Mystic_Merlin
Joined: 15 Oct 2007
Posts: 533
Location: Bangkok
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 Posted: Wed Mar 18, 2009 11:15 am Post subject: Erasing a copier's eprom with a flash light? |
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I can't remember where I read on a thread (probably not even on this forum) that you had to be careful taking photos of a copier's board as the flash could alter the content of the eprom if its window was not covered...
Well, I thought this info might light us up...
| Quote: | Erasing an EPROM and the window
The information (bits) stored in the EPROM are stored as an electrical charge on a transistor in the EPROM. There is one transistor for each bit of storage. The programming process forces the charge on the transistor where it remains trapped until the part is erased. A charged (programmed transistor) holds the bit value of 0 where an erased (unprogrammed transistor) holds the bit value of 1. Once a transistor in the EPROM is programmed, the only way to remove the trapped charge is to expose the entire chip to high intensity ultraviolet light using an EPROM ERASER. If you look at a standard EPROM you will see that it has a clear window in the center of the part. The purpose of this window is to allow the ultraviolet light to reach the transistors which compose the EPROM memory array and dissipate the electrons trapped on the transistors.
Usually an EPROM, once it has been programmed, will have a cover or sticker placed over the window. You cannot erase an EPROM or change its contents by removing this cover and exposing it to normal room light. Even in direct sunlight it would take two weeks of constant exposure to alter the chip. You cannot erase an EPROM with a black light or tanning bed, it is best to use an eraser manufactured to erase EPROMs and other programmable devices.
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source: http://www.arlabs.com/help.htm |
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