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--- eprom_dump [2017/05/29 20:17] – added meat to article. lord_nightmare
+++ eprom_dump [2019/08/14 23:21] (current) – removed mcmaster
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-Techniques for dumping bitrotten and/or damaged EPROMs:
-Bitrotten roms are eproms/eeproms/flash where the floating gate charges have decayed from age/light exposure below the threshhold to reliably read as the 'high' state. On most EPROM based devices, a high floating gate charge indicates a 0 bit, so this means the values will read as 0xFF instead of the proper value.
-There are several techniques to try to recover 'rotten' data like this:
-Change temperature. Ex: People have reported success using a hair dryer or heatgun on parts. This seems to work better than freezing parts does, maybe by 'boosting' via thermal noise the floating gate charge readout value?
-Lower reference voltage: Lowering the VCC/Reference voltage from 5v to between 4.85 and 4.97v lowers the 'threshhold' for reading back floating gate charges, which can recover some bits which are just below the threshhold. Too low of a voltage may make the chip malfunction, too high will not do anything.
-Multiple reads and binary ANDing or 'voting' of the bits: dumping a rom several dozen/hundred times and having each dump 'vote' for whether a given bit is 1 or 0, the most popular votes winning.