设计一电子钟,要求显示时、分、秒,时为24小时制 有晶体振荡器或555定时电路提供标准时间的基准信号 还要具有清零功能 扩展部分(具有校时功能,可以对小时和分单独校时,对分校时的时候,停止分向小时的进位,校时时钟源可以借用电路中的时钟 具有正点报时功能。-Design an electronic clock, require a showing hours, minutes, seconds, when a 24-hour system　a crystal oscillator or timing circuitry 555 provides a standard time reference signal　would also like to have a Clear function　extension (with the school when the function, you can separate school for hours and minutes when the right time when the campus to stop the entry points to the hours-bit, school clock source can be borrowed from time to time in the clock circuit　with punctual timekeeping function.