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1 february 2003 cmos dual syncfifo? dual 256 x 18, dual 512 x 18, dual 1,024 x 18, dual 2,048 x 18 and dual 4,096 x 18 idt72805lb idt72815lb idt72825lb idt72835lb idt72845lb commercial and industrial temperature ranges idt and the idt logo are registered trademarks. the syncfifo is a trademark of integrated device technology, inc. ? 2003 integrated device technology, inc. all rights reserved. product specifications subject to change without notice. dsc-3139/4 features: ? ? ? ? ? the idt72805lb is equivalent to two idt72205lb 256 x 18 fifos ? ? ? ? ? the idt72815lb is equivalent to two idt72215lb 512 x 18 fifos ? ? ? ? ? the idt72825lb is equivalent to two idt72225lb 1,024 x 18 fifos ? ? ? ? ? the idt72835lb is equivalent to two idt72235lb 2,048 x 18 fifos ? ? ? ? ? the idt72845lb is equivalent to two idt72245lb 4,096 x 18 fifos ? ? ? ? ? offers optimal combination of large capacity (8k), high speed, design flexibility, and small footprint ? ? ? ? ? ideal for the following applications: - network switching - two level prioritization of parallel data - bidirectional data transfer - bus-matching between 18-bit and 36-bit data paths - width expansion to 36-bit per package - depth expansion to 8,192 words per package ? ? ? ? ? 10ns read/write cycle time, 6.5ns access time ? ? ? ? ? idt standard or first word fall through timing functional block diagram ? ? ? ? ? single or double register-buffered empty and full flags ? ? ? ? ? easily expandable in depth and width ? ? ? ? ? asynchronous or coincident read and write clocks ? ? ? ? ? asynchronous or synchronous programmable almost-empty and almost-full flags with default settings ? ? ? ? ? half-full flag capability ? ? ? ? ? output enable puts output data bus in high-impedance state ? ? ? ? ? high-performance submicron cmos technology ? ? ? ? ? available in the 128-pin thin quad flatpack (tqfp). also available for the idt72805lb/72815lb/72825lb, in the 121-lead, 16 x 16 mm plastic ball grid array (pbga) ? ? ? ? ? industrial temperature range (?40 c to +85 c) is available description: the idt72805lb/72815lb/72825lb/72835lb/72845lb are dual 18-bit-wide synchronous (clocked) first-in, first-out (fifo) memories. one dual idt72805lb/ 72815lb/72825lb/72835lb/72845lb device is functionally equivalent to two input register output register offset register flag logic ffa / ira pafa efa / ora paea hfa /( wxoa ) read pointer read control logic write control logic write pointer expansion logic reset logic wena da 0 -da 17 lda rsa ( hfa )/ wxoa wxia rena rclka oea qa 0 -qa 17 rxoa rxia fla wclka input register output register ram array 256 x 18 512 x 18 1,024 x 18 2,048 x 18 4,096 x 18 offset register flag logic ffb / irb pafb efb / orb paeb hfb /( wxob ) read pointer read control logic write control logic write pointer expansion logic reset logic wenb db0-db17 ldb rsb ( hfb )/ wxob wxib renb rclkb oeb qb 0 -qb 17 rxob rxib flb wclkb 3139 drw 01 ram array 256 x 18 512 x 18 1,024 x 18 2,048 x 18 4,096 x 18
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 2 pin configurations wclka da3 da1 da0 db13 db16 rclkb ldb rsb qb17 qb16 pafa da4 wena da2 db12 db15 renb oeb efb qb15 qb14 ffa rxia wxia da5 db14 db11 gnd db17 gnd qb13 qb11 qb8 qb10 qb12 vcc db7 db10 db8 fla qa2 qa0 rxoa qa1 qa4 qa3 wxoa/ hfa paea db9 db6 vcc vcc qb9 qb7 qa5 qa6 gnd vcc gnd gnd gnd vcc gnd qb6 qb5 qa7 qa9 vcc vcc da6 da9 paeb wxob/ hfb qb3 qb4 qb1 qa8 qa10 qa12 vcc da7 da10 da8 flb qb2 qb0 rxob qa11 qa13 gnd da17 gnd da11 da14 db5 wxib rxib ffb qa14 qa15 efa oea rena da15 da12 db2 wenb db4 pafb qa16 qa17 rsa lda rckla da16 da13 db0 db1 db3 wclkb 1234567891011 a b c d e f g h j k l pin 1 3139 drw 02 pbga (bg121-1, order code: bg) top view note: 1. the pbga is only available for the idt72805lb/72815lb/72825lb in the 15 or 25 ns speed grade. idt72205lb/72215lb/72225lb/72235lb/72245lb fifos in a single package with all associated control, data, and flag lines assigned to independent pins. these devices are very high-speed, low-power first-in, first-out (fifo) memories with clocked read and write controls. these fifos are applicable for a wide variety of data buffering needs, such as optical disk controllers, local area networks (lans), and interprocessor communication. each of the two fifos contained in these devices has an 18-bit input and output port. each input port is controlled by a free-running clock (wclk), and an input enable pin ( wen ). data is read into the synchronous fifo on every clock when wen is asserted. the output port of each fifo bank is controlled by another clock pin (rclk) and another enable pin ( ren ). the read clock can be tied to the write clock for single clock operation or the two clocks can run asynchronous of one another for dual-clock operation. an output enable pin ( oe ) is provided on the read port of each fifo for three-state control of the output. the synchronous fifos have two fixed flags, empty flag/output ready ( ef / or ) and full flag/input ready ( ff / ir ), and two programmable flags, almost-empty ( pae ) and almost-full ( paf ). the offset loading of the program- mable flags is controlled by a simple state machine, and is initiated by asserting the load pin ( ld ). a half-full flag ( hf ) is available for each fifo that is implemented as a single device configuration. there are two possible timing modes of operation with these devices: idt standard mode and first word fall through (fwft) mode. in idt standard mode, the first word written to an empty fifo will not appear on the data output lines unless a specific read operation is performed. a read operation, which consists of activating ren and enabling a rising rclk edge, will shift the word from internal memory to the data output lines. in fwft mode, the first word written to an empty fifo is clocked directly to the data output lines after three transitions of the rclk signal. a ren does not have to be asserted for accessing the first word. these devices are depth expandable using a daisy-chain technique or first word fall through (fwft) mode. the xi and xo pins are used to expand the fifos. in depth expansion configuration, fl is grounded on the first device and set to high for all other devices in the daisy chain. the idt72805lb/72815lb/72825lb/72835lb/72845lb are fabricated using idt?s high-speed submicron cmos technology. description (continued)
3 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 pin configurations (continued) tqfp (pk128-1, order code: pf) top view v cc lda 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 33 34 35 36 37 38 pafa rxia ffa wxoa / hfa rxoa qa0 qa1 gnd qa2 qa3 v cc qa4 gnd qa5 qa6 qa7 qa8 gnd db7 db6 db5 db4 db3 db2 db1 db0 paeb flb wclkb wenb wxib v cc pafb rxib ffb wxob / hfb rxob 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 102 101 128 127 126 125 124 123 122 121 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 oea rsa v cc gnd efa qa17 qa16 gnd qa15 v cc qa14 qa13 gnd qa12 qa11 v cc qa10 qa9 db8 db9 db10 db11 db12 db13 db14 db15 db16 db17 rclkb renb ldb oeb rsb v cc gnd efb wxia wena wclka fla paea da0 da1 da2 da3 da4 da5 da6 da7 da8 da9 da10 da11 da12 da13 da14 da16 da17 gnd rclka rena qb0 qb1 gnd qb2 qb3 v cc qb4 gnd qb5 qb6 qb7 qb8 gnd qb9 qb10 v cc qb11 qb12 gnd qb13 qb14 v cc qb15 gnd qb16 qb17 104 103 index gnd da15 3139 drw 02a
