IDT IDT72V275L10TF 3.3 volt cmos supersync fifo Datasheet

3.3 VOLT CMOS SuperSync FIFO™
32,768 X 18
65,536 X 18
FEATURES:
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Choose among the following memory organizations:
IDT72V275
32,768 x 18
IDT72V285
65,536 x 18
Pin-compatible with the IDT72V255/72V265 SuperSync FIFOs
10ns read/write cycle time (6.5ns access time)
Fixed, low first word data latency time
Auto power down minimizes standby power consumption
Master Reset clears entire FIFO
Partial Reset clears data, but retains programmable
settings
Retransmit operation with fixed, low first word data
latency time
Empty, Full and Half-Full flags signal FIFO status
Programmable Almost-Empty and Almost-Full flags, each flag can
default to one of two preselected offsets
Program partial flags by either serial or parallel means
Select IDT Standard timing (using EF and FF flags) or First Word
Fall Through timing (using OR and IR flags)
Output enable puts data outputs into high impedance state
Easily expandable in depth and width
Independent Read and Write clocks (permit reading and writing
simultaneously)
Available in the 64-pin Thin Quad Flat Pack (TQFP) and the 64-pin
IDT72V275
IDT72V285
Slim Thin Quad Flat Pack (STQFP)
High-performance submicron CMOS technology
Industrial temperature range (-40°C to +85°C) is available
DESCRIPTION:
The IDT72V275/72V285 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.)
SuperSync FIFOs are particularly appropriate for network, video, telecommunications, data communications and other applications that need to buffer
large amounts of data.
FUNCTIONAL BLOCK DIAGRAM
WEN
D0 -D17
WCLK
LD SEN
INPUT REGISTER
OFFSET REGISTER
FLAG
LOGIC
WRITE CONTROL
LOGIC
RAM ARRAY
32,768 x 18
65,536 x 18
WRITE POINTER
OUTPUT REGISTER
MRS
PRS
RESET
LOGIC
FF/IR
PAF
EF/OR
PAE
HF
FWFT/SI
READ POINTER
READ
CONTROL
LOGIC
RT
RCLK
REN
OE
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Q0 -Q17
SuperSyncFIFO is a trademark and the IDT logo is a registered trademark of Integrated Device Technology, Inc.
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
APRIL 2001
1
 2001
Integrated Device Technology, Inc.
DSC-4512/1
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
DESCRIPTION (Continued)
In IDT Standard mode, the first word written to an empty FIFO will not appear
on the data output lines unless a specific read operation is performed. A read
operation, which consists of activating REN and enabling a rising RCLK edge,
will shift the word from internal memory to the data output lines.
In FWFT mode, the first word written to an empty FIFO is clocked directly
to the data output lines after three transitions of the RCLK signal. A REN does
not have to be asserted for accessing the first word. However, subsequent
words written to the FIFO do require a LOW on REN for access. The state 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.
The input port is controlled by a Write Clock (WCLK) input and a Write Enable
(WEN) input. Data is written into the FIFO on every rising edge of WCLK when
WEN is asserted. The output port is controlled by a Read Clock (RCLK) input
and Read Enable (REN) input. Data is read from the FIFO on every rising
edge of RCLK when REN is asserted. An Output Enable (OE) input is provided
for three-state control of the outputs.
The frequencies of both the RCLK and the WCLK signals may vary from 0
to fMAX with complete independence. There are no restrictions on the frequency
of the 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.
OE
EF/OR
RCLK
REN
RT
FF/IR
PAF
HF
VCC
PAE
LD
FWFT/SI
GND
WCLK
PRS
MRS
PIN CONFIGURATIONS
PIN 1
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
WEN
SEN
DC(1)
VCC
GND
D17
D16
D15
D14
D13
D12
D11
D10
D9
D8
D7
48
47
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
46
45
44
43
42
41
40
39
38
37
36
35
34
33
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
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
4512 drw 02
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
DESCRIPTION (Continued)
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 IDT72V275/72V285 are fabricated using IDT’s high speed submicron
CMOS technology.
These FIFOs have five flag pins, EF/OR (Empty Flag or Output Ready),
FF/IR (Full Flag or Input Ready), HF (Half-full Flag), PAE (Programmable
Almost-Empty flag) and PAF (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 1 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
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.
PARTIAL RESET (PRS)
MASTER RESET (MRS)
WRITE CLOCK (WCLK)
READ CLOCK (RCLK)
WRITE ENABLE (WEN)
READ ENABLE (REN)
OUTPUT ENABLE (OE)
LOAD (LD)
DATA IN (D0 - Dn)
SERIAL ENABLE(SEN)
FIRST WORD FALL THROUGH/SERIAL INPUT
(FWFT/SI)
DATA OUT (Q0 - Qn)
IDT
72V275
72V285
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 32,768 x 18 and 65,536 x 18 Synchronous FIFO
3
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
PIN DESCRIPTION
Symbol
D0–D17
Name
Data Inputs
I/O
I
MRS
Master Reset
I
MRS initializes the read and write pointers to zero and sets the output register to
all zeroes. During Master Reset, the FIFO is configured for either FWFT or IDT
Standard mode, one of two programmable flag default settings, and serial or
parallel programming of the offset settings.
PRS
Partial Reset
I
RT
Retransmit
I
FWFT/SI
I
WCLK
First Word Fall
Through/Serial In
Write Clock
WEN
Write Enable
I
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
When enabled by WEN, the rising edge of WCLK writes data into the FIFO and
offsets into the programmable registers for parallel programming, and when
enabled by SEN, the rising edge of WCLK writes one bit of data into the
programmable register for serial programming.
WEN enables WCLK for writing data into the FIFO memory and offset registers.
RCLK
Read Clock
I
REN
Read Enable
I
When enabled by REN, the rising edge of RCLK reads data from the FIFO
memory and offsets from the programmable registers.
REN enables RCLK for reading data from the FIFO memory and offset registers.
OE
SEN
Output Enable
Serial Enable
I
I
OE controls the output impedance of Qn.
SEN enables serial loading of programmable flag offsets.
LD
Load
I
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
DC
Don't Care
I
FF/IR
Full Flag/
Input Ready
O
EF/OR
Empty Flag/
Output Ready
O
This pin must be tied to either VCC or GND and must not toggle after Master
Reset.
In the IDT Standard mode, the FF function is selected. FF indicates whether or
not the FIFO memory is full. In the FWFT mode, the IR function is selected. IR
indicates whether or not there is space available for writing to the FIFO memory.
In the IDT Standard mode, the EF function is selected. EF indicates whether or
not the FIFO memory is empty. In FWFT mode, the OR function is selected.
OR indicates whether or not there is valid data available at the outputs.
PAF
Programmable
Almost-Full Flag
O
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
Programmable
Almost-Empty Flag
O
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
Q0–Q17
Half-Full Flag
Data Outputs
O
O
HF indicates whether the FIFO memory is more or less than half-full.
Data outputs for an 18-bit bus.
VCC
GND
Power
Ground
I
Description
Data inputs for a 18-bit bus.
+3.3 Volt power supply pins.
Ground pins.
4
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
ABSOLUTE MAXIMUM RATINGS
Symbol
VTERM
Rating
Terminal Voltage
with respect to GND
Commercial
–0.5 to +4.6
Unit
V
TSTG
Storage
Temperature
–55 to +125
°C
IOUT
DC Output Current
–50 to +50
mA
RECOMMENDED DC OPERATING
CONDITIONS
Symbol
Parameter
VCC
Supply Voltage(Com’l & Ind’l)
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.
Min.
3.0
Typ.
3.3
Max.
