Clk为50MHz的时钟信号输入；rst为复位控制按键（低电平有效）；en(0-2)通过三个按键分别控制3种状态（低电平有效）。

1.　　当en(0)=`0`时，启动加法计数并将结果动态显示到两位数码管上，同时另外的两位数码管的6段以相反方向按顺序闪烁

2.　　当en(1)=`0`时，启动减法计数并将结果动态显示到两位数码管上，同时另外的两位数码管的6段以相反方向按顺序闪烁，闪烁方向与加法的相反；

3.　　当en(2)=`0`时，启动LED闪烁功能，LED灯按顺序逐个流水闪动；

4.　　当rst=`0`时，复位清零；

-Clk 50MHz clock signal input　rst the reset control buttons (active low)　en (0-2) by three keys to control the three states (active low).

When en () = `0` when to start the addition count and the results to two digital tube dynamic display, two digital tube flashing segment in the opposite direction in order

When en (1) = `0` when you start subtraction counting and results to two digital tube dynamic display, two digital tube segment flashing sequence in the opposite direction, the the flashing direction with the addition opposite

When en (2) = `0` when start the LED flashes, LED lights flashing sequentially, water

4 When the when rst = `0`, reset cleared