EEPROM page questions...

[alank2]

So an i2c eeprom like this:

http://www2.st.com/content/ccc/resource/technical/document/datasheet/e0/4c/87/45/e8/bd/4f/11/CD00251873.pdf/files/CD00251873.pdf/jcr:content/translations/en.CD00251873.pdf

Says it has a page size of 128 bytes which is great.  Honestly I was much more impressed with these things when I found you could write an entire page at one time.

The manual says in the ECC section works on groups of 4 bytes and that if you change 1, it will rewrite the other 3 whether they have changed or not.

My first question is - ST lists their write endurance at 4M when almost everyone else says 1M.  Is this because they are looking at this 4 byte group/ECC differently than other manufacturers.  Is their "4M" the same as others 1M ?

Second question is - since this 4 bytes is obviously smaller than the page size, this would mean that an entire page can be written in a single write cycle, but does not have to be.  Given that, do these chips have any sort of logic to prevent writing the same bytes?  In other words, if you write the same 4 byte values for a group, will they be rewritten or does the device know they did not change and won't have to be rewritten?

[uncle_bob]

Hi

Any time you look at endurance on memory, it's very important to read *all* the fine print. Is it at 25C or at 70C? Is it 99% sure or 99.99% or 60% sure? There are enough variables that a good marketing guy can get creative.

Error correction *should* improve the memory endurance. If it does not - why do it

Do the chips recognize a re-write of the same data? Probably not. You tell it to write, it erases whatever it needs to and then writes it. It sounds from your description like the minimum erase group is the range of the ECC bits. That's fine if you always write 4 bytes. Maybe not so fine if you tend to write a byte here and a byte there....

Bob

[alank2]

Thanks Bob - I did some testing last night and it does indeed rewrite the same values if you ask it to in a write cycle.  I had a technique I was using for wear leveling, but looking at the way I did it the first time, I think it is time for some improvements.