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 4 symbol name i/o description da 0 ?da 17 data inputs i data inputs for an 18-bit bus. db 0 -db 17 rsa reset i when rs is set low, internal read and write pointers are set to the first location of the ram array, ff and rsb paf go high, and pae and ef go low. a reset is required before an initial write after power-up. wclka write clock i when wen is low, data is written into the fifo on a low-to-high transition of wclk, if the fifo is not full. wclkb wena write enable i when wen is low, data is written into the fifo on every low-to-high transition of wclk. when wen is wenb high, the fifo holds the previous data. data will not be written into the fifo if the ff is low. rclka read clock i when ren is low, data is read from the fifo on a low-to-high transition of rclk, if the fifo is not empty. rclkb rena read enable i when ren is low, data is read from the fifo on every low-to-high transition of rclk. when ren is high, renb the output register holds the previous data. data will not be read from the fifo if the ef is low. oea output enable i when oe is low, the data output bus is active. if oe is high, the output data bus will be in a high-impedance oeb state. lda load i when ld is low, data on the inputs d0?d11 is written to the offset and depth registers on the low-to-high ldb transition of the wclk, when wen is low. when ld is low, data on the outputs q0?q11 is read from the offset and depth registers on the low-to-high transition of the rclk, when ren is low. fla first load i in the single device or width expansion configuration, fl together with wxi and rxi determine if the mode is flb idt standard mode or first word fall through (fwft) mode, as well as whether the pae / paf flags are synchronous or asynchronous. (see table i.) in the daisy chain depth expansion configuration, fl is grounded on the first device (first load device) and set to high for all other devices in the daisy chain. wxia write expansion i in the single device or width expansion configuration, wxi together with fl and rxi determine if the mode is wxib input idt standard mode or fwft mode, as well as whether the pae / paf flags are synchronous or asynchronous. (see table 1.) in the daisy chain depth expansion configuration, wxi is connected to wxo (write expansion out) of the previous device. rxia read expansion i in the single device or width expansion configuration, rxi together with fl and wxi , determine if the mode is rxib input idt standard mode or fwft mode, as well as whether the pae / paf flags are synchronous or asynchronous. (see table 1.) in the daisy chain depth expansion configuration, rxi is connected to rxo (read expansion out) of the previous device. ffa / ira full flag/ o in the idt standard mode, the ff function is selected ff indicates whether or not the fifo memory is full. in ffb / irb input ready the fwft mode, the ir function is selected. ir indicates whether or not there is space available for writing to the fifo memory. efa / ora empty flag/ o in the idt standard mode, the ef function is selected. ef indicates whether or not the fifo memory is empty. efb / orb output ready in fwft mode, the or function is selected. or indicates whether or not there is valid data available at the outputs. paea programmable o when pae is low, the fifo is almost-empty based on the offset programmed into the fifo. the default paeb almost-empty flag offset at reset is 31 from empty for idt72805lb, 63 from empty for idt72815lb, and 127 from empty for idt72825lb/72835lb/72845lb. pafa programmable o when paf is low, the fifo is almost-full based on the offset programmed into the fifo. the default offset pafb almost-full flag at reset is 31 from full for idt72805lb, 63 from full for idt72815lb, and 127 from full for idt72825lb/72835lb/ 72845lb. wxoa / hfa write expansion o in the single device or width expansion configuration, the device is more than half full when hf is low. in the wxob / hfb out/half-full flag depth expansion configuration, a pulse is sent from wxo to wxi of the next device when the last location in the fifo is written. rxoa read expansion o in the depth expansion configuration, a pulse is sent from rxo to rxi of the next device when the last location rxob out in the fifo is read. qa 0 ?qa 17 data outputs o data outputs for an 18-bit bus. qb 0 -qb 17 v cc power +5v power supply pins. gnd ground ground pins. pin description
5 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 recommended dc operating conditions note: 1. 1.5v undershoots are allowed for 10ns once per cycle. symbol rating commercial unit v term terminal voltage ?0.5 to +7.0 v with respect to gnd t stg storage ?55 to +125 c temperature i out dc output current ?50 to +50 ma symbol parameter (1) conditions max. unit c in (2) input v in = 0v 10 pf capacitance c out (1,2) output v out = 0v 10 pf capacitance capacitance (t a = +25 c, f = 1.0mhz) notes: 1. with output deselected, ( oe v ih ). 2. characterized values, not currently tested. idt72805lb idt72815lb idt72825lb idt72835lb idt72845lb com?l & ind?l (1) t clk = 10, 15, 25 ns symbol parameter min. typ. max. unit i li (2) input leakage current (any input) ?1 ? 1 a i lo (3) output leakage current ?10 ? 10 a v oh output logic ?1? voltage, i oh = ?2 ma 2.4 ? ? v v ol output logic ?0? voltage, i ol = 8 ma ? ? 0.4 v i cc1 (4,5,6) active power supply current ? ? 100 ma i cc2 (4,7) standby current ? ? 10 ma dc electrical characteristics (commercial: v cc = 5v 10%, t a = 0 c to +70 c; industrial: v cc = 5v 10%, ta = -40 c to +85 c) notes: 1 . industrial temperature range product for the 15ns speed grade is available as a standard device. 2. measurements with 0.4 v in v cc . 3. oe v ih, 0.4 v out v cc . 4. tested with outputs open (i out = 0). 4. rclk and wclk toggle at 20 mhz and data inputs switch at 10 mhz. 5. for the idt72805lb/72815lb/72825lb the typical i cc1 = 2[1.81 + 1.12*f s + 0.02*c l *f s ] (in ma); for the idt72835lb/72845lb the typical i cc1 = 2[2.85 + 1.30*f s + 0.02*c l *f s ] (in ma). these equations are valid under the following conditions: v cc = 5v, t a = 25c, f s = wclk frequency = rclk frequency (in mhz, using ttl levels), data switching at f s /2, c l = capacitive load (in pf). 7. all inputs = v cc - 0.2v or gnd + 0.2v, except rclk and wclk, which toggle at 20 mhz. absolute maximum ratings note: 1. stresses greater than those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect reliability. symbol parameter min. typ. max. unit v cc supply voltage (com?l/ind?l) 4.5 5.0 5.5 v gnd supply voltage (com?l/ind?l) 0 0 0 v v ih input high voltage (com?l/ind?l) 2.0 ?? v v il (1) input low voltage (com?l/ind?l) ? ? 0.8 v t a operating temperature 0 ? 70 c commercial t a operating temperature 0 ? 85 c industrial
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 6 ac electrical characteristics (commercial: v cc = 5v 10%, t a = 0 c to +70 c; industrial: v cc = 5v 10%, ta = -40 c + 85 c) input pulse levels gnd to 3.0v input rise/fall times 3ns input timing reference levels 1.5v output reference levels 1.5v output load see figure 1 ac test conditions figure 1. output load * includes jig and scope capacitances. commercial com?l & ind?l (1) commercial idt72805lb10 idt72805lb15 idt72805lb25 idt72815lb10 idt72815lb15 idt72815lb25 idt72825lb10 idt72825lb15 idt72825lb25 idt72835lb10 idt72835lb15 idt72835lb25 idt72845lb10 idt72845lb15 idt72845lb25 symbol parameter min. max. min. max. min. max. unit f s clock cycle frequency ? 100 ? 66.7 ? 40 mhz t a data access time 2 6.5 2 10 3 15 ns t clk clock cycle time 10 ? 15 ? 25 ? ns t clkh clock high time 4.5 ? 6 ? 10 ? ns t clkl clock low time 4.5 ? 6 ? 10 ? ns t ds data setup time 3 ? 4 ? 6 ? ns t dh data hold time 0 ? 1 ? 1 ? ns t ens enable setup time 3 ? 4 ? 6 ? ns t enh enable hold time 0 ? 1 ? 1 ? ns t rs reset pulse width (2) 10 ? 15 ? 25 ? ns t rss reset setup time 8 ? 10 ? 15 ? ns t rsr reset recovery time 8 ? 10 ? 15 ? ns t rsf reset to flag and output time ? 15 ? 15 ? 25 ns t olz output enable to output in low-z (3) 0?0?0 ?ns t oe output enable to output valid ? 6 ? 8 ? 12 ns t ohz output enable to output in high-z (3) 1618112ns t wff write clock to full flag ? 6.5 ? 10 ? 15 ns t ref read clock to empty flag ? 6.5 ? 10 ? 15 ns t pafa clock to asynchronous programmable ? 17 ? 20 ? 35 ns almost-full flag t pafs write clock to synchronous ? 8 ? 10 ? 12 ns programmable almost-full flag t paea clock to asynchronous programmable ? 17 ? 20 ? 35 ns almost-empty flag t paes read clock to synchronous ? 8 ? 10 ? 12 ns programmable almost-empty flag t hf clock to half-full flag ? 17 ? 20 ? 35 ns t xo clock to expansion out ? 6.5 ? 10 ? 15 ns t xi expansion in pulse width 3 ? 6.5 ? 10 ? ns t xis expansion in setup time 3 ? 5 ? 10 ? ns t skew1 skew time between read clock & 5 ? 6 ? 10 ? ns write clock for ff / ir and ef / or t skew2 (4) skew time between read clock & 12 ? 15 ? 17 ? ns write clock for pae and paf 3139 drw 03 30pf* 1.1k 5v d.u.t. 680 ? notes: 1. industrial temperature range product for the 15ns speed grade is available as a standard device. 2. pulse widths less than minimum values are not allowed. 3. values guaranteed by design, not currently tested. 4. t skew2 applies to synchronous pae and synchronous paf only.
