combinational logic unit 2

UNIT-2

Mohammad Asif IqbalAssistant Professor, Deptt of ECE,JETGI, Barabanki

Multiplexers

A multiplexer has N control inputs

2N data inputs

1 output

A multiplexer routes (or connects) the selected data input to the output.

The value of the control inputs determines the data input that is selected.

Multiplexers

Z = A′.I0 + A.I1

Datainputs

Controlinput

Multiplexers

Z = A′.B'.I0 + A'.B.I1 + A.B'.I2 + A.B.I3

A B F

0 0 I0

0 1 I1

1 0 I2

1 1 I3

MSB LSB

Multiplexers

Z = A′.B'.C'.I0 + A'.B'.C.I1 + A'.B.C'.I2 + A'.B.C.I3 + A.B'.C'.I0 + A.B'.C.I1 + A'.B.C'.I2 + A.B.C.I3

MSB LSB

A B C F

0 0 0 I0

0 0 1 I1

0 1 0 I2

0 1 1 I3

1 0 0 I4

1 0 1 I5

1 1 0 I6

1 1 1 I7

Multiplexers

Encoder/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 DECODERS

A0

A1

A2

A3

A4

A5

A6

A7

ENCODER

O0

O1

O2

A0

A1

A2

O0

O1

O2

O3

O4

O5

O6

O7

DECODER

ONLY ONE INPUT ACTIVATED AT A TIME

BINARY CODE OUTPUT

BINARY CODE INPUT

ONLY ONE OUTPUT ACTIVATED 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

Decimal

to

BCD

Encoder

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 Encoder

ENCODER

1248

DECIMAL BINARY (BCD)

9 5V

8 5V

7 5V

6 5V

5 5V

4 5V

3 5V

2 5V

1 5V

74147I9I8I7I6I5I4I3I2I1

A0A1A2A3

10 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 Decoder

BCD-to-7-SegmentDecoder/

Driver

DECODERS: BCD TO 7-SEGMENT DECODER/DRIVER

BCD input

0 0 0 0

Decimal outputLED

0 0 0 10 0 1 00 0 1 10 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.

THANK YOU!