I ordered some AT28C256 EEPROMs, but none of them were cleared, they all have some garbage programmed, probably from the last user. Obviously they're supposed to be clean and new. I wanted to ask, is there any way I can determine how many write cycles are left before the EEPROM becomes useless? I know they start with 100,000 writes from the factory, but can I figure out approximately how many writes I can have without knowing the history of the EEPROM's use? I wanted to decide whether I should return them or not. If they've been used a lot, I will. If they still have a long way to go, I'll avoid the effort of returning them.

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    \$\begingroup\$ If you think the usage has been the same on all the units, you could test one or two to destruction. I would not suggest used parts for anything where reliability is very important- for one thing you don't know if they have been handled carefully wrt ESD. \$\endgroup\$ Commented Oct 31, 2020 at 15:36
  • \$\begingroup\$ Even brand new EEPROMS may contain some garbage left over from the QA tests in the factory. They do test them, right? Does the datasheet contain any provision that EEPROMs are shipped clear? \$\endgroup\$
    – fraxinus
    Commented Oct 31, 2020 at 22:41
  • \$\begingroup\$ Typically the use case that gets ppl in trouble is using eeprom as NV storage , e.g. as data logger writing to same blocks over and over again. When used appropriately as a configuration store there it is not any feasible way to wear out the eeprom write cycles. \$\endgroup\$
    – crasic
    Commented Nov 1, 2020 at 16:25

2 Answers 2


No, there is no way to know how many times they have been programmed. A typical user will only program them a few times, so you should be OK. If you plan on programming them tens of thousands of times, you should get new parts.

EEPROMs from the factory are normally unprogrammed (all 1's).

100,000 writes is a "guarantee", they won't magically die at this number. A typical part will last much longer.


As others have indicated a typical EEPROM at room temperature can do many, many more than the guaranteed 100'000 write.

There have been many tests of these performed such as:

Hackaday EEPROM killer


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