1FEBRUARY 2002
IDT72V205, IDT72V215,
IDT72V225, IDT72V235,
IDT72V245
IDT and the IDT logo are registered trademarks of Integrated Device Technology, Inc. SyncFIFO is a trademark of Integrated Device Technology, Inc.
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
2002 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice. DSC-4294/3
3.3 VOLT CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18,
2,048 x 18, and 4,096 x 18
FEATURES:
••
••
•256 x 18-bit organization array (IDT72V205)
••
••
•512 x 18-bit organization array (IDT72V215)
••
••
•1,024 x 18-bit organization array (IDT72V225)
••
••
•2,048 x 18-bit organization array (IDT72V235)
••
••
•4,096 x 18-bit organization array (IDT72V245)
••
••
•10 ns read/write cycle time
••
••
•5V input tolerant
••
••
•IDT Standard or First Word Fall Through timing
••
••
•Single or double register-buffered Empty and Full flags
••
••
•Easily expandable in depth and width
••
••
•Asynchronous or coincident Read and Write Clocks
••
••
•Asynchronous or synchronous programmable Almost-Empty
and Almost-Full flags with default settings
••
••
•Half-Full flag capability
••
••
•Output enable puts output data bus in high-impedanc state
••
••
•High-performance submicron CMOS technology
••
••
•Available in a 64-lead thin quad flatpack (TQFP/STQFP)
••
••
•Industrial temperature range (–40 °°
°°
°C to +85°°
°°
°C) is available
FUNCTIONAL BLOCK DIAGRAM
INPUT REGISTER
OUTPUT REGISTER
RAM ARRAY
256 x 18, 512 x 18
1,024 x 18, 2,048 x 18
4,096 x 18
OFFSET REGISTER
FLAG
LOGIC
FF/IR
PAF
EF/OR
PAE
HF/(WXO)
READ POINTER
READ CONTROL
LOGIC
WRITE CONTROL
LOGIC
WRITE POINTER
EXPANSION LOGIC
RESET LOGIC
WEN WCLK D0-D17 LD
RS
(HF)/WXO
WXI
REN
RCLK
OE Q0-Q17
RXO
RXI
FL
4294 drw 01
DESCRIPTION:
The IDT72V205/72V215/72V225/72V235/72V245 are functionally com-
patible versions of the IDT72205LB/72215LB/72225LB/72235LB/72245LB,
designed to run off a 3.3V supply for exceptionally low power consumption.
These devices are very high-speed, low-power First-In, First-Out (FIFO)
memories with clocked read and write controls. These FIFOs are applicable
for a wide variety of data buffering needs, such as optical disk controllers, Local
Area Networks (LANs), and interprocessor communication.
These FIFOs have 18-bit input and output ports. The input port is controlled
by a free-running clock (WCLK), and an input enable pin (WEN). Data is read
into the synchronous FIFO on every clock when WEN is asserted. The output
port is controlled by another clock pin (RCLK) and another enable pin (REN).
The Read Clock(RCLK) can be tied to the Write Clock for single clock operation
or the two clocks can run asynchronous of one another for dual-clock operation.
An Output Enable pin (OE) is provided on the read port for three-state control
of the output.
The synchronous FIFOs have two fixed flags, Empty Flag/Output Ready
(EF/OR) and Full Flag/Input Ready (FF/IR), and two programmable flags,
Almost-Empty (PAE) and Almost-Full (PAF). The offset loading of the program-
2
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
PIN CONFIGURATIONS
TQFP (PN64-1, order code: PF)
STQFP (PP64-1, order code: TF)
TOP VIEW
DESCRIPTION (CONTINUED)
PIN 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
D
16
D
17
GND
RCLK
REN
LD
OE
RS
V
CC
GND
EF
Q
17
Q
16
GND
Q
15
V
CC
Q
14
Q
13
GND
Q
12
Q
11
V
CC
Q
10
Q
9
GND
Q
8
Q
7
Q
6
Q
5
GND
Q
4
V
CC
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
D
15
D
14
D
13
D
12
D
11
D
10
D
9
D
8
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
PAE
FL
WCLK
WEN
WXI
V
CC
PAF
RXI
FF
WXO/HF
RXO
Q
0
Q
1
GND
Q
2
Q
3
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
4294 drw 02
mable flags is controlled by a simple state machine, and is initiated by asserting
the Load pin (LD). A Half-Full flag (HF) is available when the FIFO is used
in a single device configuration.
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.
These devices are depth expandable using a Daisy-Chain technique or
First Word Fall Through mode (FWFT). The XI and XO pins are used to expand
the FIFOs. In depth expansion configuration, First Load (FL) is grounded on
the first device and set to HIGH for all other devices in the Daisy Chain.
The IDT72V205/72V215/72V225/72V235/72V245 are fabricated using
IDT’s high-speed submicron CMOS technology.
3
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
PIN DESCRIPTION
Symbol Name I/O Description
D0–D17 Data Inputs I Data inputs for an 18-bit bus.
RS Reset I When RS is set LOW, internal read and write pointers are set to the first location of the RAM array, FF and PAF
go HIGH, and PAE and EF go LOW. A reset is required before an initial WRITE after power-up.
WCLK Write Clock I When WEN is LOW, data is written into the FIFO on a LOW-to-HIGH transition of WCLK, if the FIFO is not full.
WEN Write Enable I When WEN is LOW, data is written into the FIFO on every LOW-to-HIGH transition of WCLK. When WEN is
HIGH, the FIFO holds the previous data. Data will not be written into the FIFO if the FF is LOW.
RCLK Read Clock I When REN is LOW, data is read from the FIFO on a LOW-to-HIGH transition of RCLK, if the FIFO is not empty.
REN Read Enable I When REN is LOW, data is read from the FIFO on every LOW-to-HIGH transition of RCLK. When REN is HIGH,
the output register holds the previous data. Data will not be read from the FIFO if the EF is LOW.
OE Output Enable I When OE is LOW, the data output bus is active. If OE is HIGH, the output data bus will be in a high-impedance
state.
LD Load I When LD is LOW, data on the inputs D0–D11 is written to the offset and depth registers on the LOW-to-HIGH
transition of the WCLK, when WEN is LOW. When LD is LOW, data on the outputs Q0–Q11 is read from the
offset and depth registers on the LOW-to-HIGH transition of the RCLK, when REN is LOW.
FL First Load I In the single device or width expansion configuration, FL together with WXI and RXI determine if the mode is
IDT Standard mode or First Word Fall Through (FWFT) mode, as well as whether the PAE/PAF flags are
synchronous or asynchronous. (See Table 1.) In the Daisy Chain Depth Expansion configuration, FL is
grounded on the first device (first load device) and set to HIGH for all other devices in the Daisy Chain.
WXI Write Expansion I In the single device or width expansion configuration, WXI together with FL and RXI determine if the mode
Input is IDT Standard mode or FWFT mode, as well as whether the PAE/PAF flags are synchronous or asynchronous.
(See Table 1.) In the Daisy Chain Depth Expansion configuration, WXI is connected to WXO (Write Expansion
Out) of the previous device.
RXI Read Expansion I In the single device or width expansion configuration, RXI together with FL and WXI, determine if the mode
Input is IDT Standard mode or FWFT mode, as well as whether the PAE/PAF flags are synchronous or asynchronous.
(See Table 1.) In the Daisy Chain Depth Expansion configuration, RXI is connected to RXO (Read Expansion
Out) of the previous device.
