3.
NAND LOGIC GATE STRUCTURAL MODELLING
library ieee;
use ieee.std_logic_1164.all;
entity nand2 is
port (x,y: in std_logic;
z: out std_logic);
end nand2;
architecture nand2_ data of nand2 is
begin
z<=x nand y;
end nand2_ data;
Library ieee;
use ieee.std_logic_1164.all;
entity nand2_1 is
port(a,b:in std_logic;
c:out std_logic);
end nand2_1;
architecture nand2_1_struct of nand2_1 is
component nand2
port(x,y:in std_logic;
z:out std_logic);
end component;
begin
a1:nand2 port map(a,b,c);
end nand2_1_struct;
4. NOR LOGIC GATE STRUCTURAL MODELLING
library ieee;
use ieee.std_logic_1164.all;
entity nor2 is
port (x,y: in std_logic;
z: out std_logic);
end nor2;
architecture nor2_ data of nor2 is
begin
z<=x nor y;
end nor2_ data;
Library ieee;
use ieee.std_logic_1164.all;
entity nor2_1 is
port(a,b:in std_logic;
c:out std_logic);
end nor2_1;
architecture nor2_1_struct of nor2_1 is
component nor2
port(x,y:in std_logic;
z:out std_logic);
end component;
begin
a1:nor2 port map(a,b,c);
end nor2_1_struct;
5. XNOR LOGIC GATE STRUCTURAL MODELLING
library ieee;
use ieee.std_logic_1164.all;
entity xnor2 is
port (x,y: in std_logic;
z: out std_logic);
end xnor2;
architecture xnor2_ data of xnor2 is
begin
z<=x xnor y;
end xnor2_ data;
Library ieee;
use ieee.std_logic_1164.all;
entity xnor2_1 is
port(a,b:in std_logic;
c:out std_logic);
end xnor2_1;
architecture xnor2_1_struct of xnor2_1 is
component xnor2
port(x,y:in std_logic;
z:out std_logic);
end component;
begin
a1:xnor2 port map(a,b,c);
end xnor2_1_struct;
6. Design of 2 to 4 decoder
Library IEEE ;
use IEEE.STD_LOGIC_1164
entity decoder is
port(a : in STD_LOGIC_VECTOR(1 downto 0);
b : out STD_LOGIC_VECTOR(3 downto 0) );
end decoder ;
Architecture behavioral of decoder is
begin
Process(a)
begin
if (a = “00”)then
b <=”0001” ;
elsif (a= “01”)then
b <=”0010” ;
elsif (a= “10”)then
b <=”0100” ;
else
b <=”1000” ;
end if ;
end process ;
end behavioral ;
7. Design of 8 to 3 encoder
library IEEE;
use IEEE.STD_LOGIC_1164.all,
entity ENCODER8 is
port (A: in std_logic_vector (7 downto 0);
Y: out std_logic_vector (2 downto 0));
end ENCODER8;
architecture ARCH of ENCODER8 is
begin
process (A)
begin
case A is
when "00000001" => Y <= "000";
when "00000010" => Y <= "001";
when "00000100" => Y <= "010";
when "00001000" => Y <= "011";
when "00010000" => Y <= "100";
when "00100000" => Y <= "101";
when "01000000" => Y <= "110";
when "10000000" => Y <= "111";
when others => Y <= "XXX";
end case ;
end process ;
end ARCH;
9. Design of 8 to 1 multiplexer
library ieee;
use ieee.std_logic_1164.all;
entity mux8x1 is
port ( s : in std_logic_vector(2 downto 0);
d : in std_logic_vector(7 downto 0);
en : in std_logic;
y : out std_logic );
end mux8x1;
Architecture mux_8x1 of mux8x1 is
begin
process (s,d,en)
begin
if(en='0') then y<='0';
else
case s is
when "000"=> y<=d(0);
when "001"=> y<=d(1);
when "010"=> y<=d(2);
when "011"=> y<=d(3);
when "100"=> y<=d(4);
when "101"=> y<=d(5);
when "110"=> y<=d(6);
when "111"=> y<=d(7);
when others=> y<='0';
end case;
end if;
end process;
end mux_8x1;
10. Design of 4 bit binary to gray converter
library IEEE;
use IEEE.STD_LOGIC_1164.all;
entity binary_to_gray is
port(din : in STD_LOGIC_VECTOR(3 downto 0);
dout : out STD_LOGIC_VECTOR(3 downto 0));
end binary_to_gray;
architecture binary_to_gray_arc of binary_to_gray is
begin
process (din) is
begin
if (din="0000") then
dout <= "0000";
elsif (din="0001") then
dout <= "0001";
elsif (din="0010") then
dout <= "0011";
elsif (din="0011") then
dout <= "0010";
elsif (din="0100") then
dout <= "0110";
elsif (din="0101") then
dout <= "0111";
elsif (din="0110") then
dout <= "0101";
elsif (din="0111") then
dout <= "0100";
elsif (din="1000") then
dout <= "1100";
elsif (din="1001") then
dout <= "1101";
elsif (din="1010") then
dout <= "1111";
elsif (din="1011") then
dout <= "1110";
elsif (din="1100") then
dout <= "1010";
elsif (din="1101") then
dout <= "1011";
elsif (din="1110") then
dout <= "1001";
else dout <= "1000";
end if;
end process;
end binary_to_gray_arc;
