D Flip-Flop with Synchronous Reset: Verilog Implementation

This article covers the design and implementation of a D flip-flop with a synchronous reset. We’ll explore the symbol, Verilog code, test bench, simulation results, and RTL schematic.

D Flip-Flop Symbol

The following image depicts the symbol for a D flip-flop with a synchronous reset:

D Flip-Flop Verilog Code

Here’s the Verilog code for a D flip-flop with a synchronous reset:

module d_flipflop_synrst(data_in, data_out, clock, reset);
  input data_in;
  input clock, reset;
  output reg data_out;

  always @(posedge clock)
  begin
    if (reset)
      data_out <= 1'd0;
    else
      data_out <= data_in;
  end
endmodule


In this code:

- `data_in` is the input data.
- `clock` is the clock input. The flip-flop's state changes on the positive edge of the clock.
- `reset` is the synchronous reset input. When `reset` is high on a rising clock edge, the output `data_out` is set to 0.
- `data_out` is the output of the flip-flop.

## D Flip-Flop Verilog Code Testbench

This Verilog testbench verifies the functionality of the D flip-flop.

```verilog
module Tb_dflipflop_synrst();
  reg data_in;
  reg clock, reset;
  wire data_out;

  d_flipflop_synrst UUT(.data_in(data_in), .data_out(data_out), .clock(clock), .reset(reset));

  initial begin
    // Initialize Input Stimulus
    data_in = 0;
    clock = 0;
    reset = 0;
  end

  always #100 clock = ~clock;  // Generate a clock signal

  initial begin
    #200  data_in = 1'b1; reset = 1'b1;
    #200 data_in = 1'b1; reset = 1'b1;
    #300 data_in = 1'b1; reset=1'b0;
    #600 data_in = 1'b0;
    #500 data_in = 1'b1;
    #200 data_in = 1'b0;
    #400 $stop;
  end
endmodule

The testbench applies various input stimuli to the flip-flop and monitors the output to ensure correct behavior, including:

• Initializing inputs.
• Generating a clock signal with a period of 200 time units.
• Applying different values to data_in and reset at different times.
• Using $stop to terminate the simulation.

D Flip-Flop Simulation

The simulation results should demonstrate the functionality of the D flip-flop, showing how the output changes based on the data input and clock signal, and how the reset input affects the output.

D Flip-Flop RTL Schematic

The RTL (Register-Transfer Level) schematic provides a graphical representation of the D flip-flop’s internal structure.