SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 D D D D D Member of the Texas Instruments Widebus Family Independent Asynchronous Inputs and Outputs Read and Write Operations Can Be Synchronized to Independent System Clocks Programmable Almost-Full/Almost-Empty Flag Pin-to-Pin Compatible With SN74ACT7882, SN74ACT7884, and SN74ACT7811 D D D D D Input-Ready, Output-Ready, and Half-Full Flags Expandable in Word Width and/or Word Depth Fast Access Times of 11 ns With a 50-pF Load High Output Drive for Direct Bus Interface Package Options Include 68-Pin Plastic Leaded Chip Carrrier (FN) or 80-Pin Shrink Quad Flat (PN) Package D15 D16 D17 GND RDCLK RDEN1 RDEN2 OE RESET VCC GND OR VCC Q17 Q16 GND Q15 FN PACKAGE (TOP VIEW) 9 10 8 7 6 5 4 3 2 1 68 67 66 65 64 63 62 61 60 11 59 12 58 13 57 14 56 15 55 16 54 17 53 18 52 19 51 20 50 21 49 22 48 23 47 24 46 25 45 VCC Q14 Q13 GND Q12 Q11 VCC Q10 Q9 GND Q8 Q7 VCC Q6 Q5 GND Q4 Q0 Q1 GND Q2 Q3 V CC AF/AE GND IR HF V CC WRTEN2 V CC 26 44 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 DAF GND WRTCLK WRTEN1 D14 D13 D12 D11 D10 D9 VCC D8 GND D7 D6 D5 D4 D3 D2 D1 D0 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. Widebus is a trademark of Texas Instruments Incorporated. Copyright 1998, Texas Instruments Incorporated PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 1 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 GND GND Q4 Q14 Q13 GND GND Q12 Q11 VCC Q10 Q9 GND Q8 Q7 VCC Q6 Q5 Q15 VCC PN PACKAGE (TOP VIEW) 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 2 59 3 58 4 57 5 56 6 55 7 54 8 53 9 52 10 51 11 50 12 49 13 48 14 47 15 46 16 45 17 44 18 43 19 42 20 41 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 VCC VCC NC Q3 Q2 GND Q1 Q0 VCC HF IR GND GND AF/AE VCC WRTEN2 WRTEN1 WRTCLK GND NC D8 GND D7 D6 D5 D4 D3 D2 D1 D0 DAF NC 1 NC D14 D13 D12 D11 D10 D9 V CC NC GND GND Q16 Q17 VCC OR GND VCC RESET OE RDEN2 RDEN1 RDCLK GND D17 D16 D15 NC NC NC – No internal connection description A FIFO memory is a storage device that allows data to be written into and read from its array at independent data rates. The SN74ACT7881 is organized as 1024 × 18 bits. The SN74ACT7881 processes data at rates up to 67 MHz and access times of 11 ns in a bit-parallel format. Data outputs are noninverting with respect to the data inputs. Expansion is accomplished easily in both word width and word depth. The SN74ACT7881 has normal input-bus to output-bus asynchronous operation. The special enable circuitry adds the ability to synchronize independent reads and writes to their respective system clocks. The SN74ACT7881 is characterized for operation from 0°C to 70°C. 2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 logic symbol† RESET WRTCLK WRTEN1 WRTEN2 RDCLK RDEN1 OE RDEN2 DAF D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 1 Φ FIFO SN74ACT7881 – 1024 × 18 RESET 29 WRTCLK 30 & 31 5 RDCLK 4 2 INPUT RDY WRTEN ALMOST FULL/EMPTY OUTPUT RDY & EN1 HALF FULL 35 36 33 66 IR HF AF/AE OR RDEN 3 27 26 DEFINE ALMOST FULL 0 0 38 25 39 24 41 23 42 22 44 21 46 20 47 19 49 17 50 Data 15 Data 1 52 14 53 13 55 12 56 11 58 10 59 9 61 8 63 7 64 17 17 Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 † This symbol is in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12. Pin numbers shown are for the FN package. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 3 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 functional block diagram OE D0–D17 RDCLK RDEN1 RDEN2 Synchronous Read Control Location 1 Location 2 Read Pointer RAM 1024 × 18 WRTCLK WRTEN1 WRTEN2 Synchronous Write Control Write Pointer • • Register Reset Logic Q0–Q17 RESET OR StatusFlag Logic DAF IR HF AF/AE 4 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 Terminal Functions TERMINAL† NAME NO. I/O DESCRIPTION Almost-full/almost-empty flag. The AF/AE boundary is defined by the AF/AE offset value (X). This value can be programmed during reset, or the default value of 256 can be used. AF/AE is high when the FIFO contains (X + 1) or fewer words or (1025 – X) or more words. AF/AE is low when the FIFO contains between (X + 2) and (1024 – X) words. Programming procedure for AF/AE – The AF/AE flag is programmed during each reset cycle. The AF/AE offset value (X) is either a user-defined value or the default of X = 256. Instructions to program AF/AE using both methods are as follows: AF/AE 33 O User-defined X Step 1: Take DAF from high to low. Step 2: If RESET is not already low, take RESET low. Step 3: With DAF held low, take RESET high. This defines the AF/AE using X. Step 4: To retain the current offset for the next reset, keep DAF low. Default X To redefine AF/AE using the default value of X = 256, hold DAF high during the reset cycle. 27 I Define-almost-full. The high-to-low transition of DAF stores the binary value of data inputs as the AF/AE offset value (X). With DAF held low, a low pulse on RESET defines the AF/AE flag using X. 26–19, 17, 15–7 I Data inputs for 18-bit-wide data to be stored in the memory. A high-to-low transition of DAF captures data for the AF/AE offset (X) from D8–D0. HF 36 O Half-full flag. HF is high when the FIFO contains 512 or more words and is low when the number of words in memory is less than half the depth of the FIFO. IR 35 O Input-ready flag. IR is high when the FIFO is not full and low when the device is full. During reset, IR is driven low on the rising edge of the second WRTCLK pulse. IR is then driven high on the rising edge of the second WRTCLK pulse after RESET goes high. After the FIFO is filled and IR is driven low, IR is driven high on the second WRTCLK pulse after the first valid read. OE 2 I Output enable. The Q0–Q17 outputs are in the high-impedance state when OE is low. OE must be high before the rising edge of RDCLK to read a word from memory. 66 O Output-ready flag. OR is high when the FIFO is not empty and low when the FIFO is empty. During reset, OR is set low on the rising edge of the third RDCLK pulse. OR is set high on the rising edge of the third RDCLK pulse to occur after the first word is written into the FIFO. OR is set low on the rising edge of the first RDCLK pulse after the last word is read. Q0–Q17 38–39, 41–42, 44, 46–47, 49–50, 52–53, 55–56, 58–59, 61, 63–64 O Data outputs. The first data word to be loaded into the FIFO is moved to Q0–Q17 on the rising edge of the third RDCLK pulse to occur after the first valid write. RDEN1 and RDEN2 do not affect this operation. Following data is unloaded on the rising edge of RDCLK when RDEN1, RDEN2, OE, and OR are high. RDCLK 5 I Read clock. Data is read out of memory on the low-to-high transition of RDCLK if OR, OE, RDEN1, and RDEN2 are high. RDCLK is a free-running clock and functions as the synchronizing clock for all data