8-bit Ripple carry adder using 2 Four bit adder

8-bit Ripple carry adder using 2 Four bit adder:

 

module bit_8adder(

    input [7:0] a,

    input [7:0] b,

    input cin,

    output [8:0] sum);

     wire tmp;

add8_use4 A1(a[0],a[1],a[2],a[3],b[0],b[1],b[2],b[3],cin,sum[0],sum[1],sum[2],sum[3],tmp);

add8_use4 A2(a[4],a[5],a[6],a[7],b[4],b[5],b[6],b[7],tmp,sum[4],sum[5],sum[6],sum[7],sum[8]);

endmodule

 

module add8_use4(

input a0, input a1, input a2, input a3, input b0, input b1, input b2, input b3, input cin, output sum0, output sum1,output sum2,output sum3, output carry);

     wire c0,c1,c2;

fulladder FA1(a0,b0,cin,sum0,c0);

fulladder FA2(a1,b1,tmp[0],sum1,c1);

fulladder FA3(a2,b2,tmp[1],sum2,c2);

fulladder FA4(a3,b3,tmp[2],sum3,carry);

endmodule