Function of enable input in gates

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Discussion Overview

The discussion revolves around the function of the enable input in logic gates, particularly focusing on OR gates. Participants explore how the enable input affects the output based on the states of other inputs, including scenarios where the enable input is high or low.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the output of an OR gate when the enable input is high and the other inputs are low, seeking clarification on the enable input's function.
  • Another participant explains that for an OR gate, if either input is high, the output will be high, and that the enable input must be low for input pulses to pass through.
  • A different participant expresses confusion regarding the enable input's state, stating that both high and low states seem to disable the gate, and requests external resources for clarification.
  • One participant emphasizes that the behavior described applies specifically to OR gates and outlines how the output changes based on the states of the inputs and the enable input.
  • Another participant suggests a practical application of the enable input, proposing that setting it low for a specific duration could allow for counting input pulses, thus functioning as a frequency counter.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of the enable input, with some asserting that it must be low for the gate to function properly, while others suggest that a high state can also lead to a high output under certain conditions. The discussion remains unresolved regarding the precise functionality of the enable input across different scenarios.

Contextual Notes

There are limitations in the discussion regarding the definitions and conditions under which the enable input operates, as well as the specific behavior of different types of gates beyond the OR gate.

waqarrashid33
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what are the function of enable input in gates?


If in or gate we use it and it is at high and the other two inputs are at low then what will be out put...1/0?
Please clear me about the enable input
 
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If either input of an OR gate is high, then the state of the other input doesn't matter. The output will be high.

To allow input pulses to pass from input to output of the gate, then the "enable" input has to be low.

This input pin is no different to any other pin on the gate input, but its function makes it an "enable" (or disble) pin.
 
when the enable is at low the gate/I.C will be disable and when the enable is at high the gate/IC will be disable...but told that To allow input pulses to pass from input to output of the gate, then the "enable" input has to be low...what is correct..if you have any external link about it then please provide it..
 
waqarrashid33, for a good explanation of the "enable" function of logic gates see:

http://www.allaboutcircuits.com/vol_4/chpt_3/8.html
 
Last edited:
This only applies to an OR gate. Other gates are different.

http://en.wikipedia.org/wiki/Or_gate

As you can see, with an OR gate, if either or both of the inputs are high, then the output will be high. If they are both LOW, the output will be LOW

So, if you make one of the inputs LOW, then the output will depend on what the other input does.
If it is HIGH, the output will be HIGH, and if it is LOW, the output will be LOW.

Now, if you make the enable input HIGH, what can happen?
If the other input is LOW the output will be HIGH.
If the other input is HIGH, the output will be HIGH.
So the output will always be HIGH.

So, even if you put pulses (ie HIGH, LOW, HIGH...) on the other input, none of them will get through to the output.

That is why they call it a gate. It can let stuff through or stop it.

So what use is all this?
If you made the enable input LOW for exactly 1 second, you could use another circuit to count how many pulses got through and display this number on a display of some sort.
You would then have a frequency counter.
 

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