IDT72285 Integrated Device Technology, IDT72285 Datasheet - Page 12

• Manufacturer Part Number: IDT72285
• Description: 64k X 18 Supersync Fifo, 5.0v
• Manufacturer: Integrated Device Technology

inhibiting further write operations. Upon the completion of a valid read cycle, FF
will go HIGH allowing a write to occur. The FF is updated by two WCLK cycles
+ t
further write operations. Upon the completion of a valid read cycle, IR will go
LOW allowing a write to occur. The IR flag is updated by two WCLK cycles +
t
READ CLOCK (RCLK)
read on the outputs, on the rising edge of the RCLK input. It is permissible to
stop the RCLK. Note that while RCLK is idle, the EF/OR, PAE and HF flags will
not be updated. (Note that RCLK is only capable of updating the HF flag to
HIGH.) The Write and Read Clocks can be independent or coincident.
READ ENABLE (REN)
register on the rising edge of every RCLK cycle if the device is not empty.
no new data is loaded into the output register. The data outputs Q
the previous data value.
word written to an empty FIFO, must be requested using REN. When the last
word has been read from the FIFO, the Empty Flag (EF) will go LOW, inhibiting
further read operations. REN is ignored when the FIFO is empty. Once a write
is performed, EF will go HIGH allowing a read to occur. The EF flag is updated
by two RCLK cycles + t
to the outputs Q
after the first write. REN does not need to be asserted LOW. In order to access
all other words, a read must be executed using REN. The RCLK LOW to HIGH
transition after the last word has been read from the FIFO, Output Ready (OR)
will go HIGH with a true read (RCLK with REN = LOW), inhibiting further read
operations. REN is ignored when the FIFO is empty.
SERIAL ENABLE (SEN)
registers. The serial programming method must be selected during Master
Reset. SEN is always used in conjunction with LD. When these lines are both
LOW, data at the SI input can be loaded into the program register one bit for each
LOW-to-HIGH transition of WCLK. (See Figure 4.)
and no offsets are loaded. SEN functions the same way in both IDT Standard
and FWFT modes.
OUTPUT ENABLE (OE)
data from the output register. When OE is HIGH, the output data bus (Q
into a high impedance state.
LOAD (LD)
determines one of two default offset values (127 or 1,023) for the PAE and PAF
flags, along with the method by which these offset registers can be programmed,
parallel or serial. After Master Reset, LD enables write operations to and read
operations from the offset registers. Only the offset loading method currently
IDT72275/72285
CMOS SuperSync FIFO™ 32,768 x 18 and 65,536 x 18
SKEW
SKEW
To prevent data overflow in the IDT Standard mode, FF will go LOW,
To prevent data overflow in the FWFT mode, IR will go HIGH, inhibiting
WEN is ignored when the FIFO is full in either FWFT or IDT Standard mode.
A read cycle is initiated on the rising edge of the RCLK input. Data can be
When Read Enable is LOW, data is loaded from the RAM array into the output
When the REN input is HIGH, the output register holds the previous data and
In the IDT Standard mode, every word accessed at Q
In the FWFT mode, the first word written to an empty FIFO automatically goes
The SEN input is an enable used only for serial programming of the offset
When SEN is HIGH, the programmable registers retains the previous settings
When Output Enable is enabled (LOW), the parallel output buffers receive
This is a dual purpose pin. During Master Reset, the state of the LD input
after the valid RCLK cycle.
after the RCLK cycle.
n
, on the third valid LOW to HIGH transition of RCLK + t
SKEW
after the valid WCLK cycle.
n
, including the first
0
-Q
n
maintain
n
) goes
SKEW
12
selected can be used to write to the registers. Offset registers can be read only
in parallel. A LOW on LD during Master Reset selects a default PAE offset value
of 07FH (a threshold 127 words from the empty boundary), a default PAF offset
value of 07FH (a threshold 127 words from the full boundary), and parallel
loading of other offset values. A HIGH on LD during Master Reset selects a
default PAE offset value of 3FFH (a threshold 1,023 words from the empty
boundary), a default PAF offset value of 3FFH (a threshold 1,023 words from
the full boundary), and serial loading of other offset values.
of the flag offset values PAE and PAF. Pulling LD LOW will begin a serial loading
or parallel load or read of these offset values. See Figure 4, Programmable Flag
Offset Programming Sequence.
OUTPUTS:
FULL FLAG (FF/IR)
is selected. When the FIFO is full, FF will go LOW, inhibiting further write
operations. When FF is HIGH, the FIFO is not full. If no reads are performed
after a reset (either MRS or PRS), FF will go LOW after D writes to the FIFO
(D = 32,768 for the IDT72275 and 65,536 for the IDT72285). See Figure 7,
Write Cycle and Full Flag Timing (IDT Standard Mode), for the relevant timing
information.
memory space is available for writing in data. When there is no longer any free
space left, IR goes HIGH, inhibiting further write operations. If no reads are
performed after a reset (either MRS or PRS), IR will go HIGH after D writes to
the FIFO (D = 32,769 for the IDT72275 and 65,537 for the IDT72285) See
Figure 9, Write Timing (FWFT Mode), for the relevant timing information.
counts the presence of a word in the output register. Thus, in FWFT mode, the
total number of writes necessary to deassert IR is one greater than needed to
assert FF in IDT Standard mode.
double register-buffered outputs.
EMPTY FLAG (EF/OR)
function is selected. When the FIFO is empty, EF will go LOW, inhibiting further
read operations. When EF is HIGH, the FIFO is not empty. See Figure 8, Read
Cycle, Empty Flag and First Word Latency Timing (IDT Standard Mode), for
the relevant timing information.
at the same time that the first word written to an empty FIFO appears valid on
the outputs. OR stays LOW after the RCLK LOW to HIGH transition that shifts the
last word from the FIFO memory to the outputs. OR goes HIGH only with a true
read (RCLK with REN = LOW). The previous data stays at the outputs, indicating
the last word was read. Further data reads are inhibited until OR goes LOW
again. See Figure 10, Read Timing (FWFT Mode), for the relevant timing
information.
mode, OR is a triple register-buffered output.
PROGRAMMABLE ALMOST-FULL FLAG (PAF)
reaches the almost-full condition. In IDT Standard mode, if no reads are
performed after reset (MRS), PAF will go LOW after (D - m) words are written
to the FIFO. The PAF will go LOW after (32,768-m) writes for the IDT72275 and
After Master Reset, the LD pin is used to activate the programming process
This is a dual purpose pin. In IDT Standard mode, the Full Flag (FF) function
In FWFT mode, the Input Ready (IR) function is selected. IR goes LOW when
The IR status not only measures the contents of the FIFO memory, but also
FF/IR is synchronous and updated on the rising edge of WCLK. FF/IR are
This is a dual purpose pin. In the IDT Standard mode, the Empty Flag (EF)
In FWFT mode, the Output Ready (OR) function is selected. OR goes LOW
In IDT Standard mode, EF is a double register-buffered output. In FWFT
The Programmable Almost-Full flag (PAF) will go LOW when the FIFO
EF/OR is synchronous and updated on the rising edge of RCLK.
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES