65. Ripple Carry Adder

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
    // TODO: implement 1-bit full adder (structural or dataflow)
    wire [1:0] temp1;
    wire [1:0] temp2;
    assign temp1 = a + b;
    assign temp2 = temp1 + cin;
    assign sum = temp2[0];
    assign cout = temp2[1];
endmodule

// 4-bit Ripple Carry Adder – chain 4 full adders
module rca4_chain (
    input  [3:0] a,
    input  [3:0] b,
    input        cin,
    output [3:0] sum,
    output       cout
);
    // TODO: Declare internal ripple carries

    // TODO: instantiate 4 full adders and chain carries
    wire c0, c1, c2, c3, c4;
    assign c0 = cin;

    full_adder_1bit fa0 (.a(a[0]), .b(b[0]), .cin(c0), .sum(sum[0]), .cout(c1));
    full_adder_1bit fa1 (.a(a[1]), .b(b[1]), .cin(c1), .sum(sum[1]), .cout(c2));
    full_adder_1bit fa2 (.a(a[2]), .b(b[2]), .cin(c2), .sum(sum[2]), .cout(c3));
    full_adder_1bit fa3 (.a(a[3]), .b(b[3]), .cin(c3), .sum(sum[3]), .cout(c4));

    assign cout = c4;

endmodule