A Portable Serial Terminal That Should Be From The 1970s

The humble standalone serial terminal might be long gone from the collective computing experience, but in the ghostly form of a software virtual terminal and a serial converter it remains the most basic fall-back and essential tool of the computer hardware hacker. [Mitsuru Yamada] has created the product that should have been made in the serial terminal’s heyday, a standalone handheld terminal using a 6809 microprocessor and vintage HP dot matrix LEDs. In a die-cast box with full push-button keyboard it’s entirely ready to roll up to a DB-25 wall socket and log into the PDP/11 in the basement.

Using today’s parts we might achieve the same feat with a single-chip microcontroller and a small LCD or OLED panel, but with an older microcomputer there is more system-building required. The 6809 is a wise choice from the 1970s arsenal because it has some on-board RAM, thus there’s no need for a RAM chip. Thus the whole thing is achieved with only a 2716 EPROM for the software, a 6850 UART with MAX232 driver  for the serial port, and a few 74 chips for glue logic, chip selects, and I/O ports to handle keyboard and display. There’s no battery in the case, but no doubt that could be easily accommodated. Also there’s not much information on the keyboard itself, but in the video below we catch a glimpse of its wiring as the box is opened.

The value in a terminal using vintage parts lies not only in because you can, but also in something that can’t easily be had with a modern microcontroller. These parts come from a time when a computer system had to be assembled as a series of peripherals round the microprocessor because it had few onboard, leading to a far more in-depth understanding of a computer system. It’s not that a 6809 is a sensible choice in 2020, more that it’s an interesting one.

By comparison, here’s a terminal using technology from today.

38 thoughts on “A Portable Serial Terminal That Should Be From The 1970s

    1. You could have had something more portable than a Wyse, I did. About 30 years ago, after a small software company I worked for folded, I freelanced doing IT support and development to a number of the now-unsupported customers.
      I didn’t own the company’s IP but amongst other things, was able to concoct new shellscripts and C programs to produce new AR & GL reports and the like, plus do hardware and and software upgrades.
      On-site I used my Compaq LTE, a fine little DOS laptop with a small but good LCD screen, and that had a serial port. It was pretty heavy by modern standards, 2 maybe 3 kg perhaps. It also had an empty compartment in it for expansion (IIRC a modem?) but I used it to store a serial cable.
      My comms program of choice was Kermit (which I swear could talk to a broken toaster) I loved it so much. In my case it was to connect to Unisys 5000 machines (rebadged NCR Towers, SysVR2 Unix I recall) and NEC APC IV’s running Xenix, running our application in RM/COBOL (which was great – same compiled distributables for DOS, Xenix and Unix, no fuss).
      Got a lot of work done through that little LTE, both online and offline, it paid for itself a few times over.

    1. Yes, it is 6802. This is because to be use my 6802 computer PERSEUS-3 as an emulator for debugging. I tried making with 6802 without external RAM. The total of the display buffer, stack, and variables now uses 125 bytes of RAM space; the 6802’s internal RAM is 128 bytes, so it’s just barely there.

      1. WOOOOOOW!!!! I am in awe, Yamada-sama!!

        It sounds like you are ready for the Holy Grail of 8-bit programming: make a new game for the Atari 2600! The specs are even tighter than this project yet it displays to TV! Unless you already did it, of course…

        FWIW, my first computer was a Tandy / Radio Shack MC-10, the tiny Spectrum-sized short-lived sibling to the Color Computer (which did use the 6809); the MC-10 used the 6803 and both computers had specs way beyond what you’ve done here.

  1. I used to have an ADM-3a terminal I kept to configure and maintain certain systems. I had to continually guard it because people were always deciding to discard it. The ADM-3a — the terminal that looks like a urinal laid on its side. A big advantage was the integral keyboard (so people couldn’t throw that away leaving me with a useless terminal).

    Apart from the retro aspects of the internal design, the statement that this “can’t easily be had with a modern microcontroller” is patent nonsense though. I could be using a blue pill inside that box and nobody would know.

