PRELIMINARY IDT72V255 IDT72V265 3.3 VOLT CMOS SUPERSYNC FIFO 8,192 x 18, 16,384 x 18 Integrated Device Technology, Inc. * Output enable puts data outputs into high impedance * High-performance submicron CMOS technology FEATURES: * 3.3 Volt operation saves 60 percent power compared to the functionally compatible 5 Volt 72255/65 Family * 8,192 x 18-bit storage capacity (IDT72V255) * 16,384 x 18-bit storage capacity (IDT72V265) * 15ns read/write cycle time (10ns access time) * Retransmit Capability * Auto power down reduces power consumption * Master Reset clears entire FIFO, Partial Reset clears data, but retains programmable settings * 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) * Easily expandable in depth and width * Independent read and write clocks (permit simultaneous reading and writing with one clock signal) * Available in the 64-pin Thin Quad Flat Pack (TQFP), 64pin Slim Thin Quad Flat Pack (STQFP) the 68-pin Pin Grid Array (PGA) DESCRIPTION: The 72V255/72V265 are functionally compatible versions of the 72255/65 designed to run off a 3.3V supply for exceptionally low power consumption. The IDT72V255/72V265 are monolithic, CMOS, high capacity, high speed, First-In, FirstOut (FIFO) memories with clocked read and write controls. These FIFOs are applicable for a wide variety of data buffering needs, such as optical disk controllers, local area networks (LANs), and inter-processor communication. Both FIFOs have an 18-bit input port (Dn) and an 18-bit output port (Qn). The input port is controlled by a free-running clock (WCLK) and a data input enable pin (WEN). Data is written into the synchronous FIFO on every clock when WEN is asserted. The output port is controlled by another clock pin (RCLK) and enable pin (REN). The read clock can be tied to the write clock for single clock operation or the two clocks can run asynchronously for dual clock operation. An output FUNCTIONAL BLOCK DIAGRAM WEN * LD SEN D0-D17 WCLK * INPUT REGISTER RAM ARRAY 8,192 x 18 16,384 x 18 WRITE POINTER FF/IR PAF EF/OR PAE HF FLAG LOGIC * * WRITE CONTROL LOGIC OFFSET REGISTER FWFT/SI READ POINTER ** OUTPUT REGISTER MRS PRS FS RESET LOGIC READ CONTROL LOGIC * RT RCLK * * REN TIMING OE Q0-Q17 3478 drw 01 SuperSync FIFO and SyncFIFO are trademarks and the IDT logo is a registered trademark of Integrated Device Technology, Inc. MILITARY AND COMMERCIAL TEMPERATURE RANGES 1996 Integrated Device Technology For latest information contact IDT's web site at www.idt.com or fax-on-demand at 408-492-8391. DECEMBER 1995 DSC-3478/- 5.04 1 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES mode. RCLK REN RT OE VCC PAF HF PAE EF/OR PAE, PAF can be programmed independently to any point in memory. They, also, can be used irrespective of mode. Programmable offsets determine the flag threshold and can be loaded by two methods: parallel or serial. Two default offset settings are also provided, such that PAE can be set at 127 or 1023 locations from the empty boundary and the PAF threshold can be set at 127 or 1023 locations from the full boundary. All these choices are made with LD during Master Reset. In the serial method, SEN together with LD are used to load the offset registers via the Serial Input (SI). In the parallel method, WEN together with LD can be used to load the offset registers via Dn. REN together with LD can be used to read the offsets in parallel from Qn regardless of whether serial or parallel offset loading is selected. During Master Reset (MRS), the read and write pointers are set to the first location of the FIFO. The FWFT line selects IDT Standard Mode or FWFT Mode. The LD pin selects one of two partial flag default settings (127 or 1023) and, also, serial or GND FF/IR PRS MRS LD WCLK PIN CONFIGURATIONS FWFT/SI enable pin (OE) is provided on the read port for three-state control of the outputs. The IDT72V255/72V265 have two modes of operation: In the IDT Standard Mode, the first word written to the FIFO is deposited into the memory array. A read operation is required to access that word. In the First Word Fall Through Mode (FWFT), the first word written to an empty FIFO appears automatically on the outputs, no read operation required. The state of the FWFT/SI pin during Master Reset determines the mode in use. The IDT72V255/72V265 FIFOs have five flag functions, EF/OR (Empty Flag or Output Ready), FF/IR (Full Flag or Input Ready), and HF (Half-full Flag). The EF and FF functions are selected in the IDT Standard Mode. The IR and OR functions are selected in the First Word Fall Through Mode. IR indicates that the FIFO has free space to receive data. OR indicates that data contained in the FIFO is available for reading. HF is a flag whose threshold is fixed at the half-way point in memory. This flag can always be used irrespective of PIN 1 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 WEN SEN 1 2 48 47 FS VCC GND D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 3 4 5 46 45 44 6 7 8 9 10 11 12 43 42 41 40 39 38 37 PN64-1 PP64-1 13 14 15 16 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 D4 D3 D2 D6 D5 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 3478 drw 02 TQFP STQFP TOP VIEW 5.04 2 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES parallel programming. The flags are updated accordingly. The Partial Reset (PRS) also sets the read and write pointers to the first location of the memory. However, the mode setting, programming method, and partial flag offsets are not altered. The flags are updated accordingly. PRS is useful for resetting a device in mid-operation, when reprogramming offset registers may not be convenient. The Retransmit function allows the read pointer to be reset to the first location in the RAM array. It is synchronized to RCLK when RT is LOW. This feature is convenient for sending the same data more than once. If, at any time, the FIFO is not actively performing a function, the chip will automatically power down. This occurs if neither a read nor a write occurs within 10 cycles of the faster clock, RCLK or WCLK. During the Power Down state, supply current consumption (ICC2) is at a minimum. Initiating any operation (by activating control inputs) will immediately