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                                样例使用说明
                             Sample Description
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功能描述：
此样例演示通过RTC闹钟中断每隔1秒将MCU从STOP模式下唤醒，并且每次唤醒会翻转LED，LED翻转
间隔为1秒。

Function descriptions:
This sample demonstrates waking up the MCU from STOP mode every 1 second using 
RTC alarm interrupt. Each time the MCU wakes up, the LED will toggle its state. 
The LED toggling interval is 1 second.
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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. 编译并下载程序到MCU；
2. 断开swd连接线并重新上电;
3. 等待LED灯亮后，按下用户按键，LED灯关闭，进入STOP模式；
4. RTC开始计时，每隔1s就会通过闹钟中断唤醒MCU，并且翻转LED和串口打印本次闹钟的
时间。

Example execution steps:
1.Compile and download the program to the MCU.
2.Disconnect the SWD connection wire and power on again.
3.Wait for the LED to turn on, then press the user button to turn off the 
LED and enter the STOP mode.
4.The RTC starts counting, wakes up the MCU every 1s with an alarm interrupt, 
and toggles the LED and prints the time of this alarm through the serial port.
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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，  STK板        USB转TTL模块
     PA02(TX) --> RX
     PA03(RX) --> TX
     GND      --> GND
     波特率:115200

Notes:
1.When demonstrating this sample, disconnect the SWD connection and 
power cycle the board, as the debugger will set DBGMCU_CR.DBG_STOP by default.
2.  STK board    USB to TTL module
     PA02(TX) --> RX
     PA03(RX) --> TX
     GND      --> GND
     Baud rate: 115200
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