Question

Without any additional circuitry an 8:1 MUX can be used to obtain ____________

(a) Some but not all Boolean functions of 3 variables

(b) All function of 3 variables but none of 4 variables

(c) All functions of 3 variables and some but not all of 4 variables

(d) All functions of 4 variables

The question was posed to me in an interview.

Origin of the question is Multiplexers (Data Selectors) topic in division Combinational Circuits of Digital Circuits

Answer 1

The correct choice is (d) All functions of 4 variables

For explanation: A 2^n:1 MUX can implement all logic functions of (n+1) variables without any additional circuitry. Thus 8:1 MUX can implement all logic functions of (3+1) variables, for 4 variables there are 16 possible combinations. So to use 8:1 MUX use 3 inputs as select lines of MUX and the 4th input as input of MUX.