# Just a question

#### aceminer

Joined Aug 26, 2011
21
Hi guys,

Just to check, is there any exam papers i could find on the net provided with solutions as my digital logic exam is just round the corner. Would appreciate greatly any material or exam papers. I am a Year 1 CS student anyway.

#### thatoneguy

Joined Feb 19, 2009
6,359

It will help you a lot. Especially since it is FREE too!

#### aceminer

Joined Aug 26, 2011
21
Hey bertus, thanks for the link but they are apparently too hard for me to understand. I am only a Year 1 student so the course i am undergoing is relatively introductory so do you have any other links which are relatively less complicated. To be honest, i couldnt even understand the questions or the answers in the worksheet.

#### thatoneguy

Joined Feb 19, 2009
6,359
Hey bertus, thanks for the link but they are apparently too hard for me to understand. I am only a Year 1 student so the course i am undergoing is relatively introductory so do you have any other links which are relatively less complicated. To be honest, i couldnt even understand the questions or the answers in the worksheet.
Everything in the worksheet and quiz is covered in the link I posted.

#### aceminer

Joined Aug 26, 2011
21
Well i have a question which goes like this:

Given an Equation :
F = A'B'CD' + B'C'D + A'B'C' + AB'D
use a 4x1 multiplexer with an enable input plus other gates
draw out the circuit based on this equation. Anyway the enable is active-low.

I do have the answer but i cannot seem to understand why do they use A and C inputs as the select bits whereas the D inputs are belonging to the 4 x 1 multiplexer with one input being constant. Could some1 kindly please explain to me.

#### thatoneguy

Joined Feb 19, 2009
6,359
Skip to Here and draw out the truth table for the expression.

From there, look at the behavior of a 4-1 multiplexer with enable.

The ' as in A' means NOT A, and AB means A AND B, A+B is A OR B, and A'B is NOT A AND B

It's just a system of notation for text discussion of logic.