Virtual Labs

Analysis and Synthesis of Logic Functions using Multiplexers

Introduction

About the Experiment

This experiment enables a student to learn

How to realize functionality of Dual 4 Line to 1 Line Multiplexer using 74153 IC
How Dual 4 Line to 1 Line Multiplexer select the particular input to be sent to the output IY{1 = 1, 2}.
How Each of the strobe signals IG {I = 1, 2} acts as an enable signal for the corresponding 4-to-1 M multiplexer.
How to realize functionality of Quad 2 Line to 1 Line Multiplexer using 74157 IC
How Quad 2 Line to 1 Line Multiplexer select the particular input to be sent to the output IY{1 = 1, 2, 3, 4}.
How the strobe signal acts as an enable signal for each of the four 4-to-1 M multiplexers.

Theory

74153 is a dual 4 line-to-1 line multiplexer. It has the schematic representation shown in Fig 1. Selection lines A and B select the particular input to be multiplexed and applied to the output IY{1 = 1, 2}.Each of the strobe signals IG {I = 1, 2} acts as an enable signal for the corresponding multiplexer.Figure 2(a) & 2(b) shows the multiplex function of 74153 in terms of select lines. Note that each of the on-chip multiplexers act independently from the other, while sharing the same select lines A and B.

Figure 1(74153)

Strobe	Select Lines		Outputs
1G	A	B	1Y
1	x	x	0
0	0	0	1C0
0	0	1	1C1
0	1	0	1C2
0	1	1	1C3

Figure 2(a) x:don't care state

Strobe	Select Lines		Outputs
2G	A	B	2Y
1	x	x	0
0	0	0	2C0
0	0	1	2C1
0	1	0	2C2
0	1	1	2C3

Figure 2(b) x:don't care state

The above circuit diagram shows the detail gate level structure of 74153(Dual 4 line to 1 line Multiplexer)

74157 is a quad 2 line-to-1 line multiplexer. It has the schematic representation shown in Fig 3. Select line select the particular input to be multiplexed and applied to the output IY{1 = 1, 2, 3, 4}. Strobe signal acts as an enable signal for each of the four multiplexers. Figure 4(a) & 4(b) & 4(c) & 4(d) shows the multiplex function of 74157 in terms of select lines. Note that each of the on-chip multiplexers act independently from the other, while sharing the same select line.

Figure 3(74157)

Strobe	Select	Inputs		Outputs
Strobe	Select	A1	B1	1Y
H	x	x	x	L
L	L	L	x	L
L	L	H	x	H
L	H	x	L	L
L	H	x	H	H

Figure 4(a) x:don't care state

Strobe	Select	Inputs		Outputs
Strobe	Select	A2	B2	2Y
H	x	x	x	L
L	L	L	x	L
L	L	H	x	H
L	H	x	L	L
L	H	x	H	H

Figure 4(b) x:don't care state

Strobe	Select	Inputs		Outputs
Strobe	Select	A3	B3	3Y
H	x	x	x	L
L	L	L	x	L
L	L	H	x	H
L	H	x	L	L
L	H	x	H	H

Figure 4(c) x:don't care state

Strobe	Select	Inputs		Outputs
Strobe	Select	A4	B4	4Y
H	x	x	x	L
L	L	L	x	L
L	L	H	x	H
L	H	x	L	L
L	H	x	H	H

Figure 4(d)x:don't care state

The above circuit diagram shows the detail gate level structure of 74157(Quad 2 line to 1 line Multiplexer)

74151 is a 8 line-to-1 line multiplexer. It has the schematic representation shown in Fig 5. Three select lines(A,B,C) select the particular input to be multiplexed and applied to the output Y, Y is the inverted output of the original outpu(Y). Strobe signal or Enable signal should be low to ensure proper multiplexing operation.If Enable is made high,then the output Y will always be low irrespective of any logic levels asserted by select lines A, B, C and the eight inputs.

An 8-to-1 Multiplexer can be used to implement any 3-variable switching function.

For example, consider the function

F (A,B,C) = &Sigma m (0,3,5)

Then the inputs D0, D3 and D5 should be set to logic 1 while the remaining five inputs we set to logic '0'.

Thus, for A = 0, B = 0, C = 0 Y = D0 = '1'

for A = 0, B = 1, C = 1, Y = D1, = '1'

for A = 1, B = 0, C = 1, Y = D5, = '1'

For the remaining combination of A, B, C Y = '0'.

Figure 5(a)

Strobe

Select Lines

Inputs

Outputs

Figure 5(b): Truth Table