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I'd like to build an FPGA replica of a home computer based on the Intel 8080. I am not looking to design my own computer, since I would like to tap into an existing software base.

Were there any Intel 8080 based home computers?

To clarify, I would like something that meets the following criteria:

  • It is a general computing device, not a game console / arcade machine (this rules out Space Invaders)
  • A standalone machine (not a terminal like the Compucolor 8001)
  • Keyboard and video output (unlike the Altair 8800)
  • Boots to BASIC or comparably user-friendly setting
  • Non-CPU parts documented well enough; even better if an open-source emulator exists

I know there is no shortage of Z80-based home computers, so there's always the plan B of just extending my i8080 into a full-blown Z80 and going from that, but if possible, I'd like to avoid that for now.

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    See code.google.com/archive/p/vector06cc for a working example of an FPGA replica of an Intel 8080-based Soviet home computer. Be sure to check out the project wiki that has important technical details. Software-based emulation does exist, not sure about it being open-source, though. Either way, I think it would be quite realistic to get in touch with the authors as they are active on a Russian forum zx-pk.ru/forums/55-vektor.html. – DmytroL Jul 16 at 9:54
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The 8085, which came out two years after the 8080, rapidly became more popular for most applications because it required only +5 V power (as opposed to +5/-5/+12 V) and less external support circuitry. (Today there are a number of 8085 single-board computer designs available, such as glitchworks and OMEN; 8080 designs exist but seem few and far between.) Because of this, I'd suggest you should consider an 8085-based design, rather than an 8080-based design.

The supply voltage differences are obviously of no importance to you given that you're rolling your own FPGA, but the other 8085 changes make a slight to large difference depending on just to what extent you're going to emulate the hardware.

At one extreme you could simply emulate everything in the FPGA, in which case you may still want to include a few extra software-visible features that the 8085 had over the 8080, such as the SIM and RIM (set and read interrupt mask) instructions and the additional interrupts, just in case you want to port 8085 software from other systems to yours. (This shouldn't affect backwards compatibility at all.)

If you start to bring specific buses/signals out of the FPGA so that you could interface external parts to it the way you could with a real 8080 or 8085, there are more differences you'd need to be congnizant of, such as the multiplexed address/data bus of the 8085. (Intel's chips designed for use with the 8085 had built-in support for this.) But in this case you'd also need to be concerned about the interfaces presented by the original computer system you're emulating.

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    I'm happy to move from 8080 to 8085 given how small the difference seems. But are there any 8085-based home computer designs that are not modern hobby projects but mass-market enough that there could be a reasonably-sized software library? – Cactus Jul 16 at 9:29
  • @Cactus While not as popular as the Z-80 even when you exclude mass-market home computers (such as the ZX80, MSX systems, etc.), there were a fair number of 8085 systems out there back in the late '70s and early '80s, mainly running CP/M. ISTR that most commercial CP/M software was 8080-compatible, and even ZCPR, the famed Z-80 Command Processor Replacement, could be built in an 8080-compatible version until version 3.3, so I don't think you'll find huge issues with software support for an 8085-based system. – Curt J. Sampson Jul 16 at 10:20
  • That said, given that your focus is to find a (presumably commercial) "home computer" system rather than CP/M system, I don't think that the 8085 vs. 8080 distinction may make much difference for you. It's may well end up being just something to keep in mind should you a) want to port software from other systems, and/or b) interface 80s-era hardware with whatever you build. – Curt J. Sampson Jul 16 at 10:26
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    @Cactus Most notably for the 8085 would be the quite well selling Kyotronic 85 series (TRS-80 M100, Olivetti M10, etc.). They are stand alone, have BASIC, lots of other software, simple (and all parts obvious). Only TV out is not standard but needs an extension. Still, doing an all in one Kyotronic would be a cool project I'd love to see or may even join. – Raffzahn Jul 16 at 13:42
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    The very popular handheld computer TRS-80 Model 100 used the CMOS version of the 8085. You can probably find a lot of documentation for it. But as others said here, the actual good source is the CP/M 2.x universe, as it's 8080 compatible by design. – Francis Pierot Jul 17 at 14:41
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Were there any Intel 8080 based home computers?

Yes, but the number is rather small, as at the point when the idea of a home computer as we know it today (and you describe) became popular, better 'versions' of the 8080 were already available, most notably the 8085 and Z80. Importantly for low cost computer design, they did away with -5 and +12V supply, thus simplifying power supply design a lot.

Some on this list may be

  • SOL 20 of 1976. As early as it can get for a desktop computer.
  • Compucolor II of 1977. A prototypical home computer due to its consequent consumer design.
  • Interact Home Computer of 1978. Already quite late for an 8080 machine and mainly sold even later by liquidators. It might not fully fit your needs as the BASIC needs to be loaded from tape.
  • Micronique Interact of 1980 (!). The same machine, but now made and sold by a French company.
  • DAI Personal Computer of 1980. Originally designed to be the (European) TI home computer. Eventually the most ambitious machine of them all. Quite a great design for back then.

