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CMOS SuperSync FIFOTM 8,192 x 18 16,384 x 18
FEATURES
* * * * *
IDT72255LA IDT72265LA
* * * * * * * * * * * * * *
Choose among the following memory organizations: IDT72255LA -- 8,192 x 18 IDT72265LA -- 16,384 x 18 Pin-compatible with the IDT72275/72285 SuperSync FIFOs 10ns read/write cycle time (8ns access time) Fixed, low first word data latency time Auto power down minimizes standby power consumption Master Reset clears entire FIFO Partial Reset clears data, but retains programmable settings Retransmit operation with fixed, low first word data latency time Empty, Full and Half-Full flags signal FIFO status Programmable Almost-Empty and Almost-Full flags, each flag can default to one of two preselected offsets Program partial flags by either serial or parallel means Select IDT Standard timing (using EF and FF flags) or First Word Fall Through timing (using OR and IR flags) Output enable puts data outputs into high impedance state Easily expandable in depth and width Independent Read and Write clocks (permit reading and writing simultaneously)
Available in the 64-pin Thin Quad Flat Pack (TQFP) and the 64pin Slim Thin Quad Flat Pack (STQFP) High-performance submicron CMOS technology Industrial temperature range (-40C to +85C) is available Green parts available, see ordering information
DESCRIPTION
The IDT72255LA/72265LA are exceptionally deep, high speed, CMOS First-In-First-Out (FIFO) memories with clocked read and write controls. These FIFOs offer numerous improvements over previous SuperSync FIFOs, including the following: * The limitation of the frequency of one clock input with respect to the other has been removed. The Frequency Select pin (FS) has been removed, thus it is no longer necessary to select which of the two clock inputs, RCLK or WCLK, is running at the higher frequency. * The period required by the retransmit operation is now fixed and short. * The first word data latency period, from the time the first word is written to an empty FIFO to the time it can be read, is now fixed and short. (The variable clock cycle counting delay associated with the latency period found on previous SuperSync devices has been eliminated on this SuperSync family.)
FUNCTIONAL BLOCK DIAGRAM
WEN WCLK D0 -D17 L D SEN
INPUT REGISTER
OFFSET REGISTER F F /IR PAF EF /OR P AE HF FWFT/SI
WRITE CONTROL LOGIC
RAM ARRAY 8,192 x 18 16,384 x 18
FLAG LOGIC
WRITE POINTER
READ POINTER
READ CONTROL LOGIC OUTPUT REGISTER MRS P RS
RT
RESET LOGIC
RCLK REN
OE
Q0 -Q17
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IDT and the IDT logo are trademarks of Integrated Device Technology, Inc. SuperSync FIFO is a trademark of Integrated Device Technology, Inc
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2005 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice.
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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DESCRIPTION (CONTINUED)
SuperSync FIFOs are particularly appropriate for networking, video, telecommunications, data communications and other applications that need to buffer large amounts of data. The input port is controlled by a Write Clock (WCLK) input and a Write Enable (WEN) input. Data is written into the FIFO on every rising edge of WCLK when WEN is asserted. The output port is controlled by a Read Clock (RCLK) input and Read Enable (REN) input. Data is read from the FIFO on every rising edge of RCLK when REN is asserted. An Output Enable (OE) input is provided for three-state control of the outputs.
The frequencies of both the RCLK and the WCLK signals may vary from 0 to fMAX with complete independence. There are no restrictions on the frequency of one clock input with respect to the other. There are two possible timing modes of operation with these devices: IDT Standard mode and First Word Fall Through (FWFT) mode. In IDT Standard mode, the first word written to an empty FIFO will not appear on the data output lines unless a specific read operation is performed. A read operation, which consists of activating REN and enabling a rising RCLK edge, will shift the word from internal memory to the data output lines.
PIN CONFIGURATIONS
LD FWFT/SI GND WCLK PRS EF/OR RCLK REN RT OE MRS FF/IR PAF HF VCC PAE
PIN 1 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 WEN SEN DC VCC GND D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 Q17 Q16 GND Q15 Q14 VCC Q13 Q12 Q11 GND Q10 Q9 Q8 Q7 Q6 GND
D5 D4 D3 D2
D1 D0
GND Q0
Q1 GND Q2 Q3 VCC Q4 Q5
D6
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TQFP (PN64-1, ORDER CODE: PF) STQFP (PP64-1, ORDER CODE: TF) TOP VIEW
NOTE: 1. DC = Don't Care. Must be tied to GND or VCC, cannot be left open.
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DESCRIPTION (CONTINUED)
In FWFT mode, the first word written to an empty FIFO is clocked directly to the data output lines after three transitions of the RCLK signal. A REN does not have to be asserted for accessing the first word. However, subsequent words written to the FIFO do require a LOW on REN for access. The state of the FWFT/ SI input during Master Reset determines the timing mode in use. For applications requiring more data storage capacity than a single FIFO can provide, the FWFT timing mode permits depth expansion by chaining FIFOs in series (i.e. the data outputs of one FIFO are connected to the corresponding data inputs of the next). No external logic is required. These FIFOs have five flag pins, EF/OR (Empty Flag or Output Ready), FF/ IR (Full Flag or Input Ready), HF (Half-full Flag), PAE (Programmable AlmostEmpty flag) and PAF (Programmable Almost-Full flag). The EF and FF functions are selected in IDT Standard mode. The IR and OR functions are selected in FWFT mode. HF, PAE and PAF are always available for use, irrespective of timing mode. PAE and PAF can be programmed independently to switch at any point in memory. (See Table I and Table 2.) Programmable offsets determine the flag switching threshold and can be loaded by two methods: parallel or serial. Two default offset settings are also provided, so that PAE can be set to switch at 127 or 1,023 locations from the empty boundary and the PAF threshold can be set at 127 or 1,023 locations from the full boundary. These choices are made with the LD pin during Master Reset. For serial programming, SEN together with LD on each rising edge of WCLK, are used to load the offset registers via the Serial Input (SI). For parallel
programming, WEN together with LD on each rising edge of WCLK, are used to load the offset registers via Dn. REN together with LD on each rising edge of RCLK can be used to read the offsets in parallel from Qn regardless of whether serial or parallel offset loading has been selected. During Master Reset (MRS) the following events occur: The read and write pointers are set to the first location of the FIFO. The FWFT pin selects IDT Standard mode or FWFT mode. The LD pin selects either a partial flag default setting of 127 with parallel programming or a partial flag default setting of 1,023 with serial programming. The flags are updated according to the timing mode and default offsets selected. The Partial Reset (PRS) also sets the read and write pointers to the first location of the memory. However, the timing mode, partial flag programming method, and default or programmed offset settings existing before Partial Reset remain unchanged. The flags are updated according to the timing mode and offsets in effect. PRS is useful for resetting a device in mid-operation, when reprogramming partial flags would be undesirable. The Retransmit function allows data to be reread from the FIFO more than once. A LOW on the RT input during a rising RCLK edge initiates a retransmit operation by setting the read pointer to the first location of the memory array. If, at any time, the FIFO is not actively performing an operation, the chip will automatically power down. Once in the power down state, the standby supply current consumption is minimized. Initiating any operation (by activating control inputs) will immediately take the device out of the power down state. The IDT72255LA/72265LA are fabricated using IDT's high speed submicron CMOS technology.
