IDT723631_14 IDT | Alldatasheet

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DSC-2023/8©2014 Integrated Device Technology, Inc. All rights reserved. Product specifications subject to change without notice. CMOS SyncFIFO™ 512 x 36 1,024 x 36 2,048 x 36 IDT723631 IDT723641 IDT723651 IDT and the IDT logo are registered trademarks of Integrated Device Technology, Inc. The SyncFIFO is a trademark of Integrated Device Technology, Inc. COMMERCIAL AND INDUSTRIAL TEMPERATURE RANGES FEATURES: IDT723631 - 512 x 36 IDT723641 - 1,024 x 36 IDT723651 - 2,048 x 36

  • •••• Supports clock frequencies up to 67 MHz
  • •••• Fast access times of 11ns
  • •••• Free-running CLKA and CLKB can be asynchronous or coinci- dent (permits simultaneous reading and writing of data on a single clock edge)
  • •••• Clocked FIFO buffering data from Port A to Port B
  • •••• 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 synchronized by CLKB
  • •••• Available in space-saving 120-pin thin quad flat package (TQFP)
  • •••• Green parts available, see ordering information 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 11ns. The 512/1,024/2,048 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 ac- cessed again. The FIFO has flags to indicate empty and full conditions and two programmable flags (Almost-Full and Almost-Empty) to indicate when a selected number of words is 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 FUNCTIONAL BLOCK DIAGRAM Mail 1 Register Input Register Output Register CLKA CSA W/RA ENA MBA Port-A Control Logic Reset LogicRST CLKB CSB W/RB ENB MBB Port-B Control Logic MBF1 OR AE B0 - B35 3023 drw01 Mail 2 Register Write Pointer Read Pointer Status Flag Logic MBF2 IR AF FS0/SD FS1/SEN Flag Offset Registers A0 - A35 Sync Retransmit Logic RTM RFM RAM ARRAY 512 x 36 1,024 x 36 2,048 x 36

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 TQFP (PNG120, ORDER CODE: PF) TOP VIEW NOTE: 1. NC – No Connection DESCRIPTION (CONTINUED) PIN CONFIGURATION B35 B34 B33 B32 GND B31 B30 B29 B28 B27 B26 VCC B25 B24 GND B B22 B21 B20 B19 B18 GND B B16 VCC B15 B14 B13 B12 GND A35 A34 A33 A32 VCC A31 A30 GND A29 A28 A27 A26 A25 A24 A23 GND A22 VCC A21 A20 A19 A18 GND A17 A16 A15 A14 A13 VCC A12 3023 drw03 61 91 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 GND CLKA ENA W/RA CSA IR OR V CC AF AE VCC MBF2 MBA RST GND FS0/SD FS1/SEN RTM RFM VCC NC MBB GND MBF1 GND CSB W/RB ENB CLKB VCCB11 B10 GND VCC GND VCC GND GND GND A11 A10 devices may be used in parallel to create wider data paths. Expansion is also possible in word depth. These devices are 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 en- able signals. The continuous clocks for each port are independent 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 synchronous 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 Al- most-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.

