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。
(By this routine is to understand the basic principles of the DS1302 clock chip and use, understand and grasp the DS1302 clock chip driver to prepare as well as digital character digital tube display.)