The 8-bit home computer from 1975 you've never heard of

What we have here is a SWTPC 6800 Computer System from 1975. Looking at the machine, you might not guess that this machine is almost as old as the Altair 8800, only coming out about 10 months later! (And about the same age as me!) There are some fundamental differences with the approach this machine takes versus the Altair and some other neat features. Watch to see what's going on inside this machine.

There will be a few videos on this machine as I'm having an amazing time exploring it, so look for more neat stuff.

Part 1: This part!

--- Video Links

Mike Douglas's YouTube Channel with lots of videos on the SWTPC 6800:

South West Technical Products Company:

The SS-50 Bus used in this machine:

Adrian's Digital Basement Merch store:

Adrian's Digital Basement ][ (Second Channel)

Support the channel on Patreon:

-- Tools

Deoxit D5:

O-Ring Pick Set: (I use these to lift chips off boards)

Elenco Electronics LP-560 Logic Probe:

Hakko FR301 Desoldering Iron:

Rigol DS1054Z Four Channel Oscilloscope:

Head Worn Magnifying Goggles / Dual Lens Flip-In Head Magnifier:

TL866II Plus Chip Tester and EPROM programmer: (The MiniPro)

TS100 Soldering Iron:

EEVBlog 121GW Multimeter:

DSLogic Basic Logic Analyzer:

Magnetic Screw Holder:

Universal ZIP sockets: (clones, used on my ZIF-64 test machine)

RetroTink 2X Upconverter: (to hook up something like a C64 to HDMI)

Plato (Clone) Side Cutters: (order five)

Heat Sinks:

Little squeezy bottles: (available elsewhere too)

--- Links

My GitHub repository:

Commodore Computer Club / Vancouver, WA – Portland, OR – PDX Commodore Users Group

--- Instructional videos

My video on damage-free chip removal:

--- Music

Intro music and other tracks by:
Nathan Divino
@itsnathandivino

[Sevenfeet]

Oh I realize what this is. It was the first computer I ever used. My high school got one donated to it in early 1980 after a two week computer course that had been taught where students brought in their own PCs (Apple ][s. TRS-80 Model 1, Commodore PETs). The SWTPC I used had 8K of RAM, the cassette interface, a TV/keyboard and "Tiny BASIC" which took about 20 minutes to load from cassette. It was the 6800 that launched my IT career as I spent my free time as a 13/14 year old learning BASIC programming. Our school would then add a TRS-80 Model 1 with floppy drives (which never worked) that same year and a pair of Apple ][+ computers in 1981. I wish I still has for nostalgia purposes if nothing else. Thanks for featuring this.

[lindsayreid]

I bought and built one of these SWTPC computers. I even wrote quite a bit of software for it and had it working with the SSB disk drives, a Teletype 43 and later a SWTPC VDU/Keyboard combo which was in some kind of mouleded blue/cream case. I later also interconnected the SWTPC computer to a broadcast teletext receiver which let me save the "pages" to floppy disc. I also made my own S100 cards for memory and interfacing to Motorola exorciser boards. Everything was horribly expensive in those days amd one had to save up just to buy another 1K of memory! I'm pretty sure I still have some of the manuals tucked away somewhere. Sadly, I don't have the SSB DOS software you are are looking out for. Sadly all the hardware got ruined in a flood many years ago. Great memories - many thanks and the best of luck getting it operational. I still have 6800, 6821, MC14411 and 6850 Moiorola chips in anti-static tubes along with some 2102 memor chips (they were really fussy about static!).

[TechTimeTraveller]

The 6800 is one of my favorites. I have two 6800 system units, the AC-30 tape unit, several CT-1024s, the rare PR-40 printer, the ultra rare GT-6144 graphics board and the almost impossible to find joystick. The thing takes up an entire desk and a half when fully set up and the powerup sequence reminds me of a jet with all the switches!

[martindejong]

I took a train trip for 1.5 hours to visit a SWTPC shop in the city of Delft, one of the first "computer shops" in the netherlands, I was amazed by the enormous capacitors inside. And yes, they sold fully assembled machines, and also the terminal and some printers. I remember seeing a small cash register printer (40-columns) that was fitted on top of a square metal box.

[JohnMDiLiberto]

As a radio amateur as well as a retro computing enthusiast, it gives me great pride that radio amateurs of the '70s were a key demographic of early adopters of kit micro computers. And as an added historical bonus, Motorola was birthed in the 1920s, one of its earliest products being a car radio (not amateur), hence the name "motor" plus "ola" (derived from "Victrola").

[pieroc]

It's imposible to get tired of the "was saved from e-waste and actually given to me" sentence.
Kudos on you for this machine, can't wait to see it running.

[lesliefranklin]

A SWTPC 6800 was the first computer I had seen in person. The man who owned it used a teletype for I/O. That was probably in late 1975. Thanks for the trip down memory lane.

BTW, RAM chips were VERY sensitive to static electricity in those days. So often new RAM was damaged and so had to be tested as part of installation.
Also, since that is not a switching power supply, any short will most certainly cause smoke and likely cause a trail of destroyed components. Have fun. :-)

[amyslittlehelper]

This brings back many memories! I assembled several of these for customers while working for a distributor that carried the SWTPC product line back in 1976-79. This computer was designed to be as inexpensive as possible to buy. Using the MIKBUG rom monitor instead of a front panel full of switches and leds was a lot cheaper, though it did force you to have some sort of teletype or terminal to use the machine. The SS50 bus using Molex pin connectors was cheaper than gold fingered card edge connectors like the S100 bus used. The machine was simpler, easier to understand and a lot could be done with it. The 6800 was an under appreciated 8 bit CPU for its time.

