to be, the correct trace is cut).  My
> > machine has 4 RAM boards.  2 are MPM, 2 are 16K DRC boards.  For whatever
> > reason, the DRC boards are config-ed to be first (0000-3FFF) and second
> > (4000-7FFF).   Trying to strip the machine down and have as little RAM as I
> > could get away with, I just installed the single board at 0000-3FFF.  These
> > boards are (thank god) socketed, so I have some means of testing and
> > removing RAM.  The MP-M boards are not socketed, so I don't want to mess
> > with those until I have to.  I could config the second DRC board for the
> > $Exxx-$Fxxx and shove it in there.
> Don't take my word on the specific address, I should have just said you need some RAM in high mem.
> The 6810 was there to fulfill that need of RAM for the xxxBUG monitor.
> You might reenable it, or config a RAM board to cover that range (A000? to ?).
> But if you use a RAM board you have to config it so it doesn't extend up into (overlap) the ROM and IO address space.
> (I have a memory map for this on another machine not set up at this time).
> (For purposes of exercising the xxxBUG monitors you don't need memory down at $0000.)

Chris Elmquist

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