Karnaugh map for 3 variables

I am trying to create a binary adder. I have this truth table:

This is the Karnaugh map that I made for this function (see that there is a mistake: instead of c, it had to be "c-in"):

Now, as the map looks like that, it gives me that s = c + c but that is certainly false. Can anyone help me with this?

• Erm, I see a^b^c... Oct 20, 2013 at 18:39
• yeah, you-re right. that's how I found it on the website, but I don't know how to get it. please, post an answer with the explanation. I am student, and I haven't been working with this for a long time Oct 20, 2013 at 18:40
• How did you draw the Karnaugh maps? Oct 30, 2014 at 11:01

• Note: You can only group together cells and reduce using a K-Map when it is in Grey Code sequence, because grouping two elements together (and discarding the variable that changes) correspons to BC(A + A') = BC which only makes sense when one bit is changing.