As said, the time of the 8080 for new designs was already long gone when home computers became a thing, so these are rather oddities - at least in the west. History is different within the former east bloc as their hardware/CPU development lagged behind (due to cloning), while information about microprocessor applications was ready available (as Wilson already mentioned).

There are 8080 clones like the Russian КР580ВМ80А (1979) or the Polish MCY7880 (introduced rather late in the early 1980s). All of these machines were rather plain 8080 systems. Starting from Kits like Micro-80 and Радио-86РК all the way to quite modern, feature-rich systems like Vector-06C and Orion-128. The landscape was at least as diverse as in the West, if not more. All with a certain time shift.

More relevant to your task would be the rather large selection of software these machines featured, as each had (in their countries) a quite strong fellowship. On the down side, it's usually in the local language with no English documentation and hard to find, as relevant web pages are also in the same language - Google Translate is only a help after a relevant page is found.

Of all the Eastern 8080 based machines, the Czechoslovakian Tesla PMD 85 is worth a look. Despite its name, it's not an 8085 CPU, but their own MHB8080A (the semiconductor division is nowadays part of ON Semiconductor). The machine is not only remarkable for its huge amount of available software, but also for having evolved over the years from B&W to colour and into several spin-offs like the MATO - while the basic hardware is rather straightforward.


An oddity here was the otherwise usually advanced East Germany. While following the Intel lane (unlike Bulgaria), they skipped the 8080/8085 steps and went directly from i8008 (U808) to Z80 (U880) - which is a story of its own. Thus even their earliest kits (LC80) and home/small computers (Z9001/HC900) used it from the start.

Then, why not use using some Hungarian machine? Sure, all (genuine Hungarian) machines I know of (Mikrokey Primo, Triton, Aircomp) are Z80-based, but it should be fairly simple to adjust the design to work with an 8080 - especially in FPGA, were the RAM is embedded anyway. After all, you should have much less hassle to dig up documentation and software for these, shouldn't you? :)) Of course, you may need some backward translator Z80 to 8080. So not much fun.

An only slightly different way would be switching the 8080 for an 8085, like Curt sugested. In most respects, the 8085 is only a hardware update to simplify system build. Only two official new operations were included, which in addition almost never got used in full. Of course it had some lesser known but quite handy extensions.

While I can't think of a plain 8085 home computer, the CPU is most notable for being used by the quite well selling Kyotronic 85 series - usually disguised as NEC 8201/8300, Olivetti M10, Tandy M100/M102. They are stand alone, have BASIC, lots of other software (in ROM and loadable), are simple (all parts obvious). Only TV out is not by default but needs an extension. Now, doing an all-in-one Kyotronic would be a cool project I'd love to see - or may even join.


Conclusion:

I'd like to build an FPGA replica of a home computer based on the Intel 8080.

  • If you want to have some software to choose, you may settle for the Interact as the basic documentation is available in English (more advanced and most software in French) or any of the eastern (and learn Czech, Russian, ...)

  • If you want hardware that allows to build your FPGA system in incremental but complete steps, the PMD 85 is your choice.

  • If you want a well defined and satisfying system with lots of extraordinary features and few but awesome (system) software, go for the DAI (some French/Dutch might be helpful).

  • If you want to have something with a huge user and software base, maybe even useful today, go for the Kyotronic 85 (no Japanese required) .

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    Heh din't know that there was i8080 based Maťo. I know only of ZX clone named Maťo which was Z80A based. But I did not pay much attention to i8080 computers back then other than PMD-85 and Didaktik Alfa/Beta. btw the PMD-85 was a year when they developed it (1985) – Spektre Jul 17 at 8:39
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    @Spektre (Caveat: I got no idea about Czech in particular) I've been told once that Matoa (sp?) has a meaning of 'Ghostly' in Czech, so it might have been popular choice for a computer, wouldn't it? (And BTW, I most definitely need these magazines). – Raffzahn Jul 17 at 9:22
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    LoL ... I believe you meant Mátoha that can be a ghost but it refer to some ugly slow monster like creature lurking in the dark (like mud-made elementals) but mostly it address the stage when you wake up in the morning before the first cup of tea or coffee and you are sluggish like a Mátoha... the name Maťo is just familiar version of Martin. In Czech word Duch is what you call Ghost in English. – Spektre Jul 17 at 9:31
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    Heh :) fits exactly ... anyway 8bit was a thing a long after 1989 in eastern Europe... I moved to x86 platform from Z80 only around 1995 ... as the 16 bits where too expensive and hard to get back then ... not to mention there where very few people using it ... I think around 1993 the weights started to favor x86 platform in here (Former CzechoSlovakia ...) – Spektre Jul 17 at 11:17
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    @Raffzahn: we used to tell a joke back then: When the first 80386 gets to Czechoslovakia? When the US fires at us a Tomahawk missile. – Edheldil Jul 18 at 14:04
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The Intel 8080 was apparently not that popular in the West for home computers. I think it was more marketed at industrial control or whatever, but I can't say for sure. Either way, Intel soon came up with its successors, the 8088 and so on, so the plain old 8080 wasn't that common.

