CMOS SuperSync FIFO™
8,192 x 18
16,384 x 18
FEATURES
•
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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)
•
•
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IDT72255LA
IDT72265LA
Available in the 64-pin Thin Quad Flat Pack (TQFP) and the 64pin Slim Thin Quad Flat Pack (STQFP)
High-performance submicron CMOS technology
Industrial temperature range (–40°C to +85°C) is available
Green parts available, see ordering information
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 improvements 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.
• 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.)
FUNCTIONAL BLOCK DIAGRAM
WEN
D0 -D17
WCLK
INPUT REGISTER
L D SEN
OFFSET REGISTER
FLAG
LOGIC
WRITE CONTROL
LOGIC
RAM ARRAY
8,192 x 18
16,384 x 18
WRITE POINTER
F F /IR
PAF
EF /OR
P AE
HF
FWFT/SI
READ POINTER
READ
CONTROL
LOGIC
RT
OUTPUT REGISTER
MRS
P RS
RESET
LOGIC
RCLK
REN
OE
Q0 -Q17
IDT and the IDT logo are trademarks of Integrated Device Technology, Inc. SuperSync FIFO is a trademark of Integrated Device Technology, Inc
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
4670 drw01
OCTOBER 2005
1
2005 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice.
DSC-4670/2
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
DESCRIPTION (CONTINUED)
The frequencies of both the RCLK and the WCLK signals may vary from 0
to fMAX 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.
SuperSync FIFOs are particularly appropriate for networking, 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.
RCLK
REN
RT
OE
EF/OR
VCC
PAE
PAF
HF
FF/IR
LD
FWFT/SI
GND
MRS
WCLK
PRS
PIN CONFIGURATIONS
PIN 1
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
WEN
SEN
DC
VCC
GND
D17
D16
D15
D14
D13
D12
D11
D10
D9
D8
D7
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Q17
Q16
GND
Q15
Q14
VCC
Q13
Q12
Q11
GND
Q10
Q9
Q8
Q7
Q6
GND
Q1
GND
Q2
Q3
VCC
Q4
Q5
GND
Q0
D1
D0
D5
D4
D3
D2
D6
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
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TQFP (PN64-1, ORDER CODE: PF)
STQFP (PP64-1, ORDER CODE: TF)
TOP VIEW
NOTE:
1. DC = Don’t Care. Must be tied to GND or VCC, cannot be left open.
2
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
DESCRIPTION (CONTINUED)
programming, WEN together with LD on each rising edge of WCLK, are used
to load the offset registers via Dn. REN together with LD on each rising edge
of RCLK can be used to read the offsets in parallel from Qn 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.
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 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 AlmostEmpty flag) and PAF (Programmable 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 2.) Programmable 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
PARTIAL RESET (PRS)
MASTER RESET (MRS)
WRITE CLOCK (WCLK)
READ CLOCK (RCLK)
WRITE ENABLE (WEN)
READ ENABLE (REN)
OUTPUT ENABLE (OE)
LOAD (LD)
DATA OUT (Q0 - Qn)
DATA IN (D0 - Dn)
SERIAL ENABLE(SEN)
FIRST WORD FALL THROUGH/SERIAL INPUT
(FWFT/SI)
IDT
72255LA
72265LA
RETRANSMIT (RT)
EMPTY FLAG/OUTPUT READY (EF/OR)
PROGRAMMABLE ALMOST-EMPTY (PAE)
FULL FLAG/INPUT READY (FF/IR)
HALF FULL FLAG (HF)
PROGRAMMABLE ALMOST-FULL (PAF)
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Figure 1. Block Diagram of Single 8,192 x 18 and 16,384 x 18 Synchronous FIFO
3
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
PIN DESCRIPTION
Symbol
Name
I/O
Description
D0–D17
MRS
Data Inputs
Master Reset
I
I
PRS
Partial Reset
I
RT
Retransmit
I
FWFT/SI
First Word Fall
Through/Serial In
I
WCLK
Write Clock
I
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
RCLK
Write Enable
Read Clock
I
I
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
OE
Read Enable
Output Enable
I
I
REN enables RCLK for reading data from the FIFO memory and offset registers.
OE controls the output impedance of Qn.
SEN
LD
Serial Enable
Load
I
I
DC
Don't Care
I
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 VCC or GND and must not toggle after Master Reset.
FF/IR
Full Flag/
Input Ready
O
EF/OR
Empty Flag/
Output Ready
O
PAF
Programmable
Almost-Full Flag
O
PAE
Programmable
Almost-Empty Flag
O
HF
Half-Full Flag
O
Q0–Q17
V CC
Data Outputs
Power
O
GND
Ground
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 program
mable flag default settings, and serial or parallel programming of the offset settings.
PRS initializes the read and write pointers to zero and sets the output register to 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.
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.
4
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
ABSOLUTE MAXIMUM RATINGS
Symbol
VTERM
Rating
Terminal Voltage
with respect to GND
Com’l & Ind’l
–0.5 to +7.0
Unit
V
TSTG
Storage
Temperature
–55 to +125
°C
IOUT
DC Output Current
–50 to +50
mA
RECOMMENDED DC OPERATING
CONDITIONS
Symbol
NOTE:
1. Stresses greater than those listed under ABSOLUTE MAXIMUM RATINGS 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 extended periods may affect reliability.
Parameter
Min.
Typ.
Max.
Unit
VCC
Supply Voltage (Com’l/Ind’l)
4.0
5.0
5.5
V
GND
Supply Voltage (Com’l/Ind’l)
0
0
0
V
VIH
Input High Voltage (Com’l/Ind’l)
2.0
—
V
VIL(1)
Input Low Voltage (Com’l/Ind’l)
0.8
V
TA
Operating Temperature
Commercial
0
+70
°C
TA
Operating Temperature
Industrial
-40
+85
°C
NOTE:
1. 1.5V undershoots are allowed for 10ns once per cycle.
DC ELECTRICAL CHARACTERISTICS
(Commercial: VCC = 5V ± 10%, TA = 0°C to +70°C; Industrial: VCC = 5V ± 10%, TA = -40°C to +85°C)
IDT72255LA
IDT72265LA
Commercial & Industrial(1)
tCLK = 10, 15, 20 ns
Symbol
Parameter
Min.
Max.
Unit
ILI(2)
ILO(3)
Input Leakage Current
Output Leakage Current
–1
–10
1
10
µA
µA
VOH
VOL
Output Logic “1” Voltage, IOH = –2 mA
Output Logic “0” Voltage, IOL = 8 mA
2.4
—
—
0.4
V
V
ICC1(4,5,6)
Active Power Supply Current
—
80
mA
ICC2(4,7)
Standby Current
—
20
mA
NOTES:
1. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device.
