利用DS1302芯片实现RTC（Real Time Clock，实时时钟）功能。驱动DS1302芯片，给芯片赋初始值，并通过LED灯显示DS1302的实时个位秒数（0~9）。-Realize RTC (Real Time Clock) function with DS1302 chip. Drive DS1302 chip, give the chip initial value, and through the LED display DS1302 real-time seconds (0 ~