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integrated device technology, inc. commercial temperature range may 1997 1997 integrated device technology, inc. dsc-3023/3 IDT723631 idt723641 idt723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 functional block diagram features: free-running clka and clkb can be asynchronous or coincident (permits simultaneous reading and writing of data on a single clock edge) clocked fifo buffering data from port a to port b storage capacity: IDT723631 - 512 x 36 idt723641 - 1024 x 36 idt723651 - 2048 x 36 synchronous read retransmit capability mailbox register in each direction programmable almost-full and almost-empty flags microprocessor interface control logic input-ready (ir) and almost-full ( af ) flags synchronized by clka ? output-ready (or) and almost-empty ( ae ) flags syn- chronized by clkb ? low-power 0.8-micron advanced cmos technology ? supports clock frequencies up to 67 mhz ? fast access times of 11 ns ? available in 132-pin plastic quad flat package (pqf) or space-saving 120-pin thin quad flat package (tqfp) ? industrial temperature range (-40 c to +85 c) is avail- able, tested to military electrical specifications description: the IDT723631/723641/723651 is a monolithic high- speed, low-power, cmos clocked fifo memory. it supports clock frequencies up to 67 mhz and has read access times as fast as 12ns. the 512/1024/2048 x 36 dual-port sram fifo buffers data from port a to port b. the fifo memory has retransmit capability, which allows previously read data to be accessed again. the fifo has flags to indicate empty and full conditions and two programmable flags (almost full and al- most empty) to indicate when a selected number of words is the idt logo is a registered trademark and syncfifo is a trademark of integrated device technology, inc. mail 1 register input register output register clka csa w/ r a ena mba port-a control logic reset logic rst clkb csb w /rb enb mbb port-b control logic mbf1 or ae b 0 - b 35 3023 drw 01 mail 2 register write pointer read pointer status flag logic mbf2 ir af fs 0/ sd fs 1/ sen flag offset registers a 0 - a 35 10 sync retransmit logic rtm rfm 512 x 36 1024 x 36 2048 x 36 sram 36 1 for latest information contact idt's web site at www.idt.com or fax-on-demand at 408-492-8391.
2 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range description (continued) stored in memory. communication between each port may take place with two 36-bit mailbox registers. each mailbox register has a flag to signal when new mail has been stored. two or more devices may be used in parallel to create wider data paths. expansion is also possible in word depth. the IDT723631/723641/723651 is a clocked fifo, which means each port employs a synchronous interface. all data transfers through a port are gated to the low-to-high transition of a continuous (free-running) port clock by enable signals. the continuous clocks for each port are independent pin configuration of one another and can be asynchronous or coincident. the enables for each port are arranged to provide a simple interface between microprocessors and/or buses with syn- chronous control. the input-ready (ir) flag and almost-full ( af ) flag of the fifo are two-stage synchronized to clka. the output-ready (or) flag and almost-empty ( ae ) flag of the fifo are two- stage synchronized to clkb. offset values for the almost-full and almost empty flags of the fifo can be programmed from port a or through a serial input. * nc nc a 35 a 34 a 33 a 32 v cc a 31 a 30 gnd a 29 a 28 a 27 a 26 a 25 a 24 a 23 gnd a 22 v cc a 21 a 20 a 19 a 18 gnd a 17 a 16 a 15 a 14 a 13 v cc a 12 nc nc b 35 b 34 b 33 b 32 gnd b 31 b 30 b 29 b 28 b 27 b 26 v cc b 25 b 24 gnd b 23 b 22 b 21 b 20 b 19 b 18 gnd b 17 b 16 v cc b 15 b 14 b 13 b 12 gnd nc nc 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 3023 drw 02 117 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 132 131 130 129 128 127 126 125 124 123 122 121 120 119 118 nc nc b 11 b 10 b 9 b 7 b 8 v cc b 6 gnd b 5 b 4 b 3 b 2 b 1 b 0 gnd a 0 a 1 a 2 v cc a 3 a 4 a 5 gnd a 6 a 7 a 8 a 9 a 10 a 11 gnd nc 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 nc nc nc v cc clkb enb w /rb csb gnd rfm rtm v cc mbf1 mbb fs1/ se n gnd fs0/sd rst mba mbf2 ae af v cc ir csa w/ r a ena clka gnd gnd nc v cc or * electrical pin 1 in center of beveled edge. pin 1 identifier in corner. notes: 1. nc C no internal connection 2. uses yamaichi socket ic51-1324-828 pqfp (pq132-1, order code: pqf) top view
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 3 pin configuration (continued) b 35 b 34 b 33 b 32 gnd b 31 b 30 b 29 b 28 b 27 b 26 v cc b 25 b 24 gnd b 23 b 22 b 21 b 20 b 19 b 18 gnd b 17 b 16 v cc b 15 b 14 b 13 b 12 gnd a 35 a 34 a 33 a 32 v cc a 31 a 30 gnd a 29 a 28 a 27 a 26 a 25 a 24 a 23 gnd a 22 v cc a 21 a 20 a 19 a 18 gnd a 17 a 16 a 15 a 14 a 13 v cc a 12 3023 drw 03 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 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 91 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 gnd clka ena w/ r a csa ir or v cc af ae vcc mbf2 mba rst gnd fs0/sd fs1/ se n rtm rfm v cc nc mbb gnd mbf1 gnd csb w /rb enb clkb v cc b 11 b 9 b 10 b 7 b 8 b 6 b 0 b 1 b 2 b 3 b 4 b 5 gnd v cc gnd a 0 a 1 a 3 a 4 a 2 a 5 v cc gnd gnd gnd a 11 a 10 a 9 a 8 a 7 a 6 tqfp (pn120-1, order code: pf) top view note: 1. nc C no internal connection