[clomb]

Brings back fond memories of when I soldered together my first computer (Netronics Cosmac Elf - RCA 1802 with 256 bytes of ram).
Later built (soldering again) an S100 bus based 8088 system. 32 kb ram and 2 8 inch Shugart drives running CPM. Those were the days.
I look at my iPhone now and smile.

[FLDT-Alain]

So much memories. I have worked as a young trainee then beginner engineer on these machines. Actually only on the SWTPC 6809 as far as SWTPC-branded machines go. It was a very advanced machine with RAM page mapping allowing for up to 768K of RAM on an 8-bit CPU, running a small Unix-like O/S called UniFLEX.
As for the 6800, the French manufacturer Goupil was producing a machine that was very much inspired from this one from '79 on, the Goupil (the blue gen.1 and red gen. 2). Bus-based too, almost a clone actually, but a complete computer with a video controller, keyboard etc. I still remember the ROM monitor commands (was that MICMON?). It ran the FLEX 6800 o/s which was rather advanced for its time, booting from 5.25" or 8" floppies.

[lander]

Somebody loved this, I can tell it was an amateur who did everything themselves and probably learned as they went along. The dry lumpy looking solder re-work along with the Flux being left on the board as well as the lifted and re-worked solder traces are all dead give aways.

[Micro-Motive]

Even back in the 70s there was an Intel vs Motorola vs RCA community.
The S100 Buss was predominantly Intel 8080, 8085 and Zilog Z80 based, whereas the SS50 and non-S100 systems were predominantly Motorola and non Intel based.

Of course each Chip Company had their own proprietary Development Systems, varying from bare-board SBCs to fully assembled Systems with Professional Cases, Serial Terminals/Monitors, Dual 8" Floppy drives, DB25 Serial Ports, DB25 Parallel Printer Ports (Centronics Interface), and In-Circuit-Emulators (ICE).

The Intel iDS was one such offering which was used to develop Software and Hardware for Intel 80xx 8-bit Processors and Microcontrollers using the Intel Development OS, Assemblers Compilers and launguages such as BASIC and PL/M. It also ran Digital Research's CPM-80 and many CPM-80 supported softwares such as WordStar and Microsoft Basic.

There was a huge offering of SBCs, Built Systems, and Ancillary Boards and Peripherals in the late 70s and early 80s.

[jeromethiel]

I am so intrigued by this machine. This is so different, and yet the same, that it makes be smile. I am on the edge of my seat to see how it works out.

[TastyBusiness]

For a few years, a gentleman by the name of Michael Holley used to exhibit his SWTPC 6800 at VCF East. He had built the thing back in the 70s, and knew about every little nook and craney of that machine. There's a good chance if you come across online documentation about this system, it might very well have been hosted by him at one point.

[robin-g]

I saved one of these from a similar eWaste fate a year or so ago. I had no idea what it was when I got it. I really like the 6800 design. For me it was like the precursor design to the Apple 1 or 2 because it had addressable expansion slots and a ROM monitor. It’s a proper old computer. Looking forward to you getting this one working.

[Colin_Ames]

Fascinating stuff. I am looking forward to the next episode.

[paulstubbs]

Nice, years ago a work collegue had one of these (but in a wooden box). I wanted to get into the 6800, and this SWTPC machine had all I needed. So I grabbed a copy of it's memory map and I kind of cloned it.
Apart from the disk controller, I didn't copy their design, I used my own design, that perfectly copied it as far as software was concerned, so I could use all their software.
Mine was built entirely with wire-wrap, it had 3 serial ports, floppy, and 40KB of static ram using 2K ram IC's (6116).
I also built the floppy drive into the enclosure, but with provision for an extra external drive via a 37pin 'D' connector.
Pity I cannot post photo's here.

[clifffiftytwo]

Thank you so much for producing this video - it brought back so many memories from when I'd just graduated in EE and courses in digital electronics and computers were rare and new, often with xerox'd handouts rather than textbooks. I read all the magazines but a new engineer's salary still couldn't touch even the kit versions. I discovered the Motorola MEK6800D2 evaluation kit and begged one off of a Motorola engineering rep over the phone (still had to pay for it).
Not my first electronic assembly but it didn't work when I finished. I found an old Army electronics technician who let me watch as he went over the circuit carefully - he discovered two traces shorted together where the etching was incomplete and scraped it with a sewing needle until the kit leaped into life! 128 bytes of RAM which I upgraded to 256 bytes after waiting for my next paycheck.
Display was a huge issue since terminals were way too expensive as were TV modulators. The 'D2 kit got around this with the included hex keypad and LED display - I learned to hand assemble 6800 code and remember typing in a program for 10 minutes while a friend watched. It worked but all it did was blink one LED! My friend almost hurt himself laughing and told everyone the story anytime the subject 'computer' came up.
Sadly the 'D2 was recycled at some point. I'd love to have one now but they are way too expensive on e-Bay. My career included only using computers (not designing them) but they made an interesting hobby. I look forward to your newest videos and again - thanks for the memories...

[Fredthefat]

Fascinating insight into 70's tech. Thank you Adrian, look forward to the trying-to-get-it-run video.

[jamescaperelliiii]

Never heard of? I was about 12 or 13 years old and was drooling over that computer back in the 70's. At that age and at that time it might as well been a million dollars!