/*数码管前三位显示一个跑表，从000到999之间以1 秒的速度运行，

　　当按下一个独立键盘时跑表停止，松开手后跑表继续运行（用定时器设计表）

　　个独立键盘实现按下第一个时计时停止，按下第二个时计时结束，

　　 按下第三个是计数值清零从头开始*/-/* Digital tube top three display a stopwatch run between 000-999 sec 1 , stopwatch stop when pressing a separate keyboard, release the hand stopwatch continues to run (timer design table) separate keyboard press the first time the timing is stopped, press the second when the timer expires, press the third count is cleared from scratch*/