INSTITUTE OF BUSINESS ADMINISTRATION, KARACHI
Digital Logic Design (CSE-241)
Laboratory Manual
LAB # 13
Multiplexers
Objective:
In this experiment, you will design a combinational circuit and implement it with multiplexer.
F(A,B,C,D)=∑(1,3,4,11,12,13,14,15)
Equipment:
1. One- Single Polarity Variable DC Power
Supply
2. Logic Probe
Components:
1.
2.
3.
4.
One- 8 Input MUX, 74LS151
One- Hex inverter 74LS04
Switches
One- Bread Board
Note: Do consult the data sheets before connecting you ICs
THEORY:
In electronics, a multiplexer or MUX is a device that selects one of several analog or digital
input signals and forwards the selected input into a single line. A multiplexer of 2n inputs has n
select lines, which are used to select which input line to send to the output.
A 2-to-1 multiplexer has a Boolean equation where
and is the output:
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and
are the two inputs, is the selector input,
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A straightforward realization of this 2-to-1 multiplexer would need 2 AND gates, an OR gate,
and a NOT gate.
Larger multiplexer are also common and, as stated above, requires n selector pins for 2n inputs..
Other common sizes are 4-to-1, 8-to-1, and 16-to-1. Since digital logic uses binary values,
powers of 2 are used (4, 8, 16) to maximally control a number of inputs for the given number of
selector inputs.
Since a MUX consists of AND, OR and Inverter gates, as shown in the figure below.
Multiplexers could be used to implement large combinational logic circuits with ease. Consider
the following example for a better understanding.
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Example:
Implement the following Boolean function with an 8*1 multiplexer
F(A,B,C,D) = Σ(0,3,5,6,8,9,14,15)
One thing must be noticed over here that out of the 4 inputs required to implement the
combinational logic 3 are obtained from the address selection pins and one from the data in. This
convention is always followed.
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The multiplexer to be used is IC type 74151, shown in figure below.
A strobe control ‘ E’ ’ acts as an enable signal. The function table specifies the value of output
‘Y’ as function of the selection lines. Output ‘ Y’ ’ is the complement of ‘Y’. for proper
operation, the strobe input ‘ E’ ’ must be connected to ground. .
Function table for IC 74151 is given below:
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Task 1:

Construct a circuit using multiplexer 74LS151 to implement the following logic.
F(A,B,C,D)=∑(1,3,4,11,12,13,14,15)
Assignment:
Implement logics for a full adder and a full subtractor (separately) using a 74LS153
MUX.
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