tri-state buffer

Discussion in 'Homework Help' started by zulfi100, Feb 22, 2013.

  1. zulfi100

    Thread Starter Member

    Jun 7, 2012
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    Hi,
    Can some body plz guide me with the following question:

    I know about the G input and V0 output but i dont know about the control line. If G is High, V0 is either 0 or 1. In this situation we cant say its behaviour is similar to which gate? If G is Low, V0 is open.

    Zulfi.
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    Tri-state buffers are available with either active high or active low enable (control). Which one are you talking about?
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    Make a truth table for your input and output under the condition that the control signal is HI. That matches the truth table for what gate?
     
  4. zulfi100

    Thread Starter Member

    Jun 7, 2012
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    0
    Vi G V0
    L L Open
    H L Open
    L H L
    H H H

    If Vi is the input then its same like output. Its a buffer. So its not similar to any gate (Correct?). What is G here?

    Zulfi.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    You can check 74LS126, it matched what you need.

    You can also see the 74LS125, the ctrl pin is opposite of 74LS126.
     
  6. zulfi100

    Thread Starter Member

    Jun 7, 2012
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    Sorry, i cant access this page. I have even tried google but i cant connect with datasheet page.


    Zulfi.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    I tried on google chrome and IE8, they are ok.

    You can seacrh on google as 74LS126, then you will get a lot of infos.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    Since they are specifying that G is HI, the truth table is reduced to just those rows in which G is HI. Then, because all of the surviving rows have G in the same state, the entire column can be removed and just a note placed near the table indicating that it is for the case when G is HI.

    You are correct that the result is the same as a buffer, but a buffer is a logic gate just like an inverter is. It's just not a very interesting one from a logic standpoint -- but it is often a very important one from the standpoint of getting a design on paper to work in the real world.
     
  9. zulfi100

    Thread Starter Member

    Jun 7, 2012
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    Hi,
    Thanks for all of you for helping me.
    I have IE9. Its closing.

    Book (Digital principles and application, 5th edition, page=11) says its the buffer but the answer (which is another book) says that its a 'NOT gate".

    However on the same page book says that TRI-state inverter is a NOT circuit.

    This means both TRI-STATE- Buffer and TRI-STATE-Inverter are not gates (confusing?) . Is it correct?

    Zulfi.
     
  10. ScottWang

    Moderator

    Aug 23, 2012
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    TRI-STATE-Buffer -- It is a Buffer, but not an Inverter.
    TRI-STATE-Inverter -- It is a Buffer, and it is also a Not Gate.

    You can play the logic gates at here .

    And you can see the internal structure at here.
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    When enabled, a tri-state buffer is a buffer.

    When enabled, a tri-state inverter is an inverter.

    The names were not picked at random.
     
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