说明：  本程序利用8254以及8255还有扬声器实现了一个简单的七键电子琴。通过按键盘上的相应的数字键，可以产生不同的声音。
(This procedure using 8254 and 8255 there is a simple speaker to achieve the seven key electric piano. On the keyboard by pressing the corresponding number keys, you can have different voices.)