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--- eprom_dump [2017/05/29 20:42] – clean up table, and capitalization of acronyms. add note about damaged chips lord_nightmare
+++ eprom_dump [2017/05/29 20:44] – add note about vcc vs vih voltage lord_nightmare
@@ Line 5: / Line 5: @@
 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.
+  * 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. To prevent potential damage to the chip by having address/control lines driven higher than VCC, the reference input 'high' (ViH) voltage for all pins should be lowered simultaneously, but this might not always be necessary.
   * 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.