The document contains the list of experiments for the Digital System Design lab at Sri Venkateswara College of Engineering & Technology. The experiments include simulation and verification of logic gates, modeling of adders like half adder, full adder, ripple carry adder, carry look ahead adder and serial adder. Other experiments involve modeling of decoders, multiplexers, encoders and flip-flops. Additional experiments are design of counters, registers, sequence detectors, multipliers and ALU. The document also lists experiments on RAM operations and implementation of stacks and queues.

1. Sri Venkateswara College of Engineering & Technology
R.V.S Nagar, Chittoor
M.Tech. I SEMESTER (DECS)
DIGITAL SYSTEM DESIGN LAB
List of Experiments
1. Simulation and Verification of Logic Gates.
2. Design and Simulation of
(a) Half adder (b) Full adder (c) Serial Binary adder
(d) Carry Look Ahead adder (e) Ripple Carry adder
3. Simulation and Verification of
(a) Decoder (b) Mux (c) Encoder
4 Modeling of Flip-Flops
(a) SR Flip-Flops (b) D Flip-Flops
(c) JK Flip-Flops (d) T Flip-Flops
5. Design and Simulation of Counters
(a) Ring Counters (b) Johnson Counters
(c) Up-Down Counters (d) Ripple Counters (Asynchronous)
6. Design of a N- bit Register
(a) Serial-in Serial-out (b) Serial in Parallel out
(c) Parallel in Serial out (d) Parallel in Parallel out
7. Design of Sequence detector.
8. 4-Bit Multiplier (Array)
9. Design of ALU.
10. RAM (Read and Write Operations)
11. Stack and Queue Implementation.
Lab-In-charge HOD, ECE

2. LOGIC GATES
Ex. No : 01
AIM :-
To write a VHDL Code for realizing Gates
• AND, OR, NOT, NAND, NOR, XOR, XNOR
And verify the results.
AND GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity and2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end and2;
architecture data_flow of and2 is
begin
c<=a and b;
end data_flow;
architecture behavioral of and2 is
begin
process(a,b)
begin
if a='1' and b='1'
then c<='1';
else c<='0';
end if;
end process;
end behavioral;
architecture structural of and2 is
component andx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);

3. end component;
begin
A1:andx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity andx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end andx;
architecture andx of andx is
begin
z<=x and y;
end andx;

4. OR GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity or2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end or2;
architecture data_flow of or2 is
begin
c<=a or b;
end data_flow;
architecture behavioral of or2 is
begin
process(a,b)
begin
if a='0' and b='0'
then c<='0';
else c<='1';
end if;
end process;
end behavioral;
architecture structural of or2 is
component orx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
A1:orx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity orx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;

5. z : out STD_LOGIC);
end orx;
architecture orx of orx is
begin
z<=x or y;
end orx;
NOT GATE

6. PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity not1 is Port ( a : in STD_LOGIC;
b : out STD_LOGIC);
end not1;
architecture data_flow of not1 is
begin
b<=not a;
end data_flow;
architecture behavioral of not1 is
begin
process(a)
begin
if a='0'
then b<='1';
else b<='0';
end if;
end process;
end behavioral;
architecture structural of not1 is
component notx is
Port ( x : in STD_LOGIC;
y : out STD_LOGIC);
end component;
begin
A1:notx port map(a,b);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity notx is
Port ( x : in STD_LOGIC;
y : out STD_LOGIC);
end notx;
architecture notx of notx is
begin y<=not x;
end notx;

7. NAND GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity nand2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end nand2;
architecture data_flow of nand2 is
begin
c<=a nand b;
end data_flow;
architecture behavioral of nand2 is
begin
process(a,b)
begin
if a='1' and b='1'
then c<='0';
else c<='1';
end if;
end process;
end behavioral;
architecture structural of nand2 is
component nandx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
A1:nandx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity nandx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;

8. z : out STD_LOGIC);
end nandx;
architecture nandx of nandx is
begin
z<=x nand y;
end nandx;

