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.
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