OR GATE LATCH

Discussion in 'General Electronics Chat' started by pilko, Jan 25, 2009.

  1. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    This simple latch works OK on my breadboard,but doesn't work on my simulator.Am I doing something wrong?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    You probably need to connect the unused inputs of your OR-gate to ground.

    hgmjr
     
  3. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    The unused inputs are connected to ground,and it works OK on the breadboard.I cannot get it to work on my Logic Lab simulator.I thought I may be performing an illegal operation.I havn't seen this application used anywhere.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    You drawing does not indicate that the unused inputs are tied to anything. That is why I replied as I did.

    If your simulated device has its unused inputs tied to ground then it should work.

    hgmjr
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    In real hardware, I suspect that the output will come up either high or low when power is switched on, depending on the internal circuitry. I'm not sure what simulator you are using, but unused inputs of behavioral gates in LTspice are automatically inactive, so grounding them wouldn't help..
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
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    Please define the phrase "doesn't work." Is the simulator output always low? Does it follow the input? Is the o/p an analog representation of a Barry Manilow tune?
     
  7. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    I have attached the graph for both modes of operation.The breadboard version latches,the simulator vertion doesn't. Thanks for the prompt replies.
     
  8. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    I screwed up. Here is the correct diagram
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    It works in my simulator, even using CMOS logic without having all of the unused inputs grounded. Perhaps you've found a bug in your simulator software.
     
  10. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    It's a USB interface device called Digi-bee+ with simulating software called Logic-Lab plus I have just written to them hoping they can help me

    Thanks for your help everyone
     
  11. pilko

    Thread Starter Senior Member

    Dec 8, 2008
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    If it was behaving like an AND gate,the output would not go high at all
     
  12. hgmjr

    Moderator

    Jan 28, 2005
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    Pilko is correct. My goof.

    hgmjr
     
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