ENCODER (4 : 2)

• 4 inputs → 2 outputs

module encoder_4to2(
    input [3:0] d,
    output reg [1:0] y
);

always @(*) begin
    case(d)
        4'b0001: y = 2'b00;
        4'b0010: y = 2'b01;
        4'b0100: y = 2'b10;
        4'b1000: y = 2'b11;
        default: y = 2'b00;
    endcase
end

endmodule

Test Bench

module encoder_4to2(
    input [3:0] d,
    output reg [1:0] y
);

always @(*) begin
    case(d)
        4'b0001: y = 2'b00;
        4'b0010: y = 2'b01;
        4'b0100: y = 2'b10;
        4'b1000: y = 2'b11;
        default: y = 2'b00;
    endcase
end

endmodule

Decoder (2 : 4)

module decoder_2to4(
    input [1:0] a,
    output reg [3:0] y
);

always @(*) begin
    case(a)
        2'b00: y = 4'b0001;
        2'b01: y = 4'b0010;
        2'b10: y = 4'b0100;
        2'b11: y = 4'b1000;
    endcase
end

endmodule

Test Bench

module tb_decoder;

reg [1:0] a;
wire [3:0] y;

decoder_2to4 uut(.a(a), .y(y));

initial begin
    $monitor("a = %b | y = %b", a, y);

    a = 2'b00; #10;
    a = 2'b01; #10;
    a = 2'b10; #10;
    a = 2'b11; #10;

    $finish;
end

endmodule