Designing a Verilog T Flip-Flop: RTL Implementation & Testbench
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
Designing a D Flip-Flop with Asynchronous Active-Low Reset
Mastering D Latches: Design, Operation, and Key Differences
Verilog
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