Digital Logic Design

Digital Logic Design
By
Jalpa Maheshwari
1

What is DLD?
Digital logic design deals with
the basic concepts and tools to
design hardware consisting of
logic gates.
2
Wednesday,
August 22, 2018

Introduction to all basic gates:
Hardware circuit is made with the help of following logic gates namely;
 AND
 OR
 NOT
 NAND
 NOR
 XOR
 XNOR
Universal gate:
A universal gate is a gate which can implement any Boolean function without need to use any
other gate type. The NAND and NOR gates are universal gates.
In practice, this is advantageous since NAND and NOR gates are economical and easier to
fabricate and are the basic gates used in all IC digital logic families.
Intro to Basic Gates
3
Wednesday,
August 22, 2018

AND Gate
 An AND gate can have more than two inputs, but output will be single. It works as the multiplication.
 An AND gate gives output high only if the input values are high, otherwise for any low input, output
will be zero.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 0
0 1 0
1 0 0
1 1 1
C=A.B
4
Wednesday,
August 22, 2018

5
IC 7408:
Alternatives:
If AND gate is not available, one can be made using NAND and NOR gates as they are universal gates.
Wednesday,
August 22, 2018

OR Gate
 An OR gate can have more than two inputs, but output will be single. It works as the addition.
 An OR gate gives output zero if all inputs (in our case two inputs) are low. And gives output high if
any or both of the input is high.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 0
0 1 1
1 0 1
1 1 1
C=A+B
6
Wednesday,
August 22, 2018

7
IC 7432:
Alternatives:
If OR gate is not available, one can be made using NAND and NOR gates as they are universal gates.
Wednesday,
August 22, 2018

NOT Gate
 NOT gate is also known as Inverter.
 If input is low, it gives high output and vice versa. In other words, it complements or inverts its input
signal.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
Output
( 𝐀)
0 1
1 0
A= 𝐀
8
Wednesday,
August 22, 2018

9
IC 7404:
Alternatives:
If NOT gate is not available, one can be made using NAND and NOR gates as they are universal gates.
Wednesday,
August 22, 2018

NAND Gate
 A NAND gate can have more than two inputs, but output will be single. It works as the multiplication.
 A NAND gate gives output low only if the input values are high, otherwise for any high input, output
will be high. It is the complement of AND gate.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 1
0 1 1
1 0 1
1 1 0
C=𝐀. 𝐁
10
Wednesday,
August 22, 2018

11
IC 7400:
Alternatives:
If NAND gate is not available, one can be made using NOR gates as it is universal gate.
Wednesday,
August 22, 2018

NOR Gate
 A NOR gate can have more than two inputs, but output will be single. It works as the addition.
 A NOR gate gives output high if all inputs (in our case two inputs) are low. And gives output low if any
or both of the input is high. It is the complement of OR gate.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 1
0 1 0
1 0 0
1 1 0
C=𝐀 + 𝐁
Wednesday,
August 22, 2018
12

13
IC 7402:
Alternatives:
If NOR gate is not available, one can be made using NAND gates as it is universal gate.
Wednesday,
August 22, 2018

XOR Gate
 A XOR gate can have more than two inputs, but output will be single.
 A XOR gate gives output low if all inputs (in our case two inputs) are either low or high. And gives
output high if any of the input is high.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 0
0 1 1
1 0 1
1 1 0
C=𝐴 ⊕ 𝐵
Wednesday,
August 22, 2018
14

15
IC 7486:
Alternatives:
If XOR gate is not available, one can be made using NAND and NOR gates as they are universal gates.
Wednesday,
August 22, 2018

XNOR Gate
 A XNOR gate can have more than two inputs, but output will be single.
 A XNOR gate gives output high if all inputs (in our case two inputs) are either low or high. And gives
output low if any of the input is high. It is the complement of NOR gate.
Logic Diagram:
Boolean Expression:
Truth table:
InputA
(A)
InputB
(B)
Output
(C)
0 0 1
0 1 0
1 0 0
1 1 1
C=𝐴 ⊕ 𝐵
16
Wednesday,
August 22, 2018

17
IC 74266:
Alternatives:
If XNOR gate is not available, one can be made using NAND and NOR gates as they are universal gates.
Wednesday,
August 22, 2018

Digital Logic Design

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