# XOR gate circuits

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1. Feb 5, 2015

### kukumaluboy

Z(A,B,C,D) = SUM-M(1,2,4,7,8,11,13,14)

Draw circuit of Z with lowest number of 2 inputs xor-gates.

Can i have a clue? I tried drawing k map and had too many terms.

2. Feb 5, 2015

### Greg Bernhardt

Can you show us what you've done?

3. Feb 5, 2015

### kukumaluboy

So from the K map, in the 1st row, AB looks like a xor.

4. Feb 5, 2015

bump.!

5. Feb 5, 2015

### Staff: Mentor

Your observation about the first row of the map is good. Note how the third row is identical. Note also how the other rows are the negation of them. Contemplate how you might build a NOT gate from an XOR. Does it give you any ideas?

6. Feb 5, 2015

### kukumaluboy

Thanks for tip!

Ok so With a xor gate i can get a'b+ ab' as an output. Lets call this output as P.

Next step is for me to get c'd' + cd which is simply xnor? So i will use a xor(c,d)=Q. Th3n ill xor(Q,1) to get the inverse?

Now to combine both P and Q do i need to construct AND gate with xor?

7. Feb 5, 2015

### Staff: Mentor

Okay, fine. That's a XOR b. It'll come in handy.
It's getting complicated again. If I may suggest a short digression:

Did you spend any time playing with the XOR gate to try to make a NOT gate? Hint: you can assume access to constants TRUE and FALSE (or 1 and 0) to use as inputs anywhere you like. If you feed one input of an XOR with a fixed 0, what does it do to the other input? How about if you use a fixed 1? Can you think of any interesting uses for such a beast? How about if the "fixed" input were actually another signal?

8. Feb 5, 2015

### kukumaluboy

Hi! In my reply i used a fixed "1". Xor(Q, 1)

9. Feb 5, 2015

### Staff: Mentor

Okay, but maybe you can think of another signal to use for the "1" that would select the appropriate action for that XOR to match the other rows in the table? What values of cd are associated with the "straight" a XOR b, and which with its complement?

10. Feb 6, 2015

### kukumaluboy

Challenge accepted

11. Feb 6, 2015

### kukumaluboy

Hi my finam answeer

Q = XOR(A , B)
P = XOR(C , D)
ANS = XOR(Q , P)

12. Feb 6, 2015

### Staff: Mentor

That seems to work.

13. Feb 6, 2015

### Staff: Mentor

Yes, well done.