7 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 functional description timing modes: idt standard vs first word fall through (fwft) mode the idt72805lb/72815lb/72825lb/72835lb/72845lb support two different timing modes of operation. the selection of which mode will operate is determined during configuration at reset ( rs ). during a rs operation, the first load ( fl ), read expansion input ( rxi ) and write expansion input ( wxi ) pins are used to select the timing mode per the truth table shown in table 3. in idt standard mode, the first word written to an empty fifo will not appear on the data output lines unless a specific read operation is performed. a read operation, which consists of activating read enable ( ren ) and enabling a rising read clock (rclk) edge, will shift the word from internal memory to the data output lines. in fwft mode, the first word written to an empty fifo is clocked directly to the data output lines after three transitions of the rclk signal. a ren does not have to be asserted for accessing the first word. various signals, both input and output signals operate differently de- pending on which timing mode is in effect. idt standard mode in this mode, the status flags, ff , paf , hf , pae and ef operate in the manner outlined in table 1. to write data into to the fifo, write enable ( wen ) must be low. data presented to the data in lines will be clocked into the fifo on subsequent transitions of the write clock (wclk). after the first write is performed, the empty flag ( ef ) will go high. subsequent writes will continue to fill up the fifo. the programmable almost-empty flag ( pae ) will go high after n + 1 words have been loaded into the fifo, where n is the empty offset value. the default setting for this value is stated in the footnote of table 1. this parameter is also user programmable. see section on programmable flag offset loading. if one continued to write data into the fifo, and we assumed no read operations were taking place, the half-full flag ( hf ) would toggle to low once the 129th (idt72805lb), 257th (idt72815lb), 513th (idt72825lb), 1,025th (idt72835lb), and 2,049th (idt72845lb) word respectively was written into the fifo. continuing to write data into the fifo will cause the programmable almost-full flag ( paf ) to go low. again, if no reads are performed, the paf will go low after (256-m) writes for the idt72805lb, (512-m) writes for the idt72815lb, (1,024-m) writes for the idt72825lb, (2,048?m) writes for the idt72835lb and (4,096?m) writes for the idt72845lb. the offset ?m? is the full offset value. this parameter is also user programmable. see section on programmable flag offset loading. if there is no full offset specified, the paf will be low when the device is 31 away from completely full for idt72805lb, 63 away from completely full for idt72815lb, and 127 away from completely full for the idt72825lb/ 72835lb/72845lb. when the fifo is full, the full flag ( ff ) will go low, inhibiting further write operations. if no reads are performed after a reset, ff will go low after d writes to the fifo. d = 256 writes for the idt72805lb, 512 for the idt72815lb, 1,024 for the idt72825lb, 2,048 for the idt72835lb and 4,096 for the idt72845lb, respectively. if the fifo is full, the first read operation will cause ff to go high. subsequent read operations will cause paf and the half-full flag ( hf ) to go high at the conditions described in table 1. if further read operations occur, without write operations, the programmable almost-empty flag ( pae ) will go low when there are n words in the fifo, where n is the empty offset value. if there is no empty offset specified, the pae will be low when the device is 31 away from completely empty for idt72805lb, 63 away from completely empty for idt72815lb, and 127 away from completely empty for idt72825lb/72835lb/72845lb. continuing read operations will cause the fifo to be empty. when the last word has been read from the fifo, the ef will go low inhibiting further read operations. ren is ignored when the fifo is empty. first word fall through mode (fwft) in this mode, the status flags, ir , paf , hf , pae and or operate in the manner outlined in table 2. to write data into to the fifo, wen must be low. data presented to the data in lines will be clocked into the fifo on subsequent transitions of wclk. after the first write is performed, the output ready ( or ) flag will go low. subsequent writes will continue to fill up the fifo. pae will go high after n + 2 words have been loaded into the fifo, where n is the empty offset value. the default setting for this value is stated in the footnote of table 2. this parameter is also user program- mable. see section on programmable flag offset loading. if one continued to write data into the fifo, and we assumed no read operations were taking place, the hf would toggle to low once the 130th (72805lb), 258th (72815lb), 514th (72825lb), 1,026th (72835lb), and 2,050th (72845lb) word respectively was written into the fifo. continuing to write data into the fifo will cause the paf to go low. again, if no reads are performed, the paf will go low after (257-m) writes for the idt72805lb, (513-m) writes for the idt72815lb, (1,025-m) writes for the idt72825lb, (2,049?m) writes for the idt72835lb and (4,097?m) writes for the idt72845lb, where m is the full offset value. the default setting for this value is stated in the footnote of table 2. when the fifo is full, the input ready ( ir ) flag will go high, inhibiting further write operations. if no reads are performed after a reset, ir will go high after d writes to the fifo. d = 257 writes for the idt72805lb, 513 for the idt72815lb, 1,025 for the idt72825lb, 2,049 for the idt72835lb and 4,097 for the idt72845lb. note that the additional word in fwft mode is due to the capacity of the memory plus output register. if the fifo is full, the first read operation will cause the ir flag to go low. subsequent read operations will cause the paf and hf to go high at the conditions described in table 2. if further read operations occur, without write operations, the pae will go low when there are n + 1 words in the fifo, where n is the empty offset value. if there is no empty offset specified, the pae will be low when the device is 32 away from completely empty for idt72805lb, 64 away from completely empty for idt72815lb, and 128 away from completely empty for idt72825lb/72835lb/72845lb. continu- ing read operations will cause the fifo to be empty. when the last word has been read from the fifo, or will go high inhibiting further read operations. ren is ignored when the fifo is empty. programmable flag loading full and empty flag offset values can be user programmable. the idt72805lb/72815lb/72825lb/72835lb/72845lb has internal registers for these offsets. default settings are stated in the footnotes of table 1 and table 2. offset values are loaded into the fifo using the data input lines d 0 - d 11 . to load the offset registers, the load ( ld ) pin and wen pin must be held low. data present on d 0 -d 11 will be transferred in to the empty offset register on the first low-to-high transition of wclk. by continuing to hold the ld and wen pin low, data present on d 0 -d 11 will be transferred into the full offset register on the next transition of the wclk. the third transition again writes to the empty offset register. writing all offset registers does not have to occur at one time. one or two offset registers can be written and then
