ece 301 – digital electronics multiplexers and demultiplexers (lecture #12)
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ECE 301 – Digital Electronics
Multiplexers and Demultiplexers
(Lecture #12)
ECE 301 - Digital Electronics 2
Multiplexers
ECE 301 - Digital Electronics 3
Multiplexer
A multiplexer switches (or routes) data from 2N inputs to one output, where N is the
number of select (or control) inputs.
A multiplexer (mux) is a digital switch.
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Multiplexer: 2-to-1
2 inputs
1 output
1 select
S = 0 selects I0
S = 1 selects I1
Y = (I0.s') + (I
1.s)
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Multiplexer: 2-to-1 with Enable
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Multiplexer: 4-to-1
Y = (I0.s
1's
0') + (I
1.s
1's
0) + (I
2.s
1s
0') + (I
3.s
1s
0)
Two select signals
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0
w 0
w 1
0
1
w 2
w 3
0
1
f 0
1
s 1
s
Multiplexer: 4-to-1
Select signal for first level of decoders
Select signal for second level of decoders
2-to-1 Muxes
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Multiplexer: 16-to-1
w 8
w 11
s 1
w 0
s 0
w 3
w 4
w 7
w 12
w 15
s 3
s 2
f
Select signals (2) for second level of decoders
Select signals (2) for first level of decoders
4-to-1 Muxes
0123
01
23
01
23
01
23
01
23
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Designing Logic Circuits using Multiplexers
Multiplexers
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Mux: Designing Logic Circuits
• Each row in a Truth Table corresponds to a minterm
– N-input Truth Table
• Each minterm can be mapped to a multiplexer input
– N-input Multiplexer
• For each row in the Truth Table, where the output of the function is one (F = 1),
– Set the corresponding input of the multiplexer to 1
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Given the following Truth Table:
Design a logic circuit to implement this function, using a 4-to-1 Multiplexer.
Mux: Designing a Logic Circuit
0
1
0
0
1
1
1
0
1
f s 1
0
s 0
1
0
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Exercise:
Design a circuit, using a 4-to-1 Mux to realize the Boolean expression given below.
FX,Y
= m(0,2)
Mux: Desiging a Logic Circuit
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Designing Logic Circuits using Multiplexers more efficiently.
Multiplexers
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Mux: Designing Logic Circuits Efficiently
• Each row in a Truth Table corresponds to a minterm
– N-input Truth Table
• A product term of N-1 variables can be mapped to each of the multiplexer inputs
– (N-1)-input Multiplexer
• For the rows in the Truth Table,
– Group N-1 highest order inputs into pairs
– Define the output of each pair using the Nth input
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Mux: Designing a Logic Circuit
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Mux: Designing a Logic Circuit
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Exercise:
Design a circuit, using a 4-to-1 Mux to realize the Boolean expression given below.
FX,Y,Z
= m(1,2,3,6)
Mux: Designing a Logic Circuit
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Demultiplexers
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Demultiplexer
A demultiplexer switches (or routes) data from one input to 2N outputs, where N is the
number of select inputs.
A demultiplexer (mux) is also a digital switch.
A demultiplexer performs the opposite function of a multiplexer.
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Demultiplexer: 1-to-4
I
s1
s0
O0
O1
O2
O3
01
2
3
S1
S0
O0
O1
O2
O3
0 0 I 0 0 0
0 1 0 I 0 0
1 0 0 0 I 0
1 1 0 0 0 I
O0 = S
1'.S
0'.I
O1 = S
1.S
0'.I
O2 = S
1'.S
0.I
O3 = S
1.S
0.I