65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);

wire abx = a ^ b;

assign cout = (abx & cin) | (a & b); 
assign sum = abx ^ cin; 

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
    wire c1, c2, c3;

    // TODO: instantiate 4 full adders and chain carries
    full_adder_1bit u1( .a(a[0]), .b(b[0]), .cin(cin), .sum(sum[0]), .cout(c1) );
    full_adder_1bit u2( .a(a[1]), .b(b[1]), .cin(c1), .sum(sum[1]), .cout(c2) );
    full_adder_1bit u3( .a(a[2]), .b(b[2]), .cin(c2), .sum(sum[2]), .cout(c3) );
    full_adder_1bit u4( .a(a[3]), .b(b[3]), .cin(c3), .sum(sum[3]), .cout(cout) );

    // TODO: drive coutcout

endmodule