IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM Integrated Device Technology, Inc. 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 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 FUNCTIONAL BLOCK DIAGRAM R/ WL R/ WR LBL CEL OEL LBR CE R OE R UBR UBL I/O8L-I/O 15L I/O8R-I/O 15R I/O Control I/O Control I/O0L-I/O 7L I/O0R-I/O 7R (1,2) BUSY BUSYR (1,2) L A12L A0L Address Decoder MEMORY ARRAY 13 NOTES: 1. (MASTER): BUSY is output; (SLAVE): BUSY is input. 2. BUSY outputs and INT outputs are non-tri-stated push-pull. Address Decoder A12R A0R 13 ARBITRATION INTERRUPT SEMAPHORE LOGIC CEL OEL R/ WL SEML INTL(2) M/ S CER OER R/ WR SEM R INTR(2) 2683 drw 01 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. 6.16 OCTOBER 1996 DSC 2683/6 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. A12L A11L A10L A9L A8L INTL BUSYL GND M/S BUSYR INTR A0R A1R A2R A3R A4R A5R A6R A8L A7L A6L A12L A11L A10L A9L CEL 68 8 IDT7025 PN100-1 67 66 65 100-PIN TQFP TOP VIEW(3) 17 64 63 62 61 60 59 18 19 58 57 20 56 55 54 53 52 9 10 11 12 13 14 15 16 21 22 23 UBR LBR A12R A11R A10R A9R A8R A7R A6R A5R CER W R/ R GND 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 OER 6.16 UBL LBL 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 I/O7R I/O8R I/O9R I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R 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 W OEL I/O9L I/O8L I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L I/O0L Index SEML 2683 drw 02 VCC R/ L A10R A9R A8R A7R A12R A11R UBR LBR CER SEMR A7L A6L A5L A4L A3L A2L A1L A0L SEMR CEL UBL LBL W SEML VCC R/ L I/O0L OEL W I/O9R I/O6R I/O7R I/O8R OER 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 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 R/ R GND I/O8L I/O9L I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R INDEX I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L PIN CONFIGURATIONS (1,2) N/C N/C N/C N/C A5L A4L A3L A2L A1L A0L INTL BUSYL GND M/S BUSYR INTR A0R A1R A2R A3R A4R N/C N/C N/C N/C 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 11 61 I/O7L 64 66 10 I/O10L I/O13L 52 45 A11L 44 A12L IDT7025 G84-3 GND 32 84-PIN PGA TOP VIEW(3) 28 VCC A2R 7 I/O7R 1 2 I/O9R 3 I/O8R A B 5 8 I/O13R I/O15R 6 9 I/O10R 4 I/O11R 11 GND I/O12R C I/O14R 12 10 R/ 14 WR 15 OER D E A5R 17 UBR 13 LBR CER F G 22 20 A11R 16 A8R 18 A12R H J A3R 24 A6R 19 A10R A1R 25 23 SEMR GND BUSYR 27 26 83 A1L 30 INTR I/O4R INTL 36 M/S 29 A0R 80 I/O6R A0L 31 GND A2L 34 35 BUSYL A4L 37 A3L 33 A5L 39 A6L VCC A7L 40 A8L 41 WL 78 I/O2R I/O5R 42 A10L 43 A9L R/ VCC 74 GND I/O3R 84 01 CEL 53 GND 47 50 UBL 46 LBL 73 77 82 02 49 I/O1L 48 SEML 38 I/O14L I/O1R 81 03 56 I/O3L 51 OEL 57 70 79 04 54 I/O0L I/O12L I/O0R 76 05 59 I/O6L I/O9L 71 I/O15L 75 06 55 I/O2L 68 72 07 62 I/O8L I/O11L 69 08 58 I/O4L 65 67 09 60 I/O5L A4R 21 A9R A7R K 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 RECOMMENDED OPERATING TEMPERATURE AND SUPPLY VOLTAGE CEL R/WL OEL CER R/WR OER A0L – A12L A0R – A12R Address Military I/O0L – I/O15L I/O0R – I/O15R Data Input/Output SEML UBL LBL INTL BUSYL SEMR UBR LBR INTR BUSYR Commercial M/S Chip Enable