D Flip Flop with Asynchronous Reset

The D flip flop is a basic sequential element that has data input ‘d’ being driven to output ‘q’ as per clock edge. Also, the D flip-flop held the output value till the next clock cycle. Hence, it is called an edge-triggered memory element that stores a single bit.

The below D flip flop is positive edge-triggered and has asynchronous active low reset.

As soon as reset is triggered, the output gets reset

D Flip Flop with Asynchronous Reset Verilog Code

module D_flipflop (
  input clk, rst_n,
  input d,
  output reg q
  );
  
  always@(posedge clk or negedge rst_n) begin
    if(!rst_n) q <= 0;
    else       q <= d;
  end
  
endmodule

Testbench Code

module tb;
  reg clk, rst_n;
  reg d;
  wire q;
  
  D_flipflop dff(clk, rst_n, d, q);
  
  always #2 clk = ~clk;
  initial begin
    clk = 0; rst_n = 0;
    d = 0;
    
    #3 rst_n = 1;
    
    repeat(6) begin
      d = $urandom_range(0, 1);
      #3;
    end
    rst_n = 0; #3;
    rst_n = 1;
    repeat(6) begin
      d = $urandom_range(0, 1);
      #3;
    end
    $finish;
  end
  
  initial begin
    $dumpfile("dump.vcd");
    $dumpvars(1);
  end
endmodule

Waveform

Verilog Codes