8 Bit Ripple Carry Adder (RCA) using Full Adder As Basic Cell

An adder is a digital circuit that performs addition of numbers. In many computers and other kinds of processors adders are used in the arithmetic logic units or ALU. They are also used in other parts of the processor, where they are used to calculate addresses, table indices, increment and decrement operators and similar operations.

Verilog Code for 1-bit full adder

module full_adder(sum, cout, in1, in2, cin);

output wire sum;

output wire cout;

input wire in1, in2, cin;

wire temp1, temp2, temp3;

xor(sum,in1,in2,cin);

and(temp1,in1,in2);

and(temp2,in1,cin);

and(temp3,in2,cin);

or(cout,temp1,temp2,temp3);

endmodule

Verilog code for 8-bit  RCA

module ripple_8(sum,cout,in1,in2,cin);

output wire[7:0] sum;

output wire cout;

input wire[7:0] in1,in2;

input wire cin;

wire c1,c2,c3,c4,c5,c6,c7;

full_adder FA1(sum[0],c1,in1[0],in2[0],cin);

full_adder FA2(sum[1],c2,in1[1],in2[1],c1);

full_adder FA3(sum[2],c3,in1[2],in2[2],c2);

full_adder FA4(sum[3],c4,in1[3],in2[3],c3);

full_adder FA5(sum[4],c5,in1[4],in2[4],c4);

full_adder FA6(sum[5],c6,in1[5],in2[5],c5);

full_adder FA7(sum[6],c7,in1[6],in2[6],c6);

full_adder FA8(sum[7],cout,in1[7],in2[7],c7); 

endmodule

Test Bench for 8-bit ripple carry adder

module rca_tb;
// Inputs
reg [7:0] in1;
reg [7:0] in2;
reg cin;

// Outputs
wire [7:0] sum;
wire cout;

// Instantiate the Unit Under Test (UUT)
ripple_8 uut (
.sum(sum), 
.cout(cout), 
.in1(in1), 
.in2(in2), 
.cin(cin)
);

initial begin
// Initialize Inputs
in1 = 01111011;
in2 = 01111000;
cin = 0;
#10
in1 = 11111011;
in2 = 11111000;
cin = 0;
#10
in1 = 01000011;
in2 = 01101100;
cin = 0;
#10
in1 = 11000011;
in2 = 01111111;
cin = 0;
// Wait 10 ns for global reset to finish
#10;
end
      

endmodule

Note: Execute all the codes at the same time

///Output