1KHZ方波从P1.0输出0.2秒，接着0.2秒从P1.0输出电平信号，如此循环下去，就形成我们所需的报警声了。-1KHZ square wave output from P1.0 0.2 seconds, followed by 0.2 seconds from the P1.0 output level signal, so the cycle continues, we need to form the sound of the