Retriggerable vs non-retriggerable one-shot — what is the key difference? Choose the statement that correctly distinguishes how the output pulse behaves with successive triggers.

Difficulty: Easy

Correct Answer: The output pulse can be stretched with a retriggerable.

Explanation:


Introduction / Context:
One-shot multivibrators are either retriggerable or non-retriggerable. Understanding how additional triggers affect the timing pulse is crucial in pulse-width control and glitch filtering.


Given Data / Assumptions:

  • We compare output behavior under multiple triggers arriving before the pulse expires.
  • One device is retriggerable; the other is not.


Concept / Approach:
In a retriggerable one-shot, any valid trigger that occurs during the active pulse restarts the timing interval, effectively lengthening (stretching) the total pulse width. In a non-retriggerable one-shot, additional triggers received while the pulse is active are ignored until the device returns to its stable state.


Step-by-Step Solution:

Consider a pulse that lasts T seconds.Apply a second trigger at t = T/2.Retriggerable: timing restarts, so new end time ≈ t + T, total width > T.Non-retriggerable: timing continues unchanged, total width = T.


Verification / Alternative check:
Datasheets typically note "retriggering extends the output pulse" for devices like 74x123, contrasting with 74x121 (non-retriggerable).


Why Other Options Are Wrong:

  • Nonretriggerable can only be triggered once: false; it can be triggered again after it times out.
  • Retriggerable can be triggered many times: true but incomplete; the distinguishing effect is pulse extension.
  • Nonretriggerable stretches the pulse: incorrect by definition.
  • Successive triggers shorten the pulse: opposite of retrigger behavior.


Common Pitfalls:

  • Confusing "ignoring triggers while busy" with "cannot be triggered again ever".


Final Answer:
The output pulse can be stretched with a retriggerable.

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