IDT7025L25F

HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM Integrated Device Technology, Inc. IDT7025S/L FEATURES: • True Dual-Ported memory cells which allow simultaneous access of the same memory location • High-speed access — Military: 20/25/35/55/70ns (max.) — Commercial: 15/17/20/25/35/55ns (max.) • Low-power operation — IDT7025S Active: 750mW (typ.) Standby: 5mW (typ.) — IDT7025L Active: 750mW (typ.) Standby: 1mW (typ.) • Separate upper-byte and lower-byte control for multiplexed bus compatibility • IDT7025 easily expands data bus width to 32 bits or more using the Master/Slave select when cascading more than one device • M/S = H for BUSY output flag on Master M/S = L for BUSY input on Slave • Busy and Interrupt Flags • On-chip port arbitration logic • Full on-chip hardware support of semaphore signaling between ports • Devices are capable of withstanding greater than 2001V electrostatic discharge • Fully asynchronous operation from either port • Battery backup operation—2V data retention • TTL-compatible, single 5V (±10%) power supply • Available in 84-pin PGA, 84-pin quad flatpack, 84-pin PLCC, and 100-pin Thin Quad Plastic Flatpack • Industrial temperature range (–40°C to +85°C) is available, tested to military electrical specifications FUNCTIONAL BLOCK DIAGRAM R/ WL R/ WR UBL UBR LBL CEL OEL LBR CE R OE R I/O8L-I/O 15L I/O Control I/O0L-I/O 7L I/O Control I/O8R-I/O 15R I/O0R-I/O 7R BUSY (1,2) L BUSYR Address Decoder 13 (1,2) A12L A0L MEMORY ARRAY 13 Address Decoder A12R A0R NOTES: 1. (MASTER): BUSY is output; (SLAVE): BUSY is input. 2. BUSY outputs and INT outputs are non-tri-stated push-pull. CEL OEL R/ WL SEML (2) INTL ARBITRATION INTERRUPT SEMAPHORE LOGIC CER OER R/ WR SEM R INTR(2) 2683 drw 01 M/ S The IDT logo is a registered trademark of Integrated Device Technology Inc. MILITARY AND COMMERCIAL TEMPERATURE RANGES ©1996 Integrated Device Technology, Inc. For latest information contact IDT’s web site at www.idt.com or fax-on-demand at 408-492-8391. OCTOBER 1996 DSC 2683/6 6.16 1 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES DESCRIPTION: The IDT7025 is a high-speed 8K x 16 Dual-Port Static RAM. The IDT7025 is designed to be used as a stand-alone 128K-bit Dual-Port RAM or as a combination MASTER/ SLAVE Dual-Port RAM for 32-bit or more word systems. Using the IDT MASTER/SLAVE Dual-Port RAM approach in 32-bit or wider memory system applications results in fullspeed, error-free operation without the need for additional discrete logic. This device provides two independent ports with separate control, address, and I/O pins that permit independent, asynchronous access for reads or writes to any location in memory. An automatic power down feature controlled by Chip Enable ( CE ) permits the on-chip circuitry of each port to enter a very low standby power mode. Fabricated using IDT’s CMOS high-performance technology, these devices typically operate on only 750mW of power. Low-power (L) versions offer battery backup data retention capability with typical power consumption of 500µW from a 2V battery. The IDT7025 is packaged in a ceramic 84-pin PGA, an 84pin quad flatpack, an 84-pin PLCC, and a 100-pin TQFP. Military grade product is manufactured in compliance with the latest revision of MIL-STD-883, Class B, making it ideally suited to military temperature applications demanding the highest level of performance and reliability. PIN CONFIGURATIONS (1,2) VCC R/ L SEML I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L I/O0L INDEX I/O8L I/O9L I/O10L I/O11L I/O12L I/O13L GND I/O14L I/O15L VCC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R I/O7R I/O8R 11 10 9 8 7 6 5 4 3 2 1 84 83 82 81 80 79 78 77 76 75 74 12 73 13 72 14 71 15 70 16 69 17 68 18 IDT7025 67 19 J84-1 F84-2 66 20 65 21 84-PIN PLCC/ FLATPACK 64 22 TOP VIEW(3) 63 23 62 24 61 25 60 26 59 27 58 28 57 29 56 30 55 31 54 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R R/ R GND A12R A11R A12L A11L A10L A9L A8L OEL UBL LBL CEL W A7L A6L A5L A4L A3L A2L A1L A0L INTL BUSYL GND M/S BUSYR INTR A0R A1R A2R A3R A4R A5R A6R 2683 drw 02 SEMR I/O9R A10R A9R A8R A7R OER UBR LBR CER W I/O9L I/O8L I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L I/O0L VCC R/ L SEML UBL LBL A12L A11L A10L A9L OEL CEL A8L Index W I/O7R I/O8R I/O9R I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R R/ R GND SEMR A12R A11R A10R A9R A8R A7R A6R A5R OER UBR LBR CER NOTES: 1. All VCC pins must be connected to power supply. 2. All GND pins must be connected to ground supply. 3. This text does not indicate orientation of the actual part-marking. N/C N/C N/C N/C I/O10L I/O11L I/O12L I/O13L GND I/O14L I/O15L VCC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R N/C N/C N/C N/C 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 1 75 2 74 3 73 4 72 5 71 6 70 7 69 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 68 A7L A6L 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 IDT7025 PN100-1 100-PIN TQFP TOP VIEW(3) N/C N/C N/C N/C A5L A4L A3L A2L A1L A0L INTL BUSYL GND M/S INTR BUSYR A0R A1R A2R A3R A4R N/C N/C N/C N/C 24 51 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 6.16 W 2683 drw 03 2 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES PIN CONFIGURATIONS (CONT'D) (1,2) 63 61 60 58 55 54 51 48 46 45 42 11 I/O7L 66 I/O5L 64 I/O4L 62 I/O2L 59 I/O0L 56 OEL 49 SEML 50 LBL 47 A11L 44 A10L 43 A7L 40 10 I/O10L 67 I/O8L 65 I/O6L I/O3L I/O1L 57 UBL 53 CEL 52 A12L A9L A8L 41 A5L 39 09 I/O11L 69 I/O9L 68 GND VCC R/ WL A6L 38 A4L 37 08 I/O13L 72 I/O12L 71 73 33 A3L 35 A2L 34 INTL 07 I/O15L 75 I/O14L 70 VCC 74 IDT7025 G84-3 84-PIN PGA TOP VIEW(3) BUSYL 32 A0L 31 36 06 I/O0R 76 GND 77 GND 78 GND 28 M/S 29 INTR A1L 30 05 I/O1R 79 I/O2R 80 VCC A0R BUSYR 27 26 04 I/O3R 81 I/O4R 83 7 11 12 A2R 23 A1R 25 03 I/O5R 82 1 I/O7R 2 5 GND 8 GND 10 SEMR 14 17 20 A5R 22 A3R 24 02 I/O6R 84 3 I/O9R I/O10R 4 I/O13R 6 I/O15R 9 R/ 15 WR UBR 13 A11R 16 A8R 18 A6R 19 A4R 21 01 I/O8R A I/O11R B I/O12R C I/O14R D OER E LBR F CER G A12R H A10R J A9R K A7R L 2683 drw 04 Index NOTES: 1. All VCC pins must be connected to power supply. 