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Which gate, NAND or NOR is a better choice for making SR Flip Flop latch? Please, provide the reason too.

Gnanabalan Gnanalosan
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  • I think it depends on your choice. Whether you want to implement the whole design on NAND logic or NOR logic. – User Jan 30 '21 at 10:14
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    This looks like a school question without an attempt to solve. – K H Jan 30 '21 at 10:42

2 Answers2

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It depends on which one fits the application better.

NAND:

  • inputs are active-low
  • for the Q output, "set" has priority over "reset"

NOR:

  • inputs are active-high
  • for the Q output, "reset" has priority over "set"

Extra Credit

Some applications require a two-phase clock. What is the subtle, but important difference between the following two circuits?

schematic

simulate this circuit – Schematic created using CircuitLab

Dave Tweed
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  • The question is about latches. How does one input have priority over the other? – Shashank V M Jan 30 '21 at 16:27
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    @ShashankVM: In a NAND latch, if the "set" input is asserted (low), the Q output will be high regardless of the state of the "reset" input. However, in the NOR latch, asserting the "set" input (high) will be overridden if the "reset" input is also asserted, driving the Q output low. Sometimes this subtle difference is important in an application. – Dave Tweed Jan 30 '21 at 16:51
  • Thanks a lot for your reply, Mr. Dave Tweed. I am able to understand now. I did not know that Set has priority over Reset in a NAND latch and vice versa for a NOR latch. Other readers can read this https://electronics.stackexchange.com/a/323863/238188 – Shashank V M Jan 31 '21 at 04:43
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Both ways are identical except that one is active high and the other is active low.

Paul Ghobril
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