Low-Power Modes; Slowing Down System Clocks; Table 11. Low-Power Mode Summary - ST STM32F101 series Reference Manual

RM0008
5.3

Low-power modes

By default, the microcontroller is in Run mode after a system or a power Reset. Several low-
power modes are available to save power when the CPU does not need to be kept running,
for example when waiting for an external event. It is up to the user to select the mode that
gives the best compromise between low-power consumption, short startup time and
available wakeup sources.
The STM32F10xxx devices feature three low-power modes:
• Sleep mode (CPU clock off, all peripherals including Cortex
NVIC, SysTick, etc. are kept running)
•
Stop mode (all clocks are stopped)
•
Standby mode (1.8V domain powered-off)
In addition, the power consumption in Run mode can be reduce by one of the following
means:
•
Slowing down the system clocks
•
Gating the clocks to the APB and AHB peripherals when they are unused.
Mode name
Sleep
(Sleep now or
Sleep-on -
exit)
Stop
Standby
5.3.1

Slowing down system clocks

In Run mode the speed of the system clocks (SYSCLK, HCLK, PCLK1, PCLK2) can be
reduced by programming the prescaler registers. These prescalers can also be used to slow
down peripherals before entering Sleep mode.
For more details refer to

Table 11. Low-power mode summary

Entry wakeup
WFI Any interrupt
WFE Wakeup event
PDDS and LPDS
Any EXTI line
bits +
(configured in the
SLEEPDEEP bit
EXTI registers)
+ WFI or WFE
WKUP pin rising
PDDS bit + edge, RTC alarm,
SLEEPDEEP bit external reset in
+ WFI or WFE NRST pin,
IWDG reset
Section 7.3.2: Clock configuration register
DocID13902 Rev 15
Power control (PWR)
®
-M3 core peripherals like
Effect on
Effect on 1.8V V
domain clocks domain
clocks
CPU clock OFF
no effect on other
None
clocks or analog
clock sources
HSI and
All 1.8V domain HSE
clocks OFF oscillators
OFF
(RCC_CFGR).
Voltage
DD
regulator
ON
ON or in low-
power mode
(depends on
Power control
register
(PWR_CR))
OFF
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