Logic gates question

Discussion in 'Math' started by TaPaKaH, Feb 4, 2008.

  1. TaPaKaH

    Thread Starter New Member

    Feb 4, 2008
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    hi, i need alittle help here.i have a question.
    How can u have low exit when input is high, using AND and OR gates?
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
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    Just to clarify the question. Is this, how can you have a low output when one of the inputs is low, using AND and OR gates at the same time?

    Dave
     
  3. TaPaKaH

    Thread Starter New Member

    Feb 4, 2008
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    you have only high input and you must have a low output using ONLY AND and OR gates
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    I do not think it is possible.
    If you DeMorganize the gates you will see this clearly.
    Low outputs require low inputs
     
  5. Dave

    Retired Moderator

    Nov 17, 2003
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    No then. For an AND gate with one input tied to ground you will get a low output for a high (or low for that matter) input, but that is about it.

    Dave
     
  6. arthur92710

    Active Member

    Jun 25, 2007
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    An NOT or an inverter does what you need. High in Low out.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    That is quite true, but completely irrelevant since an inverter is neither an AND gate, nor an OR gate.
     
  8. Dave

    Retired Moderator

    Nov 17, 2003
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    My first instinct when I read the OP was, has the AND gate been confused with the NAND gate and the OR gate confused with the NOR gate - if so the answer is simple: to get a low output with a high input, just tie the inputs together - both the NAND and the NOR will then behave like an inverter.

    Dave
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Well of course, but we should give the OP the benfit of the doubt, that he represented the question accurately.
     
  10. Dave

    Retired Moderator

    Nov 17, 2003
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    Agreed.

    Dave
     
  11. mik3ca

    Active Member

    Feb 11, 2007
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    because logic gates require at least two inputs, and you only specified one input (which is high), and you didn't specify the other input. We will have to make your other input low.

    you will have two outputs. One from the AND gate, and one from the OR gate.
    you specified that you want One of these outputs to be low.

    So walking through, we have:

    Logic high, ORed with Logic low = High output on the OR gate.
    Logic high ANDed with Logic low = Low output on the AND gate.

    Now if you said your other input was high, then both outputs will be high.
     
  12. James Sonroll

    New Member

    Feb 22, 2008
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    It is possible if you mean only one input is high and the output is low. Then, if you mean that all inputs and either one is high and the output is low, its impossible.
     
  13. aliashar86

    Active Member

    Nov 23, 2006
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    in the beginning dave gave a valid reason that ground the circuit nd u will get a low output
     
  14. aliashar86

    Active Member

    Nov 23, 2006
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    for further clarification u must see first the "Truth Table" of both AND nd OR gates
     
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