IDT72V261LA/72V271LA
3.3 VOLT CMOS SuperSync FIFO™ 16,384 x 9 and 32,768 x 9
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
If the FIFO is full, the first read operation will cause FF to go HIGH.
Subsequent read operations will cause PAF and HF to go HIGH at the
conditions described in Table 1. If further read operations occur, without
write operations, PAE will go LOW when there are n words in the FIFO,
where n is the empty offset value. Continuing read operations will cause
the FIFO to become empty. When the last word has been read from the
FIFO, the EF will go LOW inhibiting further read operations. REN is
ignored when the FIFO is empty.
When configured in IDT Standard mode, the EF and FF outputs are
double register-buffered outputs.
Relevant timing diagrams for IDT Standard mode can be found in
Figure 7, 8 and 11.
FUNCTIONAL DESCRIPTION
TIMING MODES:
IDT STANDARD VS FIRST WORD FALL THROUGH (FWFT) MODE
The IDT72V261LA/72V271LA support two different timing modes of
operation: IDT Standard mode or First Word Fall Through (FWFT) mode.
The selection of which mode will operate is determined during Master
Reset, by the state of the FWFT/SI input.
If, at the time of Master Reset, FWFT/SI is LOW, then IDT Standard
mode will be selected. This mode uses the Empty Flag (EF) to indicate
whether or not there are any words present in the FIFO. It also uses the
Full Flag function (FF) to indicate whether or not the FIFO has any free
space for writing. In IDT Standard mode, every word read from the
FIFO, including the first, must be requested using the Read Enable
(REN) and RCLK.
If, at the time of Master Reset, FWFT/SI is HIGH, then FWFT mode
will be selected. This mode uses Output Ready (OR) to indicate whether
or not there is valid data at the data outputs (Qn). It also uses Input
Ready (IR) to indicate whether or not the FIFO has any free space for
writing. In the FWFT mode, the first word written to an empty FIFO
goes directly to Qn after three RCLK rising edges, REN = LOW is not
necessary. Subsequent words must be accessed using the Read En-
able (REN) and RCLK.
FIRST WORD FALL THROUGH MODE (FWFT)
In this mode, the status flags, IR, PAF, HF, PAE, and OR operate in
the manner outlined in Table 2. To write data into to the FIFO, WEN
must be LOW. Data presented to the DATA IN lines will be clocked into
the FIFO on subsequent transitions of WCLK. After the first write is
performed, the Output Ready (OR) flag will go LOW. Subsequent writes
will continue to fill up the FIFO. PAE will go HIGH after n + 2 words
have been loaded into the FIFO, where n is the empty offset value. The
default setting for this value is stated in the footnote of Table 2. This
parameter is also user programmable. See section on Programmable
Flag Offset Loading.
If one continued to write data into the FIFO, and we assumed no
read operations were taking place, the HF would toggle to LOW once
the 8,194th word for the IDT72V261LA and 16,386th word for the
IDT72V271LA, respectively was written into the FIFO. Continuing to
write data into the FIFO will cause the PAF to go LOW. Again, if no
reads are performed, the PAF will go LOW after (16,385-m) writes for
the IDT72V261LA and (32,769-m) writes for the IDT72V271LA, where
m is the full offset value. The default setting for this value is stated in
the footnote of Table 2.
Various signals, both input and output signals operate differently
depending on which timing mode is in effect.
IDT STANDARD MODE
In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in
the manner outlined in Table 1. To write data into to the FIFO, Write
Enable (WEN) must be LOW. Data presented to the DATA IN lines will
be clocked into the FIFO on subsequent transitions of the Write Clock
(WCLK). After the first write is performed, the Empty Flag (EF) will go
HIGH. Subsequent writes will continue to fill up the FIFO. The Program-
mable Almost-Empty flag (PAE) will go HIGH after n + 1 words have
been loaded into the FIFO, where n is the empty offset value. The
default setting for this value is stated in the footnote of Table 1. This
parameter is also user programmable. See section on Programmable
Flag Offset Loading.
When the FIFO is full, the Input Ready (IR) flag will go HIGH, inhibit-
ing further write operations. If no reads are performed after a reset, IR
will go HIGH after D writes to the FIFO. D = 16,385 writes for the
IDT72V261LA and 32,769 writes for the IDT72V271LA, respectively.
Note that the additional word in FWFT mode is due to the capacity of
the memory plus output register.
If one continued to write data into the FIFO, and we assumed no
read operations were taking place, the Half-Full flag (HF) would toggle
to LOW once the 8,193th word for IDT72V261LA and 16,385th word for
IDT72V271LA respectively was written into the FIFO. Continuing to
write data into the FIFO will cause the Programmable Almost-Full flag
(PAF) to go LOW. Again, if no reads are performed, the PAF will go
LOW after (16,384-m) writes for the IDT72V261LA and (32,768-m) writes
for the IDT72V271LA. The offset “m” is the full offset value. The default
setting for this value is stated in the footnote of Table 1. This parameter
is also user programmable. See section on Programmable Flag Offset
Loading.
If the FIFO is full, the first read operation will cause the IR flag to go
LOW. Subsequent read operations will cause the PAF and HF to go
HIGH at the conditions described in Table 2. If further read operations
occur, without write operations, the PAE will go LOW when there are n
+ 1 words in the FIFO, where n is the empty offset value. Continuing
read operations will cause the FIFO to become empty. When the last
word has been read from the FIFO, OR will go HIGH inhibiting further
read operations. REN is ignored when the FIFO is empty.
When configured in FWFT mode, the OR flag output is triple register-
buffered, and the IR flag output is double register-buffered.
Relevant timing diagrams for FWFT mode can be found in Figure 9,
10 and 12.
When the FIFO is full, the Full Flag (FF) will go LOW, inhibiting
further write operations. If no reads are performed after a reset, FF will
go LOW after D writes to the FIFO. D = 16,384 writes for the
IDT72V261LA and 32,768 for the IDT72V271LA, respectively.
7
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