2. All GND pins must be connected to ground supply. 3. This text does not indicate orientation of the actual part-marking. PIN NAMES Left Port Right Port Names Chip Enable Read/Write Enable Output Enable Address Data Input/Output Semaphore Enable Upper Byte Select Lower Byte Select Interrupt Flag Busy Flag Master or Slave Select Power Ground 2683 tbl 01 CEL R/WL OEL A0L – A12L I/O0L – I/O15L CER R/WR OER A0R – A12R I/O0R – I/O15R RECOMMENDED OPERATING TEMPERATURE AND SUPPLY VOLTAGE Grade Military Commercial Ambient Temperature –55°C to +125°C 0°C to +70°C GND 0V 0V VCC 5.0V ± 10% 5.0V ± 10% 2683 tbl 02 SEML UBL LBL INTL BUSYL M/S VCC SEMR UBR LBR INTR BUSYR GND 6.16 3 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES TRUTH TABLE I – NON-CONTENTION READ/WRITE CONTROL Inputs(1) Outputs CE H X L L L L L L X R/W X X L L L H H H X OE X X X X X L L L H UB X H L H L L H L X LB X H H L L H L L X SEM H H H H H H H H X I/O8-15 High-Z High-Z DATAIN High-Z DATAIN DATAOUT High-Z High-Z I/O0-7 High-Z High-Z High-Z DATAIN DATAIN High-Z Both Bytes Deselected Mode Deselected: Power Down Write to Upper Byte Only Write to Lower Byte Only Write to Both Bytes Read Upper Byte Only DATAOUT Read Lower Byte Only High-Z Outputs Disabled 2683 tbl 03 DATAOUT DATAOUT Read Both Bytes NOTE: 1. A0L — A12L are not equal to A0R — A12R. TRUTH TABLE II – SEMAPHORE READ/WRITE CONTROL(1) Inputs Outputs CE H X H X L L R/W H H OE L L X X X X UB X H X H L X LB X H X H X L SEM L L L L L L I/O8-15 I/O0-7 Mode DATAOUT DATAOUT Read Semaphore Flag Data Out DATAOUT DATAOUT Read Semaphore Flag Data Out DATAIN DATAIN — — DATAIN DATAIN — — Write I/O0 into Semaphore Flag Write I/O0 into Semaphore Flag Not Allowed Not Allowed 2683 tbl 04 u u X X NOTE: 1. There are eight semaphore flags written to via I/O0 and read from I/O0 - I/O15. These eight semaphores are addressed by A0 - A2. ABSOLUTE MAXIMUM RATINGS(1) Symbol VTERM (2) Rating Commercial Military –0.5 to +7.0 Unit V RECOMMENDED DC OPERATING CONDITIONS Symbol VCC GND Parameter Supply Voltage Supply Voltage Input High Voltage Input Low Voltage Min. 4.5 0 2.2 –0.5 (1) Terminal Voltage –0.5 to +7.0 with Respect to GND Operating Temperature Temperature Under Bias Storage Temperature DC Output Current 0 to +70 –55 to +125 –55 to +125 50 Typ. 5.0 0 — — Max. Unit 5.5 0 6.0(2) 0.8 V V V V 2683 tbl 06 TA TBIAS TSTG IOUT –55 to +125 –65 to +135 –65 to +150 50 °C °C °C mA VIH VIL NOTES: 1. VIL > -1.5V for pulse width less than 10ns. 2. VTERM must not exceed Vcc + 0.5V. NOTES: 2683 tbl 05 1. Stresses greater than those listed under ABSOLUTE MAXIMUM RATINGS may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability. 2. VTERM must not exceed Vcc + 0.5V for more than 25% of the cycle time or 10ns maximum, and is limited to < 20 mA for the period over VTERM > Vcc + 0.5V. CAPACITANCE(1) (TA = +25°C, f = 1.0MHz)TQFP ONLY Symbol CIN COUT Parameter Input Capacitance Output Capacitance Conditions(2) Max. VIN = 3dV VOUT = 3dV 9 10 Unit pF pF NOTES: 2683 tbl 07 1. This parameter is determined by device characterization but is not production tested. 2. 3dV references the interpolated capacitance when the input and output signals switch from 0V to 3V or from 3V to 0V. 6.16 4 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES DC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE (VCC = 5.0V ± 10%) IDT7025S Symbol |ILI| |ILO| VOL VOH Parameter Input Leakage Current (1) IDT7025L Min. — — — 2.4 Max. 5 5 0.4 — Unit µA µA V V 2683 tbl 08 Test Conditions VCC = 5.5V, VIN = 0V to VCC Min. — — — 2.4 Max. 10 10 0.4 — Output Leakage Current Output Low Voltage Output High Voltage CE = VIH, VOUT = 0V to VCC IOL = 4mA IOH = -4mA NOTE: 1. At Vcc < 2.0V input leakages are undefined. DC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1) (VCC = 5.0V ± 10%) Symbol Parameter Dynamic Operating ICC Current (Both Ports Active) Test Condition CE"A"=VIL, Outputs Open SEM = VIH f = fMAX(3) 7025X15 7025X17 7025X20 Com'l. Only Com'l. Only Version Typ.(2) Max. Typ.(2) Max. Typ.(2) Max. MIL S — — — — 160 370 L — — — — 160 320 COM S L MIL S L 170 170 — — 20 20 — — 105 105 — — 1.0 0.2 — — 100 100 310 260 — — 60 50 — — 190 160 — — 15 5 — — 170 140 170 170 — — 20 20 — — 105 105 — — 1.0 0.2 — — 100 100 310 260 — — 60 50 — — 190 160 — — 15 5 — — 170 140 160 160 20 20 20 20 95 95 95 95 1.0 0.2 1.0 0.2 90 90 90 90 290 240 90 70 60 50 240 210 180 150 30 10 15 5 225 200 155 130 7025X25 Typ.(2)Max. Unit 155 340 mA 155 280 155 155 16 16 16 16 90 90 90 90 1.0 0.2 1.0 0.2 85 85 85 85 265 220 80 65 60 50 215 180 170 140 30 10 15 5 200 170 145 120 mA mA mA mA ISB1 Standby Current (Both Ports — TTL Level Inputs) CER = CEL = VIH SEMR = SEML = VIH f = fMAX(3) COM S L MIL S L COM S L MIL S L ISB2 Standby Current (One Port — TTL Level Inputs) CE"A"=VIL and CE"B"=VIL(5) Active Port Outputs Open f = fMAX(3) SEMR = SEML = VIH ISB3 Full Standby Current Both Ports CEL and (Both Ports — All CER >VCC - 0.2V CMOS Level Inputs) VIN > VCC - 0.2V or COM S VIN < 0.2V, f = 0(4) L SEMR = SEML> VCC - 0.2V ISB4 Full Standby Current (One Port — All CMOS Level Inputs) CE"A" < 0.2 and CE"B" > VCC - 0.2V (5) SEMR = SEML> VCC - 0.2V VIN > VCC - 0.2V or VIN < 0.2V, Active Port Outputs Open, f = fMAX(3) MIL S L COM S L NOTES: 2683 tbl 09 1. "X" in part numbers indicates power rating (S or L). 2. VCC = 5V, TA = +25°C, and are not production tested. Icc dc = 120mA (typ.) 3. At f = fMAX, address and I/O'S are cycling at the maximum frequency read cycle of 1/ tRC, and using “AC Test Conditions” of input levels of GND to 3V. 4. f = 0 means no address or control lines change. 5. Port "A" may be either left or right port. Port "B" is the opposite from port "A". 6.16 5 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES DC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1)(Cont'd.) (VCC = 5.0V ± 10%) 7025X35 Symbol ICC Parameter Dynamic Operating Current (Both Ports Active) ISB1 Standby Current (Both Ports — TTL Level Inputs) ISB2 Standby Current (One Port — TTL Level Inputs) ISB3 Full Standby Current (Both Ports — All CMOS Level Inputs) Test Condition Version MIL. COM’L. MIL. COM’L. MIL. COM’L. MIL. S L S L S L S L S L S L S L S L S L S L Typ.(2) 150 150 150 150 13 13 13 13 85 85 85 85 1.0 0.2 1.0 0.2 80 80 80 80 Max. 300 250 250 210 80 65 60 50 190 160 155 130 30 10 15 5 175 150 135 110 7025X55 Typ.(2) 150 150 150 150 13 13 13 13 85 85 85 85 1.0 0.2 1.0 0.2 80 80 80 80 7025X70 Mil. Only Max. Typ.(2) Max. Unit 300 250 250 210 80 65 60 50 190 160 155 130 30 10 15 5 175 150 135 110 140 140 — — 10 10 — — 80 80 — — 1.0 0.2 — — 75 75 — — 300 250 — — 80 65 — — 190 160 — — 30 10 — — 175 150 — — mA mA mA mA mA CE = VIL, Outputs Open SEM = VIH f = fMAX(3) CEL = CER = VIH SEMR = SEML = VIH f = fMAX(3) CE"A"=VIL and CE"B"=VIH(5) Active Port Outputs Open f = fMAX(3) Both Ports CEL and CER > VCC - 0.2V SEMR = SEML = VIH VIN > VCC - 0.2V or COM’L. VIN < 0.2V, f = 0(4) SEMR = SEML > VCC - 0.2V ISB4 Full Standby Current (One Port — All CMOS Level Inputs) CE"A" < 0.2 and MIL. CE"B" > VCC - 0.2V(5) SEMR = SEML > VCC - 0.2V COM’L. VIN > VCC - 0.2V or VIN < 0.2V, Active Port Outputs Open, f = fMAX(3) NOTES: 2683 tbl 10 1. "X" in part numbers indicates power rating (S or L). 2. VCC = 5V, TA = +25°C, and are not production tested. 3. At f = fMAX, address and I/O'S are cycling at the maximum frequency read cycle of 1/tRC, and using “AC Test Conditions” of input levels of GND to 3V. 4. f = 0 means no address or control lines change. 5. Port "A" may be either left or right port. Port "B" is the opposite from port "A". DATA RETENTION CHARACTERISTICS OVER ALL TEMPERATURE RANGES (L Version Only) (VLC = 0.2V, VHC = VCC - 0.2V)(4) Symbol VDR ICCDR tCDR tR(3) (3) Parameter VCC for Data Retention Data Retention Current Chip Deselect to Data Retention Time Operation Recovery Time Test Condition VCC = 2V CE Min. 2.0 Typ.(1) — 100 100 — — Max. — 4000 1500 — — Unit V µA ns ns 2683 tbl 11 > VHC > VHC MIL. COM’L. — — 0 tRC(2) VIN > VHC or < VLC SEM NOTES: 1. TA = +25°C, VCC = 2V, and are by characterization but are not production tested. 2. tRC = Read Cycle Time 3. This parameter is guaranteed by device characterization but are not production tested. 4. At Vcc < 2.0V, input leakages are not defined. DATA RETENTION WAVEFORM DATA RETENTION MODE VCC 4.5V tCDR VDR ≥ 2V VDR 4.5V tR VIH 2683 drw 05 CE VIH 6.16 6 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES 5V 5V 1250Ω DATAOUT 1250Ω DATAOUT 775Ω 30pF 775Ω 5pF AC TEST CONDITIONS Input Pulse Levels Input Rise/Fall Times Input Timing Reference Levels Output Reference Levels Output Load GND to 3.0V 5ns Max. 1.5V 1.5V Figures 1 and 2 2683 tbl 12 BUSY INT 2683 drw 06 Figure 1. AC Output Test Load Figure 2. Output Test Load ( for tLZ, tHZ, tWZ, tOW) * including scope and jig. AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(4) Symbol READ CYCLE tRC tAA tACE tABE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA Read Cycle Time Address Access Time Chip Enable Access Time (3) Parameter IDT7025X15 Com'l. Only Min. Max. 15 — — — — 3 3 — — 15 15 15 10 — — 10 — 15 — 15 IDT7025X17 Com'l. Only Min. Max. 17 — — — — 3 3 — 0 — 10 — — 17 17 17 10 — — 10 — 17 — 17 IDT7025X20 Min. 20 — — — — 3 3 — 0 — 10 — Max. — 20 20 20 12 — — 12 — 20 — 20 IDT7025X25 Min. 25 — — — — 3 3 — 0 — 10 — Max. — 25 25 25 13 — — 15 — 25 — 25 Unit ns ns ns ns ns ns ns ns ns ns ns ns Byte Enable Access Time(3) Output Enable Access Time Output Hold from Address Change Output Low-Z Time(1, 2) Output High-Z Time (1, 2) (1,2) Chip Enable to Power Up Time 0 — 10 — Chip Disable to Power Down Time(1,2) Semaphore Flag Update Pulse (OE or SEM) Semaphore Address Access (3) IDT7025X35 Symbol READ CYCLE tRC tAA tACE tABE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA Read Cycle Time Address Access Time Chip Enable Access Time(3) Byte Enable Access Time(3) Output Enable Access Time Output Hold from Address Change Output Low-Z Time(1, 2) Output High-Z Time(1, 2) Chip Enable to Power Up Time (1,2) IDT7025X55 Min. 55 — — — — 3 3 — 0 — 15 — Max. — 55 55 55 30 — — 25 — 50 — 55 Parameter Min. 35 — — — — 3 3 — 0 — 15 — Max. — 35 35 35 20 — — 15 — 35 — 35 IDT7025X70 Mil. Only Min. Max. 70 — — — — 3 3 — 0 — 15 — — 70 70 70 35 — — 30 — 50 — 70 Unit ns ns ns ns ns ns ns ns ns ns ns ns 2683 tbl 13 Chip Disable to Power Down Time(1,2) Semaphore Flag Update Pulse (OE or SEM) Semaphore Address Access Time(3) NOTES: 1. Transition is measured ± 500mV from Low or High-impedance voltage with Output Test Load (Figure 2). 2. This parameter is guaranteed by device characterization, but is not production tested. 3. To access RAM, CE = VIL, UB or LB = VIL, and SEM = VIH. To access semephore, CE = VIH or UB & LB = VIH, and 4. "X" in part numbers indicates power rating (S or L). 6.16 SEM = VIL. 7 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES WAVEFORM OF READ CYCLES(5) tRC ADDR tAA (4) (4) tACE tAOE (4) CE OE , LB tABE UB (4) R/ W tLZ (1) tOH VALID DATA (4) DATAOUT tHZ (2) BUSYOUT tBDD (3, 4) 2683 drw 07 NOTES: 1. Timing depends on which signal is asserted last, OE, CE, LB, or UB. 2. Timing depends on which signal is de-asserted first, CE, OE, LB, or UB. 3. tBDD delay is required only in case where opposite port is completing a write operation to the same address location for simultaneous read operations BUSY has no relation to valid output data. 4. Start of valid data depends on which timing becomes effective last tABE, tAOE, tACE, tAA or tBDD. 5. SEM = VIH. TIMING OF POWER-UP POWER-DOWN CE ICC ISB tPU 50% tPD 50% 2683 drw 08 6.16 8 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE(5) Symbol WRITE CYCLE tWC tEW tAW tAS tWP tWR tDW tHZ tDH tWZ tOW tSWRD tSPS Write Cycle Time Chip Enable to End-of-Write Address Set-up Time(3) Write Pulse Width Write Recovery Time Data Valid to End-of-Write Output High-Z Time Data Hold Time(4) Write Enable to Output in High-Z Output Active from End-of-Write (1, 2) (1, 2, 4) (1, 2) (3) Parameter IDT7025X15 Com'l. Only Min. Max. 15 12 12 0 12 0 10 — 0 — 0 5 5 — — — — — — — 10 — 10 — — — IDT7025X17 Com'l. Only Min. Max. 17 12 12 