说明：  no intro
(ME300 Series MCU Development System Demonstration Program-1602LCD show stopwatch function description : 1602LCD show stopwatch control K3--- first press the button, the timer and the second press, suspended time. Third press, the cumulative time, the Fourth press, the suspension time. K4--- reset buttons : in any state, click K4 can be reset. May also show : when, minutes and seconds, milliseconds (ms with a two-level display))