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-Digital tube top three display a stopwatch, and from 1　s speeds between 000-999, when a separate keyboard is pressed the stopwatch stop, release the hand stopwatch continues to run. (The timer design table). In the previous question on the basis of three separate keyboard press the first one when the timing is stopped, press the second when timing began pressing the third count is cleared to start from scratch. Press the 16 matrix keyboard to turn on the digital display 1-16 square. Such as pressing the first to show a second display 4 ...