利用实验台上提供的定时器8253和扩展板上提供的8279以及键盘和数码显示电路，设计一个秒表，由8253中断定时，小键盘控制秒表的启停及初始值的预置。-Experimental use of the platform provided by the expansion of on-board timer 8253 and 8279 provided, as well as keyboard and digital display circuit, the design of a stopwatc