Identifying Multiplexer function inputs from Maxterms

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Ivaaaa

Joined Nov 9, 2019
3
I'm asked to find out the inputs for the following MUX. This is quite different from what I'm used to, because the selector is deliberately jumbled up and it really does test our understanding.

In class, we're usually told that the selector is AB which is generally easier. Apart from that, it is usually only 3 variables (ABC), whereas now it is 4 (ABCD).

Also, I was taught to look for the patterns via a truth table to deduce the inputs. However, this time I'm stuck with:

How should I structure the truth table?

As such, I ditched the normal method I'm used to and followed a YouTube video, which requires me to draw a k-map. In the past, for 3 variables, I didn't have to use a k-map at all.

Here's the question:


And here's what I tried doing:



Just some things I wanted to clarify if the following are correct:

1. What I've done is converted the sum of max terms to minterms (by taking the opposite values). Is this correct?
2. For my k-map, I rearranged it as AD\BC instead of the usual AB\CD so that it matches the selectors
3. From my k-map, I generated another table to match the 1s @ the AD row
4. Given my selector values, I have no idea how to deduce what value the AND gate is supposed to be

I'd like to know whether my method is correct, or if there's a better one, and any clues on how I can deduce the input for the AND gate.

Thanks!
 
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