set/reset........preset/ clear

Discussion in 'General Electronics Chat' started by Nathan Hale, Dec 5, 2013.

  1. Nathan Hale

    Thread Starter Active Member

    Oct 28, 2011
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    2
    Is a flip flop with a set/reset feature exactly the same as a flip flop with preset /clear feature?
    are set / reset same as preset/ clear?

    Can you guys please let me know the number of a flip flop IC that has preset and clear function built into it? I asked this dude from JAMECO and he said he couldnt help me.

    Thank You
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Yes, set/reset are the same as preset/clear.

    Dudes from Jameco don't know ICs, they just know part numbers. :rolleyes:

    D-type FF CD4013
    JK-type FF CD4027

    Here's a list of CMOS ICs.
     
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  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    To me they are the same. Just different names for the same function, asynchronous set reset inputs. Digikey gives me hundreds of types with set/reset.
    Maybe it's easier if you tell us what you need and we help you to find the right FF.

    Here the first one from digikey: http://www.ti.com/lit/ds/symlink/sn74hc74.pdf

    As you can see from the truth table SET (preset) turns Q on. RESET (clear) turns Q off. Clock doesn't matter for these.
     
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  4. WBahn

    Moderator

    Mar 31, 2012
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    Another wrinkle is that some parts have an active-HI set/reset and others have an active-LO set/reset. Some even have both (often an active-HI and an active-LO reset but no set input at all).
     
  5. crutschow

    Expert

    Mar 14, 2008
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    There's a good reason for active low inputs on the old TTL bipolar logic devices. TTL inputs sink input current when at logic low but only leakage current when logic high. Since the set and reset inputs are typically infrequently used, the circuit draws less power since the set and reset are sitting high most of the time thus drawing little current.
     
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