Digital Circuits

Discussion in 'Homework Help' started by ashjaya, Jan 4, 2004.

  1. ashjaya

    Thread Starter New Member

    Jan 4, 2004
    2
    0
    I'm stuck in this problem, Can somebody help me?

    Imagine a machine with four inputs and one output that functions as follows: the output is ON if exactly two of the inputs are one, and off otherwise. Draw a circuit that performs this function. Use a truth table to show that all possible input values produce the proper output.

    Thanks..
     
  2. scarydave

    New Member

    Jan 5, 2004
    2
    0
    If you draw out the truth table, you'll find there are 6 possible combinations of "winning" inputs. Assuming the inputs are labelled A, B, C, D, the combinations are:

    A.B
    A.C
    A.D
    B.C
    B.D
    C.D

    If you're only allowed to use 2-input gates, then first of all use 6 2-input AND gates to give these outputs.

    Now, we're only interested in a positive output if one and ONLY one of these combinations exists, so we need a sequence of XOR gates. Again, if we're only allowed 2-input XOR gates, you'll need 5 of them to whittle the 6 outputs down to 1.

    This should solve your problem...hope it helps!!

    Scarydave
     
  3. ashjaya

    Thread Starter New Member

    Jan 4, 2004
    2
    0
    Thanks for the help. I'm working on it right now.....

    I appreciate your help....
     
  4. ynaji

    Member

    Jan 28, 2007
    10
    0
    Truth Table

    A B C D X
    0 0 0 0 0
    0 0 0 1 0
    0 0 1 0 0
    0 0 1 1 1
    0 1 0 0 0
    0 1 0 1 1
    0 1 1 0 1
    0 1 1 1 1
    1 0 0 0 0
    1 0 0 1 1
    1 0 1 0 1
    1 0 1 1 1
    1 1 0 0 1
    1 1 0 1 1
    1 1 1 0 1
    1 1 1 1 1
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    The function is true if 2 and only 2 inputs are true.
    A B C D X
    0 0 0 0 0
    0 0 0 1 0
    0 0 1 0 0
    0 0 1 1 1
    0 1 0 0 0
    0 1 0 1 1
    0 1 1 0 1
    0 1 1 1 0
    1 0 0 0 0
    1 0 0 1 1
    1 0 1 0 1
    1 0 1 1 0
    1 1 0 0 1
    1 1 0 1 0
    1 1 1 0 0
    1 1 1 1 0
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I didn't see anything about being restricted to 2-input gates.:confused:
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Ron is correct. The problem does not even specify gates - only "circuit." The solution may be implimented with only a 74154 and a 7411.:)
     
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