wire ORed

Discussion in 'Homework Help' started by swty_todd, Apr 2, 2009.

  1. swty_todd

    Thread Starter Active Member

    Aug 3, 2008
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    My textbook says that the output of comparators can be "wire ORed".
    What does wire OReding an output mean?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    It has to do with open collector outputs. If you tie a bunch of collectors together sharing one resistor it is equivalent to an OR gate. It was a common practice in the days TTL logic was king.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    To expand a bit on Bill's post, those open collector outputs are all pulled up with a single resistor. Thus any one output can pull the common line low.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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  5. swty_todd

    Thread Starter Active Member

    Aug 3, 2008
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    sorry i forgot to mention that the above sentence was in respect to uA311 precision comparator.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    It has an open collector output - the second paragraph of the intro on the data sheet stated that the device can be wire OR'ed. Open collector outputs are open collector outputs.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
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    And of course wired OR can be accomplished by using series diode isolation between each of the 'voting' nodes and a single pull-up resistor so having open collector outputs is not the only way to be able to utilize wired OR stages.

    Lefty
     
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