4 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range pin description symbol name i/o description a0-a35 port-a data i/o 36-bit bidirectional data port for side a. ae almost-empty flag o programmable flag synchronized to clkb. it is low when the number of words in the fifo is less than or equal to the value in the almost-empty register (x). af almost-full flag. o programmable flag synchronized to clka. it is low when the number of empty locations in the fifo is less than or equal to the value in the almost-full offset register (y). b0-b35 port-b data. i/o 36-bit bidirectional data port for side b. clka port-a clock i clka is a continuous clock that synchronizes all data transfers through port-a and may be aynchronous or coincident to clkb. ir and af are synchronous to the low-to-high transition of clka. clkb port-b clock i clkb is a continuous clock that synchronizes all data transfers through port-b and may be asynchronous or coincident to clka. or and ae are synchro nous to the low-to-high transition of clkb. csa port-a chip select i csa must be low to enable a low-to-high transition of clka to read or write data on port-a. the a0-a35 outputs are in the high-impedance state when csa is high. csb port-b chip select i csb must be low to enable a low-to-high transition of clkb to read or write data on port-b. the b0-b35 outputs are in the high-impedance state when csb is high. ena port-a enable i ena must be high to enable a low-to-high transition of clka to read or write data on port-a. enb port-b enable i enb must be high to enable a low-to-high transition of clkb to read or write data on port-b. fs1/ sen, flag-offset select 1/ i fs1/ sen and fs0/sd are dual-purpose inputs used for flag offset register fs0/sd serial enable, programming. during a device reset, fs1/ sen and fs0/sd selects the flag flag offset 0/ offset programming method. three offset register programming methods are serial data available: automatically load one of two preset values, parallel load from port a, and serial load. when serial load is selected for flag offset register program- ming, fs1/ sen is used as an enable synchronous to the low-to-high transition of clka. when fs1/ sen is low, a rising edge on clka load the bit present on fs0/sd into the x and y registers. the number of bit writes required to program the offset registers is 18/20/22. the first bit write stores the y-register msb and the last bit write stores the x-register lsb. ir input-ready flag o ir is synchronized to the low-to-high transition of clka. when ir is low, the fifo is full and writes to its array are disabled. when the fifo is in retransmit mode, ir indicates when the memory has been filled to the point of the retransmit data and prevents further writes. ir is set low during reset and is set high after reset. mba port-a mailbox select i a high level chooses a mailbox register for a port-a read or write operation. mbb port-b mailbox select i a high level chooses a mailbox register for a port-b read or write operation. when the b0-b35 outputs are active, a high level on mbb selects data from the mail1 register for output and a low level selects fifo data for output. mbf1 mail1 register flag o mbf1 is set low by the low-to-high transition of clka that writes data to the mail1 register. mbf1 is set high by a low-to-high transition of clkb when a port-b read is selected and mbb is high. mbf1 is set high by a reset. 3023 tbl 01
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 5 symbol name i/o description mbf2 mail2 register flag o mbf2 is set low by the low-to-high transition of clkb that writes data to the mail2 register. mbf2 is set high by a low-to-high transition of clka when a port-a read is selected and mba is high. mbf2 is set high by a reset. or output-ready flag o or is synchronized to the low-to-high transition of clkb. when or is low, the fifo is empty and reads are disabled. ready data is present in the output register of the fifo when or is high. or is forced low during the reset and goes high on the third low-to-high transition of clkb after a word is loaded to empty memory. rfm read from mark i when the fifo is in retransmit mode, a high on rfm enables a low-to- high transition of clkb to reset the read pointer to the beginning retransmit location and output the first selected retransmit data. rst reset i to reset the device, four low-to-high transitions of clka and four low-to- high transitions of clkb must occur while rst is low. the low-to-high transition of rst latches the status of fs0 and fs1 for af and ae offset selection. rtm retransmit mode i when rtm is high and valid data is present in the fifo output register (or is high), a low-to-high transition of clkb selects the data for the begin- ning of a retransmit and puts the fifo in retransmit mode. the selected word remains the initial retransmit point until a low-to-high transition of clkb occurs while rtm is low, taking the fifo out of retransmit mode. w/ r a port-a write/read i a high selects a write operation and a low selects a read operation on select port a for a low-to-high transition of clka. the a0-a35 outputs are in the high-impedance state when w/ r a is high. w /rb port-b write/read i a low selects a write operation and a high selects a read operation on select port b for a low-to-high transition of clkb. the b0-b35 outputs are in the high-impedance state when w /rb is low. pin description (continued) 3023 tbl 02
