What is the difference between flipflop setup time and hold time?

Answer 1

Set up time is the amount of time before the clock edge that the input signal needs to be stable to guarantee it is accepted properly on the clock edge.

Hold time is the amount of time after the clock edge that same input signal has to be held before changing it to make sure it is sensed properly at the clock edge.

Whenever there are setup and hold time violations in any flip-flop, it enters a state where its output is unpredictable: this state is known as metastable state (quasi stable state); at the end of metastable state, the flip-flop settles down to either '1' or '0'. This whole process is known as metastability

Answer 2

Flip-flop setup time refers to the minimum amount of time that the data input must be stable before the clock edge for the flip-flop to correctly latch the data. Hold time, on the other hand, refers to the minimum amount of time that the data input must be stable after the clock edge for the flip-flop to correctly store the data. In summary, setup time is the minimum time before the clock edge, while hold time is the minimum time after the clock edge for proper operation of the flip-flop.