2. Measurements with 0.4 ≤ VIN ≤ VCC.
3. OE ≥ VIH, 0.4 ≤ VOUT ≤ VCC.
4. Tested with outputs disabled (IOUT = 0).
5. RCLK and WCLK toggle at 20 MHz and data inputs switch at 10 MHz.
6. Typical ICC1 = 15 + 2.1*f S + 0.02*C L*fS (in mA) with V CC = 5V, TA = 25°C, fS = WCLK frequency = RCLK frequency (in MHz, using TTL levels), data
switching at fS/2, CL = capacitive load (in pF).
7. All Inputs = VCC –0.2V or GND + 0.2V, except RCLK and WCLK, which toggle at 20 MHz.
CAPACITANCE
(TA = +25°C, f = 1.0MHz)
Symbol
Parameter(1)
Conditions
Max.
Unit
(2)
CIN
Input
Capacitance
VIN = 0V
10
pF
COUT(1,2)
Output
Capacitance
VOUT = 0V
10
pF
NOTES:
1. With output deselected, (OE ≥ VIH).
2. Characterized values, not currently tested.
5
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS(1)
(Commercial: VCC = 5V ± 10%, TA = 0°C to +70°C; Industrial: VCC = 5V ± 10%, TA = –40°C to +85°C)
Commercial
IDT72255LA10
IDT72265LA10
Symbol
Parameter
Commercial & Industrial(2)
IDT72255LA15
IDT72255LA20
IDT72265LA15
IDT72265LA20
Min.
Max.
Min.
Max.
Min.
Max.
Unit
fS
Clock Cycle Frequency
—
100
—
66.7
—
50
MHz
tA
Data Access Time
2
8
2
10
2
12
ns
tCLK
Clock Cycle Time
10
—
15
—
20
—
ns
tCLKH
Clock High Time
4.5
—
6
—
8
—
ns
tCLKL
Clock Low Time
4.5
—
6
—
8
—
ns
tDS
Data Setup Time
3
—
4
—
5
—
ns
tDH
Data Hold Time
0
—
1
—
1
—
ns
tENS
Enable Setup Time
3
—
4
—
5
—
ns
tENH
Enable Hold Time
0
—
1
—
1
—
ns
tLDS
Load Setup Time
3
—
4
—
5
—
ns
tLDH
Load Hold Time
0
—
1
—
1
—
ns
10
—
15
—
20
—
ns
(3)
tRS
Reset Pulse Width
tRSS
Reset Setup Time
10
—
15
—
20
—
ns
tRSR
Reset Recovery Time
10
—
15
—
20
—
ns
tRSF
Reset to Flag and Output Time
—
10
—
15
—
20
ns
tFWFT
Mode Select Time
0
—
0
—
0
—
ns
tRTS
Retransmit Setup Time
3
—
4
—
5
—
ns
tOLZ
Output Enable to Output in Low Z(4)
0
—
0
—
0
—
ns
tOE
Output Enable to Output Valid
2
6
3
8
3
10
ns
tOHZ
Output Enable to Output in High Z(4)
2
6
3
8
3
10
ns
tWFF
Write Clock to FF or IR
—
8
—
10
—
12
ns
tREF
Read Clock to EF or OR
—
8
—
10
—
12
ns
tPAF
Write Clock to PAF
—
8
—
10
—
12
ns
tPAE
Read Clock to PAE
—
8
—
10
—
12
ns
tHF
Clock to HF
—
16
—
20
—
22
ns
tSKEW1
Skew time between RCLK and WCLK for FF/IR
5
—
6
—
10
—
ns
tSKEW2
Skew time between RCLK and WCLK for PAE and PAF
12
—
15
—
20
—
ns
tSKEW3
Skew time between RCLK and WCLK for EF/OR
60
—
60
—
60
—
ns
tSKEW4
Skew time between RCLK and WCLK for PAE and PAF
for Re-transmit operation
15
—
17
—
25
—
ns
NOTES:
1. All AC timings apply to both Standard IDT mode and First Word Fall Through mode.
2. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device.
3. Pulse widths less than minimum values are not allowed.
4. Values guaranteed by design, not currently tested.
5V
1.1K
D.U.T.
AC TEST CONDITIONS
Input Pulse Levels
Input Rise/Fall Times
Input Timing Reference Levels
Output Reference Levels
Output Load
680Ω
GND to 3.0V
3ns
1.5V
1.5V
See Figure 2
30pF*
4670 drw04
Figure 2. Output Load
* Includes jig and scope capacitances.
6
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
FUNCTIONAL DESCRIPTION
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.
TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH
(FWFT) MODE
The IDT72255LA/72265LA 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 Enable (REN) and RCLK.
Various signals, both input and output signals operate differently depending on which timing mode is in effect.
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 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 PAF to go LOW. Again, if no reads are performed, the PAF 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.
When the FIFO is full, the Input Ready (IR) flag will go HIGH, inhibiting
further write operations. If no reads are performed after a reset, IR will go
HIGH after D writes to the FIFO. D = 8,193 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.
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 registerbuffered, and the IR flag output is double register-buffered.
Relevant timing diagrams for FWFT mode can be found in Figure 9, 10
and 12.
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 Programmable 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.
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 4,097th word for 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 (PAF) to go LOW.
Again, if no reads are performed, the PAF will go 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.
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 = 8,192 writes for the IDT72255LA and
16,384 for the IDT72265LA, respectively.
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PROGRAMMING FLAG OFFSETS
Full and Empty Flag offset values are user programmable. The
IDT72255LA/72265LA has internal registers for these offsets. Default settings are stated in the footnotes of Table 1 and Table 2. Offset values can be
programmed into the FIFO in one of two ways; serial or parallel loading
method. The selection of the loading method is done using the LD (Load)
pin. During Master Reset, the state of the LD input determines whether
serial or parallel flag offset programming is enabled. A HIGH on LD during
Master Reset selects serial loading of offset values and in addition, sets a
default PAE offset value of 3FFH (a threshold 1,023 words from the empty
boundary), and a default PAF offset value of 3FFH (a threshold 1,023
words from the full boundary). A LOW on LD during Master Reset selects
parallel loading of offset values, and in addition, sets a default PAE offset
value of 07FH (a threshold 127 words from the empty boundary), and a
default PAF offset value of 07FH (a threshold 127 words from the full
boundary). See Figure 3, Offset Register Location and Default Values.
