From what I have understood :

  1. A Flip Flop is a clocked latch i.e. flip flop = latch + clock
  2. Latch continuously checks for inputs & changes the output whenever there is a change in input
  3. Flip Flop also continuously checks input, but changes the output time determined by clock. [so, even though if inputs are changed, it may not change the output at the same time]
  4. A latch with enable [i.e. gated latch], is different from that of clocked latch.

I am reading from Digital Logic by Morris Mano & Wikipedia.


As far as I understand, the difference is indeed the clock/enable.

A flip-flop samples the inputs only at a clock event (rising edge, etc.)

A Latch samples the inputs continuously whenever it is enabled, that is, only when the enable signal is on. (or otherwise, it would be a wire, not a latch).

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  • $\begingroup$ Yet, sometimes (depends on who and where), people may use those terms interchangeably. $\endgroup$ – Ran G. Apr 7 '13 at 7:33
  • $\begingroup$ but most textbooks explain latch without enable ? $\endgroup$ – avi Apr 7 '13 at 7:49
  • $\begingroup$ this can make sense for SR-latch, but think about an ungated D-latch -- this is nothing but a wire! The SR is a bit unique since the two inputs (S/R) serve in some sense both as (D/enable), so having S=R=0 is equivalent to having Enable=0. $\endgroup$ – Ran G. Apr 7 '13 at 7:53
  • $\begingroup$ Oh yes, you are absolutely right. Now it makes sense. So, in textbook they mention ungated SR because it is easy to understand, but in practice gated/enabled latches are used. Right ? $\endgroup$ – avi Apr 7 '13 at 10:08
  • $\begingroup$ and one more thing, when I say FlipFlop it means it is always clocked & when I say Latch, then it is always with enable. [so, FlipFlop without clock & latch without enable doesn't make any sense] $\endgroup$ – avi Apr 7 '13 at 12:29

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