take the device out of the Power Down state. The IDT72V255/72V265 are depth expandable. The addition of external components is unnecessary. The IR and OR functions, together with REN and WEN, are used to extend the total FIFO memory capacity. The FS line ensures optimal data flow through the FIFO. It is tied to GND if the RCLK frequency is higher than the WCLK frequency or to Vcc if the RCLK frequency is lower than the WCLK frequency The IDT72V255/72V265 is fabricated using IDT's high speed submicron CMOS technology. PIN CONFIGURATIONS (CONT.) 11 DNC Q5 VCC Q2 Q1 GND D1 D3 D5 Q4 Q3 GND Q0 D0 D2 D4 D6 D7 10 Q6 GND 09 Q8 Q7 D9 D8 08 Q10 Q9 D11 D10 07 Q11 GND D13 D12 06 Q13 Q12 D15 D14 05 Q14 VCC D17 D16 04 GND Q15 VCC GND 03 Q17 Q16 SEN FS 02 DNC OE REN GND PAE HF FF/ IR RT RCLK EF/ OR VCC PAF GND FWFT/ SI B C D E F G H G68-1 Pin 1 Designator 01 A PGA TOP VIEW DNC LD WCLK WEN MRS PRS J K L 3478 drw 03 NOTES: 1. DNC = Do not connect 5.04 3 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES PIN DESCRIPTION Symbol D0-D17 MRS Name Data Inputs Master Reset I/O I I PRS Partial Reset I RT FWFT/SI WCLK WEN RCLK Retransmit First Word Fall Through/Serial In Write Clock I I Write Enable Read Clock I I I REN OE SEN LD Read Enable I Output Enable Serial Enable Load I I I FS Frequency Select I Full Flag/ Input Ready O Empty Flag/ Output Ready O Programmable Almost Full Flag O Programmable Almost Empty Flag O Q0-Q17 VCC Half-full Flag Data Outputs Power O O GND Ground FF/IR EF/OR PAF PAE HF Description Data inputs for a 18-bit bus. MRS initializes the read and write pointers to zero and sets the output register to all zeroes. During Master Reset, the FIFO is configured for either FWFT or IDT Standard Mode, one of two programmable flag default settings, and serial or parallel programming of the offset settings. 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. Allows data to be resent starting with the first location of FIFO memory. 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. 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 and 1023) and determines programming method, serial or parallel. After Master Reset, this pin enables writing to and reading from the offset registers. The FS setting optimizes data flow through the FIFO. 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 HIGH if the number of free locations in the FIFO memory is more than offset m which is stored in the Full Offset register. PAF goes LOW if the number of free locations in the FIFO memory is less than m. 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. PAE goes HIGH if the number of words in the FIFO memory is greater than offset n. HF indicates whether the FIFO memory is more or less than half-full. Data outputs for a 18-bit bus. +3.3 Volt power supply pins. Ground pins. 3478 tbl 01 5.04 4 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES ABSOLUTE MAXIMUM RATINGS(1) Symbol VTERM TA Rating Commercial MIilitary Unit Terminal Voltage -0.5 to +7.0 with respect to GND -0.5 to +7.0 V Operating Temperature -55 to +125 C 0 to +70 RECOMMENDED DC OPERATING CONDITIONS Symbol VCCM VCCC Parameter Military Supply Voltage Commercial Supply Voltage Min. Typ. 3.0 3.3 Max. 3.6 Unit V 3.0 3.3 3.6 V TBIAS Temperature Under -55 to +125 Bias -65 to +135 C GND Supply Voltage 0 0 0 V TSTG Storage Temperature -55 to +125 -65 to +155 C VIH 2.0 -- Vcc+0.5 V IOUT DC Output Current 50 50 mA VIH Input High Voltage Commercial Input High Voltage Military Input Low Voltage Commercial & Military 2.0 -- Vcc+0.5 V -- -- 0.8 V NOTE: 3478 tbl 02 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. VIL(1) NOTE: 3478 tbl 03 1. 1.5V undershoots are allowed for 10ns once per cycle. DC ELECTRICAL CHARACTERISTICS (Commercial: VCC = 3.3V 0.3V, TA = 0C to +70C; Military: VCC = 3.3V 0.3V, TA = -55C to +125C) DT72V255L IDT72V265L Commercial tCLK = 15, 20ns Symbol Parameter IDT72V255L IDT72V265L Military tCLK = 20, 25ns Min. Typ. Max. Min. Typ. Max. Unit ILI(1) Input Leakage Current (any input) -1 -- 1 -10 -- 10 A ILO(2) Output Leakage Current -10 -- 10 -10 -- 10 A VOH VOL Output Logic "1" Voltage, IOH = -2 mA Output Logic "0" Voltage, IOL = 8 mA 2.4 -- -- -- -- 0.4 2.4 -- -- -- -- 0.4 V V ICC1(3) Active Power Supply Current -- -- 100 -- -- 100 mA -- -- 10 -- -- 10 mA ICC2(3,4) Power Down Current (All inputs = VCC - 0.2V or GND + 0.2V, RCLK and WCLK are free-running) NOTES: 1. Measurements with 0.4 VIN VCC. 2. OE = VIH 3. Tested at f = 20 MHz with outputs unloaded. 3478 tbl 04 4. No data written or read for more than 10 cycles CAPACITANCE (TA = +25C, 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=HIGH). 2. Characterized values, not currently tested. 3478 tbl 05 5.04 5 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES AC ELECTRICAL CHARACTERISTICS(1) (Commercial: VCC =3.3V 0.3V, TA = 0C to +70C; Military: VCC = 3.3V 0.3V, TA = -55C to +125C) Commercial 72V255L15 72V265L15 Symbol Parameter Com'l & Mil. 72V255L20 72V265L20 Military 72V255L25 72V265L25 Min. Max. Min. Max. Min. Max. Unit fS Clock Cycle Frequency -- 66.7 -- 50 -- 40 MHz tA Data Access Time 2 10 2 14 3 15 ns tCLK Clock Cycle Time 15 -- 20 -- 25 -- ns tCLKH Clock High Time 6 -- 8 -- 10 -- ns tCLKL Clock Low Time 6(2) -- 8 -- 10 -- ns ns tDS Data Set-up Time 4 -- 5 -- 6 -- tDH Data Hold Time 1 -- 1 -- 1 -- ns tENS Enable Set-up Time 4 -- 5 -- 6 -- ns tENH Enable Hold Time 1 -- 1 -- 1 -- ns tLDS Load Set-up Time 4 -- 5 -- 6 -- ns tLDH Load Hold Time 10 -- 10 -- 10 -- ns (3) tRS Reset Pulse Width 15 -- 20 -- 25 -- ns tRSS Reset Set-up Time 15 -- 20 -- 25 -- ns tRSR Reset Recovery Time 15 -- 20 -- 25 -- ns tRSF Reset to Flag and Output Time -- 15 -- 20 -- 25 ns tFWFT Mode Select Time 0 -- 0 -- 0 -- ns tRTS Retransmit Set-Up Time 4 -- 5 -- 6 -- ns 0 -- 0 -- 0 -- ns 3 8 3 10 3 13 ns (4) tOLZ Output Enable to Output in Low Z tOE Output Enable to Output Valid (4) tOHZ Output Enable to Output in High Z 3 8 3 10 3 13 ns tWFF Write Clock to FF or IR -- 10 -- 12 -- 15 ns -- 10 -- 14 -- 15 ns -- -- -- 10 10 20 -- -- -- 12 12 25 -- -- -- 15 15 25 ns ns ns tREF tPAF tPAE tHF Read Clock to EF or OR Write Clock to PAF Read Clock to PAE Clock to HF tSKEW1 Skew time between RCLK and WCLK for FF and IR 12 -- 15 -- 20 -- ns tSKEW2 Skew time between RCLK and WCLK for PAE and PAF 21 -- 25 -- 35 -- ns 3478 tbl 06 NOTES: 1. All AC timings apply to both Standard IDT Mode and First Word Fall Through Mode. 2. For the RCLK line: tCLKL (min.) = 7 ns only when reading the offsets from the programmable flag registers; otherwise, use the table value. For the WCLK line, use the tCLKL (min.) value given in the table. 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 680 GND to 3.0V 3ns 1.5V 30pF* 3478 drw 04 1.5V See Figure 1 Figure 1. Output Load * Includes jig and scope capacitances. 3478 tbl 08 5.04 6 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES SIGNAL DESCRIPTIONS: INPUTS: DATA IN (D0 - D17) Data inputs for 18-bit wide data. CONTROLS: MASTER RESET (MRS) A Master Reset is accomplished whenever the Master Reset (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 1023 words from the empty boundary and PAF is assigned a threshold 1023 words from the full boundary; 1023 words corresponds to an offset value of 3FFH. Following Master Reset, serial loading of the offsets is permitted, but not parallel loading. Regardless of whether serial or parallel offset loading has been selected, parallel reading of the registers is always permitted. (See section describing the LD line 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. PARTIAL RESET (PRS) A Partial Reset is accomplished whenever the Partial Reset (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 flag settings may not be convenient. 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 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 Full 2 words should have been written into the FIFO between Reset (Master or Partial) and the time of Retransmit Setup (Full = 8,192 words for the 72V255, 16,384 words for the 72V265). 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. Writing operations can begin after one of two conditions have been met: EF is HIGH or 14 cycles of the faster clock (RCLK or WCLK) have elapsed since the RCLK rising edge enabled by the RT pulse. The deassertion time of EF during Retransmit Setup is variable. The parameter tRTF1, which is measured from the rising RCLK edge enabled by RT to the rising edge of EF is described by the following equation: tRTF1 max. = 14*Tf + 3*TRCLK (in ns) where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. Regarding FF: Note that since no more than Full - 2 writes are allowed between a Reset and a Retransmit Setup, FF will remain HIGH throughout the setup procedure. For IDT Standard mode, updating the PAE, HF, and PAF flags begins with the "first" REN-enabled rising RCLK edge following the end of Retransmit Setup (the point at which EF goes HIGH). This same RCLK rising edge is used to access the "first" memory location. HF is updated on the first RCLK rising edge. PAE is updated after two more rising RCLK edges. PAF is updated after the "first" rising RCLK edge, followed by the next two rising WCLK edges. (If the tskew2 specification is not met, add one more WCLK cycle.) If FWFT mode is selected, the FIFO will mark the beginning of the Retransmit Setup by setting OR HIGH. The change in level will only be noticeable if OR was LOW before setup. 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 are automatically displayed on the outputs. Since FWFT Mode is selected, the 5.04 7 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES first word appears on the outputs, no read request necessary. Reading all subsequent words requires a LOW on REN to enable the rising edge of RCLK. Writing operations can begin after one of two conditions have been met: OR is LOW or 14 cycles of the faster clock (RCLK or WCLK) have elapsed since the RCLK rising edge enabled by the RT pulse. The assertion time of OR during Retransmit Setup is variable. The parameter tRTF2, which is measured from the rising RCLK edge enabled by RT to the falling edge of OR is described by the following equation: tRTF2 max. = 14*Tf + 4*TRCLK (in ns) where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. Note that a Retransmit Setup in FWFT mode requires one more RCLK cycle than in IDT Standard mode. Regarding IR: Note that since no more than Full - 2 writes are allowed between a Reset and a Retransmit Setup, IR will remain LOW throughout the setup procedure. For FWFT mode, updating the PAE, HF, and PAF flags begins with the "last" rising edge of RCLK before the end of Retransmit Setup. This is the same edge that asserts OR and automatically accesses the first memory location. Note that, in this case, REN is not required to initiate flag updating. HF is updated on the "last" RCLK rising edge. PAE is updated after two more rising RCLK edges. PAF is updated after the "last" rising RCLK edge, followed by the next two rising WCLK edges. (If the tskew2 specification is not met, add one more WCLK cycle.) RT is synchronized to RCLK. The Retransmit operation is useful in the event of a transmission error on a network, since it allows a data packet to be resent. FIRST WORD FALL THROUGH/SERIAL IN (FWFT/SI) This is a dual purpose pin. During Master Reset, the state of the FWFT/SI helps determine 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) line. 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, no read request necessary. Subsequent words must be accessed using the Read Enable (REN) line. 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. FWFT/SI 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 write clock (WCLK). Data set-up and hold times must be met with respect to the LOW-to-HIGH transition of the WCLK. The write and read clocks can either be asynchronous or coincident. WRITE ENABLE (WEN) When Write Enable (WEN) is LOW, data can be loaded into the input register on the rising edge of every WCLK cycle. Data is stored in the RAM array sequentially and independently of any on-going read operation. When WEN is HIGH, the input register holds the previous data and no new data is loaded into the FIFO. 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. WEN is ignored when the FIFO is full. 