Hack An 8085 Like It’s 1985

If you have been building electronic hardware for several decades, do you still have any projects from your distant past? Do they work? An audio amplifier perhaps, or a bench power supply.

[Just4Fun] made a rather special computer in the 1980s, and it definitely still works. Describing it as “An 8085 single board computer with an EPROM emulator” though, does not convey just how special it is. This is not the modern sense of a single board computer with an SoC and a few support components. Instead it is a full system in the manner of the day in which processor, memory and peripherals are all separate components surrounded by 74 series glue logic. The whole system is wire-wrapped on a piece of perfboard and mounted very neatly in a rack. The EPROM emulator is a separate unit in a console case with hexadecimal keyboard and 7-segment display.

As the video below the break of an LED flashing demo shows, the EPROM emulator allows 8085 machine code to be entered byte by byte instead of having to be burned into a real EPROM.

[Just4Fun] leaves us with plans to replace the period EPROM emulator with a modern alternative, an EEPROM on a PCB designed to fit in the original bank of EPROM sockets. In this he suggests he might fit a bootloader and a BASIC interpreter, something entirely possible back in the day with conventional EPROMs, but probably not as cheaply.

If the 8085 has piqued your interest, you might like to read about the structure of its ALU, and its registers. if you’d like to try your hand at making an 8-bit computer of your own, we recently reviewed the RC2014, a Z80 machine.

23 thoughts on “Hack An 8085 Like It’s 1985

  1. Didn’t look wire-wrapped to me, looked like they soldered. I dug my old 8085 board out of the box in the crawlspace a while back. The board is cracked, I need to rebuild it and see if I can get it going again.

  2. Love it! The music he used in the video is a good choice to. I forgot those old 809x CPU’s were simple DIP chips. Even some higher end printers from that era used 64 Pin Quad In Line CPU’s. Can anyone remember what they were?

    Notice the big transformer and linear supply. You have give those old chips enough power to boil the water for their micro-steam-engines lol.

    +10 points for the flashing LED.

    I have, sitting in front of me, several 150x100mm SS blank PCB’s, backplane connectors and a bag of card guides to make a old style card rack computer. I will but using CPLD as glue and for programmable routing so I can fit it all in small single sided boards. Will take time though as I need to make a CNC PCB drill first. No way am I manually drilling all the holes for a backplane.

    Welcome aboard [Just4Fun] !

  3. What is that music? It sounds like it’s a theme from a TV show.

    One of these days I’m going to homebrew a 6502 box. Or, at least, that’s what I keep telling myself…

    1. That’s from U.F.O., a Gerry & Sylvia Anderson BBC (ITC?) TV show made around 1970, but set in 1980. The same folks went on to do the much better known Space: 1999 TV show a few years later.

  4. The 8085 is alive and well, running General Atomics Radiation Monitoring Systems in Nuclear Plants across America.
    The microprocessor makes up the “brain” of the GA RM-80. The RM-80 makes up Area Monitors, Duct Monitors, Liquid Monitors, High Range Monitors, Steam, Line Monitors, Effluent Monitors, as well as PIG’s and WRGM’s.
    Two Hundred and Twenty Seven of these at the Plant I work at.

    1. I thought that to but the “blinking LED” of hardware and the “Hello World” of software weren’t a thing in that era as far as I know. So you could say that the “blinking LED” is not era appropriate irrespective of color.

        1. Hello world does goes way back. It just remained in real hacker subcultures until breaking out on the interwebs as more ubiquitous in the 2000s. You kinda have to remember the 90s as the time when not everything got online. … And a lot before and during that might as well have been ancient prehistory, but for the efforts the last decafe of archive.org and others to digitize it or restore it from old media of offline tapes of yore.

  5. If anyone wants to be be really brave you can go to archive.org and look in the old Byte magazine section. They had plans for building your own IBM PC clone… And I mean building it not buying a motherboard.

    1. Cool and you can do what they did on halt and catch fire and spend all night desoldering a socketed BIOS chip to read the code off it, instead of dumping it in debug…. How did they do the BIOS in Byte anyway, suggest you buy one or publish code?

  6. I always remember a guy at the local computer club in what must have been 1981 with a kit built nascom jubilee, we’d gone along as we’d got a new to the market sinclair zx81 and I was absolutely fascinated by this thing built into a old antique tv unit, one week he’d slide in a new board that let him do a block man running and stuff like that every week. That guy was my hero and we ended up with a very heavily modified zx81 with homemade keyboard with real keys, the rom piggybacked wth a chip to push it into ram so the graphics in the ascii set could be altered and all sorts of other hacks on it.
    I bumped into someone and asked them about gerry’s nascom and if it still existed because it was what inspired me and he told me he’d swapped it for a telephone answering machine in the end.

    Oldest self built thing I have that still works is a baycom 1200 baud packet radio modem, which is well over 25 years old but still runs. Someone else etched the pcb on that though so maybe it doesn’t count.

      1. Me too actually, whoops. … though it did count as my 10th sacrifice of an electronic being, allowing me to be accepted into the Heuristic, Anciently Curated Knowledge, Esoteric Rite of Lord Ba’al… can I talk about that here? We’ve all passed through the magic smoke right?

  7. Hmm, did see my truly wiredwrapped 6809 system (my own design) and my 68000 system (modified someone elses design) when I was digging around a little, I now got the urge to see if I can fire them up. Both should just need a serial console and power.

    1. Plus the fault finding and replacing when you used surplus green with pink stripe and mauve wire for the power and forgot which was which. Was it green is more earthy so ground, so negative, or pink was more reddish so positive. FZZZT… :-D

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