jh17

代码说明：

说明：  本文件夹包含的是针对电话交换系统的C51程序源代码，包含了电话串口之间的通信功能，以及控制回铃音的程序源代码(This folder contains the telephone exchange system for the C51 source code, including a telephone communication between the serial port, and control ring back tone of the program source code)