Can you overwrite an OTP ROM? - Page 1
Forum section: electronics / beginners

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 14, 2017, 02:58:35 pm
content: hi everyone,I was playing with ROMs recently and I was wondering if I can overwrite the data in an OTP ROM, which has a UV window like some of 27 series memory EPROMs , could they be erased and rewritten, and for some which don't have a UV window could they be erased or overwritten?

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 14, 2017, 03:02:53 pm
content: OTP means One Time Programmable, so the answer should be no. Why an OTP should have a window I have no idea

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 14, 2017, 03:11:50 pm
content: You can tyically write '0' values to previously blank locations.If it has a window it isn't OTP - maybe a part-number mix-up as many of the ceramic windowed EPROMs were also offered in lower-cost plastic packages as OTP version.

author: Tandy
author_rank: Frequent Contributor
timestamp: January 14, 2017, 03:15:21 pm
content: As there is no context as to where the ROMS come from it is difficult to say. One time programmable don't usually have a window, so it might be that if this is a ROM you have pulled from some hardware that the manufacturer has used UV erasable ROMs, perhaps for a limited run of updated firmware.Essentially you have...Mask ROM: custom manufactured with the data onboard.PROM: Programmable ROM, can be programmed in a ROM programmer once.EPROM: Erasable Programmable ROM that usually can be erased using UV light exposure to a window.EEPROM: Electrically Erasable Programmable ROM, as the name suggests can be erased and re-written.

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 14, 2017, 03:18:22 pm
content: Quote from: mikeselectricstuff on January 14, 2017, 03:11:50 pmit is rather ambiguous and weird with certain manufacturers it is an OTP roms with others it can be reprogrammed, the question is how to know in this case if it is erasable or not?

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 14, 2017, 03:25:10 pm
content: Quote from: ali6x944 on January 14, 2017, 03:18:22 pmIf it is an EPROM or EEPROM it is erasable. An EPROM has a window, an EEPROM should be recognizable by the part number.

author: Howardlong
author_rank: Super Contributor
timestamp: January 14, 2017, 04:26:15 pm
content: I tend to agree with Mike on this one, given the information we have. It is generally recognised that in many cases the only difference between a UV eraseable device and an OTP one wasn't the die itself but whether the package had a window on it.

author: jaromir
author_rank: Unknown
timestamp: January 14, 2017, 04:26:31 pm
content: Quote from: ali6x944 on January 14, 2017, 02:58:35 pmSince 80's, vast majority of OTP ROMs were in fact the same chips as EPROMs, only packaged into much cheaper non-transparent plastic package.EPROMs can be erased by UV light (all cells get into "logic high" state) and those cells can be programmed (brought into "logic low").PROMs can't be erased easily * but you should be able to bring unprogrammed cells (containing "logic high" states) program into logic low, if it is of any interest to you. This trick was used in OTP MCUs back in the days, if the program took only part of ROM, you could overwrite it into series of NOPs (all zeros) and write new program into second half of ROM.* I've heard of experiments of erasing non-windowed PROMs using X-rays or elevated temperature; though theoretically plausible, failed in practice.

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 14, 2017, 05:38:42 pm
content: https://drive.google.com/file/d/0B5vW-k7HbsL4YkVWaC0yS1BaNkU/view?usp=drivesdkThe middle chip is the only one which says in its datasheet that it is erasable, this is quit annoying sometimes when u are using similar looking and exact pinouts of chips

author: MK14
author_rank: Super Contributor
timestamp: January 14, 2017, 05:53:43 pm
content: The picture seems to show three separate EPROMS, which are UV erasable.Seems to be all 2764's (8K bytes which of course is 64K bits in some datasheets) from a quick glance.

author: MK14
author_rank: Super Contributor
timestamp: January 14, 2017, 06:24:14 pm
content: Quote from: ali6x944 on January 14, 2017, 05:38:42 pmThe lowest chip datasheet, seems to say it is also an EPROM (as my earlier post says, they all seem to be EPROMS anyway).http://www.datasheets360.com/part/detail/am2764dc/5400315434036000401/?alternatePartManufacturerId=0I'm NOT 10% sure about the top chip and it does not seem to have a suitable full part number to easily search for it. But it also looks just like an EPROM, and seems to be numbered in a similar way. Very likely to be an EPROM.

author: Gyro
author_rank: Super Contributor
timestamp: January 14, 2017, 06:34:18 pm
content: You don't put a window in a chip that isn't UV erasble. They're all EPROMS.

