DocID018909 Rev 11 261/1731
RM0090 Reset and clock control for STM32F405xx/07xx and STM32F415xx/17xx(RCC)
268
7.3.21 RCC Backup domain control register (RCC_BDCR)
Address offset: 0x70
Reset value: 0x0000 0000, reset by Backup domain reset.
Access: 0 ≤ wait state ≤ 3, word, half-word and byte access
Wait states are inserted in case of successive accesses to this register.
The LSEON, LSEBYP, RTCSEL and RTCEN bits in the RCC Backup domain control
register (RCC_BDCR) are in the Backup domain. As a result, after Reset, these bits are
write-protected and the DBP bit in the PWR power control register (PWR_CR) for
STM32F405xx/07xx and STM32F415xx/17xx has to be set before these can be modified.
Refer to Section 7.1.1: System reset on page 213 for further information. These bits are only
reset after a Backup domain Reset (see Section 7.1.3: Backup domain reset). Any internal
or external Reset will not have any effect on these bits.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
BDRST
rw
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RTCEN
Reserved
RTCSEL[1:0]
Reserved
LSEBY
P
LSERD
Y
LSEON
rw rw rw rw r rw
Bits 31:17 Reserved, must be kept at reset value.
Bit 16 BDRST: Backup domain software reset
Set and cleared by software.
0: Reset not activated
1: Resets the entire Backup domain
Note: The BKPSRAM is not affected by this reset, the only way of resetting the BKPSRAM is
through the Flash interface when a protection level change from level 1 to level 0 is
requested.
Bit 15 RTCEN: RTC clock enable
Set and cleared by software.
0: RTC clock disabled
1: RTC clock enabled
Bits 14:10 Reserved, must be kept at reset value.
Bits 9:8 RTCSEL[1:0]: RTC clock source selection
Set by software to select the clock source for the RTC. Once the RTC clock source has been
selected, it cannot be changed anymore unless the Backup domain is reset. The BDRST bit
can be used to reset them.
00: No clock
01: LSE oscillator clock used as the RTC clock
10: LSI oscillator clock used as the RTC clock
11: HSE oscillator clock divided by a programmable prescaler (selection through the
RTCPRE[4:0] bits in the RCC clock configuration register (RCC_CFGR)) used as the RTC
clock
Bits 7:3 Reserved, must be kept at reset value.
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