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)。

在上题的基础上，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。

按下16个矩阵键盘依次在数码管上显示1-16的平方。如按下第一个显示1，第二个显示4...

-The top three shows a digital stopwatch, from 000 to 999 to 1　of the second speed run, a separate keyboard when you press the stopwatch stopped, let go after the stopwatch continues to run. (Design table with a timer). In the last question, based on the realization of the keyboard with the other three independent when pressed the first time to stop, when the second start time, press the third is clear from the beginning counts. Followed by pressing the keyboard matrix 16 is displayed on the digital square of 1-16. Press 1 if the first display, the second display 4 ...