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. WEN is ignored when the FIFO is full. READ CLOCK (RCLK) Data can be read on the outputs, on the rising edge of the read clock (RCLK), when Output Enable (OE) is set LOW. The write and read clocks can be asynchronous or coincident. READ ENABLE (REN) When Read Enable (REN) is LOW, data is loaded from the RAM array into the output register on the rising edge of the RCLK. When REN is HIGH, the output register holds the previous data and no new data is loaded into the output register. 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 all the data 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 after tFWL1 +tREF and a read is permitted. In the FWFT Mode, the first word written to an empty FIFO automatically goes to the outputs Qn, no need for any read request. In order to access all other words, a read must be executed using REN . When all the data has been read from the FIFO, Output Ready (OR) will go HIGH, inhibiting further read operations. REN is ignored when the FIFO is empty. Once a write is performed, OR will go LOW after tFWL2 +tREF, when the first word appears at Qn ; if a second word is written into the FIFO, then REN can be used to read it out. SERIAL ENABLE (SEN) Serial Enable is (SEN) 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, 5.04 8 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES data at the SI input can be loaded into the input register one bit for each LOW-to-HIGH transition of WCLK. 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 (OE) 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 Load line (LD) determines one of two default values (127 or 1023) for the PAE and PAF flags, along with the method by which these flags can be programmed, parallel or serial. After Master Reset, LD enables write operations to and read operations from the registers. Only the offset loading method currently selected can be used to write to the registers. Aside from Master Reset, there is no other way change the loading method. Registers can be read only in parallel; this can be LD WEN REN SEN 0 0 1 1 0 1 0 1 0 1 1 0 0 1 1 1 1 0 X X 1 X 0 X X 1 1 1 X X accomplished regardless of whether serial or the parallel loading has been selected. Associated with each of the programmable flags, PAE and PAF, is one register which can either be written to or read from. Offset values contained in these registers determine how many words need to be in the FIFO memory to switch a partial flag. 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 1023 words from the empty boundary), a default PAF offset value of 3FFH (a threshold 1023 words form the full boundary), and serial loading of other offset values. The act of writing offsets (in parallel or serial) 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. WCLK Selection RCLK X Parallel write to registers: Empty Offset Full Offset Parallel read from registers: Empty Offset Full Offset X X X Serial shift into registers: 26 bits for the 72V255 28 bits for the 72V265 1 bit for each rising WCLK edge Starting with Empty Offset Ending with Full Offset X No Operation X Write Memory Read Memory X No Operation 3478 tbl 09 NOTES: 1. Only one of the two offset programming methods, serial or parallel, is available for use at any given time. 2. The programming method can only be selected at Master Reset. 3. Parallel reading of the offset registers is always permitted regardless of which programming method has been selected. 4. The programming sequence applies to both IDT Standard and FWFT modes. Figure 2. Partial Flag Programming Sequence 5.04 9 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES Once serial offset loading has been selected, then 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 (13 bits for the 72V255, 14 bits for the 72V265), ending with the Full Offset (13 bits for the 72V255, 14 bits for the 72V265). A total of 26 bits are necessary to program the 72V255; a total of 28 bits are necessary to program the 72V265. Individual registers cannot be loaded serially; rather, both must be programmed in sequence, no padding allowed. PAE and PAF can show a valid status only after the full set of bits have been entered. The registers can be re-programmed, as long as both offsets are loaded. When LD is LOW and SEN is HIGH, no serial write to the registers can occur. Once parallel offset loading has been selected, then 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 at the inputs are written into the Full Register. The third transition of WCLK writes, once again, to the Empty Offset Register. To ensure proper programming (serial or parallel) of the offset registers, no read operation is permitted from the time of reset (master or partial) to the time of programming. (During this period, the read pointer must be pointing to the first location of the memory array.) After the programming has been accomplished, read operations may begin. Write operations to memory 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 or two offset registers can be written to 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. Write operations to memory 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 a mere 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 where it left off. 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 pertaining to that flag. 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 either of 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 (Add one more RCLK cycle if tSKEW2 is not met.) 