采用中断方式进行溢出次数累计；

从秒——分——时的计时是通过累加和数值比较实现的；

时钟显示缓冲区：时钟时间在方位数码管上进行显示，为此在内部

RAM中要设置显示缓冲区，共6个地址单元。显示缓冲区从左到右依次存放时、分、秒数值；

-Overflow interrupt the use of the number of cumulative manner　from seconds- minutes- when the time is through the cumulative realized and numerical comparison　clock display buffer: clock time in the position of digital tube display, for the internal RAM to be set up display buffer, a total of six units address. Show that the storage buffer from left to right, the minute and second values