In addition to loading offset values into the FIFO, it also possible to read
the current offset values. It is only possible to read offset values via parallel
read.
Figure 4, Programmable Flag Offset Programming Sequence, summarizes the control pins and sequence for both serial and parallel programming modes. For a more detailed description, see discussion that follows.
The offset registers may be programmed (and reprogrammed) any time
after Master Reset, regardless of whether serial or parallel programming
has been selected.
TABLE 1 — STATUS FLAGS FOR IDT STANDARD MODE
Number of
Words in
FIFO
FF PAF
HF
H
H
PAE EF
IDT72255LA
IDT72265LA
0
0
1 to n (1)
1 to n (1)
H
H
H
L
H
(n + 1) to 4,096
(n + 1) to 8,192
H
H
H
H
H
4,097 to (8,192–(m+1))
8,193 to (16,384–(m+1))
H
H
L
H
H
(8,192–m)(2) to 8,191
(16,384–m) (2) to 16,383
H
L
L
H
H
8,192
16,384
L
L
L
H
H
H
L
L
NOTES:
1. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n = 1,023 when serial offset loading is selected.
2. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or m = 1,023 when serial offset loading is selected.
TABLE 2 — STATUS FLAGS FOR FWFT MODE
Number of
Words in
FIFO (1)
FF PAF
HF
L
H
PAE EF
IDT72255LA
IDT72265LA
0
0
1 to n+1 (1)
1 to n+1 (1)
L
H
H
L
L
(n + 2) to 4,097
(n + 2) to 8,193
L
H
H
H
L
4,098 to (8,193–(m+1))(2)
8,194 to (16,385–(m+1)) (2)
L
H
L
H
L
(8,193–m) to 8,192
(16,385–m) (2) to 16,384
L
L
L
H
L
8,193
16,385
H
L
L
H
L
H
L
H
NOTES:
1. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n = 1,023 when serial offset loading is selected.
2. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or m = 1,023 when serial offset loading is selected.
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COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
72255LA — 8,192 x 18–BIT
72265LA — 16,384 x 18–BIT
12
17
0
13
17
0
EMPTY OFFSET REGISTER
EMPTY OFFSET REGISTER
DEFAULT VALUE
07FH if LD is LOW at Master Reset,
3FFH if LD is HIGH at Master Reset
17
DEFAULT VALUE
07FH if LD is LOW at Master Reset,
3FFH if LD is HIGH at Master Reset
0
12
17
0
13
FULL OFFSET REGISTER
FULL OFFSET REGISTER
DEFAULT VALUE
07FH if LD is LOW at Master Reset,
3FFH if LD is HIGH at Master Reset
DEFAULT VALUE
07FH if LD is LOW at Master Reset,
3FFH if LD is HIGH at Master Reset
4670 drw06
Figure 3. Offset Register Location and Default Values
LD
WEN
REN
SEN
0
0
1
1
0
1
0
1
0
1
1
0
X
1
1
1
1
0
X
X
1
X
0
X
X
1
1
1
X
X
WCLK
Selection
RCLK
X
Parallel write to registers:
Empty Offset
Full Offset
Parallel read from registers:
Empty Offset
Full Offset
X
X
X
Serial shift into registers:
26 bits for the 72255LA
28 bits for the 72265LA
1 bit for each rising WCLK edge
Starting with Empty Offset (LSB)
Ending with Full Offset (MSB)
X
No Operation
X
Write Memory
Read Memory
X
No Operation
4670 drw07
NOTES:
1. The programming method can only be selected at Master Reset.
2. Parallel reading of the offset registers is always permitted regardless of which programming method has been selected.
3. The programming sequence applies to both IDT Standard and FWFT modes.
Figure 4. Programmable Flag Offset Programming Sequence
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alternative to holding WEN LOW and toggling LD, parallel programming
can also be interrupted by setting LD LOW and toggling WEN.
Note that the status of a partial flag (PAE or PAF) output is invalid during the programming process. From the time parallel programming has
begun, a partial flag output will not be valid until the appropriate offset word
has been written to the register(s) pertaining to that flag. Measuring from
the rising WCLK edge that achieves the above criteria; PAF will be valid
after two more rising WCLK edges plus tPAF, PAE will be valid after the
next two rising RCLK edges plus tPAE plus tSKEW2.
The act of reading the offset registers employs a dedicated read offset
register pointer. The contents of the offset registers can be read on the Q0Qn pins when LD is set LOW and REN is set LOW. Data are read via Qn
from the Empty Offset Register on the first LOW-to-HIGH transition of RCLK.
Upon the second LOW-to-HIGH transition of RCLK, data are read from the
Full Offset Register. The third transition of RCLK reads, once again, from
the Empty Offset Register. See Figure 15, Parallel Read of Programmable
Flag Registers, for the timing diagram for this mode.
It is permissible to interrupt the offset register read sequence with reads
or writes to the FIFO. The interruption is accomplished by deasserting REN,
LD, or both together. When REN and LD are restored to a LOW level,
reading of the offset registers continues where it left off. It should be noted,
and care should be taken from the fact that when a parallel read of the flag
offsets is performed, the data word that was present on the output lines Qn
will be overwritten.
Parallel reading of the offset registers is always permitted regardless of
which timing mode (IDT Standard or FWFT modes) has been selected.
SERIAL PROGRAMMING MODE
If Serial Programming mode has been selected, as described above, then
programming of PAE and PAF values can be achieved by using a combination of the LD, SEN, WCLK and SI input pins. Programming PAE and
PAF proceeds as follows: when LD and SEN are set LOW, data on the
SI input are written, one bit for each WCLK rising edge, starting with the
Empty Offset LSB and ending with the Full Offset MSB. A total of 26 bits for
the IDT72255LA and 28 bits for the IDT72265LA. See Figure 13, Serial
Loading of Programmable Flag Registers, for the timing diagram for this
mode.
Using the serial method, individual registers cannot be programmed selectively. PAE and PAF can show a valid status only after the complete
set of bits (for all offset registers) has been entered. The registers can be
reprogrammed as long as the complete set of new offset bits is entered.
When LD is LOW and SEN is HIGH, no serial write to the registers can
occur.
Write operations to the FIFO are allowed before and during the serial
programming sequence. In this case, the programming of all offset bits does
not have to occur at once. A select number of bits can be written to the SI
input and then, by bringing LD and SEN HIGH, data can be written to
FIFO memory via Dn by toggling WEN. When WEN is brought HIGH with
LD and SEN restored to a LOW, the next offset bit in sequence is written to
the registers via SI. If an interruption of serial programming is desired, it is
sufficient either to set LD LOW and deactivate SEN or to set SEN LOW
and deactivate LD. Once LD and SEN are both restored to a LOW level,
serial offset programming continues.
