D Flip-Flops

Discussion in 'Homework Help' started by El3, Nov 6, 2014.

  1. El3

    Thread Starter Member

    Sep 13, 2014
    On a circuit board we are supposed to use for laborations there are circuits for D flip-flops that looks like this (this picture shows how the connections actually look at the circuit board, the square signs are where connections can be made):


    Here CK = Clock, D is input and Q is output.

    However when I searched the web I found pictures of D flip-flops that looked like this:


    How are these pictures of D flip-flops related? CLK and CK are of course the same, CLEAR I guess is a way to reset the output value to zero and I assume D = J and Q = Q. But what then is K and Q-bar? How can one simplify a circuit that included K and Q-bar, so that it only uses D (J) and Q?
    • d.jpg
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    • d2.jpg
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    Last edited: Nov 6, 2014
  2. MrChips


    Oct 2, 2009
    The second drawing is not a D-type flip-flop. That is a J-K flip-flop with CLEAR'.

    Q and Q' are outputs. If you do not need to use Q' just leave it unconnected.
    Some chips provide both Q and Q'. Others don't.

    You really ought to search for a D-type flip-flop.
    If you absolutely want to convert a J-K flip-flop to a D flip-flop, there is a way to do that. I leave that as an exercise for you.
  3. Papabravo


    Feb 24, 2006
    An advantage of the JK Flip-flop is that it can do four different things:

    Clear the Q output to 0. Q' goes to 1
    Set the Q output to 1. Q' goes to 0
    Toggle the Q outputs, which of course toggles the Q' output
    Hold the present state aka 'do nothing'
    There is also the similar, but slightly different JK_BAR Flip-flop.

    Now there are two types of designers: JK and non-JK. Which type do you want to be?