Peripheral firmware examples description

AN4157

14/24

Doc ID 023629 Rev 1

LED3 is used to monitor the system state as following:

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LED3 toggling: system in Run mode

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LED3 off: system in Standby mode

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LED3 toggling: system resumed from Standby mode

These steps are repeated in an infinite loop.

Note:

To measure the current consumption in Standby mode, please refer to Chapter 3.12:

Current consumption example.

3.14

Stop mode example

3.14.1

Purpose

This example shows how to enter Stop mode and wakeup using EXTI Line interrupts. The

EXTI Line sources are PA0 and RTC Alarm.

3.14.2

Description

In this example:

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The EXTI Line0 is configured to generate interrupt on falling edge.

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The EXTI line17 (RTC Alarm) is configured to generate interrupt on rising edge.

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The SysTick timer is programmed to generate an interrupt every 250 ms. In the SysTick

interrupt handler, LED3 is toggled, which indicates whether the MCU is in Stop or Run

mode.

The system enters Stop mode and waits for the RTC Alarm to be generated every 5s, or for

the user push-button to be pressed.

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If the RTC Alarm (EXTI_Line17) has been configured to wakeup the microcontroller

from Stop mode, LED4 and LED3 is On.

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If the User push-button (EXTI_Line0) has been configured to wakeup the

microcontroller from Stop mode, LED5 and LED3 is On.

LEDs are used to monitor the system state:

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LED3 ON: system in Run mode

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LED3, LED4 and LED5 OFF: system in Stop mode

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LED5 ON if EXTI Line0 is used to exit from Stop

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LED4 ON if EXTI line17(RTC Alarm) is used to exit from Stop.

3.15

RCC (reset and clock controller) example

3.15.1

Purpose

This example shows how to:

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Configure the HSE (High Speed Clock) as an RCC clock

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Use the Clock Security System (CSS) feature to generate an NMI interrupt

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Output the system clock on MCO