该文档完成了数显电子钟系统设计。能够对S（秒）、MIN（分）、Hr（小时）进行计时，按24小时计时制。采用Top_Down的设计方法。 -The document Digital electronic clock to complete the system design. Able to S (s), MIN (minutes), Hr (hour) time, according to the 24-hour clock system. Using Top_Down design met