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 8 table 1 status flags for idt standard mode number of words in fifo idt72805lb idt72815lb idt72825lb idt72835lb idt72845lb ff paf hf pae ef 00 0 0 0hhhll 1 to n (1) 1 to n (1) 1 to n (1) 1 to n (1) 1 to n (1) hh h lh (n + 1) to 128 (n + 1) to 256 (n + 1) to 512 (n + 1) to 1,024 (n + 1) to 2,048 h h h h h 129 to (256-(m+1)) (2) 257 to (512-(m+1)) (2) 513 to (1,024-(m+1)) (2) 1,025 to (2,048-(m+1)) (2) 2,049 to (4,096-(m+1)) (2) hhlhh (256-m) to 255 (512-m) to 511 (1,024-m) to 1,023 (2,048-m) to 2,047 (4,096-m) to 4,095 h l l h h 256 512 1,024 2,048 4,096 l l l h h table 2 status flags for fwft mode number of words in fifo idt72805lb idt72815lb idt72825lb idt72835lb idt72845lb ir paf hf pae or 00 0 0 0lhhlh 1 to (n + 1) (1) 1 to (n + 1) (1) 1 to (n + 1) (1) 1 to (n + 1) (1) 1 to (n + 1) (1) lhhll (n + 2) to 129 (n + 2) to 257 (n + 2) to 513 (n + 2) to 1,025 (n + 2) to 2,049 l h h h l 130 to (257-(m+1)) (2) 258 to (513-(m+1)) (2) 514 to (1,025-(m+1)) (2) 1,026 to (2,049-(m+1)) (2) 2,050 to (4,097-(m+1)) (2) lhlhl (257-m) to 256 (513-m) to 512 (1,025-m) to 1,024 (2,049-m) to 2,048 (4,097-m) to 4,096 lllhl 257 513 1,025 2,049 4,097 h l l h l notes: 1. n = empty offset (default values : idt72805lb n = 31, idt72815lb n = 63, idt72825lb/72835lb/72845lb n = 127) 2. m = full offset (default values : idt72805lb m = 31, idt72815lb m = 63, idt72825lb/72835lb/72845lb m = 127) notes: 1. n = empty offset (default values : idt72805lb n=31, idt72815lb n = 63, idt72825lb/72835lb/72845lb n = 127) 2. m = full offset (default values : idt72805lb m=31, idt72815lb m = 63, idt72825lb/72835lb/72845lb m = 127) by bringing the ld pin high, the fifo is returned to normal read/write operation. when the ld pin and wen are again set low, the next offset register in sequence is written. the contents of the offset registers can be read on the data output lines q 0 -q 11 when the ld pin is set low and ren is set low. data can then be read on the next low-to-high transition of rclk. the first transition of rclk will present the empty offset value to the data output lines. the next transition of rclk will present the full offset value. offset register content can be read out in the idt standard mode only. it cannot be read in the fwft mode. synchronous vs asynchronous programmable flag tim- ing selection the idt72805lb/72815lb/72825lb/72835lb/72845lb can be config- ured during the "configuration at reset" cycle described in table 3 with either asynchronous or synchronous timing for pae and paf flags. if asynchronous pae / paf configuration is selected (as per table 3), the pae is asserted low on the low-to-high transition of rclk. pae is reset to high on the low-to-high transition of wclk. similarly, the paf is asserted low on the low-to-high transition of wclk and paf is reset to high on the low-to-high transition of rclk. for detail timing dia- grams, see figure 13 for asynchronous pae timing and figure 14 for asynchronous paf timing. if synchronous pae / paf configuration is selected, the pae is asserted and updated on the rising edge of rclk only and not wclk. similarly, paf is asserted and updated on the rising edge of wclk only and not rclk. for detail timing diagrams, see figure 22 for synchronous pae timing and figure 23 for synchronous paf timing. register-buffered flag output selection the idt72805lb/72815lb/72825lb/72835lb/72845lb can be config- ured during the "configuration at reset" cycle described in table 4 with single, double or triple register-buffered flag output signals. the various combinations available are described in table 4 and table 5. in general, going from single to double or triple buffered flag outputs removes the possibility of metastable flag indications on boundary states (i.e, empty or full conditions). the trade-off is the addition of clock cycle delays for the respective flag to be asserted. not all combinations of register-buffered flag outputs are supported. register-buffered outputs apply to the empty flag and full flag only. partial flags are not effected. table 4 and table 5 summarize the options available.
9 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 notes: 1. in a daisy-chain depth expansion, fl is held low for the "first load device". the rxi and wxi inputs are driven by the corresponding rxo and wxo outputs of the preceding device. 2. in a daisy-chain depth expansion, fl is held high for members of the expansion other than the "first load device". the rxi and wxi inputs are driven by the corresponding rxo and wxo outputs of the preceding device. table 3 truth table for configuration at reset fl rxi wxi ef / or ff / ir pae , paf fifo timing mode 0 0 0 single register-buffered single register-buffered asynchronous standard empty flag full flag 0 0 1 triple register-buffered double register-buffered asynchronous fwft output ready flag input ready flag 0 1 0 double register-buffered double register-buffered asynchronous standard empty flag full flag 0 (1) 1 1 single register-buffered single register-buffered asynchronous standard empty flag full flag 1 0 0 single register-buffered single register-buffered synchronous standard empty flag full flag 1 0 1 triple register-buffered double register-buffered synchronous fwft output ready flag input ready flag 1 1 0 double register-buffered double register-buffered synchronous standard empty flag full flag 1 (2) 1 1 single register-buffered single register-buffered asynchronous standard empty flag full flag table 4 register-buffered flag output options idt standard mode empty flag ( ef ) full flag ( ff ) partial flags programming at reset flag timing buffered output buffered output timing mode fl rxi wxi diagrams single single asynch 0 0 0 figure 9, 10 single single sync 1 0 0 figure 9, 10 double double asynch 0 1 0 figure 24, 26 double double synch 1 1 0 figure 24, 26 table 5 register-buffered flag output options fwft mode output ready ( or ) input ready ( ir ) partial flags programming at reset flag timing fl rxi wxi diagrams triple double asynch 0 0 1 figure 27 triple double sync 1 0 1 figure 20, 21
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 10 figure 2. writing to offset registers ld wen wclk selection 0 0 writing to offset registers: empty offset full offset 0 1 no operation 1 0 write into fifo 1 1 no operation figure 3. offset register location and default values note: 1. the same selection sequence applies to reading from the registers. ren is enabled and read is performed on the low-to-high transition of rclk. note: 1. any bits of the offset register not being programmed should be set to zero. signal descriptions: inputs: data in (d 0 - d 17 ) data inputs for 18-bit wide data. controls: reset ( rsa / rsb ) reset is accomplished whenever the reset ( rsa / rsb ) input is taken to a low state. during reset, both internal read and write pointers are set to the first location. a reset is required after power-up before a write operation can take place. the half-full flag ( hfa / hfb ) and programmable almost- full flag ( pafa / pafb ) will be reset to high after t rsf . the programmable almost-empty flag ( paea / paeb ) will be reset to low after t rsf . the full flag ( ffa / ffb ) will reset to high. the empty flag ( efa / efb ) will reset to low in idt standard mode but will reset to high in fwft mode. during reset, the output register is initialized to all zeros and the offset registers are initialized to their default values. write clock (wclka/wclkb) a write cycle is initiated on the low-to-high transition of the write clock (wclka/wclkb). data setup and hold times must be met with respect to the low-to-high transition of wclk. the write and read clocks can be asynchronous or coincident. write enable ( wena / wenb ) when the wena / wenb input is low, data may be loaded into the fifo ram array on the rising edge of every wclk cycle if the device is not full. data is stored in the ram array sequentially and independently of any ongoing read operation. when wen is high, no new data is written in the ram array on each wclk cycle. to prevent data overflow in the idt standard mode, ff will go low, inhibiting further write operations. upon the completion of a valid read cycle, ff will go high allowing a write to occur. the ff flag is updated on the rising edge of wclk. to prevent data overflow in the fwft mode, input ready ( ira , irb ) will go high, inhibiting further write operations. upon the completion of a valid read cycle, ir will go low allowing a write to occur. the ir flag is updated on the rising edge of wclk. wen is ignored when the fifo is full in either fwft or idt standard mode. read clock (rclka/rclkb) data can be read on the outputs on the low-to-high transition of the read clock (rclka/rclkb), when output enable ( oea / oeb ) is set low. the write and read clocks can be asynchronous or coincident. read enable ( rena / renb ) when read enable ( rena / renb ) 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 q 0 -q n maintain the previous data value. in the idt standard mode, every word accessed at q n , 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 ( efa / efb ) will go low, inhibiting further read operations. ren is ignored when the fifo is empty. once