Midwest Scientific Instruments 6800

Chris Elmquist chrise at pobox.com
Tue Aug 2 17:04:43 CDT 2016

On Monday (08/01/2016 at 08:24PM -0700), Brad H wrote:
> Thanks Chris.. yes I think you are correct.  Here is a photo of it:
> http://s1381.photobucket.com/user/unclefalter/media/20160520_194139_zpswkjgwf17.jpg.html

Yup. PERCOM LFD-400.  Two of the EPROMs on there make up their little "DOS".
It's pretty crude in the modern sense in that you deal with everything by
tracks and sectors and the MINIDOS+ extension in the second PROM adds
simple named files but otherwise you are just saving and loading memory
images to tracks and sectors on a floppy.  Nothing handles recovery of
deleted space or allows for non-contiguous blocks within a file.  They
were just getting started with floppies around 1977 when that board was
first available.

The entry point to this DOS was usually at $C000.   So, if you can figure
out how to get your monitor to jump to an address, that's where you'd want
to go to get the DOS executing.

I don't know what the third PROM would be for on your board.  It might be
driver extensions/support for another operating system or could be really
anything.  In my system, I put a Diablo daisy wheel printer driver into
that third PROM.  The PROMs are at $C000, $C400 and $C800.

With MIKBUG monitor, to jump to $C000, you would put that address into
RAM locations  $A048 and $A049.   $A048=$C0, $A049=$00 and then use
the "G" function to GO to that address.

With SWTBUG, the "Z" function jumped to $C000 directly.

Maybe your WEEBUG has "G" or "Z"??

With both MIKBUG and SWTBUG, you could examine and change memory with "M",

*M A048
A048 C0<cr>
A049 00<cr>
A04A 55<space><cr>

> This is the CPU board.  I'm wondering why it has four EPROMs, and what the two unmarked do.  This is where I wish there were a manual.. or even a good pic of an untouched original board to compare.
> http://s1381.photobucket.com/user/unclefalter/media/20160520_194018_zps8odxjmid.jpg.html
> I'd just settle for being able to fool around in the monitor.  But I think this monitor is called WEEBUG because it's very stripped down.

Yes. I haven't heard of WEEBUG until your posting.  And see nothing after
some web searching other than this old post,


Where a guy named "Dana Peterson (Arizon)" says he was the designer of the
MSI 6800.  Maybe he can be tracked down?

Good luck.  It's a nice system.


> -------- Original message --------
> From: Chris Elmquist <chrise at pobox.com> 
> Date: 2016-08-01  8:14 PM  (GMT-08:00) 
> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org>, Brad H <vintagecomputer at bettercomputing.net> 
> Subject: Re: Midwest Scientific Instruments 6800 
> I have all kinds of SWTPC 6800 stuff here and I think I recognize your floppy controller as a PERCOM LFD-400 board.  These are somewhat unique because they are built around a sync USART (S2650) and use 10-hole hard-sector floppy media (just like Heath H17 and Northstar systems).
> Can you see any PERCOM logo on the floppy controller board?
> Are there two 2708 EPROM on that board?
> Chris
> On August 1, 2016 12:32:49 PM CDT, Brad H <vintagecomputer at bettercomputing.net> wrote:
> >Just thought I'd send out another shout out to anyone who might have
> >one of these or is familiar with them.  I've had this a while but have
> >not really been able to use it, lacking a boot disk.  It also doesn't
> >have the standard MSIBUG ROM.  I'm hoping maybe someone out there knows
> >how I could procure the original ROMs and put this back to stock.
> >I made a video showing the current 'WEEBUG' ROM in case any are curious
> >or someone out there knows about it.
> >Thanks!
> >https://youtu.be/LY7yoAVxSrM
> >
> >
> >
> >Sent from my Samsung device
> -- 
> Chris Elmquist

Chris Elmquist

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