EEPROM Read/Write Cycle

[birdman0_o]

Just wondering what exactly the rating means.
For example a 24LC256 (32k eeprom) is rated a 1 000 000 read write, does this mean the whole device or one byte of memory.

Thanks

 

[DirtyLude]

Never heard of a max number of read cycles, but max write cycles is due to there being a limit to the number of times you can write to a specific cell before it starts to get flakey and fail.

 

[birdman0_o]

Ok, so lets say after 1 000 000 it fails, what does that mean? It can't retain data any more?

 

[DirtyLude]

It means whatever you read from it is unreliable. It means individual cells. SSD's have algorithms to evenly distribute write cycles to as many cells as it can in order to maximize the life of the SSD. These basic EEPROMs don't, so if you are writting log data as fast as you can to a specific cell over and over again, you might need to worry about this and move to different cells every once in a while to avoid the issue.

There was a thread in the microcontroller forum about someone writing to internal PIC FLASH that had to worry about this issue.

 

[Birdman Adam]

I believe that would be correct. I think it would be like in your example, after the 999,999th write, some of the data wouldn't be retained. If you then tryed to read it, parts would be incorrect. Of course in reality, the chip could last reliably from 0-a bazillion writes... Never gotten even close to any of those rating though!

 

[mbarazeen]

This is a guranteed figure given by manufacturer, it confirms the lfie time of each cell is capable of having the certain number of read write cycles minimum, it may even go for millions without any problem.

 

[Mr RB]

Especially at room temperature.

 

[crutschow]

EEPROMS store a bit by transferring charge through a very thin oxide layer (by applying a relatively high voltage causing the charge to tunnel through the oxide) and storing it on the gate capacitance of a MOSFET. This process degrades the oxide slightly for each write (reads cause no degradation). Eventually the damage is high enough that the oxide becomes leaky and it no longer works as a memory.

 

[birdman0_o]

For fun, whats the lifespan if you just read from it?

 

[kchriste]

That would be equal to the data retention spec:

Data retention > 200 years

assuming the IO interface of the chip is still working. The spec is for the charge on the floating gate.

 

[birdman0_o]

That's what I was wondering about, assuming you use it under the limits, what will cause wear and tear on the IO?