IDT72255LA IDT [Integrated Device Technology], IDT72255LA Datasheet - Page 7

• Manufacturer Part Number: IDT72255LA
• Description: CMOS SUPERSYNC FIFO
• Manufacturer: IDT [Integrated Device Technology]

IDT72255LA/72265LA SUPERSYNC FIFO™
8,192 x 18, 16,384 x 18
FUNCTIONAL DESCRIPTION
TIMING MODES: IDT STANDARD vs FIRST WORD FALL
THROUGH (FWFT) MODE
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.
Standard mode will be selected. This mode uses the Empty
Flag (
present in the FIFO. It also uses the Full Flag function (
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 (
FWFT mode will be selected. This mode uses Output Ready
(
outputs (Q
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
Q
sary. Subsequent words must be accessed using the Read
Enable (
differently depending on which timing mode is in effect.
IDT STANDARD MODE
operate in the manner outlined in Table 1. To write data into to
the FIFO, Write Enable (
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 (
writes will continue to fill up the FIFO. The Programmable
Almost-Empty flag (
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.
assumed no read operations were taking place, the Half-Full
flag (
IDT72255LA and 8,193th word for IDT72265LA respectively
was written into the FIFO. Continuing to write data into the
FIFO will cause the Programmable Almost-Full flag (
go LOW. Again, if no reads are performed, the
LOW after (8,192-m) writes for the IDT72255LA and (16,384-m)
writes for the IDT72265LA. 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.
inhibiting further write operations. If no reads are performed
OR
n
The IDT72255LA/72265LA support two different timing
Various signals, both input and output signals operate
In this mode, the status flags,
If one continued to write data into the FIFO, and we
When the FIFO is full, the Full Flag (
If, at the time of Master Reset, FWFT/SI is LOW, then IDT
If, at the time of Master Reset, FWFT/SI is HIGH, then
after three RCLK rising edges,
) to indicate whether or not there is valid data at the data
HF
EF
) would toggle to LOW once the 4,097th word for
REN
REN
) to indicate whether or not there are any words
n)
. It also uses Input Ready (
) and RCLK.
) and RCLK.
PAE
WEN
) will go HIGH after n + 1 words have
) must be LOW. Data presented to
EF
) will go HIGH. Subsequent
FF
REN
,
PAF
IR
= LOW is not neces-
) to indicate whether
,
FF
HF
) will go LOW,
,
PAE
PAF
, and
PAF
will go
FF
) to
) to
EF
after a reset,
D = 8,192 writes for the IDT72255LA and 16,384 for the
IDT72265LA, respectively.
HIGH. Subsequent read operations will cause
go HIGH at the conditions described in Table 1. If further read
operations occur, without write operations,
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
REN
outputs are double register-buffered outputs.
found in Figure 7, 8 and 11.
FIRST WORD FALL THROUGH MODE (FWFT)
operate in the manner outlined in Table 2. To write data into
to the FIFO,
IN lines will be clocked into the FIFO on subsequent transi-
tions of WCLK. After the first write is performed, the Output
Ready (
to fill up the FIFO.
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.
assumed no read operations were taking place, the
toggle to LOW once the 4,098th word for the IDT72255LA and
8,194th word for the IDT72265LA, respectively was written
into the FIFO. Continuing to write data into the FIFO will cause
the
will go LOW after (8,193-m) writes for the IDT72255LA and
(16,385-m) writes for the IDT72265LA, where m is the full
offset value. The default setting for this value is stated in the
footnote of Table 2.
inhibiting further write operations. If no reads are performed after
a reset,
writes for the IDT72255LA and 16,385 writes for the IDT72265LA,
respectively. Note that the additional word in FWFT mode is due
to the capacity of the memory plus output register.
flag to go LOW. Subsequent read operations will cause the
PAF
2. If further read operations occur, without write operations,
the
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,
read operations.
register-buffered, and the
buffered.
If the FIFO is full, the first read operation will cause
When configured in IDT Standard mode, the
Relevant timing diagrams for IDT Standard mode can be
In this mode, the status flags,
If one continued to write data into the FIFO, and we
When the FIFO is full, the Input Ready (
If the FIFO is full, the first read operation will cause the
When configured in FWFT mode, the
PAF
PAE
and
is ignored when the FIFO is empty.
OR
IR
to go LOW. Again, if no reads are performed, the
will go LOW when there are n + 1 words in the FIFO,
HF
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
EF
will go HIGH after D writes to the FIFO. D = 8,193
) flag will go LOW. Subsequent writes will continue
WEN
to go HIGH at the conditions described in Table
will go LOW inhibiting further read operations.
FF
REN
must be LOW. Data presented to the DATA
will go LOW after D writes to the FIFO.
PAE
is ignored when the FIFO is empty.
will go HIGH after n + 2 words have
OR
IR
flag output is double register-
will go HIGH inhibiting further
IR
,
PAF
OR
IR
,
) flag will go HIGH,
HF
flag output is triple
PAE
,
PAF
PAE
will go LOW
EF
and
HF
, and
FF
and
would
HF
to go
PAF
7
OR
FF
IR
to