transfers out of the FIFO. OR also is driven synchronously with respect to the RDCLK signal. RDEN1 RDEN2 4 3 I Read enable. RDEN1 and RDEN2 must be high before a rising edge on RDCLK to read a word out of memory. RDEN1 and RDEN2 are not used to read the first word stored in memory. DAF D0–D17 OR RESET 1 I Reset. A reset is accomplished by taking RESET low and generating a minimum of four RDCLK and WRTCLK cycles. This ensures that the internal read and write pointers are reset and that OR, HF, and IR are low, and AF/AE is high. The FIFO must be reset upon power up. With DAF at a low level, a low pulse on RESET defines AF/AE using the AF/AE offset value (X), where X is the value previously stored. With DAF at a high level, a low-level pulse on RESET defines the AF/AE flag using the default value of X = 256. WRTCLK 29 I Write clock. Data is written into memory on a low-to-high transition of WRTCLK if IR, WRTEN1, and WRTEN2 are high. WRTCLK is a free-running clock and functions as the synchronizing clock for all data transfers into the FIFO. IR also is driven synchronously with respect to WRTCLK. WRTEN1 WRTEN2 30 31 I Write enable. WRTEN1 and WRTEN2 must be high before a rising edge on WRTCLK for a word to be written into memory. WRTEN1 and WRTEN2 do not affect the storage of the AF/AE offset value (X). † Terminals listed are for the FN package. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 5 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 ÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ RESET Don’t Care DAF 1 WRTCLK WRTEN1 Don’t Care WRTEN2 Don’t Care D0–D17 Don’t Care 1 RDCLK 2 3 Don’t Care RDEN2 Don’t Care 1 2 X† 2 RDEN1 4 3 4 OE Invalid Q0–Q17 ÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎ Invalid OR AF/AE Invalid HF Invalid IR Invalid Store the Value of Data as X Define the AF/AE Flag Using the Programmed Value of X † X is the binary value on D8–D0. Figure 1. Reset Cycle: Define AF/AE Flag Using a Programmed Value of X 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 RESET Don’t Care DAF 1 WRTCLK WRTEN1 WRTEN2 D0–D17 RDCLK RDEN1 RDEN2 OE Q0–Q17 OR AF/AE HF IR 2 3 4 1 2 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎ Don’t Care Don’t Care Don’t Care 1 2 3 4 Don’t Care Don’t Care Invalid Invalid Invalid Invalid Define the AF/AE Flag Using the Default Value of X = 256 Figure 2. Reset Cycle: Define AF/AE Flag Using the Default Value of X = 256 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 7 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ RESET Don’t Care DAF WRTCLK WRTEN1 WRTEN2 ÎÎÎ ÎÎ ÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎ ÎÎÎ ÎÎ ÎÎÎ ÎÎ ÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎ ÎÎÎ ÎÎ D0–D17 RDCLK W1 W2 W3 W4 1 2 3 W(X+2) A B RDEN1 RDEN2 ÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ OE Q0–Q17 Invalid W1 OR AF/AE HF IR DATA-WORD NUMBERS FOR FLAG TRANSITIONS TRANSITION WORD A B C W513 W(1025 – X) W1025 Figure 3. Write Cycle 8 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 C SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ RESET Don’t Care DAF WRTCLK 1 2 WRTEN1 ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ WRTEN2 D0–D17 Don’t Care F RDCLK RDEN1 RDEN2 OE Q0–Q17 W1 W1 W2 W3 W(X+1) W(X+2) A B C D E F OR AF/AE HF IR DATA-WORD NUMBERS FOR FLAG TRANSITIONS TRANSITION WORD A B C D E F W513 W514 W(1024 – X) W(1025 – X) W1024 