9. NOR GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity nor2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end nor2;
architecture data_flow of nor2 is
begin
c<=a nor b;
end data_flow;
architecture behavioral of nor2 is
begin
process(a,b)
begin
if a='0' and b='0'
then c<='1';
else c<='0';
end if;
end process;
end behavioral;
architecture structural of nor2 is
component norx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
A1:norx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity norx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;

10. z : out STD_LOGIC);
end norx;
architecture norx of norx is
begin
z<=x nor y;
end norx;

11. XOR GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity xor2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end xor2;
architecture data_flow of xor2 is
begin
c<=a xor b;
end data_flow;
architecture behavioral of xor2 is
begin
process(a,b)
begin
if a=b
then c<='0';
else c<='1';
end if;
end process;
end behavioral;
architecture structural of xor2 is
component xorx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
A1:xorx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity xorx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;

12. z : out STD_LOGIC);
end xorx;
architecture xorx of xorx is
begin
z<=x xor y;
end xorx;

13. XNOR GATE
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity xnor2 is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
c : out STD_LOGIC);
end xnor2;
architecture data_flow of xnor2 is
begin
c<=a xnor b;
end data_flow;
architecture behavioral of xnor2 is
begin
process(a,b)
begin
if a=b
then c<='1';
else c<='0';
end if;
end process;
end behavioral;
architecture structural of xnor2 is
component xnorx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
A1:xnorx port map(a,b,c);
end structural;
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity xnorx is
Port ( x : in STD_LOGIC;

14. y : in STD_LOGIC;
z : out STD_LOGIC);
end xnorx;
architecture xnorx of xnorx is
begin
z<=x xnor y;
end xnorx;

15. MODELING OF ADDERS
Ex. No : 02
AIM :-
To write a VHDL Code for
• Half adder
• Full adder
• ripple carry adder
• carry look ahead adder
• serial adder
And verify the results.
HALF ADDER
PROGRAM:-
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
entity ha is
Port ( a : in STD_LOGIC;
b : in STD_LOGIC;
sum: out STD_LOGIC;
carry: out STD_LOGIC);
end ha;
architecture data_flow of ha is
begin
sum<=a xor b;
carry<= a and b;
end data_flow;
architecture behavioral of ha is
begin
process(a,b)
begin
if a=b
then sum<='0';
else sum<='1';
end if;
if a='1' and b='1'

16. then carry<='1';
else carry<='0';
end if;
end process;
end behavioral;
architecture structural of ha is
component xorx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
component andx is
Port ( x : in STD_LOGIC;
y : in STD_LOGIC;
z : out STD_LOGIC);
end component;
begin
x1:xorx port map(a,b,sum);
A1:andx port map(a,b,carry);
end structural;

17. FULL ADDER
PROGRAM:-
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;
-- description of adder using component instantiation statements
use work.gates.all;
architecture structural of adder is
signal xor1_out,
and1_out,
and2_out,
or1_out : std_logic;
begin
xor1: xorg port map(
in1 => a,
in2 => b,
out1 => xor1_out);
xor2: xorg port map(
in1 => xor1_out,
in2 => cin,
out1 => sum);
and1: andg port map(
in1 => a,
in2 => b,
out1 => and1_out);
or1: org port map(
in1 => a,
in2 => b,
out1 => or1_out);

18. and2: andg port map(
in1 => cin,
in2 => or1_out,
out1 => and2_out);
or2: org port map(
in1 => and1_out,
in2 => and2_out,
out1 => cout);
end structural;
------------------------------------------------------------------------
-- 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),

19. sum => sum(I),
cout => carry(I));
end generate;
end structural;
-- behavioral implementation of the N-bit adder
architecture behavioral of adderN is
begin
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;

