# Thread: Multiplexer question

1. ## Multiplexer question

In a practice test I am doing, I have this problem -

"This problem requires you to design and implement the following system.
When the sum of the inputs, C0, X0, X1, is more than 1 C=1. S= exclusive
OR of inputs C0, X0, X1. Draw a truth table that implements each of the output functions C and S using the inputs C0, X0, and X1."

"When the sum of the inputs, C0, X0, X1, is more than 1 C=1"
Does this mean that C will be true for 6 out of the eight values??

"S= exclusive OR of inputs C0, X0, X1."
And this one will also have 6 true values?

Is that all there is to this? I feel like I am missing something important.

2. Hello SterlingM

Welcome to Math Help Forum!
Originally Posted by SterlingM
In a practice test I am doing, I have this problem -

"This problem requires you to design and implement the following system.
When the sum of the inputs, C0, X0, X1, is more than 1 C=1. S= exclusive
OR of inputs C0, X0, X1. Draw a truth table that implements each of the output functions C and S using the inputs C0, X0, and X1."

"When the sum of the inputs, C0, X0, X1, is more than 1 C=1"
Does this mean that C will be true for 6 out of the eight values??
No. $C$ is true (value = 1) for just 4 values: when the sum of all three inputs is more than 1. See the attached truth table.

"S= exclusive OR of inputs C0, X0, X1."
And this one will also have 6 true values?
No. $S$ is also true for just 4 values.

In the truth table, I've put in an extra column to show the value of $C_0$ XOR $X_0$, before XOR-ing this with $X_1$ to give the final value of $S$.

Grandad