Bistable Memory Elements

Discussion in 'Homework Help' started by mghg13, Sep 13, 2013.

  1. mghg13

    Thread Starter Member

    Jul 17, 2013
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    Hello, I am a student in electronics and I need some info for an homework on digital electronics

    Can anyone tell me what is meant by 'bistable memory elements' ?

    What is it made up of? I mean, from what basic digital electronic components is it made. How is it used in digital systems? Some examples where it is used??

    And what is meant by the term 'bistable' ? Are not everything in digital electronics 'bistable' (since we can have only 0 or 1)???

    Are there memory elements that are not 'bistable'?

    I just need some general info about these things so that I know on which topics should I focus.

    Thanks
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Bistable refers to a device with two (bi-) stable states. This is a flip-flop.
    Monostable refers to a device with one stable state. This is also called a One-Shot.
    Astable refers to a device with no stable states. For a binary device it oscillates back and forth between 0 and 1.
     
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  3. mghg13

    Thread Starter Member

    Jul 17, 2013
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    you mean to say that all the flip flops (JK, T, D) are the bistable memory elements?
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    That is correct. As long as no clock pulses arrive they will hold their state indefinitely -- as long as they are powered.
     
  5. ScottWang

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    Aug 23, 2012
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  6. mghg13

    Thread Starter Member

    Jul 17, 2013
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    And what about memory elements that are not bistable?
     
  7. Austin Clark

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    Dec 28, 2011
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    I don't think there is such a thing. Unless, perhaps, you count DRAM, which must be periodically "refreshed" to maintain its memory. This is close to a monostable, but monostables I've seen can only be re-triggered after they've already decayed into their default state.
     
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  8. WBahn

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    Mar 31, 2012
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    A monostable circuit is most definitely a memory element -- it's state is a function both of it's present inputs and its history. For its history to affect its state, it has to have some way of remembering that history.

    The classic 555 MMV circuits are retriggerable. If you want an output pulse that is shorter than the input trigger pulse, you need to put some kind of an edge detection circuit on the trigger input.

    Most DRAMs would not be considered monostable because the value stored in them decays whether that value was a HI or a LO, hence neither is stored in a stable fashion without refresh.

    A schmitt trigger is, technically, a memory element in that its behavior (and output) is dependent on its history. But that remembered information is not accessible directly from the output (though it can be inferred very easily) so it is pretty much never thought of as being a memory element. If it were, it would be classified as an unstable memory element because in either output state it will remain there indefinitely only as long as the inputs continue to reinforce that state.
     
  9. mghg13

    Thread Starter Member

    Jul 17, 2013
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    Thanks for all your replies!!!

    Now I would like know what are 'finite state machines' and how bistable memory elements are used in these? Give some examples
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    What have YOU found out from YOUR efforts to answer YOUR homework question?
     
  11. absf

    Senior Member

    Dec 29, 2010
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    Look at Vol. IV (Digital) Chapter 11(sequential circuits counters) above you. There is a whole page describing 'Finite State Machine'...... It's a nice read.

    Allen
     
    Last edited: Sep 15, 2013
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