Read/Write Enable Output Enable Grade Semaphore Enable Ambient Temperature GND VCC –55°C to +125°C 0V 5.0V ± 10% 0°C to +70°C 0V 5.0V ± 10% 2683 tbl 02 Upper Byte Select Lower Byte Select Interrupt Flag Busy Flag Master or Slave Select VCC Power GND Ground 2683 tbl 01 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 R/W OE UB LB SEM I/O8-15 I/O0-7 H X X X X X X X H High-Z High-Z Deselected: Power Down H H H High-Z High-Z Both Bytes Deselected L L X L H H DATAIN High-Z Write to Upper Byte Only Mode L L X H L H High-Z DATAIN Write to Lower Byte Only L L X L L H DATAIN DATAIN Write to Both Bytes L H L L H H DATAOUT High-Z Read Upper Byte Only L H L H L H High-Z L H L L L H X X H X X X DATAOUT Read Lower Byte Only DATAOUT DATAOUT Read Both Bytes High-Z High-Z Outputs Disabled NOTE: 1. A0L — A12L are not equal to A0R — A12R. 2683 tbl 03 TRUTH TABLE II – SEMAPHORE READ/WRITE CONTROL(1) Inputs Outputs CE R/W OE UB LB SEM H H L X X L DATAOUT DATAOUT Read Semaphore Flag Data Out DATAOUT DATAOUT Read Semaphore Flag Data Out X H I/O0-7 I/O8-15 Mode L H H L X X X L DATAIN DATAIN Write I/O0 into Semaphore Flag X u u X H H L DATAIN DATAIN Write I/O0 into Semaphore Flag L X X L X L — — Not Allowed L X X X L L — — Not Allowed H 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. RECOMMENDED DC OPERATING CONDITIONS ABSOLUTE MAXIMUM RATINGS(1) Symbol Military Unit Terminal Voltage –0.5 to +7.0 with Respect to GND –0.5 to +7.0 V Operating Temperature 0 to +70 –55 to +125 Temperature Under Bias –55 to +125 TSTG Storage Temperature –55 to +125 –65 to +150 °C IOUT DC Output Current 50 50 mA VTERM TA TBIAS (2) Rating Commercial –65 to +135 2683 tbl 04 Symbol °C Min. Typ. Max. Unit VCC Supply Voltage 4.5 5.0 5.5 V GND Supply Voltage 0 0 0 V VIH Input High Voltage 2.2 — 6.0(2) V — 0.8 V VIL °C Parameter Input Low Voltage –0.5 (1) 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. 2683 tbl 06 CAPACITANCE(1) (TA = +25°C, f = 1.0MHz)TQFP ONLY Symbol Parameter Conditions(2) Max. CIN Input Capacitance VIN = 3dV COUT Output Capacitance VOUT = 3dV Unit 9 pF 10 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 Parameter (1) IDT7025L Test Conditions Min. Max. Min. Max. Unit VCC = 5.5V, VIN = 0V to VCC — 10 — 5 µA CE = VIH, VOUT = 0V to VCC — 10 — 5 µA |ILI| Input Leakage Current |ILO| Output Leakage Current VOL Output Low Voltage IOL = 4mA — 0.4 — 0.4 V VOH Output High Voltage IOH = -4mA 2.4 — 2.4 — V NOTE: 1. At Vcc < 2.0V input leakages are undefined. 2683 tbl 08 DC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1) (VCC = 5.0V ± 10%) Symbol Parameter Dynamic Operating ICC Current ISB1 ISB2 Test Condition CE"A"=VIL, Outputs Open SEM = VIH (Both Ports Active) f = fMAX(3) Standby Current (Both Ports — TTL CER = CEL = VIH SEMR = SEML = VIH Level Inputs) f = fMAX(3) Standby Current CE"A"=VIL and CE"B"=VIL(5) (One Port — TTL Active Port Outputs Open Level Inputs) 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 Typ.