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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ADC的VREFINT采样功能和VREFBUF的功能，通过VREFINT推算出VREFBUF的电压。

Function descriptions:
This sample demonstrates the ADC's VREFINT sampling function and the VREFBUF 
function,which calculates the voltage of VREFBUF from VREFINT.
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测试环境：
测试用板：PY32C642_STK
MDK版本： 5.28

Test environment:
Test board: PY32C642_STK
MDK Version: 5.28
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使用步骤：
1. 编译并下载程序；
2. 串口打印出VREFBUF的参考电压值。

Example execution steps:
1. Compile and download the program and run it
2. USART printf reference voltage of VREFBUF
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注意事项：
通过USB转TTL模块连接PC与STK板,STK板与USB转TTL模块的连线方式如下；
STK板        USB转TTL模块
PB4(TX)  -->  RX
PB5(RX)  -->  TX
GND      -->  GND

Notes:
Connect the PC to the STK board through the USB to TTL module, the connection
between the STK board and the USB to TTL module is as follows:
STK board      USB to TTL module
PB4(TX)    --> RX
PB5(RX)    --> TX
GND        --> GND
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