Locked EEPROMS, can they be unlocked and re-written?

[maferv]

Hello guys,

I'm going through scrap and occasionally I find EEPROMS, for example an ATMEL AT27C010, MX27C1000, and many more. They look normal, like any other EEPROM. While I can dump the roms without problems, I can't write a single bit into the chips. I assume there's some sort of lock.

Is there a way to unlock them? Is it a hardware limitation?

Cheers.

 

[Plasma]

Those are OTP EPROMs which can be written only once.

 

[Clint]

EPROM and not EEPROM

 

[maferv]

Oh, I see. Since they come in plastic packaging I thought they were EEPROMS. My bad!
So no chance to repurpose them I guess. I'm reading some people used x-rays.

 

[Dwight Elvey]

True EEPROMs can, usually, be erased and rewritten. Also FLASH ROMS can also be erased and rewritten. The difference is EEPROMs can be rewritten on a byte by byte basis. FLASH require a minimum sized block to be erased and written. It varies from the entire chip to a number of smaller blocks.
Larger sized memories are usually FLASH.
Dwight

 

[maferv]

I managed to erase two chips as if they were regular EEPROMS (AT27C256R and M27C256B). Not all the way through though, they still have some data, and I still can't write into them. I wonder how it was possible since they are OTP EPROMS.

 

[alank2]

Interestingly in a lot of OTP type devices you can lower bits, with reprogramming but not raise them.

 

[maferv]

Very interesting, so you can re-use them to some extent. Write in the unprogrammed part and fill the previously programmed area with zeroes.
This guy explains more about it

 

[Svenska]

I managed to erase two chips as if they were regular EEPROMS (AT27C256R and M27C256B). Not all the way through though, they still have some data, and I still can't write into them. I wonder how it was possible since they are OTP EPROMS.

Many OTP devices were actually just regular EPROMs without the window...