FF/IR Full Flag/ O In the IDT Standard mode, the FF function is selected. FF indicates whether or not the FIFO memory is full. In
Input Ready the FWFT mode, the IR function is selected. IR indicates whether or not there is space available for writing to
the FIFO memory.
EF/OR Empty Flag/ O In the IDT Standard mode, the EF function is selected. EF indicates whether or not the FIFO memory is empty.
Output Ready In FWFT mode, the OR function is selected. OR indicates whether or not there is valid data available at the outputs.
PAE Programmable O When PAE is LOW, the FIFO is almost-empty based on the offset programmed into the FIFO. The default
Almost-Empty Flag offset at reset is 31 from empty for IDT72V205, 63 from empty for IDT72V215, and 127 from empty for IDT72V225/
72V235/72V245.
PAF Programmable O When PAF is LOW, the FIFO is almost-full based on the offset programmed into the FIFO. The default offset at
Almost-Full Flag reset is 31 from full for IDT72V205, 63 from full for IDT72V215, and 127 from full for IDT72V225/72V235/72V245.
WXO/HF Write Expansion O In the single device or width expansion configuration, the device is more than half full when HF is LOW. In the
Out/Half-Full Flag depth expansion configuration, a pulse is sent from WXO to WXI of the next device when the last location in the
FIFO is written.
RXO Read Expansion O In the depth expansion configuration, a pulse is sent from RXO to RXI of the next device when the last
O ut location in the FIFO is read.
Q0–Q17 Data Outputs O Data outputs for an 18-bit bus.
VCC Power +3.3V power supply pins.
GND Ground Seven ground pins.
4
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
RECOMMENDED DC OPERATING
CONDITIONS
Symbol Parameter Min. Typ. Max. Unit
VCC Supply Voltage 3.0 3.3 3.6 V
Commercial/Industrial
GND Supply Voltage 0 0 0 V
VIH Input High Voltage 2.0 — 5.5 V
Commercial/Industrial
VIL(1) Input Low Voltage -0.5 — 0.8 V
Commercial/Industrial
TAOperating Temperature 0 — 70 °C
Commercial
TAOperating Temperature -40 85 °C
Industrial
NOTE:
1. 1.5V undershoots are allowed for 10ns once per cycle.
Symbol Rating Commercial Unit
VTERM(2) Terminal Voltage –0.5 to +5 V
with respect to GND
TSTG Storage –55 to +125 °C
Temperature
IOUT DC Output Current –50 to +50 mA
Symbol Parameter(1) Conditions Max. Unit
CIN(2) Input VIN = 0V 10 pF
Capacitance
COUT(1,2) Output VOUT = 0V 10 pF
Capacitance
CAPACITANCE (TA = +25°C, f = 1.0MHz)
NOTES:
1. With output deselected, (OE ≥ VIH).
2. Characterized values, not currently tested.
IDT72V205
IDT72V215
IDT72V225
IDT72V235
IDT72V245
Commercial & Industrial(1)
tCLK = 10, 15, 20 ns
Symbol Parameter Min. Typ. Max. Unit
ILI(2) Input Leakage Current (any input) –1 — 1 µA
ILO(3) Output Leakage Current –10 — 10 µA
VOH Output Logic “1” Voltage, IOH = –2 mA 2. 4 — — V
VOL Output Logic “0” Voltage, IOL = 8 mA — — 0. 4 V
ICC1(4,5,6) Active Power Supply Current — — 30 mA
ICC2(4.7) Standby Current — — 5 mA
DC ELECTRICAL CHARACTERISTICS
(Commercial: VCC = 3.3V ± 0.3V, TA = 0°C to +70°C; Industrial: VCC = 3.3V ± 0.3V, TA = -40°C to +85°C)
NOTES:
1. Industrial Temperature Range Product for the 15ns speed grade is 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 = 2.04 + 0.88*fS + 0.02*CL*fS (in mA).
These equations are valid under the following conditions:
VCC = 3.3V, 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.
ABSOLUTE MAXIMUM RATINGS
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.
2. VCC terminal only.
5
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS
(Commercial: VCC = 3.3V ± 0.3V, TA = 0°C to +70°C; Industrial: VCC = 3.3V ± 0.3V, TA = -40°C to +85°C)
Commercial Com'l & Ind'l(1) Commercial
IDT72V205L10 IDT72V205L15 IDT72V205L20
IDT72V215L10 IDT72V215L15 IDT72V215L20
IDT72V225L10 IDT72V225L15 IDT72V225L20
IDT72V235L10 IDT72V235L15 IDT72V235L20
IDT72V245L10 IDT72V245L15 IDT72V245L20
Symbol Parameter Min. Max. Min. Max. Min. Max. Unit
fSClock Cycle Frequency — 100 — 66.7 — 50 MHz
tAData Access Time 2 6.5 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 — n s
tDS Data Set-up Time 3 — 4 — 5 — ns
tDH Data Hold Time 0.5 — 1 — 1 — ns
tENS Enable Set-up Time 3 — 4 — 5 — ns
tENH Enable Hold Time 0.5 — 1 — 1 — ns
tRS Reset Pulse Width(2) 10 — 15 — 20 — ns
tRSS Reset Set-up Time 8 — 10 — 12 — ns
tRSR Reset Recovery Time 8 — 10 — 1 2 — ns
tRSF Reset to Flag and Output Time — 1 5 — 15 — 20 ns
tOLZ Output Enable to Output in Low-Z(3) 0—0—0—ns
tOE Output Enable to Output Valid — 6 3 8 3 10 ns
tOHZ Output Enable to Output in High-Z(3) 1638310ns
tWFF Write Clock to Full Flag — 6.5 — 1 0 — 1 2 ns
tREF Read Clock to Empty Flag — 6. 5 — 10 — 1 2 n s
tPAFA Clock to Asynchronous Programmable Almost-Full Flag — 17 — 20 — 22 ns
tPAFS Write Clock to Synchronous ProgrammableAlmost-Full Flag — 8 — 10 — 12 ns
tPAEA Clock to Asynchronous Programmable Almost-Empty Flag — 17 — 20 — 22 ns
tPAES Read Clock to Synchronous Programmable Almost-Empty Flag — 8 — 10 — 12 ns
tHF Clock to Half-Full Flag — 1 7 — 2 0 — 2 2 ns
tXO Clock to Expansion Out — 6 .5 — 1 0 — 1 2 ns
tXI Expansion In Pulse Width 3 — 6.5 — 8 — ns
tXIS Expansion In Set-Up Time 3 — 5 — 8 — ns
tSKEW1 Skew time between Read Clock & Write Clock for FF/IR 5—6—8—ns
and EF/OR
tSKEW2(4) Skew time between Read Clock & Write Clock for PAE 14 — 18 — 20 — ns
and PAF
Input Pulse Levels GND to 3.0V
Input Rise/Fall Times 3ns
Input Timing Reference Levels 1.5V
Output Reference Levels 1.5V
Output Load See Figure 1
AC TEST CONDITIONS
Figure 1. Output Load
* Includes jig and scope capacitances.
30pF*
330Ω
3.3V
510Ω
D.U.T.
4294 drw 03
NOTES:
1. Industrial temperature range product for the 15ns speed grade is available as a standard device. All other speed grades are available by special order.
2. Pulse widths less than minimum values are not allowed.
3. Values guaranteed by design, not currently tested.
4. tSKEW2 applies to synchronous PAE and synchronous PAF only.