0 12 0 10 — 0 — 0 5 5 — — — — — — — 10 — 10 — — — IDT7025X20 Min. 20 15 15 0 15 0 15 — 0 — 0 5 5 Max. — — — — — — — 12 — 12 — — — IDT7025X25 Min. 25 20 20 0 20 0 15 — 0 — 0 5 5 Max. — — — — — — — 15 — 15 — — — Unit ns ns ns ns ns ns ns ns ns ns ns ns ns Address Valid to End-of-Write SEM Flag Write to Read Time SEM Flag Contention Window IDT7025X35 Symbol WRITE CYCLE tWC tEW tAW tAS tWP tWR tDW tHZ tDH tWZ tOW tSWRD tSPS Write Cycle Time Chip Enable to End-of-Write(3) Address Valid to End-of-Write Address Set-up Time Write Pulse Width Write Recovery Time Data Valid to End-of-Write Output High-Z Time(1, 2) Data Hold Time (4) (3) IDT7025X55 Min. 55 45 45 0 40 0 30 — 0 — 0 5 5 Max. — — — — — — — 25 — 25 — — — Parameter Min. 35 30 30 0 25 0 15 — 0 — 0 5 5 Max. — — — — — — — 15 — 15 — — — IDT7025X70 Mil. Only Min. Max. 70 50 50 0 50 0 40 — 0 — 0 5 5 — — — — — — — 30 — 30 — — — Unit ns ns ns ns ns ns ns ns ns ns ns ns ns Write Enable to Output in High-Z(1, 2) Output Active from End-of-Write (1, 2, 4) SEM Flag Write to Read Time SEM Flag Contention Window NOTES: 2683 tbl 14 1. Transition is measured ± 500mV from Low or High-impedance voltage with the Output Test Load (Figure 2). 2. This parameter is guaranteed by device characterization, but is not production tested. 3. To access RAM, CE = VIL, UB or LB = VIL, SEM = VIH. To access semaphore, CE = VIH or UB & LB = VIH, and SEM = VIL. Either condition must be valid for the entire tEW time. 4. The specification for tDH must be met by the device supplying write data to the RAM under all operating conditions. Although tDH and tOW values will vary over voltage and temperature, the actual tDH will always be smaller than the actual tOW. 5. "X" in part numbers indicates power rating (S or L). 6.16 9 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES TIMING WAVEFORM OF WRITE CYCLE NO. 1, R/W CONTROLLED TIMING(1,5,8) tWC ADDRESS tHZ (7) OE tAW CE or SEM (9) UB or LB (9) tAS (6) R/ tWP(2) tWR (3) W tWZ (7) tOW (4) (4) DATAOUT tDW DATAIN tDH 2683 drw 09 TIMING WAVEFORM OF WRITE CYCLE NO. 2, CE, UB, LB CONTROLLED TIMING(1,5) CE UB LB tWC ADDRESS tAW CE or SEM (9) tAS (6) tEW (2) tWR(3) UB or LB (9) R/ W tDW tDH DATAIN 2683 drw 10 NOTES: 1. R/W or CE or UB & LB must be High during all address transitions. 2. A write occurs during the overlap (tEW or tWP) of a Low UB or LB and a Low CE and a Low R/W for memory array writing cycle. 3. tWR is measured from the earlier of CE or R/W (or SEM or R/W) going High to the end-of-write cycle. 4. During this period, the I/O pins are in the output state and input signals must not be applied. 5. If the CE or SEM Low transition occurs simultaneously with or after the R/W Low transition, the outputs remain in the High-impedance state. 6. Timing depends on which enable signal is asserted last, CE, R/W, or byte control. 7. This parameter is guaranteed by device characterization, but is not production tested. Transition is measured +/- 500mV from steady state with Output Test Load (Figure 2). 8. If OE is Low during R/W controlled write cycle, the write pulse width must be the larger of tWP or (tWZ + tDW) to allow the I/O drivers to turn off and data to be placed on the bus for the required tDW. If OE is High during an R/W controlled write cycle, this requirement does not apply and the write pulse can be as short as the specified tWP. 9. To access RAM, CE = VIL, UB or LB = VIL, and SEM = VIH. To access Semaphore, CE = VIH or UB & LB = VIL, and SEM = VIL. tEW must be met for either condition. 6.16 10 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES TIMING WAVEFORM OF SEMAPHORE READ AFTER WRITE TIMING, EITHER SIDE(1) tSAA A0-A2 VALID ADDRESS tWR tAW tEW tDW DATAIN VALID tAS tWP tDH VALID ADDRESS tACE tSOP DATAOUT VALID(2) tOH SEM I/O0 R/ W tSWRD tAOE OE Write Cycle Read Cycle 2683 drw 11 NOTES: 1. CE = VIH or UB & LB = VIH for the duration of the above timing (both write and read cycle). 2. "DATAOUT VALID" represents all I/O's (I/O0-I/O15) equal to the semaphore value. TIMING WAVEFORM OF SEMAPHORE WRITE CONTENTION(1,3,4) A0"A"-A2"A" MATCH SIDE(2) “A” R/ W"A" tSPS SEM"A" A0"B"-A2"B" MATCH SIDE(2) “B” R/ W"B" SEM"B" 2683 drw 12 NOTES: 1. DOR = DOL = VIL, CER = CEL = VIH, or both UB & LB = VIH. 2. All timing is the same for left and right port. Port “A” may be either left or right port. Port “B” is the opposite from port “A”. 3. This parameter is measured from R/W"A" or SEM"A" going High to R/W"B" or SEM"B" going High. 4. If tSPS is not satisfied, there is no guarantee which side will be granted the semaphore flag. 6.16 11 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE(6) Symbol BUSY TIMING (M/S = VIH) tBAA tBDA tBAC tBDC tAPS tBDD Parameter IDT7025X15 Com'l Only Min. Max. — — — — 5 — 12 15 15 15 15 — 18 — IDT7025X17 Com'l Only Min. Max. — — — — 5 — 13 17 17 17 17 — 18 — IDT7025X20 Min. — — — — 5 — 15 Max. 20 20 20 17 — 30 — IDT7025X25 Min. — — — — 5 — 17 Max. Unit 20 20 20 17 — 30 — ns ns ns ns ns ns ns BUSY Access Time from Address Match BUSY Disable Time from Address Not Matched BUSY Access Time from Chip Enable Low BUSY Disable Time from Chip Enable High Arbitration Priority Set-up Time(2) BUSY Disable to Valid Data(3 Write Hold After BUSY(5) tWH BUSY TIMING (M/S = VIL) BUSY Input to Write(4) tWB Write Hold After BUSY(5) tWH PORT-TO-PORT DELAY TIMING tWDD tDDD Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay (1) 0 12 — — — — 30 25 0 13 — — — — 30 25 0 15 — — — — 45 35 0 17 — — — — 50 35 ns ns ns ns IDT7025X35 Symbol BUSY TIMING (M/S = VIH) tBAA tBDA tBAC tBDC tAPS tBDD tWH Parameter Min. — — — — 5 — 25 Max. 20 20 20 20 — 35 — IDT7025X55 Min. — — — — 5 — 25 Max. 45 40 40 35 — 40 — IDT7025X70 Mil. Only Min. Max. — — — — 5 — 25 45 40 40 35 — 45 — Unit ns ns ns ns ns ns ns BUSY Access Time from Address Match BUSY Disable Time from Address Not Matched BUSY Access Time from Chip Enable Low BUSY Disable Time from Chip Enable High Arbitration Priority Set-up Time(2) BUSY Disable to Valid Data(3) Write Hold After BUSY(5) BUSY Input to Write(4) Write Hold After BUSY(5) Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay (1) BUSY TIMING (M/S = VIL) tWB tWH tWDD tDDD 0 25 — — — — 60 45 0 25 — — — — 80 65 0 25 — — — — 95 80 ns ns ns ns PORT-TO-PORT DELAY TIMING NOTES: 2683 tbl 15 1. Port-to-port delay through RAM cells from writing port to reading port, refer to "Timing Waveform of Read With BUSY (M/S = VIH)" or "Timing Waveform of Write With Port-To-Port Delay (M/S = VIH)". 