使用内部中断和串口中断实现串口对字符串的接收。程序测试方式为:使用串口调试助手对单片机发送字符串，单片机将接收到的字符串反发送到串口调试助手上。-Using the internal interrupt and serial port interrupt serial string receiver. Program test: serial debugging assistant to send the string to the microcontroller, the microcontr