RM0090 Rev 18 109/1749
RM0090 Embedded Flash memory interface
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Bits 7:5 USER: User option bytes
These bits contain the value of the user option byte after reset. They can be written to program
a new user option byte value into Flash memory.
Bit 7: nRST_STDBY
Bit 6: nRST_STOP
Bit 5: WDG_SW
Note: When changing the WDG mode from hardware to software or from software to
hardware, a system reset is required to make the change effective.
Bit 4 BFB2: Dual-bank Boot option byte
0: Dual-bank boot disabled. Boot can be performed either from Flash memory bank 1 or from
system memory depending on boot pin state (default)
1: Dual-bank boot enabled. Boot is always performed from system memory.
Note: For STM32F42xx and STM32F43xx 1MB part numbers, this option bit must be kept
cleared when DB1M=0.
Bits 3:2 BOR_LEV: BOR reset Level
These bits contain the supply level threshold that activates/releases the reset. They can be
written to program a new BOR level. By default, BOR is off. When the supply voltage (V
DD
)
drops below the selected BOR level, a device reset is generated.
00: BOR Level 3 (VBOR3), brownout threshold level 3
01: BOR Level 2 (VBOR2), brownout threshold level 2
10: BOR Level 1 (VBOR1), brownout threshold level 1
11: BOR off, POR/PDR reset threshold level is applied
Note: For full details on BOR characteristics, refer to the “Electrical characteristics” section of
the product datasheet.
Bit 1 OPTSTRT: Option start
This bit triggers a user option operation when set. It is set only by software and cleared when
the BSY bit is cleared.
Bit 0 OPTLOCK: Option lock
Write to 1 only. When this bit is set, it indicates that the FLASH_OPTCR register is locked. This
bit is cleared by hardware after detecting the unlock sequence.
In the event of an unsuccessful unlock operation, this bit remains set until the next reset.
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