AN2476 datasheet(23/49 Pages) STMICROELECTRONICS

23 / 49 page

AN2476

Power supply and clocks

23/49

This procedure is performed by the function of the library described in the Section 2.7:

MRCC_EnterSTANDBYMode on page 31

The Low Power Mode Control Parameters (LP_PARAM bits in the MRCC_PWRCTRL) have

no effect in STANDBY mode.

To enter STANDBY mode, the WKPF bit must be reset. Otherwise, the STANDBY mode

entry procedure will be ignored and program execution will continue.

The user program should also take into account the case of a wake-up event occurring

during the STANDBY mode entry procedure: in this case the STANDBY mode entry

procedure will be ignored and program execution will continue.

Consumption in STANDBY mode

All the peripherals are disabled except the LPVREG (and its associated RSM). The RTC

and its clock source (OSC32K or LPOSC) can be either kept disabled or activated.

If the RTC is disabled, the consumption is reduced to the static consumption of the Low

Power Regulator (and the RSM) which is typically 20µA. The leakage currents due to the

technology are negligible and there is almost no dispersion in temperature (most of the

digital part is not powered)

Wake-up events

Wake-up from STANDBY mode can only be performed by:

●

A reset

●

A rising edge RTC alarm event. See Figure 10: Wake-up from Standby mode on

page 23

●

A rising edge on the WKP_STDBY pin

Refer to Table 5: STANDBY mode functionality on page 25.

Figure 10.

Wake-up from Standby mode

After wake-up from STANDBY mode, program execution restarts in the same way as after a

RESET (the vector reset will be fetched). However, if a wake-up event occurs during the

STANDBY entry procedure, the STANDBY mode entry procedure is ignored and the

program execution continues. The user program should take into account the case of a

wake-up event occurring during the STANDBY mode entry procedure.

Some status flags helps software to determine if it is resuming from RESET or from

STANDBY mode and if STANDBY is exited because of a wake-up event or because of an

external reset.

Refer to the Reference manual for further information on the status bits STDBF and WKPF

in the status register (MRCC_RFSR)

RTC

powered in STANDBY

P1.15 (WKP_STDBY)

Can be read by software

RTC_ALARM

CK_RTC

rising edge

detection

WKPF

Cleared by software or at power-up

EXIT FROM STANDBY

WKP_STDBY

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