8:1 Multiplexer



A multiplexer is a combinational circuit that has ‘n’ input lines, ‘m’ selection lines and single output line. It is also known as many to one circuit. Multiplexer select binary information from many input lines and routes it to single output line. Its output is depending on value of select inputs or select lines.

For N input lines, m=log n (base2) selection lines, or we can say that for 2n input lines, m selection lines are required.

8:1 Multiplexer

8:1 multiplexer circuit having 8 input lines I0, I1, I2…………..I7 , one enable input (E) , single output line (Y) and three select line (S0, S1,S2).

Block Diagram of 8:1 Multiplexer

Select line calculate using given formula,

m=log n (base2)

where, n is the no. of input and m is the no. select line.

For 8:1 mux no. of select line

m=log2 23

m= 3 log2 2 (we know that log2 2 = 1 )


In 8:1 mux having 3 select lines. So, we can select any one of the input (depend on the value of select line) by moving the dialer we can have a input at the output. Dialer move and select input depend on the value of select line.

The one more input of multiplexer is Enable input (E). The function of Enable input is to enable the circuit it means, if E=1 (enable input is high) circuit operate and the output of the circuit is depends on the value of select line. If E=0 (enable input is low) circuit not operate and output of the multiplexer is zero its not depend on the value of select line.

The truth table of 8:1 mux has been shown below.

Truth Table of 8:1 Multiplexer

Operating Principle

When the enable input is 0, the output will be 0 irrespective of any input. With E=1,we can select any one of the eight inputs and connected it to the output. For example, if S2 S1 S0 = 101, then the data input I5 is selected and output Y will follow the input I5 .

Realization Using Logic Gate

Logic Circuit Diagram of 8:1 Multiplexer

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