ST STM32F40 Series User Manual

Power controller (PWR) RM0090
97/1422 Doc ID 018909 Rev 4
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 Section 6.3.3: RCC clock configuration register (RCC_CFGR).
5.3.2 Peripheral clock gating
In Run mode, the HCLKx and PCLKx for individual peripherals and memories can be
stopped at any time to reduce power consumption.
To further reduce power consumption in Sleep mode the peripheral clocks can be disabled
prior to executing the WFI or WFE instructions.
Peripheral clock gating is controlled by the AHB1 peripheral clock enable register
(RCC_AHB1ENR), AHB2 peripheral clock enable register (RCC_AHB2ENR), AHB3
peripheral clock enable register (RCC_AHB3ENR) (see Section 6.3.12: RCC AHB1
peripheral clock enable register (RCC_AHB1ENR), Section 6.3.13: RCC AHB2 peripheral
clock enable register (RCC_AHB2ENR)), Section 6.3.14: RCC AHB3 peripheral clock
enable register (RCC_AHB3ENR)).
Table 18. Low-power mode summary
Mode name Entry Wakeup
Effect on 1.2 V
domain clocks
Effect on
V
DD
domain
clocks
Voltage regulator
Sleep
(Sleep now or
Sleep-on-exit)
WFI Any interrupt CPU CLK OFF
no effect on other
clocks or analog
clock sources
None ON
WFE Wakeup event
Stop
PDDS and LPDS
bits +
SLEEPDEEP bit
+ WFI or WFE
Any EXTI line (configured
in the EXTI registers,
internal and external lines)
All 1.2 V domain
clocks OFF
HSI and
HSE
oscillators
OFF
ON or in low- power
mode (depends on
PWR power control
register (PWR_CR)
for
STM32F405xx/07xx
and
STM32F415xx/17xx
and PWR power
control register
(PWR_CR) for
STM32F42xxx and
STM32F43xxx)
Standby
PDDS bit +
SLEEPDEEP bit
+ WFI or WFE
WKUP pin rising edge,
RTC alarm (Alarm A or
Alarm B), RTC Wakeup
event, RTC tamper events,
RTC time stamp event,
external reset in NRST
pin, IWDG reset
All 1.2 V domain
clocks OFF
HSI and
HSE
oscillators
OFF
OFF

ST STM32F40 Series Specifications

General

Brand	ST
Model	STM32F40 Series
Category	Microcontrollers
Language	English