PARTIAL RESET (PRS) WRITE CLOCK (WCLK) WRITE ENABLE (WEN) LOAD (LD) DATA IN ( 0 - Dn) D SERIAL ENABLE(SEN) FIRST WORD FALL THROUGH/SERIAL INPUT (FWFT/SI) FULL FLAG/INPUT READY (FF/IR) PROGRAMMABLE ALMOST-FULL (PAF)
MASTER RESET (MRS) READ CLOCK (RCLK) READ ENABLE (REN) OUTPUT ENABLE (OE) DATA OUT ( 0 - Qn) Q
IDT 72255LA 72265LA
RETRANSMIT (RT) EMPTY FLAG/OUTPUT READY (EF/OR) PROGRAMMABLE ALMOST-EMPTY (PAE) HALF FULL FLAG (HF)
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Figure 1. Block Diagram of Single 8,192 x 18 and 16,384 x 18 Synchronous FIFO
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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PIN DESCRIPTION
Symbol D0-D17 MRS Name Data Inputs Master Reset I/O I I Description Data inputs for a 18-bit bus. MRS initializes the read and write pointers to zero and sets the output register to all zeroes. During Master Reset, the FIFO is configured for either FWFT or IDT Standard mode, one of two program mable flag default settings, and serial or parallel programming of the offset settings. PRS initializes the read and write pointers to zero and sets the output register to all zeroes. During Partial Reset, the existing mode (IDT or FWFT), programming method (serial or parallel), and programmable flag settings are all retained. RT asserted on the rising edge of RCLK initializes the READ pointer to zero, sets the EF flag to LOW (OR to HIGH in FWFT mode) temporarily and does not disturb the write pointer, programming method, existing timing mode or programmable flag settings. RT is useful to reread data from the first physical location of the FIFO. During Master Reset, selects First Word Fall Through or IDT Standard mode. After Master Reset, this pin functions as a serial input for loading offset registers. When enabled by WEN, the rising edge of WCLK writes data into the FIFO and offsets into the programmable registers for parallel programming, and when enabled by SEN, the rising edge of WCLK writes one bit of data into the programmable register for serial programming. WEN enables WCLK for writing data into the FIFO memory and offset registers. When enabled by REN, the rising edge of RCLK reads data from the FIFO memory and offsets from the programmable registers. REN enables RCLK for reading data from the FIFO memory and offset registers. OE controls the output impedance of Qn. SEN enables serial loading of programmable flag offsets. During Master Reset, LD selects one of two partial flag default offsets (127 or 1,023) and determines the flag offset programming method, serial or parallel. After Master Reset, this pin enables writing to and reading from the offset registers. This pin must be tied to either VCC or GND and must not toggle after Master Reset. In the IDT Standard mode, the FF function is selected. FF indicates whether or not the FIFO memory is full. In the FWFT mode, the IR function is selected. IR indicates whether or not there is space available for writing to the FIFO memory. In the IDT Standard mode, the EF function is selected. EF indicates whether or not the FIFO memory is empty. In FWFT mode, the OR function is selected. OR indicates whether or not there is valid data available at the outputs. PAF goes LOW if the number of words in the FIFO memory is more than total word capacity of the FIFO minus the full offset value m, which is stored in the Full Offset register. There are two possible default values for m: 127 or 1,023. PAE goes LOW if the number of words in the FIFO memory is less than offset n, which is stored in the Empty Offset register. There are two possible default values for n: 127 or 1,023. Other values for n can be programmed into the device. HF indicates whether the FIFO memory is more or less than half-full. Data outputs for an 18-bit bus. +5 Volt power supply pins. Ground pins.
PRS
Partial Reset
I
RT
Retransmit
I
FWFT/SI WCLK
First Word Fall Through/Serial In Write Clock
I I
WEN RCLK REN OE SEN LD
Write Enable Read Clock Read Enable Output Enable Serial Enable Load
I I I I I I
DC FF/IR
Don't Care Full Flag/ Input Ready Empty Flag/ Output Ready Programmable Almost-Full Flag Programmable Almost-Empty Flag Half-Full Flag Data Outputs Power Ground
I O
EF/OR
O
PAF
O
PAE
O
HF Q0-Q17 VCC GND
O O
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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ABSOLUTE MAXIMUM RATINGS
Symbol VTERM TSTG IOUT Rating Terminal Voltage with respect to GND Storage Temperature DC Output Current Com'l & Ind'l -0.5 to +7.0 -55 to +125 -50 to +50 Unit V C mA
RECOMMENDED DC OPERATING CONDITIONS
Symbol VCC GND VIH VIL(1) TA TA Parameter Supply Voltage (Com'l/Ind'l) Supply Voltage (Com'l/Ind'l) Input High Voltage (Com'l/Ind'l) Input Low Voltage (Com'l/Ind'l) Operating Temperature Commercial Operating Temperature Industrial Min. 4.0 0 2.0 0 -40 Typ. 5.0 0 Max. 5.5 0 -- 0.8 +70 +85 Unit V V V V C C
NOTE: 1. Stresses greater than those listed under ABSOLUTE MAXIMUM 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.
NOTE: 1. 1.5V undershoots are allowed for 10ns once per cycle.
DC ELECTRICAL CHARACTERISTICS
(Commercial: VCC = 5V 10%, TA = 0C to +70C; Industrial: VCC = 5V 10%, TA = -40C to +85C)
IDT72255LA IDT72265LA Commercial & Industrial(1) tCLK = 10, 15, 20 ns Symbol ILI(2) ILO(3) VOH VOL ICC1(4,5,6) ICC2(4,7) Parameter Input Leakage Current Output Leakage Current Output Logic "1" Voltage, IOH = -2 mA Output Logic "0" Voltage, IOL = 8 mA Active Power Supply Current Standby Current Min. -1 -10 2.4 -- -- -- Max. 1 10 -- 0.4 80 20 Unit A A V V mA mA
NOTES: 1. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device. 2. Measurements with 0.4 VIN VCC. 3. OE VIH, 0.4 VOUT VCC. 4. Tested with outputs disabled (IOUT = 0). 5. RCLK and WCLK toggle at 20 MHz and data inputs switch at 10 MHz. 6. Typical ICC1 = 15 + 2.1*fS + 0.02*CL*fS (in mA) with VCC = 5V, TA = 25C, fS = WCLK frequency = RCLK frequency (in MHz, using TTL levels), data switching at fS/2, CL = capacitive load (in pF). 7. All Inputs = VCC -0.2V or GND + 0.2V, except RCLK and WCLK, which toggle at 20 MHz.
CAPACITANCE
(TA = +25C, f = 1.0MHz)
Symbol CIN
(2)
Parameter(1) Input Capacitance Output Capacitance
Conditions VIN = 0V VOUT = 0V
Max. 10 10
Unit pF pF
COUT(1,2)
NOTES: 1. With output deselected, (OE VIH). 2. Characterized values, not currently tested.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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AC ELECTRICAL CHARACTERISTICS(1)
(Commercial: VCC = 5V 10%, TA = 0C to +70C; Industrial: VCC = 5V 10%, TA = -40C to +85C)
Commercial IDT72255LA10 IDT72265LA10 Symbol fS tA tCLK tCLKH tCLKL tDS tDH tENS tENH tLDS tLDH tRS tRSS tRSR tRSF tFWFT tRTS tOLZ tOE tOHZ tWFF tREF tPAF tPAE tHF tSKEW1 tSKEW2 tSKEW3 tSKEW4 Data Access Time Clock Cycle Time Clock High Time Clock Low Time Data Setup Time Data Hold Time Enable Setup Time Enable Hold Time Load Setup Time Load Hold Time Reset Pulse Width Reset Setup Time Reset Recovery Time Reset to Flag and Output Time Mode Select Time Retransmit Setup Time Output Enable to Output in Low Z(4) Output Enable to Output Valid Output Enable to Output in High Z(4) Write Clock to FF or IR Read Clock to EF or OR Write Clock to PAF Read Clock to PAE Clock to HF Skew time between RCLK and WCLK for FF/IR Skew time between RCLK and WCLK for PAE and PAF Skew time between RCLK and WCLK for EF/OR Skew time between RCLK and WCLK for PAE and PAF for Re-transmit operation
(3)
Commercial & Industrial(2) IDT72255LA15 IDT72255LA20 IDT72265LA15 IDT72265LA20 Min. -- 2 15 6 6 4 1 4 1 4 1 15 15 15 -- 0 4 0 3 3 -- -- -- -- -- 6 15 60 17 Max. 66.7 10 -- -- -- -- -- -- -- -- -- -- -- -- 15 -- -- -- 8 8 10 10 10 10 20 -- -- -- -- Min. -- 2 20 8 8 5 1 5 1 5 1 20 20 20 -- 0 5 0 3 3 -- -- -- -- -- 10 20 60 25 Max. 50 12 -- -- -- -- -- -- -- -- -- -- -- -- 20 -- -- -- 10 10 12 12 12 12 22 -- -- -- -- Unit MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
Parameter Clock Cycle Frequency
Min. -- 2 10 4.5 4.5 3 0 3 0 3 0 10 10 10 -- 0 3 0 2 2 -- -- -- -- -- 5 12 60 15
Max. 100 8 -- -- -- -- -- -- -- -- -- -- -- -- 10 -- -- -- 6 6 8 8 8 8 16 -- -- -- --
NOTES: 1. All AC timings apply to both Standard IDT mode and First Word Fall Through mode. 2. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device. 3. Pulse widths less than minimum values are not allowed. 4. Values guaranteed by design, not currently tested.
