hdlbits 习题Adder-Exams/m2014 q4j例化版本答案参考

 module top_module (
    input [3:0] x,
    input [3:0] y, 
    output [4:0] sum);
    wire cout,cout1,cout2;
    full_adder d1(x[0],y[0],1'b0,cout,sum[0]);
    full_adder d2(x[1],y[1],cout,cout1,sum[1]);
    full_adder d3(x[2],y[2],cout1,cout2,sum[2]);
    full_adder d4(x[3],y[3],cout2,sum[4],sum[3]);
endmodule
module full_adder( input a, input b, input cin, output cout, output sum);
    assign {cout,sum}=a+b+cin;
endmodule