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Difference in output states

Discussion in 'General Electronics Discussion' started by Xenobius, Nov 12, 2017.

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  1. Xenobius


    May 15, 2012

    I was reading a datasheet and there was a quote which I don't quite understand yet.

    What is the difference between:
    • Push Pull with Active Low Output
    • Push Pull with Active High Output
    • Open Drain with Active Low Output

    What I need is to provide my own pull up resistor, and when the device outputs, it gives me a LOW but I am still interested in understanding the difference properly.

    PS: If it helps, I was reading this

  2. BobK


    Jan 5, 2010
    Push pull outputs will connect the output either to the V+ supply or to ground. They do not need a pullup resistor.

    Open drain outputs can only connect the output to ground. They need a pullup resistor to produce a high output. Open drain outputs can be wired together to implement OR logic. I.e. the signal will be low if any of the outputs is low. Push pull outputs cannot do this since they would create a short if one was low and another is high.

    Active low means the output will be low when it is outputting a TRUE or ON logic state. Active high means it will be high when doing so.

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