20. RIPPLE CARRY ADDER
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity rea is
Port (a: in std_logic _vector (3 downto 0);
b: in std_logic _vector (3 downto 0);
ci:in std_logic;
s: out std_logic _vector (3 downto 0);
co:in out std_logic);
end rea;
architecture structural of rea is
signal c:std_ logic vector(3 downto 1);
component fa is
port (a,b,cin: in std_logic;
s : out std_logic;
cout: in out std_logic);
end component;
begin
f1: fa port map( a(0), b(0), ci, s(0),c(1));
f2: fa port map(a(1), b(1), c(1), s(1),c(2));
f3: fa port map(a(2), b(2), c(2), s(2),c(3));
f4: fa port map(1)p(a(3), b(3), c(3), s(3),c(0));
end structural;

21. CARRY LOOK AHEAD ADDER
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity carry_look_ahead is
Port (a: in std_logic _vector(3 downto 0);
b : in std_logic _vector(3 downto 0);
co : out std_logic;
c : inout std_logic _vector(4 downto 0);
s : out std_logic _vector(3 downto 0);
end carry_look_ahead;
architecture structural of carry_look_ahead is
signal p,g:std_ logic _vector(3 downto 0);
signal r : std_ logic_ vector(6 downto 0);
signal i : integer;
begin
processor(a,b,c,p,g,r)
begin
l1 : for i in 0 to 3 loop
p(i)<=a(i) xor b(i);
g(i)<=a(i) and b(i);
c(0)<=’0’;
end loop l1;
r(0)<=p(2)and g(1);
r(1)<=p(2)and p(1)and g(0);
r(2)<=p(2)and p(1)and p(0)and c(0);
r(3)<=p(3)and g(2);
r(4)<=p(3)and p(2)and g(1);
r(5)<=p(3)and p(2)and p(1)and g(0);
r(6)<=p(3)and p(2)and p(1)and p(0) and c(0);
c(1)<=g(0)or ( p(0) and c(0));
c(2)<=g(1)or ( p(1) and g(0)) or( p(1)and ( p(0) and c(0));
c(3)<=g(2)or r(0) or r(1) or r(2);
c(4)<=g(3)or r(3) or r(4) or r(5) or r(6);
l2: for i in 0 to 3 loop
s(i)<=p(i) xor c(i);
end loop l2;
c(0)<=c(4);
end process;
end Behavioral;

22. SERIAL ADDER
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity serial_adder is
Port (x: in std_logic _vector(3 downto 0);
y : in std_logic _vector(3 downto 0);
clk : in std_logic;
ce:in std_logic;
cout : inout std_logic
s : out std_logic
end serial_adder;
architecture structural of serial_adder is
signal c:std_ logic_ vector(4 downto 0);
signal i : integer;
begin
processor(clk,x,y)
begin
if (ce’event and ce =’1’)then
c(0)<=’0’;
s<=’0’;
i<=’0’;
end if;
if (ce’event and clk =’1’)then
s<=(x(i)xor y(i) xor c(i);
c(i+1)<=(x(i)and y(i))or (y(i)and c(i))or (c(i)and x(i));
i<=i+1;
end if;
else
i<=0;
end if;
cout<=c(4);
end process;
end Behavioral;

23. EX.No:- 03
3:8 DECODER
AIM: To write and simulate a vhdl program for a 3 to 8 decoder and verify the
results
PROGRAM:-
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;
entity dc_counter is
port(clk:in std_logic;
q:inout std_logic_vector(3 downto 0):="0000");
end dc_counter;
architecture behave of dc_counter is
begin
process(clk)
begin
if(clk'event and clk='1')then
if(q="1001")then
q<="0000";
else
q<=q+1;
end if;
end if;
end process;
end behave;

24. 8x1 MULTIPLEXER
AIM:- To write and simulate aModelsim( VHDL) program for 8x1 Multiplexer.
PROGRAM:-
library ieee;
use ieee.std_logic_1164.all;
entity mx is
port(i:in std_logic_vector(7 downto 0);
s:in std_logic_vector(2 downto 0);
y:out std_logic);
end mx;
architecture archi of mx is
begin
process(i,s)
begin
if(s="000") then y<=i(0);
elsif(s="001") then y<=i(1);
elsif(s="010") then y<=i(2);
elsif(s="011") then y<=i(3);
elsif(s="100") then y<=i(4);
elsif(s="101") then y<=i(5);
elsif(s="110") then y<=i(6);
elsif(s="111") then y<=i(7);
end if;
end process;
end archi;