3.6
Unit
V
0
0
0
V
—
VCC + 0.5
V
GND
Supply Voltage(Com’l & Ind’l)
VIH
Input High Voltage
(Com’l & Ind’l)
2.0
VIL(1)
Input Low Voltage
(Com’l & Ind’l)
—
—
0.8
TA
Operating Temperature
Commercial
0
—
70
o
TA
Operating Temperature
Industrial
-40

85
°C
V
C
NOTE:
1. 1.5V undershoots are allowed for 10ns once per cycle.
DC ELECTRICAL CHARACTERISTICS
(Commercial: VCC = 3.3V ± 0.3V, TA = 0oC to +70oC; Industrial: VCC = 3.3V ± 0.3V, TA = -40°C to +85°C)
IDT72V275L
IDT72V285L
Com’’l & Ind’l (1)
tCLK = 10, 15, 20 ns
Symbol
(2)
Parameter
Min.
Max.
Unit
ILI
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
—
60
mA
Standby Current
—
20
mA
(4,7)
ICC2
NOTES:
1. Industrial temperature range product for the 15ns is available as a standard device.
Measurements with 0.4 ≤ VIN ≤ VCC.
OE ≥ VIH, 0.4 ≤ VOUT ≤ VCC.
Tested with outputs open (IOUT = 0).
RCLK and WCLK toggle at 20 MHz and data inputs switch at 10 MHz.
Typical ICC1 = 11 + 1.65*fS + 0.02*CL*fS (in mA) with VCC = 3.3V, tA = 25oC, 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.
2.
3.
4.
5.
6.
CAPACITANCE (TA = +25oC, 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
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
AC ELECTRICAL CHARACTERISTICS(1)
(Commercial: VCC = 3.3V ± 0.3V, TA = 0oC to +70oC; Industrial: VCC = 3.3V ± 3.3V, TA = -40°C to + 85°C)
Com’l & Ind’l (2)
IDT72V275L15
IDT72V285L15
Commercial
IDT72V275L10
IDT72V285L10
Symbol
Parameter
Commercial
IDT72V275L20
IDT72V285L20
Min.
Max.
Min.
Max.
Min.
Max.
Unit
—
100
—
66.7
—
50
MHz
fS
Clock Cycle Frequency
tA
Data 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
—
ns
tDS
Data Setup Time
3
—
4
—
5
—
ns
tDH
Data Hold Time
0.5
—
1
—
1
—
ns
tENS
Enable Setup Time
3
—
4
—
5
—
ns
tENH
Enable Hold Time
0.5
—
1
—
1
—
ns
tLDS
Load Setup Time
3
—
4
—
5
—
ns
tLDH
Load Hold Time
0.5
—
1
—
1
—
ns
tRS
Reset Pulse Width(3)
10
—
15
—
20
—
ns
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
(4)
tOHZ
Output Enable to Output in High Z
2
6
3
8
3
10
ns
tWFF
Write Clock to FF or IR
—
6.5
—
10
—
12
ns
tREF
Read Clock to EF or OR
—
6.5
—
10
—
12
ns
tPAF
Write Clock to PAF
—
6.5
—
10
—
12
ns
tPAE
Read Clock to PAE
—
6.5
—
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
Skew time between RCLK and WCLK
for EF/OR
12
—
15
—
20
—
ns
60
—
60
—
60
—
ns
tSKEW3
NOTES:
1. All AC timings apply to both Standard IDT mode and First Word Fall Through mode.
2 Industrial Temperature Range Product for the 15ns speed grade is available as a standard device.
3. Pulse widths less than minimum values are not allowed.
4. Values guaranteed by design, not currently tested.
330Ω
D.U.T.
AC TEST CONDITIONS
Input Pulse Levels
Input Rise/Fall Times
Input Timing Reference Levels
Output Reference Levels
Output Load
3.3V
510Ω
GND to 3.0V
3ns
1.5V
1.5V
See Figure 2
30pF*
4512 drw 04
Figure 2. Output Load
* Includes jig and scope capacitances.
