CMOS SUPERSYNC FIFO™
8,192 x 18
16,384 x 18
Integrated Device Technology, Inc.
IDT72255LA
IDT72265LA
FEATURES:
• Choose among the following memory organizations:
IDT72255LA
8,192 x 18
IDT72265LA
16,384 x 18
• Pin-compatible with the IDT72275/72285 SuperSync FIFOs
• 10ns read/write cycle time (8ns access time)
• Fixed, low first word data latency time
• Auto power down minimizes standby power consumption
• Master Reset clears entire FIFO
• Partial Reset clears data, but retains programmable
settings
• Retransmit operation with fixed, low first word data
latency time
• Empty, Full and Half-Full flags signal FIFO status
• Programmable Almost-Empty and Almost-Full flags, each
flag can default to one of two preselected offsets
• Program partial flags by either serial or parallel means
• Select IDT Standard timing (using
EF
and
FF
flags) or First
Word Fall Through timing (using
OR
and
IR
flags)
• Output enable puts data outputs into high impedance state
• Easily expandable in depth and width
• Independent Read and Write clocks (permit reading and
writing simultaneously)
• Available in the 64-pin Thin Quad Flat Pack (TQFP) and the
64-pin Slim Thin Quad Flat Pack (STQFP)
• High-performance submicron CMOS technology
• Industrial temperature range (–40°C to +85°C) is available
DESCRIPTION:
The IDT72255LA/72265LA are exceptionally deep, high
speed, CMOS First-In-First-Out (FIFO) memories with clocked
read and write controls. These FIFOs offer numerous improve-
ments over previous SuperSync FIFOs, including the following:
• The limitation of the frequency of one clock input with
respect to the other has been removed. The Frequency
Select pin (FS) has been removed, thus it is no longer
necessary to select which of the two clock inputs, RCLK or
WCLK, is running at the higher frequency.
• The period required by the retransmit operation is now fixed
and short.
FUNCTIONAL BLOCK DIAGRAM
WCLK
D
0
-D
17
INPUT REGISTER
OFFSET REGISTER
/
WRITE CONTROL
LOGIC
RAM ARRAY
8,192 x 18
16,384 x 18
FLAG
LOGIC
/
FWFT/SI
WRITE POINTER
READ POINTER
READ
CONTROL
LOGIC
OUTPUT REGISTER
RESET
LOGIC
RCLK
Q
0
-Q
17
SuperSyncFIFO is a trademark and the IDT logo is a registered trademark of Integrated Device Technology, Inc.
4670 drw 01
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
©2001 Integrated Device Technology, Inc
APRIL 2001
DSC-4670/1
1
IDT72255LA/72265LA SUPERSYNC FIFO™
8,192 x 18, 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
DESCRIPTION (Continued)
• The first word data latency period, from the time the first
word is written to an empty FIFO to the time it can be read,
is now fixed and short. (The variable clock cycle counting
delay associated with the latency period found on previous
SuperSync devices has been eliminated on this SuperSync
family.)
SuperSync FIFOs are particularly appropriate for network,
video, telecommunications, data communications and other
applications that need to buffer large amounts of data.
The input port is controlled by a Write Clock (WCLK) input
and a Write Enable (
WEN
) input. Data is written into the FIFO
on every rising edge of WCLK when
WEN
is asserted. The
output port is controlled by a Read Clock (RCLK) input and
Read Enable (
REN
) input. Data is read from the FIFO on every
rising edge of RCLK when
REN
is asserted. An Output Enable
(
OE
) input is provided for three-state control of the outputs.
The frequencies of both the RCLK and the WCLK signals
may vary from 0 to f
MAX
with complete independence. There
are no restrictions on the frequency of one clock input with
respect to the other.
There are two possible timing modes of operation with
these devices: IDT Standard mode and First Word Fall Through
(FWFT) mode.
In
IDT Standard mode,
the first word written to an empty
FIFO will not appear on the data output lines unless a specific
read operation is performed. A read operation, which consists
of activating
REN
and enabling a rising RCLK edge, will shift
the word from internal memory to the data output lines.
