csa_8bit.v

IP core of adder,8-bit width, three design concerpts with different effect.

`timescale 1ns/10ps
//===============================================================================
//           TOP Level --->    8-bit CSA Source Code
//                                     ---BAO Chaowei    Mar 3rd,2009
//===============================================================================
module  CSA_8bit(COUT,
                 SUM,
                 A,
                 B,
                 CIN
                 );
                 
  output         COUT;
  output  [7:0]  SUM;
  input   [7:0]  A;
  input   [7:0]  B;
  input          CIN;
  
  wire   cout0,cout1,cout2,cout3,cout4,cout5,cout6,cout7;
  
  CSA_CELL CSA_BIT0(.co     (cout0),
                    .s      (SUM[0]),
                    .a      (A[0]),
                    .b      (B[0]),
                    .ci     (CIN)
                    );
  
  CSA_CELL CSA_BIT1(.co     (cout1),
                    .s      (SUM[1]),
                    .a      (A[1]),
                    .b      (B[1]),
                    .ci     (cout0)
                    );
  
  CSA_CELL CSA_BIT2(.co     (cout2),
                    .s      (SUM[2]),
                    .a      (A[2]),
                    .b      (B[2]),
                    .ci     (cout1)
                    );
  
  CSA_CELL CSA_BIT3(.co     (cout3),
                    .s      (SUM[3]),
                    .a      (A[3]),
                    .b      (B[3]),
                    .ci     (cout2)
                    );
  
  CSA_CELL CSA_BIT4(.co     (cout4),
                    .s      (SUM[4]),
                    .a      (A[4]),
                    .b      (B[4]),
                    .ci     (cout3)
                    );

  CSA_CELL CSA_BIT5(.co     (cout5),
                    .s      (SUM[5]),
                    .a      (A[5]),
                    .b      (B[5]),
                    .ci     (cout4)
                    );

  CSA_CELL CSA_BIT6(.co     (cout6),
                    .s      (SUM[6]),
                    .a      (A[6]),
                    .b      (B[6]),
                    .ci     (cout5)
                    );

  CSA_CELL CSA_BIT7(.co     (cout7),
                    .s      (SUM[7]),
                    .a      (A[7]),
                    .b      (B[7]),
                    .ci     (cout6)
                    );

  assign   COUT  = cout7;


endmodule




//=======================1-bit cell for CSA(Carry Select Adder)=======================
module  CSA_CELL(co,
                 s,
                 a,
                 b,
                 ci
                 );
                 
  output    co;
  output    s;
  input     a;
  input     b;
  input     ci;
  
  assign   s0  = a^b;
  assign   s1  = !s0;
  assign   c0  = a&&b;
  assign   c1  = a||b;
  
  assign   s   = ci ? s1:s0;   
  assign   co  = ci ? c1:c0;   
    
endmodule