Multiplexer select lines confusion

Question

Here how do we know which variable of select lines is MSB and LSB ? Do we go in MSB->LSB ordering and take A as MSB and B as LSB or do we go by number taking B as MSB (as it is S1) and A as LSB (as it is S0) ?

Comments

S1 is MSB and S0 is LSB therefore B is MSB and A is LSB

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Where is it written like that ? I saw that it is always from MSB->LSB ordering  of select lines .Please give me reference.@akb1115

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Its default notation @Rajesh R ..S1 suggests it is higher selection line and S0 lower one so S1 corresponds to MSB and S0 LSB here..Basically S2 , S1 etc determines the priority of a variable in terms of its position in the combination of variables.

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In case of input lines, I1 will always be (S1)'S0 wherever it's position among the input lines is, right ? @Habibkhan

Also, we follow this same priority of S1 and S0 in other devices like decoder also right ?

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Yes correct @Rajesh Kumar . But in decoder there is no selection line ; there is input and output lines , the precedence of whom is shown in the diagram itself.

Here also the input lines in the multiplexer are mentioned clearly as I0 , I1 etc ..

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Select line :

S0 LSB

Sm MSB

Input line :

I0 LSB

In MSB