W1025 Figure 4. Read Cycle POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 9 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 absolute maximum ratings over operating free-air temperature range† Supply voltage range, VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.5 V to 7 V Input voltage range, VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.5 V to 7 V Voltage range applied to a disabled 3-state output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.5 V to 5.5 V Package thermal impedance, θJA (see Note 1): FN package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39°C/W PN package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62°C/W Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –65°C to 150°C † 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. NOTE 1: The package thermal impedance is calculated in accordance with JESD 51. recommended operating conditions MIN MAX 4.5 5.5 UNIT VCC VIH Supply voltage VIL IOH Low-level input voltage 0.8 V High-level output current –8 mA IOL TA Low-level output current 16 mA 70 °C High-level input voltage 2 Operating free-air temperature 0 V V electrical characteristics over recommended operating free-air temperature range (unless otherwise noted) PARAMETER TEST CONDITIONS VOH VOL VCC = 4.5 V, VCC = 4.5 V, IOH = –8 mA IOL = 16 mA II IOZ VCC = 5.5 V, VCC = 5.5 V, VI = VCC or 0 VO = VCC or 0 ICC§ VI = VCC – 0.2 V or 0 One input at 3.4 V, Other inputs at VCC or GND Ci Co VI = 0, VO = 0, POST OFFICE BOX 655303 TYP‡ MAX 2.4 UNIT V 0.5 V ±5 µA ±5 µA 400 µA 1.2 mA f = 1 MHz 4 pF f = 1 MHz 8 pF ‡ All typical values are at VCC = 5 V, TA = 25°C. § ICC is tested with outputs open. 10 MIN • DALLAS, TEXAS 75265 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 timing requirements over recommended ranges of supply voltage and operating free-air temperature (see Figures 1 through 5) ’ACT7881-15 MIN fclock tw tsu th MAX Clock frequency Pulse duration Setup time Hold time ’ACT7881-20 MIN 67 MAX ’ACT7881-30 MIN 50 33.4 WRTCLK high 5 7 8.5 WRTCLK low 7 7 11 RDCLK high 5 7 8.5 RDCLK low 7 7 11 DAF high 7 7 10 D0–D17 before WRTCLK↑ 5 5 5 WRTEN1, WRTEN2 high before WRTCLK↑ 4 5 5 OE, RDEN1, RDEN2 high before RDCLK↑ 4 5 5 Reset: RESET low before first WRTCLK↑ and RDCLK↑† 5 6 7 Define AF/AE: D0–D8 before DAF↓ 3 5 5 Define AF/AE: DAF↓ before RESET↑ 3 6 7 Define AF/AE (default): DAF high before RESET↑ 4 5 5 D0–D17 after WRTCLK↑ 0 0 0 WRTEN1, WRTEN2 high after WRTCLK↑ 0 0 0 OE, RDEN1, RDEN2 high after RDCLK↑ 0 0 0 Reset: RESET low after fourth WRTCLK↑ and RDCLK↑† 0 0 0 Define AF/AE: D0–D8 after DAF↓ 0 0 0 Define AF/AE: DAF low after RESET↑ 0 0 0 0 0 0 Define AF/AE (default): DAF high after RESET↑ † To permit the clock pulse to be utilized for reset purposes MAX UNIT MHz ns ns ns switching characteristics over recommended ranges of supply voltage and operating free-air temperature, CL = 50 pF (unless otherwise noted) (see Figure 5) PARAMETER FROM (INPUT) fmax WRTCLK or RDCLK tpd tpd‡ RDCLK↑ Any Q tpd d TO (OUTPUT) MIN MAX 67 ’ACT7881-20 MIN MAX 50 ’ACT7881-30 MIN MAX 33.4 3 12 3 13 3 18 RDCLK↑ Any Q IR 2 8 2 9.5 2 12 RDCLK↑ OR 2 8 2 9.5 2 12 6 17 6 19 6 22 6 17 6 19 6 22 WRTCLK↑ AF/AE UNIT MHz WRTCLK↑ RDCLK↑ tPLH tPHL ’ACT7881-15 ns ns ns WRTCLK↑ HF 6 14 6 17 6 21 ns RDCLK↑ HF 6 14 6 17 6 21 ns tPLH RESET↓ AF/AE 3 12 3 17 3 21 ns tPHL RESET↓ HF 3 14 3 19 3 23 ns