author: wraper
author_rank: Unknown
timestamp: January 14, 2017, 07:10:51 pm
content: It *is* possible if you erase them with radiation which comes through the case, for example, X-rays. Te effect is the same as erasing EPROMs with quartz widow by UV. Actually many OTP PROMs are the very same parts but in plastic package which makes them significantly cheaper.If ROM has a window, it is not OTP.

author: wraper
author_rank: Unknown
timestamp: January 14, 2017, 07:17:02 pm
content: Quote from: ali6x944 on January 14, 2017, 05:38:42 pmThen you had read datasheets for ICs which have different suffix and not for the parts you have. Guess this one for bottom IC :http://bg-electronics.de/datenblaetter/Schaltkreise/AM27128A3DC.pdfNowhere it says in the datasheet DC or D suffix.

author: JacobPilsen
author_rank: Regular Contributor
timestamp: January 14, 2017, 07:59:44 pm
content: Quote from: Gyro on January 14, 2017, 06:34:18 pmWhat about laser unpacking, and than apply UV ???

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 15, 2017, 03:07:03 am
content: Quote from: wraper on January 14, 2017, 07:17:02 pmU r right maybe it is because of the suffix

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 15, 2017, 03:36:21 am
content: Quote from: JacobPilsen on January 14, 2017, 07:59:44 pmInteresting, what if this happened? I think the laser would by it self erase the rom

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 16, 2017, 10:45:33 am
content: But what it can't be...The laser is of different wavelength to the erase uv wavelength required?

author: BrianHG
author_rank: Super Contributor
timestamp: January 16, 2017, 08:05:07 pm
content: Quote from: ali6x944 on January 16, 2017, 10:45:33 amYes, many years ago, I tried different UV lights in an effort to erase an eprom, including sunlight. Only the official eprom eraser fluorescent tube would actually erase the eproms.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 17, 2017, 12:16:18 am
content: Quote from: BrianHG on January 16, 2017, 08:05:07 pmIt needs a very particular wavelength - from memory around 250nm. The only thing that will do it is a germicidal lamp - I think that's what UV erasers generally used. Bright sunlight might do it after a very long time but I think a lot of that wavelength is filtrered by the Ozone layer

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 17, 2017, 04:08:36 am
content: Could it be erased by the light of electric arcs ?

author: BrianHG
author_rank: Super Contributor
timestamp: January 17, 2017, 05:43:34 am
content: Quote from: ali6x944 on January 17, 2017, 04:08:36 amMake sure all the IO pins are shorted. You are more likely to destroy the IC itself.Q: Are you looking for EProm erasers? Or just want to experiment around trying to erase them in an alternate way?

author: JacobPilsen
author_rank: Regular Contributor
timestamp: January 18, 2017, 05:25:35 pm
content: He is looking for erasing "non-window" EPROM.Experiment with UV LED:http://rayer.g6.cz/elektro/eprom.htmLaser decapsulation machine use InfraRed 1064 nm (and stop everytime when beam is reflected from chip).http://www.radiantoptronics.com/baublys

author: DBecker
author_rank: Frequent Contributor
timestamp: January 18, 2017, 08:32:08 pm
content: This question reaches back 35-40 years, which is almost the stone age in integrated circuits.40 years ago the only viable choice for high density memory was a mask-programmed ROM. A memory chip was fabricated up to the final metal layer, which contained the links to encode the program. A customer would provide the programming, a final mask was made, and the chips would be finished and packaged.The was way less involved than you might imagine. The difficult and risky steps are creating the semiconductors with deposition and diffusion. These steps can take weeks. Specifically each diffusion step can take up to a day of high temperature baking, and an entire batch can be ruined by an impurity. In contrast a metal deposition layer can be done in a few minutes. It's just exposing the photoresist (under a minute), cleaning, flashing the metal layer (five minutes to pull a vacuum, a few seconds to flash) and cleaning again. If you screw up, you can etch off the metal and try again.And the mask wasn't expensive. The feature sizes were relatively huge, and masks could be made in-house. Sometimes it was as simple as rubylith film dots laid out by hand. A pair of clerical-level staff would call and lay out the rubylith dots in an hour or so.The other approach was fused PROMs. They had thin metal strips at each matrix point that could be vaporized. The downside was that the chip had to be physically larger, and the voltage and impulse energy had to be carefully managed to vaporize the fuse completely without damaging the chip structure. PROMs were usually limited to low capacity chips that held configuration information rather than program memory.Once EPROMs arrived, the game changed completely. They die was more expensive than mask ROM, but masks were getting expensive. Decreasing feature size and increasing memory size meant that making masks was outsourced to specialty companies. That increased cost and turn-around time. Pretty quickly OTP EPROMs in cheap plastic packages dominated, with mask-programmed ROMs only used for large-volume parts (primarily game cartridges).On a personal note, I built my first EPROM programmer in 1980 or 1981 using three "precision discharged" 9V batteries for the 24V power supply needed for programming (25-26V volts supplied). I was extremely careful because I didn't want to waste the then-expensive parts. Luckily for my student budget it worked the first time.

