说明：  no intro
(LCD1602 display stopwatch. Functional Description: K3 for the control of keys. When the first press, the beginning of time, the second press, the suspension of time. The third time by pressing, the accumulated time, press the fourth time, the suspension of time. K4 for the Clear button: in any state, click the K4, can be cleared. May also display: hours, minutes, seconds, milliseconds (ms with two-level display))