a circuit for A?>=B

Discussion in 'Homework Help' started by Nec, Jan 2, 2009.

  1. Nec

    Thread Starter New Member

    Nov 21, 2008
    6
    0
    in homework, i have to create a circuit which compare two 4 bit numbers like A,B and if A is equal or greater than B, then return true value.If not, return false value.I used xnor gates and connect these gates' output to four-input and gate for equal or not, i dont have a problem in this part.But other part,greater than, i have a problem i try something but it does not work.And i couldnt write a truth table,,since it is too long.Can someone help me pls.
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Get and read the 74HC85 datasheet and see how it is done.

    You can then remove parts that are not required like "equal" and "bigger" and invert the "less than" output as your output.

    You can also remove parts that deal specifically with cascading bit length etc...

    It is not an easy task.
     
  3. Nec

    Thread Starter New Member

    Nov 21, 2008
    6
    0
    thanks a lot, it is really useful.I know it is not so easy but i have to do it.
     
  4. tuborggg

    Active Member

    Jan 3, 2009
    37
    0
    BTW, you see that it does uses a truth table as you thought is too big.
    BTW2: you can use a subtractor and check only it's msb to see if you got a positive or negetive answer and know if A<B ...
     
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