Power control (PWR)
RM0365
107/1080
DocID025202 Rev 7
Section 26.3: IWDG functional description
Section 26: Independent watchdog
•
real-time clock (RTC): this is configured by the RTCEN bit in the RTC 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
RTC 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
). 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.
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
Debug mode
By default, the debug connection is lost if the application puts the MCU in Stop or Standby
mode while the debug features are used. This is due to the fact that the ARM
®
Cortex
®
-M4
core is no longer clocked.
However, by setting some configuration bits in the DBGMCU_CR register, the software can
be debugged even when using the low-power modes extensively.
Table 27. Standby mode
Standby mode
Description
Mode entry
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP in ARM
®
Cortex
®
-M4 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