From the time serial programming has begun, neither partial flag will be
valid until the full set of bits required to fill all the offset registers has been
written. Measuring from the rising WCLK edge that achieves the above
criteria; PAF will be valid after two more rising WCLK edges plus tPAF,
PAE will be valid after the next two rising RCLK edges plus tPAE plus
tSKEW2.
It is not possible to read the flag offset values in a serial mode.
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
beginning 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 = 8,192 for the IDT72255LA and D = 16,384 for the IDT72265LA. In
FWFT mode, D = 8,193 for the IDT72255LA and D = 16,385 for the
IDT72265LA.
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 operations may begin starting with the first location in memory. Since IDT Standard 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
PARALLEL MODE
If Parallel Programming mode has been selected, as described above,
then programming of PAE and PAF values can be achieved by using a
combination of the LD, WCLK , WEN and Dn input pins. ProgrammingPAE
and PAF proceeds as follows: when LD and WEN are set LOW, data on
the inputs Dn are written into the Empty Offset Register on the first LOW-toHIGH transition of WCLK. Upon the second LOW-to-HIGH transition of WCLK,
data are written into the Full Offset Register. The third transition of WCLK
writes, once again, to the Empty Offset Register. See Figure 14, Parallel
Loading of Programmable Flag Registers, for the timing diagram for this
mode.
The act of writing offsets in parallel employs a dedicated write offset
register pointer. The act of reading offsets employs a dedicated read offset
register pointer. The two pointers operate independently; however, a read
and a write should not be performed simultaneously to the offset registers.
A Master Reset initializes both pointers to the Empty Offset (LSB) register.
A Partial Reset has no effect on the position of these pointers.
Write operations to the FIFO are allowed before and during the parallel
programming sequence. In this case, the programming of all offset
registers does not have to occur at one time. One, two or more offset registers can be written and then by bringing LD HIGH, write operations can
be redirected to the FIFO memory. When LD is set LOW again, and WEN
is LOW, the next offset register in sequence is written to. As an
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8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
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 synchronized 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.
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
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COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
SIGNAL DESCRIPTION
the read pointer to the first location of memory, then the actual retransmit,
which consists of reading out the memory contents, starting at beginning of
the memory.
Retransmit setup is initiated by holding RT LOW during a rising RCLK
edge. REN and WEN must be HIGH before bringing RT LOW.
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 operations
may begin starting with the first location in memory. Since IDT Standard
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.
INPUTS:
DATA IN (D0 - D17)
Data inputs for 18-bit wide data.
CONTROLS:
MASTER RESET (MRS)
A Master Reset is accomplished whenever the MRS input is taken to a
LOW state. This operation sets the internal read and write pointers to the first
location of the RAM array. PAE will go LOW, PAF will go HIGH, and HF
will go HIGH.
If FWFT is LOW during Master Reset then the IDT Standard mode,
along with EF and FF are selected. EF will go LOW and FF will go HIGH. If
FWFT is HIGH, then the First Word Fall Through mode (FWFT), along with
IR and OR, are selected. OR will go HIGH and IR will go LOW.
If LD is LOW during Master Reset, then PAE is assigned a threshold 127
words from the empty boundary and PAF is assigned a threshold 127
words from the full boundary; 127 words corresponds to an offset value of
07FH. Following Master Reset, parallel loading of the offsets is permitted,
but not serial loading.
If LD is HIGH during Master Reset, then PAE is assigned a threshold
1,023 words from the empty boundary and PAF is assigned a threshold
1,023 words from the full boundary; 1,023 words corresponds to an offset
value of 3FFH. Following Master Reset, serial loading of the offsets is
permitted, but not parallel loading.
Parallel reading of the registers is always permitted. (See section
describing the LD pin for further details.)
During a Master Reset, the output register is initialized to all zeroes. A
Master Reset is required after power up, before a write operation can take
place. MRS is asynchronous.
See Figure 5, Master Reset Timing, for the relevant timing diagram.
FIRST WORD FALL THROUGH/SERIAL IN (FWFT/SI)
This is a dual purpose pin. During Master Reset, the state of the FWFT/
SI input determines whether the device will operate in IDT Standard mode
or First Word Fall Through (FWFT) mode.
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 memory. It also uses the
Full Flag function (FF) to indicate whether or not the FIFO memory 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 memory 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 Enable (REN) and RCLK.
After Master Reset, FWFT/SI acts as a serial input for loading PAE and
PAF offsets into the programmable registers. The serial input function can
only be used when the serial loading method has been selected during
Master Reset. Serial programming using the FWFT/SI pin functions the
same way in both IDT Standard and FWFT modes.
PARTIAL RESET (PRS)
A Partial Reset is accomplished whenever the PRS input is taken to a
LOW state. As in the case of the Master Reset, the internal read and write
pointers are set to the first location of the RAM array, PAE goes LOW, PAF
goes HIGH, and HF goes HIGH.
Whichever mode is active at the time of Partial Reset, IDT Standard mode
or First Word Fall Through, that mode will remain selected. If the IDT
Standard mode is active, then FF will go HIGH and EF will go LOW. If the
First Word Fall Through mode is active, then OR will go HIGH, and IR will
go LOW.
Following Partial Reset, all values held in the offset registers remain
unchanged. The programming method (parallel or serial) currently active
at the time of Partial Reset is also retained. The output register is initialized
to all zeroes. PRS is asynchronous.
A Partial Reset is useful for resetting the device during the course of
operation, when reprogramming partial flag offset settings may not be
convenient.
See Figure 6, Partial Reset Timing, for the relevant timing diagram.
WRITE CLOCK (WCLK)
A write cycle is initiated on the rising edge of the WCLK input. Data setup
and hold times must be met with respect to the LOW-to-HIGH transition of the
WCLK. It is permissible to stop the WCLK. Note that while WCLK is idle, the
FF/IR, PAF and HF flags will not be updated. (Note that WCLK is only
capable of updating HF flag to LOW). The Write and Read Clocks can
either be independent or coincident.
RETRANSMIT (RT)
The Retransmit operation allows data that has already been read to be
accessed again. There are two stages: first, a setup procedure that resets
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WRITE ENABLE (WEN)
When the WEN input is LOW, data may be loaded into the FIFO RAM
array on the rising edge of every WCLK cycle if the device is not full. Data
is stored in the RAM array sequentially and independently of any ongoing
read operation.
