
RM0008
Low-, medium-, high- and XL-density reset and clock control (RCC)
Doc ID 13902 Rev 12
115/1096
7.3.9
Backup domain control register (RCC_BDCR)
Address offset: 0x20
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.
Note:
The LSEON, LSEBYP, RTCSEL and RTCEN bits of the
Backup domain control register
are in the Backup domain. As a result, after Reset, these bits are write-
protected and the DBP bit in the
Power control register (PWR_CR)
has to be set before
these can be modified. Refer to
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
RTC
EN
Reserved
RTCSEL[1:0]
Reserved
LSE
BYP
LSE
RDY
LSEON
rw
rw
rw
rw
r
rw
Bits 31:17 Reserved, always read as 0.
Bit 16
BDRST:
Backup domain software reset
Set and cleared by software.
0: Reset not activated
1: Resets the entire Backup domain
Bit 15
RTCEN:
RTC clock enable
Set and cleared by software.
0: RTC clock disabled
1: RTC clock enabled
Bits 14:10
Reserved, always read as 0.
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 RTC clock10: LSI oscillator clock used as RTC clock
11: HSE oscillator clock divided by 128 used as RTC clock
Bits 7:3 Reserved, always read as 0.
Bit 2
LSEBYP:
External low-speed oscillator bypass
Set and cleared by software to bypass oscillator in debug mode. This bit can be written only
when the external 32 kHz oscillator is disabled.
0: LSE oscillator not bypassed
1: LSE oscillator bypassed