同时用两个定时器控制蜂鸣器发声，定时器0控制频率，定时器1控制同个频率持续的时间，间隔3s依次输出1，10，50,100，200,400,800,1k（hz）的方波。 为了保证定时的准确性 晶振选择12M-The same time with two buzzer timer control, timer 0 control frequency, Timer 1 control with a frequency of duration, interval 3s sequentially outputs 1,10,50,100,200,400,800,1 k (hz) square wave. In order to ensure the accuracy of the timing crystal selection 12M