6 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range absolute maximum ratings over operating free-air temperature range (unless otherwise noted) (2) symbol rating commercial unit v cc supply voltage range -0.5 to 7 v v i (2) input voltage range -0.5 to v cc +0.5 v v o (2) output voltage range -0.5 to v cc +0.5 v i ik input clamp current, (v i < 0 or v i > v cc ) 20 ma i ok output clamp current, (v o = < 0 or v o > v cc ) 50 ma i out continuous output current, (v o = 0 to v cc ) 50 ma i cc continuous current through v cc or gnd 400 ma t a operating free air temperature range 0 to 70 c t stg storage temperature range -65 to 150 c notes: 1. stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. these are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. 2. the input and output voltage ratings may be exceeded provided the input and output current ratings are observed. symbol parameter min. max. unit vcc supply voltage 4.5 5.5 v vih high level input voltage 2 C v vil low-level input voltage C 0.8 v ioh high-level output current C -4 ma iol low-level output current C 8 ma ta operating free-air 0 70 c temperature recommended operating conditions parameter test conditions min. typ. (1) max. unit v oh v cc = 4.5v, i oh = -4 ma 2.4 v v ol v cc = 4.5 v, i ol = 8 ma 0.5 v i li v cc = 5.5 v, v i = v cc or 0 5 m a i lo v cc = 5.5 v, v o = v cc or 0 5 m a i cc v cc = 5.5 v, v i = v cc -0.2 v or 0 400 m a d i cc (2) v cc = 5.5 v, one input at 3.4 v, csa = v ih a0-a35 0 ma other inputs at v cc or gnd csb = v ih b0-b35 0 csa = v il a0-a35 1 csb = v il b0-35 1 all other inputs 1 c in v i = 0, f = 1 mhz 4 pf c out v o = 0, f = 1 mhz 8 pf electrical characteristics over recommended operating free-air tempera- ture range (unless otherwise noted) notes: 1. all typical values are at vcc = 5 v, ta = 25 c. 2. this is the supply current when each input is at least one of the specified ttl voltage levels rather than 0 v or vcc. 3023 tbl 03 3023 tbl 04 3023 tbl 05
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 7 IDT723631l15 IDT723631l20 IDT723631l30 idt723641l15 idt723641l20 idt723641l30 idt723651l15 idt723651l20 idt723651l30 symbol parameter min. max. min. max. min. max. unit f s clock frequency, clka or clkb C 66.7 C 50 C 33.4 mhz t clk clock cycle time, clka or clkb 15 C 20 C 30 C ns t clkh pulse duration, clka or clkb high 6C8C12Cns t clkl pulse duration, clka or clkb low 6C8C12Cns t ds setup time, a0-a35 before clka - and b0-b35 5C6C7Cns before clkb - t ens1 setup time, ena to clka - ; enb to clkb - 5C6C7Cns t ens2 setup time, csa , w/ r a, and mba to clka -; 7C7.5C8Cns csb , w /rb, and mbb to clkb - t rms setup time, rtm and rfm to clkb - 6C6.5C7Cns t rsts setup time, rst low before clka - 5C6C7Cns or clkb - (1) t fss setup time, fs0 and fs1 before rst high 9 C 10 C 11 C ns t sds (2) setup time, fs0/sd before clka - 5C6C7Cns t sens (2) setup time, fs1/ sen before clka - 5C6C7Cns t dh hold time, a0-a35 after clka - and b0-b35 0C0C0Cns after clkb - t enh1 hold time, ena after clka - ; enb after clkb - 0C0C0Cns t enh2 hold time, csa , w/ r a, and mba after clka - ;0C0C0Cns csb, w /rb, and mbb after clkb - t rmh hold time, rtm and rfm after clkb - 0C0C0Cns t rsth hold time, rst low after clka - or clkb - (1) 5C6C7Cns t fsh hold time, fs0 and fs1 after rst high 0C0C0Cns t sph (2) hold time, fs1/ sen high after rst high 0C0C0Cns t sdh (2) hold time, fs0/sd after clka - 0C0C0Cns t senh (2) hold time, fs1/ sen after clka - 0C0C0Cns t skew1 (3) skew time, between clka - and clkb - 9C11C13Cns for or and ir t skew2 (3) skew time, between clka - and clkb - 12 C 16 C 20 C ns for ae and af ac electrical characteristics over recommended ranges of supply voltage and operating free-air temperature notes: 1. requirement to count the clock edge as one of at least four needed to reset a fifo. 2. only applies when serial load method is used to program flag offset registers. 3. skew time is not a timimg constraint for proper device operation and is only included to illustrate the timing relationship between clka cycle and clkb cycle. 3023 tbl 06
8 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range IDT723631l15 IDT723631l20 IDT723631l30 idt723641l15 idt723641l20 idt723641l30 idt723651l15 idt723651l20 idt723651l30 symbol parameter min. max. min. max. min. max. unit f s clock frequency, clka or clkb C 66.7 C 50 C 33.4 mhz t a access time, clkb - to b0-b35 3 11 3 13 3 15 ns t pir propagation delay time, clka - to ir 1 8 1 10 1 12 ns t por propagation delay time, clkb - to or 1 8 1 10 1 12 ns t pae propagation delay time, clkb - to ae 18110112ns t paf propagation delay time, clka - to af 18110112ns t pmf propagation delay time, clka - to mbf1 08010012ns low or mbf2 high and clkb - to mbf2 low or mbf1 high t pmr propagation delay time, clka - to b0-b35 (1) 3 13.5 3 15 3 17 ns and clkb - to a0-a35 (2) t mdv propagation delay time, mbb to b0-b35 valid 3 13 3 15 3 17 ns t rsf propagation delay time, rst low to ae low115120130 ns and af high t en enable time, csa and w/ r a low to a0-a35 2 12 2 13 2 14 ns active and csb low and w /rb high to b0-b35 active t dis disable time, csa or w/ r a high to a0-a35 1 8 1 10 1 11 ns at high impedance and csb high or w /rb low to b0-b35 at high impedance ac electrical characteristics notes: 1. writing data to the mail1 register when the b0-b35 outputs are active and mbb is high. 2. writing data to the mail2 register when the a0-a35 outputs are active and mba is high. 3023 tbl 07
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 9 y register values are loaded bitwise through the fs0/sd input on each low-to-high transition of clka that the fs1/ sen input is low. eighteen-, 20-, or 22-bit writes are needed to complete the programming for the IDT723631, idt723641, or idt723651, respectively. the first-bit write stores the most significant bit of the y register, and the last-bit write stores the least significant bit of the x register. each register value can be programmed from 1 to 508 (IDT723631), 1 to 1020 (idt723641), or 1 to 2044 (idt723651). when the option to program the offset registers serially is chosen, the input-ready (ir) flag remains low until all regis- ter bits are written. the ir flag is set high by the low-to- high transition of clka after the last bit is loaded to allow normal fifo operation. fifo write/read operation the state of the port-a data (a0-a35) outputs is controlled by the port-a chip select ( csa ) and the port-a write/read select (w/ r a). the a0-a35 outputs are in the high-imped- ance state when either csa or w/ r a is high. the