5V
1.1K D.U.T.
AC TEST CONDITIONS
Input Pulse Levels Input Rise/Fall Times Input Timing Reference Levels Output Reference Levels Output Load GND to 3.0V 3ns 1.5V 1.5V See Figure 2 6
680
30pF*
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Figure 2. Output Load
* Includes jig and scope capacitances.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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FUNCTIONAL DESCRIPTION
TIMING MODES: IDT STANDARD vs FIRST WORD FALL THROUGH (FWFT) MODE The IDT72255LA/72265LA support two different timing modes of operation: IDT Standard mode or First Word Fall Through (FWFT) mode. The selection of which mode will operate is determined during Master Reset, by the state of the FWFT/SI input. If, at the time of Master Reset, FWFT/SI is LOW, then IDT Standard mode will be selected. This mode uses the Empty Flag (EF) to indicate whether or not there are any words present in the FIFO. It also uses the Full Flag function (FF) to indicate whether or not the FIFO has any free space for writing. In IDT Standard mode, every word read from the FIFO, including the first, must be requested using the Read Enable (REN) and RCLK. If, at the time of Master Reset, FWFT/SI is HIGH, then FWFT mode will be selected. This mode uses Output Ready (OR) to indicate whether or not there is valid data at the data outputs (Qn). It also uses Input Ready (IR) to indicate whether or not the FIFO has any free space for writing. In the FWFT mode, the first word written to an empty FIFO goes directly to Qn after three RCLK rising edges, REN = LOW is not necessary. Subsequent words must be accessed using the Read Enable (REN) and RCLK. Various signals, both input and output signals operate differently depending on which timing mode is in effect. IDT STANDARD MODE In this mode, the status flags, FF, PAF, HF, PAE, and EF operate in the manner outlined in Table 1. To write data into to the FIFO, Write Enable (WEN) must be LOW. Data presented to the DATA IN lines will be clocked into the FIFO on subsequent transitions of the Write Clock (WCLK). After the first write is performed, the Empty Flag (EF) will go HIGH. Subsequent writes will continue to fill up the FIFO. The Programmable Almost-Empty flag (PAE) will go HIGH after n + 1 words have been loaded into the FIFO, where n is the empty offset value. The default setting for this value is stated in the footnote of Table 1. This parameter is also user programmable. See section on Programmable Flag Offset Loading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the Half-Full flag (HF) would toggle to LOW once the 4,097th word for IDT72255LA and 8,193th word for IDT72265LA respectively was written into the FIFO. Continuing to write data into the FIFO will cause the Programmable Almost-Full flag (PAF) to go LOW. Again, if no reads are performed, the PAF will go LOW after (8,192-m) writes for the IDT72255LA and (16,384-m) writes for the IDT72265LA. The offset "m" is the full offset value. The default setting for this value is stated in the footnote of Table 1. This parameter is also user programmable. See section on Programmable Flag Offset Loading. When the FIFO is full, the Full Flag (FF) will go LOW, inhibiting further write operations. If no reads are performed after a reset, FF will go LOW after D writes to the FIFO. D = 8,192 writes for the IDT72255LA and 16,384 for the IDT72265LA, respectively.
If the FIFO is full, the first read operation will cause FF to go HIGH. Subsequent read operations will cause PAF and HF to go HIGH at the conditions described in Table 1. If further read operations occur, without write operations, PAE will go LOW when there are n words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, the EF will go LOW inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in IDT Standard mode, the EF and FF outputs are double register-buffered outputs. Relevant timing diagrams for IDT Standard mode can be found in Figure 7, 8 and 11. FIRST WORD FALL THROUGH MODE (FWFT) In this mode, the status flags, IR, PAF, HF, PAE, and OR operate in the manner outlined in Table 2. To write data into to the FIFO, WEN must be LOW. Data presented to the DATA IN lines will be clocked into the FIFO on subsequent transitions of WCLK. After the first write is performed, the Output Ready (OR) flag will go LOW. Subsequent writes will continue to fill up the FIFO. PAE will go HIGH after n + 2 words have been loaded into the FIFO, where n is the empty offset value. The default setting for this value is stated in the footnote of Table 2. This parameter is also user programmable. See section on Programmable Flag Offset Loading. If one continued to write data into the FIFO, and we assumed no read operations were taking place, the HF would toggle to LOW once the 4,098th word for the IDT72255LA and 8,194th word for the IDT72265LA, respectively was written into the FIFO. Continuing to write data into the FIFO will cause the PAF to go LOW. Again, if no reads are performed, the PAF will go LOW after (8,193-m) writes for the IDT72255LA and (16,385-m) writes for the IDT72265LA, where m is the full offset value. The default setting for this value is stated in the footnote of Table 2. When the FIFO is full, the Input Ready (IR) flag will go HIGH, inhibiting further write operations. If no reads are performed after a reset, IR will go HIGH after D writes to the FIFO. D = 8,193 writes for the IDT72255LA and 16,385 writes for the IDT72265LA, respectively. Note that the additional word in FWFT mode is due to the capacity of the memory plus output register. If the FIFO is full, the first read operation will cause the IR flag to go LOW. Subsequent read operations will cause the PAF and HF to go HIGH at the conditions described in Table 2. If further read operations occur, without write operations, the PAE will go LOW when there are n + 1 words in the FIFO, where n is the empty offset value. Continuing read operations will cause the FIFO to become empty. When the last word has been read from the FIFO, OR will go HIGH inhibiting further read operations. REN is ignored when the FIFO is empty. When configured in FWFT mode, the OR flag output is triple registerbuffered, and the IR flag output is double register-buffered. Relevant timing diagrams for FWFT mode can be found in Figure 9, 10 and 12.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
PROGRAMMING FLAG OFFSETS Full and Empty Flag offset values are user programmable. The IDT72255LA/72265LA has internal registers for these offsets. Default settings are stated in the footnotes of Table 1 and Table 2. Offset values can be programmed into the FIFO in one of two ways; serial or parallel loading method. The selection of the loading method is done using the LD (Load) pin. During Master Reset, the state of the LD input determines whether serial or parallel flag offset programming is enabled. A HIGH on LD during Master Reset selects serial loading of offset values and in addition, sets a default PAE offset value of 3FFH (a threshold 1,023 words from the empty boundary), and a default PAF offset value of 3FFH (a threshold 1,023 words from the full boundary). A LOW on LD during Master Reset selects parallel loading of offset values, and in addition, sets a default PAE offset
value of 07FH (a threshold 127 words from the empty boundary), and a default PAF offset value of 07FH (a threshold 127 words from the full boundary). See Figure 3, Offset Register Location and Default Values. In addition to loading offset values into the FIFO, it also possible to read the current offset values. It is only possible to read offset values via parallel read. Figure 4, Programmable Flag Offset Programming Sequence, summarizes the control pins and sequence for both serial and parallel programming modes. For a more detailed description, see discussion that follows. The offset registers may be programmed (and reprogrammed) any time after Master Reset, regardless of whether serial or parallel programming has been selected.
