bingxingjiafa.txt

用vhdl语言 来实现 四位并行加法器的功能 是本科生的必学内容

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 adderarchitecture 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;-- behavioral implementation of the N-bit adderarchitecture behavioral of adderN isbegin    p1: process(a, b, cin)        variable vsum : std_logic_vector(N downto 1);        variable carry : std_logic;    begin        carry := cin;        for i in 1 to N loop            vsum(i) := (a(i) xor b(i)) xor carry;            carry := (a(i) and b(i)) or                     (carry and (a(i) or b(i)));        end loop;        sum <= vsum;        cout <= carry;    end process p1;end behavioral;