ten OE Any Q 2 9 2 11 2 11 ns tdis OE Any Q 2 10 2 14 2 14 ns ‡ This parameter is measured with CL = 30 pF (see Figure 6). POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 11 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 operating characteristics, VCC = 5 V, TA = 25°C PARAMETER Cpd TEST CONDITIONS Power dissipation capacitance per 1K bits CL = 50 pF, TYP f = 5 MHz 65 UNIT pF PARAMETER MEASUREMENT INFORMATION 7V PARAMETER ten S1 500 Ω From Output Under Test tdis Test Point tpd CL = 50 pF (see Note A) S1 tPZH tPZL tPHZ tPLZ tPLH tPHL Open Closed Open Closed Open Open 500 Ω tw LOAD CIRCUIT 3V Input 0V 1.5 V VOLTAGE WAVEFORMS PULSE DURATION 0V tsu th 3V Data Input 1.5 V 1.5 V 0V 3V Output Control tPZL 3V 1.5 V 1.5 V 1.5 V 0V tPLH 1.5 V 1.5 V tPZH 1.5 V VOL Output Waveform 2 S1 at Open VOL + 0.3 V 1.5 V VOH VOH – 0.3 V ≈0V NOTE A: CL includes probe and jig capacitance. Figure 5. Load Circuit and Voltage Waveforms • DALLAS, TEXAS 75265 VOL tPHZ VOLTAGE WAVEFORMS ENABLE AND DISABLE TIMES VOLTAGE WAVEFORMS PROPAGATION DELAY TIMES POST OFFICE BOX 655303 tPLZ ≈ 3.5 V Output Waveform 1 S1 at 7 V tPHL VOH 12 1.5 V 0V VOLTAGE WAVEFORMS SETUP AND HOLD TIMES Output 1.5 V 3V Timing Input Input 1.5 V SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 TYPICAL CHARACTERISTICS PROPAGATION DELAY TIME vs LOAD CAPACITANCE 18 VCC = 5 V RL = 500 Ω TA = 25°C t pd – Propagation Delay Time – ns 17 16 15 14 13 12 11 10 0 50 100 150 200 250 300 CL – Load Capacitance – pF Figure 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 13 SN74ACT7881 1024 × 18 CLOCKED FIRST-IN, FIRST-OUT MEMORY SCAS227E – FEBRUARY 1993 – REVISED APRIL 1998 APPLICATION INFORMATION expanding the SN74ACT7881 The SN74ACT7881 is expandable in both word width and word depth. Word-depth expansion is accomplished by connecting the devices in series such that data flows through each device in the chain. Figure 8 shows two SN74ACT7881 devices configured for word-depth expansion. The common clock between the devices can be tied to either the write clock (WRTCLK) of the first device or the read clock (RDCLK) of the last device. The output-ready (OR) flag of the previous device and the input-ready (IR) flag of the next device maintain data flow to the last device in the chain whenever space is available. Figure 9 shows two SN74ACT7881 devices in word-width expansion. Word-width expansion is accomplished by simply connecting all common control signals between the devices and creating composite IR and OR signals. The almost-full/almost-empty (AF/AE) flag and half-full (HF) flag can be sampled from any one device. Word-depth expansion and word-width expansion can be used together. CLK SN74ACT7881 SN74ACT7881 WRTCLK WRTEN1 WRTCLK WRTEN1 RDCLK OR WRTCLK WRTEN1 RDCLK RDEN1 RDCLK RDEN1 WRTEN2 IR WRTEN2 IR RDEN1 RDEN2 WRTEN2 IR RDEN2 OR RDEN2 OR OE D0–D17 D0–D17 OE 5V D0–D17 Q0–Q17 Q0–Q17 OE Q0–Q17 Figure 7. Word-Depth Expansion: 2048/4096/8192 × 18 Bits, N = 2 SN74ACT7881 WRTCLK WRTEN WRTCLK WRTEN1 RDCLK RDEN1 WRTEN2 IR RDEN2 OR OE D18–D35 IR D0–D17 Q0–Q17 SN74ACT7881 RDCLK RDEN OE Q18–Q35 OR WRTCLK WRTEN1 RDCLK RDEN1 WRTEN2 IR RDEN2 OR OE D0–D17 D0–D17 Q0–Q17 Figure 8. Word-Width Expansion: 1024 × 36 Bits 14 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 Q0–Q17 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. 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