6
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
FUNCTIONAL DESCRIPTION
TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH
(FWFT) MODE
The IDT72V205/72V215/72V225/72V235/72V245 support two different
timing modes of operation. The selection of which mode will operate is
determined during configuration at Reset (RS). During a RS operation, the First
Load (FL), Read Expansion Input ( RXI), and Write Expansion Input (WXI) pins
are used to select the timing mode per the truth table shown in Table 3. 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 Read Enable (REN) and enabling a rising Read
Clock (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.
Various signals, both input and output signals operate differently depending
on which timing mode is in effect.
IDT STANDARD MODE
In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in the
manner outlined in Table 1. To write data into to the FIFO, Write Enable (WEN)
must be LOW. Data presented to the DATA IN lines will be clocked into the FIFO
on subsequent transitions of the Write Clock (WCLK). After the first write is
performed, the Empty Flag (EF) will go HIGH. Subsequent writes will continue
to fill up the FIFO. The 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 129th (72V205), 257th (72V215), 513th (72V225), 1,025th (72V235), and
2,049th (72V245) word 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 (256-m)
writes for the IDT72V205, (512-m) writes for the IDT72V215, (1,024-m) writes
for the IDT72V225, (2,048-m) writes for the IDT72V235 and (4,096–m) writes
for the IDT72V245. The offset “m” is the full offset value. This parameter is also
user programmable. See section on Programmable Flag Offset Loading. If there
is no full offset specified, the PAF will be LOW when the device is 31 away from
completely full for IDT72V205, 63 away from completely full for IDT72V215, and
127 away from completely full for the IDT72V225/72V235/72V245.
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 = 256 writes for the IDT72V205, 512 for the IDT72V215, 1,024
for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245,
respectively.
If the FIFO is full, the first read operation will cause FF to go HIGH.
Subsequent read operations will cause PAF and the Half-Full Flag (HF) to go
HIGH at the conditions described in Table 1. If further read operations occur,
without write operations, the Programmable Almost-Empty Flag (PAE) will go
LOW when there are n words in the FIFO, where n is the empty offset value.
If there is no empty offset specified, the PAE will be LOW when the device is 31
away from completely empty for IDT72V205, 63 away from completely empty
for IDT72V215, and 127 away from completely empty for IDT72V225/72V235/
72V245. Continuing read operations will cause the FIFO to be 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.
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 130th
(72V205), 258th (72V215), 514th (72V225), 1,026th (72V235), and 2,050th
(72V245) word 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 (257-m) writes for the IDT72V205, (513-m) writes
for the IDT72V215, (1,025-m) writes for the IDT72V225, (2,049–m) writes for
the IDT72V235 and (4,097–m) writes for the IDT72V245, 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 = 257 writes for the IDT72V205, 513 for the IDT72V215,
1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the
IDT72V245. 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. If there is no empty offset specified, the PAE will be
LOW when the device is 32 away from completely empty for IDT72V205, 64
away from completely empty for IDT72V215, and 128 away from completely
empty for IDT72V225/72V235/72V245. Continuing read operations will cause
the FIFO to be 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.
PROGRAMMABLE FLAG LOADING
Full and Empty flag offset values can be user programmable. The IDT72V205/
72V215/72V225/72V235/72V245 has internal registers for these offsets.
Default settings are stated in the footnotes of Table 1 and Table 2. Offset values
are loaded into the FIFO using the data input lines D0-D11. To load the offset
registers, the Load (LD) pin and WEN pin must be held LOW. Data present on
D0-D11 will be transferred in to the Empty Offset register on the first LOW-to-HIGH
transition of WCLK. By continuing to hold the LD and WEN pin low, data present
on D0-D11 will be transferred into the Full Offset register on the next transition
of the WCLK. The third transition again writes to the Empty Offset register. Writing
all offset registers does not have to occur at one time. One or two offset registers
can be written and then by bringing the LD pin HIGH, the FIFO is returned to
normal read/write operation. When the LD pin and WEN are again set LOW,
the next offset register in sequence is written.
7
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
The contents of the offset registers can be read on the data output lines Q0-
Q11 when the LD pin is set LOW and REN is set LOW. Data can then be read
on the next LOW-to-HIGH transition of RCLK. The first transition of RCLK will
present the empty offset value to the data output lines. The next transition of RCLK
will present the full offset value. Offset register content can be read out in the IDT
Standard mode only. It cannot be read in the FWFT mode.
SYNCHRONOUS vs ASYNCHRONOUS PROGRAMMABLE FLAG TIM-
ING SELECTION
The IDT72V205/72V215/72V225/72V235/72V245 can be configured
during the "Configuration at Reset" cycle described in Table 3 with either
asynchronous or synchronous timing for PAE and PAF flags.
If asynchronous PAE/PAF configuration is selected (as per Table 3), the
PAE is asserted LOW on the LOW-to-HIGH transition of RCLK. PAE is reset to
HIGH on the LOW-to-HIGH transition of WCLK. Similarly, the PAF is asserted
LOW on the LOW-to-HIGH transition of WCLK and PAF is reset to HIGH on the
LOW-to-HIGH transition of RCLK. For detail timing diagrams, see Figure 13 for
asynchronous PAE timing and Figure 14 for asynchronous PAF timing.
If synchronous PAE/PAF configuration is selected , the PAE is asserted and
updated on the rising edge of RCLK only and not WCLK. Similarly, PAF is
asserted and updated on the rising edge of WCLK only and not RCLK. For detail
timing diagrams, see Figure 22 for synchronous PAE timing and Figure 23 for
synchronous PAF timing.
REGISTER-BUFFERED FLAG OUTPUT SELECTION
The IDT72V205/72V215/72V225/72V235/72V245 can be configured
during the "Configuration at Reset" cycle described in Table 4 with single, double
or triple register-buffered flag output signals. The various combinations avail-
able are described in Table 4 and Table 5. In general, going from single to
double or triple buffered flag outputs removes the possibility of metastable flag
indications on boundary states (i.e, empty or full conditions). The trade-off is the
addition of clock cycle delays for the respective flag to be asserted. Not all
combinations of register-buffered flag outputs are supported. Register-buffered
outputs apply to the Empty Flag and Full Flag only. Partial flags are not effected.
Table 4 and Table 5 summarize the options available.