author: mash107
author_rank: Contributor
timestamp: January 19, 2017, 03:39:54 am
content: theoretically, yes.most PROMs use the same die as UV erasable PROMs, but packaged in a plastic DIP without a window. I know Atmel did this for decades until they obsoleted their ceramic DIP with a window.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 19, 2017, 11:17:16 am
content: Quote from: DBecker on January 18, 2017, 08:32:08 pmOne oddity at the height of the EPROM era was that because of the huge production volumes of windowed EPROMs, OTPs were, at least for the casual low-quantity purchaser, not significantly cheaper. Maybe this was because it was only high volume users buying OTPs.I very, very rarely see OTPs in stuff I do teardowns of, though they tend to be higher-end bits of gear. Of course back in those days anything with an EPROM of any sort was pretty high-end as all consumer stuff was mask, and industrial stuff was expensive enough not to care about savings from OTP. .

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 21, 2017, 04:28:17 pm
content: Quote from: mash107 on January 19, 2017, 03:39:54 amQuote from: mikeselectricstuff on January 19, 2017, 11:17:16 amWow this is rather interesting I didn't know that PROMs had fuses in them...The even more interesting part is why the programming voltage dropped from 25-26v in the older chips to around 12 in the newer chips? And how do the newer chips "EPROMs" store memory?

author: SeanB
author_rank: Super Contributor
timestamp: January 21, 2017, 05:38:32 pm
content: Drop in programming voltage was process driven, they changed to a smaller process, which meant a thinner oxide could store the charge, and needed a lower voltage to tunnel the electrons across the oxide layer. Older ones are however slightly more reliable, simply because the bucket of charge is so many more electrons in size, and thus leaks away slower. However in most situations this only will show up after 100 years or so, as most will keep data for at least 25 years in practise, provided you use a proper opaque label over the window, not a plain paper one but one with an integrated aluminium foil inner layer to block light.Later on EEProm was developed to a more reliable method, and this, along with some of the later Eprom variants, have a built in voltage generation source, used to generate both the internal reference voltages ( the chip internally is not digital, it is analogue, with a single bit AD converter for EPROM and now with MLC flash a few bits more) and the higher voltages required to erase ( for EEPROM) the required cells/blocks before programming, and to program the cell when they are blank.in all cases EProm has a built in voltage converter to generate substrate bias, except for the very early types, which needed a -21V substrate bias voltage, and were very unhappy if it was not present, but did not blow up till it was at around +2v, when the chip would crowbar quite nicely. Was a very big advertising headline with the 2716, advertised with bold "Single 5V supply voltage only needed" as a selling point.The good Eprom programmers verify the devices after writing, using a first pass at 5V00, a second pass at 6V00 and a third pass at 4V50, to test that the programming will be valid data over the full voltage range the device will experience in use. Military ones repeated the test 2 times again, at -55c and at +125C, to ensure they would work under all circumstances.

author: Howardlong
author_rank: Super Contributor
timestamp: January 21, 2017, 07:32:07 pm
content: The first microprocessor system I built in the mid 70s used a PROM, ISTR 128 or 256 x 8 bits. They were about 50 quid** a pop. You didn't want to get your boot monitor wrong, it was an expensive business. But equally there wasn't any means to test it beforehand, or fix it if you did get it wrong, other than spend another 50 quid. PCs didn't exist to run simulators, and there were no in circuit emulators. In those days, making a ROM emulator was an expensive proposition, even if you had something to program it with.The remnants of that machine are below, hopefully my metalwork skills have improved since I was a 12yo.** about £280 now.

