说明：  设计一个单片机控制的秒表系统。利用单片机的定时器/计数器定时和记数的原理，结合显示电路、LED数码管以及按键来设计计时器。将软、硬件有机地结合起来，使得系统能够正确地进行加、减（倒）计时，数码管能够正确地显示时间。
(Design a single-chip control system stopwatch. The use of single-chip timer/counter timing and number of the principles in mind, combined with display circuit, LED digital tube, as well as to design the timer button. Will be software and hardware combination, the system can correctly add, subtract (down) time, digital tube able to correctly display the time.)