Number of Words in FIFO
IDT72V205 IDT72V215 IDT72V225 IDT72V235 IDT72V245 FF PAF HF PAE EF
00 0 0 0HHHLL
1 to n(1) 1 to n(1) 1 to n(1) 1 to n(1) 1 to n(1) HH H LH
(n + 1) to 128 (n + 1) to 256 (n + 1) to 512 (n + 1) to 1,024 (n + 1) to 2,048 H H H H H
129 to (256-(m+1))
(2)
257 to (512-(m+1))
(2)
513 to (1,024-(m+1))
(2)
1,025 to (2,048-(m+1))
(2)
2,049 to (4,096-(m+1))
(2)
HH L HH
(256-m) to 255 (512-m) to 511 (1,024-m) to 1,023 (2,048-m) to 2,047 (4,096-m) to 4,095 H L L H H
256 512 1,024 2,048 4,096 L L L H H
TABLE 1 STATUS FLAGS FOR IDT STANDARD MODE
TABLE 2 STATUS FLAGS FOR FWFT MODE
Number of Words in FIFO
IDT72V205 IDT72V215 IDT72V225 IDT72V235 IDT72V245 IR PAF HF PAE OR
00 0 0 0LHHLH
1 to (n + 1)(1) 1 to (n + 1)(1) 1 to (n + 1)(1) 1 to (n + 1)(1) 1 to (n + 1)(1) LHHLL
(n + 2) to 129 (n + 2) to 257 (n + 2) to 513 (n + 2) to 1,025 (n + 2) to 2,049 L H H H L
130 to (257-(m+1))
(2)
258 to (513-(m+1))
(2)
514 to (1,025-(m+1))
(2)
1,026 to (2,049-(m+1))
(2)
2,050 to (4,097-(m+1))
(2)
LHLHL
(257-m) to 256 (513-m) to 512 (1,025-m) to 1,024 (2,049-m) to 2,048 (4,097-m) to 4,096
LLLHL
257 513 1,025 2,049 4,097 H L L H L
NOTES:
1. n = Empty Offset (Default Values : IDT72V205 n = 31, IDT72V215 n = 63, IDT72V225/72V235/72V245 n = 127)
2. m = Full Offset (Default Values : IDT72V205 m = 31, IDT72V215 m = 63, IDT72V225/72V235/72V245 m = 127)
NOTES:
1. n = Empty Offset (Default Values : IDT72V205 n=31, IDT72V215 n = 63, IDT72V225/72V235/72V245 n = 127)
2. m = Full Offset (Default Values : IDT72V205 m=31, IDT72V215 m = 63, IDT72V225/72V235/72V245 m = 127)
8
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
NOTES:
1. In a daisy-chain depth expansion, FL is held LOW for the "first load device". The RXI and WXI inputs are driven by the corresponding RXO and WXO outputs of the
preceding device.
2. In a daisy-chain depth expansion, FL is held HIGH for members of the expansion other than the "first load device". The RXI and WXI inputs are driven by the corresponding
RXO and WXO outputs of the preceding device.
TABLE 3 TRUTH TABLE FOR CONFIGURATION AT RESET
FL RXI WXI EF/OR FF/IR PAE, PAF FIFO Timing Mode
0 0 0 Single register-buffered Single register-buffered Asynchronous Standard
Empty Flag Full Flag
0 0 1 Triple register-buffered Double register-buffered Asynchronous FWFT
Output Ready Flag Input Ready Flag
0 1 0 Double register-buffered Double register-buffered Asynchronous Standard
Empty Flag Full Flag
0(1) 1 1 Single register-buffered Single register-buffered Asynchronous Standard
Empty Flag Full Flag
1 0 0 Single register-buffered Single register-buffered Synchronous Standard
Empty Flag Full Flag
1 0 1 Triple register-buffered Double register-buffered Synchronous FWFT
Output Ready Flag Input Ready Flag
1 1 0 Double register-buffered Double register-buffered Synchronous Standard
Empty Flag Full Flag
1(2) 1 1 Single register-buffered Single register-buffered Synchronous Standard
Empty Flag Full Flag
TABLE 4 REGISTER-BUFFERED FLAG OUTPUT OPTIONS IDT STANDARD
MODE
Empty Flag (EF) Full Flag (FF) Partial Flags Programming at Reset Flag Timing
Buffered Output Buffered Output Timing Mode FL RXI WXI Diagrams
Single Single Asynch 0 0 0 Figure 9, 10
Single Single Sync 1 0 0 Figure 9, 10
Double Double Asynch 0 1 0 Figure 24, 26
Double Double Synch 1 1 0 Figure 24, 26
TABLE 5 REGISTER-BUFFERED FLAG OUTPUT OPTIONS FWFT MODE
Output Ready (OR) Input Ready (IR) Partial Flags Programming at Reset Flag Timing
FL RXI WXI Diagrams
Triple Double Asynch 0 0 1 Figure 27
Triple Double Sync 1 0 1 Figure 20, 21
9
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 2. Writing to Offset Registers
LD WEN WCLK Selection
0 0 Writing to offset registers:
Empty Offset
Full Offset
0 1 No Operation
1 0 Write Into FIFO
1 1 No Operation
Figure 3. Offset Register Location and Default Values
SIGNAL DESCRIPTIONS:
INPUTS:
DATA IN (D0 - D17)
Data inputs for 18-bit wide data.
CONTROLS:
RESET (RS)
Reset is accomplished whenever the Reset (RS) input is taken to a LOW
state. During reset, both internal read and write pointers are set to the first
location. A reset is required after power-up before a write operation can take
place. The Half-Full Flag (HF) and Programmable Almost-Full Flag (PAF) will
be reset to HIGH after tRSF. The Programmable Almost-Empty Flag (PAE) will
be reset to LOW after tRSF. The Full Flag (FF) will reset to HIGH. The Empty
Flag (EF) will reset to LOW in IDT Standard mode but will reset to HIGH in FWFT
mode. During reset, the output register is initialized to all zeros and the offset
registers are initialized to their default values.
WRITE CLOCK (WCLK)
A write cycle is initiated on the LOW-to-HIGH transition of the Write Clock
(WCLK). Data setup and hold times must be met with respect to the LOW-to-HIGH
transition of WCLK.
The Write and Read Clocks can be asynchronous or coincident.
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 flag is updated on the rising
edge of WCLK.
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 on the rising edge of WCLK.
WEN is ignored when the FIFO is full in either FWFT or IDT Standard mode.
READ CLOCK (RCLK)
Data can be read on the outputs on the LOW-to-HIGH transition of the Read
Clock (RCLK), when Output Enable (OE) is set LOW.
The Write and Read Clocks can be asynchronous or coincident.
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
on the rising edge of RCLK.
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.
OUTPUT ENABLE (OE)
When Output Enable (OE) is enabled (LOW), the parallel output buffers
receive data from the output register. When OE is disabled (HIGH), the Q output
data bus is in a high-impedance state.
LOAD (LD)
The IDT72V205/72V215/72V225/72V235/72V245 devices contain two
12-bit offset registers with data on the inputs, or read on the outputs. When the
Load (LD) pin is set LOW and WEN is set LOW, data on the inputs D0-D11 is
written into the Empty Offset register on the first LOW-to-HIGH transition of the
Write Clock (WCLK). When the LD pin and WEN are held LOW then data is
written into the Full Offset register on the second LOW-to-HIGH transition of
WCLK. The third transition of WCLK again writes to the Empty Offset register.
However, writing all offset registers does not have to occur at one time. One
or two offset registers can be written and then by bringing the LD pin HIGH, the
FIFO is returned to normal read/write operation. When the LD pin is set LOW,
and WEN is LOW, the next offset register in sequence is written.
EMPTY OFFSET REGISTER
17 11 0
001FH (72V205) 003FH (72V215):
007FH (72V225/72V235/72V245)
FULL OFFSET REGISTER
17 11 0
DEFAULT VALUE
DEFAULT VALUE
001FH (72V205) 003FH (72V215):
007FH (72V225/72V235/72V245)
4294 drw 04
NOTE:
1. Any bits of the offset register not being programmed should be set to zero.
NOTE:
1 . The same selection sequence applies to reading from the registers. REN is enabled and
read is performed on the LOW-to-HIGH transition of RCLK.
10
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
When the LD pin is LOW and WEN is HIGH, the WCLK input is disabled;
then a signal at this input can neither increment the write offset register pointer,
nor execute a write.
The contents of the offset registers can be read on the output lines when
the LD pin is set LOW and REN is set LOW; then, data can be read on the LOW-
to-HIGH transition of the Read Clock (RCLK). The act of reading the control
registers employs a dedicated read offset register pointer. (The read and write
pointers operate independently). Offset register content can be read out in the
IDT Standard mode only. It is inhibited in the FWFT mode.
