DocID025810 Rev 3

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AN4434

Cycling endurance

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If the total percentage of cumulated cycles (last row in Table 3) is lower than 100%, the data

stored in the EEPROM are safely cycled.

If the total percentage of cumulated cycles is above 100%, the intrinsic safe margin for

cycling is exceeded and a data relocation strategy must be defined. This can be done by

distributing the number of cycles over several memory locations as follows:

•

define a cycling limit for each data block according to the application needs and product

performance (as shown in Table 3).

•

count the numbers of cycles executed on each data block (counter value can be stored

in the EEPROM).

•

when the counter exceeds the defined limit, the cycled data block must be relocated to

another physically independent memory address. The software developer should

define this new data block to be duplicated in a location inside a different page and,

when possible, not with the same byte address inside the new page. The counter itself

must also be stored in a new location.

In addition, to optimize the number of cycles in the EEPROM and keep the other data blocks

safe in the memory array:

•

define data classes (located in the same page) where data with similar update rates are

gathered together. This will optimize the use of the Page mode instead of the byte

mode.

•

the areas containing the read-only parameters and the cycled items should be

separated and made as much as possible independent from each other. Two types of

data should not share the same pages and, where possible, the same locations inside

the related page.

•

for EEPROM with embedded ECCx4 (see Section 1.2.3), it is recommended to store

data bytes sharing the same class inside N groups (ex: 9 data bytes should be stored in

3 groups, that is group1=4 data bytes, group2=4 data bytes and group3=1 data byte

plus 3 bytes unused). In this way, another class of data (let’s call it class2) cannot share

a group used by class1 and each write cycle will concern either class1 data or class2

data but never class1 data and class2 data.