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Power control (PWR) RM0033

76/1381 RM0033 Rev 9

4.3.5 Standby mode

The Standby mode allows to achieve the lowest power consumption. It is based on the

Cortex

-M3 deepsleep mode, with the voltage regulator disabled. The 1.2 V domain is

consequently powered off. The PLLs, the HSI oscillator and the HSE oscillator are also

switched off. SRAM and register contents are lost except for registers in the backup domain

(RTC registers, RTC backup register and backup SRAM), and Standby circuitry (see

Figure 3).

Entering Standby mode

The Standby mode is entered according to Section : Entering low-power mode, when the

SLEEPDEEP bit in the Cortex

-M3 System Control register is set.

Refer to Table 11 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 17.3 in Section 17: Independent watchdog (IWDG).

• 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

• 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 Standby mode is exited according to Section : Exiting low-power mode. The SBF status

flag in PWR_CR (see Section 4.4.2: PWR power control/status register (PWR_CSR))

indicates that the MCU was in Standby mode. All registers are reset after wakeup from

Standby except for PWR_CR.

The microcontroller exits Standby mode when an external Reset (NRST pin), an IWDG

Reset, a rising edge on WKUP pin, an RTC alarm, a tamper event, or a time stamp event is

detected. All registers are reset after wakeup from Standby except for PWR 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 PWR

power control/status register (PWR_CSR) indicates that the MCU was in Standby mode.

Refer to Table 11 for more details on how to exit Standby mode.

ST STM32F207 series User Manual

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