说明：  片机电子钟的计时脉冲基准是由外部晶振的频率经过12分频后提供，采用内部的定时/计数器来实现计时功能。所以，外接晶振频率精确度直接影响电子钟计时的准确性。
(Machine electronic time clock pulse baseline is by an external crystal oscillator frequency, after 12 minutes after the frequency, using an internal timer/counter to achieve the timing function. Therefore, the external crystal frequency accuracy of a direct impact on the accuracy of the electronic time clock.)