A read and a write should not be performed simultaneously to the offset
registers.
FIRST LOAD (FL)
For the single device mode, see Table 3 for additional information. In the
Daisy Chain Depth Expansion configuration, FL is grounded to indicate it is the
first device loaded and is set to HIGH for all other devices in the Daisy Chain.
(See Operating Configurations for further details.)
WRITE EXPANSION INPUT (WXI)
This is a dual purpose pin. For single device mode, see Table 3 for
additional information. WXI is connected to Write Expansion Out (WXO) of the
previous device in the Daisy Chain Depth Expansion mode.
READ EXPANSION INPUT (RXI)
This is a dual purpose pin. For single device mode, see Table 3 for
additional information. RXI is connected to Read Expansion Out (RXO) of the
previous device in the Daisy Chain Depth Expansion mode.
OUTPUTS:
FULL FLAG/INPUT READY (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, FF will go LOW after D writes to the FIFO. D = 256 writes for the
IDT72V205, 512 for the IDT72V215, 1,024 for the IDT72V225, 2,048 for the
IDT72V235 and 4,096 for the IDT72V245.
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.
IR will go HIGH after D writes to the FIFO. D = 257 writes for the IDT72V205,
513 for the IDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235
and 4,097 for the IDT72V245. Note that the additional word in FWFT mode
is due to the capacity of the memory plus output register.
FF/IR is synchronous and updated on the rising edge of WCLK.
EMPTY FLAG/OUTPUT READY (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.
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 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.
EF/OR 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 FIFO
reaches the almost-full condition. In IDT Standard mode, if no reads are
performed after Reset (RS), the PAF will go LOW after (256-m) writes for the
IDT72V205, (512-m) writes for the IDT72V215, (1,024-m) writes for the
IDT72V225, (2,048–m) writes for the IDT72V235 and (4,096–m) writes for the
IDT72V245. The offset “m” is defined in the Full Offset register.
In FWFT mode, if no reads are performed, PAF will go LOW after 257-m
for the IDT72V205, 513-m for the IDT72V215, 1,025 for the IDT72V225, 2,049
for the IDT72V235 and 4,097 for the IDT72V245. The default values for m are
noted in Table 1 and 2.
If asynchronous PAF configuration is selected, the PAF is asserted LOW
on the LOW-to-HIGH transition of the Write Clock (WCLK). PAF is reset to HIGH
on the LOW-to-HIGH transition of the Read Clock (RCLK). If synchronous PAF
configuration is selected (see Table 3), the PAF is updated on the rising edge
of WCLK.
PROGRAMMABLE ALMOST-EMPTY FLAG (PAE)
The PAE flag will go LOW when the FIFO reaches the almost-empty
condition. In IDT Standard mode, PAE will go LOW when there are n words
or less in the FIFO. In FWFT mode, the PAE will go LOW when there are n + 1
words or less in the FIFO. The offset "n" is defined as the empty offset. The default
values for n are noted in Table 1 and 2.
If there is no empty offset specified, the Programmable Almost-Empty Flag
(PAE) will be LOW when the device is 31 away from completely empty for
IDT72V205, 63 away from completely empty for IDT72V215, and 127 away
from completely empty for IDT72V225/72V235/72V245.
If asynchronous PAE configuration is selected, the PAE is asserted LOW on
the LOW-to-HIGH transition of the Read Clock (RCLK). PAE is reset to HIGH
on the LOW-to-HIGH transition of the Write Clock (WCLK). If synchronous PAE
configuration is selected (see Table 3), the PAE is updated on the rising edge
of RCLK.
WRITE EXPANSION OUT/HALF-FULL FLAG (WXO/HF)
This is a dual-purpose output. In the Single Device and Width Expansion
mode, when Write Expansion In (WXI) and/or Read Expansion In (RXI) are
grounded, this output acts as an indication of a half-full memory.
After half of the memory is filled, and at the LOW-to-HIGH transition of the next
write cycle, the Half-Full Flag goes LOW and will remain set until the difference
between the write pointer and read pointer is less than or equal to one half of
the total memory of the device. The Half-Full Flag (HF) is then reset to HIGH
by the LOW-to-HIGH transition of the Read Clock (RCLK). The HF is
asynchronous.
In the Daisy Chain Depth Expansion mode, WXI is connected to WXO of
the previous device. This output acts as a signal to the next device in the Daisy
Chain by providing a pulse when the previous device writes to the last location
of memory.
READ EXPANSION OUT (RXO)
In the Daisy Chain Depth Expansion configuration, Read Expansion In
(RXI) is connected to Read Expansion Out (RXO) of the previous device. This
output acts as a signal to the next device in the Daisy Chain by providing a pulse
when the previous device reads from the last location of memory.
DATA OUTPUTS (Q0-Q17)
Q0-Q17 are data outputs for 18-bit wide data.
11
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
NOTES:
1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that FF will go HIGH during the current clock cycle. If the time between the rising
edge of RCLK and the rising edge of WCLK is less than tSKEW1, then FF may not change state until the next WCLK edge.
2. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during Reset.
Figure 5. Reset Timing(2)
Figure 6. Write Cycle Timing with Single Register-Buffered
FF
(IDT Standard Mode)
WCLK
D
0
- D
17
WEN
FF
t
CLK
t
CLKH
t
CLKL
t
DS
t
ENS
t
DH
t
ENH
t
WFF
t
WFF
DATA IN VALID
NO OPERATION
RCLK
t
SKEW1(1)
REN 4294 drw 06
RS
REN, WEN, LD
PAE
PAF, WXO/
HF, RXO
Q
0
- Q
17
OE = 0
OE = 1
(1)
4294 drw 05
t
RSS
CONFIGURATION SETTING
t
RSR
FL, RXI, WXI
RCLK, WCLK
FF/IR
EF/OR
FWFT Mode
IDT Standard Mode
(3)
(2)
t
RSF
t
RSF
t
RSF
t
RSF
t
RSF
t
RSR
t
RS
FWFT Mode
IDT Standard Mode
(4)
NOTES:
1. Single device mode (FL, RXI, WXI) = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0). FL, RXI, WXI should be static (tied to VCC or GND).
2. The clocks (RCLK, WCLK) can be free-running asynchronously or coincidentally.
3 . After reset, the outputs will be LOW if OE = 0 and tri-state if OE = 1.
4. In FWFT mode IR goes LOW based on the WCLK edge after Reset.
12
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 8. First Data Word Latency with Single Register-Buffered
EF
(IDT Standard Mode)
NOTES:
1. When tSKEW1 minimum specification, tFRL (maximum) = tCLK + tSKEW1. When tSKEW1 < minimum specification, tFRL (maximum) = either 2*tCLK + tSKEW1 or tCLK + tSKEW1. The
Latency Timing applies only at the Empty Boundary (EF = LOW).
2. The first word is available the cycle after EF goes HIGH, always.
3. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during Reset.
Figure 7. Read Cycle Timing with Single Register-Buffered
EF
(IDT Standard Mode)
NOTES:
1. tSKEW1 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that EF will go HIGH during the current clock cycle. If the time between the rising
edge of WCLK and the rising edge of RCLK is less than tSKEW1, then EF may not change state until the next RCLK edge.
2. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during Reset.
