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                                样例使用说明
                             Sample Description
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功能描述：
此样例演示了将系统时钟设置为LSE，并通过MCO引脚输出系统时钟。

Function descriptions:
This example demonstrates setting the system clock to LSE and outputting the
system clock through the MCO pin.
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测试环境：
测试用板：PY32F072_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: PY32F072_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. 按下用户按键；
3. 用示波器监测PA08引脚上的频率，观察是否和配置的LSE频率一致。

Example execution steps:
1. Compile and download the program to the MCU.
2. Press the user button.
3. Use an oscilloscope to monitor the frequency on pin PA08 and observe if it 
   matches the configured LSE frequency.
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注意事项：
1. 样例中默认启动的系统时钟是HSI，只有按下用户按键后，系统时钟才会切换到LSE。

Notes:
1. The default system clock in the sample is HSI. The system clock will only 
   switch to LSE when the user button is pressed.
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