Please help me out im solving the question
I have to construct quad 9-1- line MUX with four single 8-1- line MUX and one quadruple 2-1- line MUX.The MUX should be interconnected and inputs labelled so that the selection codes 0000 through 1000 can be directly applied to the MUX selection inputs without added logic.
I dont know what I should do with the unused inputs while constructing larger MUX from smaller MUX??

 

Just ignore the inputs that aren't used. The 2 -1 mux drives the disable lines of the 8 - 1 mux, and the 2-1 mux input becomes part of the binary number.

 

OKAY..It means that if I have to cnstruct 15-1 line MUX from two 8-1 line MUX,then I should ignore the unused input(16th input) of the second MUX.
Is it right if I assert this unused input into the 3-input-OR gate which also contains the outputs coming from two(8-1 line MUX)..???