ISCET associate ?

Discussion in 'General Electronics Chat' started by RFrog, Jul 16, 2008.

  1. RFrog

    Thread Starter New Member

    Jul 16, 2008
    2
    0
    Hello,

    I recently took (and passed) the associate ISCET exam. There is one question that still bothers me. It is:

    If a TTL output is providing 0V, what is this called?:
    A: Current sourcing
    B: Current sinking
    c: Asserted
    D: Unasserted

    It seems to me that both B and D are correct. Is this so? What would be the best answer?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It's B: current sinking.
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    Yes, it's B. Neither C or D is correct.

    A signal may be asserted (or deasserted) either high or low depending upon the operation required in the design.

    For instance, a xstr that enables a relay by sinking current would be a low assertion at the relay coil terminal (other terminal would be at voltage), and would typically use a NOT indicator in the signal/net name; such as ~RELAYEN, RELAYEN*, /RELAYEN, or have an overbar (you could also call it RELAYOFF without the negation, but to the same effect -- in this case high, or open, would mean off).
     
    Last edited: Jul 23, 2008
  4. RFrog

    Thread Starter New Member

    Jul 16, 2008
    2
    0
    Excellent! That was my answer.

    Thanks!
     
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