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 output lines when LD is set LOW and REN is set LOW; then, 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. It is permissible to interrupt the offset register access sequence with reads or writes to memory . The interruption is accomplished by deasserting REN, LD, or both together. When REN and LD are restored to a LOW level, access of the registers continues where it left off. LD functions the same way in both IDT Standard and FWFT modes. FREQUENCY SELECT input (FS) An internal state machine manages the movement of data through the Supersync FIFO. The FS line determines whether RCLK or WCLK will synchronize the state machine. Tie FS to VCC if the RCLK line is running at a lower frequency than the WCLK line. In this case, the state machine will be synchronized to WCLK. Tie FS to GND if the RCLK line is running at a higher frequency than the WCLK line. In this case, the state machine will be synchronized to RCLK. Note that FS must be set so the clock line running at the higher frequency drives the state machine; this ensures efficient handling of the data within the FIFO. If the same clock signal drives both the WCLK and the RCLK pins, then tie FS to GND. The frequency of the clock tied to the state machine (referred to as the "selected clock") may be changed at any time, so long as it is always greater than or equal to the frequency of the clock that is not tied to the state machine (referred to as the "non-selected clock"). The frequency of the non-selected clock can also be varied with time, so long as it never exceeds the frequency of the selected clock. To be more specific, the frequencies of both RCLK and WCLK may be varied during FIFO operation, provided that, at any given point in time, the cycle period of the selected clock is equal to or less than the cycle period of the non-selected clock. The selected clock must be continuous. It is, however, permissible to stop the non-selected clock. Note, so long as RCLK is idle, EF/OR and PAE will not be updated. Likewise, as long as WCLK is idle, FF/IR and PAF will not be updated. Changing the FS setting during FIFO operation (i.e. reading or writing) is not permitted; however, such a change at the time of Master Reset or Partial Reset is all right. FS is an asynchronous input. 5.04 10 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES 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 (i.e. the write pointer catches up to the read pointer), FF will go LOW, inhibiting further write operation. 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 8,192 writes to the IDT72V255 and 16,384 writes to the IDT72V265. 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 operation. If no reads are performed after a reset (either MRS or PRS), IR will go HIGH after 8,193 writes for the IDT72V255 and 16,385 writes for the IDT72V265. 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 synchronized to WCLK. It is double-registered to enhance metastable immunity. 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 (i.e. the read pointer catches up to the write pointer), EF will go LOW, inhibiting further read operations. When EF is HIGH, the FIFO is not empty. When writing the first word to an empty FIFO, the deassertion time of EF is variable, and can be represent by the First Word Latency parameter, tFWL1, which is measured from the rising WCLK edge that writes the first word to the rising RCLK edge that updates the flag. tFWL1 includes any delays due to clock skew and can be expressed as follows: tFWL1 max. = 10*Tf + 2*TRCLK (in ns) where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. Since no read can take place until EF goes HIGH, the tFWL1 delay determines how early the first word can be available at Qn. This delay has no effect on the reading of subsequent words. 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 goes HIGH one cycle after RCLK shifts the last word from the FIFO memory to the outputs. Then further data reads are inhibited until OR goes LOW again. When writing the first word to an empty FIFO, the assertion time of OR is variable, and can be represented by the First Word Latency parameter, tFWL2, which is measured from the rising WCLK edge that writes the first word to the rising RCLK edge that updates the flag. tFWL2 includes any delay due to clock skew and can be expressed as follows: tFWL2 max. = 10*Tf + 3*TRCLK (in ns) where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. Note that the First Word Latency in FWFT mode is one RCLK cycle longer than in IDT Standard mode. The tFWL2 delay determines how early the first word can be available at Qn. This delay has no effect on the reading of subsequent words. 72V265 - 16,384 x 18-Bit 72V255 - 8,192 x 18-Bit 17 17 12 17 0 0 13 EMPTY OFFSET REGISTER EMPTY OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset 12 17 0 13 0 FULL OFFSET REGISTER FULL OFFSET REGISTER DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset DEFAULT VALUE 07FH if LD is LOW at Master Reset, 3FFH if LD is HIGH at Master Reset 3478 drw 06 3478 drw 05 NOTE: 1. Any bits of the offset register not being programmed should be set to zero. Figure 3. Offset Register Location and Default Values 5.04 11 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES EF/OR is sychronized to the RCLK. It is double-registered to enhance metastable immunity. PROGRAMMABLE ALMOST-FULL FLAG (PAF) The Programmable Almost-Full Flag (PAF) will go LOW when the FIFO reaches the Almost-Full condition as specified by the offset m stored in the Full Offset register. At the time of Master Reset, depending on the state of LD, one of two possible default offset values are chosen. If LD is LOW, then m = 07FH and the PAF switching threshold is 127 words from the Full boundary, if LD is HIGH, then m = 3FFH and the PAF switching threshold is 1023 words away from the Full boundary. Any integral value of m from 0 to the maximum FIFO depth minus 1 (8,191 words for the 72V255, 16,383 words for the 72V265) can be programmed into the Full Offset register. In IDT Standard Mode, if no reads are performed after reset (MRS or PRS), PAF will go LOW after (8,192-m) writes to the IDT72V255, and (16,384-m) writes to the IDT72V265. In FWFT Mode, if no reads are performed after reset (MRS or PRS), PAF will go LOW after (8,193-m) writes to the IDT72V255, and (16,385-m) writes to the IDT72V265. In this case, the first word written to an empty FIFO does not stay in memory, but goes unrequested to the output register; therefore, it has no effect on determining the state of PAF. Note that even though PAF is programmed to switch LOW during the first word latency period (tFWL), attempts to read data will be ignored until EF goes HIGH indicating that data is available at the output port. This is true for both timing modes. PAF is synchronous and updated on the rising edge of WCLK. It is double-registered to enhance metastable immunity. PROGRAMMABLE ALMOST-EMPTY FLAG (PAE) TABLE I -- STATUS FLAGS FOR IDT STANDARD MODE Number of Words in FIFO Memory 72V255 (1) 72V265 0 0 1 to n (2) 1 to n (2) FF PAF HF PAE EF H H H L L H H H L H (n+1) to 4,096 (n+1) to 8,192 H H H H H 4,097 to (8192-(m+1)) 8,193 to (16,384-(m+1)) H H L H H H L L H H L L L H (8,192-m) (3) to 8,191 (16,384-m) (3) to 16,383 16,384 8,192 NOTES: 1. Data in the output register does not count as a 'word in FIFO memory". Since in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register (no read operation necessary), it is not included in the FIFO memory count. 2. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n=1023 when serial offset loading is selected. 3. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or n=1023 when serial offset loading is selected. H 3478 tbl 10 TABLE II -- STATUS FLAGS FOR FWFT MODE Number of Words in FIFO Memory 72V255 (1) 72V265 0 0 1 to n (2) 1 to n (2) IR PAF HF PAE L H H L H (4) L H H L L H H L OR (n+1) to 4,096 (n+1) to 8,192 L H 4,097 to (8192-(m+1)) 8,193 to (16,384-(m+1)) L H L H L L L L H L H L L H L (8,192-m) (3) to 8,191 8,192 (16,384-m) (3) to 16,383 16,384 3478 tbl 11 NOTES: 1. Data in the output register does not count as a 'word in FIFO memory". Since in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register (no read operation necessary), it is not included in the FIFO memory count. 2. n = Empty Offset, Default Values: n = 127 when parallel offset loading is selected or n=1023 when serial offset loading is selected. 3. m = Full Offset, Default Values: m = 127 when parallel offset loading is selected or n=1023 when serial offset loading is selected. 4. Following a reset (Master or Partial), the FIFO memory is empty and OR = HIGH. After writing the first word, the FIFO memory remains empty, the data is placed into the output register, and OR goes LOW. In this case, or any time the last word in the FIFO memory has been read into the output register; a rising RCLK edge, enabled by REN, will set OR HIGH. 5.04 12 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES The Programmable Almost-Empty Flag (PAE) will go LOW when the FIFO reaches the Almost-Empty condition as specified by the offset n stored in the Empty Offset register. At the time of Master Reset, depending on the state of LD, one of two possible default offset values are chosen. If LD is LOW, then n = 07FH and the PAE switching threshold is 127 words from the Empty boundary, if LD is HIGH, then n = 3FFH and the PAE switching threshold is 1023 words away from the Empty boundary. Any integral value of n from 0 to the maximum FIFO depth minus 1 (8,191 words for the 72V255, 16,383 words for the 72V265) can be programmed into the Empty Offset register. In IDT Standard Mode, if no reads are performed after reset (MRS or PRS), the PAE will go HIGH after (n + 1) writes to the IDT72V255/72V265. In FWFT Mode, if no reads are performed after reset (MRS or PRS), the PAE will go HIGH after (n+2) writes to the IDT72V255/72V265. In this case, the first word written to an empty FIFO does not stay in memory, but goes unrequested to the output register; therefore, it has no effect on determining the state of PAE. Note that even though PAE is programmed to switch HIGH during the first word latency period (tFWL), attempts to read data will be ignored until EF goes HIGH indicating that data is available at the output port. This is true for both timing modes. PAE is synchronous and updated on the rising edge of RCLK. It is double-registered to enhance metastable immunity. HALF-FULL FLAG (HF) This output indicates a half-full memory. The rising WCLK edge that fills the memory 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 also 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, where D is the maximum FIFO depth (8,192 words for the IDT72V255, 16,384 words for the IDT72V265). In FWFT Mode, if no reads are performed after reset (MRS or PRS), HF will go LOW after (D/2+2) writes to the IDT72V255/ 72V265. In this case, the first word written to an empty FIFO does not stay in memory, but goes unrequested to the output register; therefore, it has no effect on determining the state of HF. Because HF uses both RCLK and WCLK for synchronization purposes, it is asynchronous. DATA OUTPUTS (Q0-Q17) Q0-Q17 are data outputs for 18-bit wide data. 5.04 13 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tRS MRS tRSS tRSR tRSS tRSR REN WEN tRSR tFWFT FWFT/SI tRSS LD tRSR (1) tRSS RT tRSS SEN tRSF If FWFT = HIGH, OR = HIGH 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 (1) Q0 - Q17 OE = LOW 3478 drw 07 Figure 4. Master Reset Timing 5.04 14 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tRS PRS tRSS tRSR tRSS tRSR REN WEN tRSS RT tRSS SEN tRSF If FWFT = HIGH, OR = HIGH 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 (1) Q0 - Q17 OE = LOW 3478 drw 08 Figure 5. Partial Reset Timing 5.04 15 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tCLK tCLKH WCLK 1 tCLKL 2 tD S tD H D0 - D17 DATAIN VALID tENS tENH WEN NO OPERATION tWFF tWFF FF tSKEW1(1) RCLK REN 3478 drw 09 NOTES: 1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that FF will go HIGH (after one WCLK cycle plus tWFF). If the time between the rising edge of RCLK and the rising edge of WCLK is less than tSKEW1, then the FF deassertion may be delayed an extra WCLK cycle. 2. LD = HIGH Figure 6. Write Cycle Timing (IDT Standard Mode) 5.04 16 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tCLK tCLKH tCLKL RCLK tENS tENH REN NO OPERATION tREF tREF EF tA Q0 - Q17 LAST WORD tOLZ tOE tOHZ OE (1) tFWL1 WCLK tENH WEN tENS tDHS tDS D0 - D17 FIRST WORD 3478 drw 10 NOTES: 1. tFWL1 contributes a variable delay to the overall first word latency (this parameter includes delays due to skew): tFWL1 max. (in ns) = 10*Tf + 2* TRCLK where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period 2. LD = HIGH Figure 7. Read Cycle Timing (IDT Standard Mode) 5.04 17 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES WCLK tDS D0 D17 D0 D1 first valid write tENS WEN (1) tFWL1 RCLK tREF EF REN tA Q0 NOTES: 1. Q17 tFWL1 max. (in ns) = 10* Tf + 2* TRCLK tOLZ Where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period 2. LD = HIGH OE tA D0 D1 tOE 3478 drw 11 Figure 8. First Data Word Latency (IDT Standard Mode) 5.04 18 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 NO WRITE WCLK 1 tSKEW1 MILITARY AND COMMERCIAL TEMPERATURE RANGES NO WRITE 2 1 (1) tSKEW1(1) tDS D0 - D17 2 DATA tDS WRITE Wd tWFF tWFF tWFF FF WEN RCLK tENH REN OE tENS tENS LOW tA Q0 - Q17 tENH tA DATA IN OUTPUT REGISTER DATA READ NEXT DATA READ 3478 drw 12 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 an extra WCLK cycle. 