For students

1. ENCODERS
&
DECODERS
Combinational Logic

2. GROUP MEMBERS
■ ABDUL BASIT - 14CS01
■ HAMMAD RASHID - 14CS39
■ UMAIR SIMJEE - 14CS71
■ HAFIZ FAIZAN - 14CS15

3. INTRODUCTION
■ Encoders and Decoders are combinational logic circuits.
■ Combinatorial logic is a concept in which two or more input
states define one or more output states.
■ We Implement Combinational logic circuit using Boolean
Algebra.
■ Combinational logic is used in circuits to perform Boolean
algebra on input signals.
■ Part Of ALU processes, That performs mathematics is carried out
through combinational logics.

4. Contd.
■ An encoder is a device which transforms the data into some bits known
only to it and the decoder is a device which transforms those coded bits to
generate the original data again.
■ Encoding and Decoding is done for the safe transmission of data.
■ To encode something is to convert an unambiguous piece of information
into a form of code that is not so clearly understood.
■ To decode is to perform the reverse operation: converting a code back
into an unambiguous form.
■ The Main Difference between a decoder and encoder is that a decoder has
binary code as an input while an encoder has binary code as an output.

5. ENCODER
■ An encoder is an electronic device used to convert an analogue signal to a
digital signal.
■ It has a number of input lines, but only one of the inputs is activated at a
given time and produces an N-bit output code that depends on the
activated input.

6. ENCODER
SCHEMATIC DIAGRAM
■ The encoder accepts 2^N inputs and
produces N-number of outputs. For
example, in 4-2 encoder, if we give 4
inputs it produces only 2 outputs.
■ When we have 8 bits encoder, it
means N = 3 and the output will be 3
binary digit output.

7. ENCODER
TRUTH TABLE
■ The value of output depends upon
the logic gate being used.
■ Different gates yield different
output.

8. ENCODER
Octal To Binary Encoder
■ Octal-to-Binary take 8 inputs and provides 3 outputs.
■ At any one time, only one input line has a value of 1.
■ Truth Table
■

9. ENCODER
SCHEMATIC DIAGRAM

10. ENCODER
PRIORITY ENCODER
■ A priority encoder is a circuit or algorithm that compresses multiple binary inputs
into a smaller number of outputs.
■ If 2 or more inputs are equal to 1 at the same time, the input having the highest
priority will take precedence. Internal hardware will check this condition and
priority is set.

11. ENCODER
4 BIT PRIORITY ENCODER – TRUTH TABLE

12. DECODER
■ A decoder is a logic circuit that accepts a set of inputs that
represents a binary number and activates only the output
that corresponds to the input number.
■ In other words, a decoder circuit looks at its inputs,
determines which binary number is present there, and
activates the one output that corresponds to that number,
all other outputs remain inactive.

13. DECODER
■ A decoder is a circuit that changes a code into a set of
signals.
■ In its general form, a decoder has N input lines to handle
N bits and form one to 2^N output lines to indicate the
presence of one or more N-bit combinations.
■ An AND gate can be used as the basic decoding element
because it produces a high output only when all inputs are
high.

14. DECODER
■ Binary decoder
■ 2-bit decoder
■ 3-bit decoder
■ BCD-to-decimal decoder
■ BCD-to-Seven-Segment Decoder

15. DECODER
■ Binary decoder
The output is 1 only when:
A0 = 1
A2 = 0
A3 = 0
A4 = 1

16. DECODER
2 TO 4 LINE DECODER – SCHEMATIC DIAGRAM and TRUTH TABLE

17. DECODER
3 TO 8 LINE DECODER – TRUTH TABLE

18. DECODER
3 TO 8 LINE DECODER – SCHEMATIC DIAGRAM

19. DECODER
BCD TO DECIMAL DECODER

20. DECODER
BCD TO SEVEN SEGMENT DECODER
 Digital readouts on many digital products often use
LED seven-segment displays.
 Each digit is created by lighting the appropriate
segments. The segments are labeled a,b,c,d,e,f,g
 The decoder takes a BCD input and outputs the correct
code for the seven-segment display.