本系统中可以实现“启动/停止”、“清零”等功能。LED数据端口使用的是P0口，由于采用了共阴数码管，且面包板上空间有限，未加扩流三极管，只使用了上拉电阻。为使电路工作更加稳定，加了上电复位电路。

-" Start/stop" , " clear"　function can be achieved in the system. LED data port P0 port common cathode due to the digital control and bread board space is limited, not add expansion flow triode, only use a pull-up resistor. For more stable circuit, plus a power-on reset circuit.