Digital ElectronicsDigital Electronics

Electronics TechnologyElectronics Technology

Landon Johnson

Encoding, Decoding, andSeven-Segment Displays

Encoder/Decoder Encoder/Decoder CompetenciesCompetencies

52. Given four different input combinations to a 10 line to 4 line encoder, the student will state the output combinations with 100% accuracy.

53. Given four different input combinations for a 4 line to 10 line decoder, the student will state the output combinations with 100% accuracy.

Encoder/Decoder VocabularyEncoder/Decoder Vocabulary

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 DECODERSENCODERS AND DECODERS

A 0

A 1

A 2

A 3

A 4

A 5

A 6

A 7

ENCODER

O 0

O 1

O 2

A 0

A 1

A 2

O 0

O 1

O 2

O 3

O 4

O 5

O 6

O 7

DECODER

ONLY ONE INPUT ONLY ONE INPUT ACTIVATED AT A TIMEACTIVATED AT A TIME

BINARY CODE OUTPUTBINARY CODE OUTPUT

BINARY CODE INPUTBINARY CODE INPUT

ONLY ONE OUTPUT ONLY ONE OUTPUT ACTIVATED AT A TIMEACTIVATED AT A TIME

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

0

Decimalto

BCDEncoder

BCD output

Decimal input0 0 0 0

5

0 1 0 1

7

0 1 1 1

3

0 0 1 1

• Encoders are available in IC form.

• This encoder translates from decimal input to BCD output.

10 line to 4 line Encoder10 line to 4 line Encoder

ENCODER1248

DECIMAL BINARY (BCD)

9 5V

8 5V

7 5V

6 5V5 5V

4 5V3 5V

2 5V1 5V

74147I9I8I7I6I5I4I3I2I1

A0A1A2A3

10 line to 4 line Encoder10 line to 4 line Encoder

0

1

2

3

4

5

6

7

8

9

DECODER

BINARY (BCD)

DECIMAL

1 0V

2 0V

4 0V

8 0V

74LS42

A3A2A1A0

9876543210

4 line to 10 line Decoder4 line to 10 line Decoder

BCD-to-7-SegmentDecoder/

Driver

DECODERS: BCD TO 7-SEGMENT DECODER/DRIVER

BCD input

0 0 0 00 0 0 0

Decimal outputLED

0 0 0 10 0 0 10 0 1 00 0 1 00 0 1 10 0 1 10 1 0 00 1 0 0

• Electronic decoders are available in IC form.• This decoder translates from BCD to decimal.• Decimals are shown on an 7-segment LED display.• This IC also drives the 7-segment LED display.

BCD-to-7-SegmentDecoder/

Driver

BCD inputDecimal output

0 0 1 1

?

Q #1- What is the decimal output from the decoder that appears on the 7-segment display?

Answer: 3

Q #2- What is the decimal output from the decoder that appears on the 7-segment display?

0 0 0 0

Answer: 0

Q #3- What is the decimal output from the decoder that appears on the 7-segment display?

1 0 0 1

Answer: 9

Q #4- What is the decimal output from the decoder that appears on the 7-segment display?

Answer: 7

0 1 1 1

Q #5- What is the decimal output from the decoder that appears on the 7-segment display?

Answer: 6

0 1 1 0

TEST

BCD-TO-SEVEN SEGMENT DECODER DRIVER

5V

abcdef g .

V+

74LS47A3A2A1A0

testRBI

gfedcba

RBO

TEST

A 0

A 1

A 2

A 3

A 4

A 5

A 6

A 7

ENCODER

O 0

O 1

O 2

O 3

A 8

A 9

TEST

A 0

A 1

A 2

O 0

O 1

O 2

O 3

O 4

O 5

O 6

O 7

DECODER

O 8

O 9

A 3

TESTANSWER THE FOLLOWING QUESTIONS WITH ONE OR MORE OF THESE WORDS: MUX, DEMUX, ENCODER, DECODER.

A. Has more inputs than outputs. ENCODER, MUX

B. Uses select inputs. MUX, DEMUX

C. Can be used in parallel-to-serial conversion. MUX

D. Produces a binary code at its output. ENCODER

E. Only one of its outputs is activated at one time. DEMUX, DECODER

F. Used to route input signals to one of several outputs. MUX

G. Used to generate arbitrary logic functions. MUX, DEMUX

H. 3 line-to-8 line or binary to octal. DECODER

I. Data Selectors are also MUX.