a write is performed, ef will go high allowing a read to occur. the ef flag is updated on the rising edge of rclk. in the fwft mode, the first word written to an empty fifo automatically goes to the outputs q n , on the third valid low to high transition of rclk + t skew 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 ( ora / orb ) will go high with a true read (rclk with ren = low), inhibiting further read operations. ren is ignored when the fifo is empty. output enable ( oea / oeb ) when output enable ( oea / oeb ) is enabled (low), the parallel output buffers receive data from the output register. when oe is disabled (high), the q output data bus is in a high-impedance state. load ( lda / ldb ) the idt72805lb/72815lb/72825lb/72835lb/72845lb devices con- tain two 12-bit offset registers with data on the inputs, or read on the outputs. when the load ( lda / ldb ) pin is set low and wen is set low, data on the inputs d0-d11 is written into the empty offset register on the first low- to-high transition of the write clock (wclk). when the ld pin and wen are held low then data is written into the full offset register on the second low-to-high transition of wclk. the third transition of wclk again writes to the empty offset register. however, writing all offset registers does not have to occur at one time. one or two offset registers can be written and then by bringing the ld pin high, the fifo is returned to normal read/write operation. when the ld pin is set low, and wen is low, the next offset register in sequence is written. empty offset register 17 11 0 full offset register 17 11 0 default value 001fh (72805) 003fh (72815): 007fh (72825/72835/72845) default value 001fh (72805) 003fh (72815): 007fh (72825/72835/72845) 3139 drw 04
11 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 when the ld pin is low and wen is high, the wclk input is disabled; then a signal at this input can neither increment the write offset register pointer, nor execute a write. the contents of the offset registers can be read on the output lines when the ld pin is set low and ren is set low; then, data can be read on the low-to-high transition of the read clock (rclk). the act of reading the control registers employs a dedicated read offset register pointer. (the read and write pointers operate independently). offset register content can be read out in the idt standard mode only. it is inhibited in the fwft mode. a read and a write should not be performed simultaneously to the offset registers. first load ( fla / flb ) for the single device mode, see table i for additional information. in the daisy chain depth expansion configuration, fla / flb is grounded to indicate it is the first device loaded and is set to high for all other devices in the daisy chain. (see operating configurations for further details.) write expansion input ( wxia / wxib ) this is a dual purpose pin. for single device mode, see table i for additional information. wxia / wxib is connected to write expansion out ( wxoa / wxob ) of the previous device in the daisy chain depth expansion mode. read expansion input ( rxia / rxib ) this is a dual purpose pin. for single device mode, see table i for additional information. rxia / rxib is connected to read expansion out ( rxoa / rxob ) of the previous device in the daisy chain depth expansion mode. outputs: full flag/input ready ( ffa / ira , ffb / irb ) this is a dual purpose pin. in idt standard mode, the full flag ( ffa / ffb ) function is selected. when the fifo is full, ff will go low, inhibiting further write operations. when ff is high, the fifo is not full. if no reads are performed after a reset, ff will go low after d writes to the fifo. d = 256 writes for the idt72805lb, 512 for the idt72815lb, 1,024 for the idt72825lb, 2,048 for the idt72835lb and 4,096 for the idt72845lb. in fwft mode, the input ready ( ira / irb ) function is selected. ir goes low when memory space is available for writing in data. when there is no longer any free space left, ir goes high, inhibiting further write operations. ir will go high after d writes to the fifo. d = 257 writes for the idt72805, 513 for the idt72815, 1,025 for the idt72825, 2,049 for the idt72835 and 4,097 for the idt72845. note that the additional word in fwft mode is due to the capacity of the memory plus output register. ff / ir is synchronous and updated on the rising edge of wclk. empty flag/output ready ( efa / ora , efb / orb ) this is a dual purpose pin. in the idt standard mode, the empty flag ( efa / efb ) function is selected. when the fifo is empty, ef will go low, inhibiting further read operations. when ef is high, the fifo is not empty. in fwft mode, the output ready ( ora / orb ) function is selected. or goes low at the same time that the first word written to an empty fifo appears valid on the outputs. or stays low after the rclk low to high transition that shifts the last word from the fifo memory to the outputs. or goes high only with a true read (rclk with ren = low). the previous data stays at the outputs, indicating the last word was read. further data reads are inhibited until or goes low again. ef / or is synchronous and updated on the rising edge of rclk. programmable almost-full flag ( pafa / pafb ) the programmable almost-full flag ( pafa / pafb ) will go low when fifo reaches the almost-full condition. in idt standard mode, if no reads are performed after reset ( rs ), the paf will go low after (256-m) writes for the idt72805lb, (512-m) writes for the idt72815lb, (1,024-m) writes for the idt72825lb, (2,048?m) writes for the idt72835lb and (4,096?m) writes for the idt72845lb. the offset ?m? is defined in the full offset register. in fwft mode, if no reads are performed, paf will go low after (257- m) writes for the idt72805lb, (513-m) writes for the idt72815lb, (1,025- m) writes for the idt72825lb, (2,049-m) writes for the idt72835lb and (4,097-m) writes for the idt72845lb. the default values for m are noted in table 1 and 2. if asynchronous paf configuration is selected, the paf is asserted low on the low-to-high transition of the write clock (wclk). paf is reset to high on the low-to-high transition of the read clock (rclk). if synchronous paf configuration is selected (see table i), the paf is updated on the rising edge of wclk. programmable almost-empty flag ( paea / paeb ) the pae flag will go low when the fifo reads the almost-empty condition. in idt standard mode, pae will go low when there are n words or less in the fifo. in fwft mode, the pae will go low when there are n+1 words or less in the fifo. the offset ?n? is defined as the empty offset. the default values for n are noted in table 1 and 2. if asynchronous pae configuration is selected, the pae is asserted low on the low-to-high transition of the read clock (rclk). pae is reset to high on the low-to-high transition of the write clock (wclk). if synchronous pae configuration is selected (see table i), the pae is updated on the rising edge of rclk. write expansion out/half-full flag ( wxoa / hfa , wxob / hfb ) this is a dual-purpose output. in the single device and width expansion mode, when write expansion in ( wxia / wxib ) and/or read expansion in ( rxia / rxib ) are grounded, this output acts as an indication of a half-full memory. after half of the memory is filled, and at the low-to-high transition of the next write cycle, the half-full flag goes low and will remain set until the difference between the write pointer and read pointer is less than or equal to one half of the total memory of the device. the half-full flag ( hfa / hfb ) is then reset to high by the low-to-high transition of the read clock (rclk). the hf is asynchronous. in the daisy chain depth expansion mode, wxi is connected to wxo of the previous device. this output acts as a signal to the next device in the daisy chain by providing a pulse when the previous device writes to the last location of memory. read expansion out ( rxoa / rxob ) in the daisy chain depth expansion configuration, read expansion in ( rxia / rxib ) is connected to read expansion out ( rxoa / rxob ) of the previous device. this output acts as a signal to the next device in the daisy chain by providing a pulse when the previous device reads from the last location of memory. data outputs (q 0 -q 17 , qb 0 -qb 17 ) q0-q17 are data outputs for 18-bit wide data.
