EEPW论坛

需求描述：XB_HIGH_IN输入下降沿时，H_Trig_OUT立即输出一个负脉冲

仿真结果：H_Trig_OUT输出的波形有4个clk的延时，求大神指教是什么导致了这4个clk的延迟

程序代码：

module TESTCODE(

         input XB_HIGH_IN,

         input clk,

         input rst,

         output reg H_Trig_OUT

);

 

parameter T100us = 12'd3;

reg  H_fir,H_sec;

reg  H_change_trig;

reg  H_vld;

reg  [11:0]H_count;

 

always@(posedge clk or negedge rst)

if(!rst)

         begin

         H_fir<=1'b1;

         H_sec<=1'b1;

         H_change_trig<=1'b0;

         end

else

  begin

  H_fir<=XB_HIGH_IN;

  H_sec<=H_fir;

  H_change_trig<=~H_fir&H_sec;//下降沿

  End

//输出负脉冲

always @(posedge clk or negedge rst)

if(!rst)

begin

H_count<=12'd0;

H_vld<=1'b0;

H_Trig_OUT<=1'b1;

end

 

else

begin

         if(H_change_trig==1'b1)H_vld<=1'b1;

         if(H_vld==1'b1)

         begin

                   H_count<=H_count+1'b1;

                   H_Trig_OUT<=1'b0;

                   if(H_count==T100us)

                            begin

                                     H_count<=12'd0;

                                     H_vld<=1'b0;

                                     H_Trig_OUT<=1'b1;

                            end

         end

end

 

endmodule

测试代码：

module test;

 

         // Inputs

         reg XB_HIGH_IN;

         reg clk;

         reg rst;

 

         // Outputs

         wire H_Trig_OUT;

 

         // Instantiate the Unit Under Test (UUT)

         TESTCODE uut (

                   .XB_HIGH_IN(XB_HIGH_IN),

                   .clk(clk),

                   .rst(rst),

                   .H_Trig_OUT(H_Trig_OUT)

         );

parameter period =250;///////40MHZ

         initial begin

                   // Initialize Inputs

                   XB_HIGH_IN = 1;

                   clk = 0;

                   rst = 0;

 

                   // Wait 100 ns for global reset to finish

                   #100;

      rst = 1; 

                   // Add stimulus here

                   forever begin

                   #(period/2);     

                   clk=~clk;

                   end 

         end

  initial begin

                   forever begin

                   #(period*20);

                   XB_HIGH_IN<=1'b1;       

                   #(period*20);

                   XB_HIGH_IN<=1'b0;       

                   end

         end

endmodule