AN2629 datasheet(13/43 Pages) STMICROELECTRONICS

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AN2629

Power supply

Doc ID 13922 Rev 2

13/43

I/O states in Standby mode

In Standby mode, all I/O pins are high impedance except:

●

Reset pad (still available)

●

TAMPER pin if configured for tamper or calibration out

●

WKUP pin, if enabled

1.2.6

Debug mode

By default, the debug connection is lost if the application puts the MCU in Stop or Standby

mode while the debug features are used. This is due to the fact that the Cortex™-M3 core is

no longer clocked.

However, by setting some configuration bits in the DBGMCU_CR register, the software can

be debugged even when using the low-power modes extensively.

1.2.7

Auto-wakeup (AWU) from low-power mode

The RTC can be used to wakeup the MCU from low-power mode without depending on an

external interrupt (Auto-wakeup mode). The RTC provides a programmable time base for

waking up from Stop or Standby mode at regular intervals. For this purpose, two of the three

alternative RTC clock sources can be selected by programming the RTCSEL[1:0] bits in the

Backup domain control register (RCC_BDCR):

●

Low-power 32.768 kHz external crystal oscillator (LSE OSC).

This clock source provides a precise time base with very low-power consumption (less

than 1µA added consumption in typical conditions)

●

Low-power internal RC Oscillator (LSI RC)

This clock source has the advantage of saving the cost of the 32.768 kHz crystal. This

internal RC Oscillator is designed to add minimum power consumption.

To wakeup from Stop mode with an RTC alarm event, it is necessary to:

●

Configure the EXTI Line 17 to be sensitive to rising edge

●

Configure the RTC to generate the RTC alarm

To wakeup from Standby mode, there is no need to configure the EXTI Line 17.

Table 5.

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, external Reset in

NRST pin, IWDG

Reset.

Wakeup latency

Regulator start up + Reset phase

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