hdlbits-Bcdadd100

Bcdadd100

You are provided with a BCD one-digit adder named bcd_fadd that adds two BCD digits and carry-in, and produces a sum and carry-out.

module bcd_fadd (
    input [3:0] a,
    input [3:0] b,
    input     cin,
    output   cout,
    output [3:0] sum );

Instantiate 100 copies of bcd_fadd to create a 100-digit BCD ripple-carry adder. Your adder should add two 100-digit BCD numbers (packed into 400-bit vectors) and a carry-in to produce a 100-digit sum and carry out.

Hint

An instance array or generate statement would be useful here.

solution

module top_module( 
    input [399:0] a, b,
    input cin,
    output cout,
    output [399:0] sum );
	
    reg [399:0] cout_inside;
    assign cout = cout_inside[396];
    bcd_fadd fadd(a[3:0], b[3:0], cin, cout_inside[0], sum[3:0]);
    
    generate
        genvar i;
        for (i=4;i<400;i=i+4) begin :add100
            bcd_fadd fadd(a[i+3:i], b[i+3:i], cout_inside[i-4], cout_inside[i], sum[i+3:i]);
        end
    endgenerate
endmodule