说明：  利用伟福Lab2000P系列单片机实验仪上提供的键盘，使数字键1、2、3、4、5、6、7作为电子琴按键，按下即发出相应的音调。用8255的PA.0 口发出音频脉冲,驱动喇叭
(Wei Fu Lab2000P using MCS experiment provided on the keyboard, so that the number keys 1,2,3,4,5,6,7 as flower button, press the corresponding tone is issued. By 8255 the PA.0 I sent the audio pulse, horn-driven)