说明：  C语言编译，蜂鸣器简易电子琴实验,学习I/O的高级操作，控制蜂鸣器发出悦耳的按键音。P1.4在这里是单引脚数据输出，作为蜂鸣器的控制信号当高低电平的频率不一样时，将发出不同声音，据此设计音乐演奏程序。
(C language compiler, buzzer simple organ experiential learning I/O, high-level operation, the control buttons buzzer sounded sweet tone. P1.4 Here is a single pin data output, as the buzzer of the control signal. When the high-low frequency not the same, it will make different sounds, light, design music programs.)