ASCI u68 (SystemX)

[Brent Hilpert]

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:
	http://www.old-computers.com/museum/computer.asp?st=1&c=758
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 display).

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).