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HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
Integrated Device Technology, Inc.
IDT7015S/L
FEATURES:
* True Dual-Ported memory cells which allow simultaneous access of the same memory location * High-speed access -- Military: 20/25/35ns (max.) -- Commercial: 12/15/17/20/25/35ns (max.) * Low-power operation -- IDT7015S Active: 750mW (typ.) Standby: 5mW (typ.) -- IDT7015L Active: 750mW (typ.) Standby: 1mW (typ.) * IDT7015 easily expands data bus width to 18 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
* Interrupt and Busy Flags * On-chip port arbitration logic * Full on-chip hardware support of semaphore signaling between ports * Fully asynchronous operation from either port * Devices are capable of withstanding greater than 2001V electrostatic discharge * TTL-compatible, single 5V (10%) power supply * Available in ceramic 68-pin PGA, 68-pin PLCC, and an 80-pin TQFP * Industrial temperature range (-40C to +85C) is available, tested to military electrical specifications
DESCRIPTION:
The IDT7015 is a high-speed 8K x 9 Dual-Port Static RAMs. The IDT7015 is designed to be used as stand-alone Dual-Port RAM or as a combination MASTER/SLAVE DualPort RAM for 18-bit-or-more word systems. Using the IDT
FUNCTIONAL BLOCK DIAGRAM
OEL
R/WL
OER
CEL
CER
R/WR
I/O0L- I/O8L I/O Control I/O Control
I/O0R-I/O8R
BUSYL
(1,2)
BUSYR
Address Decoder
13
(1,2)
A12L A0L
MEMORY ARRAY
Address Decoder
A12R A0R
13
OEL
R/WL
CEL
ARBITRATION INTERRUPT SEMAPHORE LOGIC
CER
OER
R/WR
SEML
INTL
(2)
M/S
SEMR
INTR
(2)
2954 drw 01
NOTES: 1. In MASTER mode: BUSY is an output and is a push-pull driver In SLAVE mode: BUSY is input. 2. BUSY outputs and INT outputs are non-tri-stated push-pull drivers.
The IDT logo is a registered trademark of Integrated Device Technology, Inc.
MILITARY AND COMMERCIAL TEMPERATURE RANGES
(c)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-2954/2
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
MASTER/SLAVE Dual-Port RAM approach in 18-bit or wider memory system applications results in full-speed, 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 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. The IDT7015 is packaged in a ceramic 68-pin PGA, a 64pin PLCC and an 80-pin TQFP (Thin Quad FlatPack). 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)
R/WL I/O1L I/O0L I/O8L
SEML
4
INDEX I/O2L I/O3L I/O4L I/O5L GND I/O6L I/O7L VCC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
9
8
7
6
5
3
N/C N/C VCC A12L A11L A10L A9L A8L A7L A6L
2 1 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52
(3)
OEL
CEL
IDT7015 (8K x 9) J68-1 PLCC TOP VIEW
A5L A4L A3L A2L A1L A0L
INTL
BUSYL BUSYR
INTR
51 50 49 48 47 46 45
GND M/S
44 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
A0R A1R A2R A3R A4R
I/O7R I/O8R
SEMR
R/WR
N/C N/C GND A12R A11R A10R A9R A8R A7R A6R A5R
OER
CER
2954 drw 02
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 imply orientation of Part-Mark.
