说明：  8253用定时器2来产生896Hz的音频信号使喇叭发声，我们可以改变定时器2的计数值来改变声音频率，通过发声的延时程序来获得时间长短不同的声音，于是就可以通过编程；来获得声调（频率）和节奏（延时长短），使计算机演奏出乐曲来。
(8253 with a 896Hz timer 2 to generate the audio signal to the speaker sound, we can change the timer 2 count to change the sound frequency, through the voice of the length of time delay procedures to get different voices, so they can be programmed to get the tone (frequency) and rhythm (delay length), playing the music to the computer.)