a0-a35 outputs are active when both csa and w/ r a are low. data is loaded into the fifo from the a0-a35 inputs on a low-to-high transition of clka when csa and the port-a mailbox select (mba) are low, w/ r a, the port-a enable (ena), and the input-ready (ir) flag are high (see table 2). writes to the fifo are independent of any concurrent fifo read. the port-b control signals are identical to those of port-a with the exception that the port-b write/read select ( w /rb) is the inverse of the port-a write/read select (w/ r a). the state of the port-b data (b0-b35) outputs is controlled by the port- b chip select ( csb ) and the port-b write/read select ( w /rb). the b0-b35 outputs are in the high-impedance state when either csb is high or w /rb is low. the b0-b35 outputs are active when csb is low and w /rb is high. data is read from the fifo to its output register on a low- to-high transition of clkb when csb and the port-b mailbox select (mbb) are low, w /rb, the port-b enable (enb), and the output-ready (or) flag are high (see table 3). reads from the fifo are independent of any concurrent fifo writes. the setup- and hold-time constraints to the port clocks for the port-chip selects and write/read selects are only for enabling write and read operations and are not related to high- signal description reset the IDT723631/723641/723651 is reset by taking the reset ( rst ) input low for at least four port-a clock (clka) and four port-b (clkb) low-to-high transitions. the reset input may switch asynchronously to the clocks. a reset initializes the memory read and write pointers and forces the input-ready (ir) flag low, the output-ready (or) flag low, the almost-empty ( ae ) flag low, and the almost-full ( af ) flag high. resetting the device also forces the mailbox flags ( mbf1 , mbf2 ) high. after a fifo is reset, its input-ready flag is set high after at least two clock cycles to begin normal operation. a fifo must be reset after power up before data is written to its memory. almost-empty flag and almost-full flag off- set programming two registers in the IDT723631/723641/723651 are used to hold the offset values for the almost-empty and almost full flags. the almost-empty ( ae ) flag offset register is labeled x, and the almost-full ( af ) flag offset register is labeled y. the offset register can be loaded with a value in three ways: one of two preset values are loaded into the offset registers, parallel load from port a, or serial load. the offset register programming mode is chosen by the flag select (fs1, fs0) inputs during a low-to-high transition on the rst input (see table 1). preset values if the preset value of 8 or 64 is chosen by the fs1 and fs0 inputs at the time of a rst low-to-high transition according to table 1, the preset value is automatically loaded into the x and y registers. no other device initialization is necessary to begin normal operation, and the ir flag is set high after two low-to-high transitions on clka. parallel load from port a to program the x and y registers from port a, the device is reset with fs0 and fs1 low during the low-to-high transition of rst . after this reset is complete, the ir flag is set high after two low-to-high transitions on clka. the first two writes to the fifo do not store data in its memory but load the offset registers in the order y, x. each offset register of the IDT723631, idt723641, and idt723651 uses port-a inputs (a8-a0), (a9-a0), and (a10-a0), respectively. the highest number input is used as the most significant bit of the binary number in each case. each register value can be pro- grammed from 1 to 508 (IDT723631), 1 to 1020 (idt723641), and 1 to 2044 (idt723651). after both offset registers are programmed from port a, subsequent fifo writes store data in the sram. serial load to program the x and y registers serially, the device is reset with fs0/sd and fs1/ sen high during the low-to- high transition of rst . after this reset is complete, the x and note: 1. x register holds the offset for ae; y register holds the offset for af. table 1. flag programming fs1 fs0 rst rst x and y registers (1) hh - serial load hl - 64 lh - 8 ll - parallel load from port a 3023 tbl 08
10 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range impedance control of the data outputs. if a port enable is low during a clock cycle, the port chip select and write/read select may change states during the setup- and hold time window of the cycle. when the output-ready (or) flag is low, the next data word is sent to the fifo output register automatically by the clkb low-to-high transition that sets the output-ready flag high. when or is high, an available data word is clocked to the fifo output register only when a fifo read is selected by the port-b chip select ( csb ), write/read select ( w /rb), enable (enb), and mailbox select (mbb). synchronized fifo flags each IDT723631/723641/723651 fifo flag is synchro- nized to its port clock through at least two flip-flop stages. this is done to improve the flags reliability by reducing the prob- ability of metastable events on their outputs when clka and clkb operate asynchronously to one another. or and ae are synchronized to clkb. ir and af are synchronized to clka. table 4 shows the relationship of each flag to the number of words stored in memory. output-ready flag (or) the output-ready flag of a fifo is synchronized to the port clock that reads data from its array (clkb). when the output- ready flag is high, new data is present in the fifo output csb csb w w /rb enb mbb clkb b0-a35 outputs port functions h x x x x in high-impedance state none l l l x x in high-impedance state none llhl - in high-impedance state none llhh - in high-impedance state mail2 write l h l l x active, fifo output register none lhhl - active, fifo output