Voja’s EEPROM Emulator From 1991

We’re glad we’re not the only hacker-packrats out there! [Voja Antonic] recently stumbled on an EPROM emulator that he’d made way back in 1991. It’s a sweet build, so take your mind back 25 years if you can. Put on “Nevermind” and dig into a nicely done retro project.

The emulator is basically a PIC 16C54 microcontroller and some memory, with some buffers for input and output. On one side, it’s a plug-in replacement for an EPROM — the flash memory of a bygone era. On the other side, it connects via serial port to a PC. Instead of going through the tedious process of pulling the EPROM, erasing and reprogramming it, this device uploads new code in a jiffy.


No need to emulate ancient EPROMS? You should still check out this build — the mechanics are great! We love the serial-port backplane that is soldered on at a 90° angle. The joint is a card-edge connector electrically, but also into a nice little box, reminiscent of [Voja]’s other FR4 fabrication tricks. The drilled hole with the LED poking out is classy. We’re never going to make an EPROM emulator, but we’re absolutely going to steal some of the fabrication techniques.

[Voja] is a Hackaday contributor, badge-designer, mad hacker, inspired clock-builder, and developer of (then) Yugoslavia’s first DIY PC.

22 thoughts on “Voja’s EEPROM Emulator From 1991

  1. Takes me back to a long forgotten era where elektronic components could also perform structural tasks, alongside their electrical functions. Voja did a very nice job back then, try to build a housing with SMD components nowadays…

    1. Difference is now you don’t need to build a housing out of SMD components- parts are small enough not to require it. And PCB based construction still works just fine.

  2. Wait. Is it an EEPROM emulator or an EPROM emulator? (Despite the author using then interchangeably, they are different things. The latter makes more sense, IMO, because you had to manually erase them with UV.)

        1. Grrr… I typed EEPROM so many times by force of habit, then changed them “all”. Of course, searching the body of the text doesn’t get the title.

          I’m leaving it in, b/c changing the title is lame. But let the record show that it’s an EPROM replacement.

    1. Technically, you would be replacing an EPROM with an EEPROM that can be re-loaded with a serial interface. I used to dream of having these things back in the day, but they didn’t have very suitable parts for them yet, and the ones they did have were REALLY expensive. That of course was when memory in general was expensive. So, instead I had forty or fifty 27xxx series EPROMS that I erased with a germicidal light – no closed case interlock eraser for me, you just had to remember to never look at the light. I guess you could call that the Wild West of the hobbyist world.

  3. Nice. I remember using a fancy EPROM programmer/emulator in the late ’90s. IIRC it cost ~£1.5K (and wasn’t a Dataman). Shortly after, we switched to using EEPROMs…

    1. PICs were strange beasts, when they came from VLSI peripheral buried controllers’ attics up to the surface into the sun, like some ghastly troglodytes, compared to 68HC11’s and 8051’s, but they brought cheap single-chip MCU era to the hobbyist masses. PICs were revolutionary in more then one way. They redrawn the border between “use simple logic” and “use MCU” projects, and were instrument of commercial death of PAL/GAL PLDs which were often used for medium complexity projects. It turned out that GAL speed was not that much needed, and CMOS PICs with their on-chip RC oscilator clock generators could do much more complicated tasks with much better power budget, PCB real estate and short BOM. Microchip was also first MCU manufacturer to give away for free to anyone (not just universities or large customers) their IDE and to publish device programming specification publicly, instead of giving them to device programmer manufacturers under NDA. All of this is common and not a big deal today, but back then it was a Revolution!

    1. These products are pretty cool, and for 175$ not bad in price. Still – you would need to do a fair amount of development to justify the cost as an individual. I do like the fact that it does multiple families as well as different pin configurations – with data logging too.

  4. For those who are interested in Ham radio there are a lot of old mobile radios out there for the commercial and public safety bands that can operate on the ham bands but are EPROM controlled. The original programmers were rediculously expensive and it takes some work to reverse-engineer the ROM. Once you do though you get a fairly inexpensive radio that is built like a tank. Many of these things are really built to last with thick steel cases and high tolerance parts. They also tend to handle higher duty cycles than traditional ham gear. That matters when you go to use digital modes.

    Usually I see such things re-sold with reprogrammed EPROMS. Occasionally I see them with the EPROMS replaced with bigger EEPROMS and toggle switches ran to the ‘extra’ address lines so that you get multiple channel banks.

    Something I have wanted to try is building an EPROM emulator for this purpose. Rather than a bunch of channels and banks I am thinking one could simply look at wether the requested channel number is higher or lower than the previous (like how a rotary encoder works) and get a full out VFO! Of course, displaying what frequency you are on could be a challenge unless the intention is to actually modify the device.

    If you are going to actually modify the device then maybe simply replacing the whole VFO with a DDS chip is a better route anyway…

  5. Throughout the 80s we’d make an emulator from a stack of static memories and a address decoder chip. The memories would be stacked one above the other and all the pins except for the chip select pin. The address decoder rode on top also connected to the address bus. It decoded the the addresses to turn on the chip select. The stack was built on an IC socket so it could be plugged into the EPROM socket.

    We used these with in circuit emulators (ICE) so the code was downloaded through the ICE.

    1. My EPROM emulator was a bit later when we had larger SRAM chips. It was basically a battery backed low power SRAM that I used to carry between a cheap PC parallel port programmer and the target device. It ran on 3 AA batteries. Nothing as nice as Voja’s

  6. A cheap-to-build EPROM emulator would be quite useful for anyone running tests on old arcade boards to figure out how they worked (replace the program ROMs with a suitable emulated ROM chip and download new code each time you want to test instead of needing to burn new chips every time)

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