Video: Evaluating the Output of XOR Gates

The diagram shows an XOR gate. If input A is 0 and input B is 0, what will the output be?

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Video Transcript

The diagram shows an XOR gate. If input A is zero and input B is zero, what will the output be?

Okay, so, in this diagram, we’ve been given an XOR gate. And we’ve been told that for this XOR gate, both input A and B have values of zero. Based on this information, we need to work out what the output is. So, to do this we need to recall the truth table for an XOR gate. So, here’s the truth table for an XOR gate.

Now an easy way to remember this is that an XOR gate is an exclusive OR Gate. In other words, if exclusively one of the inputs has a value of one, then the output will be one as well. Otherwise, the output will be zero. So, basically, what we mean by this is that if both input A and input B are zero, then the output is zero as well.

However, if input A is zero and input B is one, then the output is one because in this case exclusively one input is one. In this case, it’s input B. And the same is true for the next row. We can see that input A is one, but input B is zero. That gives us an output of one. However, in the situation where both inputs are one, the output is zero. And so, what we see is that exclusively one input or the other must be one in order to give us an output of one. And that’s how to memorize the truth table for an XOR gate.

But anyway, so, coming back to the question, we’ve been told that both input A and input B are set to zero. So, to find out the value of the output, we look at the first row of the table. Input A is zero and input B is zero as well. This row tells us that the output must be zero also. And so, we’ve got the answer to our question. For an XOR gate, if both inputs are set to zero, then the output will be zero as well.

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