TABLE 1 -- STATUS FLAGS FOR IDT STANDARD MODE
IDT72255LA 0 Number of Words in FIFO 1 to n (1) (n + 1) to 4,096 4,097 to (8,192-(m+1)) (8,192-m)(2) to 8,191 8,192 IDT72265LA 0 1 to n (1) (n + 1) to 8,192 8,193 to (16,384-(m+1)) (16,384-m) (2) to 16,383 16,384 FF PAF H H H H H L H H H H L L HF H H H L L L PAE EF L L H H H H L H H H 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
IDT72255LA 0 Number of Words in FIFO (1) 1 to n+1 (1) (n + 2) to 4,097 4,098 to (8,193-(m+1))(2) (8,193-m) to 8,192 8,193 IDT72265LA 0 1 to n+1 (1) (n + 2) to 8,193 8,194 to (16,385-(m+1)) (2) (16,385-m) (2) to 16,384 16,385 FF PAF L L L L L H H H H H L L HF H H H L L L PAE EF L L H H H H H L L L L L
NOTES: 1. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n = 1,023 when serial offset loading is selected. 2. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or m = 1,023 when serial offset loading is selected.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
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72255LA -- 8,192 x 18-BIT
17 12 EMPTY OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset 17 12 FULL OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset 0 17 0 17
72265LA -- 16,384 x 18-BIT
13 EMPTY OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset 13 FULL OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset
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0
0
Figure 3. Offset Register Location and Default Values
LD
WEN
REN
SEN
WCLK
RCLK
Selection
0
0
1
1
X
Parallel write to registers: Empty Offset Full Offset Parallel read from registers: Empty Offset Full Offset
0
1
0
1
X
0
1
1
0
X
Serial shift into registers: 26 bits for the 72255LA 28 bits for the 72265LA 1 bit for each rising WCLK edge Starting with Empty Offset (LSB) Ending with Full Offset (MSB) No Operation
X
1
1
1
X
X
1
0
X
X
X X X
Write Memory
1 1
X 1
0 1
X X
Read Memory No Operation
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X
NOTES: 1. The programming method can only be selected at Master Reset. 2. Parallel reading of the offset registers is always permitted regardless of which programming method has been selected. 3. The programming sequence applies to both IDT Standard and FWFT modes.
Figure 4. Programmable Flag Offset Programming Sequence
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
SERIAL PROGRAMMING MODE If Serial Programming mode has been selected, as described above, then programming of PAE and PAF values can be achieved by using a combination of the LD, SEN, WCLK and SI input pins. Programming PAE and PAF proceeds as follows: when LD and SEN are set LOW, data on the SI input are written, one bit for each WCLK rising edge, starting with the Empty Offset LSB and ending with the Full Offset MSB. A total of 26 bits for the IDT72255LA and 28 bits for the IDT72265LA. See Figure 13, Serial Loading of Programmable Flag Registers, for the timing diagram for this mode. Using the serial method, individual registers cannot be programmed selectively. PAE and PAF can show a valid status only after the complete set of bits (for all offset registers) has been entered. The registers can be reprogrammed as long as the complete set of new offset bits is entered. When LD is LOW and SEN is HIGH, no serial write to the registers can occur. Write operations to the FIFO are allowed before and during the serial programming sequence. In this case, the programming of all offset bits does not have to occur at once. A select number of bits can be written to the SI input and then, by bringing LD and SEN HIGH, data can be written to FIFO memory via Dn by toggling WEN. When WEN is brought HIGH with LD and SEN restored to a LOW, the next offset bit in sequence is written to the registers via SI. If an interruption of serial programming is desired, it is sufficient either to set LD LOW and deactivate SEN or to set SEN LOW and deactivate LD. Once LD and SEN are both restored to a LOW level, serial offset programming continues. From the time serial programming has begun, neither partial flag will be valid until the full set of bits required to fill all the offset registers has been written. Measuring from the rising WCLK edge that achieves the above criteria; PAF will be valid after two more rising WCLK edges plus tPAF, PAE will be valid after the next two rising RCLK edges plus tPAE plus tSKEW2. It is not possible to read the flag offset values in a serial mode. PARALLEL MODE If Parallel Programming mode has been selected, as described above, then programming of PAE and PAF values can be achieved by using a combination of the LD, WCLK , WEN and Dn input pins. ProgrammingPAE and PAF proceeds as follows: when LD and WEN are set LOW, data on the inputs Dn are written into the Empty Offset Register on the first LOW-toHIGH transition of WCLK. Upon the second LOW-to-HIGH transition of WCLK, data are written into the Full Offset Register. The third transition of WCLK writes, once again, to the Empty Offset Register. See Figure 14, Parallel Loading of Programmable Flag Registers, for the timing diagram for this mode. The act of writing offsets in parallel employs a dedicated write offset register pointer. The act of reading offsets employs a dedicated read offset register pointer. The two pointers operate independently; however, a read and a write should not be performed simultaneously to the offset registers. A Master Reset initializes both pointers to the Empty Offset (LSB) register. A Partial Reset has no effect on the position of these pointers. Write operations to the FIFO are allowed before and during the parallel programming sequence. In this case, the programming of all offset registers does not have to occur at one time. One, two or more offset registers can be written and then by bringing LD HIGH, write operations can be redirected to the FIFO memory. When LD is set LOW again, and WEN is LOW, the next offset register in sequence is written to. As an
10
alternative to holding WEN LOW and toggling LD, parallel programming can also be interrupted by setting LD LOW and toggling WEN. Note that the status of a partial flag (PAE or PAF) output is invalid during the programming process. From the time parallel programming has begun, a partial flag output will not be valid until the appropriate offset word has been written to the register(s) pertaining to that flag. Measuring from the rising WCLK edge that achieves the above criteria; PAF will be valid after two more rising WCLK edges plus tPAF, PAE will be valid after the next two rising RCLK edges plus tPAE plus tSKEW2. The act of reading the offset registers employs a dedicated read offset register pointer. The contents of the offset registers can be read on the Q0Qn pins when LD is set LOW and REN is set LOW. Data are read via Qn from the Empty Offset Register on the first LOW-to-HIGH transition of RCLK. Upon the second LOW-to-HIGH transition of RCLK, data are read from the Full Offset Register. The third transition of RCLK reads, once again, from the Empty Offset Register. See Figure 15, Parallel Read of Programmable Flag Registers, for the timing diagram for this mode. It is permissible to interrupt the offset register read sequence with reads or writes to the FIFO. The interruption is accomplished by deasserting REN, LD, or both together. When REN and LD are restored to a LOW level, reading of the offset registers continues where it left off. It should be noted, and care should be taken from the fact that when a parallel read of the flag offsets is performed, the data word that was present on the output lines Qn will be overwritten. Parallel reading of the offset registers is always permitted regardless of which timing mode (IDT Standard or FWFT modes) has been selected. RETRANSMIT OPERATION The Retransmit operation allows data that has already been read to be accessed again. There are two stages: first, a setup procedure that resets the read pointer to the first location of memory, then the actual retransmit, which consists of reading out the memory contents, starting at the beginning of memory. Retransmit setup is initiated by holding RT LOW during a rising RCLK edge. REN and WEN must be HIGH before bringing RT LOW. At least one word, but no more than D - 2 words should have been written into the FIFO between Reset (Master or Partial) and the time of Retransmit setup. D = 8,192 for the IDT72255LA and D = 16,384 for the IDT72265LA. In FWFT mode, D = 8,193 for the IDT72255LA and D = 16,385 for the IDT72265LA. If IDT Standard mode is selected, the FIFO will mark the beginning of the Retransmit setup by setting EF LOW. The change in level will only be noticeable if EF was HIGH before setup. During this period, the internal read pointer is initialized to the first location of the RAM array. When EF goes HIGH, Retransmit setup is complete and read operations may begin starting with the first location in memory. Since IDT Standard mode is selected, every word read including the first word following Retransmit setup requires a LOW on REN to enable the rising edge of RCLK. See Figure 11, Retransmit Timing (IDT Standard Mode), for the relevant timing diagram. If FWFT mode is selected, the FIFO will mark the beginning of the Retransmit setup by setting OR HIGH. During this period, the internal read pointer is set to the first location of the RAM array. When OR goes LOW, Retransmit setup is complete; at the same time, the contents of the first location appear on the outputs. Since FWFT mode is selected, the first word appears on the outputs, no LOW on REN is necessary. Reading all subsequent words requires a LOW on REN to
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
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.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
SIGNAL DESCRIPTION INPUTS:
DATA IN (D0 - D17) Data inputs for 18-bit wide data.
CONTROLS:
MASTER RESET (MRS) A Master Reset is accomplished whenever the MRS input is taken to a LOW state. This operation sets the internal read and write pointers to the first location of the RAM array. PAE will go LOW, PAF will go HIGH, and HF will go HIGH. If FWFT is LOW during Master Reset then the IDT Standard mode, along with EF and FF are selected. EF will go LOW and FF will go HIGH. If FWFT is HIGH, then the First Word Fall Through mode (FWFT), along with IR and OR, are selected. OR will go HIGH and IR will go LOW. If LD is LOW during Master Reset, then PAE is assigned a threshold 127 words from the empty boundary and PAF is assigned a threshold 127 words from the full boundary; 127 words corresponds to an offset value of 07FH. Following Master Reset, parallel loading of the offsets is permitted, but not serial loading. If LD is HIGH during Master Reset, then PAE is assigned a threshold 1,023 words from the empty boundary and PAF is assigned a threshold 1,023 words from the full boundary; 1,023 words corresponds to an offset value of 3FFH. Following Master Reset, serial loading of the offsets is permitted, but not parallel loading. Parallel reading of the registers is always permitted. (See section describing the LD pin for further details.) During a Master Reset, the output register is initialized to all zeroes. A Master Reset is required after power up, before a write operation can take place. MRS is asynchronous. See Figure 5, Master Reset Timing, for the relevant timing diagram. PARTIAL RESET (PRS) A Partial Reset is accomplished whenever the PRS input is taken to a LOW state. As in the case of the Master Reset, the internal read and write pointers are set to the first location of the RAM array, PAE goes LOW, PAF goes HIGH, and HF goes HIGH. Whichever mode is active at the time of Partial Reset, IDT Standard mode or First Word Fall Through, that mode will remain selected. If the IDT Standard mode is active, then FF will go HIGH and EF will go LOW. If the First Word Fall Through mode is active, then OR will go HIGH, and IR will go LOW. Following Partial Reset, all values held in the offset registers remain unchanged. The programming method (parallel or serial) currently active at the time of Partial Reset is also retained. The output register is initialized to all zeroes. PRS is asynchronous. A Partial Reset is useful for resetting the device during the course of operation, when reprogramming partial flag offset settings may not be convenient. See Figure 6, Partial Reset Timing, for the relevant timing diagram. RETRANSMIT (RT) The Retransmit operation allows data that has already been read to be accessed again. There are two stages: first, a setup procedure that resets
the read pointer to the first location of memory, then the actual retransmit, which consists of reading out the memory contents, starting at beginning of the memory. Retransmit setup is initiated by holding RT LOW during a rising RCLK edge. REN and WEN must be HIGH before bringing RT LOW. If IDT Standard mode is selected, the FIFO will mark the beginning of the Retransmit setup by setting EF LOW. The change in level will only be noticeable if EF was HIGH before setup. During this period, the internal read pointer is initialized to the first location of the RAM array. When EF goes HIGH, Retransmit setup is complete and read operations may begin starting with the first location in memory. Since IDT Standard mode is selected, every word read including the first word following Retransmit setup requires a LOW on REN to enable the rising edge of RCLK. See Figure 11, Retransmit Timing (IDT Standard Mode), for the relevant timing diagram. If FWFT mode is selected, the FIFO will mark the beginning of the Retransmit setup by setting OR HIGH. During this period, the internal read pointer is set to the first location of the RAM array. When OR goes LOW, Retransmit setup is complete; at the same time, the contents of the first location appear on the outputs. Since FWFT mode is selected, the first word appears on the outputs, no LOW on REN is necessary. Reading all subsequent words requires a LOW on REN to enable the rising edge of RCLK. See Figure 12, Retransmit Timing (FWFT Mode), for the relevant timing diagram. 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. 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.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
WRITE ENABLE (WEN) When the WEN input is LOW, data may be loaded into the FIFO RAM array on the rising edge of every WCLK cycle if the device is not full. Data is stored in the RAM array sequentially and independently of any ongoing read operation. When WEN is HIGH, no new data is written in the RAM array on each WCLK cycle. To prevent data overflow in the IDT Standard mode, FF will go LOW, inhibiting further write operations. Upon the completion of a valid read cycle, FF will go HIGH allowing a write to occur. The FF is updated by two WCLK cycles + tSKEW after the RCLK cycle. To prevent data overflow in the FWFT mode, IR will go HIGH, inhibiting further write operations. Upon the completion of a valid read cycle, IR will go LOW allowing a write to occur. The IR flag is updated by two WCLK cycles + tSKEW after the valid RCLK cycle. WEN is ignored when the FIFO is full in either FWFT or IDT Standard mode. 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. READ ENABLE (REN) When Read Enable is LOW, data is loaded from the RAM array into the output register on the rising edge of every RCLK cycle if the device is not empty. When the REN input is HIGH, the output register holds the previous data and no new data is loaded into the output register. The data outputs Q0-Qn maintain the previous data value. In the IDT Standard mode, every word accessed at Qn, including the first word written to an empty FIFO, must be requested using REN. When the last word has been read from the FIFO, the Empty Flag (EF) will go LOW, inhibiting further read operations. REN is ignored when the FIFO is empty. Once a write is performed, EF will go HIGH allowing a read to occur. The EF flag is updated by two RCLK cycles + tSKEW after the valid WCLK cycle. In the FWFT mode, the first word written to an empty FIFO automatically goes to the outputs Qn, on the third valid LOW to HIGH transition of RCLK + tSKEW after the first write. REN does not need to be asserted LOW. In order to access all other words, a read must be executed using REN. The RCLK LOW to HIGH transition after the last word has been read from the FIFO, Output Ready (OR) will go HIGH with a true read (RCLK with REN = LOW), inhibiting further read operations. REN is ignored when the FIFO is empty. SERIAL ENABLE (SEN) The SEN input is an enable used only for serial programming of the offset registers. The serial programming method must be selected during Master Reset. SEN is always used in conjunction with LD. When these lines are both LOW, data at the SI input can be loaded into the program register one bit for each LOW-to-HIGH transition of WCLK. (See Figure 4.) When SEN is HIGH, the programmable registers retains the previous settings and no offsets are loaded. SEN functions the same way in both IDT Standard and FWFT modes.
