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Just curious as to why do non volatile memories like EEPROM in an AVR have a write limit ?

Also is this limit per location/adress in the memory or on the memory as a whole ?

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marked as duplicate by Dave Tweed Jul 21 at 0:58

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24LCxxxx series EEPROMs and built in EEPROMs in the PICs have a limit per location. I don't this is the case for all models of EEPROM, though. –  Nick Alexeev Jul 20 at 22:50
    
If the erase cycle erases one location then it's per location, if it's a block, then it is per block. I think so anyway. S08PT60 (Freescale 8-bit MCU), for example, have a two byte erase sector. –  Spehro Pefhany Jul 20 at 22:57
    
@SpehroPefhany, I know that when I program AVR controllers there is an option to erase the entire EEPROM, but I have not seen much regarding erasing blocks like in flash. Perhaps I have just done too little with EEPROM. –  sherrellbc Jul 21 at 0:30

1 Answer 1

It is due to the process of how the memories work.

To write a value the threshold of the device is shifted by storing charge in a floating gate that lies between the control gate and the channel. The process of injecting and removing charge stresses the gate oxide to the point where it leaks , just ever so little. the problem is that this process is slightly damaging and the effect is accumulative.

The wear-out is roughly proportional to number of write/erase cycles with variation on a bit by bit basis.

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