2. LD = HIGH Figure 9. Full Flag Timing (IDT Standard Mode) 5.04 19 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES WCLK tDS tDS DATA WRITE 1 D0 - D17 DATA WRITE 2 tENH tENS tENS tENH WEN (1) tFWL1 tFWL1 (1) RCLK tREF tREF tREF EF REN OE LOW tA Q0 - Q17 DATA IN OUTPUT REGISTER WORD 1 3478 drw 13 NOTES: 1. tFWL1 max. (in ns) = 10*Tf + 2*TRCLK Where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the period. 2. LD = HIGH Figure 10. Empty Flag Timing (IDT Standard Mode) 5.04 20 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES WCLK tENH tENS tENH SEN tLDH tLDS tLDH LD tDS (1) BIT 0 SI BIT 0 BIT X EMPTY OFFSET BIT X FULL OFFSET (1) 3478 drw 14 Figure 11. Serial Loading of Programmable Flag Registers (IDT Standard and FWFT modes) NOTE: 1. For the 72V255, X = 12. For the 72V265, X = 13. tCLK tCLKH tCLKL WCLK tLDH tLDS LD tENS tENH tDS tDH WEN D0 - D17 PAF OFFSET PAE OFFSET 3478 drw 15 Figure 12. Parallel Loading of Programmable Flag Registers (IDT Standard and FWFT modes) 5.04 21 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tCLK tCLKL tCLKH RCLK tLDS tLDH tENS tENH tLDH LD tENH REN tA tA DATA IN OUTPUT REGISTER Q0 - Q17 PAE OFFSET PAF OFFSET 3478 drw 16 Figure 13. Parallel Read of Programmable Flag Registers (IDT Standard and FWFT modes) NOTE: 1. OE=LOW tCLKL tCLKH WCLK tENS tENH WEN PAE n Words in FIFO memory (1,2) n+1 words in FIFO memory n words in FIFO memory (3) tPAE tPAE tSKEW2 RCLK 1 1 2 tENS 2 tENH REN 3478 drw 17 NOTES: 1. PAE offset = n 2. Data in the output register does not count as a "word in FIFO memory". Since, in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register (no read operation necessary), it is not included in the FIFO memory count. 3. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge for PAE to 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. Figure 14. Programmable Almost Empty Flag Timing (IDT Standard and FWFT modes) 5.04 22 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES tCLKL tCLKH WCLK tENS 1 2 1 2 tENH WEN tPAF PAF tPAF D - m Words in FIFO Memory (1,2) D - (m+1) Words in FIFO Memory tSKEW2 (3) D-(m+1) Words in FIFO Memory RCLK tENS tENH REN 3478 drw 18 NOTES: 1. PAF offset = m, D = 8,192 for IDT 72V255, 16,384 word for IDT 72V265. 2. Data in the output register does not count as a "word in FIFO memory". Since, in FWFT mode, the first word written to an empty FIFO goes unrequested to the output register (no read operation necessary), it is not included in the FIFO memory count. 3. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge for PAF to 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 an extra WCLK cycle. Figure 15. Programmable Almost Full Flag Timing (IDT Standard and FWFT modes) tCLKH tCLKL WCLK tENS tENH WEN tHF HF D/2 Words D/2 + 1 Words D/2 Words tHF RCLK tENS REN 3478 drw 19 NOTE: 1. D = maximum FIFO depth = 8,192 for IDT 72V255, 16,384 word for IDT 72V265. Figure 16. Half - Full Flag Timing (IDT Standard and FWFT modes) 5.04 23 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES WCLK 2 1 tENS tENH tRTS tENS tENH tDS tDH WEN tDS tDH Wx D0 - D17 W[x + 1] tSKEW2 RCLK (3) tENS tENH 1 tRTS 2 3 (1,2) tRTF1 tENS tENH REN tA Q0 - Q17 tA W[y+1] Wy W1 tENS tENH RT tREF tREF EF tPAE PAE tHF HF tPAF PAF (4) FF 3037 drw 20 NOTES: 1. tRTF1 contributes a variable delay to the overall retransmit recovery time: tRFTF1 max = 14*Tf + 3*TRCLK (in ns) Where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. 2. Retransmit set up is complete after EF returns HIGH, only then can a read operation begin. Write operations are permitted after one of two conditions have been met: EF is HIGH or 14 cycles of the faster clock (RCLK or WCLK) have elapsed since the RCLK rising edge enabled by the RT pulse. 3. Following Retransmit Setup, the rising edge of RCLK that accesses the first memory location also initiates the updating of HF, PAE, and PAF. 4. No more than D-2 words (D = 8,192 words for the 72V255, 16,384 words for the 72V265) should have been written to the FIFO between Reset (Master or Partial) and Retransmit Setup. Therefore, FF will be HIGH throughout the Restransmit Setup procedure. 5. OE=LOW Figure 17. Retransmit Timing (IDT Standard mode) 5.04 24 5.04 W1 DATA IN OUTPUT REGISTER tDS t ENS (1) tREF tA tFWL2 W2 tDH Wn+1 tDS W1 W[n +2] 1 tSKEW2 (2) W[n+3] 2 tHF W[D/2+1] W[D/2+2] W[D/2+3] tPAE W[n+4] tDS 2 tPAF W[D-m)] W[D-m+1] W[D-m+2] W[D-m+3] W[D-m+4] tDS 1 WD W[D+1] 3478 drw 21 tWFF tENH Figure 18. Write Timing (First Word Fall Through Mode) NOTES: 1. tFWL2 max. (in ns) = 10*Tf + 3*TRCLK where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. 2. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge for PAE to 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. PAE offset = n, PAF offset = m, D = maximum FIFO depth = 8,192 words for the IDT72V255, 16,384 words for the IDT72V265. IR PAF HF PAE OR Q0 - Q17 REN RCLK D0 - D17 WEN WCLK IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES 25 5.04 tENS W1 tOHZ W[D+1] tDS tDH F tWF W1 tOE tENS tENH (1) tA W2 tSKEW1 1 tA 2 tWFF W3 Wm+1 tA W[m+2] tSKEW2(2) 1 2 tPAF W[m+3] W[D/2] tHF tA W[D/2+1] W[D-n] tA 2 W[D-n+3] tPAE tA W[D-n+1] W[D-n+2] 1 WD tA tREF 3478 drw 22 W[D+1] Figure 19. Read Timing (First Word Fall Through Mode) NOTES: 1. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that IR will go LOW (after one WCLK cycle plus tWFF). If the time between the rising ege of RCLK and the rising edge of WCLK is less than tSKEW1, then the IR assertion may be delayed an extra WCLK cycle. 2. tSKEW2 is the minimum time between a rising RCLK edge and a rising WCLK edge for PAF to go HIGH (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 an extra WCLK cycle. 