When WEN is HIGH, no new data is written in the RAM array on each
WCLK cycle.
To prevent data overflow in the IDT Standard mode, FF will go LOW,
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 + tSKEW after the RCLK cycle.
To prevent data overflow in the FWFT mode, IR will go HIGH, inhibiting
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 + tSKEW after the valid RCLK cycle.
WEN is ignored when the FIFO is full in either FWFT or IDT Standard
mode.
OUTPUT ENABLE (OE)
When Output Enable is enabled (LOW), the parallel output buffers
receive data from the output register. When OE is HIGH, the output data
bus (Qn) goes into a high impedance state.
LOAD (LD)
This is a dual purpose pin. During Master Reset, the state of the LD
input 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 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.
After Master Reset, the LD pin is used to activate the programming
process 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.
READ CLOCK (RCLK)
A read cycle is initiated on the rising edge of the RCLK input. Data can
be 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.
OUTPUTS:
READ ENABLE (REN)
When Read Enable is LOW, data is loaded from the RAM array into the
output register on the rising edge of every RCLK cycle if the device is not
empty.
When the REN input is HIGH, the output register holds the previous data
and no new data is loaded into the output register. The data outputs Q0-Qn
maintain the previous data value.
In the IDT Standard mode, every word accessed at Qn, including the first
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 + tSKEW after the valid WCLK cycle.
In the FWFT mode, the first word written to an empty FIFO automatically
goes to the outputs Qn, on the third valid LOW to HIGH transition of RCLK +
tSKEW 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.
FULL FLAG (FF/IR)
This is a dual purpose pin. In IDT Standard mode, the Full Flag (FF)
function 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 = 8,192 for the IDT72255LA and 16,384 for the
IDT72265LA). See Figure 7, Write Cycle and Full Flag Timing (IDT Standard Mode), for the relevant timing information.
In FWFT mode, the Input Ready (IR) function is selected. IR goes LOW
when 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 = 8,193 for the IDT72255LA and 16,385
for the IDT72265LA) See Figure 9, Write Timing (FWFT Mode), for the
relevant timing information.
The IR status not only measures the contents of the FIFO memory, but
also 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.
FF/IR is synchronous and updated on the rising edge of WCLK. FF/IR
are double register-buffered outputs.
SERIAL ENABLE (SEN)
The SEN input is an enable used only for serial programming of the
offset 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.)
When SEN is HIGH, the programmable registers retains the previous
settings and no offsets are loaded. SEN functions the same way in both IDT
Standard and FWFT modes.
EMPTY FLAG (EF/OR)
This is a dual purpose pin. In the IDT Standard mode, the Empty Flag
(EF) 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.
In FWFT mode, the Output Ready (OR) function is selected. OR goes
LOW 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
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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.
EF/OR is synchronous and updated on the rising edge of RCLK.
In IDT Standard mode, EF is a double register-buffered output. In FWFT
mode, OR is a triple register-buffered output.
LOW when there are n words or less in the FIFO. The offset “n” is the
empty offset value. The default setting for this value is stated in the footnote
of Table 1.
In FWFT mode, the PAE will go LOW when there are n+1 words or less
in the FIFO. The default setting for this value is stated in the footnote of
Table 2.
See Figure 17, Programmable Almost-Empty Flag Timing (IDT Standard and FWFT Mode), for the relevant timing information.
PAE is synchronous and updated on the rising edge of RCLK.
PROGRAMMABLE ALMOST-FULL FLAG (PAF)
The Programmable Almost-Full flag (PAF) will go LOW when the FIFO
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 (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.
In FWFT mode, the PAF 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.
See Figure 16, Programmable Almost-Full Flag Timing (IDT Standard
and FWFT Mode), for the relevant timing information.
PAF is synchronous and updated on the rising edge of WCLK.
HALF-FULL FLAG (HF)
This output indicates a half-full FIFO. The rising WCLK edge that fills the
FIFO beyond half-full sets HF LOW. The flag remains LOW until the difference between the write and read pointers becomes less than or equal to
half of the total depth of the device; the rising RCLK edge that accomplishes
this condition sets HF HIGH.
In IDT Standard mode, if no reads are performed after reset (MRS or
PRS), HF will go LOW after (D/2 + 1) writes to the FIFO, where D = 8,192
for the IDT72255LA and 16,384 for the IDT72265LA.
In FWFT mode, if no reads are performed after reset (MRS or PRS), HF
will go LOW after (D-1/2 + 2) writes to the FIFO, where D = 8,193 for the
IDT72255LA and 16,385 for the IDT72265LA.
See Figure 18, Half-Full Flag Timing (IDT Standard and FWFT Modes),
for the relevant timing information. Because HF is updated by both RCLK
and WCLK, it is considered asynchronous.
PROGRAMMABLE ALMOST-EMPTY FLAG (PAE)
The Programmable Almost-Empty flag (PAE) will go LOW when the FIFO
reaches the almost-empty condition. In IDT Standard mode, PAE will go
DATA OUTPUTS (Q0-Q17)
(Q0 - Q17) are data outputs for 18-bit wide data.
14
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
tRS
MRS
tRSS
tRSR
tRSS
tRSR
REN
WEN
tRSR
tFWFT
FWFT/SI
tRSS
tRSR
LD
tRSS
RT
tRSS
SEN
If FWFT = HIGH, OR = HIGH
tRSF
EF/OR
If FWFT = LOW, EF = LOW
tRSF
If FWFT = LOW, FF = HIGH
FF/IR
If FWFT = HIGH, IR = LOW
tRSF
PAE
tRSF
PAF, HF
tRSF
OE = HIGH
Q0 - Qn
OE = LOW
4670 drw08
Figure 5. Master Reset Timing
15
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
PRS
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
tRS
tRSS
tRSR
tRSS
tRSR
REN
WEN
tRSS
RT
tRSS
SEN
If FWFT = HIGH, OR = HIGH
tRSF
EF/OR
If FWFT = LOW, EF = LOW
If FWFT = LOW, FF = HIGH
tRSF
FF/IR
If FWFT = HIGH, IR = LOW
tRSF
PAE
tRSF
PAF, HF
tRSF
OE = HIGH
Q0 - Qn
OE = LOW
4670 drw09
Figure 6. Partial Reset Timing
16
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
tCLK
tCLKH
NO WRITE
WCLK
tSKEW1
NO WRITE
tCLKL
2
1
1
(1)
(1)
tDS
D0 - Dn
2
tSKEW1
tDH
tDS
tDH
DX
DX+1
tWFF
tWFF
tWFF
tWFF
FF
WEN
RCLK
tENS
tENS
tENH
tENH
REN
tA
Q0 - Qn
tA
DATA IN OUTPUT REGISTER
DATA READ
NEXT DATA READ
4670 drw10
NOTES:
1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that FF will go high (after one WCLK cycle pus tWFF). If the time between the
rising edge of the RCLK and the rising edge of the WCLK is less than tSKEW1, then the FF deassertion may be delayed one extra WCLK cycle.
