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                                样例使用说明
                             Sample Description
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功能描述：
此样例演示了在sleep模式下，使用GPIO事件唤醒。

Function descriptions:
This sample demonstrates waking up in sleep mode using GPIO events.
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测试环境：
测试用板：PY32F031_STK
MDK版本： 5.28
IAR版本： 9.20
GCC 版本：GNU Arm Embedded Toolchain 10.3-2021.10

Test environment:
Test board: PY32F031_STK
MDK Version: 5.28
IAR Version: 9.20
GCC Version: GNU Arm Embedded Toolchain 10.3-2021.10
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使用步骤：
1. 编译下载程序到MCU，并运行；
2. LED灯亮，按下按键，LED灯灭，进入sleep模式；
3. 在PA06上产生一个下降沿，程序退出sleep模式；
4. LED以200ms的间隔进行翻转。

Example execution steps:
1. compile and download the program to MCU and run it;
2. When the LED is on press the key,the LED goes off and enters sleep mode;
3. generate a falling edge on PA06 and the program exits sleep mode;
4. the LED are toggled in 200ms intervals.
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注意事项：
1，演示此样例功能时需要断开swd连接线并重新上电，因为默认情况下，仿真器会把
DBGMCU_CR.DBG_STOP置位。
2，注意关闭systick中断，防止该中断唤醒MCU。

Notes:
1. to demonstrate this sample function, you need to disconnect the swd 
connection wire and re-power,because by default, the emulator will set the 
DBGMCU_CR.DBG_STOP.
2. Be careful to turn off the systick interrupt to avoid this interrupt waking 
up the MCU.
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