DIGITAL ELECTRONICS Decoder

Chapter 10Chapter 10

BINARY ARITHMETIC,

DECODING AND MUX LOGIC UNITS

Ch10L2-"Digital Principles and Design", Raj Kamal, Pearson Education, 2006 2

Lesson 2

Decoder


Outline

• Decoder • 1 of 2 and 1 of 4 line decoder• 1 of 8 • 4 of 16 line decoder• Function specific decoders


Decoder• A decoder is a circuit that selects the

binary information from a set of inputs• A decoder selects a unique

combination of inputs according to the information and generate output at a unique output at a line (or lines)


Decoder• Assume that we have 2n circuits to

implement different functions. One is for addition; other is for subtraction; other for incrementing; and so on. We have to select only one by giving appropriate input.

• A 1 of 2n decoder will let us select only one using n-bit input. For example, we want to decode and get a selected output when the input is 0001 (like an instruction) and activate the addition circuit, one of 16 circuits


Decoder• Assume that we have 10 digits, which

corresponds to 7 segments of LEDs in an LED display unit. We have to select only one unique set of outputs by giving a unique set of input bits.

• A 7-segment decoder will let us select only one. For example, we want to decode and get a selected output when 4-bit input is 1000 and decoder activates all seven segments of the LEDs to display digit 8.


1 to n Decoder

• A circuit, which takes the n-bit input, activates only one of the output out of 2n outputs and remaining remains inactive.

• Inactive output can be taken as tristate or 1 or 0

• Active output be taken as 1 or 0


Outline

• Decoder • 1 of 2 and 1 of 4 line decoders• 1 of 8 line decoder• 4 of 16 line decoder• Function specific decoders


1 of 2 Decoder with active 0 output

0 0 *

Inputs Outputs A Y0 Y1

1 * 0

* means tristate or 1

Y0Y1

A



0 1 *

Inputs Outputs A Y0 Y1

1 * 1


Y0Y1

A



0 0 0 * * *

Inputs Outputs A1 A0 Y0 Y1 Y2 Y3

0 1 * 0 * *1 0 * * 0 *1 1 * * * 0


Y1Y0

Y2Y3

A0A1


Outline




0 0 0 0 *** *

Inputs Outputs A2 A1 A0 Y0 ..... Y7

.. .. .. .. ..

1 1 1 * *** 0


...Y0

Y7

A0A1A2


1 of 8 Decoder with three control (enabling/disabling) pins

X X X

≠≠≠≠100 ***** *

Inputs Outputs

A2 A1 A0 Y0 ...Y70 0 0 100 0 *** * 1 1 1 100 *** 0

When G2 = 1, the G1 and G0 both 0s, then only one of the Y output activates. X means 1 or 0.

ControlInputs

G2G1G0


MSI 74138 —1 of 8 Decoder with three control (enabling/disabling) pins

Y0

Y7

G2G1G0

Y1Y2

Y3Y4

Y5Y6

A0A1A2


Outline

• Decoder • 1 of 2 and 1 of 4 line decoders• 1 of 8 line decoder• 4 line of 16 line decoder • Function specific decoders


MSI 74154 —1 of 16 (4 line to 16 line) Decoder with three control (enabling/disabling) pins

Y0

Y15

A3

G1G0

Y1Y2

Y14

A0A1A2 .

.

.


Outline



BCD to Decimal line decoder

MSIIC 7442

A4A3A2A1A0

Y0

Y9

Y1Y2

Y0

.

Y10

Active means 1Inactive means 0


Multi-line decoder BCD to 7-segment LED display

MSIIC 7447

A3A2A1A0

Y0

e

bc

a

g

Active means 0Inactive means 1

d

f


Summary


Decoder

• Decoder active one output pin among 2n output pins and has n inputs to enable circuit to select corresponding output.

• Specific function decoder gives outputs on set of pins as per the given set of inputs


Decoder

• A decoder can have inactive outputs in tristate and active output as 0 or 1

• A decoder can have control gate pins


End of Lesson 2 on

Decoder


THANK YOU

DIGITAL ELECTRONICS Decoder

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