register fifo read l h l h x active, mail1 register none lhhh - active, mail1 register mail1 read (set mbf1 high) table 3. port-b enable function table csa csa w/ r r a ena mba clka a0-a35 outputs port functions h x x x x in high-impedance state none l h l x x in high-impedance state none lhhl - in high-impedance state fifo write lhhh - in high-impedance state mail1 write l l l l x active, mail2 register none llhl - active, mail2 register none l l l h x active, mail2 register none llhh - active, mail2 register mail2 read (set mbf2 high) table 2. port-a enable function table 3023 tbl 09 3023 tbl 10 register. when the output-ready flag is low, the previous data word is present in the fifo output register and attempted fifo reads are ignored. a fifo read pointer is incremented each time a new word is clocked to its output register. the state machine that controls an output-ready flag monitors a write-pointer and read-pointer comparator that indicates when the fifo sram status is empty, empty+1, or empty+2. from the time a word is written to a fifo, it can be shifted to the fifo output register in a minimum of three cycles of clkb. therefore, an output- ready flag is low if a word in memory is the next data to be sent to the fifo output register and three clkb cycles have not elapsed since the time the word was written. the output- ready flag of the fifo remains low until the third low-to- high transition of clkb occurs, simultaneously forcing the output-ready flag high and shifting the word to the fifo output register. a low-to-high transition on clkb begins the first syn- chronization cycle of a write if the clock transition occurs at time t skew1 or greater after the write. otherwise, the subse- quent clkb cycle may be the first synchronization cycle (see figure 6). input ready flag (ir) the input ready flag of a fifo is synchronized to the port clock that writes data to its array (clka). when the input-
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 11 level. an almost-empty flag is set high by the second low- to-high transition of clkb after the fifo write that fills memory to the (x+1) level. a low-to-high transition of clkb begins the first synchronization cycle if it occurs at time t skew2 or greater after the write that fills the fifo to (x+1) words. otherwise, the subsequent clkb cycle may be the first synchronization cycle (see figure 8). almost-full flag ( af af ) the almost-full flag of a fifo is synchronized to the port clock that writes data to its array (clka). the state machine that controls an almost-full flag monitors a write-pointer and read-pointer comparator that indicates when the fifo sram status is almost full, almost full-1, or almost full-2. the almost- full state is defined by the contents of register y. this register is loaded with a preset value during a fifo reset, programmed from port a, or programmed serially (see almost-empty flag and almost-full flag offset programming). the almost-full flag is low when the number of words in the fifo is greater than or equal to (512-y), (1024-y), or (2048-y) for the IDT723631, idt723641, or idt723651, respectively. the almost-full flag is high when the number of words in the fifo is less than or equal to [512-(y+1)], [1024-(y+1)], or [2048-(y+1)] for the IDT723631, idt723641, or idt723651, respectively. a data word present in the fifo output register has been read from memory. two low-to-high transitions of clka are required after a fifo read for its almost-full flag to reflect the new level of fill. therefore, the almost-full flag of a fifo containing [512/1024/ 2048-(y+1)] or less words remains low if two cycles of clka have not elapsed since the read that reduced the number of words in memory to [512/1024/2048-(y+1)]. an almost-full flag is set high by the second low-to-high transition of clka after the fifo read that reduces the number of words in memory to [512/1024/2048-(y+1)]. a low-to-high tran- sition of clka begins the first synchronization cycle if it occurs at time t skew2 or greater after the read that reduces the number of words in memory to [512/1024/2048-(y+1)]. oth- erwise, the subsequent clka cycle may be the first synchro- nization cycle (see figure 9). number of words in the fifo (1,2) synchronized synchronized to clkb to clka IDT723631 idt723641 idt723651 or ae ae af af ir 000llhh 1 to x 1 to x 1 to x h l h h (x+1) to [512-(y+1)] (x+1) to [1024-(y+1)] (x+1) to [2048-(y+1)] h h h h (512-y) to 511 (1024-y) to 1023 (2048-y) to 2047 h h l h 512 1024 2048 h h l l notes: 1. x is the almost-empty offset for ae . y is the almost-full offset for af . 2. when a word is present in the fifo output register, its previous memory location is free. table 4. fifo flag operation 3023 tbl 11 ready flag is high, a memory location is free in the sram to write new data. no memory locations are free when the input- ready flag is low and attempted writes to the fifo are ignored. each time a word is written to a fifo, its write pointer is incremented. the state machine that controls an input-ready flag monitors a write-pointer and read pointer comparator that indicates when the fifo sram status is full, full-1, or full-2. from the time a word is read from a fifo, its previous memory location is ready to be written in a minimum of three cycles of clka. therefore, an input-ready flag is low if less than two cycles of clka have elapsed since the next memory write location has been read. the second low-to-high transition on clka after the read sets the input-ready flag high, and data can be written in the following cycle. a low-to-high transition on clka begins the first syn- chronization cycle of a read if the clock transition occurs at time t skew1 or greater after the read. otherwise, the subse- quent clka cycle may be the first synchronization cycle (see