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 12 figure 6. write cycle timing with single register-buffered ff (idt standard mode) figure 5. reset timing (2) rs ren , wen , ld pae paf , wxo / hf , rxo t rsr q 0 - q 17 oe = 0 oe = 1 (1) 3139 drw 05 t rss configuration setting t rsr fl , rxi , wxi rclk, wclk ff / ir t rsf ef / or fwft mode idt standard mode (3) (2) t rsf t rsf t rsf t rsf t rs wclk d 0 - d 17 wen ff t clk t clkh t clkl t ds t ens t dh t enh t wff t wff data in valid no operation rclk t skew1 (1) ren 3139 drw 06 notes: 1. t skew1 is the minimum time between a rising rclk edge and a rising wclk edge to guarantee that ff will go high during the current clock cycle. if the time between the rising edge of rclk and the rising edge of wclk is less than t skew1 , then ff may not change state until the next wclk edge. 2. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during reset. notes: 1. single device mode ( fl , rxi , wxi ) = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0). fl , rxi , wxi should be static (tied to v cc or gnd). 2. the clocks (rclk, wclk) can be free-running asynchronously or coincidentally. 3. after reset, the outputs will be low if oe = 0 and tri-state if oe = 1.
13 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 figure 7. read cycle timing with single register-buffered ef (idt standard mode) notes: 1. t skew1 is the minimum time between a rising wclk edge and a rising rclk edge to guarantee that ef will go high during the current clock cycle. if the time between the rising edge of wclk and the rising edge of rclk is less than t skew1 , then ef may not change state until the next rclk edge. 2. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during reset. figure 8. first data word latency with single register-buffered ef (idt standard mode) no operation rclk ren ef t clk t clkh t clkl t ens t enh t ref t ref valid data t a t olz t oe t ohz q 0 - q 17 oe wclk wen t skew1 (1) 3139 drw 07 wclk d 0 - d 17 wen rclk ef q 0 - q 17 ren t ds t skew1 t ens t ref t a 0 12 3 d ddd 01 dd (first valid write) t oe t olz oe t a t frl (1) d 4 t ens 3139 drw 08 notes: 1. when t skew1 minimum specification, t frl (maximum) = t clk + t skew1 . when t skew1 < minimum specification, t frl (maximum) = either 2*t clk + t skew1 or t clk + t skew1 . the latency timing applies only at the empty boundary ( ef = low). 2. the first word is available the cycle after ef goes high, always. 3. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during reset.
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 14 figure 10. single register-buffered empty flag timing (idt standard mode) notes: 1. t skew1 is the minimum time between a rising rclk edge and a rising wclk edge to guarantee that ff will go high during the current clock cycle. if the time between the rising edge of rclk and the rising edge of wclk is less than t skew1 , then ff may not change state until the next wclk edge. 2. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during reset. figure 9. single register-buffered full flag timing (idt standard mode) data read wclk d 0 - d 17 wen rclk ff q 0 - q 17 t a t wff data write ren t wff t enh t ens t ds t wff t ds data write next data read t a no write no write data in output register oe low t skew1 (1) t skew1 (1) t enh t ens 3139 drw 09 wclk d 0 - d 17 wen rclk ef q 0 - q 17 oe t ds t ens t a t skew1 data write 1 data read t enh t ref t ds t ens data write 2 t enh t ref ren data in output register t frl (1) low 3139 drw 10 t ref t skew1 t frl (1) notes: 1. when t skew1 minimum specification, t frl (maximum) = t clk + t skew1. when t skew1 < minimum specification, t frl (maximum) = either 2 * t clk + t skew1, or t clk + t skew1. the latency timing apply only at the empty boundary ( ef = low). 2. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,1,1), (1,0,0) or (1,1,1) during reset.
15 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 figure 12. read programmable registers (idt standard mode) figure 13. asynchronous programmable almost-empty flag timing (idt standard and fwft modes) notes: 1. n = pae offset. 2. for idt standard mode. 3. for fwft mode. 4. pae is asserted low on rclk transition and reset to high on wclk transition. 5. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,0,1), (0,1,0), (0,1,1) or (1,1,1) during reset. wclk t clkh t clkl t clk t ens t enh ld wen d 0 -d 15 t ds t dh pae offset paf offset d 0 -d 11 pae offset t ens 3139 drw 11 rclk t clkh t clkl t clk t ens t enh ld ren q 0 -q 15 pae offset paf offset pae offset unknown t a t ens 3139 drw 12 wclk t clkh t clkl t ens t enh wen pae t ens t paea n + 1 words in fifo (2) , n + 2 words in fifo (3) n words in fifo (2) , n + 1 words in fifo (3) rclk t paea ren 3139 drw 13 n words in fifo (2) , n + 1 words in fifo (3) figure 11. write programmable registers (idt standard and fwft modes)
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 16 figure 15. half-full flag timing (idt standard and fwft modes) figure 14. asynchronous programmable almost-full flag timing (idt standard and fwft modes) notes: 1. m = paf offset. 2. d = maximum fifo depth. in idt standard mode: d = 256 for the idt72805, 512 for the idt72815, 1,024 for the idt72825, 2,048 for the idt72835 and 4,096 for the idt72845. in fwft mode: d = 257 for the idt72805, 513 for the idt72815, 1,025 for the idt72825, 2,049 for the idt72835 and 4,097 for the idt72845. 3. paf is asserted to low on wclk transition and reset to high on rclk transition. 4. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,0,1), (0,1,0), (0,1,1) or (1,1,1) during reset. notes: 1. d = maximum fifo depth. in idt standard mode: d = 256 for the idt72805, 512 for the idt72815, 1,024 for the idt72825, 2,048 for the idt72835 and 4,096 for the idt72845. in fwft mode: d = 257 for the idt72805, 513 for the idt72815, 1,025 for the idt72825, 2,049 for the idt72835 and 4,097 for the idt72845. 2. for idt standard mode. 3. for fwft mode. 4. select this mode by setting ( fl , rxi , wxi ) = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0) during reset. wclk t clkh t clkl t ens t enh wen paf t ens t pafa d - (m + 1) words in fifo rclk t pafa ren (1) 3139 drw 14 d - m words in fifo d - (m + 1) words in fifo wclk t ens t enh wen hf t ens t hf rclk t hf ren 3139 drw 15 t clkl t clkh d/2 words in fifo (2) , [ + 1 ] words in fifo (3) d/2 + 1 words in fifo (2) , [ + 2 ] words in fifo (3) d-1 2 d/2 words in fifo (2) , [ + 1 ] words in fifo (3) d-1 2 d-1 2
17 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 note: 1. read from last physical location. figure 17. read expansion out timing note: 1. write to last physical location. figure 16. write expansion out timing figure 18. write expansion in timing figure 19. read expansion in timing wclk wen t ens wxo t clkh t xo note 1 t xo 3139 drw 16 rclk ren t ens rxo t clkh t xo note 1 t xo 3139 drw 17 wxi wclk t xi t xis 3139 drw 18 rxi rclk t xi t xis 3139 drw 19
