说明：  8255与键盘扫描单元完成按键扫描功能，并将读到的按键值依次显示在数码管上，按键是4行*4列共16个按键
(8255 with the completion of the keyboard key scanning scanning unit, and read the key value is in turn displayed on the digital control, the key is 4* 4 rows of 16 keys)