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 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 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 Flag the Almost-Empty register (X). AF Almost-Full O Programmable flag synchronized to CLKA. It is LOW when the number of empty locations in FIFO is less than or equal to the Flag 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 asynchronous or coincide nt 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 coincide nt to CLKA. OR and AE are synchronous to the LOW-to-HIGH transition of CLKB. CSA Port-A Chip 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 Select high-impedance state when CSA is HIGH. CSB Port-B Chip 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 Select 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/ Flag-Offset I FS1/SEN and FS0/SD are dual-purpose inputs used for flag Offset register programming. During a device reset, FS1/SEN and SEN, Select 1/ FS0/SD selects the flag offset programming method. Three Offset register programming methods are available: automatically Serial Enable load one of two preset values, parallel load from port A, and serial load. FS0/SD Flag Offset 0/ When serial load is selected for flag Offset register programming, FS1/ SEN is used as an enable synchronous to the LOW-to- Serial Data 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 O IR is s ynchronized to the LOW-to-HIGH transition of CLKA. When IR is LOW, the FIFO is full and writes to its array are Flag 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 I A HIGH level chooses a mailbox register for a port-A read or write operation. Select MBB Port-B Mailbox I A HIGH level chooses a mailbox register for a port-B read or write operation. When the B0-B35 outputs are act ive, a HIGH Select level on MBB selects data from the mail1 register for output and a LOW level selects FIFO data for output. MBF1 Mail1 Register 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 Flag LOW-to-HIGH transition of CLKB when a port-B readis selected and MBB is HIGH. MBF1 is set HIGH by a reset. MBF2 Mail2 Register 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 Flag 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 O OR is synchronized to the LOW-to-HIGH transition of CLKB. When OR is LOW, the FIFO is empty and reads are disabled. Flag 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 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 Mark 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 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 Mode selects the data for the beginning 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/RA Port-A Write/ I A HIGH selects a write operation and a LOW selects a read operation on port A for a LOW-to-HIGH transition of CLKA. The Read Select A0-A35 outputs are in the high-impedance state when W/RA is HIGH. W/RB Port-B Write/ I A LOW selects a write operation and a HIGH selects a read operation on port B for a LOW-to-HIGH transition of CLKB. The Read Select B0-B35 outputs are in the high-impedance state when W/RB is LOW.

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 IDT723631 IDT723641 IDT723651 Commercial t A = 15 ns Parameter Test Conditions Min. Typ. (1) Max. Unit VOH VCC = 4.5V, I OH = –4 mA 2.4 — — V VOL VCC = 4.5V, I OL = 8 mA — — 0.5 V ILI VCC = 5.5V, V I = VCC or 0 — — ±5 μA ILO VCC = 5.5V, V O = VCC or 0 — — ±5 μA ICC VCC = 5.5V, V I = VCC –0.2V or 0 — — 400 μA ΔICC(2,3) VCC = 5.5V, One Input at 3.4V, CSA = VIH A0-A35 — 0 — mA Other Inputs at VCC or GND CSB = VIH B0-B35 — 0 — CSA = VIL A0-A35 — — 1 CSB = VIL B0-35 — — 1 All Other Inputs — — 1 CIN VI = 0, f = 1 MHz — 4 — pF COUT VO = 0, f = 1 MHZ — 8 — pF ABSOLUTE MAXIMUM RATINGS OVER OPERATING FREE-AIR TEMPERATURE RANGE (UNLESS OTHERWISE NOTED)(2) Symbol Rating Commercial Unit VCC Supply Voltage Range –0.5 to 7 V VI(2) Input Voltage Range –0.5 to VCC+0.5 V VO(2) Output Voltage Range –0.5 to VCC+0.5 V IIK Input Clamp Current, (VI < 0 or VI > VCC) ±20 mA IOK Output Clamp Current, (VO = < 0 or VO > VCC) ±50 mA IOUT Continuous Output Current, (VO = 0 to VCC) ±50 mA ICC Continuous Current Through VCC or GND ±400 mA TSTG Storage Temperature Range –65 to 150 °C ELECTRICAL CHARACTERISTICS OVER RECOMMENDED OPERATING FREE-AIR TEMPERATURE RANGE (UNLESS OTHERWISE NOTED) NOTES: 1. All typical values are at V CC = 5V, T A = 25 °C. 2. This is the supply current when each input is at least one of the specified TTL voltage levels rather than 0V or V CC. 3. For additional I CC information, see the following page. NOTES: 1. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress rati ngs only and functional operation of the device at these or any other conditions beyond those indicated under "Recommended Operating Conditions" is not implied. Exposur e 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 — V VIL LOW-Level Input Voltage — 0.8 V IOH HIGH-Level Output Current — –4 mA IOL LOW-Level Output Current — 8 mA TA Operating Free-air Temperature 0 70 °C RECOMMENDED OPERATING CONDITIONS

Figure 1. Typical Characteristics: Supply vs Clock Frequency inputs driven by TTL HIGH levels are known, the power dissipation can be calculated with the equation below.