PIN NAMES
Left Port Right Port Names Chip Enable Read/Write Enable Output Enable Address Data Input/Output Semaphore Enable Interrupt Flag Busy Flag Master or Slave Select Power Ground
2954 tbl 01
CEL
R/WL
CER
R/WR
OEL
A0L - A12L I/O0L - I/O8L
OER
A0R - A12R I/O0R - I/O8R
SEML INTL BUSYL
M/S VCC
SEMR INTR BUSYR
GND
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
PIN CONFIGURATIONS (CON'T.) (1,2)
I/O0L I/O8L I/O1L R/WL
SEML
A12L A11L A10L
OEL
VCC
CEL
NC
A9L A8L
NC
NC
A7L A6L
INDEX
79 78 77 76
70 69
68 67
75
66
65 64 63
62
72 71
80
74 73
61
NC NC
60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42
NC I/O2L I/O3L I/O4L I/O5L GND I/O6L I/O7L VCC NC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R NC
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
NC A5L A4L A3L A2L A1L A0L
INTL
IDT7015 (8K X 9) PN-80 TQFP TOP VIEW
(3)
BUSYL
GND M/S
BUSYR
INTR
A0R A1R A2R A3R A4R NC NC
22 23
21
27 28
30 31
33 34
26
35
37 38
36
24 25
29
32
39
40
20
41
I/O7R I/O8R
R/WR
NC GND
NC NC
A11R
A10R A9R A8R
SEMR
A12R
A7R
CER
OER
A6R
A5R NC
NC
2954 drw 03
51 11 53 A7L 55 A9L A5L 52 A6L 54 A8L
50 A4L 49 A3L
48 A2L 47 A1L
46 44 42 A0L BUSYL M/S 45
INTL
40
INTR
38 A1R
36 A3R 35 A4R 32 A7R 30 A9R 34 A5R 33 A6R 31 A8R
10
43 41 39 37 GND BUSYR A0R A2R
09
08
57 56 A11L A10L 59 58 VCC A12L 61 60 N/C N/C 63
IDT7015 (8K x 9) G68-1 68-PIN PGA TOP VIEW (3)
07
28 29 A11R A10R 26 27 GND A12R 24 N/C 25 N/C 23
06
05
SEML CEL
64
62
65 04
OEL R/WL
67 66 I/O0L I/O8L 1 3 68 I/O1L I/O2L I/O4L 2 4 I/O3L I/O5L A B C 5 7 9 11 13 15 GND I/O7L GND I/O1R VCC I/O4R 6 8 I/O6L VCC D E 10 12 14 16 I/O0R I/O2R I/O3R I/O5R F G H J
SEMR
20
22
CER
03
OER
21 R/WR
02
18 19 I/O7R I/O8R 17 I/O6R K L
2954 drw 04
01
NOTES: 1. All Vcc must be connected to power supply. 2. All GND must be connected to ground supply. 3. This text does not imply orientation of Part-Mark.
INDEX
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TRUTH TABLE: NON-CONTENTION READ/WRITE CONTROL
Inputs(1) Outputs
CE
H L L X
R/W W X L H X
OE
X X L H
SEM
H H H X
I/O0-8 High-Z DATAIN DATAOUT High-Z Deselected: Power-Down Write to Memory Read Memory Outputs Disabled
Mode
NOTE: 1. Condition: A0L -- A12L is not equal to A0R -- A12R.
2954 tbl 02
TRUTH TABLE: SEMAPHORE READ/WRITE CONTROL Inputs Outputs
(1)
CE
H H L
R/W W
OE
L X X
SEM
L L L
I/O0-8 DATAOUT DATAIN -- Write I/O0 into Semaphore Flag Not Allowed
Mode Read Semaphore Flag Data Out (I/O0-8)
u
X
H
NOTE: 1. There are eight semaphore flags written to via I/O0 and read from I/O0-8 . These eight semaphores are addressed by A0 - A2.
2954 tbl 03
ABSOLUTE MAXIMUM RATINGS(1)
Symbol VTERM
(2)
Rating
Commercial
Military -0.5 to +7.0
Unit V
RECOMMENDED OPERATING TEMPERATURE AND SUPPLY VOLTAGE
Grade Military Commercial Ambient Temperature -55C to +125C 0C to +70C GND 0V 0V VCC 5.0V 10% 5.0V 10%
2954 tbl 05
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
TA TBIAS TSTG IOUT
-55 to +125 -65 to +135 -65 to +150 50
C C C mA
RECOMMENDED DC OPERATING CONDITIONS
Symbol VCC GND VIH VIL Parameter Supply Voltage Supply Voltage Input High Voltage Input Low Voltage Min. 4.5 0 2.2 -0.5
(1)
Typ. 5.0 0 -- --
Max. Unit 5.5 0 6.0(2) 0.8 V V V V
2954 tbl 06
NOTES: 2954 tbl 04 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 < 20mA for the period of VTERM > Vcc + 0.5V.
NOTES: 1. VIL > -1.5V for pulse width less than 10ns. 2. VTERM must not exceed Vcc + 0.5V.