2. To ensure that the earlier of the two ports wins. 3. tBDD is a calculated parameter and is the greater of 0ns, tWDD – tWP (actual), or tDDD – tDW (actual). 4. To ensure that the write cycle is inhibited pn Port "B" during contention with Port "A". 5. To ensure that a write cycle is completed on Port "B" after contention with Port "A". 6. "X" in part numbers indicates power rating (S or L). 6.16 12 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES TIMING WAVEFORM OF WRITE PORT-TO-PORT READ AND BUSY (M/S = VIH)(2,4,5) BUSY tWC ADDR"A" MATCH tWP R/ W"A" tAPS (1) tDW VALID tDH DATAIN "A" ADDR"B" tBAA MATCH tBDA tBDD BUSY"B" tWDD DATAOUT "B" tDDD (3) 2683 drw 13 VALID NOTES: 1. To ensure that the earlier of the two ports wins. tAPS is ignored for M/S = VIL (slave). 2. CEL = CER = VIL. 3. OE = VIL for the reading port. 4. If M/S = VIL (slave), BUSY is an input. Then for this example BUSY"A" = VIH and BUSY"B" input is shown above. 5. All timing is the same for left and right ports. Port "A" may be either the left of right port. Port "B" is the opposite Port from Port "A". TIMING WAVEFORM OF WRITE WITH BUSY BUSY tWP R/ "A" W tWB(3) BUSY"B" tWH (1) R/ "B" W (2) 2683 drw 14 NOTES: 1. tWH must be met for both BUSY input (slave) output master. 2. Busy is asserted on port "B" Blocking R/W"B", until BUSY"B" goes High. 3. tWB is only for the 'Slave' Version. 6.16 13 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES WAVEFORM OF BUSY ARBITRATION CONTROLLED BY CE TIMING (M/S = VIH)(1) CE ADDR"A" and "B" ADDRESSES MATCH CE"A" tAPS(2) CE"B" tBAC tBDC 2683 drw 15 BUSY"B" WAVEFORM OF BUSY ARBITRATION CYCLE CONTROLLED BY ADDRESS MATCH TIMING (M/S = VIH)(1) ADDR"A" tAPS ADDR"B" (2) ADDRESS "N" MATCHING ADDRESS "N" tBAA tBDA 2683 drw 16 BUSY"B" NOTES: 1. All timing is the same for left and right ports. Port “A” may be either the left or right port. Port “B” is the port opposite from “A”. 2. If tAPS is not satisfied, the busy signal will be asserted on one side or another but there is no guarantee on which side busy will be asserted. AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1) Symbol INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0 — — — — 15 15 0 0 — — — — 15 15 0 0 — — — — 20 20 0 0 — — — — 20 20 ns ns ns ns Parameter IDT7025X15 Com'l. Only Min. Max. IDT7025X17 Com'l. Only Min. Max. IDT7025X20 Min. Max. IDT7025X25 Min. Max. Unit IDT7025X35 Symbol INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0 — — — — 25 25 Parameter Min. Max. IDT7025X55 Min. 0 0 — — Max. — — 40 40 IDT7025X70 Mil. Only Min. Max. 0 0 — — — — 50 50 Unit ns ns ns ns 2683 tbl 16 NOTE: 1. "X" in part numbers indicates power rating (S or L). 6.16 14 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES WAVEFORM OF INTERRUPT TIMING(1) tWC ADDR"A" tAS (3) INTERRUPT SET ADDRESS (2) tWR(4) CE"A" R/ W"A" tINS(3) INT"B" 2683 drw 17 tRC ADDR"B" tAS (3) INTERRUPT CLEAR ADDRESS (2) CE"B" OE"B" tINR(3) INT"B" NOTES: 1. All timing is the same for left and right ports. Port “A” may be either the left or right port. Port “B” is the port opposite from “A”. 2. See Interrupt Flag truth table. 3. Timing depends on which enable signal ( CE or R/W ) is asserted last. 4. Timing depends on which enable signal ( CE or R/W ) is de-asserted first. 2683 drw 18 TRUTH TABLES TRUTH TABLE III — INTERRUPT FLAG(1) R/ Left Port Right Port A0L-A12L 1FFF X X 1FFE WL CEL L X X L OEL X X X L INTL X X L (3) (2) R/WR X X L X CER X L L X OER X L X X A0R-A12R X 1FFF 1FFE X INTR L (2) Function Set Right INTR Flag Set Left INTL Flag Reset Right INTR Flag Reset Left INTL Flag 2683 tbl 17 L X X X H(3) X X H NOTES: 1. Assumes BUSYL = BUSYR = VIH. 2. If BUSYL = VIL, then no change. 3. If BUSYR = VIL, then no change. 4. INTR and INTL must be initialized at power-up. 6.16 15 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES TRUTH TABLE IV — ADDRESS BUSY ARBITRATION Inputs Outputs CEL X H X L CER X X H L A0L-A12L A0R-A12R NO MATCH MATCH MATCH MATCH BUSYL(1) BUSYR(1) H H H (2) H H H (2) Function Normal Normal Normal Write Inhibit(3) NOTES: 2683 tbl 18 1. Pins BUSYL and BUSYR are both outputs when the part is configured as a master. BUSY are inputs when configured as a slave. BUSYx outputs on the IDT7025 are push pull, not open drain outputs. On slaves the BUSY asserted internally inhibits write. 2. "L" if the inputs to the opposite port were stable prior to the address and enable inputs of this port. "H" if the inputs to the opposite port became stable after the address and enable inputs of this port. If tAPS is not met, either BUSYL or BUSYR = Low will result. BUSYL and BUSYR outputs cannot be low simultaneously. 3. Writes to the left port are internally ignored when BUSYL outputs are driving low regardless of actual logic level on the pin. Writes to the right port are internally ignored when BUSYR outputs are driving low regardless of actual logic level on the pin. TRUTH TABLE V — EXAMPLE OF SEMAPHORE PROCUREMENT SEQUENCE(1,2) Functions No Action Left Port Writes "0" to Semaphore Right Port Writes "0" to Semaphore Left Port Writes "1" to Semaphore Left Port Writes "0" to Semaphore Right Port Writes "1" to Semaphore Left Port Writes "1" to Semaphore Right Port Writes "0" to Semaphore Right Port Writes "1" to Semaphore Left Port Writes "0" to Semaphore Left Port Writes "1" to Semaphore D0 - D15 Left 1 0 0 1 1 0 1 1 1 0 1 D0 - D15 Right 1 1 1 0 0 1 1 0 1 1 1 Semaphore free Left port has semaphore token No change. Right side has no write access to semaphore Right port obtains semaphore token No change. Left port has no write access to semaphore Left port obtains semaphore token Semaphore free Right port has semaphore token Semaphore free Left port has semaphore token Semaphore free 2683 tbl 19 Status NOTES: 1. This table denotes a sequence of events for only one of the eight semaphores on the IDT7025. 