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 AC ELECTRICAL CHARACTERISTICS OVER RECOMMENDED RANGES OF SUPPLY VOLTAGE AND OPERATING FREE-AIR TEMPERATURE (Commercial: VCC = 5.0V ± 10%, TA = 0°C to +70°C Commercial IDT723631L15 IDT723641L15 IDT723651L15 Symbol Parameter Min. Max. Unit fS Clock Frequency, CLKA or CLKB – 66.7 MHz tCLK Clock Cycle Time, CLKA or CLKB 15 – ns tCLKH Pulse Duration, CLKA or CLKB HIGH 6 – ns tCLKL Pulse Duration, CLKA or CLKB LOW 6 – ns tDS Setup Time, A0-A35 before CLKA↑and B0-B35 before CLKB↑ 5– n s tENS1 Setup Time, ENA to CLKA↑; ENB to CLKB↑ 5– n s tENS2 Setup Time, CSA, W/RA, and MBA to CLKA↑; CSB, W/RB and MBB to CLKB↑ 7– n s tRMS Setup Time, RTM and RFM to CLKB↑ 6– n s tRSTS Setup Time, RST LOW before CLKA↑ or CLKB↑(1) 5– n s tFSS Setup Time, FS0 and FS1 before RST HIGH 9 – ns tSDS(2) Setup Time, FS0/SD before CLKA↑ 5– n s tSENS(2) Setup Time, FS1/SEN before CLKA↑ 5– n s tDH Hold Time, A0-A35 after CLKA↑ and B0-B35 after CLKB↑ 0– n s tENH1 Hold Time, ENA after CLKA↑; ENB after CLKB↑ 0– n s tENH2 Hold Time, CSA, W/RA, and MBA after CLKA↑; CSB, W/RB and MBB after CLKB↑ 0– n s tRMH Hold Time, RTM and RFM after CLKB↑ 0– n s tRSTH Hold Time, RST LOW after CLKA↑ or CLKB↑(1) 5– n s tFSH Hold Time, FS0 and FS1 after RST HIGH 0 – ns tSPH(2) Hold Time, FS1/SEN HIGH after RST HIGH 0 – ns tSDH(2) Hold Time, FS0/SD after CLKA↑ 0– n s tSENH(2) Hold Time, FS1/SEN after CLKA↑ 0– n s tSKEW1(3) Skew Time, between CLKA↑ and CLKB↑ for OR and IR 9 – ns tSKEW2(3) Skew Time, between CLKA↑and CLKB↑ for AE and AF 12 – ns 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 timing constraint for proper device operation and is only included to illustrate the timing relationship b etween CLKA cycle and CLKB cycle. 4. Design simulated but not tested (typical values).

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 Commercial IDT723631L15 IDT723641L15 IDT723651L15 Symbol Parameter Min. Max. Unit fS Clock Frequency, CLKA or CLKB – 66.7 MHz tA Access Time, CLKB ↑ to B0-B35 3 11 ns tPIR Propagation Delay Time, CLKA↑ to IR 1 8 ns tPOR Propagation Delay Time, CLKB↑ to OR 1 8 ns tPAE Propagation Delay Time, CLKB↑ to AE 18 n s tPAF Propagation Delay Time, CLKA↑ to AF 18 n s tPMF Propagation Delay Time, CLKA↑ to MBF1 LOW or MBF2 08 n s HIGH and CLKB ↑ to MBF2 LOW or MBF1 HIGH tPMR Propagation Delay Time, CLKA↑ to B0-B35(1) and 3 13.5 ns CLKB↑ to A0-A35 (2) tMDV Propagation Delay Time, MBB to B0-B35 Valid 3 13 ns tRSF Propagation Delay Time, RST LOW to AE LOW and AF HIGH 1 15 ns tEN Enable Time, CSA and W/RA LOW to A0-A35 Active and 2 12 ns CSB LOW and W/RB HIGH to B0-B35 Active tDIS Disable Time, CSA or W/RA HIGH to A0-A35 at high-impedance 1 8 ns and CSB HIGH or W/RB LOW to B0-B35 at high-impedance 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. AC ELECTRICAL CHARACTERISTICS (Commercial: VCC = 5.0V ± 10%, TA = 0°C to +70°C

