1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: I put this into a k-map and it has 5 terms! is somthing wrong?

  1. Oct 17, 2005 #1
    Okay i have 4 inputs, A,B,C,D, and when i put it into a K-map i got 5 terms, its a prime number circuit. It will output 1 if the number is prime, example...
    2,3,5,7,11,13. So 1101 == 13 would output a 1.
    A = 1, B = 1, C = 0, D = 1; Output = 1
    From suming up the min terms on my truth table i got the following boolean expression:
    Note: 'A means A complemented

    'A'BC'D + 'A'BCD + 'AB'CD + 'ABCD + A'BCD + AB'CD

    I put it into a K-map and got the following:
    'A'BC'D + 'ACD + 'ABD + 'BCD + B'CD

    Does that look right to you? I already wasted an hour implemented the wrong diagram because i screwed up the k-map and i want to make sure i didn't screw it up again. Thanks.
  2. jcsd
  3. Oct 17, 2005 #2


    User Avatar
    Gold Member

    Last edited by a moderator: May 2, 2017
  4. Oct 17, 2005 #3
    Thanks for the responce...but ]shouldn't u loop some more? Here is what I got...but it still isn't right because when i create a circuit out of it using MAX PLUS II, it says A is not needed!! which makes no sense to me...
    Here is my k-map...
    http://img137.imageshack.us/img137/5189/lastscan6nq.jpg [Broken]
    Last edited by a moderator: May 2, 2017
  5. Oct 18, 2005 #4


    User Avatar
    Gold Member

    Ah yes. I see where I forgot to loop.
    I think you make some mistakes in the k-map
    Code (Text):
    'A'BC'D + 'ACD + 'ABD + 'BCD + B'CD
    Thats what you have. I'm look at the k-map and I cant see 'A'BC'D in the k-map. I see A'BCD. Why is it that you put the upper right most 1 by itself. Just looping it with the 1 to the left of it is good enough. Looking at the last row I see that you have 'BCD. How did you end up with that?
    Here is what I got
    Code (Text):
    'A'BC + 'ACD + 'ABD + B'CD + A'BCD
    I'm also taking this course right now, I know how confusing this topic can get.
    Last edited: Oct 18, 2005
  6. Oct 21, 2005 #5
    That is wrong, but thanks! I figured it out finally!
  7. Oct 30, 2005 #6
    For whatever it is worth, there are four terms, each of three variables. In other words, each loop encompasses two cells.

    I have a couple of suggestions (in real life - - - if your instructor does it the other way, you are stuck with it in class). First, try using the apostrophe after the variable to show a "negation", this is a bit more familiar to most of us. (It is unfortunate that most of our typing program packages don't provide for an "overline".) Second, make "A" your low-order variable. Then, A'B'CD' would be "0100". This makes it a little easier to put it into an ordered K-Map (I keep preaching the use of ordered maps - - - but most still don't bother.) Third, try to learn and use the ordered K-Map somewhere down the line. It makes the operation far more automatic and gives more capability.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook