Binary to Gray Code Converter

October 14, 2025

Solving Approach

We can use the left shift operator to XOR the binary number with the left shifted version of itself and obtain the gray code.

Code

/*Write your code here*/
module bin2gray4 (input [3:0] bin_in, output [3:0] gray_out);
    wire [3:0] w1;
    assign w1 = (bin_in>>1'd1);
    assign gray_out = bin_in^w1;
endmodule

Upvote

Downvote

Please login to run the code.

Testbench Code

`timescale 1ns/1ps

module tb_bin2gray4;
    // Input
    reg  [3:0] bin_in;

    // DUT output
    wire [3:0] gray_out;

    // Expected output
    reg  [3:0] expected_gray_out;

    // Mismatch signal
    wire mismatch = (gray_out !== expected_gray_out);

    integer TOTAL_TEST_CASES = 0;
    integer TOTAL_PASSED_TEST_CASES = 0;
    integer TOTAL_FAILED_TEST_CASES = 0;

    // Instantiate DUT
    bin2gray4 dut (
        .bin_in(bin_in),
        .gray_out(gray_out)
    );

    // VCD dump (Inputs -> Outputs -> Expected -> mismatch)
    initial begin
        $dumpfile("tb_bin2gray4.vcd");
        $dumpvars(0,
            tb_bin2gray4.bin_in,             // input
            tb_bin2gray4.gray_out,           // output
            tb_bin2gray4.expected_gray_out,  // expected
            tb_bin2gray4.mismatch            // mismatch flag
        );
    end

    // Golden model (same vector formula)
    task compute_expected;
        input [3:0] t_bin;
        begin
            expected_gray_out = t_bin ^ (t_bin >> 1);
        end
    endtask

    task run_one;
        input [3:0] t_bin;
        begin
            bin_in = t_bin;
            compute_expected(t_bin);
            #1; // settle

            TOTAL_TEST_CASES++;
            if (!mismatch) begin
                TOTAL_PASSED_TEST_CASES++;
            end else begin
                TOTAL_FAILED_TEST_CASES++;
                $display("FAILED: bin=%b | gray=%b expected=%b mismatch=%b",
                         bin_in, gray_out, expected_gray_out, mismatch);
            end
        end
    endtask

    integer i;
    initial begin
        // Exhaustive: cover all 16 input values
        for (i = 0; i < 16; i = i + 1)
            run_one(i[3:0]);

        // Print full truth table (≤ 16 lines)
        $display("bin  -> gray");
        $display("------------");
        for (i = 0; i < 16; i = i + 1) begin
            bin_in = i[3:0];
            compute_expected(i[3:0]);
            #1;
            $display("%b -> %b (exp=%b mismatch=%b)",
                     bin_in, gray_out, expected_gray_out, mismatch);
        end

        // Summary
        $display("======================================");
        $display("TOTAL_TEST_CASES=%0d", TOTAL_TEST_CASES);
        $display("TOTAL_PASSED_TEST_CASES=%0d", TOTAL_PASSED_TEST_CASES);
        $display("TOTAL_FAILED_TEST_CASES=%0d", TOTAL_FAILED_TEST_CASES);
        $display("ALL_TEST_CASES_PASSED=%s",
                 (TOTAL_FAILED_TEST_CASES==0) ? "true" : "false");
        $display("======================================");
        $finish;
    end
endmodule