25. MODELING OF FLIP - FLOPS
Ex. No : 04
AIM : -
To write a VHDL Code for
• SR Flip-Flop
• D Flip-Flop
• JK Flip-Flop
• T Flip-Flop
And verify the results.
SR - FLIP - FLOP
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity srff is
Port (s : in std_logic;
r : in std_logic;
clk : in std_logic;
q : in out std_logic;
qbar : in out std_logic);
end srff;
architecture Behavioral of srff is
begin
Process (s,clk,r)
begin
if (clk’event and clk =’1’)then
if(s=’0’and r=’0’)then
q<=q;
qbar<=qbar;
elsif(s=’1’and r=’0’)then
q<=’1’;
qbar<=’0’;
elsif(s=’0’and r=’1’)then
q<=’0’;
qbar<=’1’;
else

26. q<=not q ;
qbar<=not qbar;
end if:
else
q<=q;
qbar<=qbar;
end if:
end process;
end Behavioral;
architecture data_flow of sr_ff is
signal s1,s2:std_ logic;
begin
s1<=s nand clk;
s2<=r nand clk;
q<=s1 nand qbar;
qbar<=s2 nand q;
end data_flow;
architecture structural of srff is
signal s1,s2:std_ logic;
component nand2 is
port (a,b: in std_logic;
c : out std_logic);
end component;
begin
n1: nand2 port map(s,clk,s1);
n2: nand2 port map(r,clk,s2);
n3: nand2 port map(s1,qbar,q);
n4: nand2 port map(s2,q,qbar);
end structural;

27. D - FLIP - FLOP
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity dff is
Port (d : in std_logic;
clk : in std_logic;
q : in out std_logic;
qbar : in out std_logic);
end dff;
architecture Behavioral of dff is
begin
Process (d,clk)
Begin
if (clk’event and clk =’1’)then
if(d=’0’)then
q<=’0’;
qbar<=’1’;
else
q<=’1’;
qbar<=’0’;
end if:
else
q<=q;
qbar<= qbar;
end if:
end process;
end Behavioral;
architecture data_flow of d_ff is
signal s1,s2:std_ logic;
begin
s1<=d nand clk;
s2<=not d nand clk;
q<=s1 nand qbar;
qbar<=s2 nand q;
end data_flow;

28. architecture structural of d_ff is
signal s1,s2,s3:std_ logic;
component nand2 is
port (a,b: in std_logic;
c : out std_logic);
end component;
component not1 is
port (a: in std_logic;
c : out std_logic);
end component;
begin
x1: not1 port map(d,s3);
n1: nand2 port map(d,clk,s1);
n2: nand2 port map(s3,clk,s2);
n3: nand2 port map(s1,qbar,q);
n4: nand2 port map(s2,q,qbar);
end structural;

29. JK - FLIP - FLOP
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity jkff is
Port (j : in std_logic;
k : in std_logic;
clk : in std_logic;
q : in out std_logic;
qbar : in out std_logic);
end jkff;
architecture Behavioral of jkff is
begin
Process (j,clk,k)
begin
if (clk’event and clk =’1’)then
if(j=’0’and k=’0’)then
q<=q;
qbar<=qbar;
elsif(j=’0’and k=’1’)then
q<=’0’;
qbar<=’1’;
elsif(j=’1’and k=’0’)then
q<=’1’;
qbar<=’0’;
else
q<=not q ;
qbar<=not qbar;
end if:
else
q<=q;
qbar<=qbar;
end if:
end process;
end Behavioral;

30. architecture data_flow of jk_ff is
signal s1,s2:std_ logic;
begin
s1<=k and clk and q;
s2<=j and clk and qbar;
q<=s1 nor qbar;
qbar<=s2 nor q;
end data_flow;
architecture structural of jk_ff is
signal s1,s2:std_ logic;
component nor2 is
port (a,b: in std_logic;
c : out std_logic);
end component;
begin
component and3 is
port (a,b,c: in std_logic;
d : out std_logic);
end component;
begin
x1: and3 port map(k,clk,q,s1);
x2: and3 port map(j,clk,qbar,s2);
x3: nor2 port map(s1,qbar,q);
x4: and2 port map(s2,q,qbar);
end structural;

