利用8255扩展并行端口（硬件电路参见CodeDisplay_8255.DSN）。当KEY按下时，利用8255的PC口输入二进制值编码（6位），将该值转换成十进制后显示在2位7段LED显示器上。(Using 8255 to extend parallel ports (see CodeDisplay_8255.DSN for hardware circuits). When the KEY is pressed, the binary value encoding (6 bits) is entered using the 8255 PC port, and the value is converted to decimal to display on the 2 bit 7 segment LED display.)