Asynchronous Input

Asynchronous inputs are those that operate independently of a clock signal and other inputs. They override the state of a circuit and force them into a predefined state.

Asynchronous inputs are an integral part of flip-flops. They are referred to as "SET" and "RESET" or "PRESET" and "CLEAR"...

SET sets the output Q to "1"
RESET sets the output Q to "0"

In contrast, the R, S, J, K and D inputs of flip flops are synchronous inputs. Synchronous inputs have only in combination with a clock signal impact on the state at the output Q.

Examples of circuits with synchronous inputs...