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 When the option to program the Offset registers serially is chosen, the Input Ready (IR) flag remains LOW until all register 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. Timing diagrams for the serial load of offset registers can be found in Figure 4. 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/RA). The A0-A35 outputs are in the high-impedance state when either CSA or W/ RA is HIGH. The A0-A35 outputs are active when both CSA and W/ RA 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/RA, the port-A Enable (ENA), and the Input Ready (IR) flag are HIGH (see Table 2). Writes to the FIFO are independent of any concur- rent FIFO read (see Figure 5). The port-B control signals are identical to those of port-A with the excep- tion that the port-B Write/Read select ( W/RB) is the inverse of the port-A Write/Read select (W/RA). 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 (see Figure 6). 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 op- erations and are not related to high-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 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 OR 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 synchronized to its port Clock through at least two flip-flop stages. This is done to improve the flags’ reliability by reducing the probability of metastable events on their outputs 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 OFFSET PROGRAMMING Two registers in these devices 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. For relevant Reset and Preset value loading timing diagrams, see Figure 2. 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 programmed from 1 to 508 (IDT723631), 1 to 1,020 (IDT723641), and 1 to 2,044 (IDT723651). After both Offset registers are programmed from port A, subsequent FIFO writes store data in the SRAM. Timing diagrams for the parallel load of offset registers can be found in Figure 3. 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 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. There are 18-, 20-, or 22-bit writes needed to complete the programming for the IDT723631, IDT723641, or IDT723651, respectively. The first-bit write stores the most significant bit of the Y regis- ter, 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 1,020 (IDT723641), or 1 to 2,044 (IDT723651). NOTE: 1. X register holds the offset for AE; Y register holds the offset for AF. FS1 FS0 RST X and Y Registers (1) HH ↑ Serial Load HL ↑ 64 LH ↑ 8 LL ↑ Parallel Load From Port A TABLE 1 — FLAG PROGRAMMING

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 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 OR flag is HIGH, new data is present in the FIFO output register. When the OR flag is LOW, the previ- ous 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 OR 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 OR 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 OR flag of the FIFO remains LOW until the third LOW-to-HIGH transition of CLKB occurs, simultaneously forcing the OR flag HIGH and shifting the word to the FIFO output register. A LOW-to-HIGH transition on CLKB begins the first synchronization cycle of a write if the clock transition occurs at time tSKEW1 or greater after the write. Otherwise, the subsequent CLKB cycle may be the first synchroniza- tion cycle (see Figure 7). 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 IR flag is HIGH, a memory location is free in the SRAM to write new data. No memory locations are free when the IR 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 IR 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 IR 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 synchronization cycle of a read if the clock transition occurs at time tSKEW1 or greater after the read. Otherwise, the subsequent CLKA cycle may be the first synchroniza- tion cycle (see Figure 8). ALMOST-EMPTY FLAG (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 AE 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, pro- TABLE 3 — PORT-B ENABLE FUNCTION TABLE CSB W /RB ENB MBB CLKB B0-A35 Outputs Port Functions HXXXX I n High-Impedance State None L L L X X In High-Impedance State None LL HL ↑ In High-Impedance State None LL H H ↑ 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 2 — PORT-A ENABLE FUNCTION TABLE CSA W/RA ENA MBA CLKA A0-A35 Outputs Port Functions HXXXX I n 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 LLLLX Active, Mail2 Register None LL HL ↑ Active, Mail2 Register None L L L H X Active, Mail2 Register None LL H H ↑ Active, Mail2 Register Mail2 Read (Set MBF2 HIGH)

