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/
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Nations Technologies Inc.
Tel
：
+86-755-86309900
：
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
Enter VBAT mode
When VDD is powered down, it will enter VBAT mode at any time.
Exit VBAT mode
When VDD returns to the power-on reset threshold, the MCU exits VBAT mode. After VDD is restored, the core
area of the MCU will be completely executed according to the power-on sequence. After waking up from VBAT
mode, code execution is identical to execution after reset. The PWR_CTRLSTS.VBATF status flag indicates that the
MCU exits from VBAT mode.
Low-power auto-wakeup
（
AWU
）
mode
In automatic wake-up mode, the RTC can be used to wake up from different low-power modes without relying on
external interrupts. The RTC provides a programmable clock reference for timed wake-up from STOP0, STOP2 and
STANDBY modes. To do this, two of the three optional RTC clock sources can be selected by software programming
RCC_BDCTRL.RTCSEL[1:0] as follows:
32.768kHz external crystal clock (LSE OSC)
This clock source provides an accurate clock reference with very low power consumption.
RC internal crystal clock (LSI RC)
This clock source has the advantage of saving the cost of the 32.768 kHz crystal, but the clock accuracy is worse
than the LSE.
To wake up from STOP2 mode using the RTC alarm event, you need:
Configure EXTI 17 rising edge trigger.
Configure RTC to enable RTC alarm event.
To wake up from STANDBY mode using RTC alarm event, EXTI 17 does not need to be configured.
VBAT mode cannot wake up via RTC.
PWR registers
4.4.1
PWR register overview
Table 4-3 PWR register overview
Offset
Register
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
000h
PWR_CTRL
Reserved
M
S
B
DB
KP
PRS[2:0]
P
VD
E
N
C
S
B
VB
AT
C
W
KU
P
P
DS
L
P
S
Reset Value
0
0
0
0
0
0
0
0
0
0
004h
PWR_CTRLSTS
Reserved
W
KU
P
E
N
Reserved
VB
AT
F
P
VD
O
S
B
F
W
KU
P
F
Reset Value
0
0 0
0
0