WCLK
D
0
- D
17
WEN
RCLK
EF
Q
0
- Q
17
REN
t
DS
t
SKEW1
t
ENS
t
REF
t
A
D
0
D
1
D
2
D
3
D
0
D
1
(first valid write)
t
OE
t
OLZ
OE
t
A
t
FRL(1)
D
4
t
ENS
4294 drw 08
NO OPERATION
RCLK
REN
EF
t
CLK
t
CLKH
t
CLKL
t
ENS
t
ENH
t
REF
t
REF
VALID DATA
t
A
t
OLZ
t
OE
t
OHZ
Q
0
- Q
17
OE
WCLK
WEN
t
SKEW1(1)
4294 drw 07
13
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 10. Single Register-Buffered Empty Flag Timing (IDT Standard Mode)
NOTES:
1. When tSKEW1 minimum specification, tFRL (maximum) = tCLK + tSKEW1. When tSKEW1 < minimum specification, tFRL (maximum) = either 2 * tCLK + tSKEW1, or tCLK + tSKEW1. The
Latency Timing apply only at the Empty Boundary (EF = LOW).
2. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during Reset.
NOTES:
1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that FF will go HIGH during the current clock cycle. If the time between the rising
edge of RCLK and the rising edge of WCLK is less than tSKEW1, then FF may not change state until the next WCLK edge.
2. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during Reset.
Figure 9. Single Register-Buffered Full Flag Timing (IDT Standard Mode)
WCLK
D
0
- D
17
WEN
RCLK
EF
Q
0
- Q
17
OE
t
DS
t
ENS
t
A
t
SKEW1
DATA WRITE 1
DATA READ
t
ENH
t
REF
t
DS
t
ENS
DATA WRITE 2
t
ENH
t
REF
REN
DATA IN OUTPUT REGISTER
t
FRL(1)
LOW
4294 drw 10
t
REF
t
SKEW1
t
FRL(1)
DATA READ
WCLK
D
0
- D
17
WEN
RCLK
FF
Q
0
- Q
17
t
A
t
WFF
DATA WRITE
REN
t
WFF
t
ENH
t
ENS
t
DS
t
WFF
t
DS
DATA
WRITE
NEXT DATA READ
t
A
NO WRITE NO WRITE
DATA IN OUTPUT REGISTER
OE LOW
t
SKEW1
(1)
t
SKEW1
(1)
t
ENH
t
ENS
4294 drw 09
14
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 13. Asynchronous Programmable Almost-Empty Flag Timing (IDT Standard and FWFT Modes)
Figure 11. Write Programmable Registers (IDT Standard and FWFT Modes)
Figure 12. Read Programmable Registers (IDT Standard Mode)
NOTES:
1 . n = PAE offset.
2. For IDT Standard Mode.
3. For FWFT Mode.
4. PAE is asserted LOW on RCLK transition and reset to HIGH on WCLK transition.
5. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,0,1), (0,1,0), (0,1,1) or (1,1,1) during Reset.
WCLK
tCLKH tCLKL
tENS tENH
WEN
PAE
tENS
tPAEA n + 1 words in FIFO(2),
n + 2 words in FIFO(3) n words in FIFO(2),
n + 1 words in FIFO(3)
RCLK
tPAEA
REN
4294 drw 13
n words in FIFO(2),
n + 1 words in FIFO(3)
RCLK
t
CLKH
t
CLKL
t
CLK
t
ENS
t
ENH
LD
REN
Q
0
- Q
15
PAE OFFSET PAF OFFSET PAE OFFSET
UNKNOWN
t
A
t
ENS
4294 drw 12
WCLK
t
CLKH
t
CLKL
t
CLK
t
ENS
t
ENH
LD
WEN
D
0
- D
15
t
DS
t
DH
PAE OFFSET PAF OFFSET D
0
- D
11
PAE OFFSET
t
ENS
4294 drw 11
15
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
NOTES:
1. D = maximum FIFO Depth.
In IDT Standard Mode: D = 256 for the IDT72V205, 512 for the IDT72V215, 1,024 for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245.
In FWFT Mode:
D = 257 for the IDT72V205, 513 for the IDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the IDT72V245.
2. For IDT Standard Mode.
3. For FWFT Mode.
4. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0) during Reset.
Figure 15. Half-Full Flag Timing (IDT Standard and FWFT Modes)
Figure 14. Asynchronous Programmable Almost-Full Flag Timing (IDT Standard and FWFT Modes)
NOTES:
1. m = PAF offset.
2. D = maximum FIFO Depth.
In IDT Standard Mode: D = 256 for the IDT72V205, 512 for the IDT72V215, 1,024 for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245.
In FWFT Mode:
D = 257 for the IDT72V205, 513 for the IDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the IDT72V245.
3. PAF is asserted to LOW on WCLK transition and reset to HIGH on RCLK transition.
4. Select this mode by setting (FL, RXI, WXI) = (0,0,0), (0,0,1), (0,1,0), (0,1,1) or (1,1,1) during Reset.
WCLK
t
ENS
t
ENH
WEN
HF
t
ENS
t
HF
RCLK
t
HF
REN
4294 drw 15
t
CLKL
t
CLKH
D/2 words in FIFO
(2)
,
[
+ 1
]
words in FIFO
(3)
D-1
2
D/2 + 1 words in FIFO
(2)
,
[
+ 2
]
words in FIFO
(3)
D-1
2
D/2 words in FIFO
(2)
,
[
+ 1
]
words in FIFO
(3)
D-1
2
WCLK
t
CLKH
t
CLKL
t
ENS
t
ENH
WEN
PAF
t
ENS
t
PAFA
D - (m + 1) words
in FIFO
RCLK t
PAFA
REN
(1)
4294 drw 14
D - m words
in FIFO
D - (m + 1) words in FIFO
16
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 18. Write Expansion In Timing
Figure 19. Read Expansion In Timing
NOTE:
1. Read from Last Physical Location.
Figure 17. Read Expansion Out Timing
NOTE:
1. Write to Last Physical Location.
Figure 16. Write Expansion Out Timing
RXI
RCLK
t
XI
t
XIS
4294 drw 19
WXI
WCLK
t
XI
t
XIS
4294 drw 18
RCLK
REN
t
ENS
RXO
t
CLKH
t
XO
Note 1 t
XO
4294 drw 17
WCLK
WEN
tENS
WXO
tCLKH
tXO
Note 1 tXO
4294 drw 16
17
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 20. Write Timing with Synchronous Programmable Flags (FWFT Mode)
NOTES:
1. tSKEW1 is the minimum time between a rising WCLK edge and a rising RCLK edge for OR to go LOW after two RCLK cycles plus tREF. If the time between the rising edge of WLCK and the rising edge of RCLK is less than tSKEW1,
then the OR deassertion may be delayed one extra RCLK cycle.
2. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge for PAE to go HIGH during the current clock cycle. 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, D = maximum FIFO depth = 257 words for the IDT72V205, 513 words for the IDT72V215, 1,025 words for the IDT72V225, 2,049 words for the IDT72V235 and 4,097 words for the IDT72V245.
5. Select this mode by setting (FL, RXI, WXI) = (1,0,1) during Reset.
W1W2W4W[n +2] W[D-m-1]
W[D-m-2] W[D-1] WD
W[n+3] W[n+4] W[D-m] W[D-m+1]
WCLK
WEN
D0 - D17
RCLK
tDH
tDS
tENS
tSKEW1
REN
Q0 - Q17
PAF
HF
PAE
IR
tDS tDS tDS
tSKEW2
tA
tREF
OR
tPAES
tHF
tPAFS
tWFF
W[D-m+2]
W1
tENH
4294 drw 20
DATA IN OUTPUT REGISTER
(2)
W3
123
11
D-1
2+1
][
WD-1 +2
][
W2D-1 +3
][
W2
18
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 21. Read Timing with Synchronous Programmable Flags (FWFT 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 plus tWFF. If the time between the rising edge of RLCK and the rising edge of WCLK is less than
tSKEW1, then the IR assertion may be delayed an extra WCLK cycle.
2. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge for PAF to go HIGH during the current clock cycle. If the time between the rising edge of RCLK and the rising edge of WCLK is less th an tSKEW2,
then the PAF deassertion time may be delayed an extra WCLK cycle.
3. LD = HIGH
4. n = PAE offset, m = PAF offset, D = maximum FIFO depth = 257 words for the IDT72V205, 513 words for the IDT72V215, 1,025 words for the IDT72V225, 2,049 words for IDT72V235 and 4,097 words for IDT72V245.
5. Select this mode by setting (FL, RXI, WXI) = (1,0,1) during Reset.
WCLK 12
WEN
D0 - D17
RCLK
tENS
REN
Q0 - Q17
PAF
HF
PAE
IR
OR
W1W1W2W3Wm+2 W[m+3]
tOHZ
tSKEW1
tENH
tDS tDH
tOE tAtAtA
tPAFS
tWFF
tWFF
tENS
OE
tSKEW2
WD
4294 drw 21
tPAES
W[D-n]W[D-n-1]
tAtA
tHF
tREF
W[D-1] WD
tA
W[D-n+1]W[m+4] W[D-n+2]
(1) (2)
1tENS
D-1 ][
WD-1 ][
W
19
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 22. Synchronous Programmable Almost-Empty Flag Timing (IDT Standard and FWFT Modes)
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 for PAE to go HIGH during the current clock cycle. 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.
5. PAE is asserted and updated on the rising edge of RCLK only.
6. Select this mode by setting (FL, RXI, WXI) = (1,0,0), (1,0,1), or (1,1,0) during Reset.
NOTES:
1. m = PAF offset.
2. D = maximum FIFO Depth.
In IDT Standard Mode: D = 256 for the IDT72V205, 512 for the IDT72V215, 1,024 for the IDT72V225, 2,048 for the IDT72V235 and 4,096 for the IDT72V245.
In FWFT Mode:
D = 257 for the IDT72V205, 513 for the IDT72V215, 1,025 for the IDT72V225, 2,049 for the IDT72V235 and 4,097 for the IDT72V245.
3. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge for PAF to go HIGH during the current clock cycle. 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 an extra WCLK cycle.
4. PAF is asserted and updated on the rising edge of WCLK only.
5. Select this mode by setting (FL, RXI, WXI) = (1,0,0), (1,0,1), or (1,1,0) during Reset.
Figure 23. Synchronous Programmable Almost-Full Flag Timing (IDT Standard and FWFT Modes)
WCLK
tENH
tCLKH tCLKL
WEN
PAF
RCLK
REN 4294 drw 23
tENS tENH
tENS
D-(m+1)WordsinFIFO D - m Words in FIFO
tPAFS D-(m+1)Words
in FIFO
tPAFS
tSKEW2(3)
tPAFS
WCLK
t
ENH
t
CLKH
t
CLKL
WEN
PAE
RCLK
REN
4294 drw 22
t
ENS
t
ENH
t
ENS
n words in FIFO
(2)
,
n + 1words in FIFO
(3)
n + 1 words in FIFO
(2)
,
n + 2 words in FIFO
(3)
t
SKEW2
t
PAES
n Words in FIFO
(2)
,
n + 1 words in FIFO
(3)
(4)
t
PAES
20
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 25. Write Cycle Timing with Double Register-Buffered
FF
(IDT Standard Mode)
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 plus tWFF. If the time between the rising
edge of RCLK and the rising edge of WCLK is less than tSKEW1, then the FF deassertion time may be delayed an extra WCLK cycle.
2. LD = HIGH.
3. Select this mode by setting (FL, RXI, WXI) = (0,1,0) or (1,1,0) during Reset.
Figure 24. Double Register-Buffered Full Flag Timing (IDT Standard Mode)
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 plus tRFF. If the time between the rising
edge of RCLK and the rising edge of WCLK is less than tSKEW1. then the FF deassertion may be delayed an extra WCLK cycle.
2. LD = HIGH.
3. Select this mode by setting (FL, RXI, WXI) = (0,1,0) or (1,1,0) during Reset.
WCLK
D
0
-
D
17
WEN
FF
RCLK
REN
t
DS
t
WFF
t
WFF
DATA IN VALID
NO OPERATION
(1)
t
SKEW1
4294 drw 25
t
ENS
t
DH
t
ENH
12
t
CLKH
t
CLKL
t
CLK
D0 - D17
WEN
RCLK
FF
REN
tENH tENH
Q0 - Q17 DATA READ NEXT DATA READ
DATA IN OUTPUT REGISTER
LOW
OE
tSKEW1 DATA WRITE
4294 drw 24
WCLK
NO WRITE
1212tDS
NO WRITE
tWFF
tWFF tWFF
tA
tENS tENS
tSKEW1
tDS
tA
Wd
(1) (1)
21
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 27.
OR
Flag Timing and First Word Fall Through when FIFO is Empty (FWFT mode)
NOTES:
1. tSKEW1 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 tSKEW1. then the EF deassertion may be delayed an extra RCLK cycle.
2. LD = HIGH
3. Select this mode by setting (FL, RXI, WXI) = (0,1,0) or (1,1,0) during Reset.
Figure 26. Read Cycle Timing with Double Register-Buffered
EF
(IDT Standard Timing)
NOTES:
1. tSKEW1 is the minimum time between a rising WCLK edge and a rising RCLK edge for OR to go HIGH during the current cycle. If the time between the rising edge of WLCK and
the rising edge of RCLK is less than tSKEW1, then the OR deassertion may be delayed one extra RCLK cycle.
2. LD = HIGH, OE = LOW
3. Select this mode by setting (FL, RXI, WXI) = (0,0,1) or (1,0,1) during Reset.
W
1
W
2
W
4
W
[n +2]
W
[n+3]
WCLK
WEN
D0 - D17
RCLK
t
DH
t
DS
t
ENS
t
SKEW1
REN
Q0
-
Q17
t
DS
t
A
t
REF
OR
W
1
DATA IN OUTPUT REGISTER
(1)
W
3
123
t
ENH
t
REF
4294 drw 27
NO OPERATION
RCLK
REN
EF
t
CLKL
t
ENH
t
REF
LAST WORD
t
A
t
OLZ
t
OE
Q
0
-
Q
17
OE
WCLK
WEN
4294 drw 26
D
0
-
D
17
t
ENS
t
ENS
t
ENH
t
DS
t
DH
FIRST WORD
t
OHZ
t
CLK
12
t
REF
t
SKEW1
t
CLKH
(1)
22
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
OPERATING CONFIGURATIONS
SINGLE DEVICE CONFIGURATION
A single IDT
72V205/72V215/72V225/72V235/72V245 may be used when
the application requirements are for 256/512/1,024/2,048/4,096 words or less.
These FIFOs are in a single Device Configuration when the First Load (FL),
Write Expansion In (WXI) and Read Expansion In (RXI) control inputs are
configured as (FL, RXI, WXI = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or
(1,1,0) during reset (Figure 28).