2. There are eight semaphore flags written to via I/O0 and read from all I/O's (I/O0-I/O15). These eight semaphores are addressed by A0 - A2. FUNCTIONAL DESCRIPTION The IDT7025 provides two ports with separate control, address and I/O pins that permit independent access for reads or writes to any location in memory. The IDT7025 has an automatic power down feature controlled by CE. The CE controls on-chip power down circuitry that permits the respective port to go into a standby mode when not selected (CE High). When a port is enabled, access to the entire memory array is permitted. writes to memory location 1FFF (HEX) and to clear the interrupt flag (INTR), the right port must access the memory location 1FFF, The message (16 bits) at 1FFE or 1FFF is userdefined, since it is an addressable SRAM location. If the interrupt function is not used, address locations 1FFE and 1FFF are not used as mail boxes, but as part of the random access memory. Refer to Truth Table for the interrupt operation. INTERRUPTS If the user chooses to use the interrupt function, a memory location (mail box or message center) is assigned to each port. The left port interrupt flag (INTL) is asserted when the right port writes to memory location 1FFE (HEX), where a write is defined as the CER = R/WR = VIL per the Truth Table. The left port clears the interrupt by an address location 1FFE access when CEL = OEL = VIL, R/WL is a "don't care". Likewise, the right port interrupt flag (INTR) is asserted when the left port BUSY LOGIC Busy Logic provides a hardware indication that both ports of the RAM have accessed the same location at the same time. It also allows one of the two accesses to proceed and signals the other side that the RAM is “Busy”. The busy pin can then be used to stall the access until the operation on the other side is completed. If a write operation has been attempted from the side that receives a busy indication, the write signal is gated internally to prevent the write from proceeding. 6.16 16 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES MASTER Dual Port RAM CE BUSYR BUSYL SLAVE Dual Port RAM CE BUSYR BUSYL MASTER Dual Port RAM CE BUSYR BUSYL BUSYL SLAVE Dual Port RAM CE BUSYR BUSYR 2683 drw 19 BUSYL Figure 3. Busy and chip enable routing for both width and depth expansion with IDT7025 RAMs. The use of busy logic is not required or desirable for all applications. In some cases it may be useful to logically OR the busy outputs together and use any busy indication as an interrupt source to flag the event of an illegal or illogical operation. If the write inhibit function of busy logic is not desirable, the busy logic can be disabled by placing the part in slave mode with the M/S pin. Once in slave mode the BUSY pin operates solely as a write inhibit input pin. Normal operation can be programmed by tying the BUSY pins high. If desired, unintended write operations can be prevented to a port by tying the busy pin for that port low. The busy outputs on the IDT 7025 RAM in master mode, are push-pull type outputs and do not require pull up resistors to operate. If these RAMs are being expanded in depth, then the busy indication for the resulting array requires the use of an external AND gate. can be initiated with either the R/W signal or the byte enables. Failure to observe this timing can result in a glitched internal write inhibit signal and corrupted data in the slave. SEMAPHORES The IDT7025 is an extremely fast Dual-Port 8K x 16 CMOS Static RAM with an additional 8 address locations dedicated to binary semaphore flags. These flags allow either processor on the left or right side of the Dual-Port RAM to claim a privilege over the other processor for functions defined by the system designer’s software. As an example, the semaphore can be used by one processor to inhibit the other from accessing a portion of the Dual-Port RAM or any other shared resource. The Dual-Port RAM features a fast access time, and both ports are completely independent of each other. This means that the activity on the left port in no way slows the access time of the right port. Both ports are identical in function to standard CMOS Static RAM and can be read from, or written to, at the same time with the only possible conflict arising from the simultaneous writing of, or a simultaneous READ/WRITE of, a non-semaphore location. Semaphores are protected against such ambiguous situations and may be used by the system program to avoid any conflicts in the non-semaphore portion of the Dual-Port RAM. These devices have an automatic power-down feature controlled by CE, the Dual-Port RAM enable, and SEM, the semaphore enable. The CE and SEM pins control on-chip power down circuitry that permits the respective port to go into standby mode when not selected. This is the condition which is shown in Truth Table where CE and SEM are both high. Systems which can best use the IDT7025 contain multiple processors or controllers and are typically very high-speed systems which are software controlled or software intensive. These systems can benefit from a performance increase offered by the IDT7025's hardware semaphores, which provide a lockout mechanism without requiring complex programming. Software handshaking between processors offers the WIDTH EXPANSION WITH BUSY LOGIC MASTER/SLAVE ARRAYS When expanding an IDT7025 RAM array in width while using busy logic, one master part is used to decide which side of the RAM array will receive a busy indication, and to output that indication. Any number of slaves to be addressed in the same address range as the master, use the busy signal as a write inhibit signal. Thus on the IDT7025 RAM the busy pin is an output if the part is used as a master (M/S pin = H), and the busy pin is an input if the part used as a slave (M/S pin = L) as shown in Figure 3. If two or more