3. LD = HIGH 4. PAE Offset = n, PAF offset = m, D = maximum FIFO depth = 8,192 words for the IDT72V255, 16,384 words for the IDT72V265. IR PAF HF PAE OR Q0 - Q 17 OE REN RCLK D0 - D17 WEN WCLK IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES 26 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES WCLK 1 tENS tENH 2 tRTS tENS tENH tDS tDH WEN tDS tDH D0 - D17 Wx W[x + 1] tSKEW2 RCLK tENS tENH 1 tRTS (3) 2 3 (1, 2) tRTF1 tENS tENH REN tA Q0 - Q17 Wy tA tA W[y+1] W2 W1 tENS tENH RT tREF tREF OR tPAE PAE tHF HF tPAF PAF IR (4) 3478 drw 23 NOTES: 1. tRTF2 contribute a variable delay to the overall retransmit time: tRTF2 max = 14*Tf + 4*TRCLK (in ns) Where Tf is either the RCLK or the WCLK period, whichever is shorter, and TRCLK is the RCLK period. 2. Retransmit set up is complete after OR returns LOW, only then can a read operation begin. Write operations are permitted after one of two conditions have been met: OR is LOW or 14 cycles of the faster clock (RCLK or WCLK) have elapsed since the RCLK rising edge enabled by the RT pulse. 3. Following Retransmit Setup, the rising edge of RCLK that accesses the first memory location also initiates the updating of HF, PAE, and PAF. 4. No more than D-2 words (D = 8,192 words for the 72V255, 16,384 words for the 72V265) should have been written to the FIFO between Reset (Master or Partial) and Retransmit Setup. Therefore, IR will be LOW throughout the Retransmit Setup procedure. 5. OE=LOW Figure 20. Retransmit Timing (FWFT mode) 5.04 27 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES OPERATING CONFIGURATIONS SINGLE DEVICE CONFIGURATION A single IDT72V255/72V265 may be used when the appli- cation requirements are for 8,192/16,384 words or less. The IDT72V255/72V265 can always be used in Single Device Configuration, whether IDT Standard Mode or FWFT Mode has been selected. No special set up procedure is necessary. PARTIAL RESET (PRS) MASTER RESET (MRS) WRITE CLOCK (WCLK) READ CLOCK (RCLK) WRITE ENABLE (WEN) READ ENABLE (REN) LOAD (LD) OUTPUT ENABLE (OE) DATA OUT (Q0 - Q17) DATA IN (D0 - D17) SERIAL ENABLE(SEN) FIRST WORD FALL THROUGH/SERIAL INPUT (FWFT/SI) IDT 72V255/ 72V265 FULL FLAG/INPUT READY (FF/IR) RETRANSMIT (RT) EMPTY FLAG/OUTPUT READY (EF/OR) PROGRAMMABLE ALMOST EMPTY (PAE) HALF FULL FLAG (HF) PROGRAMMABLE ALMOST FULL (PAF) FREQUENCY SELECT (FS) 3478 drw 24 Figure 21. Block Diagram of Single 8,192x18/16,384x18 Synchronous FIFO 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 22 demonstrates an 36-word width by using two IDT72V255/72V265s. Any word width can be attained by adding additional IDT72V255/ 72V265s. DEPTH EXPANSION CONFIGURATION The IDT72V255/72V265 can easily be adapted to applications requiring more than 8,192/16,384 words of buffering. In FWFT mode, the FIFOs can be arranged in series (the data outputs of one FIFO connected to the data inputs of the next)- no external logic necessary. The resulting configuration provides a total depth equivalent to the sum of the depths associated with each single FIFO. Figure 23 shows a depth expansion using two IDT72V255/72V265s. 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. 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. The OR assertion time is variable and is described with the help of the tFWL2 parameter, which includes including delay caused by clock skew: tFWL2 max.= 10*Tf + 3*TRCLK where TRCLK is the RCLK period and Tf is either the RCLK or the WCLK period, whichever is shorter. The maximum amount of time it takes for a word to pass from the inputs of the first FIFO to the outputs of the last FIFO in the chain is the sum of the delays for each individual FIFO: tFWL2(1) + tFWL2(2) + ... + tFWL2(N)+ N*TRCLK where N is the number of FIFOs in the expansion. Note that the additional RCLK term accounts for the time it takes to pass data between FIFOs. The ripple down delay is only noticeable for the first word 5.04 28 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES PARTIAL RESET (PRS) MASTER RESET (MRS) FIRST WORD FALL THROUGH/ SERIAL INPUT (FWFT/SI) RETRANSMIT (RT) DATA IN (Dn) 36 18 18 READ CLOCK (RCLK) WRITE CLOCK (WCLK) READ ENABLE (REN) WRITE ENABLE (WEN) OUTPUT ENABLE (OE) LOAD (LD) IDT 72V255/ FULL FLAG/INPUT READY (FF/IR) #1 72V265/ (1) GATE IDT 72V255/ 72V265/ FULL FLAG/INPUT READY (FF/IR) #2 PROGRAMMABLE (PAF) HALF FULL FLAG (HF) PROGRAMMABLE (PAE) EMPTY FLAG/OUTPUT READY (EF/OR) #1 (1) EMPTY FLAG/OUTPUT READY (EF/OR) #2 GATE #1 18 #2 36 DATA OUT (Qn) 18 FREQUENCY SELECT (FS) 3478 drw 25 NOTE: 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. Figure 22. Block Diagram of 8,192x36/16,384x36 72V255/72V265 Width Expansion 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. The amount of time it takes for IR of the first FIFO in the chain to assert after a word is read from the last FIFO is the sum of the delays for each individual FIFO: N*(3*TWCLK) where N is the number of FIFOs in the expansion and TWCLK is the WCLK period. Note that one of the three WCLK cycle accounts for TSKEW1 delays. In a Supersync depth expansion, set FS individually for each FIFO in the chain. The Transfer Clock line should be tied to either WCLK or RCLK, whichever is faster. Both these actions result in moving, as quickly as possible, data to the end of the chain and free locations to the beginning of the chain. TRANSFER CLOCK WRITE CLOCK WCLK WRITE ENABLE WEN INPUT READY IR RCLK OR 72V255/ 72V265 REN OE DATA BUS * 18 Dn Qn WCLK RCLK WEN REN IR 72V255/ 72V265 GND 18 READ ENABLE OR OUTPUT READY OE OUTPUT ENABLE Qn Dn READ CLOCK 18 DATA OUT FS FS 3478 drw 26 Figure 23. Block Diagram of 16,384x18/32,768x18 Supersync Depth Expansion 5.04 29 IDT72V255/72V265 3.3Volt SyncFIFO 8,192 x 18, 16,384 x 18 MILITARY AND COMMERCIAL TEMPERATURE RANGES ORDERING INFORMATION IDT XXXXX Device Type X Power XX Speed X Package X Process / Temperature Range BLANK B Commercial (0C to +70C) Military (-55C to +125C) Compliant to MIL-STD-883, Class B G PF TF Pin Grid Array (PGA) Thin Plastic Quad Flatpack Slim Thin Quad Flatpack 15 Com'l Only 20 Com'l & Mil. 25 Mil. Only Clock Cycle Time (tCLK) Speed in Nanoseconds L Low Power 72V255 72V265 8,192 x 18 3.3V Synchronous FIFO 16,384 x 18 3.3V Synchronous FIFO 3478 drw 27 5.04 30