Alpha Breathing

Evocation

ENCODER & DECODER

INTRODUCTION ENCODER- a digital circuit that produces a binary output code depending on which of its inputs are activated.

DECODER- a digital circuit that converts an input binary code into a single numeric output.

ENCODERS AND DECODERS REPRESENTATION A0 A1 A2 A3 A4 A5 A6 A7

O0 O1 O2 ENCODER

A0 A1 A2 DECODER

O0 O1 O2 O3 O4 O5 O6 O7

THE 8421 BCD CODE • BCD stands for Binary-Coded Decimal. • A BCD number is a four-bit binary group that represents one of the ten decimal digits 0 through 9. Example: Decimal number 4926 4 9 2 6 8421 BCD coded number

0100 1001 0010 0110

ELECTRONIC ENCODER -

DECIMAL TO BCD BCD output Decimal input

7 5

3

00 10 0 11 Decimal to BCD Encoder

0

• Encoders are available in IC form. • This encoder translates from decimal input to BCD output.

10 line to 4 line Encoder

10 line to 4 line Encoder BINARY (BCD)

DECIMAL 8 ENCODER 9 5V 8 5V 7 5V 6 5V 5 5V 4 5V 3 5V 2 5V 1 5V

74147 I9 I8 I7 A3 I6 A2 I5 A1 I4 A0 I3 I2 I1

4

2

1

Decoder – Accepts a value and decodes it • Output corresponds to value of n inputs

– Consists of: • Inputs (n) • Outputs (2n , numbered from 0  2n - 1) • Selectors / Enable (active high or active low)

The truth table of 2-to-4 Decoder

2-to-4 Decoder

2-to-4 Decoder

The truth table of 3-to-8 Decoder A2

A1

A0

D0

0

0

0

1

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

D1

D2

D3

D4

D5

D6

D7

1 1 1 1 1

1 1

3-to-8 Decoder

3-to-8 Decoder with Enable

Decoder Expansion • Decoder expansion – Combine two or more small decoders with enable inputs to form a larger decoder – 3-to-8-line decoder constructed from two 2-to4-line decoders • The MSB is connected to the enable inputs • if A2=0, upper is enabled; if A2=1, lower is enabled.

Decoder Expansion

Combining two 2-4 decoders to form one 3-8 decoder using enable switch

The highest bit is used for the enables

How about 4-16 decoder • Use how many 3-8 decoder? • Use how many 2-4 decoder?

Encoders • Perform the inverse operation of a decoder – 2n (or less) input lines and n output lines

Encoders

Encoders with OR gates

Encoders • Perform the inverse operation of a decoder –2n (or less) input lines and n output lines

Priority Encoder – Accepts multiple values and encodes them • Works when more than one input is active – Consists of: • Inputs (2n) • Outputs – when more than one output is active, sets output to correspond to highest input – V (indicates whether any of the inputs are active) • Selectors / Enable (active high or active low)

D3

D2

D1

D0

A1

A0

V

0

0

0

0

x

X

0

0

0

0

1

0

0

1

0

0

1

0

0

1

1

0

0

1

1

0

1

1

0

1

0

0

1

0

1

0

1

0

1

1

0

1

0

1

1

0

1

0

1

0

1

1

1

1

0

1

1

0

0

0

1

1

1

1

0

0

1

1

1

1

1

0

1

0

1

1

1

1

0

1

1

1

1

1

1

1

0

0

1

1

1

1

1

0

1

1

1

1

1

1

1

0

1

1

1

1

1

1

1

1

1

1

Priority Encoder

Puzzles

33

Mind Map – Encoder and Decoder Hexadecimal to binary encoder

Priority Encoder

Encoder

Decimal BCD to encoder

Applications

Block diagram

Octal to binary encoder

Code conversion

Truth table 2 to 4 line decoder

Decoder

Counter system

Applications Logic diagram

3 to 8 line Decoder

Block diagram

Truth table

Logic diagram

A to D counter Display system

Summary Encoders & Decoders

Truth table K-Map Logic Diagram

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