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I've got a problem understanding how an EPROM (UV-erasable) works.

This question may seem very dumb, but what would happen, if I just try to write contents to an EPROM, which has already been written to? Will it just not work? Or will the contents on the EPROM be corrupted? I don't really understand why I can't just overwrite the whole thing, without erasing it first through UV-Exposure.

Maybe somebody with a better understanding of this can explain it to me. Thanks in advance for your help.

SamGibson
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s137
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    get a pencil and some paper .... draw 8 squares ... that is one byte of EPROM .... all squares contain a `1` (erased) .... now store some `0` bits by using the pencil to fill the squares .... you can do that multiple times with multiple bits .... erase all squares to get `1` s back – jsotola Aug 02 '20 at 17:17
  • thanks that's just what I wanted to know! – s137 Aug 02 '20 at 18:10

1 Answers1

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EPROM cells can only be electrically written 1->0 and can only be erased with UV 0->1

So you can electrically overwrite as many times as you like, and get the correct result, provided you never want to change a 0 to a 1.

To change even one cell from 0-1 you have to erase the entire array (well, unless you're really accurate with a UV laser and/or masking the bare die, but that's more like hacking).

Spehro Pefhany
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