-- 在
quartus 6.0 下通过编译，说明一个文件中并非只能有一个实体 2007.12.5
------------------------------------------------------------------------
-- Single-bit
adder------------------------------------------------------------------------
library IEEE;
use IEEE.std_logic_1164.all;
entity adder is
port (a : in std_logic;
b : in std_logic;
cin : in std_logic;
sum : out std_logic;
cout : out std_logic);
end adder;
-- description of adder using concurrent signal assignments
architecture rtl of adder is
begin
sum <= (a xor b) xor cin;
cout <= (a and b) or (cin and a) or (cin and b);
end rtl;
------------------------------------------------------------------------
-- N-bit adder
-- The width of the adder is determined by generic N
------------------------------------------------------------------------
library IEEE;
use IEEE.std_logic_1164.all;
entity adderN is
generic(N : integer := 16);
port (a : in std_logic_vector(N downto 1);
b : in std_logic_vector(N downto 1);
cin : in std_logic;
sum : out std_logic_vector(N downto 1);
cout : out std_logic);
end adderN;
-- structural implementation of the N-bit adder
architecture structural of adderN is
component adder
port (a : in std_logic;
b : in std_logic;
cin : in std_logic;
sum : out std_logic;
cout : out std_logic);
end component;
signal carry : std_logic_vector(0 to N);
begin
carry(0) <= cin;
cout <= carry(N);
-- instantiate a single-bit adder N times
gen: for I in 1 to N generate
add: adder port map(
a => a(I),
b => b(I),
cin => carry(I - 1),
sum => sum(I),
cout => carry(I));
end generate;
end structural;
