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Let us contribute to a cleaner Earth, Go Green Updated: May 31, 2020

Design

  
  
module tff ( 	input clk,
            	input rstn,
            	input t,
            output reg q);
  
  always @ (posedge clk) begin
    if (!rstn) 
      q <= 0;
    else
    	if (t)
      		q <= ~q;
    	else
      		q <= q;
  end
endmodule

  

Testbench

  
  
module tb;
  reg clk;
  reg rstn;
  reg t;
  
  tff u0 (	.clk(clk),
          	.rstn(rstn),
          	.t(t),
          .q(q));
  
  always #5 clk = ~clk;
  
  initial begin  
    {rstn, clk, t} <= 0;
    
    $monitor ("T=%0t rstn=%0b t=%0d q=%0d", $time, rstn, t, q);
    repeat(2) @(posedge clk);
    rstn <= 1;
    
    for (integer i = 0; i < 20; i = i+1) begin
      reg [4:0] dly = $random;
      #(dly) t <= $random;
    end
	#20 $finish;
  end
endmodule

  
Simulation Log
ncsim> run
T=0 rstn=0 t=0 q=x
T=5 rstn=0 t=0 q=0
T=15 rstn=1 t=0 q=0
T=19 rstn=1 t=1 q=0
T=25 rstn=1 t=1 q=1
T=35 rstn=1 t=1 q=0
T=43 rstn=1 t=0 q=0
T=47 rstn=1 t=1 q=0
T=55 rstn=1 t=0 q=1
T=59 rstn=1 t=1 q=1
T=65 rstn=1 t=1 q=0
T=67 rstn=1 t=0 q=0
T=71 rstn=1 t=1 q=0
T=75 rstn=1 t=0 q=1
T=79 rstn=1 t=1 q=1
T=83 rstn=1 t=0 q=1
T=87 rstn=1 t=1 q=1
T=95 rstn=1 t=0 q=0
Simulation complete via $finish(1) at time 115 NS + 0

Click to try this example in a simulator!   

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