Fooling around with EPROMs - share your stories!

Question

As I've had a habit of collecting old (relatively speaking) computer hardware, one of the things that always strikes dread into me is an electrical failure in an EPROM/EEPROM/Flash chip which normally means curtains for a given device because the firmware is not stored elsewhere and replicating it is difficult. Further to this, earlier Flash memory had retention times of 10 years under harsh conditions, so losing a device due to flash retention failure is a high possibility - the course I was teaching in university had problems with their development boards losing their bootloader after 10-12 years in service, so we have definitely seen this.

As a result, I embarked on trying to save the contents of *ROMs I had in my reach. The first thing I needed was a programmer, so I bought an XG autoelectric TL866CS and some adapters, which I reviewed. From there, I reasoned that if someone wanted to update the firmware on an old CERDIP EPROM, they would need a UV eraser, so I grabbed a cheap one, tore it down and repaired it since it arrived broken. There, I also detailed a little experiment with erasing an EPROM and seeing what the erase profile looked like.

It then struck me, while EPROMs are relatively reusable, they can be damaged by stray static electricity and by over-erasure, so I pondered what the modern options were, so I went and did some shopping which turned up quite a few parts which might be made-compatible and reprogrammable in case you wanted to just have functionality rather than part-for-part exchange.

Finally, I dumped some old VGA BIOSes from ISA and PCI graphic cards and examined the data, discovering the bitmapped font tables. Cool. This is just the beginning of my adventures - but owing to time restrictions, more delving will have to wait.

As I suppose many of the members here would have more experience than I would with EPROMs, and the Vintage Hardware area has been very quiet, I thought I'd make this post a question/discussion rather than just a post about these beautiful chips and the code they contain. Feel free to share your stories, and in return, I promise a few likes and helpfuls your way . Further to this, I hope some of this information is helpful in some way.

- Gough

shabaz · Answer

Hi Gough! I remember buying an EPROM programmer from a car boot sale for £0.50 ($1) it really was a 1970's heap of trash it must have been the lowest end model possible, the LED 7-segments dimmed when in operation, but it still worked! And for a few years I made some good pocket money remapping Ford RS Cosworth ECU's : ) I think a local mechanic still has it, I let him have it after I was done with it. For erasing EPROMs, even the UK sunshine is ok for that Motorola provided loads of EPROM parts to speed up development of some other projects, so I'd label them all and cycle them in the sun : ) For yet another project, I was really stuck, I could only obtain the one-time programmable parts, which really were windowless EPROMs as I understand. No budget for the very hefty cost in-circuit emulators (think they cost a few $10k). Basically I had a few tubefuls of chances to get the code working : ) No pressure! As an exercise in taking care, students should get given compilers with only a few dozen compile attempts : )

dougw · Answer

I fired up my AIM65 after 35 years and it still worked fine. In the picture you can see 5 EPROMs, 1 is erasable, the other 4 are OTP (one-time-programmable). My recollection is that the equivalent exposure to a UV lamp erase cycle was 2 weeks of direct sunlight. Some people would toss an old computer like this in the trash. Such a thought would not even cross my mind.

Former Member · Answer

I still play with eeproms. Have a nice stash of 2716's. Made this simple programmer from the junkbox for making steering logic using the chips:

mcb1 · Answer

The company I worked for had a good little earner by reprogramming the EPROM's in the money machines (hole in the wall). The bank would turn up with the masters, we'd copy them onto lots of others and charge them. We also used EPROM's in the truckstops. When I frst joined I noted they were cable tied in, and thought it strange. Apparently because the boards were upside down, sometimes they'd fall out, and the cure (I was told it was from the manufacturer) was to use cable ties. Needless to say I educated them on why they falling out and we swapped the sockets. I've used an EPROM in a rudamentary controller I designed. We mapped the output and setup a range of address'es that got stepped thru to produce a moving output. We had 4 'pages' that were 4 higher bit address'es to effectively give 4 different pattern options. I wrote a VB program to allow you to see the effect and it generated the hex file. I think there are still some working around the town in the jackpot systems, along with some shooting stars in two casinos. I have heard that sunlight will erase them but the ones we dealt with needed nearly 8 hours if I recall. Mark

DAB · Answer

I can vouch for the sensitivity to static charge on EProms. Back in the late 1970's and early 1980's I had to be very careful around those devices. For some reason, I generate a lot of charge when walking, especially on vinyl floors. Some people claimed I could destroy an EPROM at ten feet, though I suspect they exaggerated. I just made a habit of carrying the conductive foam for carrying the EPROMs and successfully took them to many locations and even overseas by air. I even still have the UV lamp I used to erase them, though I am not sure I have a programmer. In their day, EPROMs were a great way to update systems. All I had to do was pop new EPROMS in and take the old ones back home for reuse. It has taken a long time before I would trust these new fangled devices to store programs for updates. Though I have found the SD Cards to be pretty reliable. Your post brought back a lot of memories for me. DAB

Problemchild · Answer

One thing to note is that you can some times save the day with "duff" EPROM contents by varying the supply voltage slightly. Also if you have several of a given device then hopefully y ou can recreate a complete image from several broken ones stiched together( all a bit manual but doable!!)

Problemchild · Answer

The turned pin sockets were indeed pritty good and you can still get them although you can get the 32/40 pin strips more easily these days. I've seen the cable tie thing mostly in mobile applications were vibration must of been an issue. That said if you need to cut and replace the tie each time you reprogram it's not effective. You will need to use re-usable ones in that instance!

Problemchild · Answer

"updates" are a great way to gain lots of EPROMs for your own projects as well of course!!

shabaz · Answer

ohh that brings back memories : ) My secondary school (high-school) project was a lighting controller, and it used an EPROM full of patterns, stepped by a counter and a 555 most probably! There was also a semiconductor manufacturer who had a range of ICs which were pretty much just that, a very tiny PLD, a bit of SRAM, and I can't remember what else, and they were marketed as a companion for microcontrollers, to do the glue logic side of it basically. But I can't remember the manufacturer (think the name began with W, but not sure). Maybe Cypress bought them, since the Cypress PSoC has a bit of everything? Just speculation though, I really can't remember those original parts very well.

dougw · Answer

I have used them as state machines - simply supply a counter on the address pins and you have a completely general purpose programmable state machine. I might be tempted to use them for that even today since I have a drawer full of virgin EPROMs. However programming and erasing would require re-acquiring the technology. I have also used them as a straight lookup table to convert grey code to binary.

DAB · Answer

I have a fair number of EProm types, but I think you have me beat. DAB

dougw · Answer

All 5 EPROMS are the same pinout - standard 8Kx8. Leading edge at the time. The UV windows were different shapes for different manufacturers.

shabaz · Answer

They still are 10 times the price : ( but as far as I can see, if an IC is worth socketing then it is worth the pin sockets. It used to be possible to get pins on tape (like a flexible zero-height SIL header socket), you'd cut the tape to the correct length and push it all in and solder. They were really handy, would be nice to locate some more. I've never found them since though. I had to use the individual pins for the 3-digit LCD project .

Fooling around with EPROMs - share your stories!

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