31. T - FLIP - FLOP
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity tff is
Port (t : in std_logic;
clk : in std_logic;
q : in out std_logic;
qbar : in out std_logic);
end tff;
architecture Behavioral of tff is
begin
Process (t,clk,)
begin
if (clk’event and clk =’1’)then
if(t=’0’)then
q<=q;
qbar<=qbar;
else
q<=not q ;
qbar<=not qbar;
end if:
else
q<=q;
qbar<=qbar;
end if:
end process;
end Behavioral;
architecture data_flow of t_ff is
signal s1,s2:std_ logic;
begin
s1<=t and clk and q;

32. s2<=t and clk and qbar;
q<=s1 nor qbar;
qbar<=s2 nor q;
end data_flow;
architecture structural of t_ff is
signal s1,s2 : std_ logic;
component nor2 is
port (a,b: in std_logic;
c : out std_logic);
end component;
begin
component and3 is
port (a,b,c: in std_logic;
d : out std_logic);
end component;
begin
x1: and3 port map(t,clk,q,s1);
x2: and3 port map(t,clk,qbar,s2);
x3: nor2 port map(s1,qbar,q);
x4: and2 port map(s2,q,qbar);
end structural;

33. DESIGN AND SIMULATION OF COUNTERS
Ex. No : 05
AIM :-
To write a VHDL Code for
• Ring Counters
• Johnson Counters
• Up-Down Counters
• Ripple Counters (Asynchronous)
And verify the results.
BCD COUNTER
PROGRAM:
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity mod_n_coun is
Port (ce: in std_logic ;
clk: in std_logic;
q:in out std_logic _vector (3 downto 0));
end mod_n_coun ;
architecture Behavioral of mod_n_coun is
begin
Process (ce,clk);
begin
if (ce’event and ce =’1’)then
q<=”0000”;
end if:
if (clk’event and clk =’1’)then
if (ce=’1’)then
q<=q+1;
end if;
if (q>=”1001”)then
q<=”0000”;
end if;
end if;
end process;
end Behavioral;

34. BINARY UP DOWN COUNTER
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity bin_up_down is
Port (up: in std_logic ;
down: in std_logic;
ce: in std_logic ;
clk: in std_logic;
q:in out std_logic _vector (3 downto 0));
end bin_up_down;
architecture Behavioral of bin_up_down is
begin
Process (up, down, ce, clk);
begin
if (ce’event and ce =’1’)then
q<=”0000”;
end if:
if (clk’event and clk =’1’)then
if (up=’1’)then
q<=q+1;
else if(down=’1’)then
q<=q-1;
end if;
end if;
end process;
end Behavioral;

35. ASYNCHRONOUS COUNTER
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity asy_count is
Port (ce: in std_logic;
clk: in std_logic;
n:in std_logic _vector (3 downto 0);
q:in out std_logic _vector (3 downto 0));
end asy_count;
architecture Behavioral of asy_count is
begin
Process (ce, clk,q);
begin
if (ce’event and ce =’1’)then
q<=”0000”;
end if:
if(q<n)then
if (clk’event and clk =’1’)then
q(0)<=not q(0);
if (q(0) =’1’)then
q(1)<=not q(1);
if (q(1) =’1’)then
q(2)<=not q(2);
if (q(2) =’1’)then
q(3)<=not q(3);
end if;
end if;
end if;
end if;
else
q<=”0000”;
end if;
end process;
end Behavioral;

