说明：  本程序是实现PC和51单片机之间的串行通信，通信协议是MODBUS，这是本人经过调试过的。C语言开发，程序里有详细注释，可读性很好！
(This process is achieved between the PC and the 51 single-chip serial communication, communication protocol is MODBUS, this is after I debugged. C language development, the program notes in a detailed and readable very good!)