AN2540 Datasheet, PDF (1/25 Pages) STMicroelectronics – EEPROM emulation in STR91xFxx devices

AN2540
Application note
EEPROM emulation in
STR91xFxx devices
Introduction
Replacing external EEPROM with emulated EEPROM from the embedded-Flash memory of
the microcontroller is a complex development. This application note is aimed at readers that
are already familiar with the techniques used to secure the content of evolutive information
in the external EEPROM of embedded applications.This application note explains the
differences between external/internal EEPROMs and embedded-Flash memory. It also
gives advice on how to replace external EEPROM with emulated-EEPROM using the
on-chip Flash memory of STR91xFxx devices.
This document also focuses on some embedded aspects in emulated-EEPROM data
storage, that are assumed to be known by the reader.
Overview
Electrically erasable and programmable read-only memory (EEPROM) is a key component
in many embedded applications requiring non-volatile storage of data that are updated at a
byte, half-word or word granularity during run time.
On the other hand, the microcontrollers used in those systems are more and more based on
embedded-Flash memory. To eliminate components, save silicon area and reduce system
cost, the STR91xFxx Flash memory could eventually replace the external EEPROM for
simultaneous code and data storage.
However unlike Flash memory, external EEPROM does not require a block erase operation
to free up space before data can be rewritten. A special software management is required to
store data into Flash memory.
Obviously the emulation software scheme depends on many factors including the EEPROM
reliability, Flash memory architecture and product requirements. Two approaches to
implementation are described in detail in this application note using the on-chip Flash
memory of the STR91xFxx microcontrollers.
April 2013
Rev 2
1/25
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