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Homework Help: Karnaugh map - Any reason to flip it, ever?

  1. Oct 20, 2011 #1
    Why, hello there. I'm doing Karnaugh maps. I'm using them to device gates to express the numbers 0, 1, 2, 3, 4 in a seven segmented digital display.

    Our teacher has provided us with predrawn Karnaugh maps, where we simply fill in the 1's and 0's.

    However, he's decided to invert the diagram, so that the first line reads: 0, 4, 12, 8, and the first column reads: 0, 1, 3, 2. I'm used to it being the other way around.

    And he specifically writes that "we'll be using a different order than what were used to in lectures".

    Is there any reason for this at all, or is it just to throw us off a bit? I can't figure out if there's any actual advantage to it.
  2. jcsd
  3. Oct 20, 2011 #2
    There are several ways to write K maps, it really depends on where your variables are situated. The way I learned it, for a 3 variable K map in1 will be in the bottom right, in2 will be in the top middle and in3 will be on the left(bottom). However the configuration is, you can still figure out what goes where by selecting any box and seeing where it lies for each variable.

    Also, a little special rule for K maps is that you read the columns from top to bottom, left to right. If labeled the way that I described for the 3 variable K map, then you will get the following numbers:
    C1: 1, 2, 4, 3
    C2: 5, 6, 8, 7
    C3: 12, 13, 15, 14
    C4: 8, 9, 11, 10

    Notice how for each column, the 3rd and 4th digit is switched and also notice that C3 and C4 are switched (This is the same way you described in your post). You will notice that in1 is at the bottom right, in2 is at the top middle, in3 is at the left bottom, and in4 is at the right middle.

    The way that you probably learned in lecture, you probably have in1, in2, in3 and in4 situated in different positions. Hope this helps explain the convention.
    Last edited: Oct 20, 2011
  4. Oct 20, 2011 #3


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    HOW you draw a Kmap is irrelevant. As long as you fill it in and interpret it according to the labels, there's no problem. It CAN be annoying if you get used to a particular format to have to deal with one in a different format, but the transformation is always trivial.
  5. Oct 20, 2011 #4


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    Beats me why he would do that. I don't see any conceptual difference in figuring out the logic, and your previous way has the advantage that the bits are in the order


    which is the way you would write a binary number.
  6. Oct 20, 2011 #5

    I want to clarify, because I understand how the map works, and I've made a lot of them now, so I feel I'm good at the map using 1 to 4 variables.

    This is my preferred map:
    0 1 3 2
    4 5 7 6
    12 13 15 14
    8 9 11 10

    Basically what you wrote. I'm familiar with this setup, I realize the 3rd and 4th columns are switched, likewise with the 3rd and 4th rows.

    But what he had us use for this task was:

    0 4 12 8
    1 5 13 9
    3 7 15 11
    2 6 14 10

    So what I'm asking is if anybody knows if there are any advantages to using the latter layout, rather than the former. Is it just a matter of preference?
  7. Oct 20, 2011 #6
    Alright, thanks people, much appreciated indeed. I guess it was just done to make sure we understand the actual method, rather than automatically using it without considering the order of things, or whatnot. Thanks again! ;)
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