Reading/programming the embedded Flash memory

PM0075

16/31

Doc ID 17863 Rev 2

Figure 3.

Flash memory Mass Erase procedure

2.3.5

Option byte programming

The option bytes are programmed differently from normal user addresses. The number of

option bytes is limited to 8 (4 for write protection, 1 for read protection, 1 for configuration

and 2 for user data storage). After unlocking the FPEC, the user has to authorize the

programming of the option bytes by writing the same set of KEYS (KEY1 and KEY2) to the

FLASH_OPTKEYR register to set the OPTWRE bit in the FLASH_CR register (refer to

Section 2.3.1 for key values). Then the user has to set the OPTPG bit in the FLASH_CR

register and perform a half-word write operation at the desired Flash address.

FPEC preliminarily reads the value of the addressed option byte and checks that it has been

erased. If not, the program operation is skipped and a warning is issued by the PGERR bit in

the FLASH_SR register. The end of the program operation is indicated by the EOP bit in the

FLASH_SR register.

The FPEC takes the LSB and automatically computes the MSB (which is the complement of

the LSB) and starts the programming operation. This guarantees that the option byte and its

complement are always correct.

Read FLASH_CR_LOCK

FLASH_CR_LOCK

= 1

Yes

No

Yes

No

Perform unlock sequency

Write into FLASH_CR_MER

to 1

Write FLASH_CR_STRT to 1

FLASH_SR_BSY

= 1

Check the erase operation by

reading all the addresses in

the user memory

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