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?
OTP means One Time Programmable, so the answer should be no. Why an OTP should have a window I have no idea
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.
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.
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.
it 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?
it 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?
If it is an EPROM or EEPROM it is erasable. An EPROM has a window, an EEPROM should be recognizable by the part number.
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.
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?
Since 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.
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.
You don't put a window in a chip that isn't UV erasble. They're all EPROMS.
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.
You don't put a window in a chip that isn't UV erasble. They're all EPROMS.
What about laser unpacking, and than apply UV ???
You don't put a window in a chip that isn't UV erasble. They're all EPROMS.
What about laser unpacking, and than apply UV
Interesting, what if this happened? I think the laser would by it self erase the rom
But what it can't be...
The laser is of different wavelength to the erase uv wavelength required?
But what it can't be...
The laser is of different wavelength to the erase uv wavelength required?
Yes, 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.
But what it can't be...
The laser is of different wavelength to the erase uv wavelength required?
Yes, 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.
It 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
Could it be erased by the light of electric arcs ?
Could it be erased by the light of electric arcs ?
Make 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?
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.
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.
