1.2選1多路選擇器

 1 library IEEE;
 2 use IEEE.STD_LOGIC_1164.ALL;
 3 ENTITY mux21 IS
 4   PORT ( a,b : IN STD_LOGIC;
 5            s : IN STD_LOGIC;
 6            y : OUT STD_LOGIC );
 7 END ENTITY mux21;
 8  
 9 ARCHITECTURE one OF mux21 IS
10   BEGIN
11      y <= a WHEN s = ‘0‘ ELSE
12           b WHEN
 
 s = ‘1‘;
13 END ARCHITECTURE one;

2.鎖存器

 1 library IEEE;
 2 use IEEE.STD_LOGIC_1164.ALL;
 3 
 4 entity latch is
 5     Port ( d : in STD_LOGIC;
 6          ena : in STD_LOGIC;
 7            q : out STD_LOGIC
 8          );
 9 end entity latch;
10 
11 architecture one of latch is
12  signal sig_save : STD_LOGIC
 
;
13  begin
14    process (d,ena)
15     begin
16     
17      if ena = ‘1‘ then
18      sig_save <= d;
19      end if ;
20      
21      q <= sig_save ;
22    end process ;
23 end architecture one;

3.全加器

 1 --或門邏輯描述
 2 library IEEE;
 3 use IEEE.STD_LOGIC_1164.ALL;
 4 
 5 ENTITY or2 IS
 6   PORT
 
 (a,b :IN STD_LOGIC; c : OUT STD_LOGIC );
 7 END ENTITY or2;
 8 ARCHITECTURE fu1 OF or2 IS
 9   BEGIN
10    c <= a OR b ;
11 END ARCHITECTURE fu1;
12 
13 --半加器描述
14 LIBRARY IEEE;
15 USE IEEE.STD_LOGIC_1164.ALL;
16 
17 ENTITY h_adder IS
18   PORT (a,b : IN STD_LOGIC; co,so : OUT STD_LOGIC);
19 END ENTITY h_adder;
20 ARCHITECTURE fh1 OF h_adder IS
21  BEGIN
22   so <= (a OR b)AND(a NAND b);--與非的作用：實現1+1=0
23   co <= NOT( a NAND b);--與非：只有在1 NAND 1時返回0，其他情況返回1
24 END ARCHITECTURE fh1;
25 
26 --全加器頂層設計描述
27 
28 LIBRARY IEEE;
29 USE IEEE.STD_LOGIC_1164.ALL;
30 
31 ENTITY f_adder IS
32   PORT ( ain,bin,cin : IN STD_LOGIC;
33             cout,sum : OUT STD_LOGIC );
34 END ENTITY f_adder;
35 
36 ARCHITECTURE fd1 OF f_adder IS
37 COMPONENT h_adder
38  PORT ( a,b : IN STD_LOGIC;
39       co,so : OUT STD_LOGIC);
40  END COMPONENT;
41  COMPONENT or2
42    PORT (a,b : IN STD_LOGIC;
43            c : OUT STD_LOGIC);
44 END COMPONENT;
45 SIGNAL d,e,f : STD_LOGIC;
46  BEGIN
47  u1 : h_adder PORT MAP( a =>ain,b =>bin,co=>d,so =>e);
48  u2 : h_adder PORT MAP( a =>e,b =>cin,co =>f,so =>sum);
49  u3 : or2 PORT MAP(a =>d,b =>f,c =>cout);
50 END ARCHITECTURE fd1 ;

用VHDL設計多路選擇器、鎖存器和全加器