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AN2540 - Application note

Appropriate solution for Emulated EEPROM in the STR91xFxx

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Appropriate solution for Emulated EEPROM in the

STR91xFxx

The STR91xFxx microcontrollers support the hardware and software architecture necessary

to emulate EEPROM memory using the on-chip Flash memory.

2.1

STR91xFxx on-chip Flash memory features

■ The STR91x internal Flash memory consists of two banks: Main Flash memory (Bank 0)

and Secondary Flash memory (Bank 1). The Main Flash memory is up to 512 Kbytes in

size and includes up to eight 64-Kbyte sectors. The Secondary Flash memory is 32

Kbytes in size and consists of four 8-Kbyte sectors, it can be useful for the wear-leveling

feature (refer to Section 4.2).

■ One of the STR9 embedded Flash memory features is Read-while-Write (RWW) Dual

Bank operations. This means that the Main Flash memory (Bank0) can be used for code

storage and the smaller Secondary Flash memory, for data storage (EEPROM

emulation).

■ The Flash memory can be erased on a sector or bank basis, and programmed on a 16-

bit half-word basis.

■ Each bank can be programmed and erased over 100 000 cycles.

■ 20-year data retention.

■ Each sector can be individually protected and unprotected against program and erase

operations.

■ As the Flash memory has a shorter write access time, critical parameters can be stored

faster in the emulated EEPROM than in an external serial EEPROM.

■ Interrupt servicing during program/erase is possible.

■ CPU program does not need to be copied into RAM during program/erase: RAM less used

to perform EEPROM emulation.

■ Program/Erase Suspend and Resume commands supported. That is, Flash memory

sector erase may be suspended while data is read from other sectors in the same Flash

memory bank, and then resumed after reading.

2.2

STR91xFxx Flash memory library

The Flash memory programming library is a set of optimized C routines. It contains all that is

needed to program the Flash memory embedded in STR9 devices.

The Flash memory library contains the following source files:

■ 91x_fmi.c, that contains the function codes

■ 91x_fmi.h, that contains the function prototypes

To use the functions provided by the Flash memory library, these two files must be added to

the project. With the STR9 software (SW) library (FMI driver) it is easy to implement the

EEPROM emulation software.

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