(2)Max. Unit 155 340 mA 155 280 COM S L 170 170 310 260 170 170 310 260 160 160 290 240 155 155 265 220 S L — — — — — — — — 20 20 90 70 16 16 80 65 COM S L 20 20 60 50 20 20 60 50 20 20 60 50 16 16 60 50 S — — — — 95 240 90 215 L — — — — 95 210 90 180 COM S 105 190 105 190 95 180 90 170 L 105 160 105 160 95 150 90 140 S L — — — — — — — — 1.0 0.2 30 10 1.0 0.2 30 10 CMOS Level Inputs) VIN > VCC - 0.2V or COM S VIN < 0.2V, f = 0(4) L SEMR = SEML> VCC - 0.2V 1.0 0.2 15 5 1.0 0.2 15 5 1.0 0.2 15 5 1.0 0.2 15 5 — — — — — — — — 90 90 225 200 85 85 200 170 100 100 170 140 100 100 170 140 90 90 155 130 85 85 145 120 MIL MIL SEMR = SEML = VIH ISB3 ISB4 7025X25 Full Standby Current Both Ports CEL and (Both Ports — All CER >VCC - 0.2V 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 MIL S L COM S L mA mA mA mA 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 Test Condition Parameter ICC ISB1 ISB2 Version Max. Typ.(2) CE = VIL, Outputs Open SEM = VIH MIL. S L 150 150 300 250 150 150 300 250 140 140 300 250 (Both Ports Active) f = fMAX(3) COM’L. S L 150 150 250 210 150 150 250 210 — — — — Standby Current (Both Ports — TTL CEL = CER = VIH SEMR = SEML = VIH MIL. S L 13 13 80 65 13 13 80 65 10 10 80 65 Level Inputs) f = fMAX(3) COM’L. S L 13 13 60 50 13 13 60 50 — — — — Standby Current CE"A"=VIL and CE"B"=VIH(5) MIL. S 85 190 85 190 80 190 L 85 160 85 160 80 160 COM’L. S 85 155 85 155 — — L 85 130 85 130 — — MIL. S L 1.0 0.2 30 10 1.0 0.2 30 10 1.0 0.2 30 10 S L 1.0 0.2 15 5 1.0 0.2 15 5 — — — — S L 80 80 175 150 80 80 175 150 75 75 175 150 S L 80 80 135 110 80 80 135 110 — — — — (One Port — TTL Active Port Outputs Open Level Inputs) f = fMAX(3) Full Standby Current (Both Ports — All Both Ports CEL and CER > VCC - 0.2V CMOS Level Inputs) VIN > VCC - 0.2V or COM’L. VIN < 0.2V, f = 0(4) SEMR = SEML > VCC - 0.2V CE"A" < 0.2 and MIL. CE"B" > VCC - 0.2V(5) SEMR = SEML > VCC - 0.2V Full Standby Current (One Port — All ISB4 Typ.(2) 7025X70 Mil. Only Max. Typ.(2) Max. Unit Dynamic Operating Current SEMR = SEML = VIH ISB3 7025X55 CMOS Level Inputs) COM’L. VIN > VCC - 0.2V or VIN < 0.2V, Active Port Outputs Open, f = fMAX(3) mA mA mA mA mA 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 Parameter Test Condition VDR VCC for Data Retention VCC = 2V ICCDR Data Retention Current CE > VHC VIN > VHC or < VLC tCDR (3) Chip Deselect to Data Retention Time tR(3) SEM Min. Typ.(1) Max. Unit 2.0 — — V MIL. — 100 4000 µA COM’L. — 100 1500 > VHC Operation Recovery Time 0 — — ns tRC(2) — — ns 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. 2683 tbl 11 DATA RETENTION WAVEFORM DATA RETENTION MODE VCC 4.5V VDR ≥ 2V tCDR CE VIH 4.5V tR VDR VIH 2683 drw 05 6.16 6 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES AC TEST CONDITIONS 5V Input Pulse Levels GND to 3.0V Input Rise/Fall Times 1250Ω 5ns Max. Input Timing Reference Levels BUSY INT 1.5V Output Load 1250Ω DATAOUT 1.5V Output Reference Levels 5V DATAOUT 775Ω 30pF 775Ω 5pF Figures 1 and 2 2683 tbl 12 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 Parameter IDT7025X15 Com'l. Only Min. Max. IDT7025X17 Com'l. Only Min. Max. IDT7025X20 IDT7025X25 Min. Max. Min. Max. Unit READ CYCLE tRC Read Cycle Time tAA Address Access Time 15 — 17 — 20 — 25 — ns — 15 — 17 — 20 — 25 ns tACE Chip Enable