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。-Use AT89S51 microcontroller have a "tick, tick, ..." alarm sound from the P1.0 port output, resulting in a frequency of 1KHz, according to the above figure we can see: 1KHZ square-wave output of 0.2 seconds from the P1.0, followed by 0.2 seconds from the P1.0 output level signals, and so cycle continues, the result we need to sound the alarm.