2. LD = HIGH, OE = LOW, EF = HIGH
Figure 7. Write Cycle and Full Flag Timing (IDT Standard Mode)
tCLK
tCLKH
RCLK
1
tENS
tCLKL
2
tENH
tENS
tENH
tENH
tENS
NO OPERATION
NO OPERATION
tREF
tREF
tREF
tA
tA
Q0 - Qn
LAST WORD
tOLZ
LAST WORD
tA
D0
D1
tOLZ
tOHZ
tOE
(1)
tSKEW3
WCLK
tENS
tDS
D0 - Dn
D0
tENH
tENS
tENH
tDHS
tDS
tDH
D1
4670 drw 11
NOTES:
1. tSKEW3 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that EF will go HIGH (after one RCLK cycle plus tREF). If the time between the
rising edge of WCLK and the rising edge of RCLK is less than tSKEW3, then EF deassertion may be delayed one extra RCLK cycle.
2. LD = HIGH.
3. First word latency: 60ns + tREF + 1*TRCLK.
Figure 8. Read Cycle, Empty Flag and First Data Word Latency Timing (IDT Standard Mode)
17
OCTOBER 17, 2005
18
tDS
W1
tENS
W2
2
DATA IN OUTPUT REGISTER
1
tSKEW3(1)
tDH
W3
3
tREF
tA
W4
tDS
W1
W[n +2]
W[n+3]
1
tPAE
tSKEW2(2)
2
W[n+4]
W[
D-1
]
tDS
W[
D-1
]
tHF
W[
D-1
]
W[D-m-2]
tDS
W[D-m-1]
W[D-m]
1
tPAF
W[D-m+1]
W[D-m+2]
W[D-1]
WD
4670 drw 12
tWFF
tENH
Figure 9. Write Timing (First Word Fall Through Mode)
NOTES:
1. tSKEW3 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that OR will go LOW after two RCLK cycles plus tREF. If the time between the rising edge of WCLK and the rising edge of RCLK is
less than tSKEW3, then OR assertion may be delayed one extra RCLK cycle.
2. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that PAE will go HIGH after one RCLK cycle plus tPAE. If the time between the rising edge of WCLK and the rising edge of RCLK is
less than tSKEW2, then the PAE deassertion may be delayed one extra RCLK cycle.
3. LD = HIGH, OE = LOW
4. n = PAE offset, m = PAF offset and D = maximum FIFO depth.
5. D = 8,193 for IDT72255LA and 16,385 for IDT72265LA.
6. First word latency: 60ns + tREF + 2*TRCLK.
Q0 - Q17
RCLK
D0 - D17
WCLK
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
OCTOBER 17, 2005
19
W1
tOHZ
tWFF
tENS
tDH
tDS
WD
tENH
tENS
W1
tOE
tA
W2
1
(1)
tSKEW1
tA
2
tWFF
W3
Wm+2
(2)
tSKEW2
W[m+3]
tA
tPAF
W[m+4]
W[
D-1
]
tHF
W[
tA
D-1
]
W[D-n-1]
tA
W[D-n]
1
tPAE
W[D-n+1]
W[D-n+2]
W[D-1]
tA
tENS
WD
4670 drw 13
tREF
Figure 10. Read Timing (First Word Fall Through Mode)
NOTES:
1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that IR will go LOW after one WCLK cycle plus tWFF. If the time between the rising edge of RCLK and the rising edge of WCLK
is less than tSKEW1, then the IR assertion may be delayed one extra WCLK cycle.
2. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that PAF will go HIGH after one WCLK cycle plus tPAF. If the time between the rising edge of RCLK and the rising edge of WCLK
is less than tSKEW2, then the PAF deassertion may be delayed one extra WCLK cycle.
3. LD = HIGH
4. n = PAE Offset, m = PAF offset and D = maximum FIFO depth.
5. D = 8,193 for IDT72255LA and 16,385 for IDT72265LA.
Q0 - Q17
RCLK
D0 - D17
WCLK
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
RCLK
1
tENS
tENH
2
tENS
tRTS
tENH
REN
tA
Q0 - Qn
tA
Wx
tA
Wx+1
W1
(3)
W2
(3)
tSKEW4
1
WCLK
2
tRTS
WEN
tENS
tENH
RT
tREF
tREF
(5)
EF
tPAE
PAE
tHF
HF
tPAF
PAF
4670 drw 14
NOTES:
1. Retransmit setup is complete after EF returns HIGH, only then can a read operation begin.
2. OE = LOW.
3. W1 = first word written to the FIFO after Master Reset, W2 = second word written to the FIFO after Master Reset.
4. No more than D –2 may be written to the FIFO between Reset (Master or Partial) and Retransmit setup. Therefore, FF will be HIGH throughout the Retransmit setup procedure.
D = 8,192 for IDT72255LA and 16,384 for IDT72265LA.
5. EF goes HIGH at 60 ns + 1 RCLK cycle + tREF.
Figure 11. Retransmit Timing (IDT Standard Mode)
20
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
RCLK
1
tENH
tENS
3
2
4
tENH
tENH
tRTS
REN
tA
tA
Q0 - Qn
Wx
Wx+1
W1
(4)
W2
W3
tSKEW4
1
WCLK
2
tRTS
WEN
tENS
tENH
RT
tREF
tREF
(5)
OR
tPAE
PAE
tHF
HF
tPAF
PAF
4670 drw15
NOTES:
1. Retransmit setup is complete after OR returns LOW.
2. No more than D –2 words may be written to the FIFO between Reset (Master or Partial) and Retransmit setup. Therefore, IR will be LOW throughout the Retransmit setup
procedure. D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA.
3. OE = LOW
4. W1, W2, W3 = first, second and third words written to the FIFO after Master Reset.
5. OR goes LOW at 60 ns + 2 RCLK cycles + tREF.
Figure 12. Retransmit Timing (FWFT Mode)
WCLK
tENS
tLDS
tENH
tENH
tLDH
tLDH
tDH
tDS
SI
BIT 0
BIT X
EMPTY OFFSET
(1)
BIT 0
BIT X
FULL OFFSET
(1)
4670 drw 16
NOTE:
1. X = 12 for the IDT72255LA and X = 13 for the IDT72265LA.
Figure 13. Serial Loading of Programmable Flag Registers (IDT Standard and FWFT Modes)
21
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
t CLK
t CLKH
t CLKL
WCLK
t LDS
t LDH
t LDH
t ENS
t ENH
tENH
t DS
tDH
t DH
PAE
OFFSET
D0 - D15
PAF
OFFSET
4670 drw 17
Figure 14. Parallel Loading of Programmable Flag Registers (IDT Standard and FWFT Modes)
t CLK
t CLKH
t CLKL
RCLK
t LDS
t LDH
t ENS
t LDH
t ENH
t ENH
tA
tA
DATA IN OUTPUT
REGISTER
Q0 - Q15
PAE
OFFSET
PAF
OFFSET
4670 drw 18
NOTE:
1. OE = LOW
Figure 15. Parallel Read of Programmable Flag Registers (IDT Standard and FWFT Modes)
t CLKH
t CLKL
WCLK
1
tENS
1
2
2
tENH
tPAF
D - (m+1) words in FIFO
tPAF
(2)
D - m words in FIFO
(2)
(3)
D-(m+1) words
in FIFO(2)
t SKEW2
RCLK
tENS
tENH
4670 drw 19
NOTES:
1. m = PAF offset.
2. D = maximum FIFO depth.
In IDT Standard mode: D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA.
In FWFT mode: D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA.
3. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that PAF will go HIGH (after one WCLK cycle plus tPAF). If the time between the
rising edge of RCLK and the rising edge of WCLK is less than tSKEW2, then the PAF deassertion time may be delayed one extra WCLK cycle.
4. PAF is asserted and updated on the rising edge of WCLK only.
Figure 16. Programmable Almost-Full Flag Timing (IDT Standard and FWFT Modes)
22
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
t CLKH
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
t CLKL
WCLK
tENS
tENH
n words in FIFO (2),
n+1 words in FIFO (3)
tSKEW2 (4)
RCLK
n words in FIFO (2),
n+1 words in FIFO (3)
n+1 words in FIFO (2),
n+2 words in FIFO (3)
tPAE
tPAE
1
2
1
tENS
2
tENH
4670 drw 20
NOTES:
1. n = PAE offset.
2. For IDT Standard mode
3. For FWFT mode.
4. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that PAE will go HIGH (after one RCLK cycle plus tPAE). If the time between
the rising edge of WCLK and the rising edge of RCLK is less than t SKEW2, then the PAE deassertion may be delayed one extra RCLK cycle.
5. PAE is asserted and updated on the rising edge of WCLK only.
Figure 17. Programmable Almost-Empty Flag Timing (IDT Standard and FWFT Modes)
tCLKH
tCLKL
WCLK
tENH
tENS
tHF
D/2 + 1 words in FIFO(1),
D/2 words in FIFO(1),
[
]
+1
[
(2)
words in FIFO
]
+ 2 words in FIFO(2)
D/2 words in FIFO(1),
[
]
+1
words in FIFO(2)
tHF
RCLK
tENS
4670 drw 21
NOTES:
1. For IDT Standard mode: D = maximum FIFO depth. D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA.
2. For FWFT mode: D = maximum FIFO depth. D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA.
Figure 18. Half-Full Flag Timing (IDT Standard and FWFT Modes)
23
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
OPTIONAL CONFIGURATIONS
IDT Standard mode, such problems can be avoided by creating composite flags, that is, ANDing EF of every FIFO, and separately ANDing FF of
every FIFO. In FWFT mode, composite flags can be created by ORing
OR of every FIFO, and separately ORing IR of every FIFO.
Figure 23 demonstrates a width expansion using two IDT72255LA/
72265LA devices. D0 - D17 from each device form a 36-bit wide input
bus and Q0-Q17 from each device form a 36-bit wide output bus. Any
word width can be attained by adding additional IDT72255LA/72265LA
devices.
WIDTH EXPANSION CONFIGURATION
Word width may be increased simply by connecting together the
control signals of multiple devices. Status flags can be detected from
any one device. The exceptions are the EF and FF functions in IDT
Standard mode and the IR and OR functions in FWFT mode. Because
of variations in skew between RCLK and WCLK, it is possible for EF/FF
deassertion and IR/OR assertion to vary by one cycle between FIFOs. In
PARTIAL RESET (
)
MASTER RESET (
)
FIRST WORD FALL THROUGH/
SERIAL INPUT (FWFT/SI)
RETRANSMIT (
)
Dm+1 - Dn
m+n
DATA IN
m
D0 - Dm
n
READ CLOCK (RCLK)
WRITE CLOCK (WCLK)
READ ENABLE (
WRITE ENABLE (
OUTPUT ENABLE (
LOAD (
)
FULL FLAG/INPUT READY (
/ ) #1
FULL FLAG/INPUT READY (
/ ) #2
IDT
72255LA
72265LA
IDT
72255LA
72265LA
(1)
GATE
PROGRAMMABLE (
HALF-FULL FLAG (
)
)
)
EMPTY FLAG/OUTPUT READY (
/
) #1
EMPTY FLAG/OUTPUT READY (
/
) #2
(1)
)
)
PROGRAMMABLE (
)
FIFO
#1
FIFO
#2
m
n
Qm+1 - Qn
Q0 - Qm
GATE
m+n
DATA OUT
4670 drw 22
NOTES:
1. Use an AND gate in IDT Standard mode, an OR gate in FWFT mode.
2. Do not connect any output control signals directly together.
3. FIFO #1 and FIFO #2 must be the same depth, but may be different word widths.
Figure 19. Block Diagram of 8,192 x 36 and 16,384 x 36 Width Expansion
24
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFO™
8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
DEPTH EXPANSION CONFIGURATION (FWFT MODE ONLY)
The IDT72255LA can easily be adapted to applications requiring depths
greater than 8,192 and 16,384 for the IDT72265LA with an 18-bit bus
width. In FWFT mode, the FIFOs can be connected in series (the data
outputs of one FIFO connected to the data inputs of the next) with no
external logic necessary. The resulting configuration provides a total
depth equivalent to the sum of the depths associated with each single
FIFO. Figure 24 shows a depth expansion using two IDT72255LA/72265LA
devices.
Care should be taken to select FWFT mode during Master Reset for all
FIFOs in the depth expansion configuration. The first word written to an
empty configuration will pass from one FIFO to the next ("ripple down")
until it finally appears at the outputs of the last FIFO in the chain–no read
operation is necessary but the RCLK of each FIFO must be free-running.