In
FWFT mode,
the first word written to an empty FIFO is
clocked directly to the data output lines after three transitions
of the RCLK signal. A
REN
does not have to be asserted for
accessing the first word. However, subsequent words written
to the FIFO do require a LOW on
REN
for access. The state
PIN CONFIGURATIONS
FWFT/SI
GND
WCLK
RCLK
V
CC
/
PIN 1
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
1
2
DC
V
CC
GND
D17
D16
D15
D14
D13
D12
D11
D10
D9
D8
D7
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
Q17
Q16
GND
Q15
Q14
V
CC
Q13
Q12
Q11
GND
Q10
Q9
Q8
Q7
Q6
GND
D5
D4
D3
D2
D1
D0
GND
Q0
Q1
GND
Q2
Q3
V
CC
Q4
Q5
D6
/
4670 drw 02
TQFP (PN64-1, order code: PF)
STQFP (PP64-1, order code: TF)
TOP VIEW
2
IDT72255LA/72265LA SUPERSYNC FIFO™
8,192 x 18, 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
DESCRIPTION (Continued)
of the FWFT/SI input during Master Reset determines the
timing mode in use.
For applications requiring more data storage capacity than
a single FIFO can provide, the FWFT timing mode permits
depth expansion by chaining FIFOs in series (i.e. the data
outputs of one FIFO are connected to the corresponding data
inputs of the next). No external logic is required.
These FIFOs have five flag pins,
EF
/
OR
(Empty Flag or
Output Ready),
FF
/
IR
(Full Flag or Input Ready),
HF
(Half-full
Flag),
PAE
(Programmable Almost-Empty flag) and
PAF
(Pro-
grammable Almost-Full flag). The
EF
and
FF
functions are
selected in IDT Standard mode. The
IR
and
OR
functions are
selected in FWFT mode.
HF
,
PAE
and
PAF
are always
available for use, irrespective of timing mode.
PAE
and
PAF
can be programmed independently to switch
at any point in memory. (See Table I and Table II.) Program-
mable offsets determine the flag switching threshold and can
be loaded by two methods: parallel or serial. Two default
offset settings are also provided, so that
PAE
can be set to
switch at 127 or 1,023 locations from the empty boundary and
the
PAF
threshold can be set at 127 or 1,023 locations from the
full boundary. These choices are made with the
LD
pin during
Master Reset.
For serial programming,
SEN
together with
LD
on each
rising edge of WCLK, are used to load the offset registers via
the Serial Input (SI). For parallel programming,
WEN
together
with
LD
on each rising edge of WCLK, are used to load the
offset registers via D
n
.
REN
together with
LD
on each rising
edge of RCLK can be used to read the offsets in parallel from
Q
n
regardless of whether serial or parallel offset loading has
been selected.
During Master Reset (
MRS
) the following events occur:
The read and write pointers are set to the first location of the
FIFO. The FWFT pin selects IDT Standard mode or FWFT
mode. The
LD
pin selects either a partial flag default setting
of 127 with parallel programming or a partial flag default
setting of 1,023 with serial programming. The flags are
updated according to the timing mode and default offsets
selected.
The Partial Reset (
PRS
) also sets the read and write
pointers to the first location of the memory. However, the
timing mode, partial flag programming method, and default or
programmed offset settings existing before Partial Reset
remain unchanged. The flags are updated according to the
timing mode and offsets in effect.
PRS
is useful for resetting
a device in mid-operation, when reprogramming partial flags
would be undesirable.
The Retransmit function allows data to be reread from the
FIFO more than once. A LOW on the
RT
input during a rising
RCLK edge initiates a retransmit operation by setting the read
pointer to the first location of the memory array.
If, at any time, the FIFO is not actively performing an
operation, the chip will automatically power down. Once in the
power down state, the standby supply current consumption is
minimized. Initiating any operation (by activating control
inputs) will immediately take the device out of the power down
state.
The IDT72255LA/72265LA are fabricated using IDT’s high
speed submicron CMOS technology.
