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Help with monostable and signals

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Look at Q and Q-bar in your very first image.

What is the relationship between them?

On the second one -- look at the imput and the output. They are identical. Does this suggest you may be missing something?

Same thing for the third example.

Go back to the first example. Look at the (dare I say it) runt pulses on A, Q and Q-bar. WHere have they gone in the second example? Is there any reason for them not to be there? What about the third case?
 

Merlin3189

Aug 4, 2011
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You're certainly doing the right sort of thing, but there seem to be some errors.
In p1IWa (A) looks like (Xbar AND Qbar) when it should be (X AND Qbar)
In oJdZe you show input B stays low, but still Q changes. Q can change only as a result of changes of B.
In 7nERK I think you have (B) looks like the inverse of (A XOR Qbar), but maybe the gate is drawn missing the inverted output? Also Q seems to change incorrectly with regard to B. Presumably Q should rise only when B rises.
Ooops! I've just noticed, in 7nERK you've plotted 1 low and 0 high, so I may have got it wrong here. But on checking I find it still doesn't make sense. I would suggest you always have 0 as the base line and 1 above, unless there's a very good reason to do otherwise. (Though you have been very good to label the axis.) If you chop and change, it just adds one more source for errors.
The other general point I would suggest, is to start off with everything in the quiescent state. Assume Q=0 and Qbar=1, and that the input (A or Xbar) is 0. Do not start off assuming any others are 0, work them out, so that for eg in 7nERK, B starts off at 1 as you correctly show in the right hand graphs. Then when you change the input, work thorough the logic changing them in order. No outputs change instantly. There is always a propagation delay however brief, which means logic values change in sequence. I often exaggerate these delays, so that I can pencil in little arrows showing which change causes which other change.

Hope some of this is helpful
 
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