OUTPUT ENABLE (OE) When Output Enable is enabled (LOW), the parallel output buffers receive data from the output register. When OE is HIGH, the output data bus (Qn) goes into a high impedance state. LOAD (LD) This is a dual purpose pin. During Master Reset, the state of the LD input determines one of two default offset values (127 or 1,023) for the PAE and PAF flags, along with the method by which these offset registers can be programmed, parallel or serial. After Master Reset, LD enables write operations to and read operations from the offset registers. Only the offset loading method currently selected can be used to write to the registers. Offset registers can be read only in parallel. A LOW on LD during Master Reset selects a default PAE offset value of 07FH (a threshold 127 words from the empty boundary), a default PAF offset value of 07FH (a threshold 127 words from the full boundary), and parallel loading of other offset values. A HIGH on LD during Master Reset selects a default PAE offset value of 3FFH (a threshold 1,023 words from the empty boundary), a default PAF offset value of 3FFH (a threshold 1,023 words from the full boundary), and serial loading of other offset values. After Master Reset, the LD pin is used to activate the programming process of the flag offset values PAE and PAF. Pulling LD LOW will begin a serial loading or parallel load or read of these offset values. See Figure 4, Programmable Flag Offset Programming Sequence.
OUTPUTS:
FULL FLAG (FF/IR) This is a dual purpose pin. In IDT Standard mode, the Full Flag (FF) function is selected. When the FIFO is full, FF will go LOW, inhibiting further write operations. When FF is HIGH, the FIFO is not full. If no reads are performed after a reset (either MRS or PRS), FF will go LOW after D writes to the FIFO (D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA). See Figure 7, Write Cycle and Full Flag Timing (IDT Standard Mode), for the relevant timing information. In FWFT mode, the Input Ready (IR) function is selected. IR goes LOW when memory space is available for writing in data. When there is no longer any free space left, IR goes HIGH, inhibiting further write operations. If no reads are performed after a reset (either MRS or PRS), IR will go HIGH after D writes to the FIFO (D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA) See Figure 9, Write Timing (FWFT Mode), for the relevant timing information. The IR status not only measures the contents of the FIFO memory, but also counts the presence of a word in the output register. Thus, in FWFT mode, the total number of writes necessary to deassert IR is one greater than needed to assert FF in IDT Standard mode. FF/IR is synchronous and updated on the rising edge of WCLK. FF/IR are double register-buffered outputs. EMPTY FLAG (EF/OR) This is a dual purpose pin. In the IDT Standard mode, the Empty Flag (EF) function is selected. When the FIFO is empty, EF will go LOW, inhibiting further read operations. When EF is HIGH, the FIFO is not empty. See Figure 8, Read Cycle, Empty Flag and First Word Latency Timing (IDT Standard Mode), for the relevant timing information. In FWFT mode, the Output Ready (OR) function is selected. OR goes LOW at the same time that the first word written to an empty FIFO appears valid on the outputs. OR stays LOW after the RCLK LOW to HIGH transition
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
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. PROGRAMMABLE ALMOST-FULL FLAG (PAF) The Programmable Almost-Full flag (PAF) will go LOW when the FIFO reaches the almost-full condition. In IDT Standard mode, if no reads are performed after reset (MRS), PAF will go LOW after (D - m) words are written to the FIFO. The PAF will go LOW after (8,192-m) writes for the IDT72255LA and (16,384-m) writes for the IDT72265LA. The offset "m" is the full offset value. The default setting for this value is stated in the footnote of Table 1. In FWFT mode, the PAF will go LOW after (8,193-m) writes for the IDT72255LA and (16,385-m) writes for the IDT72265LA, where m is the full offset value. The default setting for this value is stated in the footnote of Table 2. See Figure 16, Programmable Almost-Full Flag Timing (IDT Standard and FWFT Mode), for the relevant timing information. PAF is synchronous and updated on the rising edge of WCLK. PROGRAMMABLE ALMOST-EMPTY FLAG (PAE) The Programmable Almost-Empty flag (PAE) will go LOW when the FIFO reaches the almost-empty condition. In IDT Standard mode, PAE will go
LOW when there are n words or less in the FIFO. The offset "n" is the empty offset value. The default setting for this value is stated in the footnote of Table 1. In FWFT mode, the PAE will go LOW when there are n+1 words or less in the FIFO. The default setting for this value is stated in the footnote of Table 2. See Figure 17, Programmable Almost-Empty Flag Timing (IDT Standard and FWFT Mode), for the relevant timing information. PAE is synchronous and updated on the rising edge of RCLK. HALF-FULL FLAG (HF) This output indicates a half-full FIFO. The rising WCLK edge that fills the FIFO beyond half-full sets HF LOW. The flag remains LOW until the difference between the write and read pointers becomes less than or equal to half of the total depth of the device; the rising RCLK edge that accomplishes this condition sets HF HIGH. In IDT Standard mode, if no reads are performed after reset (MRS or PRS), HF will go LOW after (D/2 + 1) writes to the FIFO, where D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA. In FWFT mode, if no reads are performed after reset (MRS or PRS), HF will go LOW after (D-1/2 + 2) writes to the FIFO, where D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA. See Figure 18, Half-Full Flag Timing (IDT Standard and FWFT Modes), for the relevant timing information. Because HF is updated by both RCLK and WCLK, it is considered asynchronous. DATA OUTPUTS (Q0-Q17) (Q0 - Q17) are data outputs for 18-bit wide data.
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
MRS
tRS tRSS tRSR
REN tRSS WEN tFWFT FWFT/SI tRSS LD tRSS RT tRSS SEN tRSF EF/OR tRSF FF/IR tRSF PAE tRSF PAF, HF tRSF Q0 - Qn OE = LOW
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tRSR
tRSR
tRSR
If FWFT = HIGH, OR = HIGH If FWFT = LOW, EF = LOW If FWFT = LOW, FF = HIGH If FWFT = HIGH, IR = LOW
OE = HIGH
Figure 5. Master Reset Timing
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
PRS
tRS tRSS tRSR
REN tRSS WEN tRSS RT tRSS SEN tRSF EF/OR tRSF FF/IR tRSF PAE tRSF PAF, HF tRSF Q0 - Qn
OE = HIGH OE = LOW If FWFT = HIGH, OR = HIGH If FWFT = LOW, EF = LOW If FWFT = LOW, FF = HIGH If FWFT = HIGH, IR = LOW
tRSR
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Figure 6. Partial Reset Timing
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IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
tCLK
NO WRITE
tCLKH
2
tCLKL tSKEW1
(1)
NO WRITE 1 2
WCLK
tSKEW1
1
(1)
tDS
DX
tDH
tDS
DX+1
tDH
D0 - Dn
tWFF
tWFF
tWFF
tWFF
FF
WEN RCLK
tENS tENH tENS tENH
REN
tA tA
DATA READ NEXT DATA READ
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Q0 - Qn
DATA IN OUTPUT REGISTER
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)
tCLKH RCLK tENS tENH
NO OPERATION NO OPERATION 1 2
tCLK
tCLKL tENS tENH tENS tENH
tREF
tREF tA LAST WORD LAST WORD tOHZ tOLZ D0
tREF
tA Q0 - Qn tOLZ tOE tSKEW3 WCLK tENS tENH tENS tENH
(1)
tA D1
tDS D0 - Dn D0
tDHS
tDS D1
tDH
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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)
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OCTOBER 17, 2005
WCLK
1
tENS tDS W3 W4 tSKEW2(2)
2 3 1 2
tDS W[n +2] W[n+3] W[n+4] W[D-m-2] W[D-m-1] W[D-m] W[D-m+1] W[D-m+2] W[D-1] W[
D-1 D-1 D-1
tDH
tDS
tDS W[ WD
tENH
D0 - D17
W1
W2
]
]
W[
]
tSKEW3(1)
RCLK
1
tA W1 tREF
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
Q0 - Q17
DATA IN OUTPUT REGISTER
tPAE
tHF
tPAF
18
tWFF
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NOTES: 1. tSKEW3 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that OR will go LOW after two RCLK cycles plus tREF. If the time between the rising edge of WCLK and the rising edge of RCLK is less than tSKEW3, then OR assertion may be delayed one extra RCLK cycle. 2. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that PAE will go HIGH after one RCLK cycle plus tPAE. If the time between the rising edge of WCLK and the rising edge of RCLK is less than tSKEW2, then the PAE deassertion may be delayed one extra RCLK cycle. 3. LD = HIGH, OE = LOW 4. n = PAE offset, m = PAF offset and D = maximum FIFO depth. 5. D = 8,193 for IDT72255LA and 16,385 for IDT72265LA. 6. First word latency: 60ns + tREF + 2*TRCLK.
