Is there a such thing as a UV EPROM whose contents cannot be burned unless the UV-sensor is uncovered?

  • \$\begingroup\$ What if you combine two. One one-bit UV erasable which sets a readonly bit for a normal EEPROM downstream. Put that inside one capsule and you are done. \$\endgroup\$
    – winny
    Sep 17, 2016 at 13:11

2 Answers 2


I think we can answer your question quickly by reducing it to

Is there a such thing as a UV-EEPROM?

I have never heard of one.

  • EPROMs (Erasable Programmable Read Only Memories) required the quartz window to allow erasure by UV light.
  • EEPROMs (Electrically Erasable Programmable Read Only Memory) doesn't need the quartz window since they can be erased electrically.

There is no need for a UV-EEPROM. I'm sure it could be made but why bother?

See EEPROM is a "Read Only Memory," so why can I write to it? for further details.

Edit after OP changed question to UV-EPROM.

Is there a such thing as a UV EPROM whose contents cannot be burned unless the UV-sensor is uncovered?

There is no UV sensor in an EPROM. The quartz window exposes the chip to UV for erasure only. There is no way to tell whether the window is covered or not. To do this would require aditional circuitry on the chip and a guaranteed external light source. How would you propose to detect someone programming a chip in the dark?

Edit after resolving the problem through chat:

OP was missing some knowledge of operation of EPROMs and could not understand why the chip would not accept his program. The problem was caused by not erasing before programming.

Erasure typically sets the bits high so that every byte reads 0xFF. Programming burns the bits to 0 as required and leaves any bits that should be a 1 unchanged. You can not program a 1 into a bit that has been set to 0. Only UV erasure does that.

  • \$\begingroup\$ Ahh I didn't read your answer through all the way! I am sorry... Yes there is no (E)EPROM that is UV. Haven't had enough coffee this morning. \$\endgroup\$
    – Snoop
    Sep 17, 2016 at 12:31
  • \$\begingroup\$ I have re-worded the question. \$\endgroup\$
    – Snoop
    Sep 17, 2016 at 12:34
  • \$\begingroup\$ That wasn't good! ;^) See the update. Why are you asking such a question anyway? \$\endgroup\$
    – Transistor
    Sep 17, 2016 at 12:39
  • \$\begingroup\$ So I guess the answer is... no? \$\endgroup\$
    – Snoop
    Sep 17, 2016 at 12:44
  • \$\begingroup\$ The answer is no. Is this something that woke you up in the night or is there a problem you're trying to solve. \$\endgroup\$
    – Transistor
    Sep 17, 2016 at 12:46

Depends whether you mean "erase and program" or "program from blank" or "combust" when you say "burn".

You can program a blank EPROM with the sensor (the entire die) covered.

However you can't erase and re-program it.

Which is why the permanently covered ones are known as OTP (One-Time Programmable) EPROMs. These were attractive in production. Their attraction was their price, because the quartz window was an expensive packaging option.

So the only re-programming you can do on an OTP Eprom is to set '1' bits to '0', since the erased state is '1' in every bit. If you DID need to patch one, it made for some interesting constraints on the patch...


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