说明：  通过d/a转换器产生模拟信号，使用pc机作为简易电子琴。使计算机数字键1、2、3、4、5、6、7作为电子琴键。硬件8253，8255，dac0632
(through d/a converter produce analog signals, the use of PCs as simple flower. The computer keys, as an electronic Qinjian. Hardware 8253,8255, dac0632)