6
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
FUNCTIONAL DESCRIPTION
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 IDT72V275/72V285 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 16,386th
word for the IDT72V275 and 32,770th word for the IDT72V285, 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
(32,769-m) writes for the IDT72V275 and (65,537-m) writes for the IDT72V285,
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 = 32,769 writes for the IDT72V275 and 65,537 writes
for the IDT72V285, 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 16,385th word for IDT72V275 and 32,769th word for IDT72V285
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 (32,768-m) writes for the
IDT72V275 and (65,536-m) writes for the IDT72V285. 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 = 32,768 writes for the IDT72V275 and 65,536 for the
IDT72V285, respectively.
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.
PROGRAMMING FLAG OFFSETS
Full and Empty Flag offset values are user programmable. The IDT72V275/
72V285 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.
7
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
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
72V275
72V285
FF
0
0
H
H
H
L
L
H
H
H
L
H
1 to n
(1)
1 to n
(1)
PAF HF
PAE EF
(n+1) to 16,384
(n+1) to 32,768
H
H
H
H
H
16,385 to (32,768-(m+1))
32,769 to (65,536-(m+1))
H
H
L
H
H
(32,768-m) (2) to 32,767
(65,536-m) (2) to 65,535
H
L
L
H
H
32,768
65,536
L
L
L
H
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.
TABLE 2. STATUS FLAGS FOR FWFT MODE
Number of
Words in
FIFO
72V275
72V285
IR
0
0
L
H
H
L
H
L
H
H
L
L
L
H
H
H
L
L
H
L
H
L
1 to n+1
1 to n+1 (1)
(1)
(n+2) to 32,769
(n+2) to 16,385
16,386 to (32,769-(m+1))
(2)
32,770 to (65,537-(m+1))
(2)
PAF HF
PAE OR
(32,769-m) to 32,768
(65,537-m) to 65,536
L
L
L
H
L
32,769
65,537
H
L
L
H
L
4512 drw 05
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.
8
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
72V275 (32,768 x 18_BIT)
17
72V285 (65,536 x 18_BIT)
15 14
0
17
16 15
EMPTY OFFSET REGISTER
EMPTY OFFSET REGISTER
DEFAULT VALUE
007FH if LD is LOW at Master Reset,
03FFH if LD is HIGH at Master Reset
17
0
DEFAULT VALUE
007FH if LD is LOW at Master Reset,
03FFH if LD is HIGH at Master Reset
0
15 14
17
0
16 15
FULL OFFSET REGISTER
FULL OFFSET REGISTER
DEFAULT VALUE
007FH if LD is LOW at Master Reset,
03FFH if LD is HIGH at Master Reset
DEFAULT VALUE
007FH if LD is LOW at Master Reset,
03FFH if LD is HIGH at Master Reset
4512 drw 06
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
RCLK
X
X
X
X
72V275
72V285
X
X
Parallel write to registers:
Empty Offset
Full Offset
Parallel read from registers:
Empty Offset
Full Offset
Serial shift into registers:
30 bits for the 72V275
32 bits for the 72V285
1 bit for each rising WCLK edge
Starting with Empty Offset (LSB)
Ending with Full Offset (MSB)
No Operation
Write Memory
Read Memory
X
No Operation
4512 drw 07
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
9
IDT72V275/72V285
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 30 bits for the
IDT72V275 and 32 bits for the IDT72V285. 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.
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. Programming PAE
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-to-HIGH
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 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
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
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 Q0-Qn
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.
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 = 32,768 for the
IDT72V275 and D = 65,536 for the IDT72V285. In FWFT mode, D = 32,769
for the IDT72V275 and D= 65,537 for the IDT72V285.
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.
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 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.
10
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
SIGNAL DESCRIPTION
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:
MRS
MASTER RESET (MRS
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.
PRS
PARTIAL RESET (PRS
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.
RT
RETRANSMIT (RT
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 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 the
memory.
WEN
WRITE ENABLE (WEN
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.
11
IDT72V275/72V285
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.
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.
REN
READ ENABLE (REN
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.
SEN
SERIAL ENABLE (SEN
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.
OE
OUTPUT ENABLE (OE
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.