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 18 figure 20. write timing with synchronous programmable flags (fwft mode) notes: 1. t skew1 is the minimum time between a rising wclk edge and a rising rclk edge for or to go low after two rclk cycles plus t ref . if the time between the rising edge of wlck and the rising edge of rclk is less than t skew1 , then the or deassertion may be delayed one extra rclk cycle. 2. t skew2 is the minimum time between a rising wclk edge and a rising rclk edge for pae to go high during the current clock cycle. if the time between the rising edge of wclk and the rising edge of rclk is less tha n t skew2 , then the pae deassertion may be delayed one extra rclk cycle. 3. ld = high, oe = low 4. n = pae offset, m = paf offset, d = maximum fifo depth = 257 words for the idt72805, 513 words for the idt72815, 1,025 words for the idt72825, 2,049 w ords for the idt72835 and 4,097 words for the idt72845. 5. select this mode by setting ( fl , rxi , wxi ) = (1,0,1) during reset. w 1 w 2 w 4 w [n +2] w [d-m-1] w [d-m-2] w [d-1] w d w [n+3] w [n+4] w [d-m] w [d-m+1] wclk wen d 0 - d 17 rclk t dh t ds t ens t skew1 ren q 0 - q 17 paf hf pae ir t ds t ds t ds t skew2 t a t ref or t paes t hf t pafs t wff w [d-m+2] w 1 t enh 3139 drw 20 data in output register (2) w 3 1 2 3 1 1 d-1 ] [ w d-1 ] [ w d-1 ] [ w
19 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 figure 21. read timing with synchronous programmable flags (fwft mode) notes: 1. t skew1 is the minimum time between a rising rclk edge and a rising wclk edge to guarantee that ir will go low after one wclk plus t wff . if the time between the rising edge of rlck and the rising edge of wclk is less than t skew1 , then the ir assertion may be delayed an extra wclk cycle. 2. t skew2 is the minimum time between a rising rclk edge and a rising wclk edge for paf to go high during the current clock cycle. if the time between the rising edge of rclk and the rising edge of wclk is less tha n t skew2 , then the paf deassertion time may be delayed an extra wclk cycle. 3. ld = high 4. n = pae offset, m = paf offset, d = maximum fifo depth = 257 words for the idt72805, 513 words for the idt72815, 1,025 words for the idt72825, 2,049 w ords for idt72835 and 4,097 words for idt72845. 5. select this mode by setting ( fl , rxi , wxi ) = (1,0,1) during reset. wclk 12 wen d 0 - d 17 rclk t ens ren q 0 - q 17 paf hf pae ir or w 1 w 1 w 2 w 3 w m+2 w [m+3] t ohz t skew1 t enh t ds t dh t oe t a t a t a t pafs t wff t wff t ens oe t skew2 w d 3139 drw 21 t paes w [d-n] w [d-n-1] t a t a t hf t ref w [d-1] w d t a w [d-n+1] w [m+4] w [d-n+2] (1) (2) 1 t ens d-1 ] [ w d-1 ] [ w
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 20 figure 22. synchronous programmable almost-empty flag timing (idt standard and fwft modes) figure 23. synchronous programmable almost-full flag timing (idt standard and fwft modes) notes: 1. n = pae offset. 2. for idt standard mode. 3. for fwft mode. 4. t skew2 is the minimum time between a rising wclk edge and a rising rclk edge for pae to go high during the current clock cycle. if the time between the rising edge of wclk and the rising edge of rclk is less than t skew2 , then the pae deassertion may be delayed one extra rclk cycle. 5. pae is asserted and updated on the rising edge of rclk only. 6. select this mode by setting ( fl , rxi , wxi ) = (1,0,0), (1,0,1), or (1,1,0) during reset. notes: 1. m = paf offset. 2. d = maximum fifo depth. in idt standard mode: d = 256 for the idt72805, 512 for the idt72815, 1,024 for the idt72825, 2,048 for the idt72835 and 4,096 for the idt72845. in fwft mode: d = 257 for the idt72805, 513 for the idt72815, 1,025 for the idt72825, 2,049 for the idt72835 and 4,097 for the idt72845. 3. t skew2 is the minimum time between a rising rclk edge and a rising wclk edge for paf to go high during the current clock cycle. if the time between the rising edge of rclk and the rising edge of wclk is less than t skew2 , then the paf deassertion time may be delayed an extra wclk cycle. 4. paf is asserted and updated on the rising edge of wclk only. 5. select this mode by setting ( fl , rxi , wxi ) = (1,0,0), (1,0,1), or (1,1,0) during reset. wclk t enh t clkh t clkl wen pae rclk ren 3139 drw 22 t ens t enh t ens n words in fifo (2) , n + 1words in fifo (3) n + 1 words in fifo (2) , n + 2 words in fifo (3) t skew2 t paes n words in fifo (2) , n + 1 words in fifo (3) (4) t paes wclk t enh t clkh t clkl wen paf rclk ren 3139 drw 23 t ens t enh t ens d-(m+1) words in fifo d - m words in fifo d -(m+1) words in fifo t pafs t pafs t skew2 (3)
21 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 figure 25. write cycle timing with double register-buffered ff (idt standard mode) notes: 1. t skew1 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 t wff . if the time between the rising edge of rclk and the rising edge of wclk is less than t skew1 , then the ff deassertion time may be delayed an extra wclk cycle. 2. ld = high. 3. select this mode by setting ( fl , rxi , wxi ) = (0,1,0) or (1,1,0) during reset. figure 24. double register-buffered full flag timing (idt standard mode) notes: 1. t skew1 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 t rff . if the time between the rising edge of rclk and the rising edge of wclk is less than t skew1 , then the ff deassertion may be delayed an extra wclk cycle. 2. ld = high. 3. select this mode by setting ( fl , rxi , wxi ) = (0,1,0) or (1,1,0) during reset. d 0 - d 17 wen rclk ff ren t enh t enh q 0 - q 17 data read next data read data in output register low oe t skew1 data write 3139 drw 24 wclk no write 1 2 1 2 t ds no write t wff t wff t wff t a t ens t ens t skew1 t ds t a wd (1) (1) wclk d 0 - d 17 wen ff rclk ren t ds t wff t wff data in valid no operation (1) t skew1 3139 drw 25 t ens t dh t enh 1 2 t clkh t clkl t clk
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 22 figure 27. or flag timing and first word fall through when fifo is empty (fwft mode) notes: 1. t skew1 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 t ref . if the time between the rising edge of wclk and the rising edge of rclk is less than t skew1 . then the ef deassertion may be delayed an extra rclk cycle. 2. ld = high 3. select this mode by setting ( fl , rxi , wxi ) = (0,1,0) or (1,1,0) during reset. figure 26. read cycle timing with double register-buffered ef (idt standard timing) notes: 1. t skew1 is the minimum time between a rising wclk edge and a rising rclk edge for or to go high during the current cycle. if the time between the rising edge of wlck and the rising edge of rclk is less than t skew1 , then the or deassertion may be delayed one extra rclk cycle. 2. ld = high, oe = low 3. select this mode by setting ( fl , rxi , wxi ) = (0,0,1) or (1,0,1) during reset. no operation rclk ren ef t clkl t enh t ref last word t a t olz t oe q 0 - q 17 oe wclk wen 3139 drw 26 d 0 - d 17 t ens t ens t enh t ds t dh first word t ohz t clk 12 t ref t skew1 t clkh (1) w 1 w 2 w 4 w [n +2] w [n+3] wclk wen d 0 - d 17 rclk t dh t ds t ens t skew1 ren q 0 - q 17 t ds t a t ref or w 1 data in output register (1) w 3 1 2 3 t enh t ref 3139 drw 27
