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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TIM1的外部时钟模式1功能，选择ETR(PA12)引脚作为外部时钟输入源，并使能
更新中断，在中断中翻转LED灯。

Function descriptions:
This sample demonstrates the External Clock Mode 1 functionality of TIM1. It 
selects the ETR (PA12) pin as the external clock input source and enables the 
update interrupt. In the interrupt, the LED light will toggle.
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测试环境：
测试用板：PY32MD320_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: PY32MD320_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. PA12引脚，输入外部时钟；
3. 可观察到MCU从PA12引脚上每检测到800个脉冲，会让LED灯翻转一次。

Example execution steps:
1.Compile and download the program to the MCU and run it.
2.Input the external clock to the PA12 pin.
3.You can observe that the LED light will toggle each time the MCU 
detects 800 pulses.
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注意事项：

Notes:
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