51单片机3个按键（两个独立按键控制启停，一个单片机自身复位按键控制清零）控制8位数码管显示从小时到毫秒的跑表-51 microcontroller three buttons (two separate start-stop button control, a single chip microcomputer control their own pressing the reset button reset) control eight digital tube display　hours to milliseconds stopwatch