Power control (PWR) RM0440
248/2126 RM0440 Rev 4
Refer to Table 45: Stop 0 mode for details on how to enter the Stop 0 mode.
If Flash memory programming is ongoing, the Stop 0 mode entry is delayed until the
memory access is finished.
If an access to the APB domain is ongoing, The Stop 0 mode entry is delayed until the APB
access is finished.
In Stop 0 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 42.3: IWDG functional description.
• real-time clock (RTC): this is configured by the RTCEN bit in the RTC domain control
register (RCC_BDCR)
• Internal RC oscillator (LSI): this is configured by the LSION bit in the Control/status
register (RCC_CSR).
• External 32.768 kHz oscillator (LSE): this is configured by the LSEON bit in the RTC
domain control register (RCC_BDCR).
Several peripherals can be used in Stop 0 mode and can add consumption if they are
enabled and clocked by LSI or LSE, or when they request the HSI16 clock: LPTIM1, I2Cx
(x=1,2,3,4) U(S)ARTx(x=1,2...5), LPUART.
The DACx (x=1,2,3,4), the OPAMPs and the comparators can be used in Stop 0 mode, the
PVM and the PVD as well. If they are not needed, they must be disabled by software to save
their power consumptions.
The ADCx (x=1,2,3,4,5), temperature sensor and VREFBUF buffer can consume power
during the Stop 0 mode, unless they are disabled before entering this mode.
Exiting the Stop 0 mode
The Stop 0 mode is exit according Section : Entering low power mode.
Refer to Table 45: Stop 0 mode for details on how to exit Stop 0 mode.
When exiting Stop 0 mode by issuing an interrupt or a wakeup event, the HSI16 oscillator is
selected as system clock. If the device is configured to wake up in Low-power run mode, the
HPRE bits in RCC_CFGR register must be configured prior to entering Stop 0 mode to
provide a frequency not greater than 2 MHz.
When the voltage regulator operates in low-power mode, an additional startup delay is
incurred when waking up from Stop 0 mode with HSI16. By keeping the internal regulator
ON during Stop 0 mode, the consumption is higher although the startup time is reduced.
When exiting the Stop 0 mode, the MCU is either in Run mode (Range 1 or Range 2
depending on VOS bit in PWR_CR1) or in Low-power run mode if the bit LPR is set in the
Power control register 1 (PWR_CR1).
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