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Student ? ( Logic Gates)

Discussion in 'Homework Help' started by radiobarn, Oct 29, 2015.

  1. radiobarn

    radiobarn New Member

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    There is a question, probably elementary but im new at this, ? Is Design, draw, and wire a 5 input NAND circuit using one 2 input OR gate, one 2 input NAND gate , and one 4 input NAND gate.

    Ive been drawing this circuit for a couple hours and have no idea, I know a 5 input NAND gate will only go low if all inputs are high, but with the 2 input NAND in there going low with its inputs high, I cant solve how to build this circuit, please help. Thank you.
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Do you know how to apply DeMorgan's Theorem?

    What happens if you tie the two input pins of the Nand gate together?
     
  3. Les Jones

    Les Jones Well-Known Member

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    As this looks like a homework question just giving you the answer will not teach you to understand. So here is a tip. Apply DeMorgan's Theorem to the 2 input OR gate. The result will be a 2 input AND gate for NEGATIVE logic. The solution I came up with results in a 6 input NAND gate but you could just tie 2 inputs together or tie one input high.

    Les.
     
  4. dave

    Dave New Member

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  5. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    1)At first I tried to take the OR + NAND and make some thing to go ahead the 4-NAND. In 20 seconds I could not see it.
    2)What do we have? 4 input NAND + 2 input NAND
    >>To make a 6 input NAND we would need (the 4 input NAND) OR (the 2 input NAND).
     
  6. radiobarn

    radiobarn New Member

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    Thanks for the replys, yes this is a lab question where we are supposed to draw a schematic and the build it out and test on a breadboard. I still cant seem to make anything that will act like a 5 input NAND from these components, Im not sure how the OR gate should have any relevance in the circuit, tying the legs together makes it irrelevant, tying the 2 legs of the 2 input NAND together makes an inverter, the closest thing I can come up is different combinations where all 5 inputs are high will result in a low output, but there will be other situations as well that give a low output.
     
  7. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    A = B+C = (or gate)
    by Demorgan, A' = (A+B)' = A'B' implies output is 0 when both A is 0 AND B is 0. (Duality)

    Does this give you any ideas how you could combine the outputs of the two NAND gates????
     
  8. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Make a truth table for this circuit: It has four inputs, so only 16 states. What logic function is it equivalent to?

    gat.gif
     
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  9. radiobarn

    radiobarn New Member

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    I see it now, thanks Mike. I get myself confused with active and unactive outputs, i build it that way a few times im sure and when I looked at it , i thought well that wont work. Thinking too hard. Thanks again
     

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