CAPACITANCE(1)
(TA = +25C, f = 1.0MHz) TQFP ONLY
Symbol CIN COUT Parameter Input Capacitance Output Capacitance Conditions(2) VIN = 3dV VOUT = 3dV Max. 9 10 Unit pF pF
2954 tbl 07 NOTES: 1. This parameter is determined by device characteristics 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 .
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
DC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE (VCC = 5.0V 10%)
7015S Symbol |ILI| |ILO| VOL VOH Parameter Input Leakage Current
(1)
7015L Min. -- -- -- 2.4 Max. 5 5 0.4 -- Unit A A V V
2954 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 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. S L S L S L S L S L S L S L S L S L S L 7015X12 Com'l. Only Typ.(2) Max. -- -- 170 170 -- -- 25 25 -- -- 105 105 -- -- 1.0 0.2 -- -- 100 100 -- -- 325 275 -- -- 70 60 -- -- 200 170 -- -- 15 5 -- -- 180 150 7015X15 Com'l. Only Typ.(2) Max. -- -- 170 170 -- -- 25 25 -- -- 105 105 -- -- 1.0 0.2 -- -- 100 100 -- -- 310 260 -- -- 60 50 -- -- 190 160 -- -- 15 5 -- -- 170 140 7015X17 Com'l. Only Typ.(2) Max. Unit -- -- 170 170 -- -- 25 25 -- -- 105 109 -- -- 1.0 0.2 -- -- 100 100 -- -- 310 260 -- -- 60 50 -- -- 190 160 -- -- 15 5 -- -- 170 140 mA mA mA mA mA
CE = VIL, Outputs Open SEM = VIH
f = fMAX(3)
CER = CEL = VIH SEMR = SEML = VIH
f = fMAX(3)
CE"A"=VIL and CE"B" = VIH(5) MIL. Active Port Outputs Open SEMR = SEML = VIH Both Ports CEL and CER > VCC - 0.2V CE"A"< 0.2V 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) VIN > VCC - 0.2V or VIN < 0.2V, f = 0(4) SEMR = SEML > VCC - 0.2V f = fMAX(3) COM'L. MIL. COM'L.
ISB4
Full Standby Current (One Port -- All CMOS Level Inputs)
MIL.
COM'L.
mA
NOTES: 2954 tbl 09 1. "X" in part numbers indicates power rating (S or L). 2. VCC = 5V, TA = +25C, and are not production tested. ICCDC = 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 of port "A".
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IDT7015S/L HIGH-SPEED 8K x 9 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%)
7015X20 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. COM'L. S L S L S L S L S L S L S L S L S L S L Typ.(2) -- -- 160 160 -- -- 20 20 -- -- 95 95 -- -- 1.0 0.2 -- -- 90 90 Max. -- -- 290 240 -- -- 60 50 -- -- 180 150 -- -- 15 5 -- -- 155 130 7015X25 7015X35 Typ.(2) Max. Typ.(2) Max. Unit 155 155 155 155 16 16 16 16 90 90 90 90 1.0 0.2 1.0 0.2 85 85 85 85 340 280 265 220 80 65 60 50 215 180 170 140 30 10 15 5 200 170 145 120 150 150 150 150 13 13 13 13 85 85 85 85 1.0 0.2 1.0 0.2 80 80 80 80 300 250 250 210 80 65 60 50 190 160 155 130 30 10 15 5 175 150 135 110 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)
ISB4
Full Standby Current (One Port -- All CMOS Level Inputs)
Both Ports CEL and CER > VCC - 0.2V VIN > VCC - 0.2V or VIN < 0.2V, f = 0(4) SEMR = SEML > VCC - 0.2V CE"A"< 0.2V 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)
SEMR = SEML = VIH
MIL.
mA
COM'L.
NOTES: 1. "X" in part numbers indicates power rating (S or L). 2. VCC = 5V, TA = +25C, and are not production tested. ICCDC = 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 of port "A".
2954 tbl 10
OUTPUT LOADS AND AC TEST CONDITIONS
Input Pulse Levels Input Rise/Fall Times(1) Output Reference Levels Output Load
NOTE: 1. 3ns Max. for tAA=12ns
5V 893 DATAOUT
5V 893 DATAOUT
GND to 3.0V 5ns Max. 1.5V Figure 1 and 2
Input Timing Reference Levels 1.5V
BUSY INT
347 30pF
347
5pF *
2954 drw 05
2954 drw 06
Figure 1. AC Output Test Load
Figure 2. Output Test Load (For tLZ, tHZ, tWZ, tOW) Including scope and jig.
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(4)
Symbol READ CYCLE tRC tAA tACE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA Read Cycle Time Address Access Time Chip Enable Access Time(3) Output Enable Access Time Output Hold from Address Change Output Low-Z Time
(1, 2)
Parameter
IDT7015X12 Com'l. Only Min. Max. 12 -- -- -- 3 3 -- 0
(2)
IDT7015X15 Com'l. Only Min. Max. 15 -- -- -- 3 3 -- 0 -- 10 -- -- 15 15 10 -- -- 10 -- 15 -- 15
IDT7015X17 Com'l. Only Min. Max. 17 -- -- -- 3 3 -- 0 -- 10 -- -- 17 17 10 -- -- 10 -- 17 -- 17
Unit ns ns ns ns ns ns ns ns ns ns ns
-- 12 12 8 -- -- 10 -- 12 -- 12
Output High-Z Time(1, 2) Chip Enable to Power Up Time(2) Chip Disable to Power Down Time Semaphore Address Access Time Semaphore Flag Update Pulse (OE or SEM)
-- 10 --
IDT7015X20 Symbol READ CYCLE tRC tAA tACE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA NOTES:
1. 2. 3. 4.
IDT7015X25 Min. 25 -- -- -- 3 3 -- 0 -- 10 -- Max. -- 25 25 13 -- -- 15 -- 25 -- 25
IDT7015X35 Min. 35 -- -- -- 3 3 -- 0 -- 15 -- Max. -- 35 35 20 -- -- 20 -- 35 -- 35 Unit ns ns ns ns ns ns ns ns ns ns ns
2954 tbl 11
Parameter Read Cycle Time Address Access Time Chip Enable Access Time(3) Output Enable Access Time Output Hold from Address Change Output Low-Z Time
(1, 2) (1, 2)
Min. 20 -- -- -- 3 3 -- 0 -- 10 --
Max. -- 20 20 12 -- -- 12 -- 20 -- 20
Output High-Z Time
Chip Enable to Power Up Time(2) Chip Disable to Power Down Time(2) Semaphore Flag Update Pulse (OE or SEM) Semaphore Address Access Time
Transition is measured 200mV from Low- or High-impedance voltage with the Output test load (Figure 2). This parameter is guaranteed by device characterization but not tested. To access RAM, CE = VIL and SEM = VIH. To access semaphore, CE = VIH and SEM = VIL. "X" in part numbers indicates power rating (S or L).
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
WAVEFORM OF READ CYCLES(5)
tRC ADDR tAA (4) tACE tAOE
(4) (4)
CE
OE
R/W
tLZ DATAOUT
(1)
tOH VALID DATA
(4)
tHZ(2)
BUSYOUT
tBDD
(3, 4)
2954 drw 07
NOTES: 1. Timing depends on which signal is asserted last, OE or CE. 2. Timing depends on which signal is de-asserted first, CE or OE. 3. tBDD delay is required only in cases where the 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 tAOE, tACE, tAA or tBDD. 5. SEM = VIH.
TIMING OF POWER-UP / POWER-DOWN
CE
tPU ICC
50%
tPD
50%
2954 drw 08
ISB
6.12
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IDT7015S/L HIGH-SPEED 8K x 9 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) (1, 2) (3)
Parameter
IDT7015X12 Com'l. Only Min. Max. 12 10 10 0 10 2 10 -- 0 -- 3 5 5 -- -- -- -- -- -- -- 10 -- 10 -- -- --
IDT7015X15 Com'l. Only Min. Max. 15 12 12 0 12 2 10 -- 0 -- 3 5 5 -- -- -- -- -- -- -- 10 -- 10 -- -- --
IDT7015X17 Com'l. Only Min. Max. 17 12 12 0 12 2 10 -- 0 -- 0 5 5 -- -- -- -- -- -- -- 10 -- 10 -- -- --
Unit ns ns ns ns ns ns ns ns ns ns ns ns ns
Address Valid to End-of-Write
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
IDT7015X20 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) (1, 2) (3)
IDT7015X25 Min. 25 20 20 0 20 2 15 -- 0 -- 3 5 5 Max. -- -- -- -- -- -- -- 15 -- 15 -- -- --
IDT7015X35 Min. 35 30 30 0 25 2 15 -- 0 -- 3 5 5 Max. -- -- -- -- -- -- -- 20 -- 20 -- -- -- Unit ns ns ns ns ns ns ns ns ns ns ns ns ns
Parameter
Min. 20 15 15 0 15 2 15 -- 0 -- 3 5 5
Max. -- -- -- -- -- -- -- 12 -- 12 -- -- --
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
NOTES: 2954 tbl 12 1. Transition is measured 200mV from Low or High-impedance voltage with the Output test load (Figure 2). 2. This parameter is guaranteed by device characterization but not tested. 3. To access RAM, CE = VIL and SEM = VIH. To access semaphore, CE = 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).
