小程序--------旋转按钮

module rot(led,rot_a,rot_b,rotary_press,clk,rst
    );
   
output   [7:0]led;

input    rot_a;
input    rot_b;
input    rotary_press;
input    clk;
input    rst;

//internal signals
wire         rot_a_pulse;
wire         rot_b_pulse;
wire         rotary_push_down;

reg     [1:0]rot_a_buffer;
reg     [1:0]rot_b_buffer;
reg     [1:0]rotary_press_buffer;

reg          rot_clk;
reg     [6:0]cnt1;
reg     [5:0]cnt2;
reg          rot_left;
reg          rot_right;
reg     [7:0]led_pattern;

//--module code-----
//------------------

//---generate rot_clk
clk)
  if(rst)
    begin
      cnt1<=7'd0;
    end
  else
    begin
      cnt1<=cnt1+1;
    end
   
clk)
  if(rst)
    begin
      rot_clk<=1'b0;
      cnt2<=6'd0;
    end   
  else
    begin
      if(cnt1==7'b111_1111)
        begin
          rot_clk<=1'b1;
          cnt2<=6'd1;
        end
      else
        begin
          rot_clk<=1'b0;
          cnt2<=cnt2+1;
        end
    end
   
//----  
rot_clk)
  if(rst)
    begin
      rot_a_buffer<=2'b00;
    end
  else
    begin
      rot_a_buffer[0]<=rot_a;
      rot_a_buffer[1]<=rot_a_buffer[0];
    end  
   
rot_clk)
  if(rst)
    begin
            rot_b_buffer<=2'b00;
    end
  else
    begin
      rot_b_buffer[0]<=rot_b;
      rot_b_buffer[1]<=rot_b_buffer[0];
    end 
 
rot_clk)
 if(rst)
    begin
            rotary_press_buffer<=2'b00;
    end
 else
    begin
      rotary_press_buffer[0]<=rotary_press;
      rotary_press_buffer[1]<=rotary_press_buffer[0];
    end 
 

assign  rot_a_pulse=~rot_a_buffer[0]&&rot_a_buffer[1];
assign  rot_b_pulse=~rot_b_buffer[0]&&rot_b_buffer[1];
assign  rotary_push_down=~rotary_press_buffer[0]&&rotary_press_buffer[1];

rot_clk)
  if(rst)
    begin
      rot_left<=1'b0;
      rot_right<=1'b0;
    end
  else
    begin
      if((rot_a_buffer[1]==1'b0)&&(rot_b_pulse==1'b1))
        begin
          rot_left<=1'b1;
        end
      else
        begin
          rot_left<=1'b0;
        end
      if((rot_b_buffer[1]==1'b0)&&(rot_a_pulse==1'b1))
        begin
          rot_right<=1'b1;
        end
      else
        begin
          rot_right<=1'b0;
        end
    end

endmodule

旋转按钮驱动程序，是基于Spartan3E板子实现的......  需要注意的是，去抖电路的实现，这里应用了分段式分频写法，是综合速度更快。