J-K flip flops!!?

Question

what is the purpose of the preset function on a J-K flip flop? It seems to me to be unnecessary. What am I missing?

That is an asynchronous input (not dependant on the rising edge of the clock). Sometimes it is necessary to force the Q output to a logic '1' regardless of the clock state or edge. Usually this would happen to set an initial state of the flip-flop at power-up before the clock starts.

The same thing applies to the clear input (which forces Q=0 asynchronously).


Thanks for your answer, I guess I was looking for a real world senario in which you would need to the preset to force Q to a 1?

Answer 1

That is an asynchronous input (not dependant on the rising edge of the clock). Sometimes it is necessary to force the Q output to a logic '1' regardless of the clock state or edge. Usually this would happen to set an initial state of the flip-flop at power-up before the clock starts.

The same thing applies to the clear input (which forces Q=0 asynchronously).

.

Answer 2

preset/clear is for power up. because all flip flops come up in an undetermined state, you use it to set the entire circuit in a known state.

eg: State machines, counters etc -- you don't want it in some unknown or "non starting" state

Answer 3

huh?