DocID13902 Rev 15 76/1128
RM0008 Power control (PWR)
80
5.3.5 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 1.8 V domain is
consequently powered off. The PLL, the HSI oscillator and the HSE oscillator are also
switched off. SRAM and register contents are lost except for registers in the Backup domain
and Standby circuitry (see Figure 4).
Entering Standby mode
Refer to Table 1 5 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 19.3: IWDG functional description in Section 19: 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
register (RCC_CSR).
• 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 microcontroller exits the Standby mode when an external reset (NRST pin), an IWDG
reset, a rising edge on the WKUP pin or the rising edge of an RTC alarm occurs (see
Figure 179: RTC simplified block diagram). All registers are reset after wakeup from
Standby except for 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 Power
control/status register (PWR_CSR) indicates that the MCU was in Standby mode.
Refer to Table 1 5 for more details on how to exit Standby mode.
Table 15. Standby mode
Standby mode Description
Mode entry
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP in Cortex
®
-M3 System Control register
– Set PDDS bit in Power Control register (PWR_CR)
– Clear WUF bit in Power Control/Status register (PWR_CSR)
Mode exit
WKUP pin rising edge, RTC alarm event’s rising edge, external Reset in
NRST pin, IWDG Reset.
Wakeup latency Reset phase
To Next Page
Loading...
Need help?
General
