UltraScale Architecture Memory Resources

Chapter 2: Built-in FIFO
FWFT Mode
In a first-word fall-through (FWFT) FIFO, the data is placed on the DOUT bus before RDEN
is asserted. When writing the first word to an EMPTY FIFO, the first word is directly
transferred to the output, and appears on the DOUT bus at the same time EMPTY is
deasserted.
To prevent data loss in the system, this first output value does not disappear from the DOUT
bus until RDEN is asserted. If no more data is available, EMPTY is asserted and the next word
written to the FIFO again directly transfers to the output. Because the data appears on
DOUT before the read operation, it can take one more last read operation for the FIFO to
assert EMPTY (go empty). In either case, the same number of read operations as write
operations are required to return the FIFO to an empty state. See Figure 2-5 and Figure 2-6.
X-Ref Target - Figure 2-5
Figure 2-5:
FWFT FIFO with One Data Word in the FIFO
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UG573 (v1.2) February 24, 2015