Access Time (3) — 15 — 17 — 20 — 25 ns tABE Byte Enable Access Time(3) — 15 — 17 — 20 — 25 ns tAOE Output Enable Access Time — 10 — 10 — 12 — 13 ns tOH Output Hold from Address Change 3 — 3 — 3 — 3 — ns tLZ Output Low-Z Time(1, 2) 3 — 3 — 3 — 3 — ns tHZ (1, 2) — 10 — 10 — 12 — 15 ns Output High-Z Time (1,2) tPU Chip Enable to Power Up Time 0 — 0 — 0 — 0 — ns tPD Chip Disable to Power Down Time(1,2) — 15 — 17 — 20 — 25 ns tSOP Semaphore Flag Update Pulse (OE or SEM) 10 — 10 — 10 — 10 — ns — 15 — 17 — 20 — 25 ns tSAA (3) Semaphore Address Access Symbol Parameter IDT7025X35 IDT7025X55 Min. Max. Min. Max. IDT7025X70 Mil. Only Min. Max. Unit READ CYCLE tRC Read Cycle Time 35 — 55 — 70 — ns tAA Address Access Time — 35 — 55 — 70 ns tACE Chip Enable Access Time(3) — 35 — 55 — 70 ns tABE Byte Enable Access Time(3) — 35 — 55 — 70 ns tAOE Output Enable Access Time — 20 — 30 — 35 ns tOH Output Hold from Address Change 3 — 3 — 3 — ns tLZ Output Low-Z Time(1, 2) 3 — 3 — 3 — ns tHZ Output High-Z Time(1, 2) — 15 — 25 — 30 ns (1,2) tPU Chip Enable to Power Up Time 0 — 0 — 0 — ns tPD Chip Disable to Power Down Time(1,2) — 35 — 50 — 50 ns tSOP Semaphore Flag Update Pulse (OE or SEM) 15 — 15 — 15 — ns tSAA Semaphore Address Access Time(3) — 35 — 55 — 70 ns 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 2683 tbl 13 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 CE tAOE OE (4) tABE (4) , LB UB W R/ tOH tLZ (1) DATAOUT VALID DATA (4) 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 tPU tPD 50% 50% ISB 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 Parameter IDT7025X15 Com'l. Only Min. Max. IDT7025X17 Com'l. Only Min. Max. IDT7025X20 IDT7025X25 Min. Max. Min. Max. Unit WRITE CYCLE tWC Write Cycle Time (3) 15 — 17 — 20 — 25 — ns 12 — 12 — 15 — 20 — ns tEW Chip Enable to End-of-Write tAW Address Valid to End-of-Write 12 — 12 — 15 — 20 — ns tAS Address Set-up Time(3) 0 — 0 — 0 — 0 — ns tWP Write Pulse Width 12 — 12 — 15 — 20 — ns tWR Write Recovery Time 0 — 0 — 0 — 0 — ns tDW Data Valid to End-of-Write 10 — 10 — 15 — 15 — ns — 10 — 10 — 12 — 15 ns 0 — 0 — 0 — 0 — ns — 10 — 10 — 12 — 15 ns tHZ Output High-Z Time tDH Data Hold Time(4) tWZ tOW tSWRD tSPS (1, 2) (1, 2) Write Enable to Output in High-Z Output Active from End-of-Write (1, 2, 4) SEM Flag Write to Read Time SEM Flag Contention Window Symbol 0 — 0 — 0 — 0 — ns 5 — 5 — 5 — 5 — ns 5 — 5 — 5 — 5 — ns Parameter IDT7025X35 IDT7025X55 Min. Min. Max. Max. IDT7025X70 Mil. Only Min. Max. Unit WRITE CYCLE tWC Write Cycle Time 35 — 55 — 70 — ns tEW Chip Enable to End-of-Write(3) 30 — 45 — 50 — ns tAW Address Valid to End-of-Write 30 — 45 — 50 — ns (3) tAS Address Set-up Time 0 — 0 — 0 — ns tWP Write Pulse Width 25 — 40 — 50 — ns tWR Write Recovery Time 0 — 0 — 0 — ns tDW Data Valid to End-of-Write 15 — 30 — 40 — ns tHZ Output High-Z Time(1, 2) — 15 — 25 — 30 ns (4) tDH Data Hold Time 0 — 0 — 0 — ns tWZ Write Enable to Output in High-Z(1, 2) — 15 — 25 — 30 ns 0 — 0 — 0 — ns 5 — 5 — 5 — ns 5 — 5 — 5 — ns tOW tSWRD tSPS 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 UB or LB (9) (9) (3) tWP(2) tAS (6) tWR W R/ tWZ (7) DATAOUT tOW (4) (4) tDW tDH DATAIN 2683 drw 09 TIMING WAVEFORM OF WRITE CYCLE NO. 2, CE, UB, LB CONTROLLED TIMING(1,5) tWC ADDRESS tAW CE or SEM (9) (6) tAS tWR(3) tEW (2) UB or LB (9) W R/ 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) tOH tSAA A0-A2 VALID ADDRESS tWR tAW tEW SEM VALID ADDRESS tACE tSOP tDW DATAIN VALID I/O0 tAS W tWP DATAOUT VALID(2) tDH R/ 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" SIDE(2) “A” MATCH W"A" R/ SEM"A" tSPS A0"B"-A2"B" SIDE(2) “B” MATCH W"B" R/ 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 Parameter IDT7025X15 Com'l Only Min. Max. IDT7025X17 Com'l Only Min. Max. IDT7025X20 IDT7025X25 Min. Max. Min. Max. Unit — 15 — — 15 — 17 — 20 — 20 ns 17 — 20 — 20 ns — 15 — 17 — 20 — 20 ns — 5 15 — 17 — 17 — 17 ns — 5 — 5 — 5 — ns — 12 18 — 18 — 30 — 30 ns — 13 — 15 — 17 — ns BUSY TIMING (M/S = VIH) tBDC 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 tAPS Arbitration Priority Set-up Time(2) tBAA tBDA tBAC 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 tBDD 0 — 0 — 0 — 0 — ns 12 — 13 — 15 — 17 — ns — 30 — 30 — 45 — 50 ns — 25 — 25 — 35 — 35 ns PORT-TO-PORT DELAY TIMING tWDD tDDD Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay Symbol (1) Parameter IDT7025X35 IDT7025X55 IDT7025X70 Mil. Only Min. Max. Min. Max. Min. Max. — 20 — 45 — 45 ns — 20 — 40 — 40 ns — 20 — 40 — 40 ns Unit BUSY TIMING (M/S = VIH) tBDC 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 — 20 — 35 — 35 ns tAPS Arbitration Priority Set-up Time(2) 5 — 5 — 5 — ns BUSY Disable to Valid Data(3) Write Hold After BUSY(5) — 35 — 40 — 45 ns 25 — 25 — 25 — ns 0 — 0 — 0 — ns 25 — 25 — 25 — ns — 60 — 80 — 95 ns — 45 — 65 — 80 ns tBAA tBDA tBAC tBDD tWH BUSY TIMING (M/S = VIL) tWB tWH BUSY Input to Write(4) Write Hold After BUSY(5) PORT-TO-PORT DELAY TIMING tWDD tDDD Write Pulse to Data Delay(1) (1) Write Data Valid to Read Data Delay 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) tWC MATCH ADDR"A" tWP W"A" R/ tDW tDH VALID DATAIN "A" tAPS (1) MATCH ADDR"B" tBAA tBDA tBDD BUSY"B" tWDD DATAOUT "B" VALID tDDD (3) 2683 drw 13 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 tWP W R/ "A" tWB(3) BUSY"B" W R/ "B" tWH (1) (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) ADDR"A" and "B" ADDRESSES MATCH CE"A" tAPS(2) CE"B" tBAC tBDC BUSY"B" 2683 drw 15 WAVEFORM OF BUSY ARBITRATION CYCLE CONTROLLED BY ADDRESS MATCH TIMING (M/S = VIH)(1) ADDRESS "N" ADDR"A" tAPS (2) MATCHING ADDRESS "N" ADDR"B" tBAA tBDA BUSY"B" 2683 drw 16 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 Parameter IDT7025X15 Com'l. Only Min. Max. IDT7025X17 Com'l. Only Min. Max. IDT7025X20 IDT7025X25 Min. Max. Min. Max. Unit 0 — 0 — ns INTERRUPT TIMING tAS Address Set-up Time tWR Write Recovery Time 0 — 0 — 0 — 0 — ns tINS Interrupt Set Time — 15 — 15 — 20 — 20 ns tINR Interrupt Reset Time — 15 — 15 — 20 — 20 ns Symbol 0 — Parameter 0 — IDT7025X35 IDT7025X55 Min. Max. Min. Max. IDT7025X70 Mil. Only Min. Max. Unit INTERRUPT TIMING tAS Address Set-up Time 0 — 0 — 0 — ns tWR Write Recovery Time 0 — 0 — 0 — ns tINS Interrupt Set Time — 25 — 40 — 50 ns tINR Interrupt Reset Time — 25 — 40 — 50 ns NOTE: 1. "X" in part numbers indicates power rating (S or L). 