LD
LOAD (LD
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
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
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.
OUTPUTS:
FF
IR
FULL FLAG (FF
FF/IR
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 = 32,768 for the IDT72V275 and 65,536 for the IDT72V285). 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 = 32,769 for the IDT72V275 and 65,537 for the
IDT72V285) 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.
EF
OR
EMPTY FLAG (EF
EF/OR
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 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.
12
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
PAF
PROGRAMMABLE ALMOST-FULL FLAG (PAF
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 (32,768-m) writes for the IDT72V275
and (65,536-m) writes for the IDT72V285. 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 (32,769-m) writes for the
IDT72V275 and (65,537-m) writes for the IDT72V285, 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.
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.
HF
HALF-FULL FLAG (HF
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 = 32,768
for the IDT72V275 and 65,536 for the IDT72V285.
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 = 32,769 for the
IDT72V275 and 65,537 for the IDT72V285.
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.
PAE
PROGRAMMABLE ALMOST-EMPTY FLAG (PAE
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 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.
DATA OUTPUTS (Q0-Q17)
(Q0 - Q17) are data outputs for 18-bit wide data.
13
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
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
Figure 5. Master Reset Timing
14
4512 drw 08
IDT72V275/72V285
PRS
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
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
Figure 6. Partial Reset Timing
15
4512 drw 09
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
t CLK
t CLKH
NO WRITE
WCLK
t SKEW1
tCLKL
NO WRITE
2
1
1
(1)
(1)
t DS
D0 - Dn
2
t SKEW1
t DH
t DS
t DH
DX
DX+1
t WFF
t WFF
t WFF
t WFF
FF
WEN
RCLK
t ENS
t ENS
t ENH
t ENH
REN
tA
tA
Q0 - Qn
DATA READ
DATA IN OUTPUT REGISTER
NEXT DATA READ
4512 drw 10
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
tENS
tENH
REN
tENH
tENH
tENS
NO OPERATION
NO OPERATION
tREF
tREF
tREF
EF
tA
tA
Q0 - Qn
LAST WORD
tOLZ
OE
LAST WORD
tOHZ
tA
D0
D1
t OLZ
tOE
(1)
tSKEW3
WCLK
tENS
tENH
tENS
tDHS
tDS
tENH
WEN
tDS
D0 - Dn
D0
tDH
D1
4512 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)
16
1
tENS
WEN
tDS
D0 - D17
W1
W3
W2
W4
W[n +2]
1
W[n+3]
W[n+4]
W[ D-1
]
W[ D-1
]
W[ D-1
]
W[D-m-2]
tENH
W[D-m-1]
W[D-m]
W[D-m+1]
W[D-m+2]
W[D-1]
WD
tSKEW2(2)
tSKEW3(1)
RCLK
tDS
tDS
tDS
tDH
2
3
1
IDT72V275/72V285
WCLK
2
REN
tA
Q0 - Q17
DATA IN OUTPUT REGISTER
W1
tREF
OR
PAE
HF
tPAE
tHF
17
tPAF
PAF
tWFF
4512 drw 12
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 = 32,769 for IDT72V275 and 65,537 for IDT72V285.
6. First word latency: 60ns + tREF + 2*TRCLK.
Figure 9. Write Timing (First Word Fall Through Mode)
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
IR
tENS
1
(1)
tSKEW1
tENH
2
tSKEW2
IDT72V275/72V285
WCLK
(2)
WEN
tDS
D0 - D17
tDH
WD
RCLK
1
tENS
tENS
REN
OE
tOHZ
Q0 - Q17
tOE
W1
W1
tA
tA
W2
tA
tA
W3
Wm+2
W[m+3]
W[m+4]
W [ D-1
]
W [ D-1
tA
tA
]
W[D-n-1]
W[D-n]
W[D-n+1]
W[D-n+2]
W[D-1]
WD
tREF
OR
tPAE
PAE
tHF
HF
18
tPAF
PAF
tWFF
tWFF
4512 drw 13
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 = 32,769 for IDT72V275 and 65,537 for IDT72V285.
