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Flip-Flops Analogy?

  1. Dec 10, 2006 #1
    Okay, Im having a difficult time understanding how flip-flops work. Can anyone give me an Analogy in mechanical terms like plumbing for each common individual Flip-Flop. Im really confused on how I read and follow the diagrams for FF's. :(
  2. jcsd
  3. Dec 10, 2006 #2


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    Flip-flops are just storage elements. When you clock them, whatever value is present at the input (D) is stored inside it. The value stored inside it is then made available at the output (Q).

    - Warren
  4. Dec 10, 2006 #3
    Thanks for the prompt response.

    So when do Clocks come in and how does it affect the output? How does it cycle in respect to the CLK? Sorry, im so confused.
  5. Dec 10, 2006 #4
    I don't know about plumbing...but here's my take...(I'm pretty dumb so don't think I'm dumbing it down for you)

    flip-flops are used to store a single bit (like memory). two common types of flip-flops are J-K and D flip-flops.

    I'll start with D:

    the main inputs are: D and clock.
    the output: Q

    when there is a rising edge on the clock (a signal going from LOW to HIGH), whatever is on the input D, will be 'stored', and that's what will appear on Q.

    now for J-K:

    instead of D, you have two inputs J and K,

    if there is a rising edge on the clock, and J is HIGH, Q will be HIGH (SET). If J is LOW and K is HIGH, Q will be LOW (RESET). If both J and K are high, it will toggle Q (made opposite).

    Now for plumbing:
    D is like what's in the toilet, and Q is what's in your septic tank. flushing the toilet is analogous to the rising edge of the clock. I have no clue how to explain J-K flip flops with plumbing. hope i helped
  6. Dec 10, 2006 #5


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    The output does not change, except immediately after a clock edge comes along. When the clock edge comes along, the flip-flop stores its input, and that input value propagates to its output.

    (If the input is the same as the current output, the flip-flop does not change state, and the output does not change.)

    The output cannot change again until another clock comes along.

    - Warren
  7. Dec 11, 2006 #6


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    Maybe my post here will be too basic, but for me the light bulb went off back in school when I first learned how bits are stored in a memory device. The first circuit I learned about was the cross-coupled transistor cell, where the differential output voltage represents a 0 or 1, and that state stays there after you set it as long as the power is on. You can change the state to toggle to the other bit value, but the value is stored there as memory and won't change on its own. Like this:


    When I saw that concept, I finally saw how it was possible to have computer memories work physically. Definitely a cool moment.

    Then a little later, I learned about cross-coupled NAND gates used for switch debouncing, and then after that, how you use cross-coupled gate structures to build up the different flipflop variants. As described at this wikipedia.org article:


    Once you get that motivation and background, flipflops (and the more subtle issues they have with things like metastability) make a whole lot more sense.
  8. Jan 4, 2007 #7
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