本实验将实现如下功能：STM32通过串口和上位机的对话，STM32在收到上位机发过来的字符串后，原原本本的返回给上位机。 注意在上位机输入的字符串末尾加入回车键，否则无响应！-The experiment will achieve the following functions: STM32 through the serial port and PC dialogue, STM32 received PC sent over the string, the return exactly t