But in the Soviet Union the KR580VM80A is basically the same thing as an 8080. It saw some use in some home computers (but was markedly less common than Z80 derivatives and PDP-11 derivatives).

The Orion-128 and Specialist are two examples of DIY computers that match your criteria, except that they boot to a monitor, not to BASIC.

The Baltijets Juku from Estonia I believe booted to BASIC, but I don't know that much is known about its internals.

The Vector 06C from the Moldovan SSR is at any rate well-understood and boots to BASIC and has a library of software including homebrew games and has a lively community even today.

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    Wow, what a pleasant surprise to see Vector 06C mentioned on StackExchange! And, more surprisingly, it already has an FPGA replica: code.google.com/archive/p/vector06cc – DmytroL Jul 16 at 9:51
  • I would add Lviv PC-01(vcfed.org/forum/showthread.php?31665-Lviv-PC-01) as well as perhaps Irisha, Korvet and several others. Korvet in particular would be an interesting challenge to create an FPGA replica as it was one of the most powerful Soviet machines running on Intel 8080. – DmytroL Jul 16 at 9:59
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    By the way, the Lviv PC-01 has a mixture of Russian and Ukrainian on the branding! From what I can tell it really says "Персональный компьютер Львів" on the front. What's up with that? Was that normal in Soviet Ukraine? – Wilson Jul 16 at 10:14
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    The Juku does boot into BASIC if ROMs are present. Otherwise (with the Bulgarian disk drive) it's a plain CP/M machine. At least mine is that way. – Raffzahn Jul 16 at 12:09
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    @Wilson Yes, this was normal. In the times of USSR (and Soviet Ukraine was a part of USSR till late Aug, 1991) Russian was the official language used for labeling because computers produced in Soviet Ukraine could be sold in Soviet Russia or any other part of the USSR. However, make/model names such as Львів could exist in a national language. – DmytroL Jul 17 at 10:58
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I've found two computers that fit my bill of a "home computer" that use the Intel 8080 processor:

  • The Compucolor II from 1977 uses an SMC CRT5027 / TMS9927 video chip to produce color graphics. An open source emulator is available on GitHub. This one is very promising.

  • The Interact Model One from 1978 has a name that is very unsuited for googling, after all, which computer didn't have a Model One and what emulator isn't Interactive... I've found this page in French but the downloadable Zip only contains a Windows executable.

  • +2 for the Interact :) – Raffzahn Jul 16 at 12:10
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PMD85 was reasonably popular in Czechoslovakia, there is a lot of documentation (if you can to read Slovak or Czech), there are several emulators, including an Open Source one.

  • Good point. Where was the CPU sourced? It was cloned/manufactured in CS or imported from GDR or USSR? – Wilson Jul 16 at 8:18
  • Also there was a very similar (but much less popular) computer called Maťo, basically forgotten today – Wilson Jul 16 at 8:21
  • @Wilson It used a local Czechoslovak clone (MHB8080) – Radovan Garabík Jul 16 at 10:35
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    @Wilson (re: Maťo) there were also other clones, (unlike Maťo) quite compatible with the original PMD85 - Didaktik Alfa & Beta. Maťo has the dubious fame of being perhaps the last 8-bit computer aimed at low cost home market, while simultaneously not being compatible with anything ("almost compatible" does not count) – Radovan Garabík Jul 16 at 16:44
  • @RadovanGarabík +1 for the Didaktik Alfa/Beta everyone knows just Z80 based Gama these days – Spektre Jul 17 at 12:11
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The DAI Personal Computer (Belgium, 1980) used an 8080A. It had some interesting features (optional maths coprocessor, servo-controlled microcassette data storage) but was rather expensive.

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I think the 8080A based Triton meets your requirements (although it was a kit computer).

http://www.computinghistory.org.uk/det/6210/Transam-Triton/

I remember adding a S100 based 8K memory expansion out of 2114L chips.

I regret chucking it out when I moved home.

  • Great one - forgot about that. Thanks. – Raffzahn Jul 16 at 21:19
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I don't know if these meet all of the criteria, but posting them since no one has .

Polymorphic POLY 88 - 8080 ? 8080A ? ( Heres states it was a 8080A )

Micral G and Micral S - 8080

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