RM0008 Power control (PWR)
57/690
4.3.6 Auto-wakeup (AWU) from low-power mode
The RTC can be used to wakeup the MCU from low-power mode without depending on an
external interrupt (Auto-wakeup mode). The RTC provides a programmable time base for
waking up from Stop or Standby mode at regular intervals. For this purpose, two of the three
alternative RTC clock sources can be selected by programming the RTCSEL[1:0] bits in the
Backup domain control register (RCC_BDCR):
● Low-power 32.768 kHz external crystal oscillator (LSE OSC).
This clock source provides a precise time base with very low-power consumption (less
than 1µA added consumption in typical conditions)
● Low-power internal RC Oscillator (LSI RC)
This clock source has the advantage of saving the cost of the 32.768 kHz crystal. This
internal RC Oscillator is designed to add minimum power consumption.
To wakeup from Stop mode with an RTC alarm event, it is necessary to:
● Configure the EXTI Line 17 to be sensitive to rising edge
● Configure the RTC to generate the RTC alarm
To wakeup from Standby mode, there is no need to configure the EXTI Line 17.
4.4 Power control registers
4.4.1 Power control register (PWR_CR)
Address offset: 0x00
Reset value: 0x0000 0000 (reset by wakeup from Standby mode)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
Res.
1514131211109876543210
Reserved DBP PLS[2:0] PVDE CSBF CWUF PDDS LPDS
Res rwrwrwrwrwrc_w1rc_w1rwrw
Bits 31:9 Reserved, always read as 0.
Bit 8 DBP: Disable backup domain write protection.
In reset state, the RTC and backup registers are protected against parasitic write access. This bit must
be set to enable write access to these registers.
0: Access to RTC and Backup registers disabled
1: Access to RTC and Backup registers enabled
To Next Page
Loading...
Need help?
General
