在学习VHDL，写的小代码贴上来吧，备忘。先写一位全加器，然后利用一位全加器搭成四位全加器。

library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_arith.all; use ieee.std_logic_unsigned.all; entity full_add_1 is port( a : in std_logic; b : in std_logic; cin : in std_logic; cout : out std_logic; sum : out std_logic); end full_add_1; architecture behavour of full_add_1 is begin sum <= ((a xor b)xor cin); cout <= (((a xor b)and cin))or(a and b); end behavour;

library ieee; use ieee.std_logic_1164.all; library work; entity full_add4 is port ( cin : in STD_LOGIC; a : in STD_LOGIC_VECTOR(3 downto 0); b : in STD_LOGIC_VECTOR(3 downto 0); cout : out STD_LOGIC; sum : out STD_LOGIC_VECTOR(3 downto 0) ); end full_add4; architecture bdf_type of full_add4 is component full_add_1 port(a : in STD_LOGIC; b : in STD_LOGIC; cin: in STD_LOGIC; cout: out STD_LOGIC; sum: out STD_LOGIC ); end component; signal cout_wire : STD_LOGIC_VECTOR(2 downto 0); begin b2v_inst : full_add_1 PORT MAP(a => a(0), b => b(0), cin => cin, cout => cout_wire(0), sum => sum(0)); b2v_inst1 : full_add_1 PORT MAP(a => a(1), b => b(1), cin => cout_wire(0), cout => cout_wire(1), sum => sum(1)); b2v_inst2 : full_add_1 PORT MAP(a => a(2), b => b(2), cin => cout_wire(1), cout => cout_wire(2), sum => sum(2)); b2v_inst3 : full_add_1 PORT MAP(a => a(3), b => b(3), cin => cout_wire(2), cout => cout, sum => sum(3)); END bdf_type; testbench:

library ieee; use ieee.std_logic_1164.all; entity full_add4_tb is end full_add4_tb; architecture behaviour of full_add4_tb is component full_add4 port ( cin : IN STD_LOGIC; a : IN STD_LOGIC_VECTOR(3 DOWNTO 0); b : IN STD_LOGIC_VECTOR(3 DOWNTO 0); cout : OUT STD_LOGIC; sum : OUT STD_LOGIC_VECTOR(3 DOWNTO 0)); end component; signal a: std_logic_vector(3 DOWNTO 0):="0000"; signal b: std_logic_vector(3 DOWNTO 0):="0000"; signal cin: std_logic:='0'; signal sum: std_logic_vector(3 downto 0); signal cout: std_logic; begin u1: full_add4 port map( a =>a, b =>b, cin =>cin, cout =>cout, sum =>sum); process begin wait for 0 ns; a<="1111";b<="1110"; wait for 10 ns; a<="1101";b<="1100"; wait for 10 ns; a<="1011";b<="1110"; wait for 10 ns; a<="0011";b<="1000"; wait for 10 ns; a<="0001";b<="0011"; wait for 10 ns; end process; end behaviour;