同步下降沿检测

module cy4(
       input sig_a,
       input clk,
       input rstb,
       output sig_a_faledge
       );
reg sig_a_d1;
always @(posedge clk or negedge rstb)
  if(!rstb) sig_a_d1 <= 'b0;
  else sig_a_d1 <= sig_a;
assign sig_a_faledge = !sig_a & sig_a_d1;

endmodule
           

测试脚本代码：

`timescale 1 ns/ 1 ps

module cy4_vlg_tst();

reg eachvec;

reg clk;

reg rstb;

reg sig_a;

wire sig_a_faledge;

cy4 i1 (

.clk(clk),

.rstb(rstb),

.sig_a(sig_a),

.sig_a_faledge(sig_a_faledge)

);

initial

begin

sig_a = 1;

clk = 0;

rstb = 0;

100;

rstb = 1;

100;

sig_a = 0;

100;

stop; s t o p ; display(“Running testbench”);

end

always #20 clk = ~clk ;

endmodule