Datasheet

DocID024030 Rev 10 33/239
STM32F427xx STM32F429xx Functional overview
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Additional 32-bit registers contain the programmable alarm subseconds, seconds, minutes,
hours, day, and date.
Like backup SRAM, the RTC and backup registers are supplied through a switch that is
powered either from the V
DD
supply when present or from the V
BAT
pin.
3.20 Low-power modes
The devices support three low-power modes to achieve the best compromise between low
power consumption, short startup time and available wakeup sources:
• Sleep mode
In Sleep mode, only the CPU is stopped. All peripherals continue to operate and can
wake up the CPU when an interrupt/event occurs.
• Stop mode
The Stop mode achieves the lowest power consumption while retaining the contents of
SRAM and registers. All clocks in the 1.2 V domain are stopped, the PLL, the HSI RC
and the HSE crystal oscillators are disabled.
The voltage regulator can be put either in main regulator mode (MR) or in low-power
mode (LPR). Both modes can be configured as follows (see Table 5: Voltage regulator
modes in stop mode):
– Normal mode (default mode when MR or LPR is enabled)
– Under-drive mode.
The device can be woken up from the Stop mode by any of the EXTI line (the EXTI line
source can be one of the 16 external lines, the PVD output, the RTC alarm / wakeup /
tamper / time stamp events, the USB OTG FS/HS wakeup or the Ethernet wakeup).
• Standby mode
The Standby mode is used to achieve the lowest power consumption. The internal
voltage regulator is switched off so that the entire 1.2 V domain is powered off. The
PLL, the HSI RC and the HSE crystal oscillators are also switched off. After entering
Standby mode, the SRAM and register contents are lost except for registers in the
backup domain and the backup SRAM when selected.
The device exits the Standby mode when an external reset (NRST pin), an IWDG reset,
a rising edge on the WKUP pin, or an RTC alarm / wakeup / tamper /time stamp event
occurs.
The standby mode is not supported when the embedded voltage regulator is bypassed
and the 1.2 V domain is controlled by an external power.
Table 5. Voltage regulator modes in stop mode
Voltage regulator
configuration
Main regulator (MR) Low-power regulator (LPR)
Normal mode MR ON LPR ON
Under-drive mode MR in under-drive mode LPR in under-drive mode
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