author: timb
author_rank: Super Contributor
timestamp: January 21, 2017, 10:41:06 pm
content: Quote from: mikeselectricstuff on January 17, 2017, 12:16:18 amAwhile back I needed to program a new UVEPROM for some test equipment I was restoring. It just so happened I had an old PC motherboard on hand with a windowed EEPROM (for the BIOS) that would work. Unfortunately I didn't have an EPROM eraser handy...What I *did* have, however, was a humidifier that contained a UV bulb in the bottom, designed to kill germs in the water between the tank and filter. So, I simply attached the EPROM to the lamp housing with a piece of Kapton tape, turned it on for 10 minutes and voila, I had an erased EPROM!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 22, 2017, 02:56:38 pm
content: Quote from: SeanB on January 21, 2017, 05:38:32 pm.. and not just for writing, they needed wacky voltages for reading as well.Speaking of process changes, this is a nice illustration of how the same part number changed over about 10 years

author: SeanB
author_rank: Super Contributor
timestamp: January 22, 2017, 03:54:12 pm
content: Quote from: mikeselectricstuff on January 22, 2017, 02:56:38 pmQuite a lot of die shrink over the 11 years difference, but I bet ST still has a few thousand of those old large dies for the military customers, as they are stuck on that process, and a smaller die means a recertification of the process, as it likely has a slightly different program voltage, write method and more importantly a different readout of chip ID during programming. They might have them already diced, tested and in CERDIP as well, as they probably stopped ordering that large window long time ago, quartz glass is a lot more expensive than ceramic, but storage blank ( or with a factory test pattern written in for long term degradation test as a free check, paid for by the customer of course) in tubes and in hermetic package probably is not a lot more store space than the dies in a case along with the blank ceramic cases.Bet the customers still have a few dozen old 396 machines running MSDOS5.0 with a programmer plugged into the ISA bus as well for them, though they probably have nice new 19in LCD displays with a CGA/HGC/MDA/EGA to VGA converter in the cable.

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 23, 2017, 05:04:34 am
content: Quote from: timb on January 21, 2017, 10:41:06 pmAmazing, I'm searching about a uv lap to do the same but I saw this video, in the video is using what looks like a discharge tube or a Xeon flash of some sort to erase the chip...See video:https://youtu.be/_sSuzDg4ntA

author: james_s
author_rank: Super Contributor
timestamp: January 23, 2017, 05:30:11 am
content: The germicidal lamps used in EPROM erasers are internally the same as any ordinary fluorescent tube except the glass is made of quartz which transmits the short wave UV from the mercury vapor discharge that regular glass is quite opaque to. The windows in UV erasable EPROMs are also made of quartz for this reason.

author: bitseeker
author_rank: Super Contributor
timestamp: January 23, 2017, 07:19:57 am
content: Quote from: timb on January 21, 2017, 10:41:06 pmWhat an uncanny place to find the solution.So, what's the preferred solution for restoring old equipment that used EPROMs that have since failed? Vintage gear archaeology, EEPROM, Flash? I recall seeing some OTP ROMs at Mouser or somewhere.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 23, 2017, 09:44:47 am
content: Quote from: ali6x944 on January 23, 2017, 05:04:34 amMany years ago one of the UK programmer manufacturers company sold an eraser that worked like this - it was a larger handheld unit than in the video and worked pretty well. I still have one somewhere.Found this pic of one that has been badged by someone else :I think it was basically a standard flash tube but with a quartz envelope - may have had a special gas mix. Or it could be they found that normal flash tubes would work as-is.Something I recall was they were rather vague about tube life, but said they would supply replacements at reasonable cost if it died.

author: timb
author_rank: Super Contributor
timestamp: January 23, 2017, 09:56:29 am
content: Quote from: bitseeker on January 23, 2017, 07:19:57 amYou can replace some UVEPROMs with EEPROMs (may require you to make an adapter board if the pinout is different or if you want to use a SMD part to replace a DIP one).Generally though, the easiest method is to simply buy New Old Stock UVEPROMs off eBay. I bought an entire tube of brand new 256kbit ones awhile back for $25 (even though I only needed two; it was cheaper that way).I also picked up a cheap Chinese UV eraser for $10 from Amazon. The quality isn't very good, but it works for the amount of chips I erase. (I can't use my humidifier to erase them in the winter, since that's when it's actually full of water!)

author: bitseeker
author_rank: Super Contributor
timestamp: January 23, 2017, 10:13:37 pm
content: Thanks, Tim. I have some old gear in the queue and I suspect one of them might be having problems reading its EPROM. I'll check out eBay if it turns out to need replacement.

author: timb
author_rank: Super Contributor
timestamp: January 23, 2017, 11:06:08 pm
content: Quote from: bitseeker on January 23, 2017, 10:13:37 pmFeel free to PM me first, as I've actually got several tubes full of NOS EPROMs; I'd be more than happy to send you as many you need for a much better price than eBay. I can even pre-erase or program them if you need. (All this assumes I have the size you need!)

author: bitseeker
author_rank: Super Contributor
timestamp: January 24, 2017, 01:30:46 am
content: Quote from: timb on January 23, 2017, 11:06:08 pmWill do. Thanks, Tim!