master parts were used when expanding in width, a split decision could result with one master indicating busy on one side of the array and another master indicating busy on one other side of the array. This would inhibit the write operations from one port for part of a word and inhibit the write operations from the other port for the other part of the word. The busy arbitration, on a master, is based on the chip enable and address signals only. It ignores whether an access is a read or write. In a master/slave array, both address and chip enable must be valid long enough for a busy flag to be output from the master before the actual write pulse 6.16 DECODER 17 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES maximum in system flexibility by permitting shared resources to be allocated in varying configurations. The IDT7025 does not use its semaphore flags to control any resources through hardware, thus allowing the system designer total flexibility in system architecture. An advantage of using semaphores rather than the more common methods of hardware arbitration is that wait states are never incurred in either processor. This can prove to be a major advantage in very high-speed systems. HOW THE SEMAPHORE FLAGS WORK The semaphore logic is a set of eight latches which are independent of the Dual-Port RAM. These latches can be used to pass a flag, or token, from one port to the other to indicate that a shared resource is in use. The semaphores provide a hardware assist for a use assignment method called “Token Passing Allocation.” In this method, the state of a semaphore latch is used as a token indicating that shared resource is in use. If the left processor wants to use this resource, it requests the token by setting the latch. This processor then verifies its success in setting the latch by reading it. If it was successful, it proceeds to assume control over the shared resource. If it was not successful in setting the latch, it determines that the right side processor has set the latch first, has the token and is using the shared resource. The left processor can then either repeatedly request that semaphore’s status or remove its request for that semaphore to perform another task and occasionally attempt again to gain control of the token via the set and test sequence. Once the right side has relinquished the token, the left side should succeed in gaining control. The semaphore flags are active low. A token is requested by writing a zero into a semaphore latch and is released when the same side writes a one to that latch. The eight semaphore flags reside within the IDT7025 in a separate memory space from the Dual-Port RAM. This address space is accessed by placing a low input on the SEM pin (which acts as a chip select for the semaphore flags) and using the other control pins (Address, OE, and R/W) as they would be used in accessing a standard Static RAM. Each of the flags has a unique address which can be accessed by either side through address pins A0 – A2. When accessing the semaphores, none of the other address pins has any effect. When writing to a semaphore, only data pin D0 is used. If a low level is written into an unused semaphore location, that flag will be set to a zero on that side and a one on the other side (see Table III). That semaphore can now only be modified by the side showing the zero. When a one is written into the same location from the same side, the flag will be set to a one for both sides (unless a semaphore request from the other side is pending) and then can be written to by both sides. The fact that the side which is able to write a zero into a semaphore subsequently locks out writes from the other side is what makes semaphore flags useful in interprocessor communications. (A thorough discussing on the use of this feature follows shortly.) A zero written into the same location from the other side will be stored in the semaphore request latch for that side until the semaphore is freed by the first side. When a semaphore flag is read, its value is spread into all data bits so that a flag that is a one reads as a one in all data bits and a flag containing a zero reads as all zeros. The read value is latched into one side’s output register when that side's semaphore select (SEM) and output enable (OE) signals go active. This serves to disallow the semaphore from changing state in the middle of a read cycle due to a write cycle from the other side. Because of this latch, a repeated read of a semaphore in a test loop must cause either signal (SEM or OE) to go inactive or the output will never change. A sequence WRITE/READ must be used by the semaphore in order to guarantee that no system level contention will occur. A processor requests access to shared resources by attempting to write a zero into a semaphore location. If the semaphore is already in use, the semaphore request latch will contain a zero, yet the semaphore flag will appear as one, a fact which the processor will verify by the subsequent read (see Table III). As an example, assume a processor writes a zero to the left port at a free semaphore location. On a subsequent read, the processor will verify that it has written successfully to that location and will assume control over the resource in question. Meanwhile, if a processor on the right side attempts to write a zero to the same semaphore flag it will fail, as will be verified by the fact that a one will be read from that semaphore on the right side during subsequent read. Had a sequence of READ/WRITE been used instead, system contention problems could have occurred during the gap between the read and write cycles. It is important to note that a failed semaphore request must be followed by either repeated reads or by writing a one into the same location. The reason for this is easily understood by looking at the simple logic diagram of the semaphore flag in Figure 4. Two semaphore request latches feed into a semaphore flag. Whichever latch is first to present a zero to the semaphore flag will force its