.数码管前三位显示一个跑表，从000到999之间以1 秒速度运行，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)。用另外三个独立键盘实现按下第一个时计时停止，按下第二个时计时开始，按下第三个是计数值清零从头开始。- digital tube top three shows a stopwatch,　000 to 999 to 1/100th of a second speed, a separate keyboard is pressed when the stopwatch stopped, loosen hand stopwatch continues to run. (using the timer design).

On the basis of the above questions, with the other three independent keyboard to achieve press the first time to stop, according to the first two hours when the start, according to the first three is the number of data cleared　scratch.