36. MODELING OF SHIFT REGISTERS COUNTERS
Ex. No : 06
AIM :-
To write VHDL Program for realizing Shift Registers
• Serial-in Serial-out
• Serial in Parallel out
• Parallel in Serial out
• Parallel in Parallel out
And verify the results.
SHIFT REGISTERS
Serial in serial out (SISO)
PROGRAM:
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
Entity siso is
Port (si: in std_logic;
clk: in std_logic;
so:in out std_logic);
end siso;
architecture structural of siso is
component d_ff is
Port( d,clk: in std_logic;
q,qbar :in out std_logic);
end component;
Signal a1, a2, a3, d1, d2, d3, d4:std_logic;
begin
11:d_ff port map (si, clk, a1, d1);
12:d_ff port map (a1, clk, a2, d2);
13:d_ff port map (a2, clk, a3, d3);
14:d_ff port map (a3, clk, so, d4);
end structural;

37. SIPO
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
Entity sipo is
Port (si: in std_logic;
clk: in std_logic;
po:in out std_logic_vector(3 downto 0));
end sipo;
architecture structural of sipo is
signal d:std _logic_ vector(4 downto 0);
component d_ff
Port (d,clk: in std_logic;
q,qbar :in out std_logic);
end component;
begin
a1:d_ff port map (si, clk, po(3),d(3));
a2:d_ff port map( po(3), clk, po(2),d(2));
a3:d_ff port map (po(2), clk, po(1),d(1));
a4:d_ff port map (po(1), clk, po(0),d(0));
end structural;

38. PISO
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity piso is
Port (pi: in std_logic _vector (3 downto 0);
c: in std_logic;
clk: in std_logic;
so:in out std_logic);
end piso;
architecture structural of piso is
signal d:std_ logic vector(3 downto 0);
signal q:std _logic vector(3 downto 1);
signal a:std_ logic vector(3 downto 1);
signal r:std _logic;
component d_ff is
Port (d,clk: in std_logic;
q,qbar :in out std_logic);
end component;
component aoi is
Port (a,b,c,d: in std_logic;
c: out std_logic);
end component;
begin
a1:aio port map (q (3),r,c,pi(2)a(3));
a2:aio port map( q (2),r,c,pi(1)a(2));
a3:aio port map (q (1),r,c,pi(0)a(1));
11:d_ff port map( pi(3), clk, q(3),d(3));
12:d_ff port map(a(3), clk, q(2),d(2));
13:d_ff port map(a(2), clk, q(1),d(1));
14:d_ff port map(a(1), clk, so,d(0));
end structural;

39. PIPO
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity pipo is
Port (pi: in std_logic _vector (3 downto 0);
clk: in std_logic;
po:in out std_logic _vector (3 downto 0));
end pipo;
architecture structural of pipo is
signal d:std_ logic vector(4 downto 0);
component d_ff is
Port (d,clk: in std_logic;
q,qbar :in out std_logic);
end component;
begin
11:d_ff port map( pi(3), clk, po(3),d(3));
12:d_ff port map( pi(2), clk, po(2),d(2));
13:d_ff port map( pi(1), clk, po(1),d(1));
14:d_ff port map( pi(0), clk, po(0),d(0));
end structural;

40. Serial in serial out (SISO)
Serial Input
Clk
Serial Out
Serial in Parallel out (SIPO)
Serial Input
Clk
Parallel Out
Q(n-2) Q(n-3) Q(0)Q(n-1)
Q(n-2) Q(n-3) Q(0)Q(n-1)

41. Parallel in out Serial (PISO)
Parallel In
Clk
Serial Out
Parallel in Parallel out(PIPO)
Parallel In
Clk
Load
Parallel Out
SISO PIPO
SIN CLK SOUT
1 U
0 1
0 0
1 0
1 1
1 1
0 1
INPUT OUTPUT
SIN CLK
Q0 Q1 Q2 Q3
1 U U U U
0 1 U U U
0 0 1 U U
1 0 0 1 U
1 1 0 0 1
1 1 1 0 0
Q(n-2) Q(n-3) Q(0)Q(n-1)
Q(n-2) Q(n-3) Q(0)Q(n-1)