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 24, 2017, 05:54:12 am
content: Quote from: timb on January 23, 2017, 11:06:08 pmThanks alot man, this is really kind of u

author: ali6x944
author_rank: Frequent Contributor
timestamp: January 25, 2017, 04:13:58 am
content: Quote from: mikeselectricstuff on January 23, 2017, 09:44:47 amWhere the tubes like this:https://plus.google.com/115108013327841958420/posts/LdtYh4pXTpUI noticed when I had the light from my phone a silvery looking thing inside the tube I suspect it to be just reflections or what I hope it is mercury vapor...I know it is unlikely but just hoping...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 25, 2017, 09:52:51 am
content: It looks like a standard mid-sized xenon tube, don't recall if it was linear or U shape.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 13, 2017, 02:29:57 am
content: I think it is possible after all to erase it using Xeon flash:http://www.protonbasic.co.uk/archive/index.php/t-48209.html

author: helius
author_rank: Super Contributor
timestamp: May 13, 2017, 03:09:53 am
content: Be careful bodging together UV erasers. The UV-C wavelengths they use are germicidal, and lethal to human cells as well (particularly the delicate ones in your cornea). They are powerful inducers of skin cancers.Properly designed erasers (like these) have interlocks, so the bulb is only energized if the light-tight EPROM drawer is closed.

author: SeanB
author_rank: Super Contributor
timestamp: May 13, 2017, 03:03:23 pm
content: The flash erasers just used a regular linear or U shape flash tube, standard part as they are quartz glass to withstand the high pressure and thermal shock of regular flash use. Then they used a standard 120uF photoflash capacitor as power bank, with a modified charge circuit to get high recharge speeds, so you could do 1 pulse per second to erase. Typically 4 flashes and the PROM was like it left the factory, all FF.You could use just a regular flash unit, just take the front soda glass or plastic window out, as it is a UV filter for the tube. Then place on window of the EPROM, trigger 5 times and it is done.

author: BrianHG
author_rank: Super Contributor
timestamp: May 13, 2017, 04:33:33 pm
content: For strobe eraser, use an old camera with xenon flash, working from 2xAA cells. Though they are a flat tube, you have the driver circuit, it comes packages in a reflector, just remove the front plastic lens and place over the eprom & all of the strobe will be focused right into the window thanks to the reflector housing.If you want shorter bursts, just shrink the 330uf power cap. It will also charge faster this way.

author: bitseeker
author_rank: Super Contributor
timestamp: May 13, 2017, 10:34:45 pm
content: That's pretty cool. I had never tried a flash before. Beats waiting 15 min.

author: Gyro
author_rank: Super Contributor
timestamp: May 14, 2017, 09:38:29 am
content: Just a quick warning that most camera flashes use the reflector as the external trigger electrode. Without the insulation of the plastic lens you might give the EPROM (or yourself) a few kV spike. Just be careful of the spacing.

author: BrianHG
author_rank: Super Contributor
timestamp: May 14, 2017, 06:16:41 pm
content: Quote from: Gyro on May 14, 2017, 09:38:29 amUnfortunately the plastic lens may block a lot of the UV range needed for the erasing.

author: bktemp
author_rank: Super Contributor
timestamp: May 14, 2017, 07:36:25 pm
content: Many cheap flash tubes are made out of borosilicate glass instead of quartz glass. Typical borosilicate glass blocks most of the UV-C light needed for erasing EPROMs.

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 18, 2017, 01:06:07 pm
content: how would u know if it is borosilicate glass? dose it have any color difference?

author: Gyro
author_rank: Super Contributor
timestamp: May 18, 2017, 01:40:05 pm
content: I don't know about quartz flash tubes in particular but Quartz tubes normally use a thin foil to take the connection through the end pinch. This is due to the difficulty in matching the thermal coefficient of expansion of Quartz using normal metal leadouts.