Twiggys [was: Re: ka... ching!]

Brad H vintagecomputer at
Sun Oct 9 17:07:14 CDT 2016

-------- Original message --------
From: "Ian S. King" <isking at> 
Date: 2016-10-09  2:30 PM  (GMT-08:00) 
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at> 
Subject: Re: Twiggys [was: Re: ka... ching!] 

On Sun, Oct 9, 2016 at 2:37 AM, Dave G4UGM <dave.g4ugm at> wrote:

> > -----Original Message-----
> > From: cctalk [mailto:cctalk-bounces at] On Behalf Of Brad H
> > Sent: 09 October 2016 07:41
> > To: General Discussion: On-Topic and Off-Topic Posts
> > <cctalk at>; jwsmail at
> > Subject: Re: Twiggys [was: Re: ka... ching!]
> >
> >
> >
> > I'd like to learn more about programming, esp for my 6800.  It'd be fun
> to test
> > its limits and see what uses I can find for the graphics board I got. I
> just don't
> > understand how they programmed the thing. All the hex stuff throws me
> > off.  :)
> Does it have a serial interface and memory. In which case it was probably
> programmed in Assembler.
> When I started with 6800 board and 256 bytes of memory, and toggle
> switches to load it I used to hand assemble the programs to get the
> hex/binary.
> I soon got bored of the toggle switches and built a little box with an old
> calculator keyboard and display and some TTL so I could enter data quickly.
> Dave
> I recently acquired a SWTPC 6800, a machine I remember from when it was
new.  :-)  There are many programming environments available for it - I'm
working to get Forth running on mine, then I'll branch out.

It's been said that the 6800 inherited a lot of ideas from the PDP-8, and I
agree with that to some extent.  The ISA is actually very clean and neat,
once you wrap your head around it - I used to program 6800 assembler
professionally, my first paid job as a programmer!  Unlike the PDP-8, I/O
is memory-mapped.  Depending on what monitor ROM you have (if any), you may
have different system services available.  One very useful system is the
one that can read S-records from the serial input, allowing you to easily
transfer programs onto the machine.

If you want to grok the 6800 in fullness, there are online scans of
Motorola's programming manual for the device.  Another great resource is
the site, even if you don't have a SWTPC machine (what do you

Have fun with it!  Cheers -- Ian

Ian S. King, MSIS, MSCS, Ph.D. Candidate
The Information School <>
Dissertation: "Why the Conversation Mattered: Constructing a Sociotechnical
Narrative Through a Design Lens

Archivist, Voices From the Rwanda Tribunal <>
Value Sensitive Design Research Lab <>

University of Washington

>There is an old Vulcan saying: "Only Nixon >could go to China."

I've an original SWTPC 6800.  Also have an ASCI System X and a Tektronix 6800 board bucket.  Right now I'm enjoying working with the SWTPC.  I'm trying to deck it out as completely as one could have.
I don't quite understand assembly.. I assume to program in that, as with BASIC you need to load an 'assembler' language first?  I tried this with my Digital Group system with 5 different tapes marked 'assembler' but never got them to load.  Not sure if I understand the concept.

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