说明：  DS1302实时时钟芯片驱动程序,系统时钟7.3728MHZ，设置熔丝位为外部高频石英晶体振荡，启动时间4.1ms。
(DS1302 real-time clock chip driver, the system clock 7.3728MHZ, set the fuse bit for the external high-frequency quartz crystal oscillation, startup time of 4.1ms.)