用AT89S51单片机产生“嘀、嘀、…”报警声从P1.0端口输出，产生频率为1KHz，根据上面图可知：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-AT89S51 microcontroller with have a " tick, tick, ..."　alarm sound output from the P1.0 port to produce a frequency of 1KHz, according to the above diagram can see: 1KHZ square wave output from P1.0 0.2 seconds, followed by 0.2 seconds from the P1.0 output level signals, so the cycle continues, the result will sound the alarm that we need