side of the semaphore flag low and the other side high. This condition will continue until a one is written to the same semaphore request latch. Should the other side’s semaphore request latch have been written to a zero in the meantime, the semaphore flag will flip over to the other side as soon as a one is written into the first side’s request latch. The second side’s flag will now stay low until its semaphore request latch is written to a one. From this it is easy to understand that, if a semaphore is requested and the processor which requested it no longer needs the resource, the entire system can hang up until a one is written into that semaphore request latch. The critical case of semaphore timing is when both sides request a single token by attempting to write a zero into it at the same time. The semaphore logic is specially designed to resolve this problem. If simultaneous requests are made, the logic guarantees that only one side receives the token. If one side is earlier than the other in making the request, the first side to make the request will receive the token. If both requests arrive at the same time, the assignment will be arbitrarily made to one port or the other. One caution that should be noted when using semaphores 6.16 18 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES is that semaphores alone do not guarantee that access to a resource is secure. As with any powerful programming technique, if semaphores are misused or misinterpreted, a software error can easily happen. Initialization of the semaphores is not automatic and must be handled via the initialization program at power-up. Since any semaphore request flag which contains a zero must be reset to a one, all semaphores on both sides should have a one written into them at initialization from both sides to assure that they will be free when needed. USING SEMAPHORES—SOME EXAMPLES Perhaps the simplest application of semaphores is their application as resource markers for the IDT7025’s Dual-Port RAM. Say the 8K x 16 RAM was to be divided into two 4K x 16 blocks which were to be dedicated at any one time to servicing either the left or right port. Semaphore 0 could be used to indicate the side which would control the lower section of memory, and Semaphore 1 could be defined as the indicator for the upper section of memory. To take a resource, in this example the lower 4K of Dual-Port RAM, the processor on the left port could write and then read a zero in to Semaphore 0. If this task were successfully completed (a zero was read back rather than a one), the left processor would assume control of the lower 4K. Meanwhile the right processor was attempting to gain control of the resource after the left processor, it would read back a one in response to the zero it had attempted to write into Semaphore 0. At this point, the software could choose to try and gain control of the second 4K section by writing, then reading a zero into Semaphore 1. If it succeeded in gaining control, it would lock out the left side. Once the left side was finished with its task, it would write a one to Semaphore 0 and may then try to gain access to Semaphore 1. If Semaphore 1 was still occupied by the right side, the left side could undo its semaphore request and perform other tasks until it was able to write, then read a zero into Semaphore 1. If the right processor performs a similar task with Semaphore 0, this protocol would allow the two processors to swap 4K blocks of Dual-Port RAM with each other. The blocks do not have to be any particular size and can even be variable, depending upon the complexity of the software using the semaphore flags. All eight semaphores could be used to divide the Dual-Port RAM or other shared resources into eight parts. Semaphores can even be assigned different meanings on different sides rather than being given a common meaning as was shown in the example above. Semaphores are a useful form of arbitration in systems like disk interfaces where the CPU must be locked out of a section of memory during a transfer and the I/O device cannot tolerate any wait states. With the use of semaphores, once the two devices has determined which memory area was “off-limits” to the CPU, both the CPU and the I/O devices could access their assigned portions of memory continuously without any wait states. Semaphores are also useful in applications where no memory “WAIT” state is available on one or both sides. Once a semaphore handshake has been performed, both processors can access their assigned RAM segments at full speed. Another application is in the area of complex data structures. In this case, block arbitration is very important. For this application one processor may be responsible for building and updating a data structure. The other processor then reads and interprets that data structure. If the interpreting processor reads an incomplete data structure, a major error condition may exist. Therefore, some sort of arbitration must be used between the two different processors. The building processor arbitrates for the block, locks it and then is able to go in and update the data structure. When the update is completed, the data structure block is released. This allows the interpreting processor to come back and read the complete data structure, thereby guaranteeing a consistent data structure. L PORT SEMAPHORE REQUEST FLIP FLOP D0 WRITE D Q R PORT SEMAPHORE REQUEST FLIP FLOP Q D D0 WRITE SEMAPHORE READ Figure 4. IDT7025 Semaphore Logic SEMAPHORE READ 2683 drw 21 6.16 19 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES ORDERING INFORMATION IDT XXXXX Device Type A Power 999 Speed A Package A Process/ Temperature Range Blank B PF G J F 15 17 20 25 35 55 70 S L 7025 Commercial (0°C to +70°C) Military (–55°C to +125°C) Compliant to MIL-STD-883, Class B 100-pin TQFP (PN100-1) 84-pin PGA (G84-3) 84-pin PLCC (J84-1) 84-pin Flatpack (F84-2) Commercial Only Commercial Only Speed in nanoseconds Military Only Standard Power Low Power 128K (8K x 16) Dual-Port RAM 2683 drw 21 6.16 20