Module Fourbitadder.docx

module fourbitadder(a,b,cin,sum,cout); input [3:0]a; input [3:0]b; output [3:0]sum; input cin; output cout; wire c0,c1,c2; fulladder1 fa0(a[0],b[0],cin,sum[0],c0); fulladder1 fa1(a[1],b[1],c0,sum[1],c1); fulladder1 fa2(a[2],b[2],c1,sum[2],c2); fulladder1 fa3(a[3],b[3],c2,sum[3],cout); endmodule

module fulladder1(input a,input b,input cin,output sum,output cy); wire s1,c1,c2; half_adder ha1(a,b,s1,c1); half_adder ha2(s1,cin,sum,c2); or or1(cy,c1,c2); endmodule

module half_adder(input a,b,output sum,carry); xor(sum,a,b); and(carry,a,b); endmodule

Test beanch:

module tb_fulladder_4(); reg[3:0]a; reg[3:0]b; reg cin; wire[3:0] sum; wire cout; fourbitadder tb_fulladder(a,b,cin,sum,cout); initial begin #10 a=4'b0000;b=4'b0000;cin=0; #10 a=4'b0010;b=4'b0110;cin=0; #20 $finish; end endmodule