clock

  定时器每100us中断一次，在中断服务程序中,对中断次数进行计数，100us计数10000次就是1秒。然后再对秒计数得到分和小时值，并送入显示缓冲区。(Timer interrupt every 100us, in the interrupt service routine, the interrupt number of counts, 100us count is 1 second 10000. Then seconds count the minutes and hours values 椠渀琀漀 the display buffer.)