本程序是采用T3定时器产生可调频率方波，程序注释了一个定时器赋初值的简便方法，这在串口通信产生波特率定时器赋初值时很有用-This procedure is to use T3 timer produces adjustable frequency square wave, and the program notes a timer initialization, the simple method in the serial communication produce baud rate ti