Figure 28. Block Diagram of Single 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18 Synchronous FIFO
NOTE:
1. Do not connect any output control signals directly together.
Figure 29. Block Diagram of 256 x 36, 512 x 36, 1,024 x 36, 2,048 x 36, 4,096 x 36
Synchronous FIFO Memory Used in a Width Expansion Configuration
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 Empty Flag/Output Ready and Full Flag/Input Ready.
Because of variations in skew between RCLK and WCLK, it is possible for flag
assertion and deassertion to vary by one cycle between FIFOs. To avoid
problems the user must create composite flags by gating the Empty Flags/Output
Ready of every FIFO, and separately gating all Full Flags/Input Ready. Figure
29 demonstrates a 36-word width by using two IDT72V205/72V215/72V225/
72V235/72V245s. Any word width can be attained by adding additional
IDT72V205/72V215/72V225/72V235/72V245s. These FIFOs are in a single
Device Configuration when the First Load (FL), Write Expansion In (WXI) and
Read Expansion In (RXI) control inputs are configured as (FL, RXI,
WXI = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0) during reset (Figure
29). Please see the Application Note AN-83.
WRITE CLOCK (WCLK)
WRITE ENABLE (WEN)
READ CLOCK (RCLK)
READ ENABLE (REN)
LOAD (LD)OUTPUT ENABLE (OE)
DATA IN (D)
DATA OUT (Q)
FULL FLAG/INPUT
READY (FF/IR)
PROGRAMMABLE (PAE)
HALF FULL FLAG (HF)EMPTY FLAG/OUTPUT
READY (EF/OR)
PROGRAMMABLE (PAF)
RESET (RS)
72V205
72V215
72V225
72V235
72V245
72V205
72V215
72V225
72V235
72V245
RESET (RS)
36
36
18 18
18
18
FF/IR EF/OR
4294 drw 29
FL WXI RXI
FL WXI RXI
FF/IR EF/OR
WRITE CLOCK (WCLK)
WRITE ENABLE (WEN)
READ CLOCK (RCLK)
READ ENABLE (REN)
LOAD (LD)OUTPUT ENABLE (OE)
DATA IN (D
0
- D
17
)DATA OUT (Q
0
- Q
17
)
FULL FLAG/INPUT READY (FF/IR)
PROGRAMMABLE (PAE)
HALF-FULL FLAG (HF)
EMPTY FLAG/OUTPUT READY (EF/OR)
PROGRAMMABLE (PAF)
RESET (RS)
IDT
72V205
72V215
72V225
72V235
72V245
4294 drw 28
FL RXI WXI
23
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 30. Block Diagram of 768 x 18, 1,536 x 18, 3,072 x 18, 6,144 x 18, 12,288 x 18 Synchronous
FIFO Memory With Programmable Flags used in Depth Expansion Configuration
LOAD
WRITE CLOCK
WRITE ENABLE
READ CLOCK
READ ENABLE
OUTPUT ENABLE
DATA IN DATA OUT
RESET
IDT
72V205
72V215
72V225
72V235
72V245
WXO
WXI
RXO
RXI
FIRST LOAD (FL)
FL
Vcc
Vcc
WXO
WXI
RXO
RXI
WXO
WXI
RXO
RXI
IDT
72V205
72V215
72V225
72V235
72V245
IDT
72V205
72V215
72V225
72V235
72V245
FF/IR
PAF
EF/OR
PAE
FF/IR
PAF
EF/OR
PAE
FF/IR
PAF
EF/OR
PAE
EF/OR
PAE
FF/IR
PAF
4294 drw 30
RCLK
REN
OE
WCLK
WEN
RS
FL
RCLK
REN
OE
WCLK
WEN
RS
RCLK
REN
OE
WCLK
WEN
RS
LD
LD
Dn Qn
Dn Qn
Dn Qn
LD
DEPTH EXPANSION CONFIGURATION — DAISY CHAIN TECHNIQUE
(WITH PROGRAMMABLE FLAGS)
These devices can easily be adapted to applications requiring more than
256/512/1,024/2,048/4,096 words of buffering. Figure 30 shows Depth
Expansion using three IDT72V205/72V215/72V225/72V235/72V245s.
Maximum depth is limited only by signal loading.
Follow these steps:
1. The first device must be designated by grounding the First Load (FL)
control input.
2. All other devices must have FL in the HIGH state.
3. The Write Expansion Out (WXO) pin of each device must be tied to
the Write Expansion In (WXI) pin of the next device. See Figure 30.
4.The Read Expansion Out (RXO) pin of each device must be tied to the
Read Expansion In (RXI) pin of the next device. See Figure 30.
5.All Load (LD) pins are tied together.
6.The Half-Full Flag (HF) is not available in this Depth Expansion
Configuration.
7.EF, FF, PAE, and PAF are created with composite flags by ORing
together every respective flags for monitoring. The composite PAE
and PAF flags are not precise.
8.In Daisy Chain mode, the flag outputs are single register-buffered and
the partial flags are in asynchronous timing mode.
24
IDT72V205/72V215/72V225/72V235/72V245 3.3V CMOS SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
Figure 31. Block Diagram of 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18, 8,192 x 18
Synchronous FIFO Memory With Programmable Flags used in Depth Expansion Configuration
Dn
INPUT READY
WRITE ENABLE
WRITE CLOCK
WEN
WCLK
IR
DATA IN
RCLK READ CLOCK
RCLK
REN
OE OUTPUT ENABLE
OUTPUT READY
Qn
Dn
IR
GND
WEN
WCLK
OR
REN
OE
Qn
READ ENABLE
OR
DATA OUT
TRANSFER CLOCK
4294 drw 31
n n
RXI
HF
72V205
72V215
72V225
72V235
72V245
WXI
FL
V
CC
GND
(0,1)
72V205
72V215
72V225
72V235
72V245
RXI WXI
FL
V
CC
GND
(0,1)
PAF
HF
PAE
n
DEPTH EXPANSION CONFIGURATION (FWFT MODE)
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 31 shows a depth
expansion using two IDT72V205/72V215/72V225/72V235/72V245 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:
(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 that the tSKEW1
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.
25
CORPORATE HEADQUARTERS for SALES: for TECH SUPPORT:
2975 Stender Way 800-345-7015 or 408-727-6116 (408) 330-1753
Santa Clara, CA 95054 fax: 408-492-8674 FIFOhelp@idt.com
www.idt.com
DATASHEET DOCUMENT HISTORY
05/02/2001 pgs. 4, 5 and 25.
01/11/2002 pg. 4.
02/01/2002 pg. 4.
IDT XXXXX
Device Type X
Power XX
Speed X
Package X
BLANK
Clock Cycle Time (t
CLK
)
Speed in Nanoseconds
Process /
Temperature
Range
4294 drw 32
Commercial Only
Commercial (0°C to +70°C)
Industrial (-40°C to +85°C)
I
(1)
PF
TF Thin Plastic Quad Flatpack (TQFP, PN64-1)
Slim Thin Plastic Quad Flatpack (STQFP, PP64-1)
10
15
20 Com’l & Ind’l
Commercial Only
L Low Power
72V205
72V215
72V225
72V235
72V245
256 x 18 3.3V SyncFIFO
512 x 18 3.3V SyncFIFO
1,024 x 18 3.3V SyncFIFO
2,048 x 18 3.3V SyncFIFO
4,096 x 18 3.3V SyncFIFO
NOTES:
1. Industrial temperature range product for the 15ns speed grade is available as a standard device. All other speed grades are available by special order.
ORDERING INFORMATION