PARTIAL RESET (
WRITE CLOCK (WCLK)
WRITE ENABLE (
LOAD (
)
)
)
MASTER RESET (
)
READ CLOCK (RCLK)
READ ENABLE (
OUTPUT ENABLE (
DATA OUT (Q
0
- Q
n
)
IDT
72255LA
72265LA
RETRANSMIT (
)
/
)
)
)
)
DATA IN (D
0
- D
n
)
SERIAL ENABLE(
)
FIRST WORD FALL THROUGH/SERIAL INPUT
(FWFT/SI)
FULL FLAG/INPUT READY (
PROGRAMMABLE ALMOST-FULL (
/ )
)
EMPTY FLAG/OUTPUT READY (
PROGRAMMABLE ALMOST-EMPTY (
HALF FULL FLAG (
)
4670 drw 03
Figure 1. Block Diagram of Single 8,192 x 18 and 16,384 x 18 Synchronous FIFO
3
IDT72255LA/72265LA SUPERSYNC FIFO™
8,192 x 18, 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
PIN DESCRIPTION
Symbol
D
0
–D
17
Name
Data Inputs
Master Reset
I/O
I
I
Description
Data inputs for a 18-bit bus.
MRS
initializes the read and write pointers to zero and sets the output register to
all zeroes. During Master Reset, the FIFO is configured for either FWFT or IDT
Standard mode, one of two programmable flag default settings, and serial or
parallel programming of the offset settings.
all zeroes. During Partial Reset, the existing mode (IDT or FWFT), programming
method (serial or parallel), and programmable flag settings are all retained.
RT
asserted on the rising edge of RCLK initializes the READ pointer to zero, sets
the
EF
flag to LOW (
OR
to HIGH in FWFT mode) temporarily and does not disturb
the write pointer, programming method, existing timing mode or programmable flag
settings.
RT
is useful to reread data from the first physical location of the FIFO.
During Master Reset, selects First Word Fall Through or IDT Standard mode.
After Master Reset, this pin functions as a serial input for loading offset registers
When enabled by
WEN
, the rising edge of WCLK writes data into the FIFO and
offsets into the programmable registers for parallel programming, and when
enabled by
SEN
, the rising edge of WCLK writes one bit of data into the
programmable register for serial programming.
WEN
enables WCLK for writing data into the FIFO memory and offset registers.
When enabled by
REN
, the rising edge of RCLK reads data from the FIFO
memory and offsets from the programmable registers.
REN
enables RCLK for reading data from the FIFO memory and offset registers.
OE
controls the output impedance of Q
n.
SEN
enables serial loading of programmable flag offsets.
During Master Reset,
LD
selects one of two partial flag default offsets (127 or
1,023) and determines the flag offset programming method, serial or parallel. After
Master Reset, this pin enables writing to and reading from the offset registers.
This pin must be tied to either V
CC
or GND and must not toggle after Master
Reset.
In the IDT Standard mode, the
FF
function is selected.
FF
indicates whether or
not the FIFO memory is full. In the FWFT mode, the
IR
function is selected.
IR
indicates whether or not there is space available for writing to the FIFO memory.
In the IDT Standard mode, the
EF
function is selected.
EF
indicates whether or
not the FIFO memory is empty. In FWFT mode, the
OR
function is selected.
OR
indicates whether or not there is valid data available at the outputs.
PAF
goes LOW if the number of words in the FIFO memory is more than
total word capacity of the FIFO minus the full offset value m, which is stored in the
Full Offset register. There are two possible default values for m: 127 or 1,023.
PAE
goes LOW if the number of words in the FIFO memory is less than offset n,
which is stored in the Empty Offset register. There are two possible default values
for n: 127 or 1,023. Other values for n can be programmed into the device.
HF
indicates whether the FIFO memory is more or less than half-full.
Data outputs for an 18-bit bus.
+5 Volt power supply pins.
Ground pins.
