This document introduces basic logic functions including NOT, AND, and OR. It discusses how George Boole developed Boolean algebra to represent logic statements with symbols. The three basic logic functions are represented by distinctive symbols and implemented with digital circuits. NOT inverts the input logic level, AND outputs HIGH only when all inputs are HIGH, and OR outputs HIGH when one or more inputs are HIGH.

1. Basic Logic Functions
Module 3
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Module 3 – Basic Logic Functions
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LCST – Logic Circuits and Switching Theory
Source: Digital Fundamentals by Floyd, T. 11th Edition

2. Introduction
 In its basic form, logic is the realm of human reasoning that
tells you a certain proposition (declarative statement) is true if
certain conditions are true.
 Propositions can be classified as true or false.
 Many situations and processes that you encounter in your daily
life can be expressed in the form of propositional, or logic,
functions.
 Since such functions are true/false or yes/no statements,
digital circuits with their two-state characteristics are
applicable.
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Module 3 – Basic Logic Functions
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3. Learning Objectives
 After completing this module, the learners
should be able to:
1. List three basic logic functions
2. Define the NOT function
3. Define the AND function
4. Define the OR function
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Module 3 – Basic Logic Functions
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4. Basic Logic Functions
 In the 1850s, the Irish logician and mathematician George
Boole developed a mathematical system for formulating logic
statements with symbols so that problems can be written and
solved in a manner similar to ordinary algebra.
 Boolean algebra, as it is known today, is applied in the design
and analysis of digital systems and will be covered in Chapter
4.
 The term logic is applied to digital circuits used to implement
logic functions.
 Several kinds of digital logic circuits are the basic elements
that form the building blocks for such complex digital systems
as the computer.
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Module 3 – Basic Logic Functions
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5. Basic Logic Functions
 Three basic logic functions (NOT, AND, and OR) are indicated
by standard distinctive shape symbols
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Module 3 – Basic Logic Functions
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6. NOT
 The NOT function changes one logic level to the opposite logic
level.
 The NOT function is implemented by a logic circuit known as an
inverter.
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Module 3 – Basic Logic Functions
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7. AND
 The AND function produces a HIGH output only when all the
inputs are HIGH.
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Module 3 – Basic Logic Functions
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8. OR
 The OR function produces a HIGH output when one or more
inputs are HIGH.
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Module 3 – Basic Logic Functions
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9. Mastery Exercises
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1. When does the NOT function produce a HIGH output?
 When the input is LOW
2. When does the AND function produce a HIGH output?
 When all inputs are HIGH
3. When does the OR function produce a HIGH output?
 When any or all inputs are HIGH
4. What is an inverter?
 An inverter is a NOT circuit.
5. What is a logic gate?
 A logic gate is a circuit that performs a logic operation
(AND, OR).
Module 3 – Basic Logic Functions
Prepared by:; fscjr.