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RM0401 Rev 3 55/771

RM0401 Embedded Flash memory interface

3.6.2 Programming user option bytes

To run any operation on this sector, the option lock bit (OPTLOCK) in the Flash option

control register (FLASH_OPTCR) must be cleared. To be allowed to clear this bit, you have

to perform the following sequence:

1. Write OPTKEY1 = 0x0819 2A3B in the Flash option key register (FLASH_OPTKEYR)

2. Write OPTKEY2 = 0x4C5D 6E7F in the Flash option key register (FLASH_OPTKEYR)

The user option bytes can be protected against unwanted erase/program operations by

setting the OPTLOCK bit by software.

Modifying user option bytes

To modify the user option value, follow the sequence below:

1. Check that no Flash memory operation is ongoing by checking the BSY bit in the

FLASH_SR register

2. Write the desired option value in the FLASH_OPTCR register.

3. Set the option start bit (OPTSTRT) in the FLASH_OPTCR register

4. Wait for the BSY bit to be cleared.

Note: The value of an option is automatically modified by first erasing the user configuration sector

and then programming all the option bytes with the values contained in the FLASH_OPTCR

3.6.3 Read protection (RDP)

The user area in the Flash memory can be protected against read operations by an

entrusted code. Three read protection levels are defined:

• Level 0: no read protection

When the read protection level is set to Level 0 by writing 0xAA into the read protection

option byte (RDP), all read/write operations (if no write protection is set) from/to the

nWRP: Flash memory write protection option bytes

Section 0 to 4 can be write protected

Bits 4:0

nWRPi

If SPRMOD is reset (default value) :

0: Write protection active on sector i.

1: Write protection not active on sector i.

If SPRMOD is set (active):

0: PCROP protection not active on sector i.

1: PCROP protection active on sector i.

Table 10. Description of the option bytes (continued)

ST STM32F410 User Manual

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