6.12
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TIMING WAVEFORM OF WRITE CYCLE NO. 1, R/W CONTROLLED TIMING(1,5,8) W
tWC ADDRESS tHZ
(7)
OE
tAW
CE
or SEM
(9)
tAS (6) R/W tWZ DATA OUT
(4) (7)
tWP
(2)
tWR (3)
tOW
(4)
tDW DATA IN
tDH
2954 drw 09
TIMING WAVEFORM OF WRITE CYCLE NO. 2, CE CONTROLLED TIMING(1,5)
tWC ADDRESS tAW
CE
or SEM
(9)
tAS R/W
(6)
tEW (2)
tWR(3)
tDW DATAIN
tDH
2954 drw 10
NOTES: 1. R/W or CE must be High during all address transitions. 2. A write occurs during the overlap (tEW or tWP) of 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 or R/W. 7. This parameter is guaranteed by device characterization but is not production tested, transition is measured +/-200mV from steady state with the 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 and SEM = VIH. To access Semaphore, CE = VIH and SEM = VIL. tEW must be met for either condition.
6.12
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IDT7015S/L HIGH-SPEED 8K x 9 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 R/W tSWRD tAOE tWP tDH VALID ADDRESS tACE tSOP DATAOUT VALID(2) tOH
SEM
I/O
OE
Write Cycle Read Cycle
2954 drw 11
NOTES: 1. CE = VIH for the duration of the above timing (both write and read cycle). 2. "DATAOUT VALID" represents all I/O's (I/O0-I/O8) 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"
SEM"A"
A0"B"-A2 "B" MATCH
tSPS
SIDE(2) "B"
R/W"B"
SEM"B"
2954 drw 12
NOTES: 1. DOR = DOL =VIH, CER = CEL =VIH. 2. All timing is the same for left and right ports. Port "A" may be either left or right port. "B" is the opposite port from "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 obtain the semaphore flag.
6.12
11
IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS OVER THE OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(6)
Symbol BUSY TIMING (M/S = VIH) S tBAA tBDA tBAC tBDC tAPS tBDD tWH Parameter IDT7015X12 Com'l. Only Min. Max. -- -- -- -- 5 -- 11 0 11 -- -- 12 12 12 12 -- 15 -- -- -- 25 20 IDT7015X15 Com'l. Only Min. Max -- -- -- -- 5 -- 13 0 13 -- -- 15 15 15 15 -- 18 -- -- -- 30 25 IDT7015X17 Com'l. Only Min Max. -- -- -- -- 5 -- 13 0 13 -- -- 17 17 17 17 -- 18 -- -- -- 30 25 Unit ns ns ns ns 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)
(3)
BUSY Disable to Valid Data Write Hold After BUSY(5) BUSY TIMING (M/S = VIL) S BUSY Input to Write(4) tWB tWH Write Hold After BUSY(5)
PORT-TO-PORT DELAY TIMING tWDD tDDD
Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay(1)
IDT7015X20 Symbol BUSY TIMING (M/S = VIH) S tBAA tBDA tBAC tBDC tAPS tBDD tWH Parameter Min. -- -- -- -- 5 -- 15 Max. 20 20 20 17 -- 30 --
IDT7015X25 Min. -- -- -- -- 5 -- 17 Max. 20 20 20 17 -- 30 --
IDT7015X35 Min. -- -- -- -- 5 -- 25 Max. 20 20 20 20 -- 35 -- 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
(3) (2)
BUSY Disable to Valid Data Write Hold After BUSY(5) BUSY TIMING (M/S = VIL) S tWB BUSY Input to Write(4) tWH Write Hold After BUSY(5)
PORT-TO-PORT DELAY TIMING tWDD
0 15
-- --
0 17
-- --
0 25
-- --
ns ns
Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay
(1)
-- --
45 30
-- --
50 35
-- --
60 45
ns ns
2940 tbl 13
tDDD
NOTES: 1. Port-to-port delay through RAM cells from writing port to reading port, refer to "Timing Wave form of Write with Port-to-Port Read and 2. To ensure that the earlier of the two ports wins. 3. tBDD is a calculated parameter and is the greater of 0, tWDD - tWP (actual), or tDDD - tDW (actual). 4. To ensure that the write cycle is inhibited on port "B" during contention on port "A". 5. To ensure that a write cycle is completed on port "B" after contention on port "A". 6. "X" in part numbers indicates power rating (S or L).
