51单片机控制的计时程序，名称：用1602LCD设计的秒表  说明：首先按下K1键时开始计时，自此按下时暂停，第三次按下时继续累积计时，再次按下时停止计时，K2键用于清零秒表-51 microprocessor controlled timer program name: The first press K1 key to start counting, since pressed pause, continue to accumulate timing when pressing