ASCI u68 (SystemX)

Brad unclefalter at
Fri Oct 16 21:30:36 CDT 2015

Here's some detail shots of the unit (including two of the front and back of
the mainboard).  Note the 6821 in the middle that has 'BAD' scratched into




-----Original Message-----
From: cctalk [mailto:cctalk-bounces at] On Behalf Of Brent
Sent: Friday, October 16, 2015 6:12 PM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at>
Subject: Re: ASCI u68 (SystemX)

On 2015-Oct-16, at 9:16 AM, Brad wrote:
> Hey guys,
> Posting this to various forums in the hopes of finding someone in the 
> know - I have this ASCI u68 system (6800 cpu) that I understand was 
> used in educational environments.  I kind of have it running but know 
> little about assembly language programming, etc.  Or the unit itself.  
> Have any of you ever messed with these?  It looks like it has a serial 
> connector on its mainboard.. was trying to figure out a way if I could 
> patch it to one of my terminals.
> Also trying to find some simple 6800 assembly programs/routines to 
> test it and see if it really works properly.  There is an MC6821S chip 
> on it (there are three of them actually) and one in the middle is 
> marked 'BAD'.  I understand those handle peripherals.
> I'd also heard rumours there was a second board available for these 
> that gave them BASIC.  I've never seen such a board for sale anywhere 
> - wondered if anyone had seen one in the wild.

I'm not acquainted with this model, but found pic here:
Too bad the pic is so small, can't make out much.

Looks like a pretty buffed out microproc trainer system, but such things
were getting a little passe by 1979, at least if that was a new design for
the 6800.
Motorola was producing a similar thing in the form of the MEK6800 3 or more
years earlier (Motorola Evalution Kit 6800, with hex keypad and LED

Having the keypad and LED hex display there, it's native mode is likely to
be running a monitor operated through that keypad & display.
What one would expect is to be able to enter machine language into memory
via the keypad and then jump to it to execute.
All sorts of things are possible. It could be using their own monitor, it
could be using a modified version of JBUG (moto's monitor for the MEK6800),
or MikBUG, it could have moto's serial line monitor in ROM which might be a
switch config option or you jump to via the keypad and then control it from
a console terminal, it might have routines for IO to the serial line in ROM,
and so on.

You can anticipate one of the 6821s will be for IO control of the keypad/hex
display, one of them is probably general purpose IO lines out to one of
those connectors.

If there is no 6850 or other UART, the third 6821 may be for a bit-banged
serial line, as moto had routines for doing that going back to their early
monitor and evaluation boards (which I never understood - it was more
trouble than just using their own 6850 UART).

A closeup pic could be a little more informative.

(I have some degree of experience with the 6800: written assorted assembly
programs for the 6800 going back to hand assembled programs for a moto
evaluation board in 1978, have a SWTPC 6800, and a MEK6800).

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