42. PISO
PIPO
MOD-N BCD Counter
Q0
Q1
Clk
Q2
Q3
INPUT
OUTPUT
LOAD CLK IN0 IN1 IN1 IN1 SOUT
1 0 0 1 U
X 1 1 0 0 1
X 1 1 1 0 0
X 1 1 1 1 0
X 1 1 1 1 1
INPUT OUTPUT
LOAD CLK
10 11 I2 I3 Q0 Q1 Q2 Q3
X 1 0 0 1 U U U U
X 1 0 0 1 1 0 0 1
X 1 1 0 1 1 0 0 1
0 1 0 0 1 1 0 1
X 0 1 0 0 0 1 0 0
INPUT OUTPUT
SIN CLK
Q0 Q1 Q2 Q3
1 U U U U
0 1 U U U
0 0 1 U U
1 0 0 1 U
1 1 0 0 1
1 1 1 0 0
MOD-N
BCD
Counter

43. BINARY UP DOWN COUNTER
Q0
UP
DN Q1
Clk Q2
Q3
ASYNCHRONOUS COUNTER
Q0
Clk
Q1
Q0
Q2
Q1
Q3
Q2
CLR
BINARY
UP
DOWN
COUNTER
Asynchronous
Counter

44. MODELLING OF MULTIPLIERS
Ex. No : 08
AIM :-
To write VHDL Program for realizing multipliers like Array
Multiplier and verify the results.
PROGRAM:-
library IEEE;
Use IEEE.STD_LOGIC_1164.All;
Use IEEE.STD_LOGIC_ARITH.All;
Use IEEE.STD_LOGIC_UNSIGNED.All;
entity unsign_mul is
Port (x: in std_logic _vector(3 downto 0);
y : in std_logic _vector(3 downto 0);
l : in std_logic;
p : inout std_logic _vector(7 downto 0);
end unsign_mul;
architecture Behavioral of unsign_mul is
signal m : std_ logic_ vector(7 downto 0);
signal i : integer;
begin
processor(x,y,i)
begin
if (l’event and l =’1’)then
q<=”00000000”;
m<=”0000”&x;
i<=0;
else
qbar<=qbar;
if(i<4)then
if(y(i)=’1’)then
q<=p+m;
else
p<=p;
i<=i+1 after 50 ps;
m<=m(6 downto 0)&’0’;
end if;
end if;
end process;
end Behavioral;

45. RAM
Ex. No : 09
AIM :-
To write VHDL Program for RAM and verify the results.
PROGRAM:-
library ieee;
use ieee.std_logic_1164.all;
entity ram is
port(din:in std_logic_vector(7 downto 0);
rd,wr,clk:in std_logic;
locn:in integer range 0 to 7;
dout:out std_logic_vector(7 downto 0));
end ram;
architecture behav of ram is
type mem is array(integer range 0 to 7) of std_logic_vector(7 downto 0);
signal sram:mem;
begin
process(clk,rd,wr)
begin
if((rd and wr)/='1')then
if(clk'event and clk='1')then
if(rd='1')then
dout<=sram(locn);
else if(wr='1')then
sram(locn)<=din;
end if;
end if;
end if;
end if;
end process;
end behav;

46. STACK AND QUEUE IMPLEMENTATIONS
Ex. No : 10
AIM :-
To write VHDL Program for Stack and Queue Implementations
and verify the results.
PROGRAM:-
library ieee;
use ieee.std_logic_1164.all;
entity stack is
port ( rd,wr,clk,clr:in std_logic;
data: inout std_logic_vector(7 downto 0);
ful:out std_logic);
end stack;
architecture que of stack is
type store is array(natural range <>)of std_logic_vector(7 downto 0);
signal address: integer range 0 to 15;
signal memory:store(0 to 15);
begin
process (data ,rd ,wr,clr,clk)
begin
if clr='1' then
memory<=(others=>(others=>'0'));
ful<='0';
address<=0;
elsif(clk='1'and clk'event)then
if address=15 then
ful<='1';
else
memory(address)<=data;
address<=address+1;
end if;
elsif (rd='1')then
if (address=0)then
ful<='0';
else
data<=memory(address);
address<=address-1;
end if;
end if;
end process;
end que;