
Power control (PWR)
RM0008
Doc ID 13902 Rev 12
Entering Standby mode
Refer to
for more details on how to enter Standby mode.
In Standby mode, the following features can be selected by programming individual control
bits:
●
Independent watchdog (IWDG): the IWDG is started by writing to its Key register or by
hardware option. Once started it cannot be stopped except by a reset. See
Section 19.3: IWDG functional description
Section 19: Independent watchdog
●
real-time clock (RTC): this is configured by the RTCEN bit in the Backup domain control
register (RCC_BDCR)
●
Internal RC oscillator (LSI RC): this is configured by the LSION bit in the Control/status
register (RCC_CSR).
●
External 32.768 kHz oscillator (LSE OSC): this is configured by the LSEON bit in the
Backup domain control register (RCC_BDCR)
Exiting Standby mode
The microcontroller exits the Standby mode when an external reset (NRST pin), an IWDG
reset, a rising edge on the WKUP pin or the rising edge of an RTC alarm occurs (see
Figure 179: RTC simplified block diagram
). All registers are reset after wakeup from
Standby except for
Power control/status register (PWR_CSR)
After waking up from Standby mode, program execution restarts in the same way as after a
Reset (boot pins sampling, vector reset is fetched, etc.). The SBF status flag in the
control/status register (PWR_CSR)
indicates that the MCU was in Standby mode.
Refer to
for more details on how to exit Standby mode.
I/O states in Standby mode
In Standby mode, all I/O pins are high impedance except:
●
Reset pad (still available)
●
TAMPER pin if configured for tamper or calibration out
●
WKUP pin, if enabled
Table 15.
Standby mode
Standby mode
Description
Mode entry
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP in Cortex™-M3 System Control register
– Set PDDS bit in Power Control register (PWR_CR)
– Clear WUF bit in Power Control/Status register (PWR_CSR)
Mode exit
WKUP pin rising edge, RTC alarm event’s rising edge, external Reset in
NRST
pin, IWDG Reset.
Wakeup latency
Reset phase