FLASH option key register
OPTKEY | Option byte key The LOCK bit in the FLASH_NSCR1 must be cleared before doing the unlock sequence for OPTLOCK bit. The following values must be written consecutively to unlock the FLASH_NSCR1.OPTSTRT and OBL_LAUNCH register bits concerning user option operations: KEY1: 0x08192A3B KEY2: 0x4C5D6E7F |