Question

These two questions relate to computer architecture:

If you wanted to choose between 16 outcomes, what size of Decoder would you need/how many bits would it be?

What size (in bits) of a selector would you need for a multiplexor with 18 inputs?

(Please explain and/or give examples of how you found the answer).

Answer 1

For 16 outcome there is 4 input as 2⁴ is 16 so size of decoder is 4 to 16. For implementating of 4 to 16 decoder we use 2 decoder with size 3 to 8 as calculated below.

Here m1= number of output of lower order decoder =8

m2=number of output of higher order decoder =16Required number of lower order decoder=m2/m1=16/2=2

So two 3 to 8 decoder required.

3 input directly given as input to the both decoder and 4^th input is connected directly to the enable E of higher decoder and complement of 4^th input connect to the enable E of lower decoder.

Selector line should be n such that multiplexer has 2ⁿ input here in given example input is 18 we choose n=4 then it give 16 which is not enough so take n=5 so it give 32 which is > number of input thus selection line is 5 and size of selector is 5 bit.

At any point if you have any query feel free ask me.