按下S1从单片机第1个引脚上输出频率为1KHz的方波，再按下S1则停止输出方波； 方波频率误差小于1 。 晶振频率：11.0592MHz-Press S1 output the first one on the microcontroller pins 1KHz square wave frequency, and then press the square wave output S1 is stopped Square-wave frequency error is less