BUSY (M/S = VIH)".
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TIMING WAVEFORM OF READ WITH BUSY (M/S = VIH)(2,4,5) S
tWC ADDR"A" MATCH tWP R/W"A" tDW DATAIN "A" tAPS ADDR"B"
(1)
tDH VALID
MATCH tBDA tBDD
BUSY"B"
tWDD DATAOUT "B" tDDD
(3)
2954 drw 13
VALID
NOTES: 1. To ensure that the earlier of the two ports wins. tAPS is ignored for M/S=VIL. 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 or right port. Port "B" is the port opposite from port "A".
TIMING WAVEFORM OF WRITE WITH BUSY
tWP R/W"A" tWB
BUSY"B"
tWH( 1 )
R/W"B"
(2)
NOTES: 2954 drw 14 1. tWH must be met for both BUSY input (SLAVE) and output (MASTER). 2. BUSY is asserted on port "B" blocking R/W"B", until BUSY"B" goes High. 3. 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 port "A".
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
WAVEFORM OF BUSY ARBITRATION CONTROLLED BY CE TIMING (M/S = VIH)(1) S
ADDR"A" and "B" ADDRESSES MATCH
CE"A"
tAPS (2)
CE"B"
tBAC tBDC
BUSY"B"
2954 drw 15
WAVEFORM OF BUSY ARBITRATION CYCLE CONTROLLED BY ADDRESS MATCH TIMING (M/S = VIH)(1) S
ADDR"A" tAPS ADDR"B" tBAA
(2)
ADDRESS "N"
MATCHING ADDRESS "N" tBDA
BUSY"B"
2954 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 INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0 -- -- -- -- 12 12 0 0 -- -- IDT7015X20 Symbol INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0 -- -- -- -- 20 20 0 0 -- -- -- -- 20 20 0 0 -- -- -- -- 25 25 ns ns ns ns
2739 tbl 14
Parameter
IDT7015X12 Com'l. Only Min. Max.
IDT7015X15 Com'l. Only Min. Max. -- -- 15 15
IDT7015X17 Com'l. Only Min Max. 0 0 -- -- -- -- 17 17 IDT7015X35 Min. Max.
Unit ns ns ns ns
IDT7015X25 Min. Max.
Parameter
Min.
Max.
Unit
NOTE: 1. "X" in part numbers indicates power rating (S or L).
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IDT7015S/L HIGH-SPEED 8K x 9 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
INT"B"
(3)
2954 drw 17
tRC ADDR"B" tAS
(3)
INTERRUPT CLEAR ADDRESS
(2)
CE"B"
OE"B"
tINR
INT"B"
(3)
2954 drw 18
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 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.
TRUTH TABLES TRUTH TABLE I -- INTERRUPT FLAG(1)
Left Port R/WL W L X X X Right Port A12L-A0L 1FFF X X 1FFE
CEL CE
L X X L
OEL OE
X X X L
INTL INT
X X L(3) H
(2)
R/WR W X X L X
CER CE
X L L X
OER OE
X L X X
A12R-A0R X 1FFF 1FFE X
INTR INT
L
(2) (3)
Function Set Right INTR Flag Set Left INTL Flag Reset Right INTR Flag Reset Left INTL Flag
2954 tbl 15
H
X X
NOTES: 1. Assumes BUSYL = BUSYR = VIH. 2. If BUSYL = VIL, then no change. 3. If BUSYR = VIL, then no change.