figure 7). almost-empty flag ( ae ae ) the almost-empty flag of a fifo is synchronized to the port clock that reads data from its array (clkb). the state machine that controls an almost-empty flag monitors a write- pointer and read-pointer comparator that indicates when the fifo sram status is almost empty, almost empty+1, or almost empty+2. the almost-empty state is defined by the contents of register x. this register is loaded with a preset value during a fifo reset,programmed from port a, or pro- grammed serially (see almost-empty flag and almost-full flag offset programming above). the almost-empty flag is low when the fifo contains x or less words and is high when the fifo contains (x+1) or more words. a data word present in the fifo output register has been read from memory. two low-to-high transitions of clkb are required after a fifo write for the almost-empty flag to reflect the new level of fill; therefore, the almost-empty flag of a fifo containing (x+1) or more words remains low if two cycles of clkb have not elapsed since the write that filled the memory to the (x+1)
12 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range synchronous retransmit the synchronous retransmit feature of the IDT723631/ 723641/723651 allows fifo data to be read repeatedly starting at a user-selected position. the fifo is first put into retransmit mode to select a beginning word and prevent on- going fifo write operations from destroying retransmit data. data vectors with a minimum length of three words can retransmit repeatedly starting at the selected word. the fifo can be taken out of retransmit mode at any time and allow normal device operation. the fifo is put in retransmit mode by a low-to-high transition on clkb when the retransmit mode (rtm) input is high and or is high. the rising clkb edge marks the data present in the fifo output register as the first retransmit data. the fifo remains in retransmit mode until a low-to-high transition occurs while rtm is low. when two or more reads have been done past the initial retransmit word, a retransmit is initiated by a low-to-high transition on clkb when the read-from-mark (rfm) input is high. this rising clkb edge shifts the first retransmit word to the fifo output register and subsequent reads can begin immediately. retransmit loops can be done endlessly while the fifo is in retransmit mode. rfm must be low during the clkb rising edge that takes the fifo out of retransmit mode. when the fifo is put into retransmit mode, it operates with two read pointers. the current read pointer operates normally, incrementing each time a new word is shifted to the fifo output register and used by the or and ae flags. the shadow read pointer stores the sram location at the time the device is put into retransmit mode and does not change until the device is taken out of retransmit mode. the shadow read pointer is used by the ir and af flags. data writes can proceed while the fifo is in retransmit mode, but af is set low by the write that stores (512 - y), (1024 - y), or (2048 - y) words after the first retransmit word for the IDT723631, idt723641, or idt723651, respectively. the ir flag is set low by the 512th, 1024th, or 2048th write after the first retransmit word for the IDT723631, idt723641, or idt723651, respectively. when the fifo is in retransmit mode and rfm is high, a rising clkb edge loads the current read pointer with the shadow read-pointer value and the or flag reflects the new level of fill immediately. if the retransmit changes the fifo status out of the almost-empty range, up to two clkb rising edges after the retransmit cycle are needed to switch ae high (see figure 11).the rising clkb edge that takes the fifo out of retransmit mode shifts the read pointer used by the ir and af flags from the shadow to the current read pointer. if the change of read pointer used by ir and af should cause one or both flags to transmit high, at least two clka synchroniz- ing cycles are needed before the flags reflect the change. a rising clka edge after the fifo is taken out of retransmit mode is the first synchronizing cycle of ir if it occurs at time t skew1 or greater after the rising clkb edge (see figure 12). a rising clka edge after the fifo is taken out of retransmit mode is the first synchronizing cycle of af if it occurs at time t skew2 or greater after the rising clkb edge (see figure 14). mailbox registers two 36-bit bypass registers are on the IDT723631/723641/ 723651 to pass command and control information between port a and port b. the mailbox-select (mba, mbb) inputs choose between a mail register and a fifo for a port data transfer operation. a low-to-high transition on clka writes a0-a35 data to the mail1 register when a port-a write is selected by csa , w/ r a, and ena with mba high. a low- to-high transition on clkb writes b0-b35 data to the mail2 register when a port-b write is selected by csb , w /rb, and enb with mbb high. writing data to a mail register sets its corresponding flag ( mbf1 or mbf2 ) low. attempted writes to a mail register are ignored while its mail flag is low. when the port-b data (b0-b35) outputs are active, the data on the bus comes from the fifo output register when the port-b mailbox select (mbb) input is low and from the mail1 register when mbb is high. mail2 data is always present on the port-a data (a0-a35) outputs when they are active. the mail1 register flag ( mbf1 ) is set high by a low-to-high transition on clkb when a port-b read is selected by csb , w / rb, and enb with mbb high. the mail2 register flag (mbf2) is set high by a low-to-high transition on clka when a port-a read is selected by csa , w/ r a, and ena with mba high. the data in a mail register remains intact after it is read and changes only when new data is written to the register.
