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Gate:
A device that performs a basic operation
on
electrical signals.
Circuits:
Gates combined to perform more
complicated tasks.

How do we describe the behavior of gates and circuits?
Boolean expressions:
Uses Boolean algebra, a mathematical notation for expressing
two-valued logic.
Logic diagrams:
A graphical representation of a circuit; each gate has its
own symbol.
Truth tables:
A table showing all possible input value and the
Associated output values.

A logic gate is an idealized or physical device implementing a Boolean
function, a logical operation performed on one or more binary inputs that
produces a single binary output.
There are usually three types of main gates;
– NOT Gate
– AND Gate
– OR Gate
GateS

NOT Gate
A NOT gate accepts one input signal (0 or 1) and
returns the opposite signal as output

AND Gate
An AND gate accepts two input signals If both are 1, the
output is 1; otherwise, the output is 0.

OR Gate
An OR gate accepts two input signals If both are 0,
the output is 0; otherwise, the output is 1.

UNIVERSAL GATES
=>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.
There are usually three types of main gates;
– NAND Gate
– NOR Gate

NAND Gate
The NAND gate accepts two input signals.
If both are 1, the output is 0; otherwise,
the output is 1.
Figure 4.5 Various representations of a NAND gate

NOR Gate
Figure 4.6 Various representations of a NOR gate
The NOR gate accepts two input signals.
If both are 0, the output is 1; otherwise,
the output is 0

XOR Gate
Figure 4.4 Various representations of an XOR gate
An XOR gate accepts two input signals
If both are the same, the output is 0; otherwise,
the output is 1.

XOR Gate
Note the difference between the XOR gate
and the OR gate; they differ only in one
input situation
When both input signals are 1, the OR gate
produces a 1 and the XOR produces a 0
XOR is called the exclusive OR

Review of Gate Processing
A NOT gate inverts its single input
An AND gate produces 1 if both input values are 1
An OR gate produces 0 if both input values are 0
An XOR gate produces 0 if input values are the
same
A NAND gate produces 0 if both inputs are 1
A NOR gate produces a 1 if both inputs are 0

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INTRODUCTION OF LOGIC GATES

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