ST STM32L0x3 User Manual

Flash program memory and data EEPROM (FLASH) RM0367
84/1043 RM0367 Rev 7
To lock the Flash program memory again, the software only needs to set PRGLOCK bit in
FLASH_PECR. When locked again, PRGLOCK bit needs a new sequence to return to 0. If
PELOCK returns to 1 (locked), PRGLOCK is automatically locked, too.
Unlocking the Option bytes area
An additional write protection is implemented on the Option bytes area. It is necessary to
unlock OPTLOCK to reload or write/erase the Option bytes area.
After a reset, the Option bytes area is not accessible in write mode: OPTLOCK bit in the
FLASH_PECR register is set. A write access to the Option bytes area is granted by clearing
OPTLOCK.
The following sequence is used to unlock the Option bytes area:
1. Unlock the FLASH_PECR register (see the Unlocking the data EEPROM and the
FLASH_PECR register section).
2. Write OPTKEY1 = 0xFBEAD9C8 to the FLASH_OPTKEYR register.
3. Write OPTKEY2 = 0x24252627 to the FLASH_OPTKEYR register.
For code example, refer to A.3.4: Unlocking the option bytes area code example.
If the keys are written with PELOCK = 1, no error is generated, OPTLOCK remains at 1 and
it will be unlocked when re-executing the sequence with PELOCK to 0.
Any wrong key sequence will lock up OPTLOCK in FLASH_PECR until the next reset, and
return a hard fault. A hard fault is returned in any of the four cases below:
• After the first write access if the OPTKEY1 value entered is erroneous.
• During the second write access if OPTKEY1 is correctly entered but the OPTKEY2
value does not match.
• If there is any attempt to write a third value to OPTKEYR (this is also true for the
debugger).
• If there is any attempt to write a different register of the memory interface between
OPTKEY1 and OPTKEY2.
When properly executed, the unlocking sequence clears the OPTLOCK bit and the Option
bytes area is write-accessible.
To lock the Option bytes area again, the software only needs to set OPTLOCK bit in
FLASH_PECR. When relocked, OPTLOCK bit needs a new sequence to return to 0. If
PELOCK returns to 1 (locked), OPTLOCK is automatically locked, too.
Select between different types of operations
When the necessary unlock sequence has been executed (PELOCK, PRGLOCK and
OPTLOCK), the user can enable different types of write and erase operations, writing the
right configuration in the FLASH_PECR register. The bits involved are:
• PRG
• DATA
• FIX
• ERASE
• FPRG

ST STM32L0x3 Specifications

General

Brand	ST
Model	STM32L0x3
Category	Microcontrollers
Language	English