AN2077 データシートの表示（PDF） - STMicroelectronics

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AN2077

EEPROM Emulation with STR71x

STMicroelectronics 

EEPROM Emulation with STR71x

– the erase (if necessary because one Flash bank is full) should be done just before Flash pro-

gramming

– the Flash programming should start only after the successful completion of the erasing proc-

ess.

As the erase process can take few seconds, this may require the use of software-controlled

voltage regulators to allow the Flash to be erased after the main system is stopped (e.g. when

the ignition key is removed).

3.2.1.3 Safety aspects

Depending on safety constraints, the usage of a 3rd bank may be considered: instead of using

2 banks alternatively, 3 banks are used alternatively; in the event of a failure (hardware or non-

recoverable software error) inside a bank, there are still 2 banks available. Such a technique

is already used in some applications for EEPROM emulation using stand-alone Flash memo-

ries.

3.3 FIELD REPROGRAMMING WITH STR71XF

Flash programming/reprogramming in the field, requires the ability to deal safely with all the

possible events that may occur in the application.

This analysis is application-dependent and has to be carefully conducted by the user. This

section assumes that users have experience with all the generic aspects of field reprogram-

ming and will focus only on STR71xF specific events.

3.3.1 Field events and Flash reliability

User’s applications must meet ST’s recommendations for Flash programming and erasing.

Failure to do so could result in lower data retention and/or altered Flash reliability. The condi-

tions leading to an altered data retention or to an altered reliability depend on the command is-

sued to the Flash and the event that occurred during this command (supply out of range,

reset).

From FMEA’s (Failure Modes and Effects Analysis) perspective, customers should consider

that when ST’s recommendations are not implemented, Flash reliability can be altered. When

ST’s advice is followed and provided all field specific events are within ST recommendations

(see hereafter), the Flash will meet ST published specification.

3.3.2 List of Events and Suggested Handling Methods

3.3.2.1 Reset

Reset is one of the events possible during field reprogramming, whatever the possible causes

of reset (spurious reset, external hardware reset, reset due to power-shut down).

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