working with an external eeprom...having problem in memory

[venkates2218]

I'm going to use external eeprom 24LC256 with PIC MCU...
My doubt is in eeprom's datasheet they mentioned 1000000 write/read cycle...
Is this is limit for eeprom to write and read data...
What happen when write/read operation exit this specified values means..?

 

[KlausST]

Hi,

It is not write/read, it is write/erase.

--> you may read as often as you like.
And it is "per byte".

If you write every minute to the same EEPROM address, then it takes about 2 years to be a t 1million.

What happens: it is called "wear out". The contents of the cell is not reliable anymore.
There are "wear leveling" algorithms.

One simple method can be: read the content first, and write only if the newvalue is different.

Klaus

 

[betwixt]

I think the problem is related to charge dissipation in the adjacent memory cells on the silicon. If you imagine an array of cells and you keep writing to one in the middle, eventually the ones around it start to change state. The life expectancy doesn't mean the cell stops working, it just means that after at least 1 million write operations, the contents of adjacent cells may become unreliable. Note that 1 million is a worst case figure, in most instances it would take much longer. If the memory is erased, except for the natural effects of aging, it is restored to good condition again. Reading has no effect on the cell life, you can do it as many times as you like.

If your application really does need to write many times it would be better to use SRAM with battery or capacitor backup.

Brian.