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3 Application example: EEPROM emulation using ST10F27x Flash library

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Application example: EEPROM emulation using

ST10F27x Flash library

3.1

Purpose

The purpose of this example is to show how a portion of the ST10F27x embedded Flash

can be used to replace a serial EEPROM to store and update non volatile data in order to

save the cost of an external EEPROM.

3.2

Principle

The implementation shown in this application note requires that a minimum of two Flash

sectors of identical size are allocated to non volatile data storage. In this example, the sector

1 and sector 2, 8 kbytes each, of the Flash bank 0 are used.

Those sectors are write accessed in 32-bit.

A header field occupying the first 32-bit word of each sector represents the sector’s status.

In order to use Flash to store several non volatile variables, we need to divide the two

sectors identically into several parts, one per variable.

For each variable, the size of the memory space is allocated according to its update

frequency. The first 32-bit value of each variable is stored at the base address of its

allocated memory space. When updated, the new value is stored at the next available

address: base address + 4, base address + 8 and so on until no room remains from its

allocated memory.

Example:

In the sector 1, we assume 3 variables: A, B and C will be stored and updated.

In a typical application, the majority of non volatile data is updated infrequently and a few is

updated more frequently.

than C so more memory space should be allocated to A and B than C.

In this application, sector 1 is divided as follows:

●

0x2000-0x2FFF memory space will be allocated to variable A

●

0x3000-0x3FEB memory space will be allocated to variable B

●

0x3FEC-0x3FFF memory space will be allocated to variable C

t

A

t

B

t

C