4bit RCA

Theory:

The RCA (Ripple Carry Adder) is a basic and widely used adder circuit in digital electronics, especially for adding two binary numbers. The Ripple Carry Adder works by adding the corresponding bits from the two numbers one at a time, starting from the least significant bit (LSB) to the most significant bit (MSB). The carry from each bit addition "ripples" through to the next bit.

Circuit diagram:

Verilog code:

module ripple_carry_adder (

input [1:0] A, B, // 2-bit inputs A and B

input Cin, // Carry-in

output [1:0] Sum, // 2-bit Sum output

output Cout // Carry-out

);

// Intermediate carry signal for the first bit

wire C1;

// Sum and carry calculations using dataflow

assign Sum[0] = A[0] ^ B[0] ^ Cin; // Sum for the LSB (S0)

assign C1 = (A[0] & B[0]) | (Cin & (A[0] ^ B[0])); // Carry for the LSB (C1)

assign Sum[1] = A[1] ^ B[1] ^ C1; // Sum for the MSB (S1)

assign Cout = (A[1] & B[1]) | (C1 & (A[1] ^ B[1])); // Carry-out for MSB (Cout)

endmodule

TESTBENCH CODE:

module test_ripple_carry_adder;

// Declare the input and output variables for the RCA module

reg [1:0] A, B; // 2-bit input A and B

reg Cin; // Carry-in input

wire [1:0] Sum; // 2-bit Sum output

wire Cout; // Carry-out output

// Instantiate the ripple_carry_adder module

ripple_carry_adder RCA (

.A(A),

.B(B),

.Cin(Cin),

.Sum(Sum),

.Cout(Cout)

);

initial begin

// Display the header for the truth table

$display("A B Cin | Sum Cout");

$display("-----------------------");

// Test Case 1: A = 00, B = 00, Cin = 0

A = 2'b00; B = 2'b00; Cin = 0;

#10; // Wait for 10 time units