Re: Silly error in 8 by 8 Bit Multiplier !!

Altera_Forum · ‎05-08-2010

Hi

Actually I have wrote a code for 8 by 8 Bit Multiplier

that uses CARRY LOOK AHEAD ADDER for the addition

But

The program gives me RIGHT results for some numbers and WRONG results for other numbers

So Can any one check the code for me and tell me where the problem is

Thank you very much

I appreciate your help

CODE:

entity Multiplier is

port

(

A : in bit_vector (7 downto 0);

D : in bit_vector (7 downto 0);

Result : out bit_vector (15 downto 0)

);

end entity;

Architecture M of Multiplier is

Begin

Process (A,D)

variable R : bit_vector (7 downto 0);

variable Carry : bit_vector (8 downto 0);

variable Cout : bit;

variable P : bit_vector (7 downto 0);

variable G : bit_vector (7 downto 0);

variable Sum: bit_vector (7 downto 0);

variable Temp1: bit_vector (7 downto 0);

variable Temp2: bit_vector (7 downto 0);

variable B : bit_vector (7 downto 0);

begin

R:= "00000000";

B:=D;

for i in 0 to 7 loop

If (B(0)= '1') then

Carry(0):= '0';

for j in 0 to 7 loop

G(j):= A(j) and R(j);

P(j):= A(j) or R(j);

Carry(j+1):= G(j) or (P(j) and Carry(j));

Sum(j):= P(j) xor Carry(j);

R(j):= Sum(j);

end loop;

Cout:= Carry(8);

Temp1:= R(0) & B(7 downto 1);

B:= Temp1;

Temp2:= Cout & R(7 downto 1);

R:= Temp2;

Else

Temp1:= R(0) & B(7 downto 1);

B:= Temp1;

Temp2:= Cout & R(7 downto 1);

R:= Temp2;

End IF;

End Loop;

Result(15 downto 8)<= R;

Result(7 downto 0)<=B;

End Process;

End Architecture;

Altera_Forum · ‎05-08-2010

for an 8 bit adder, try this code instead:


library ieee;
use ieee.numeric_std.all;
entity adder is
  port (
    A : in unsigned(7 downto 0);
    D : in unsigned(7 downto 0);
    result : out unsigned(8 downto 0)
  );
architecture rtl of adder is
begin
  result <= ('0' & A) + ('0' & D);
end rtl;

Altera_Forum · ‎05-08-2010

Thank you for your reply

But Actually I have to use the carry look Ahead Adder in my code

So can you please check where the problem is in my code

Thank you

I appreciate your help

Altera_Forum · ‎05-09-2010

write a testbench and run some simulations