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eprom_dump [2017/05/29 16:17]
lord_nightmare added meat to article.
eprom_dump [2017/05/29 16:42]
lord_nightmare clean up table, and capitalization of acronyms. add note about damaged chips
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-Techniques for dumping ​bitrotten ​and/or damaged EPROMs:+Techniques for dumping ​bit-rotten ​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.+Bit-rotten ​roms are EPROMs/EEPROMs/flash where the floating gate charges have decayed from age/light exposure below the threshold ​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:+There are several techniques to try to recover ​bit-rotten data like this: 
 +  * Change temperature. Ex: People have reported success using a hair dryer or heat-gun 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 below 4.97v or so lowers the '​threshold'​ for reading back floating gate charges, which can recover some bits which are just below the threshold. Too low of a voltage may make the chip malfunction,​ too high will not have any effect. 
 +  * Multiple reads and binary ANDing or '​voting'​ of the bits: dumping a chip several dozen/​hundred times and having each dump '​vote'​ for whether a given bit is 1 or 0, the most popular votes winning. Binary AND is simpler, but this causes problems if a bit should read as 1 and erratically reads as 0.
  
-Change temperature. Ex: People have reported success using a hair dryer or heatgun on parts. This seems to work better ​than freezing parts doesmaybe by '​boosting'​ via thermal noise the floating gate charge readout value?+Combining 2 or more of these techniques is significantly more effective ​than using them separatelyso people have had much better luck both heating and simultaneously under-volting chips than doing either one separately.
  
-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 bitsdumping 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.+Damaged Chips:
  
 +There are more or less two classes of damage to an IC which will prevent it from reading: Damage to the leadframe and bond wires, and damage to the die itself.
 +
 +Heat might help for leadframe/​bond wire damage (if it cannot be directly/​permanently repaired with conductive epoxy or solder, etc) as it may make the metal expand enough to make contact with the other side it was broken off of.
  
 
 
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