Part # Application Notes Corded Terminals Cordless Terminal Factory Automation Hvac Home Appliances Control Home Automation Medical Met datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: EEPROM emulation in STR91xF devices


Part Details:

AN2540 Application note EEPROM emulation in STR91xF 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 STR91xF 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 STR91xF 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 STR91xF microcontrollers. June 2007 Rev 1 1/25 www.st.com Contents AN2540 - Application note Contents 1 Embedded Flash memory vs. EEPROM: main differences . . . . . . . . . . 5 1.1 Difference in write access time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Difference in writing method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Difference in erase time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Appropriate solution for Emulated EEPROM in the STR91xF . . . . . . . . 7 2.1 STR91xF on-chip Flash memory features . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 STR91xF Flash memory library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Implementing the EEPROM emulation . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 1st method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.1 Application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2.2 EEPROM software description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3 2nd method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.1 Application example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.3.2 EEPROM software description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.4 Program execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4 Embedded application aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.1


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