This is Master-Slave D Latch (Edge-Triggered D Flip-Flop).
When nPRESET is low an active-low SET is applied to the output S-R latch which forces Q high.
When nCLEAR is low an active-low RESET is applied to the output S-R latch which forces Q low.
Preset and Clear are asynchronous functions. Since nPRESET and nCLEAR are independent from CLK, they are also called DIRECT SET and DIRECT RESET.
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