I have salvaged a pair of M27C1001. According to the datasheet it is either UV erasable or OTP - depending on the package. It is said the chip itself is the same - the OTP variant has only cheaper plastic package without the expensive quartz window. Of course there is no reason for this except for curiosity(*): if the chip is truly the same is it possible to erase it somehow despite it does not have the window?
EDIT: (*) I mean I have no use for the EPROM and I could buy a new/better one. The only reason why I ask is curiosity. I understand my curiosity is not the reason why manufacturers add the window.
Sure it is. Go to the next atomic power plant, dribe the operator, get near the core, leve it ~ 1 hour, get out there again. You might wnat to go to 3 mile iland or fukushima or pripjat, if you prefer open sky operation.
The quartz window is not there to satisfy your curiosity, the memory is erased by exposure to ultraviolet light, so there has to be a way to expose the chip to the light. The OTP variant (One Time Programmable) is not erasable because it has the solid case that does not allow exposure to UV.
The chip may still be usable, depending on your intended use, and what the current contents of the memory are. All bits are set to a logic 1 in the erase state, and are programmed to a logic 0 state. A lot of processors use 00 hexidecimal as a no op instruction that does nothing but continue on to the next instruction, so if you have enough unprogrammed memory on the chip, you can overwrite the unwanted code with 0x00 and the processor will run through all the No-op instructions until it reaches the code you want to run.
Another option might be to mill a hole in the casing in the position used for the quartz window. I'm not familiar with whether the case actually contacts the chip itself, but if the eprom is otherwise unusable there isn't much to lose by trying.
Yes, it's identical. In the old days they did have ROMs & PROMs but when EPROMs were introduced they became super-popular and it was a LOT easier to develop, debug, and improve firmware and/or upgrade.
After the design & firmware was stable it could be changed to a PROM (or ROM) (less expensive) but they weren't plug-in compatible so the board would have to be re-designed. So, the manufacturers decided to make the EPROMs without the window available at a lower price.
I think one company I was working for switched to OTP EPROMs on one product that had been in production and "stable" for a few years. Mostly, I've only seen regular EPROMs with the window.
...Where I work now, I was just working on some old units with a EPROMs that were returned for repair. Two of the units had "failed" EPROMs, plus the firmware was not the latest. (The "latest" firmware is from 1998. ) Luckily, we still had the EPROM eraser (I wasn't sure) and it still worked. And, we have a programmer that we currently use for plug-in flash chips and it also programs EPROMs. After erasing & re-programming, they were good!
) Luckily, we still had the EPROM eraser (I wasn't sure) and it still worked. And, we have a programmer that we currently use for plug-in flash chips and it also programs EPROMs. After erasing & re-programming, they were good!