Reading/programming the STM32Wxxx embedded Flash memory

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Doc ID 17766 Rev 5

On every system reset, the option byte loader (OBL) reads the information block and stores

the data into the Option byte register (FLASH_OBR) and the Write protection register

(FLASH_WRPR). Each option byte also has its complement in the information block. During

option loading, by verifying the option bit and its complement, it is possible to check that the

loading has correctly taken place. If this is not the case, an option byte error (OPTERR) is

generated. When a comparison error occurs, the corresponding option byte is forced to

0xFF. The comparator is disabled when the option byte and its complement are both equal

to 0xFF (Electrical Erase state).

All option bytes (but not their complements) are available to configure the product. The

option registers are accessible in read mode by the CPU. See Section 3: Register

descriptions for more details.