D flip flop from T flip flops

Discussion in 'Homework Help' started by amorphos, Apr 2, 2015.

  1. amorphos

    Thread Starter New Member

    Apr 2, 2015
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    Question: Show how a D flip-flop can be constructed using a T flip-flop and other logic gates.
     
  2. Papabravo

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    Feb 24, 2006
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    Are you sure it is possible?
    The converse of making a T from a D is easy.
     
  3. WBahn

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    Mar 31, 2012
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    Any circuit that you can make with any of the basic edge-triggered FF types (JK, D, T) you can make with either of the other two. This includes implementing the other two FF types.
     
  4. WBahn

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    You need to show YOUR best effort to solve YOUR homework problem.
     
  5. Papabravo

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    I guess I'll be interested in the result.
     
  6. WBahn

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    Think about it for a moment and it will probably come to you with a head slap.

    With a DFF if you tell me what the value of D is (during the critical setup/hold window) I can tell you what the value of Q will be after the next active clock edge.

    If I give you a TFF and you know what its current Q output is and I tell you what I want the next Q output to be, can you tell me if you want it to toggle or not?
     
  7. Papabravo

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    I suppose, if gating the clock is fair game. I didn't make that assumption initially, since I would seldom if ever do that in practice.
     
  8. WBahn

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    Why do you think you would have to gate the clock?

    Perhaps the confusion is on just what a TFF is:

    http://en.wikipedia.org/wiki/Flip-flop_(electronics)#T_flip-flop
     
  9. Papabravo

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    Ah..you're right. In my text (ca. 1960), the toggle flip-flop had only a single input, the clock input. That explains why I was having a hard time visualizing how to do it. That and nobody ever made an integrated circuit that implemented one, could explain a my confusion. Old dogs should really try to learn new tricks.
     
  10. MrChips

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    Oct 2, 2009
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    (Edit: I started typing a response 5 hours ago but got distracted.)

    Yes, it is possible.
    A T-flip flop has a T input.

    Draw a truth table of all possible states of the present Q and the given D input. Show the desired T input required to implement the D-type flip-flop result.
    You should be able to arrive at a logic function to give the solution.
     
  11. Papabravo

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    As I explained I was laboring under an antiquated definition from a very old text. With the proper definition of the device it is straightforward.
     
  12. MrChips

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    Understood. That is why 5 hours ago I wanted to point out that a T-type filp-flop has a T-input.
     
  13. Papabravo

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    It's all good, and now I know something I didn't know when I woke up this morning.
     
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