Question

Design an 8-bit full adder using Verilog (Use only 1-bit full adders). Write the design code, test-bench code of it, and test your design with six inputs.

Note: Only use Verilog to design 8-bit full adder.

Answer 1

Answer:

A full adder adds 3 one bit adders , often written as A,B & Cin.

A & B are the operands and Cin is the bit carried from the previous less significant stage.

Code for 8 bit full adder:

module FA(a,b,c,s,co);
input [7:0]a,b;
output [8:0]s;
output co;
input c;
Carry c1(a[0],b[0],c,s[0],cx0);
Carry c2(a[1],b[1],cx0,s[1],cx1);
Carry c3(a[2],b[2],cx1,s[2],cx2);
Carry c4(a[3],b[3],cx2,s[3],cx3);
Carry c5(a[4],b[4],cx3,s[4],cx4);
Carry c6(a[5],b[5],cx4,s[5],cx5);
Carry c7(a[6],b[6],cx5,s[6],cx6);
Carry c8(a[7],b[7],cx6,s[7],s[8]);
assign co = s[8];
endmodule


module Carry(a,b,c,s,co);
input a,b;
input c;
output s,co;
wire out4;
wire out6;
and (out1,a,b);
xor (out2,a,b);
and (out3,out2,c);
or (out4,out3,out1);
assign co = out4;
xor (out5,a,b);
xor (out6,out5,c);
assign s = out6;
endmodule

Module Testing carry :

// Inputs

          reg [7:0] a;

          reg [7:0] b;

          reg c;

          wire [8:0] s;

          wire co;

          CLA uut (

                   .a(a),

                   .b(b),

                   .c(c),

                   .s(s),

                   .co(co)

          );

          initial begin

                   // Initialize Inputs

                   a = 8'b01101010;

                   b = 8'b10111101;

                   c = 0;

          end

endmodule