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
OCTOBER 17, 2005
Figure 9. Write Timing (First Word Fall Through Mode)
WCLK 2 tSKEW2
(2)
tENS
tENH
1 (1) tSKEW1
tDS
tDH
D0 - D17
WD
RCLK 1 tENS
tENS
tOHZ tA tA W3 W[D-n-1] W[D-n] W[D-1] Wm+2 W[m+3] W[m+4] W[
D-1 D-1
tOE tA tA tA W[D-n+1] W[D-n+2] W2
tA
Q0 - Q17
W1
W1
]
W[
]
WD tREF
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
tPAE
tHF
19
tPAF tWFF
tWFF
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NOTES: 1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that IR will go LOW after one WCLK cycle plus tWFF. If the time between the rising edge of RCLK and the rising edge of WCLK is less than tSKEW1, then the IR assertion may be delayed one extra WCLK cycle. 2. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that PAF will go HIGH after one WCLK cycle plus tPAF. If the time between the rising edge of RCLK and the rising edge of WCLK is less than tSKEW2, then the PAF deassertion may be delayed one extra WCLK cycle. 3. LD = HIGH 4. n = PAE Offset, m = PAF offset and D = maximum FIFO depth. 5. D = 8,193 for IDT72255LA and 16,385 for IDT72265LA.
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OCTOBER 17, 2005
Figure 10. Read Timing (First Word Fall Through Mode)
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
RCLK
tENS tENH tRTS
1 tENS
2 tENH
REN
tA tA Wx+1 tSKEW4 W1
(3)
tA W2
(3)
Q0 - Qn
Wx
WCLK
tRTS
1
2
WEN
tENS tENH
RT
tREF tREF
(5)
EF
tPAE
PAE
tHF
HF
tPAF
PAF
4670 drw 14
NOTES: 1. Retransmit setup is complete after EF returns HIGH, only then can a read operation begin. 2. OE = LOW. 3. W1 = first word written to the FIFO after Master Reset, W2 = second word written to the FIFO after Master Reset. 4. No more than D -2 may be written to the FIFO between Reset (Master or Partial) and Retransmit setup. Therefore, FF will be HIGH throughout the Retransmit setup procedure. D = 8,192 for IDT72255LA and 16,384 for IDT72265LA. 5. EF goes HIGH at 60 ns + 1 RCLK cycle + tREF.
Figure 11. Retransmit Timing (IDT Standard Mode)
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OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
RCLK
tENS tENH tRTS
1
2
3 tENH
4 tENH
REN
tA tA W1
(4)
Q0 - Qn WCLK
Wx tSKEW4 1 tRTS 2
Wx+1
W2
W3
WEN
tENS tENH
(5)
RT
tREF tREF
OR
tPAE
PAE
tHF
HF
tPAF
PAF
4670 drw15
NOTES: 1. Retransmit setup is complete after OR returns LOW. 2. No more than D -2 words may be written to the FIFO between Reset (Master or Partial) and Retransmit setup. Therefore, IR will be LOW throughout the Retransmit setup procedure. D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA. 3. OE = LOW 4. W1, W2, W3 = first, second and third words written to the FIFO after Master Reset. 5. OR goes LOW at 60 ns + 2 RCLK cycles + tREF.
Figure 12. Retransmit Timing (FWFT Mode)
WCLK
tENS
tENH tENH
tLDS
tLDH
tLDH
tDS
tDH
BIT X EMPTY OFFSET
(1)
SI
BIT 0
BIT 0 FULL OFFSET
BIT X
(1)
4670 drw 16
NOTE: 1. X = 12 for the IDT72255LA and X = 13 for the IDT72265LA.
Figure 13. Serial Loading of Programmable Flag Registers (IDT Standard and FWFT Modes)
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OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
tCLK tCLKL
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
tCLKH
WCLK
tLDS tLDH tLDH
tENS
tENH
tENH
tDS
tDH PAE OFFSET PAF OFFSET
tDH
D0 - D15
4670 drw 17
Figure 14. Parallel Loading of Programmable Flag Registers (IDT Standard and FWFT Modes)
tCLK tCLKH tCLKL
RCLK
tLDS tLDH tLDH
tENS
tENH
tENH
tA
tA PAE OFFSET PAF OFFSET
4670 drw 18
Q0 - Q15
NOTE: 1. OE = LOW
DATA IN OUTPUT REGISTER
Figure 15. Parallel Read of Programmable Flag Registers (IDT Standard and FWFT Modes)
tCLKH
tCLKL 1 tENS tENH 2 1 2
WCLK
tPAF D - (m+1) words in FIFO
(2)
tPAF D - m words in FIFO tSKEW2
(3) (2)
D-(m+1) words in FIFO(2)
RCLK
tENS tENH
4670 drw 19
NOTES: 1. m = PAF offset. 2. D = maximum FIFO depth. In IDT Standard mode: D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA. In FWFT mode: D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA. 3. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that PAF will go HIGH (after one WCLK cycle plus tPAF). If the time between the rising edge of RCLK and the rising edge of WCLK is less than tSKEW2, then the PAF deassertion time may be delayed one extra WCLK cycle. 4. PAF is asserted and updated on the rising edge of WCLK only.
Figure 16. Programmable Almost-Full Flag Timing (IDT Standard and FWFT Modes)
22 OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
tCLKH tCLKL
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
WCLK
tENS tENH
n words in FIFO (2), n+1 words in FIFO (3) tSKEW2 (4) tPAE 2 tENS
n+1 words in FIFO (2), n+2 words in FIFO (3)
n words in FIFO (2), n+1 words in FIFO (3) tPAE 1 2
RCLK
1
tENH
4670 drw 20
NOTES: 1. n = PAE offset. 2. For IDT Standard mode 3. For FWFT mode. 4. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that PAE will go HIGH (after one RCLK cycle plus tPAE). If the time between the rising edge of WCLK and the rising edge of RCLK is less than 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 WCLK
tCLKL tENH
tENS
tHF
D/2 words in FIFO(1),
D/2 + 1 words in FIFO(1),
[
RCLK
+ 1] words in FIFO
(2)
[
+ 2] words in FIFO(2)
D/2 words in FIFO(1),
[
+ 1] words in FIFO(2)
tHF
tENS
4670 drw 21
NOTES: 1. For IDT Standard mode: D = maximum FIFO depth. D = 8,192 for the IDT72255LA and 16,384 for the IDT72265LA. 2. For FWFT mode: D = maximum FIFO depth. D = 8,193 for the IDT72255LA and 16,385 for the IDT72265LA.