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 LOW-to-HIGH transition of CLKA begins the first synchronization cycle if it occurs at time tSKEW2 or greater after the read that reduces the number of words in memory to [512/1,024/2,048-(Y+1)]. Otherwise, the subsequent CLKA cycle may be the first synchronization cycle (see Figure 10). SYNCHRONOUS RETRANSMIT The synchronous retransmit feature of these devices allow 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 ongoing 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 memory 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), (1,024 - Y), or (2,048 - Y) words after the first retransmit word for the IDT723631, IDT723641, or IDT723651, respectively. The IR flag is set LOW by the 512th, 1,024th, or 2,048th write after the first retransmit word for the IDT723631, IDT723641, or IDT723651, respectively. 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. 3. Data in the output register does not count as a "word i n FIFO memory". Since in FWFT mode, the first words written to an emp ty FIFO goes unrequested to the output register (no read operation necessary), it is not included in the memory count. TABLE 4 — FIFO FLAG OPERATION grammed from port A, or programmed serially (see Almost-Empty flag and Almost-Full flag offset programming above). The AE 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 AE flag to reflect the new level of fill; therefore, the AE 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) level. An AE 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 9). ALMOST-FULL FLAG (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 AF 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 AF flag is LOW when the number of words in the FIFO is greater than or equal to (512-Y), (1,024-Y), OR (2,048-Y) for the IDT723631, IDT723641, or IDT723651, respectively. The AF flag is HIGH when the number of words in the FIFO is less than or equal to [512-(Y+1)], [1,024-(Y+1)], or [2,048-(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 AF flag to reflect the new level of fill. Therefore, the AF flag of a FIFO containing [512/1,024/2,048-(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 [512/1,024/2,048-(Y+1)]. An AF 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 [512/1,024/2,048-(Y+1)]. A Number of Words in the FIFO(1,2,3) Synchronized Synchronized to CLKB to CLKA IDT723631 IDT723641 IDT723651 OR AE AF IR

000 L L H H

1 to X 1 to X 1 to X H L H H (512-Y) to 511 (1,024-Y) to 1,023 (2,048-Y) to 2,047 H H L H 512 1,024 2,048 H H L L

IDT723631/723641/723651 CMOS SyncFIFO™ 512 x 36, 1,024 x 36 and 2,048 x 36 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 12). 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 synchronizing 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 13). 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/ RA, 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/RA, 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. Mail Register and Mail Register Flag timing can be found in Figure 15 and 16.

Figure 7. OR Flag Timing and First Data Word Fall Through when the FIFO is Empty occur one CLKB cycle later than shown.

  1. Includes probe and jig capacitance

Figure 18. Load Circuit and Voltage Waveforms

3 VtPLZ

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ORDERING INFORMATION

Thin Quad Flat Pack (TQFP, PNG120) Commercial (0°C to +70°C) Low Power 723631 723641 723651 3023 drw22 Clock Cycle Time (tCLK) Speed in NanosecondsCommercial Only PF BLANK L 512 x 36 SyncFIFO 1,024 x 36 SyncFIFO 2,048 x 36 SyncFIFO GreenG XXXXXX Device Type X XX X X Power Speed Package Process/ Temperature Range X X BLANK Tube or Tray Tape and Reel DATASHEET DOCUMENT HISTORY 07/25/2001 pgs. 1, 5, 7, 8 and 21. 02/11/2009 pgs. 1 and 21. 03/24/2014 pgs. 1, 2, 4, 6, 7 and 20.