SWTP SS-50 Web page


Last update to this page, June 17 2023. All content (C) Herb Johnson 2023 except content created by others who retain copyrights as they see fit.

I have a little bit of SS-50 systems and Motorola processor based computers (excluding Apple Macs). But I lived and worked in the SS-50 era as a digital engineer. So I'm aware of its history and impact. In June 2023, a colleage and friend who revived SS-50 in recent years, Bob Applegate of Corsham Technology, passed away. So I constructed this Web page to consolidate my SS-50 and Motorola items and put them in context. - Herb Johnson

SS-50 History

The SS-50 6800 architecture created by SWTPC in the mid-1970's was well respected, not hard to build, and performed comparably to 8080 systems of the era. Other companies produced SS-50 products; in time some moved into other bus architectures that supported Motorola processors. FLEX OS was comparable to CP/M. And that base of software and hardware led to 6809 and 68000 SS-50 systems into the early 1990's. They found use as business and industrial systems and personal systems, again as did other 8 and 16-bit microcomputer architectures.

I discuss the SS-50 bus signals, on my Web page about a Z80 SS-50 board. Bob Applegate's SS-50 description as copied by me is on that linked Web page. For SS-50 board examples, my SWTPC 6800 system is described on paged as linked below.

As IBM PC's and compatibles began to dominate personal and business computing, and home-video-gaming computers became less expensive and consumer items; the class of boxey-bussed-board systems (SS-50, S-100, etc.) became out of favor in that space.

Several years ago, my colleague and friend Bob Applegate, revived production of SS-50 boards, and sold them under the business name Corsham Technology. Here's a 2018 photo of Bob, exhibiting SS-50 products at VCF-East in that year. Bob passed away in June 2023; that encouraged me to consolidate my SS-50 information through this Web page.

my SWTP 6800 system and related work

In mid-June 2010 I recieved a SWTP 6800 system from Bruce J. Black. I've described the items on my SWTPC 6800 Web page at the time. In July 2010I cleaned up the 6800 system, and powered up the dual floppy-drive portion, as described on this linked Web page

In May 2019, I obtained a Z80 based CPU board for the SS-50 bus! Check out the details on the SSZ-80 from Design Ltd.

In Feb-April 2019, I was contacted by Mike Lee who decided to restore his vintage MC1602 computer. The computer was based on the Motorola 6800, and used ROM monitors called "SmithBUG" and "MIKBUG". MIKBUG was provided by Motorola on their development boards and as source. With Mike's sources and binaries, I recovered Smithbug by Ed Smith, and found some history about it. Here's the details and code for Smithbug and MIKBUG.

I took some time in Nov 2011, to revive William Colley's 6800 cross assembler A68. It was written in C by William Colley and submitted by him to the old "C User's Group. It's compiled for 32-bit Windows in MS-DOS mode, using the lcc-32 C cross compiler which is freely available. - Herb Johnson

In Feb 2018, I obtained a EXORset 30 development system, Motorola 6809-based, from engineer Matt Jordan. He obtained it from another engineer who first worked with it in the 1980's. Thanks to them both, for preserving this system. In late April 2018, I brought The EXORset back into operation again. Here's the story of that system and its documentation. I also had EXORset correspondence in 2013 with Frédéric Le Duigou in France. He has a number of Motorola-based vintage systems including EXORset. Here's a Web page I made in Jan 2013 about his SWTPC 6800 and his collection.

Other SWTPC systems and related resources

In March 2013 I restored a Motorola MEK6800D2 board to operation. Sold it a few years later. But in 2019 I added some JBUG information to the page.

Michael Holley established a swtpc.com Web site, for the SWTPC 6800 and 6809 systems. The site was last edited in mid-2006. In November 2019, Michael Holley neglected to renew the domain name registration. But by Feb 2020, deramp.com mirrored the swtpc.com Web site.

In the fall of 2011, I corresponded with Martin Eberhard, another 6800 system owner. He has a number of MITS "Altair 680" systems. MITS created what became the S-100 bus with their Altair 8800 with the Intel 8080 processor. They are less-well known for their Altair 680. I created a Web page from Martin's correspondence about his work on restoring his Altair 680 system and some software he wrote to support it. [I do not have a MITS 680 system.]

Bob Applegate's Corsham Technology Web site.
Corsham Tech's github site.
As noted above, Bob passed away in June 2023, so these resources may not persist.

Contact information:
Herb Johnson
New Jersey, USA
To email @ me, see
see my ordering Web page.

Copyright © 2023 Herb Johnson