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Module3 Combinational Circuit

The document provides an overview of combinational and sequential circuits, highlighting their definitions, characteristics, and key components. It details various combinational circuit building blocks such as multiplexers and decoders, including their functions and applications. Additionally, it explains sequential circuits, emphasizing their reliance on both current inputs and past states, along with their memory elements.

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32 views134 pages

Module3 Combinational Circuit

The document provides an overview of combinational and sequential circuits, highlighting their definitions, characteristics, and key components. It details various combinational circuit building blocks such as multiplexers and decoders, including their functions and applications. Additionally, it explains sequential circuits, emphasizing their reliance on both current inputs and past states, along with their memory elements.

Uploaded by

saikrishnanwork
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Computer Hardware & System

Essentials
Combinational Circuit Building Blocks
Introduction to Combinational Circuits
• Definition: A combinational circuit is a type of digital circuit
where the output depends only on the present combination of
input values.
• Key Characteristics:
• No memory elements (i.e., no feedback loops).
• Outputs are determined by the current inputs.
Combinational vs. Sequential Circuits
Combinational Circuits:
•Output depends on the current inputs.
•No feedback or memory.

Sequential Circuits:
•Output depends on both current inputs and previous states.
•Includes memory elements like flip-flops.
Basic Building Blocks
• Common Combinational Circuit Blocks:

• Adders (Half-Adder, Full-Adder)


• Multiplexers (MUX)
Selects one of many inputs
Applications in data routing
• Decoders
Converts binary to one-hot encoding
Used in memory addressing
• Encoders
Converts one-hot to binary
Priority encoders
What is a Multiplexer?

•A combinational circuit that selects one of several input lines and routes it
to a single output
•Also called "data selector"
•Selection controlled by select lines
•2ⁿ inputs require n select lines
Components of a Multiplexer
o Data inputs (2ⁿ lines)
o Select inputs (n lines)
o Single output
o Enable input (optional)

Number of select lines = log₂(number of inputs)


Types of Multiplexers
1.2-to-1 MUX
• 2 data inputs
• 1 select line
• Simplest form

2.4-to-1 MUX
• 4 data inputs
• 2 select lines
• Common in practice

3.8-to-1 MUX
• 8 data inputs
• 3 select lines
• More complex applications
Applications of Multiplexers
Data Routing
▪ Selecting data from different sources
▪ Bus systems
Memory Systems
▪ Address selection
▪ Data path control
Communication Systems
▪ Channel selection
▪ Time-division multiplexing
ALU Operations
▪ Function selection
▪ Operation control
2-to-1 Multiplexer
2-to-1 Multiplexer Logic Circuit

OUT = (I1 AND NOT(S)) OR (I2 AND S)


4-to-1 Multiplexer
4-to-1 Multiplexer Logic Circuit
8to-1 Multiplexer
8-to-1 Multiplexer Logic Circuit
What is a Decoder?
➢ A combinational circuit that converts binary information from n
input lines to 2ⁿ output lines
➢ Each output line represents one unique input combination
➢ Also known as n-to-2ⁿ decoder
➢ Basic building block in digital systems
Applications
Applications
Applications
Applications
Sequential Circuits

What are Sequential Circuits?

Circuits whose outputs depend on:


▪ Present inputs
▪ Past history (previous states)
Contains memory elements

Examples: Counters, Registers, Memory units


Key Components
Memory Elements

•Flip-flops
•Latches
•Registers

Control Elements

•Clock signals
•Enable/Reset inputs
S R Flip-Flops

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