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Active pull/push,open collector,three state

  1. Aug 17, 2005 #1
    I'm a mechanical engineer starting with electronics.I am unable to understand concepts like pull\push, open collector, tristate etc.
    Please help me with tips,links,books etc.
  2. jcsd
  3. Aug 17, 2005 #2

    Nomally the output of a logic chip is a one or a zero and this is done by
    making the pin on the chip present a high or low voltage. This is push-pull.

    Depending on what you connect to the pin, current could flow either
    into or out of the pin for either a one or a zero.

    Also, you would never want to connect two outputs together because
    they could fight each other.

    A tri-state output can be "opened-up" under logic control so it looks
    like the pin has been disconnected from the chip. This lets you connect
    several outputs together in a way where the logic can decide which of
    them is doing the outputing. It's a push-pull with a disable feature.

    Open collector is when it's only pull, not push. The pin can only pull
    current into it, it's can't push current out. This lets you connect
    several outputs and they won't fight but you don't have to have
    any disable logic. There is usually something called a "pull-up resistor"
    to replace the missing transistor in a push-pull arrangement.
  4. Aug 17, 2005 #3


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    Staff: Mentor

    Sorry if I'm starting to sound like a broken record here, but this is the best intro to electronics book I've found -- really good at several levels from basic up through intermediate:

    "The Art of Electronics" by Horowitz and Hill
    Amazon: https://www.amazon.com/exec/obidos/...102-7181016-1112941?v=glance&s=books&n=507846

    I can pretty much guarantee that you won't be disappointed by this book. Check it out in your library first if you want before buying it.

    Great explanation by Antiphon, BTW.
    Last edited by a moderator: May 2, 2017
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