    1. My first terminal was a Teletype ASR-33, but I digress. My first home computer glass teletype was a Lear Siegler ADM-3A. And I soldered it together on my bedroom carpet! It has somewhere around 110 7400 series TTL I.C.s on a single large circuit board. Miraculously, it worked fine when I finished assembling it. I used that terminal for several years until I got a Hazeltine 1500.

      To your second paragraph, yes, of course you could put nearly anything in that retro box and make it work.

    2. We are now in the 21st century, and I think of it as a reliving of the technological legacy the 20th century. I think this is the same as if we could relive the 18th century by playing the music of Johann Sebastian Bach.

  2. I used the 6809 at the place I worked and did some Radio Shack Color Computer work on the side, but that is a processor only (a step up from Motorola’s original 6800) and I can assure you it has no on-chip RAM. You must be thinking of other 6800 parts, including those marketed as microcontrollers, like the 6801, 6802, 6805, 6808, etc.

  3. I love these retro character led displays but it’s a shame how relatively expensive they are. I know why they are but as much as I’d love to do more projects with them the cost is definitely a prohibitive factor.

    1. Configuring a character-rich indicator with an LED display like this one would cost more than 10 times more than an LCD, but I did this as a somewhat reckless example. It’s not viable as a mass production machine.

  4. The power consumption is horrible as well. They don’t use modern high efficiency LEDs, so they have to run a lot of current to get reasonable brightness. Anyone want to start up a manufacturing company to make these with modern LEDs?

    1. I made a “small” display with 32×4 characters with a bunch of 2nd hand display I lucked into awhile ago and with every character lit she sure gets toasty! I would love to see a resurgence of this style of display module using modern superbright led dies and embedded control semiconductor but I imagine the market would be pretty niche for that sort of thing when lcds and even oleds are much cheaper and more efficient still. The closest thing I’ve seen are a few people on the io page have designed their own tiny discrete led displays using tiny smd leds (I was inspired in turn to try this myself on a project or two).

      1. Okay, do we go all conspiracy theory on this? How about someone contacts a Chinese vendor of LEDs and asks about buying a quantity of bare die of various colors of modern GaN (etc.) LEDs. We keep ‘fishing’ vendors until one asks what we want them for–make it really clear we’re a small startup with a ‘big idea’. Bashfully explain the concept to them then wait for it to be ‘stolen’ and later buy the parts cheap on AliExpress.

        Sound plausable?

    2. In this terminal, the power consumption of the LED modules is set to a slightly darker setting, but when the @ character is displayed as 96 characters, it is 5V x 635mA = 3.18W. With LEDs, the power consumption fluctuates greatly depending on the number of characters displayed.

  5. He used an MC6802 which is more similar to MC6800 with RAM (and like the MC6803 processor in the Tandy MC-10) than the MC6809 (as currently indicated by the article). I love the aesthetic of his projects. Lots of brushed aluminum and Zamac.

    1. I tried making it with 6802 without external RAM.

      I use die-cast aluminum often because it is easy to process by hand. I mounted my homemade equipments in an enclosure so that it can be maintained and used for more than 10 years.

    1. I was never sure why the 6502 became the MPU of choice for so many home computers. Has to be just the price. When I was making my first computer (couldn’t afford any of the offerings in 1979), I ruled out the 6502 out of hand, because of its 256-byte limit on the stack, making it impractical to write a compiler for it. None of the other MPUs of the time had this kind of restriction, and I ended up using a Z-80A.

      1. There are stories discussing this all over: price was the reason the 6502 was developed at all, as Motorola was charging insane prices for their parts. I don’t remember how the Intel & Zilog (if they were around yet) parts compared, but the result was an entirely new semi company founded just to make the cheapest computer parts possible.

        There is even a story where they were selling them out of a drum at some swap meet or show for just five dollars! Moto’s price was 5-10x that!

    1. Does your parts bin have wrapping type IC sockets, etc.? Mini computers from the 60’s and 70’s and the computers in the Apollo spacecraft are also wired with wrapping.

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