改變P1.3腳的電平，然後延時。這樣，這個循環就使得P1.3口輸出一個頻率為2.5khz~4khz的方波。在實驗平臺上運行程序時，d4區的蜂鳴器將發出響聲。-Change P1.3 foot level, and then delayed. In this way, the cycle makes the P1.3 port on the output of a frequency 2.5khz ~ 4khz the square wave. In the experimental platform, run the program, d4 zone buzzer will beep.