Decoders 74 138

Decoder by using 74 138

Program Code : 

module simpledecoder(
    input [1:0] A,
    output reg [3:0] O
    );
always @*
    begin
    case(A)
        2'b00: O<=4'b0001;
        2'b01: O<=4'b0010;
        2'b10: O<=4'b0100;
        2'b11: O<=4'b1000;
        default O<=4'b0000;   
    endcase
    end
endmodule

Simple Decoder using DATA FLOW MODELLING 2 by 2 Decoder

module simpledecoder(
    input [1:0] A,
    output reg [3:0] O
    );
always @*
    begin
    case(A)
        2'b00: O<=4'b0001;
        2'b01: O<=4'b0010;
        2'b10: O<=4'b0100;
        2'b11: O<=4'b1000;
        default O<=4'b0000;   
    endcase
    end
endmodule

Simple Decoder 2 by 2 using Structural Modelling :module simpledecoderusingstructuralm(
    input [1:0] A,
    output [3:0] O
    );

decode call(A,O);

endmodule
module decode(
        input [1:0]a,
        output reg [3:0]o
        );
always@*
    begin
    if(a==2'b00)
    o<=4'b0001;
    if(a==2'b01)
    o<=4'b0010;
    if(a==2'b10)
    o<=4'b0100;
    if(a==2'b11)
    o<=4'b1000;
    end   
endmodule       

3 to 8 Decoder Using Behavioural Modellingmodule decoder3to8activehigh(
    input [2:0] A,
    output reg [7:0] O,
    input [0:0] EI
    );
wire a,b,c;
assign a=A[0],
         b=A[1],
         c=A[2];
always@*

        if(EI)   
        begin       
        O<=8'b00000000;
        O[7]<=a&b&c;
        O[6]<=a&b&(~c);       
        O[5]<=a&(~b)&c;
        O[4]<=a&(~b)&(~c);
        O[3]<=(~a)&b&c;
        O[2]<=(~a)&b&(~c);
        O[1]<=(~a)&(~b)&c;       
        O[0]<=(~a)&(~b)&(~c);
        end
endmodule

Decoder 3 to 8 using CASE Statementmodule decoder3to8usingbehavioural(
    input [2:0] A,
    output reg [7:0] O,
    input [0:0] EI
    );

always @*
    if(EI)
        begin
        case(A)
        3'b000: O<=8'b00000001;
        3'b001: O<=8'b00000010;
        3'b010: O<=8'b00000100;
        3'b011: O<=8'b00001000;
        3'b100: O<=8'b00010000;
        3'b101: O<=8'b00100000;
        3'b110: O<=8'b01000000;
        3'b111: O<=8'b10000000;
        default O<=8'b00000000;
        endcase
        end
    else
        O<=8'b00000000;
       
endmodule

74138 Decoder using Case statement

module decoder74138usingbehaviouralmodelling(
    input [2:0] A,
    output reg [7:0] O_L,
    input [0:0] G1,
    input [0:0] G2A_L,
    input [0:0] G2B_L
    );
always @*
    if(G1&(~G2A_L)&(~G2B_L))
    begin
    case(A)
        3'b000: O_L<=8'b11111110;
        3'b001: O_L<=8'b11111101;
        3'b010: O_L<=8'b11111011;
        3'b011: O_L<=8'b11110111;
        3'b100: O_L<=8'b11101111;
        3'b101: O_L<=8'b11011111;
        3'b110: O_L<=8'b0111111;
        3'b111: O_L<=8'b01111111;       
        default O_L<=8'b11111111;
    endcase
    end
    else
        O_L<=8'b11111111;
endmodule

3 to 8 encoder using Data Flow modelling

module decoder74138dataflow(
    input [2:0] A,
    output [7:0] O,
    input [0:0] G1,
    input [0:0] G2A,
    input [0:0] G2B
    );
wire a,b,c;
assign a=A[2],
         b=A[1],   
         c=A[0];
assign O[0]=~((G1)&(~G2A)&(~G2B)&(~a)&(~b)&(~c));        
assign O[1]=~((G1)&(~G2A)&(~G2B)&(~a)&(~b)&(c));
assign O[2]=~((G1)&(~G2A)&(~G2B)&(~a)&(b)&(~c));
assign O[3]=~((G1)&(~G2A)&(~G2B)&(~a)&(b)&(c));
assign O[4]=~((G1)&(~G2A)&(~G2B)&(a)&(~b)&(~c));
assign O[5]=~((G1)&(~G2A)&(~G2B)&(a)&(~b)&(c));
assign O[6]=~((G1)&(~G2A)&(~G2B)&(a)&(b)&(~c));
assign O[7]=~((G1)&(~G2A)&(~G2B)&(a)&(b)&(c));

endmodule