TITLE: Determining don't-care values in a Karnaugh Map
QUESTION [6 upvotes]: I'm having a hard time understanding how to find the don't-care values in a Karnaugh map. What does it even mean? If I have a boolean function, say $f(a,b,c,d)=a'bc+abc'+bc'd+a'bc'd$, how would I determine don't-care values? What would I be looking for?

REPLY [3 votes]: To solve the problem, try to write the function in a simplified form. Now draw a $k$-map for both the simplified function and the original function. Compare the the two functions and any $1$'s that are present in one and not in the other will be your don't cares.