PM0075

Reading/programming the embedded Flash memory

Doc ID 17863 Rev 2

19/31

Unprotection

To disable the write protection, two application cases are provided:

●

Case 1: Read protection disabled after the write unprotection:

–

Erase the entire option byte area by using the OPTER bit in the Flash memory

control register (FLASH_CR)

–

Program the correct RDP code 0x00A5 to unprotect the memory. This operation

first forces a Mass Erase of the main Flash memory.

–

Reset the device (system reset) to reload the option bytes (and the new WRP[3:0]

bytes), and to disable the write protection

●

Case 2: Read protection maintained active after the write unprotection, useful for in-

application programming with a user boot loader:

–

Erase the entire option byte area by using the OPTER bit in the Flash memory

control register (FLASH_CR)

–

Reset the device (system reset) to reload the option bytes (and the new WRP[3:0]

bytes), and to disable the write protection.

2.4.3

Option byte block write protection

The option bytes are always read-accessible and write-protected by default. To gain write

access (Program/Erase) to the option bytes, a sequence of keys (same as for lock) has to

be written into the OPTKEYR. A correct sequence of keys gives write access to the option

bytes and this is indicated by OPTWRE in the FLASH_CR register being set. Write access

can be disabled by resetting the bit through software.

2.5

Option byte description

There are eight option bytes. They are configured by the end user depending on the

application requirements. As a configuration example, the watchdog may be selected in

hardware or software mode.

A 32-bit word is split up as follows in the option bytes.

The organization of these bytes inside the information block is as shown in Table 8.

The option bytes can be read from the memory locations listed in Table 8 or from the Option

byte register (FLASH_OBR).

Note:

The new programmed option bytes (user, read/write protection) are loaded after a system

reset.

Table 7.

Option byte format

31-24

23-16

15 -8

7-0

complemented option

byte1

Option byte 1

complemented option

byte0

Option byte 0