EEPROM question

[sandeepa]

Hello all
When they say the life of an EEPROM is say 1 million write cycles,what exactly does that mean?
What happens to any of its locations after its been updated a million times?

Thanks

 

[Exo]

It may start to degrade. Some bits not beeing able to be written to anymore or lose their data.

 

[sandeepa]

Hello all

That is really great because now I can hope that is the only problem.

I was updating the EEPROM every second without considering the fact that it will wear out.After a while the unit would stop functioning,which is what should have happened if the data in the EEPROM got cleared.

I also suppose that it could possibly start retaining some data again,after being switched off for some time?

Thanks.

 

[Exo]

I also suppose that it could possibly start retaining some data again,after being switched off for some time?

No, if it's worn out then it's gone for good.
Normally you use eeprom to store soms user preferences and such, wich don't change very often.

It isn't meant to be used as RAM and be updated every second.

 

[Oznog]

Switching the part off will not help. The 1M write cycles is the cumulative sum off everything a particular EEPROM location has written over its life.

Realistically, the EEPROM can be expected to sustain far more than its rated 1M cycles. There is only a remote chance the EEPROM location will fail after the rated number of writes. I don't think anyone has reported wearing out the EEPROM.

EEPROM is pretty slow to write too, another reason not to use it as RAM.

There are other reasons EEPROM may fail to write. Check errata for your part. Some have reported not putting a capacitor close to the Vdd/Vss pin caused enough power fluctuation to mess up the EEPROM operations.

 

[bmcculla]

EEPROM works by trapping electrons using an insulating layer. To write to EEPROM a high voltage (usually 12V) is applied to one side of the insulator. This voltage is enough to cause electorns to crash through the insulator and get trapped (or pushed out of the elecron trap). The problem is that crashing through the insulator causes a small amount of damage each time. After a certain amount of damage the insulator stops being an insulator and will allow electrons to escape. This will cause the bit to be permanently stuck at 1 or 0 (I forget which one it is).

If you need to write to non volatile memory all the time take a look at Battery Backed ram or Ramtron's Ferro-electric ram. Batery backed ram has no limit on the number of writes (but it stops working if the backup battry dies). Ferroelectric ram has a write life of like 10^15 writes - which is effectivly infinite.