UNREGISTERED indicates that the FIFO does not use the block RAM output register. REGISTERED indicates that the output register is used and that the FIFO controls it such that the FIFO’s DOUT behaves like an additional FIFO word. This setting does not add any latency to the DOUT but has an impact on clock-to-out and WRCLK to EMPTY deassertion latency.
DO_PIPELINED indicates that the output register adds an additional pipeline stage to the DOUT path, with REGCE and RSTREG inputs so that the output register can be controlled. This setting has an impact on clock-to-out and WRCLK to EMPTY deassertion latency.