Presentation Outline: 6–1 Half and Full Adders 6–2 Parallel Binary Adders 6–5 Decoders 6–6 Encoders 6–8 Multiplexers (Data Selectors) 6–9 Demultiplexers

1. PRESENTATION TOPIC : CHAPTER 6
Function of Combinational Logic
Submitted By…
Md Sefat Anam
ID: 173-0379-203,
Dept. of CSE , FST.
Submitted To…
Alea Afrin
Lecturer, Dept. of EEE,
Faculty of Science & Technology
Submitted Date…
04 August 2019

2.  Basic Overview of logic function
 Basic Adder
 Decoders
 Encoders
 Multiplexer
 Demultiplexer

3.  The AND gate

4.  The OR gate

5.  The NOT gate (or inverter)

6.  The NAND gate

7.  The NOR gate

8.  The Exclusive OR gate

9.  The Exclusive XNOR gate

10.  An adder is a digital logic circuit in electronics
that implements addition of numbers. Adders
are classified into two types: half adder and
full adder. The half adder circuit has two
inputs: A and B, which add two input digits
and generate a carry and sum. The full adder
circuit has three inputs: A and C, which add
the three input numbers and generate a carry
and sum. This Presentation gives brief
information about half adder and full adder in
tabular forms and circuit diagrams
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11.  Half adder is a combinational logic circuit with two
inputs and two outputs. The half adder circuit is
designed to add two single bit binary number A and
B. It is the basic building block for addition of
two single bit numbers. This circuit has two
outputs carry and sum
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Block Diagram

12. 12
Half-Adder Logic Circuit

13.  Inputs: A and B
 Outputs: S (for sum) and C (for carry)
 The simplified Boolean functions for the two inputs can be
obtained directly from the truth table.
Truth-Table of Half-Adder
Sum = A XOR B
Carry = A AND B

14.  Full adder is developed to overcome the
drawback of Half Adder circuit. It can add two
one-bit numbers A and B, and carry c. The
full adder is a three input and two output
combinational circuit.
Block Diagram

15.  A full adder can be implemented with two
half adders and an OR gate
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Logic circuit of Full-Adder

16.  A full adder is a combinational circuit that forms the arithmetic
sum of three input bits
◦ It consists of three inputs and two outputs.
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Truth-Table of Full-Adder

17.  An Encoder is a combinational circuit that performs
the reverse operation of Decoder. It has maximum of
2n input lines and ‘n’ output lines. It will produce a
binary code equivalent to the input, which is active
High. Therefore, the encoder encodes 2n input lines
with ‘n’ bits. It is optional to represent the enable
signal in encoders.
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18. 18
Logic circuit of Encoder
Block Diagram of Encoder

19. 19
Function
Truth Table of Encoder

20. 20
 Decoder is a combinational circuit that has ‘n’
input lines and maximum of 2noutput lines.
One of these outputs will be active High based
on the combination of inputs present, when
the decoder is enabled. That means decoder
detects a particular code. The outputs of the
decoder are nothing but the min terms of ‘n’
input variables (lines), when it is enabled

21. 21
Logic circuit of Decoder
Block Diagram of Decoder

22. 22
Function
Truth-Table of Decoder

23. 23
 Multiplexer is a combinational circuit that has
maximum of 2n data inputs, ‘n’ selection lines and
single output line. One of these data inputs will be
connected to the output based on the values of
selection lines.
 Since there are ‘n’ selection lines, there will be
2n possible combinations of zeros and ones. So,
each combination will select only one data input.
Multiplexer is also called as Mux.

24. 24
Truth Table
Output Equation :
Block Diagram

25.  De-Multiplexer is a combinational circuit that
performs the reverse operation of Multiplexer. It has
single input, ‘n’ selection lines and maximum of
2noutputs. The input will be connected to one of
these outputs based on the values of selection lines.
 Since there are ‘n’ selection lines, there will be
2n possible combinations of zeros and ones. So,
each combination can select only one output. De-
Multiplexer is also called as De-Mux.
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26. 26
Function
Block Diagram
Truth Table

27. Have any question ?