AN2476 datasheet(39/49 Pages) STMICROELECTRONICS

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AN2476

Operating measurements

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Wake-up time measurements

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Definition:

Two wake-up time measurements can be made. The STR75x can be restarted either

from the low-power mode on the internal free oscillator (FREEOSC ) or on the main

oscillator, restarting it if necessary (OSC4M PLL).

–

FREEOSC: Time between wake-up trigger event and the first fetched instruction

by the core.

–

OSC4M PLL: Time between the wake-up trigger event and the execution of the

instruction once the clock has been started by either the library function or in the

interrupt handler routine.

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Measurement: Place the oscilloscope on:

–

Pin 60 (I/O P1.15: WKP_STDBY) and pin 42 (I/O P0.16) to measure the wake-up-

time in a FREEOSC configuration. This time is measured between the rising edge

on pin 60 and a falling edge on pin 42.

–

Pin 60 (I/O P1.15: WKP_STDBY) and Pin 32 (I/O P2.18) to measure the wake-up-

time in a OSC4M PLL configuration. This time is measured between the rising

edge on pin 60 and a falling edge on pin 32.

3.2

Software provided with this application note

There are 3 folders in the ZIP file provided with this application note:

3.2.1

Standby mode

This example shows how to put the system in STANDBY mode and how to wake-up again

using external RESET, WKP_STDBY pin or RTC Alarm (if RTC_ON is set in 75x_conf.h

file).

Of course this software used the standard STR750 library and this example show how to

used the function MRCC_EnterSTANDBYMode(). Refer to Chapter 2.7:

MRCC_EnterSTANDBYMode on page 31 for further information.

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Choose RTC using clock:

Comment the following line in the 75x_conf.h file, if the RTC clock is not required in

STANDBY mode in the application:

#define RTC_ON

In the associated software, the system clock is set to 60 MHz, the EXTIT line7 is

configured to generate an interrupt on falling edge.

●

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

The RTC is programmed to generate an interrupt each 1 second. In the RTC interrupt

handler, an LED connected to P2.18 pin is toggled, and an LED connected to P0.16 is

on. This is used to indicate whether the MCU is in STANDBY or RUN mode.

–

When a falling edge is detected on EXTIT line7, an interrupt is generated. In the

EXTIT handler routine the RTC is configured to generate an alarm event after 10

seconds. Then the system enters STANDBY mode causing the P2.18 pin to stop

toggling.

–

A rising edge on WKP_STDBY pin or an external RESET will wake-up the system

from STANDBY. If within 10 seconds neither rising edge on WKP_STDBY nor

external RESET are generated, the RTC alarm wakes-up the system. After that

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