3 input NAND Gates for function

Discussion in 'General Electronics Chat' started by Adriana, Nov 15, 2014.

  1. Adriana

    Thread Starter New Member

    Nov 15, 2014
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    Hi all!

    I have a 74HC10 component with 3 input NAND-gates and I am trying to use it to connect a function which is

    X="overline/inversion of"(AB)

    Could someone please help out with the circuit diagram?
    I am not sure what to do with the third input in the NAND-gate.

    /Adriana
     
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Is the function you describe ("X="overline/inversion of"(AB)") look familiar? It's a common logic gate…

    As far as your question about an unused input, draw out the truth table for a three input NAND gate. Look at the output if one input is tied low. Is it the same as the truth table for a two input NAND? Repeat the exercise if one input is held high. The result of this exercise will show you what to do with the unused input.


     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    (AB)' isn't that De Morgan's Law?
     
  4. Adriana

    Thread Starter New Member

    Nov 15, 2014
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    Sorry Im not really following, could you please elaborate?
    I have done the truth table, but still dont get it..

    Btw yes X=(AB)' would have beena better way to express the problem statement :)
     
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Here is the truth table for a 2 input NAND gate, which is (AB)'
    image.jpg
    And for a 3 input NAND gate
    image.jpg
    Now take a look only at the portion of the table where A is low. Do the columns B, C and Y look like a 2 input NAND gate? Do the same exercise for the portion of the table where A is high (A=1)?

    What value should you tie an input of the unused pin of a 3 input NAND, for the remaining pins to act like a 2 input NAND gate?
     
    Adriana likes this.
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    The basic AND will output logic one only if every input is logic one. The NAND is just an AND with an inverter on the output.

    You can tie an unused AND or NAND input to Vcc.
     
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