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 13 figure 2. programming the almost-full flag and almost-empty flag offset values from port a figure 1. fifo reset loading x and y with a preset value of eight note: 1. csa = low, w/ r a = high, mba = low. it is not necessary to program offset register on consecutive clock cycles. clka rst ir ae af mbf1 , mbf2 clkb or fs1,fs0 3023 drw 04 t rsts t rsth t fsh t fss t pir 0,1 t rsf t por t rsf t rsf t pir 3023 drw 05 clka rst ir a0 - a35 fs1,fs0 ena t enh1 t ens1 4 t pir first word stored in fifo ae offset (x) af offset (y) t fss t fsh t ds t dh
14 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range figure 4. fifo write-cycle timing note: 1. it is not necessary to program offset register bits on consecutive clock cycles. fifo write attempts are ignored until ir is set high. figure 3. programming the almost-full flag and almost-empty flag offset values serially figure 5. fifo read-cycle timing clka ir ena mba csa w/ r a t clkh t clkl t clk t ens2 t ens2 t ens2 t ens1 t enh2 t enh2 t enh2 t enh1 t ens1 t enh1 t enh1 t ens1 3023 drw 07 a0 - a35 t ds t dh w1 w2 no operation high 3023 drw 08 clkb or enb b0 - b35 mbb csb w /rb t clk t clkh t clkl t ens1 t a t mdv t en t a t ens1 t enh1 t ens1 t enh1 w1 w2 w3 t enh1 t dis no operation high clka rst ir fs1/ sen fs0/sd 4 af offset (y) msb ae offset (x) lsb 3023 drw 06 t fss t fss t fsh t sph t sens t senh t sds t sdh t sens t senh t sds t sdh t pir
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 15 note: 1. tskew1 is the minimum time between a rising clka edge and a rising clkb edge for or to transition high and to clock the next word to the fifo output register in three clkb cycles. if the time between the rising clka edge and rising clkb edge is less than tskew1, then the transition of or high and the first word load to the output register may occur one clkb cycle later than shown. csa w r a mba ir a0 - a35 clkb or csb w /rb mbb ena enb b0 -b35 clka 12 3 3023 drw 09 t clkh t clkl t clk t ens2 t ens1 t enh2 t enh1 t ds t dh t skew1 t clk t clkl t por t por t ens1 t enh1 t a old data in fifo output register w1 old data in fifo1 output register low high low high low t clkh w1 high (1) figure 6. or flag timing and first data word fallthrough when the fifo is empty
16 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range note: 1. tskew1 is the minimum time between a rising clkb edge and a rising clka edge for ir to transition high in the next clka cycle. if the time between the rising clkb edge and rising clka edge is less than tskew1, then ir may transition high one clka cycle later than shown. figure 7. ir flag timing and first available write when the fifo is full notes: 1. tskew2 is the minimum time between a rising clka edge and a rising clkb edge for ae to transition high in the next clkb cycle. if the time between the rising clka edge and rising clkb edge is less than tskew2, then ae may transition high one clkb cycle later than shown. 2. fifo write ( csa = low, w/ r a = high, mba = low), fifo read ( csb = low, w /rb = high, mbb = low). figure 8. timing for ae ae when fifo is almost empty csb or w /rb mbb enb b0 -b35 clkb ir clka csa w r a a0 - a35 mba ena 3023 drw 10 12 t clk t clkh t clkl t ens1 t enh1 t a t skew1 t clk t clkh t clkl t pir t pir t ens2 t ens1 t ds t enh2 t enh1 t dh previous word in fifo output register next word from fifo low high low high low high (1) fifo full write ae clka enb ena clkb 3023 drw 11 2 1 t ens1 t enh1 t skew2 t pae t pae t ens1 t enh1 x word in fifo (x+1) words in fifo (1)
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 17 notes: 1. tskew2 is the minimum time between a rising clka edge and a rising clkb edge for af to transition high in the next clka cycle. if the time between the rising clkb edge and rising clka edge is less than tskew2, then af may transition high one clka cycle later than shown. 2. depth is 512 for the IDT723631, 1024 for the idt723641, and 2048 for the idt723651. 3. fifo write ( csa = low, w/ r a = high, mba = low), fifo read ( csb = low, w /rb = high, mbb = low). figure 9. timing for af af when fifo is almost full note: 1. csb = low, w/rb = high, mbb = low. no input enables other than rtm and rfm are needed to control retransmit mode or begin a retransmit. other enables are shown only to relate retransmit operations to the fifo output register. figure 10. retransmit timing showing minimum retransmit length af clka enb ena clkb 3023 drw 12 12 t skew2 t ens1 t enh1 t paf t ens1 t enh1 t paf [depth -(y+1)] words in fifo (depth -y) words in fifo (1) (2) (2) clkb enb rtm rfm or b0-b35 w0 w1 w2 w0 w1 high t a t a t a t a initiate retransmit mode with w0 as first word retransmit from selected position end retransmit mode 3023 drw 13 t ens1 t enh1 t rms t rmh t rms t rmh t rms t rmh note: 1. x is the value loaded in the almost empty flag offset register. figure 11. ae ae maximum latency when retransmit increases the number of stored words above x. clkb rtm rfm ae t pae x or fewer words from empty (x+1) or more words from empty 3023 drw 14 t rms t rmh 1 2 high
