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Simple question regarding KarnaughDiagrams ?

  1. Oct 9, 2011 #1
    Is there a difference between drawing one that goes x1x2 horizontal and x3x4 vertical or one that goes x2x1 and x4x3?

    suppose you are doing a SOP and u got Epsilon(m0,m2,m8,m12)

    then for the first map u get f=x3'x4' but the other diagram gives f=x2'x1'

    does it matter or is it all the same?
     
  2. jcsd
  3. Oct 9, 2011 #2

    phinds

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    In my experience, it is irrelevant how you draw the map; what matters is that you label it correctly based on your drawing and then consistently follow the labels.

    So, you if you had two columns you could label the first one A (implying that the second r is NOT-A) or you could label the second one A (implying that the first one is NOT-A). It doesn't matter.
     
  4. Oct 9, 2011 #3
    but you are getting two different answers.
     
  5. Oct 9, 2011 #4

    phinds

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    I have no idea what you are talking about.
     
  6. Oct 10, 2011 #5
    which one is correct?

    A:
    [PLAIN]http://img41.imageshack.us/img41/7519/73372374.jpg [Broken]

    B:
    [PLAIN]http://img684.imageshack.us/img684/7462/73298056.jpg [Broken]


    i guess the problem is how do u write the truthtable u start with x4 or with x1 on the right side....
     
    Last edited by a moderator: May 5, 2017
  7. Oct 10, 2011 #6

    phinds

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    Your maps describe totally different functions, so NATURALLY they are different in the Karnaugh map. You don't seem to understand how to fill in the maps if you are trying to map the same thing in both versions.

    If filled in correctly, both versions would show the same functions.
     
  8. Oct 10, 2011 #7
    yes but the problem is how do u start the truthtable? are the m's fixed or not?
     
  9. Oct 10, 2011 #8

    phinds

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    What do you mean "yes but" ??? "Yes but" says to me that you understand that you made a mistake. Fix the mistake and your question goes away.
     
  10. Oct 10, 2011 #9
    look the question is:

    create a K-map of SOP E m(0,4,8,12)

    how would the map look like A or B and are the ms fixed
     
  11. Oct 10, 2011 #10

    phinds

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    Sorry, I don't have a clue what that means. I use Kmaps for boolean expressions like

    A and NOT B and C and NOT D
     
  12. Oct 10, 2011 #11

    LCKurtz

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    Your expression for the second one should be

    [tex]\overline{X}_2\ \overline{X}_1[/tex]
    instead of having the bar over the whole thing. Then they are both correct. While you can put the variables in in any order, I would suggest putting them in the same order that you would write a binary number, with the least significant bit on the right. I would have called the variables [itex]y_3y_2y_1y_0[/itex] and in that order.
     
    Last edited by a moderator: May 5, 2017
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