AN2540 - Application note

Embedded application aspects

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4.4

Emulated EEPROM parameters

4.4.1

Program/Erase parameter cycling

One program/erase cycle consists of one or more write accesses and one sector erase

operation.

When the EEPROM technology is used, each byte can be programmed and erased a finite

number of times, typically in the range of 10 000 to 100 000.

However, when the Flash memory is used, the minimum erase size is the sector and the

number of Program/Erase cycles applied to a sector is the number of erase cycles. The

STR91xFxx electrical characteristics guarantee 100 000 Program/Erase cycles per sector.

Generally the maximum life of the EEPROM is thereby limited to the update rate of the most

frequently written parameter.

is done on a 16-bit half-word basis. If we consider that the memory space allocated to

variable C is always filled before the memory spaces allocated to variables A and B, the

expected number of erase cycles depends on variable C. As 6896 bytes are allocated to C,

the variable can be updated 3448 times before it is switched to the other sector and the first

sector is erased. Two sectors are used that can be erased 100 000 times so the total

number of cycles we can expect for C is:

3448 × 2 × 100 000 = 689 600 000 cycles.

Table 8.

Status combinations and actions to be taken

Sector 1

Sector 0

ERASED

RECEIVE_DATA

VALID_DATA

TRANSFER

COMPLETE

ERASED

Invalid state so

erase both

sectors and

format sector 0

Invalid state so

erase both

sectors and

format sector 0

Use sector 0 as

valid sector and

erase sector 1

Invalid state: erase

both sectors and

format sector 0

RECEIVE_DATA

Invalid state:

erase both

sectors and

format sector 0

Invalid state:

erase both

sectors and

format sector 0

Use sector 0 as

valid sector &

erase sector1 &

transfer data from

sector0 to sector1

Use sector 1 as valid

sector & erase sector 0

VALID_DATA

Use sector 1 as

valid sector and

erase sector 0

Use sector 1 as

valid sector &

erase sector 0 &

transfer data from

sector1 to sector0

Invalid state:

erase both sectors

and format

sector0

Use sector 1 as valid

sector and erase

sector 0

TRANSFER

COMPLETE

Invalid state:

erase both

sectors and

format sector 0

Use sector 0 as

valid sector and

erase sector 1

Use sector 0 as

valid sector and

erase sector 1

Invalid state: erase

both sectors and

format sector 0