Digital Techniques

1. WELCOME
TO YOUR PRESENTATION
ON
ENCODER AND DECODER

2. ENCODER AND DECODER
ENCODER
Encoder is combinational logic circuit which is design to perform inverse operation of Decoder. Encoder has ‘n’
number of inputs and ‘m’ number of output.
Block diagram of Encoder
Types of Encoder
 Decimal to BCD Encoder
 Octal to Binary Encoder
 Hexadecimal to Binary Encoder
 Priority Encoder

3. DECIMAL TO BCD ENCODER
The decimal-to-binary encoder usually consists of 10 input lines and 4 output lines. Each input line corresponds to each decimal digit and 4 outputs correspond to the
BCD code. This encoder accepts the decoded decimal data as an input and encodes it to the BCD output which is available on the output lines.
BLOCK DIAGRAM :

4. TRUTHTABLE : EQUATIONS :
Decimal
Input
BCD Output
A3 A2 A1 A0
0 0 0 0 0
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
A3 = Y9 + Y8
A2 = Y7 + Y6 + Y5 +Y4
A1 = Y7 + Y6 + Y3 +Y2
A0 = Y9 + Y7 +Y5 +Y3 + Y1

5. LOGIC DIAGRAM

6. OCTAL TO BINARY ENCODER
 The 8 to 3 Encoder or octal to Binary encoder consists of 8 inputs: Y7 to Y0 and 3 outputs: A2, A1 & A0. Each input line corresponds to each octal
digit and three outputs generate corresponding binary code.
BLOCK DIAGRAM :
Octal to
Binary
Encoder

7. TRUTHTABLE : EQUATIONS :
Octal Input BCD Output
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 A2 A1 A0
1 0 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0 1
0 0 1 0 0 0 0 0 0 1 0
0 0 0 1 0 0 0 0 0 1 1
0 0 0 0 1 0 0 0 1 0 0
0 0 0 0 0 1 0 0 1 0 1
0 0 0 0 0 0 1 0 1 1 0
0 0 0 0 0 0 0 1 1 1 1
A2 = Y7 + Y6 + Y5 + Y4
A1 = Y7 + Y6 + Y3 + Y2
A0 = Y7 + Y5 + Y3 + Y1

8. LOGIC DIAGRAM

9. PRIORITY ENCODER
 A 4 to 2 priority encoder has 4 inputs: Y3, Y2, Y1 & Y0, and 2 outputs: A1 & A0. Here, the input, Y3 has the highest priority, whereas the input, Y0
has the lowest priority. In this case, even if more than one input is ‘1’ at the same time, the output will be the (binary) code corresponding to the input,
which is having higher priority.
BLOCK DIAGRAM :
Priority
Priority
Encoder

10. TRUTHTABLE
Inputs Outputs
Y3 Y2 Y1 Y0 A1 A0
0 0 0 0 X X
0 0 0 1 0 0
0 0 1 X 0 1
0 1 X X 1 0
1 X X X 1 1

11. K-MAP FOR A1 K-MAP FOR A0

12. LOGIC DIAGRAM

13. APPLICATIONS
 Encoders are very common electronic circuits used in all digital systems.
• Encoders are used to translate the decimal values to the binary in order to perform binary functions such as addition, subtraction, multiplication, etc.
 Other applications especially for Priority Encoders may include detecting interrupts in microprocessor applications.
ADVANTAGES OF ENCODER
 Highly reliable and accurate.
 Higher Resolution.
 Low cost Feedback.
 Compact in size.
DISADVANTAGES OF ENCODER
 Direct Light source interference.
 The subject of magnetic radio interference.
 Susceptible to dirt, oil and dust contaminated.

14. DECODER
Decoder is a Combinational logic circuit it has ‘n’ number of input and 2^n of outputs. Decoder is same as demultiplexer without any data input.
Types of Decoders
 2:4 Decoder
 3:8 Decoder

15. 2:4 DECODER
A decoder is a combinational logic circuit that has ‘n’ input signal lines and 2n
output lines. In the 2:4 decoder, we have 2 input lines and 4 output lines. In
addition, we provide ‘enable‘ to the input to ensure the decoder is functioning whenever enable is 1 and it is turned off when enable is 0.
BLOCK DIAGRAM:

16. TRUTHTABLE : EQUATIONS :
Inputs Outputs
A B Y0 Y1 Y2 Y3
0 0 1 0 0 0
0 1 0 1 0 0
1 0 0 0 1 0
1 1 0 0 0 1
Y0= A.B
Y1= A.B
Y2=A.B
Y3=A.B

17. LOGIC DIAGRAM :

18. 3:8 DECODER
3:8 decoder can be used for decoding any 3-bit code to provide eight outputs, corresponding to eight different combinations of the input code.It is also called a binary-to-
octal decoder since the inputs represent 3-bit binary numbers and the outputs represent the eight digits in the octal number system.
BLOCK DIAGRAM :

19. TRUTHTABLE : EQUATIONS :
Inputs Outputs
A B C D0 D1 D2 D3 D4 D5 D6 D7
0 0 0 1 0 0 0 0 0 0 0
0 0 1 0 1 0 0 0 00 0 0
0 1 0 0 0 1 0 0 0 0 0
0 1 1 0 0 0 1 0 0 0 0
1 0 0 0 0 0 0 1 0 0 0
1 0 1 0 0 0 0 0 1 0 0
1 1 0 0 0 0 0 0 0 1 0
1 1 1 0 0 0 0 0 0 0 1
D0= A.B.C
D1= A.B.C
D2= A.B.C
D3= A.B.C
D4= A.B.C
D5= A.B.C
D6= A.B.C
D7= A.B.C

20. LOGIC DIAGRAM :

21. DIFFERENCE BETWEEN ENCODER AND DECODER
Sr.No Encoder Decoder
1. Encoder circuit basically converts the applied information signal into
a coded digital bit stream.
Decoder performs reverse operation and recovers the original
information signal from the coded bits.
2. The number of inputs accepted by an encoder is 2n. The number of input accepted by decoder is only n inputs.
3. The output lines for an encoder is n. The output lines of an decoder is 2n.
4. The encoder generates coded data bits as its output. The decoder generates an active output signal in response to the coded
data bits.
5. The operation performed is simple. The operation performed is complex.

22. THANK YOU