A simple truth table that I somehow screwed up:



I showed the truth tabel for this as follows, with x being my answers:

A B X
0 0 0
0 1 1
1 0 1
1 1 0

That looks sooooo right to me. Can someone explain where I went wrong?

Thank you

 

A simple truth table that I somehow screwed up:

View attachment 52316

I showed the truth tabel for this as follows, with x being my answers:

A B X
0 0 0
0 1 1
1 0 1
1 1 0

That looks sooooo right to me. Can someone explain where I went wrong?

Thank you

Yes I see what is wrong. On the output you see a small circle. That small circle is a symbol denoting that the output is inverted. So your circuit is XOR with inverted output. You may also se this on a input. The meaning is the same here

 

T06afre already mentioned the point.
You can see the truth table of 74LS86 and compare with yours.

 

Exactly. Your truth table is for an XOR gate. The one in the image is XNOR. Simply invert the outputs, as denoted by the small "bubble" on the output, and you're all set.

Regards,
Matt

 

Thank you for the replies.

Okay, I missed seeing that little circle, all I saw was the XOR gate. If I understand correctly, that little circle is basically a not gate, it inverts the output values.

So, instead of

A B X
0 0 0
0 1 1
1 0 1
1 1 0

The truth table should have been

A B X
0 0 1
0 1 0
1 0 0
1 1 1

Correct?

 

Thank you for the replies.

Okay, I missed seeing that little circle, all I saw was the XOR gate. If I understand correctly, that little circle is basically a not gate, it inverts the output values.

So, instead of

A B X
0 0 0
0 1 1
1 0 1
1 1 0

The truth table should have been

A B X
0 0 1
0 1 0
1 0 0
1 1 1

Correct?

Exactly right. And yes, the bubble serves the same purpose as a not gate connected to the output or input. Same idea.

You seem to have it now

Regards

 

And that is why you got the other answer wrong also.

 

Exactly right. And yes, the bubble serves the same purpose as a not gate connected to the output or input. Same idea.

You seem to have it now

Yes, I do, thank you for your assistance.

And that is why you got the other answer wrong also.

Yes, I saw that right away as soon as I got this answer resolved. I still do have one outstanding question on the other post, would you mind taking a look? http://forum.allaboutcircuits.com/showthread.php?t=81290 Thanks again!

 

Yes, I do, thank you for your assistance.

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