fulladder.vhd

来自「用VHDL实现的除法器,非常好使,仿真通过了」· VHDL 代码 · 共 61 行

-------------------------------------------------------------------------------
-- Description :
-- Should force the compiler to use a full-adder cell instead of simple logic
-- gates. Otherwise, a full-adder cell of the target library has to be
-- instantiated at this point (see second architecture).
-------------------------------------------------------------------------------

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;

-------------------------------------------------------------------------------

entity FullAdder is

  port (A, B, CI : in std_logic;  	-- operands
        S, CO : out std_logic);  	-- sum and carry out

end FullAdder;

-------------------------------------------------------------------------------

architecture Structural of FullAdder is 

  signal Auns, Buns, CIuns, Suns : unsigned(1 downto 0);  -- unsigned temp
  
begin

  -- type conversion: std_logic -> 2-bit unsigned
  Auns <= '0' & A;
  Buns <= '0' & B;
  CIuns <= '0' & CI;

  -- should force the compiler to use a full-adder cell
  Suns <= Auns + Buns + CIuns;

  -- type conversion: 2-bit unsigned -> std_logic
  S <= Suns(0);
  CO <= Suns(1);

end Structural;

-------------------------------------------------------------------------------

--architecture Structural of FullAdder is 

--  component ad01d1
--    port (A, B, CI : in std_logic;
--	  S, CO : out std_logic);
--  end component;

--begin

--  fa : ad01d1
--    port map (A, B, CI, S, CO);

--end Structural;

-------------------------------------------------------------------------------