18 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range figure 13. af af timing from the end of retransmit mode when (y+1) or more write locations are available notes: 1. tskew2 is the minimum time between a rising clkb edge and a rising clka edge for af to transition high in the next clka cycle. if the time between the rising clkb edge and rising clka edge is less than tskew2, then af may transition high one clka cycle later than shown. 2. depth is 512 for the IDT723631, 1024 for the idt723641, and 2048 for the idt723651. 3. y is the value loaded in the almost-full flag offset register. note: 1. tskew1 is the minimum time between a rising clkb edge and a rising clka edge for ir to transition high in the next clka cycle. if the time between the rising clkb edge and rising clka edge is less than tskew1, then ir may transition high one clka cycle later than shown. figure 12. ir timing from the end of retransmit mode when one or more write locations are available t skew1 clka ir clkb rtm fifo filled to first restransmit word 1 2 one or more write locations available 3023 drw 15 (1) t pir t rms t rmh clka af clkb rtm t skew2 (depth -y) or more words past first restransmit word 1 2 (y+1) or more write locations available 3023 drw 16 (1) t pae t rms t rmh (2)
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 19 figure 14. timing for mail1 register and mbf1 mbf1 flag 3023 drw 17 clka ena a0 - a35 mba csa w/ r a clkb mbf1 csb mbb enb b0 - b35 w /rb w1 t ens2 t enh2 t ds t dh t pmf t pmf t en t mdv t pmr t ens1 t enh1 t dis w1 (remains valid in mail1 register after read) fifo output register
20 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range figure 15. timing for mail2 mail2 register and mbf2 mbf2 flag 3023 drw 18 clkb enb b0 - b35 mbb csb w /rb clka mbf2 csa mba ena a0 - a35 w/ r a w1 t ens2 t enh2 t ds t dh t pmf t pmf t ens1 t enh1 t dis t en t pmr w1 (remains valid in mail2 register after read)
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 21 figure 16 calculating power dissipation the i cc (f) current for the graph in figure 16 was taken while simultaneously reading and writing the fifo on the idt723641 with clka and clkb set to fs. all data inputs and data outputs change state during each clock cycle to consume the highest supply current. data outputs were disconnected to normalize the graph to a zero-capacitance load. once the capacitance load per data-output channel and the number of IDT723631/723641/723651 inputs driven by ttl high levels are known, the power dissipation can be calculated with the equation below. with i cc (f) taken from figure 16, the maximum power dissipation (pt) of the IDT723631/723641/723651 may be calculated by: p t = v cc x [i cc(f) + (n x d i cc x dc)] + ? (c l x v cc 2 x f o ) where: n = number of inputs driven by ttl levels d i cc = increase in power supply current for each input at a ttl high level dc = duty cycle of inputs at a ttl high level of 3.4 c l = output capacitance load f o = switching frequency of an output when no reads or writes are occurring on the IDT723631/723641/723651, the power dissipated by a single clock (clka or clkb) input running at frequency fs is calculated by: p t = v cc x f s x 0.209 ma/mhz typical characteristics supply current vs clock frequency 010 20 30 40 50 60 70 0 50 100 150 200 250 v cc = 5.0 v f ?clock frequency ?mhz s i cc(f) ?supply current ?ma f = 1/2 f data t = 25 c a c = 0pf l v cc = 4.5 v v cc = 5.5 v 3023 drw 19 s
22 IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range note: 1. includes probe and jig capacitance figure 17. load circuit and voltage waveforms 3023 drw 20 parameter measurement information from output under test 30 pf 1.1 k w 5 v 680 w 3 v gnd timing input data, enable input gnd 3 v 1.5 v 1.5 v voltage waveforms setup and hold times voltage waveforms pulse durations voltage waveforms enable and disable times voltage waveforms propagation delay times 3 v gnd gnd 3 v 1.5 v 1.5 v 1.5 v 1.5 v t w output enable low-level output high-level output 3 v ol gnd 3 v 1.5 v 1.5 v 1.5 v 1.5 v ? oh ov ? gnd oh ol 1.5 v 1.5 v 1.5 v 1.5 v input in-phase output high-level input low-level input v v v v 1.5 v 3 v t s t h t plz t phz t pzl t pzh t pd t pd (1)
IDT723631/723641/723651 cmos syncfifo ? 512 x 36, 1024 x 36, 2048 x 36 commercial temperature range 23 ordering information blank pf pqf 15 20 30 l 723631 723641 723651 3023 drw 21 commercial (0 c to +70 c) thin quad flat pack (tqfp, pn120-1) plastic quad flat pack (pqfp, pq132-1) low power 512 x 36 synchronous fifo 1024 x 36 synchronous fifo 2048 x 36 synchronous fifo xxxxxx idt device type xxx x x power speed package process/ temperature range commercial only clock cycle time (t clk ) speed in nanoseconds

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