Figure 10. Read Timing (First Word Fall Through Mode)
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
IR
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
2
1
RCLK
tENH
tENS
tENS
tRTS
tENH
REN
tA
Q0 - Qn
tA
Wx
tA
Wx+1
W1
(3)
W2
(3)
tSKEW2
1
WCLK
2
tRTS
WEN
tENS
tENH
RT
tREF
tREF
(5)
EF
tPAE
PAE
tHF
HF
tPAF
PAF
4512 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 = 32,768
for IDT72V275 and 65,536 for IDT72V285.
5. EF goes HIGH at 60ns + 1 RCLK cycle + tREF.
Figure 11. Retransmit Timing (IDT Standard Mode)
19
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
tENH
tENS
3
2
1
RCLK
4
tENH
tENH
tRTS
REN
tA
tA
Q0 - Qn
Wx
Wx+1
W1
(4)
W2
W3
tSKEW2
1
WCLK
2
tRTS
WEN
tENS
tENH
RT
tREF (5)
tREF
OR
tPAE
PAE
tHF
HF
tPAF
PAF
4512 drw 15
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 = 32,769 for the IDT72V275 and 65,537 for the IDT72V285.
3. OE = LOW
4. W1, W2, W3 = first, second and third words written to the FIFO after Master Reset.
5. OR goes LOW at 60ns + 2 RCLK cycles + tREF.
Figure 12. Retransmit Timing (FWFT Mode)
WCLK
t ENS
tENH
tENH
SEN
tLDS
tLDH
tLDH
LD
tDH
tDS
SI
BIT 0
BIT X
EMPTY OFFSET
(1)
BIT 0
BIT X
FULL OFFSET
NOTE:
1. X = 14 for the IDT72V275 and X = 15 for the IDT72V285.
Figure 13. Serial Loading of Programmable Flag Registers (IDT Standard and FWFT Modes)
20
(1)
4512 drw 16
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
t CLK
t CLKH
t CLKL
WCLK
t LDS
t LDH
t LDH
t ENS
t ENH
t ENH
LD
WEN
t DS
t DH
t DH
PAE
OFFSET
D0 - D15
PAF
OFFSET
4512 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 LDH
LD
t ENS
t ENH
t ENH
REN
tA
tA
DATA IN OUTPUT
REGISTER
Q0 - Q15
PAE
OFFSET
PAF
OFFSET
4512 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
t ENS
1
2
2
t ENH
WEN
t PAF
PAF
t PAF
D - (m+1) words in FIFO(2)
D - m words in FIFO(2)
t SKEW2
(3)
D-(m+1) words
in FIFO(2)
RCLK
t ENS
t ENH
REN
4512 drw 19
NOTES:
1. m = PAF offset .
2. D = maximum FIFO depth.
In IDT Standard mode: D = 32,768 for the IDT72V275 and 65,536 for the IDT72V285.
In FWFT mode: D = 32,769 for the IDT72V275 and 65,537 for the IDT72V285.
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)
21
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
t CLKH
t CLKL
WCLK
t ENS
t ENH
WEN
PAE
n words in FIFO (2),
n+1 words in FIFO (3)
t SKEW2 (4)
RCLK
n+1 words in FIFO
n+2 words in FIFO
n words in FIFO (2),
n+1 words in FIFO (3)
(2)
,
(3)
t PAE
t PAE
1
2
1
t ENS
2
t ENH
REN
4512 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 tSKEW2, 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
WEN
tHF
HF
D/2 + 1 words in FIFO(1),
D/2 words in FIFO(1),
D-1
2 +1
[
[D-1
2
] words in FIFO(2)
]
+ 2 words in FIFO(2)
D/2 words in FIFO(1),
[D-1
2
]
+ 1 words in FIFO(2)
tHF
RCLK
tENS
REN
4512 drw 21
NOTES:
1. For IDT Standard mode: D = maximum FIFO depth. D = 32,768 for the IDT72V275 and 65,536 for the IDT72V285.
2. For FWFT mode: D = maximum FIFO depth. D = 32,769 for the IDT72V275 and 65,537 for the IDT72V285.
Figure 18. Half-Full Flag Timing (IDT Standard and FWFT Modes)
22
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
OPTIONAL CONFIGURATIONS
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 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 19 demonstrates a width expansion using two IDT72V275/72V285
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 IDT72V275/72V285 devices.
