AN2061

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4.2 Data programing / erasing with ST10F2xx

Flash programing / erasing in the field, requires to be able 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 sec-

tion assumes that users have experience with all the generic aspects of field reprogramming;

this section will focus only on ST10 specific events.

4.2.1 Flash field reprogramming

This paragraph is giving few advises for the field reprogramming of data. Those advice are not

specific to ST10; they are generic to any embedded application that reprograms itself a Data-

set.

The main points to control during Flash programing / erasing are:

– completion of the programing / erasing process itself,

– events that may interrupt the reprogramming process.

4.2.1.1 Completion of the programming process

The programming process is completed when the last word to be programmed has been pro-

grammed correctly (i.e.: status returned by the Flash is OK). Usually, the last word pro-

grammed is an update of the status word (or status bits) of the new Data-set.

If, for any reason, the programming process is interrupted, at the next restart, the value read

may be either erroneous or good but with a limited retention time.

This should influence how users are coding the status bits and how supply failures are detect-

ed (early warning) or prevented (CPU controlled voltage regulator). It is here difficult to be spe-

cific as choices will depend on application requirements and constraints.

4.2.1.2 Completion of the erasing process

As explained in Section 2.3, the completion of the erasing process before programming in a

bank is very important. Single bit information to record successful erase process should be

avoided. Whenever possible:

– 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 pro-

cess.

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

age regulators to allow to erase the Flash after the main system is stopped (ex: ignition key is

removed).

4.2.1.3 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 for non-automotive applications for EEPROM emulation using stand-alone

Flash memories.