AN2476 datasheet(41/49 Pages) STMICROELECTRONICS

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AN2476

Operating measurements

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3.2.2

STOP mode

This example shows how to put the system in STOP mode and then to wake-up from this

mode using an external interrupt, an RTC alarm or an NCKD (no clock detected) interrupt.

●

Choose the Board:

The choice of board to be used to perform the measurements is defined in the

75x_conf.h file. Comment/uncomment the appropriate lines, depending on the chosen

board:

#define STR750_EVAL

//#define Uniboard

●

Choose the STOP mode:

Uncomment one of these lines in the 75x_conf.h file to select the STOP mode

configuration:

//#define MRCC_STOP_Default

//#define STOP_MVREG_Off

//#define STOP_OSC4M_Off

//#define STOP_FLASH_Off

//#define STOP_FLASH_PLL_Off

#define STOP_FLASH_OSC4M_Off

●

Choose RTC using clock:

Comment the following line in the 75x_conf.h file if the RTC is not used to wake-up from

STOP mode:

#define RTC_ON

In the associated software, the system clock is set to 60 MHz and an interrupt is

generated if no clock is present on OSC4M.

●

If the RTC is on (by uncommenting the line #define RTC_ON in the 75x_conf.h file):

The EXTIT line7(P1.05) and EXTIT line15 are configured to generate interrupts on a

rising edge and the RTC is programmed to generate an interrupt each 1 second. The

EXTIT line15 is shared between the RTC_Alarm event and the WKP_STDBY pin

(P1.15).

In the RTC interrupt handler, an LED connected to P2.18 pin is toggled and used to

indicate whether the MCU is in STOP or RUN mode.

The system enters mode as follows:

After system power on, an LED connected to P2.18 pin is toggled each 1 second

After 5 seconds the RTC is configured to generate an alarm event after a delay of

10 seconds

The system then enters STOP mode causing the P2.18 pin to stop toggling.

The system exits STOP mode as follows:

To wake-up from STOP mode either a rising edge can be applied on EXTIT line15,

EXTIT line7 or the 4MHz external Quartz oscillator can be disconnected.

If within 10 seconds none of those actions are performed, the RTC alarm wakes-

up the system.

The LED connected to P0.16 is then switched on and the VCO of the PLL

(FREEOSC) supplies the system clock.

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