编写串口通信程序，要求PC机先发送02H，单片机发送“HELLO”，如果PC机发送55H，单片机发送“THIS IS A WELL BEGIN!”-Procedures for the preparation of serial communication, PC-request sent to 02H, single-chip microcomputer to send "HELLO", if the PC sent 55H, single-chip microcomputer Send "THIS IS A WELL BEGIN!"