Asynchronous Presets and Clears

Asynchronous Preset (PRE) and Clear (CLR) are direct, overriding control inputs for Flip-Flops and Latches. They are necessary for us to control the starting state for these components, such as during device start-up.

These inputs are asynchronous $-$ it doesn’t matter whether clock is low or high, they still override the output Q immediately.

Example Control Input Setup for a D-latch:

Summary bq

Clear forces output low regardless of the other inputs (S=0)
Preset forces output high regardless of the other inputs (S=1)

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