RM0367 Rev 7 121/1043
RM0367 Flash program memory and data EEPROM (FLASH)
122
3.8 Option bytes
On the NVM, an area is reserved to store a set of Option bytes which are used to configure
the product. Some option bytes are written in factory while others can be configured by the
end user.
The configuration managed by an end user is stored the Option bytes area (32 bytes). To be
taken into account, a boot sequence must be executed. This boot sequence occurs after a
power-on reset when exiting from Standby mode, or by reloading the option bytes by
software (Section 3.8.3: Reloading Option bytes by software). The Option bytes are
automatically loaded during the boot. They are used to set the content of the FLASH_OPTR
and FLASH_WRPROTx registers.
Every word, when read during the boot, is interpreted as explained in Table 24: the lower 16
bits contain the data to copy in the memory interface registers and the higher 16 bits contain
the complemented value used to check that the data read are correct. If there is an error
during loading operation (the higher part is not the complement of the lower one), the default
value is stored in the registers. The check is done by configuration. Section 3.8.2 explains
what happens when there is a mismatch on protection configurations.
During a write, no control is done to check if the higher part of a word is the complement of
the lower part: this check must be performed by the user application.
3.8.1 Option bytes description
The Option bytes can be read from the memory locations listed in Table 25.
Refer to Section 3.7.8: Option bytes register (FLASH_OPTR) and Section 3.7.9: Write
protection register 1 (FLASH_WRPROT1) for the meaning of each bit.
Table 24. Option byte format
31-24 23-16 15-8 7-0
Complemented
Option byte 1
Complemented
Option byte 0
Option byte 1 Option byte 0
Table 25. Option byte organization
Address [31:16] [15:0]
0x1FF8 0000 nFLASH_OPTR[15:0] FLASH_OPTR[15:0]
0x1FF8 0004 nFLASH_OPTR[31:16] FLASH_OPTR[31:16]
0x1FF8 0008 nFLASH_WRPROT1[15:0] FLASH_WRPROT1[15:0]
0x1FF8 000C nFLASH_WRPROT1[31:16] FLASH_WRPROT1[31:16]
0x1FF8 0010 nFLASH_WRPROT2[15:0] FLASH_WRPROT2[15:0]
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