PARTIAL RESET (PRS)
MASTER RESET (MRS)
FIRST WORD FALL THROUGH/
SERIAL INPUT (FWFT/SI)
RETRANSMIT (RT)
Dm+1 - Dn
m+n
DATA IN
D0 - Dm
m
n
READ CLOCK (RCLK)
WRITE CLOCK (WCLK)
READ ENABLE (REN)
WRITE ENABLE (WEN)
OUTPUT ENABLE (OE)
LOAD (LD)
FULL FLAG/INPUT READY (FF/IR) #1
IDT
72V275
72V285
IDT
72V275
72V285
EMPTY FLAG/OUTPUT READY (EF/OR) #1
(1)
GATE
(1)
FULL FLAG/INPUT READY (FF/IR) #2
EMPTY FLAG/OUTPUT READY (EF/OR) #2
PROGRAMMABLE (PAF)
HALF-FULL FLAG (HF)
PROGRAMMABLE (PAE)
FIFO
#1
FIFO
#2
m
n
Qm+1 - Qn
GATE
m+n
DATA OUT
4512 drw 22
Q0 - Qm
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 32,768 x 36 and 65,536 x 36 Width Expansion
outputs) after a word has been written to the first FIFO is the sum of the delays
for each individual FIFO:
DEPTH EXPANSION CONFIGURATION (FWFT MODE ONLY)
The IDT72V275 can easily be adapted to applications requiring depths
greater than 32,768 and 65,536 for the IDT72V285 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 20 shows a depth expansion
using two IDT72V275/72V285 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
(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 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.
23
IDT72V275/72V285
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGE
•
FWFT/SI
WRITE CLOCK
TRANSFER CLOCK
FWFT/SI
WCLK
WRITE ENABLE
WEN
INPUT READY
IR
RCLK
OR
IDT
72V275
72V285
REN
OE
DATA IN
FWFT/SI
•
Dn
RCLK
WEN
REN
READ ENABLE
OR
OUTPUT READY
OE
OUTPUT ENABLE
IR
IDT
72V275
72V285
GND
n
Qn
READ CLOCK
WCLK
n
n
Dn
DATA OUT
Qn
4512 drw 23
Figure 20. Block Diagram of 65,536 x 18 and 131,072 x 18 Depth Expansion
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
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.
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
24
ORDERING INFORMATION
IDT
XXXXX
X
Device Type
Power
XX
Speed
X
Package
X
Process /
Temperature
Range
BLANK
I(1)
PF
TF
Commercial (0OC to +70OC)
Industrial (-40OC to +85OC)
10
15
20
Commercial Only
Com’l & Ind’l
Commercial Only
L
Low Power
72V275
72V285
32,768 x 18 3.3V SuperSyncFIFO
65,635 x 18 3.3V SuperSyncFIFO
Thin Plastic Quad Flatpack (TQFP, PN64-1)
Slim Thin Quad Flatpack (STQFP, PP64-1)
Clock Cycle Time (tCLK)
Speed in Nanoseconds
4512 drw 24
NOTE:
1. Industrial temperature range product for the 15ns speed grade is available as a standard device.
DATASHEET DOCUMENT HISTORY
04/24/2001
pgs. 1, 5, 6 and 25
2975 Stender Way
Santa Clara, CA 95054
800-345-7015
fax: 408-492-8674
www.idt.com
SuperSyncFIFO is a trademark and the IDT logo is a registered trademark of Integrated Device Technology, Inc.
25