8253stopwatch

代码说明：

  通过PC机内8253定时器设置时间常数，使其每隔10MS产生一次中断，并通过定时中断 ，接管中断服务程序，由汇编语言实现主程序，中断服务程序的编写。(PC-8253 timer to set the time constant, so that every 10MS generate an interrupt and timer interrupt and take over the interrupt service routine, assembly language main program, the interrupt service routine to write.)