DT72281_13 Datasheet, PDF (11/26 Pages) Integrated Device Technology – CMOS SuperSync FIFO

IDT72281/72291
CMOS SuperSync FIFO™ 65,536 x 9 and 131,072 x 9
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
RETRANSMIT OPERATION
The Retransmit operation allows data that has already been read to be
accessed again. There are two stages: first, a setup procedure that resets
the read pointer to the first location of memory, then the actual retransmit,
which consists of reading out the memory contents, starting at the begin-
ning of memory.
Retransmit setup is initiated by holding RT LOW during a rising RCLK
edge. REN and WEN must be HIGH before bringing RT LOW. At least
one word, but no more than D– 2 words should have been written into
the FIFO between Reset (Master or Partial) and the time of Retransmit
setup. D = 65,536 for the IDT72281 and D = 131,072 for the IDT72291
in IDT Standard mode. In FWFT mode, D = 65,537 for the IDT72281
and D = 131,073 for the IDT72291.
If IDT Standard mode is selected, the FIFO will mark the beginning of
the Retransmit setup by setting EF LOW. The change in level will only be
noticeable if EF was HIGH before setup. During this period, the internal
read pointer is initialized to the first location of the RAM array.
When EF goes HIGH, Retransmit setup is complete and read opera-
tions may begin starting with the first location in memory. Since IDT Stan-
dard mode is selected, every word read including the first word following
Retransmit setup requires a LOW on REN to enable the rising edge of
RCLK. See Figure 11, Retransmit Timing (IDT Standard Mode), for the
relevant timing diagram.
If FWFT mode is selected, the FIFO will mark the beginning of the
Retransmit setup by setting OR HIGH. During this period, the internal read
pointer is set to the first location of the RAM array.
When OR goes LOW, Retransmit setup is complete; at the same time,
the contents of the first location appear on the outputs. Since FWFT mode
is selected, the first word appears on the outputs, no LOW on REN is
necessary. Reading all subsequent words requires a LOW on REN to
enable the rising edge of RCLK. See Figure 12, Retransmit Timing (FWFT
Mode), for the relevant timing diagram.
For either IDT Standard mode or FWFT mode, updating of the PAE,
HF and PAF flags begin with the rising edge of RCLK that RT is setup.
PAE is synchronized to RCLK, thus on the second rising edge of RCLK
after RT is setup, the PAE flag will be updated. HF is asynchronous, thus
the rising edge of RCLK that RT is setup will update HF. PAF is synchro-
nized to WCLK, thus the second rising edge of WCLK that occurs tSKEW
after the rising edge of RCLK that RT is setup will update PAF. RT is
synchronized to RCLK.
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