D Flip Flop Application

Discussion in 'General Electronics Chat' started by baseball07, Sep 23, 2008.

  1. baseball07

    Thread Starter Active Member

    Apr 24, 2007
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    0
    Hey guys. I have something I want to do with a DFF (7474) but I am not sure how to actually do it. First, I would like the output, Q, to be high all the time, which is going to be the control line of a tri state buffer. Is there a way I can pull the CLK to Vdd via a resistor so it is always high?

    I then want to trigger the CRL with a low, so the output Q clears then returns high again once CLK gets a trigger.

    Is this possible? THe problem I am having is how do I hold the output Q high before it receives any pulse from CLK?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There is an explicit SET input (pins 4 and 10) that are independent of the clock. You might want to have the D input pulled high if you control the clock. Use a 4.7K resistor for the pullup.

    I can't translate the "CRL" input, unless you mean CLR.
     
  3. baseball07

    Thread Starter Active Member

    Apr 24, 2007
    39
    0
    I am sorry, I ment to say CLR. Ok so I pulled the D input high with a resistor. Now When I pulse CLR low, the output Q goes low as it should. Then when I pulse the CLK low, the Q output goes back high, but not when I pulse it high. Is this correct? I though Q takes on D input on the rising Clock, not a low pulse. Thoughts?
     
  4. veritas

    Active Member

    Feb 7, 2008
    167
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    double check your data sheet for edge sensitivity. If it's falling edge sensitive, you could invert your clock as a last resort.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    282
    The 7474 clocks on the falling edge.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,136
    1,786
    Annn..h! Sorry, but it is rising edge for the 7474!
     
  7. Lucysmith

    New Member

    Oct 3, 2008
    3
    0
    well make a search on this topic in google search bar or you can read a e-book of digital electronics by M.Morris Mano
     
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