Each time the data word appears at the outputs of one FIFO, that device's
OR line goes LOW, enabling a write to the next FIFO in line.
For an empty expansion configuration, the amount of time it takes for OR
of the last FIFO in the chain to go LOW (i.e. valid data to appear on the last
FIFO's outputs) after a word has been written to the first FIFO is the sum of
the delays for each individual FIFO:
that the tSKEW3 specification is not met between WCLK and transfer clock,
or RCLK and transfer clock, for the OR flag.
The "ripple down" delay is only noticeable for the first word written to an
empty depth expansion configuration. There will be no delay evident for
subsequent words written to the configuration.
The first free location created by reading from a full depth expansion
configuration will "bubble up" from the last FIFO to the previous one until it
finally moves into the first FIFO of the chain. Each time a free location is
created in one FIFO of the chain, that FIFO's IR line goes LOW, enabling
the preceding FIFO to write a word to fill it.
For a full expansion configuration, the amount of time it takes for IR of the
first FIFO in the chain to go LOW after a word has been read from the last
FIFO is the sum of the delays for each individual FIFO:
(N – 1)*(3*transfer clock) + 2 TWCLK
where N is the number of FIFOs in the expansion and TWCLK is the
WCLK period. Note that extra cycles should be added for the possibility
that the tSKEW1 specification is not met between RCLK and transfer clock,
or WCLK and transfer clock, for the IR flag.
The Transfer Clock line should be tied to either WCLK or RCLK, whichever is faster. Both these actions result in data moving, as quickly as
possible, to the end of the chain and free locations to the beginning of the
chain.
(N – 1)*(4*transfer clock) + 3*TRCLK
where N is the number of FIFOs in the expansion and TRCLK is the
RCLK period. Note that extra cycles should be added for the possibility
FWFT/SI
•
WRITE CLOCK
TRANSFER CLOCK
FWFT/SI
WCLK
RCLK
FWFT/SI
•
WCLK
READ CLOCK
RCLK
READ ENABLE
WRITE ENABLE
IDT
72255LA
72265LA
IDT
72255LA
72265LA
INPUT READY
OUTPUT READY
OUTPUT ENABLE
GND
DATA IN
n
Dn
Qn
n
n
Dn
DATA OUT
Qn
4670 drw 23
Figure 20. Block Diagram of 16,384 x 18 and 32,768 x 18 Depth Expansion
25
OCTOBER 17, 2005
ORDERING INFORMATION
IDT
XXXXX
X
Device Type
Power
XX
Speed
X
Package
X
X
Process /
Temperature
Range
BLANK
I(1)
Commercial (0°C to +70°C)
Industrial (-40°C to +85°C)
G
Green
PF
TF
Thin Plastic Quad Flatpack (TQFP, PN64-1)
Slim Thin Quad Flatpack (STQFP, PP64-1)
10
15
20
Commercial Only
Com'l & Ind'l
Com‘l & Ind’l
LA
Low Power
72255
72265
8,192 x 18 — SuperSync FIFO
16,384 x 18 — SuperSync FIFO
Clock Cycle Time (tCLK)
Speed in Nanoseconds
4670 drw24
NOTES:
1. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device.
2. Green parts available. For specific speeds and packages contact your sales office.
DATASHEET DOCUMENT HISTORY
04/25/2001
10/17/2005
pgs. 1, 5, 6 and 26.
pgs. 1, 6, 20, 21 and 26. PCN#F0509-01.
CORPORATE HEADQUARTERS
6024 Silver Creek Valley Road
San Jose, CA 95138
for SALES:
800-345-7015 or 408-284-8200
fax: 408-284-2775
www.idt.com
26
for Tech Support:
408-360-1753
email: [email protected]
5 VOLT CMOS SuperSync FIFO™
8,192 x 18
16,384 x 18
IDT72255LA
IDT72265LA
ADDENDUM
DIFFERENCES BETWEEN THE IDT72255LA/72265LA AND IDT72255L/72265L
IDT has improved the performance of the IDT72255/72265 SuperSync™ FIFOs. The new versions are designated by the “LA” mark. The LA part is pinfor-pin compatible with the original “L” version. Some difference exist between the two versions. The following table details these differences.
Item
NEW PART
OLD PART
IDT72255LA
IDT72265LA
IDT72255L
IDT72265L
Comments
Pin #3
DC (Don’t Care) - There is
no restriction on WCLK and
RCLK. See note 1.
FS (Frequency Select)
In the LA part this pin must be tied
to either VCC or GND and must
not toggle after reset.
First Word Latency
(IDT Standard Mode)
60ns(2) + tREF + 1 TRCLK(4)
tFWL1 = 10*Tf(3) + 2TRCLK(4)(ns)
First word latency in the LA part is
a fixed value, independent of the
frequency of RCLK or WCLK.
First Word Latency
(FWFT Mode)
60ns(2) + tREF + 2 TRCLK(4)
tFWL2 = 10*Tf(3) + 3TRCLK(4)(ns)
First word latency in the LA part is
a fixed value, independent of the
frequency of RCLK or WCLK.
Retransmit Latency
(IDT Standard Mode)
60ns(2) + tREF + 1 TRCLK(4)
tRTF1 = 14*Tf(3) + 3TRCLK(4)(ns)
Retransmit latency in the LA part is
a fixed value, independent of the
frequency of RCLK or WCLK.
60ns(2) + tREF + 2 TRCLK(4)
tRTF2 = 14*Tf(3) + 4TRCLK(4)(ns)
Retransmit latency in the LA part is
a fixed value, independent of the
frequency of RCLK or WCLK.
80mA
180mA
Active supply current
20mA
15mA
Standby current
15 + 2.1*fS + 0.02*CL*fS(mA)
Not Given
Typical ICC1 Current calculation
Retransmit Latency
(FWFT Mode)
I CC1
I CC2
(5)
Typical ICC1
NOTES:
1. WCLK and RCLK can vary independently and can be stopped. There is no restriction on operating WCLK and RCLK.
2. This is tSKEW3.
3. Tf is the period of the ‘selected clock’.
4. TRCLK is the cycle period of the read clock.
5. Typical ICC1 is based on VCC = 5V, tA = 25°C, fS = WCLK frequency = RCLK frequency (in MHz using TTL levels), data switching at fS/2, CL = Capacitive Load (in pF).
IDT and the IDT logo are trademarks of Integrated Device Technology, Inc and the SuperSyncFIFO is a trademark of Integrated Device Technology, Inc.
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2005 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice.