# Finding the K-map of an = comparator

I have this sheet for practice but I can't figure out how to find the outputs of it:

To fill out the first part: EQ[n](equal so far?)

yes(4) yes(3) no(2) no(1) no(0)

So, what is EQout going to be for each case? I don't understand that part at all. Also, it asks for a building block circuit? I have not learned about those yet.

There seems to be a lot of terms that I do not understand yet, maybe this sheet is too advanced.

Anyway, if someone could help me understand that would be very great. I really appreciate any help, thank you.

EDIT:

The X's represent "don't care terms" but I'm not sure if that is valid here.

EDIT: Tried to solve my question below: https://electronics.stackexchange.com/a/358585/175939 please reply with any criticisms.

• the first one ... you start on left and fill in the table with a yes or no. ... the question being "is A equal to B up to this point" ... do not forget that you are only looking at the comparator blocks one at a time ... EQ[4] has a value of 1 ... EQ[3] reflects the equality of A[3] and B[3] and so on Commented Feb 25, 2018 at 17:57
• you need to show some effort to answer the questions. ... at this point, it appears that you have not done any work. Commented Feb 25, 2018 at 17:59
• think about why the "2s place" has a "no" ... then look at your K-map again Commented Feb 25, 2018 at 19:10

Here are a couple of hints.

1. The building block is the square box for each example. Your task is to figure out what logic equations go in that box. For example the logic circuit in the first exercise will be the same in all four of the boxes.
2. For the first example the EQout will be '1' when the EQin is '1' and A and B are both '1's or '0's.
• I edited my post above with the Yes and No answers and a filled out K-map. I'm still not sure if I did it correctly, would you be able to check it really quick? Also, in bold it asks to find the function be isn't already given? Commented Feb 25, 2018 at 18:34
• In this example you cannot use Don'tCares. Also in the K-Map you missed the case where EQin=1 and X&Y are the same at 00. Commented Feb 25, 2018 at 19:50
• Yeah, I wasn't sure about the very first one. Since "don't care terms" don't work here, what would I do when X and Y = 1 and EQin = 0/No/False? Should everything be zero except for the two cases already found? Also, if you wouldn't find, the question also asks for me to "figure out the function for the building block circuit," but I'm not entirely sure what that means here. By the way, I really do appreciate your help. Commented Feb 25, 2018 at 20:29
• Finding the function of the building block is writing the logic equations for the output of the box on the diagram with respect to its inputs. For the EQout case there will be just two ones in the K-Map. Commented Feb 25, 2018 at 21:34
• if you're still interested in helping me I have more questions/answers. For the completed K-map I have ones when x=1, y=1, and EQin=1; x=0, y=0, and EQin=1. Hopefully, that is correct. Also, I have another question over here electronics.stackexchange.com/questions/358315/… Commented Feb 26, 2018 at 16:33

I'll try to answer my question. Here's my work, please tell me if I got something wrong or right. Thank you.

Here's my K-map:

     X,Y: 00 01 11 10
EQin
0         0  0  0  0
1         1  0  1  0


With that I get the boolean expression for EQout: $$EQout=\bar{x}\bar{y}EQin+xyEQin$$ I hope that is correct. I really do appciate any help.