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TRUTH TABLE II -- ADDRESS BUSY ARBITRATION
Inputs
CEL CE CER CE
Outputs
BUSYL BUSY
A0L-A12L A0R-A12R
NO MATCH MATCH MATCH MATCH
(1)
BUSYR BUSY
(1)
Function Normal Normal Normal Write Inhibit(3)
X H X L
X X H L
H H H (2)
H H H (2)
NOTES: 2954 tbl 16 1. Pins BUSYL and BUSYR are both outputs when the part is configured as a master. Both are inputs when configured as a slave. BUSYX outputs on the IDT7015 are push-pull, not open drain outputs. On slaves the BUSYX input internally inhibits writes. 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 t APS is not met, either BUSYL or BUSYR = Low will result. BUSYL and BUSYR outputs can not 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 III -- 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 - D8 Left 1 0 0 1 1 0 1 1 1 0 1 D0 - D8 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
2954 tbl 17
Status
NOTES: 1. This table denotes a sequence of events for only one of the eight semaphores on the IDT7015. 2. There are eight semaphore flags written to via I/O0 and read from I/O0-8. These eight semaphores are addressed by A0 - A2.
FUNCTIONAL DESCRIPTION
The IDT7015 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 IDT7015 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. memory location 1FFF and to clear the interrupt flag (INTR), the right port must access memory location 1FFF. The message (9 bits) at 1FFE or 1FFF is user-defined 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 are still part of the random access memory. Refer to Truth Table for the interrupt operation.
BUSY LOGIC 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 where a write is defined as the CE = R/W = VIL per the Truth Table. The left port clears the interrupt by an address location 1FFE access when CER =OER =VIL, R/W is a "don't care". Likewise, the right port interrupt flag (INTR) is asserted when the left port writes to 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. The use of busy logic is not required or desirable for all
6.12
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
MASTER Dual Port RAM BUSY (L)
CE
BUSY (R)
SLAVE Dual Port RAM BUSY (L)
CE
BUSY (R)
BUSY (L)
MASTER Dual Port RAM BUSY (L)
CE
BUSY (R)
SLAVE Dual Port RAM BUSY (L)
CE
BUSY (R) BUSY (R)
2954 drw 19
Figure 3. Busy and chip enable routing for both width and depth expansion with IDT7015 RAMs.
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 IDT7015 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 the R/W signal. Failure to observe this timing can result in a glitched internal write inhibit signal and corrupted data in the slave.
SEMAPHORES
The IDT7015 are extremely fast Dual-Port 8Kx9 Static RAMs 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 IDT7015 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 IDT7015's hardware semaphores, which provide a lockout mechanism without requiring complex programming.
WIDTH EXPANSION WITH BUSY LOGIC MASTER/SLAVE ARRAYS
When expanding an IDT7015 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 IDT7015 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
6.12
DECODER
17
IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
Software handshaking between processors offers the maximum in system flexibility by permitting shared resources to be allocated in varying configurations. The IDT7015 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 IDT7015 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 is that semaphores alone do not guarantee that access to a
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IDT7015S/L HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
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 IDT7015's Dual-Port RAM. Say the 8K x 9 RAM was to be divided into two 4K x 9 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 SEMAPHORE READ
D Q
R PORT SEMAPHORE REQUEST FLIP FLOP
Q D
D0 WRITE
SEMAPHORE READ
2954 drw 20
Figure 4. IDT7015 Semaphore Logic
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IDT7015S/L HIGH-SPEED 8K x 9 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 Commercial (0C to +70C) Military (-55C to +125C) Compliant to MIL-STD-883, Class B
PF G J 12 15 17 20 25 35 S L 7015
80-pin TQFP (PN80-1) 68-pin PGA (G68-1) 68-pin PLCC (J68-1) Commercial Only Commercial Only Commercial Only
Speed in nanoseconds
Standard Power Low Power 72K (8K x 9) Dual-Port RAM
2954 drw 21
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