EEPROM Read/Write Cycle

birdman0_o

Active Member

• Nov 20, 2009

• #1

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

Well-Known Member

• Nov 20, 2009

• #2

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

Active Member

• Nov 20, 2009

• #3

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

 

DirtyLude

Well-Known Member

• Nov 20, 2009

• #4

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

New Member

• Nov 20, 2009

• #5

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!

 

Last edited: Nov 20, 2009

mbarazeen

Member

• Nov 20, 2009

• #6

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

Well-Known Member

• Nov 21, 2009

• #7

Especially at room temperature.

 

crutschow

Well-Known Member

Most Helpful Member

• Nov 21, 2009

• #8

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.

 

Last edited: Nov 21, 2009

birdman0_o

Active Member

• Nov 21, 2009

• #9

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

 

K

kchriste

New Member

Forum Supporter

• Nov 21, 2009

• #10

That would be equal to the data retention spec:

Data retention > 200 years

Click to expand...

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

 

birdman0_o

Active Member

• Nov 21, 2009

• #11

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