说明：  通过本例程了解 DS1302时钟芯片的基本原理和使用 ,理解并掌握DS1302时钟芯片，驱动程序的编写以及实现数字字符在数码管中的显示
(Through this routine to understand the basic principles and use of the DS1302 clock chip, understand and master the DS1302 clock chip, driver programming and the realization of digital characters in the digital tube display)