单片机控制交流蜂鸣器演奏简单的乐曲。 硬件接法：P1.2控制交流蜂鸣器，发声频率等于P1.2的方波振荡频率 运行效果：蜂鸣器演奏出动听的乐曲-Single-chip microcomputer to control the exchange of simple buzzer playing music. Hardware connection: P1.2 to control the exchange of buzzer, audible frequency equal to the s