准确延时，数码管显示！用于电子时钟#include//***函数定义***voidlong_delay(void);//长延时voidshort_delay(void);//短延时voiddelay10ms(unsignedchar);//延时10MSvoidwrite7279(unsignedchar,unsignedchar);//写入到HD7279unsignedcharread7279(unsignedchar);//从HD7279读入voidsend_byte(unsignedchar);//发送一个字节unsignedcharreceive_byt