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Homework Help: Help with D-Type flip flops?

  1. Jun 20, 2010 #1
    1. The problem statement, all variables and given/known data

    In the Feynman Lectures on Computing, he uses this as an example of a D-Type flip flop.

    [PLAIN]http://img526.imageshack.us/img526/1490/dtypeflipflop.jpg [Broken]

    Where the boxes are comprised of:

    [PLAIN]http://img228.imageshack.us/img228/7421/flipflopt.jpg [Broken]

    And the [tex]\phi^{1}[/tex] is a pulse represented by:

    [PLAIN]http://img3.imageshack.us/img3/8563/clockg.jpg [Broken]

    The output should be equal to the input, but only after a clock pulse. But every time I run through it, I get the opposite result.

    2. Relevant equations

    Basic boolean logic.

    3. The attempt at a solution

    From my understanding of Flip flops, (S => Q), as well as (R => NOT Q). Also the two Q outputs are always complementary. So if the only two possible bit pattern inputs were 01, and 10 (corresponding to the inputs "SR"), then the outputs would be 10, 01 respectively.

    With the clocks in place, the flip flop boxes take turns updating their output.

    From the first diagram, let the area between the first NOT and flipflop inputs be represented by "A", and the space between the two flip flop boxes by "B".

    Then following the diagram:
    [PLAIN]http://img444.imageshack.us/img444/3754/chartfl.jpg [Broken]

    Clearly, my truth table does the opposite of what I want. The circuit becomes Q=NOT D, but only after a pulse. What am I doing wrong? Or could it be that the book is wrong?
    Last edited by a moderator: May 4, 2017
  2. jcsd
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