Figure 18. Half-Full Flag Timing (IDT Standard and FWFT Modes)
23 OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
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 23 demonstrates a width expansion using two IDT72255LA/ 72265LA devices. D0 - D17 from each device form a 36-bit wide input bus and Q0-Q17 from each device form a 36-bit wide output bus. Any word width can be attained by adding additional IDT72255LA/72265LA devices.
PARTIAL RESET ( MASTER RESET (
) )
FIRST WORD FALL THROUGH/ SERIAL INPUT (FWFT/SI) RETRANSMIT ( m+n DATA IN ) Dm+1 - Dn D0 - Dm m n READ CLOCK (RCLK) WRITE CLOCK (WCLK) READ ENABLE ( WRITE ENABLE ( LOAD ( FULL FLAG/INPUT READY (
(1)
) ) ) / / ) #1
(1)
) OUTPUT ENABLE ( ) IDT 72255LA 72265LA IDT 72255LA 72265LA PROGRAMMABLE (
/ ) #1 / ) #2 ) )
EMPTY FLAG/OUTPUT READY ( EMPTY FLAG/OUTPUT READY ( FIFO #1 FIFO #2 Q0 - Qm n Qm+1 - Qn m+n
GATE
FULL FLAG/INPUT READY (
) #2
GATE
PROGRAMMABLE ( HALF-FULL FLAG (
m
DATA OUT
4670 drw 22
NOTES: 1. Use an AND gate in IDT Standard mode, an OR gate in FWFT mode. 2. Do not connect any output control signals directly together. 3. FIFO #1 and FIFO #2 must be the same depth, but may be different word widths.
Figure 19. Block Diagram of 8,192 x 36 and 16,384 x 36 Width Expansion
24
OCTOBER 17, 2005
IDT72255LA/72265LA CMOS SuperSync FIFOTM 8,192 x 18 and 16,384 x 18
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
DEPTH EXPANSION CONFIGURATION (FWFT MODE ONLY) The IDT72255LA can easily be adapted to applications requiring depths greater than 8,192 and 16,384 for the IDT72265LA with an 18-bit bus width. In FWFT mode, the FIFOs can be connected in series (the data outputs of one FIFO connected to the data inputs of the next) with no external logic necessary. The resulting configuration provides a total depth equivalent to the sum of the depths associated with each single FIFO. Figure 24 shows a depth expansion using two IDT72255LA/72265LA devices. Care should be taken to select FWFT mode during Master Reset for all FIFOs in the depth expansion configuration. The first word written to an empty configuration will pass from one FIFO to the next ("ripple down") until it finally appears at the outputs of the last FIFO in the chain-no read operation is necessary but the RCLK of each FIFO must be free-running. Each time the data word appears at the outputs of one FIFO, that device's OR line goes LOW, enabling a write to the next FIFO in line. For an empty expansion configuration, the amount of time it takes for OR of the last FIFO in the chain to go LOW (i.e. valid data to appear on the last FIFO's outputs) after a word has been written to the first FIFO is the sum of the delays for each individual FIFO: (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. 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.
FWFT/SI
*
FWFT/SI WCLK
TRANSFER CLOCK RCLK
WRITE CLOCK WRITE ENABLE INPUT READY
*
FWFT/SI WCLK RCLK
READ CLOCK READ ENABLE
IDT 72255LA 72265LA GND
IDT 72255LA 72265LA
OUTPUT READY OUTPUT ENABLE n DATA OUT
DATA IN
n Dn Qn
n
Dn
Qn
4670 drw 23
Figure 20. Block Diagram of 16,384 x 18 and 32,768 x 18 Depth Expansion
25
OCTOBER 17, 2005
ORDERING INFORMATION
IDT XXXXX Device Type X Power XX Speed X Package X X Process / Temperature Range BLANK I(1) G PF TF 10 15 20 LA 72255 72265 Commercial (0C to +70C) Industrial (-40C to +85C) Green Thin Plastic Quad Flatpack (TQFP, PN64-1) Slim Thin Quad Flatpack (STQFP, PP64-1) Commercial Only Com'l & Ind'l Com`l & Ind'l Low Power 8,192 x 18 -- SuperSync FIFO 16,384 x 18 -- SuperSync FIFO
4670 drw24
Clock Cycle Time (tCLK) Speed in Nanoseconds
NOTES: 1. Industrial temperature range product for 15ns and 20ns speed grades are available as a standard device. 2. Green parts available. For specific speeds and packages contact your sales office.
DATASHEET DOCUMENT HISTORY
04/25/2001 10/17/2005 pgs. 1, 5, 6 and 26. pgs. 1, 6, 20, 21 and 26. PCN#F0509-01. CORPORATE HEADQUARTERS 6024 Silver Creek Valley Road San Jose, CA 95138 for SALES: 800-345-7015 or 408-284-8200 fax: 408-284-2775 www.idt.com
26
for Tech Support: 408-360-1753 email: FIFOhelp@idt.com
5 VOLT CMOS SuperSync FIFOTM 8,192 x 18 16,384 x 18
ADDENDUM
IDT72255LA IDT72265LA
DIFFERENCES BETWEEN THE IDT72255LA/72265LA AND IDT72255L/72265L
IDT has improved the performance of the IDT72255/72265 SuperSyncTM FIFOs. The new versions are designated by the "LA" mark. The LA part is pinfor-pin compatible with the original "L" version. Some difference exist between the two versions. The following table details these differences.
Item
NEW PART IDT72255LA IDT72265LA
OLD PART IDT72255L IDT72265L FS (Frequency Select)
Comments
Pin #3
DC (Don't Care) - There is no restriction on WCLK and RCLK. See note 1. 60ns(2) + tREF + 1 TRCLK(4)
In the LA part this pin must be tied to either VCC or GND and must not toggle after reset. First word latency in the LA part is a fixed value, independent of the frequency of RCLK or WCLK. First word latency in the LA part is a fixed value, independent of the frequency of RCLK or WCLK. Retransmit latency in the LA part is a fixed value, independent of the frequency of RCLK or WCLK. Retransmit latency in the LA part is a fixed value, independent of the frequency of RCLK or WCLK. Active supply current Standby current Typical ICC1 Current calculation
First Word Latency (IDT Standard Mode) First Word Latency (FWFT Mode) Retransmit Latency (IDT Standard Mode) Retransmit Latency (FWFT Mode) ICC1 ICC2 Typical ICC1
(5)
tFWL1 = 10*Tf(3) + 2TRCLK(4)(ns)
60ns(2) + tREF + 2 TRCLK(4)
tFWL2 = 10*Tf(3) + 3TRCLK(4)(ns)
60ns(2) + tREF + 1 TRCLK(4)
tRTF1 = 14*Tf(3) + 3TRCLK(4)(ns)
60ns(2) + tREF + 2 TRCLK(4)
tRTF2 = 14*Tf(3) + 4TRCLK(4)(ns)
80mA 20mA 15 + 2.1*fS + 0.02*CL*fS(mA)
180mA 15mA Not Given
NOTES: 1. WCLK and RCLK can vary independently and can be stopped. There is no restriction on operating WCLK and RCLK. 2. This is tSKEW3. 3. Tf is the period of the `selected clock'. 4. TRCLK is the cycle period of the read clock. 5. Typical ICC1 is based on VCC = 5V, tA = 25C, fS = WCLK frequency = RCLK frequency (in MHz using TTL levels), data switching at fS/2, CL = Capacitive Load (in pF).
IDT and the IDT logo are trademarks of Integrated Device Technology, Inc and the SuperSyncFIFO is a trademark of Integrated Device Technology, Inc.
COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES
27
2005 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice.

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