MRS
PRS
RT
Partial Reset
I
PRS
initializes the read and write pointers to zero and sets the output register to
Retransmit
I
FWFT/SI
WCLK
First Word Fall
Through/Serial In
Write Clock
I
I
WEN
RCLK
Write Enable
Read Clock
Read Enable
Output Enable
Serial Enable
Load
I
I
I
I
I
I
REN
OE
SEN
LD
DC
Don't Care
Full Flag/
Input Ready
Empty Flag/
Output Ready
Programmable
Almost-Full Flag
Programmable
Almost-Empty Flag
Half-Full Flag
Data Outputs
Power
Ground
I
O
FF
/
IR
EF
/
OR
PAF
PAE
HF
Q
0
–Q
17
V
CC
GND
O
O
O
O
O
4
IDT72255LA/72265LA SUPERSYNC FIFO™
8,192 x 18, 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
ABSOLUTE MAXIMUM RATINGS
Symbol
V
TERM
T
STG
I
OUT
Rating
Terminal Voltage
with respect to GND
Storage
Temperature
DC Output Current
Com’l & Ind’l
–0.5 to +7.0
–55 to +125
–50 to +50
Unit
V
°C
mA
RECOMMENDED DC OPERATING CONDITIONS
Symbol
Parameter
V
CC
Supply Voltage
Commercial/Industrial
GND
V
IH
V
IL(1)
T
A
T
A
Supply Voltage
Input High Voltage
Commercial/Industrial
Input Low Voltage
Commercial/Industrial
Operating Temperature
Commercial
Operating Temperature
Industrial
Min.
4.5
0
2.0
—
0
–40
Typ.
5.0
0
—
—
—
—
Max.
5.5
0
—
0.8
70
85
Unit
V
V
V
V
°C
°C
NOTE:
1. Stresses greater than those listed under ABSOLUTE MAXIMUM RAT-
INGS may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions
above those indicated in the operational sections of this specification is
not implied. Exposure to absolute maximum rating conditions for ex-
tended periods may affect reliability.
NOTE:
1. 1.5V undershoots are allowed for 10ns once per cycle.
DC ELECTRICAL CHARACTERISTICS
(Commercial: V
CC
= 5V
±
10%, T
A
= 0°C to +70°C; Industrial: V
CC
= 5V
±
10%, T
A
= –40°C to +85°C )
IDT72255LA
IDT72265LA
Commercial & Industrial
(1)
t
CLK
= 10, 15, 20 ns
Symbol
I
LI
I
LO
(3)
V
OH
V
OL
I
CC1
(4,5,6)
I
CC2
(4,7)
(2)
Parameter
Input Leakage Current
Output Leakage Current
Output Logic “1” Voltage, I
OH
= –2 mA
Output Logic “0” Voltage, I
OL
= 8 mA
Active Power Supply Current
Standby Current
Min.
–1
–10
2.4
—
—
—
Max.
1
10
—
0.4
80
20
Unit
µA
µA
V
V
mA
mA
NOTES
:
1. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device.
2. Measurements with 0.4
≤
V
IN
≤
V
CC
.
3.
OE
≥
V
IH,
0.4
≤
V
OUT
≤
V
CC.
4. Tested with outputs disabled (I
OUT
= 0).
5. RCLK and WCLK toggle at 20 MHz and data inputs switch at 10 MHz.
6. Typical I
CC1
= 15 + 2.1*f
S
+ 0.02*C
L
*f
S
(in mA) with V
CC
= 5V, t
A
= 25°C, f
S
= WCLK frequency = RCLK frequency (in MHz, using TTL levels),
data switching at f
S
/2, C
L
= capacitive load (in pF).
7. All Inputs = V
CC
- 0.2V or GND + 0.2V, except RCLK and WCLK, which toggle at 20 MHz.
CAPACITANCE
(T
A
= +25°C, f = 1.0MHz)
Symbol
C
IN
(2)
C
OUT
(1,2)
Parameter
(1)
Input
Capacitance
Output
Capacitance
Conditions
V
IN
= 0V
V
OUT
= 0V
Max.
10
10
Unit
pF
pF
NOTES:
1. With output deselected, (
OE
≥
V
IH
).
2. Characterized values, not currently tested.
5
电源技术
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
