计时采用定时器的方法，不但节省了单片机的资源，而且定时精度高。故做精确定时或者单片机资源有限时，提倡用定时器的方法。(The timer method is used for timing, which not only saves the resources of the single chip, but also has a high timing accuracy. Therefore, it is recommended to use the timer method when maki