2683 tbl 16 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 INTERRUPT SET ADDRESS ADDR"A" (2) (3) tWR(4) tAS CE"A" W"A" R/ tINS(3) INT"B" 2683 drw 17 tRC INTERRUPT CLEAR ADDRESS ADDR"B" (2) tAS (3) 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) WL R/ Left Port CEL OEL Right Port A0L-A12L INTL R/WR CER OER A0R-A12R INTR L L X 1FFF X X X X X X X X X X X L L 1FFF H(3) X (3) L L X 1FFE X (2) X X X X X X X X L X L 1FFE L 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. L (2) Function Set Right INTR Flag Reset Right INTR Flag Set Left INTL Flag Reset Left INTL Flag 2683 tbl 17 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 CEL CER A0L-A12L A0R-A12R Outputs BUSYL(1) BUSYR(1) Function X X NO MATCH H H Normal H X MATCH H H Normal X H MATCH H H Normal L L MATCH (2) (2) 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 D0 - D15 Left D0 - D15 Right Status No Action 1 1 Semaphore free Left Port Writes "0" to Semaphore 0 1 Left port has semaphore token Right Port Writes "0" to Semaphore 0 1 No change. Right side has no write access to semaphore Left Port Writes "1" to Semaphore 1 0 Right port obtains semaphore token Left Port Writes "0" to Semaphore 1 0 No change. Left port has no write access to semaphore Right Port Writes "1" to Semaphore 0 1 Left port obtains semaphore token Left Port Writes "1" to Semaphore 1 1 Semaphore free Right Port Writes "0" to Semaphore 1 0 Right port has semaphore token Right Port Writes "1" to Semaphore 1 1 Semaphore free Left Port Writes "0" to Semaphore 0 1 Left port has semaphore token Left Port Writes "1" to Semaphore 1 1 Semaphore free 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. 2683 tbl 19 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 BUSY LOGIC 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 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 BUSYL MASTER Dual Port RAM BUSYL BUSYL CE SLAVE Dual Port RAM BUSYL BUSYR CE SLAVE Dual Port RAM BUSYL BUSYR CE BUSYR DECODER MASTER Dual Port RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES CE BUSYR BUSYR 2683 drw 19 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. 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 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 6.16 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 R PORT SEMAPHORE REQUEST FLIP FLOP D0 WRITE D SEMAPHORE REQUEST FLIP FLOP Q Q SEMAPHORE READ D D0 WRITE SEMAPHORE READ Figure 4. IDT7025 Semaphore Logic 6.16 2683 drw 21 19 IDT7025S/L HIGH-SPEED 8K x 16 DUAL-PORT STATIC RAM MILITARY AND COMMERCIAL TEMPERATURE RANGES ORDERING INFORMATION IDT XXXXX Device Type A 999 A A Power Speed Package Process/ Temperature Range Blank Commercial (0°C to +70°C) B Military (–55°C to +125°C) Compliant to MIL-STD-883, Class B PF G J F 100-pin TQFP (PN100-1) 84-pin PGA (G84-3) 84-pin PLCC (J84-1) 84-pin Flatpack (F84-2) 15 17 20 25 35 55 70 Commercial Only Commercial Only S L Standard Power Low Power 7025 128K (8K x 16) Dual-Port RAM Speed in nanoseconds Military Only 2683 drw 21 6.16 20