CrazyEngineers
CrazyEngineers

  • Active Low:?

    Nishant Patel

    Member

    Updated: Oct 26, 2024
    Views: 1.1K
    Why do we use Active low signals in digital circuits?
    what is the reason to do so?
    Give your opinion friends.
    0
    Replies
Howdy guest!
Dear guest, you must be logged-in to participate on CrazyEngineers. We would love to have you as a member of our community. Consider creating an account or login.
Replies

  • Nishant Patel

    Member • Dec 11, 2012

    any idea friends.............................
    i don't get it...........................
    Are you sure? This action cannot be undone.
    Cancel

  • ABCD ABCD

    Member • Dec 12, 2012

    Active high means: 0 = "off" ; 1 = "on"
    Active low means: 1 = "off" ; 0 = "on"

    Used for Digital Gates like AND, OR, NOT etc., based on the requirement of output.
    Are you sure? This action cannot be undone.
    Cancel

  • [Prototype]

    Member • Dec 12, 2012

    There are actually various reasons and one could argue.

    Active high inputs are those inputs which gets invoked on high (or +5v). When they are not in use, we generally tend to keep them unconnected WHICH IS NOT A 0v CONDITION. Its an high impedance state and external random signals may somehow cause an spike or glitch. This is generally not an problem with data pins but if this happens to be on RESET signal, it'll totally bring failure of the application that was running.

    Hence, signals like Reset & crucial control signals are always active low and you keep them tied to VCC when not in use. This ensures that circuit will not face any false triggers like we saw in case of active high signals.

    Another reason is, the transition from High to Low is comparatively faster than transition from Low to High. This helps decreasing the propagation delay of the signal & hence increasing the speed.
    Are you sure? This action cannot be undone.
    Cancel

  • Nishant Patel

    Member • Dec 12, 2012

    Hmm, that's true.
    Thank you for information friend........
    Are you sure? This action cannot be undone.
    Cancel

  • ABCD ABCD

    Member • Dec 13, 2012

    [Prototype]
    There are actually various reasons and one could argue.

    Active high inputs are those inputs which gets invoked on high (or +5v). When they are not in use, we generally tend to keep them unconnected WHICH IS NOT A 0v CONDITION. Its an high impedance state and external random signals may somehow cause an spike or glitch. This is generally not an problem with data pins but if this happens to be on RESET signal, it'll totally bring failure of the application that was running.

    Hence, signals like Reset & crucial control signals are always active low and you keep them tied to VCC when not in use. This ensures that circuit will not face any false triggers like we saw in case of active high signals.

    Another reason is, the transition from High to Low is comparatively faster than transition from Low to High. This helps decreasing the propagation delay of the signal & hence increasing the speed.
    I'm wont conform with the faster transition delay. I dont think it will change. Any sources for it.

    What you talking about in the first part, i think, is nothing but pulling up mode. Also, give me the reference for this. But, you are partly right.
    Are you sure? This action cannot be undone.
    Cancel

  • [Prototype]

    Member • Dec 13, 2012

    mreccentric
    I'm wont conform with the faster transition delay. I dont think it will change. Any sources for it.

    What you talking about in the first part, i think, is nothing but pulling up mode. Also, give me the reference for this. But, you are partly right.
    As I said, one could argue on the reasons...

    For reference, I remember it from 2nd year when one of our teacher told us. He told more, but I can't remember all. I saw this thread before, but didn't replied because I am myself not sure on those points but since, there was nothing, I thought its better to give some direction to OP.

    Btw, the two transitions are not of same time. There's a little difference for sure, may be small, but it'll be there. So is the energy required for high -> low vs low -> high.
    Are you sure? This action cannot be undone.
    Cancel

  • ABCD ABCD

    Member • Dec 13, 2012

    OK... will be nice if you can find more information about it. Thanks for sharing 😉
    Are you sure? This action cannot be undone.
    Cancel
Home Channels Search Login Register