PM0073

Reading/programming the STM32Wxxx embedded Flash memory

Doc ID 17766 Rev 5

21/34

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

application programming with a user bootloader:

1.

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

register (FLASH_CR).

2.

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

bytes), and to disable the write protection.

2.3.3

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; this is indicated by OPTWRE in the FLASH_CR register being set. Write access can

be disabled by resetting the bit through software.

2.4

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: Option

byte organization (wireless line devices).

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

organization (wireless line devices) 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

Table 8.

Option byte organization (wireless line devices)

Address

[31:24]

[23:16]

[15:8]

[7:0]

0x0804 0800

nRsvd0

Rsvd0

nRDP

RDP

0x0804 0804

nRsvd2

Rsvd2

nRvsd1

Rvsd1

0x0804 0808

nWRP1

WRP1

nWRP0

WRP0

0x0804 080C

nWRP3

WRP3

nWRP2

WRP2