23 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 operating configurations single device configuration each of the two fifos contained in a single idt72805lb/72815lb/ 72825lb/72835lb/72845lb may be used as a stand-alone device when the application requirements are for 256/512/1,024/2,048/4,096 words or less. these fifos are in a single device configuration when the first load ( fl ), write expansion in ( wxi ) and read expansion in ( rxi ) control inputs are configured as ( fl , rxi , wxi = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0) during reset (figure 28). figure 28. block diagram of single 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18 synchronous fifo (one of the two fifos contained in the idt72805lb/72815lb/72825lb/72835lb/72845lb) figure 29. block diagram of the two fifos contained in one idt72805lb/72815lb/72825lb/72835lb/72845lb configured for a 36-bit width expansion width expansion configuration word width may be increased simply by connecting together the control signals of fifo a and b. status flags can be detected from any one device. the exceptions are the empty flag/output ready and full flag/input ready. because of variations in skew between rclk and wclk, it is possible for flag assertion and deassertion to vary by one cycle between fifos. to avoid problems the user must create composite flags by gating the empty flags/output ready of every fifo, and separately gating all full flags/input ready. figure 29 demonstrates a 36-word width by using one idt72805lb/72815lb/72825lb/72835lb/72845lbs. any word width can be attained by adding additional idt72805lb/72815lb/72825lb/72835lb/ 72845lbs. these fifos are in a single device configuration when the first load ( fl ), write expansion in ( wxi ) and read expansion in ( rxi ) control inputs are configured as ( fl , rxi , wxi = (0,0,0), (0,0,1), (0,1,0), (1,0,0), (1,0,1) or (1,1,0) during reset (figure 29). please see the application note an-83. write clock (wclk) write enable ( wen ) read clock (rclk) read enable ( ren ) load ( ld ) output enable ( oe ) data in (d 0 - d 17 ) data out (q 0 - q 17 ) full flag/input ready ( ff / ir ) programmable ( pae ) half-full flag ( hf ) empty flag/output ready ( ef / or ) programmable ( paf ) reset ( rs ) idt 72805 72815 72825 72835 72845 3139 drw 28 fl rxi wxi fifo a or b write clock (wclk) write enable ( wen ) read clock (rclk) read enable ( ren ) load ( ld ) output enable ( oe ) data in (d) data out (q) full flag/input ready ( ff / ir ) programmable ( pae ) half full flag ( hf ) empty flag/output ready ( ef / or ) programmable ( paf ) reset ( rs ) fifo a fifo b reset ( rs ) 36 36 18 18 18 18 ff / ir ef / or 3139 drw 29 fl wxi rxi fl wxi rxi ff / ir ef / or note: 1. do not connect any output control signals directly together.
commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 24 figure 30. block diagram of 8,192 x 18 synchronous fifo memory with programmable flags used in depth expansion configuration depth expansion configuration ? daisy chain technique (with programmable flags) these devices can easily be adapted to applications requiring more than 256/512/1,024/2,048/4,096 words of buffering. figure 30 shows depth expansion using one idt72805lb/72815lb/72825lb/72835lb/72845lbs. maximum depth is limited only by signal loading. follow these steps: 1.the first device must be designated by grounding the first load ( fl ) control input. 2. all other devices must have fl in the high state. 3. the write expansion out ( wxo ) pin of each device must be tied to the write expansion in ( wxi ) pin of the next device. see figure 30. 4. the read expansion out ( rxo ) pin of each device must be tied to the read expansion in ( rxi ) pin of the next device. see figure 30. 5. all load ( ld ) pins are tied together. 6. the half-full flag ( hf ) is not available in this depth expansion configuration. 7. ef , ff , pae , and paf are created with composite flags by oring together every respective flags for monitoring. the composite pae and paf flags are not precise. 8. in daisy chain mode, the flag outputs are single register-buffered and the partial flags are in asynchronous timing mode. load write clock write enable read clock read enable output enable data in data out reset first load ( fl ) vcc wxoa wxia rxoa rxia wxob wxib rxob rxib idt72845 ffa / ira pafa efa / ora paea pafb paeb ef / or pae ff / ir paf 3139 drw 30 rclkb renb oeb wclkb wenb rsb fla rclka rena oea wclka wena rsa lda dan qan dbn qbn ldb fifo a 4,096 x 18 fifo b 4,096 x 18 ffa / ira efa / ora
25 commercial and industrial temperature ranges idt72805lb/72815lb/72825lb/72835lb/72845lb cmos dual syncfifo tm 256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18 figure 31. block diagram of 512 x 18, 1,024 x 18, 2,048 x 18, 4,096 x 18, 8,192 x 18 synchronous fifo memory with programmable flags used in depth expansion configuration dn input ready write enable write clock wen wclk ir data in rclk read clock rclk ren oe output enable output ready qn dn ir gnd wen wclk or ren oe qn read enable or data out transfer clock 3139 drw 31 n n n rxi hf 72805 72815 72825 72835 72845 wxi fl v cc gnd (0,1) 72805 72815 72825 72835 72845 rxi wxi fl v cc gnd (0,1) paf hf pae depth expansion configuration (fwft mode) in fwft mode, the fifos can be connected in series (the data outputs of one fifo connected to the data inputs of the next) with no external logic necessary. the resulting configuration provides a total depth equivalent to the sum of the depths associated with each single fifo. figure 31 shows a depth expansion using one idt72805lb/72815lb/72825lb/72835lb/ 72845lb 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*t rclk where n is the number of fifos in the expansion and t rclk is the rclk period. note that extra cycles should be added for the possibility that the t skew1 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 t wclk where n is the number of fifos in the expansion and t wclk is the wclk period. note that extra cycles should be added for the possibility that the t skew1 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.
26 corporate headquarters for sales: for tech support: 2975 stender way 800-345-7015 or 408-727-6116 408-330-1753 santa clara, ca 95054 fax: 408-492-8674 email: fifohelp @idt.com www.idt.com ordering information idt xxxxx device type x power xx speed x package x blank clock cycle time (t clk ) speed in nanoseconds process / temperature range 3139 drw32 commercial only com'l & ind'l commercial only i (1) commercial (0 c to +70 c) industrial (-40 c to +85 c) bg (2) pf ball grid array (pbga, bg121-1) thin quad flatpack (tqfp, pk128-1) 10 15 20 lb low power 72805 72815 72825 72835 72845 256 x18 ? dual syncfifo 512 x18 ? dual syncfifo 1,024 x18 ? dual syncfifo 2,048 x18 ? dual syncfifo 4,096 x18 ? dual syncfifo notes: 1. industrial temperature range product for the 15ns speed grade is available as a standard device. 2. the pbga is only available for the idt72805lb/72815lb/72825lb in the 15 or 25 ns speed grade. datasheet document history 05/01/2001 pgs. 1, 5, 6, and 26. 02/12/2003 pgs. 1, 2, and 26

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