Flip-Flops

Flip-flops are sequential logic circuits — unlike combinational circuits (gates), their output depends not only on the current inputs but also on the previous state. Flip-flops are the fundamental building blocks of memory, registers, and counters in digital systems.

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Combinational vs Sequential Logic

Type	Output depends on	Memory?	Examples
Combinational	Current inputs only	No	AND, OR, NOT gates, adders
Sequential	Current inputs AND previous state	Yes	Flip-flops, registers, counters

Key Term: A flip-flop stores one bit of information. It has two stable states (0 and 1) and can be set to either state by applying appropriate inputs.

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The SR Flip-Flop (Set-Reset)

The SR flip-flop has two inputs: S (Set) and R (Reset), and two outputs: Q and NOT Q (the complement of Q).

Behaviour: