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HIGH-SPEED 3.3V 4K x 16 DUAL-PORT STATIC RAM
Features
x x x
IDT70V24S/L
x
x
True Dual-Ported memory cells which allow simultaneous reads of the same memory location High-speed access - Commercial: 15/20/25/35/55ns (max.) - Industrial: 20/25/35/55ns (max.) Low-power operation - IDT70V24S Active: 400mW (typ.) Standby: 3.3mW (typ.) - IDT70V24L Active: 380mW (typ.) Standby: 660W (typ.) Separate upper-byte and lower-byte control for multiplexed bus compatibility
x
x x x
x x x x
IDT70V24 easily expands data bus width to 32 bits or more using the Master/Slave select when cascading more than one device M/S = VIH for BUSY output flag on Master M/S = VIL for BUSY input on Slave BUSY and Interrupt Flag On-chip port arbitration logic Full on-chip hardware support of semaphore signaling between ports Fully asynchronous operation from either port LVTTL-compatible, single 3.3V (0.3V) power supply Available in 84-pin PGA, 84-pin PLCC and 100-pin TQFP Industrial temperature range (-40C to +85C) is available for selected speeds
Functional Block Diagram
R/WL
UBL
R/WR
UBR
LBL CEL OEL
LBR CER OER
I/O8L-I/O15L I/O Control I/O0L-I/O7L I/O Control
I/O8R-I/O15R I/O0R-I/O7R
BUSY
(1,2)
BUSYR (1,2)
Address Decoder
12
L
A11L A0L
MEMORY ARRAY
12
Address Decoder
A11R A0R
CEL OEL
R/WL
ARBITRATION INTERRUPT SEMAPHORE LOGIC
CER OER
R/WR
SEML (2) INTL
NOTES: 1. (MASTER): BUSY is output; (SLAVE): BUSY is input. 2. BUSY outputs and INT outputs are non-tri-stated push-pull.
M/S
SEMR INTR(2)
2911 drw 01
MARCH 2000
1
DSC-2911/8
(c)2000 Integrated Device Technology, Inc.
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Description
The IDT70V24 is a high-speed 4K x 16 Dual-Port Static RAM. The IDT70V24 is designed to be used as a stand-alone 64K-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 full-speed, errorfree 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, asyn-chronous 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 400mW of power. The IDT70V24 is packaged in a ceramic 84-pin PGA, an 84-Pin PLCC and a 100-pin Thin Quad Flatpack.
VCC R/WL
I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L I/O0L
SEML CEL UBL LBL
Pin Configurations(1,2,3)
OEL
INDEX 11 10 9 8 7 6 5 4 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
I/O8L I/O9L I/O10L I/O11L I/O12L I/O13L GND I/O14L I/O15L VCC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R I/O7R I/O8R
3 2 1 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55
N/C
A11L A10L A9L A8L
A7L A6L A5L A4L A3L A2L A1L A0L
IDT70V24J J84-1(4) 84-Pin PLCC Top View(5)
INTL BUSYL
GND M/S
BUSYR INTR
A0R A1R A2R A3R A4R A5R A6R
2911 drw 02
29 30 31 32 54 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
N/C A11R A10R A9R A8R
I/O9R I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R
SEMR CER UBR LBR
R/WR GND
OER
A7R
I/O9L I/O8L I/O7L I/O6L I/O5L I/O4L I/O3L I/O2L GND I/O1L I/O0L
SEML CEL UBL LBL
VCC R/WL
NOTES: 1. All VCC pins must be connected to power supply. 2. All GND pins must be connected to ground supply. 3. J84-1 package body is approximately 1.15 in x 1.15 in x .17 in. PN100-1 package body is approximately 14mm x 14mm x 1.4mm. 4. This package code is used to reference the package diagram. 5. This text does not indicate orientation of the actual part-marking.
N/C N/C N/C N/C I/O10L I/O11L I/O12L I/O13L GND I/O14L I/O15L VCC GND I/O0R I/O1R I/O2R VCC I/O3R I/O4R I/O5R I/O6R N/C N/C N/C N/C
100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 1 75 74 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 73 72 71 70 69 68 67 66
N/C A11L A10L A9L A8L A7L A6L
N/C N/C N/C N/C A5L A4L A3L A2L A1L A0L
65 64 63 62 61 60 59 58 57 56 55 54 53 52
IDT70V24PF PN100-1(4) 100-Pin TQFP Top View(5)
OEL
Index
INTL BUSYL
GND M/S
BUSYR INTR
A0R A1R A2R A3R A4R N/C N/C N/C N/C
2911 drw 03
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
I/O7R I/O8R I/O9R I/O10R I/O11R I/O12R I/O13R I/O14R GND I/O15R
6.42 2
SEMR CER UBR LBR
R/WR GND
N/C A11R A10R A9R A8R A7R A6R A5R
OER
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Pin Configurations(1,2,3) (con't.)
63 61 60 58 55 54 51 48 46 45 42
11
I/O7L
66
I/O5L
64
I/O4L
62
I/O2L
59
I/O0L
56
OEL
49
SEML
50
LBL
47
A11L
44
A10L
43
A7L
40
10
I/O10L
67
I/O8L
65
I/O6L
I/O3L
I/O1L
57
UBL
53
CEL
52
N/C
A9L
A8L
41
A5L
39
09
I/O11L
69
I/O9L
68
GND
VCC
R/WL
A6L
38
A4L
37
08
I/O13L
72
I/O12L
71 73 33
A3L
35
A2L
34
07
I/O15L
75
I/O14L
70
VCC
74
BUSYL IDT70V24G G84-3(4) 84-Pin PGA Top View(5)
32
A0L
31
INTL
36
06
I/O0R
76
GND
77
GND
78
GND
28
M/S
29
A1L
30
05
I/O1R
79
I/O2R
80
VCC
A0R
INTR
26
BUSYR
27
04
I/O3R
81
I/O4R
83 7 11 12
A2R
23
A1R
25
03
I/O5R
82 1
I/O7R
2 5
GND
8
GND
10
SEMR
14 17 20
A5R
22
A3R
24
02
I/O6R
84 3
I/O9R
I/O10R
4
I/O13R
6
I/O15R
9
R/WR
15
UBR
13
A11R
16
A8R
18
A6R
19
A4R
21
01
I/O8R A
I/O11R B
I/O12R C
I/O14R D
OER E
LBR F
CER G
N/C H
A10R J
A9R K
A7R L
2911 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. Package body is approximately 1.12 in x 1.12 in x .16 in. 4. This package code is used to reference the package diagram. 5. This text does not indicate orientation of the actual part-marking.
Pin Names
Left Port Right Port Names Chip Enable Read/Write Enable Output Enable Address Data Input/Output Semaphore Enable Upper Byte Select Lower Byte Select Interrupt Flag Busy Flag Master or Slave Select Power Ground
2911 tbl 01
CEL
R/WL
CER
R/WR
OEL
A0L - A11L I/O0L - I/O15L
OER
A0R - A11R I/O0R - I/O15R
SEML UBL LBL INTL BUSYL
SEMR UBR LBR INTR BUSYR
M/S VCC GND
6.42 3
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Truth Table I: Non-Contention Read/Write Control
Inputs(1) Outputs
CE
H X L L L L L L X
R/W X X L L L H H H X
OE
X X X X X L L L H
UB
X H L H L L H L X
LB
X H H L L H L L X
SEM
H H H H H H H H X
I/O8-15 High-Z High-Z DATAIN High-Z DATAIN DATAOUT High-Z DATAOUT High-Z
I/O0-7 High-Z High-Z High-Z DATAIN DATAIN High-Z DATAOUT DATAOUT High-Z
Mode Deselected: Power Down Both Bytes Deselected Write to Upper Byte Only Write to Lower Byte Only Write to Both Bytes Read Upper Byte Only Read Lower Byte Only Read Both Bytes Outputs Disabled
2911 tbl 02
NOTE:
1. A0L -- A11L A0R -- A11R
Truth Table II: Semaphore Read/Write Control(1)
Inputs Outputs
CE
H X H X L L
R/W H H X X
OE
L L X X X X
UB
X H X H L X
LB
X H X H X L
SEM
L L L L L L
I/O8-15 DATAOUT DATAOUT DATAIN DATAIN
____
I/O0-7 DATAOUT DATAOUT DATAIN DATAIN
____
Mode Read Data in Semaphore Flag Read Data in Semaphore Flag Write DIN0 into Semaphore Flag Write DIN0 into Semaphore Flag Not Allowed Not Allowed
2911 tbl 03
____
____
NOTE:
1. There are eight semaphore flags written to via I/O0 and read from all of the I/O's (I/O0-I/O15). These eight semaphores are addressed by A0-A2.
6.42 4
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Absolute Maximum Ratings(1)
Symbol VTERM(2) Rating Terminal Voltage with Respect to GND Temperature Under Bias Storage Temperature DC Output Current Commercial & Industrial -0.5 to +4.6 Unit V
Maximum Operating Temperature and Supply Voltage(1)
Grade Commercial Ambient Temperature 0OC to +70OC -40OC to +85OC GND 0V 0V Vcc 3.3V + 0.3V 3.3V + 0.3V
2911 tbl 05
TBIAS TSTG IOUT
-55 to +125 -55 to +125 50
o
C C
Industrial
o
NOTES: 1. This is the parameter TA.
mA
2911 tbl 04
NOTES: 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 +0.3V for more than 25% of the cycle time or 10ns maximum, and is limited to < 20mA for the period over VTERM > Vcc + 0.3V.
Recommended DC Operating Conditions
Symbol VCC GND VIH Parameter Supply Voltage Ground Input High Voltage Input Low Voltage Min. 3.0 0 2.0 -0.3(1) Typ. 3.3 0
____ ____
Max. 3.6 0 VCC+0.3 0.8
(2)
Unit V V V V
2911 tbl 06
(TA = +25C, f = 1.0MHz)
Symbol CIN COUT Parameter Input Capacitance Output Capacitance Conditions
(2)
Capacitance
VIL
Max. 9 11
Unit pF pF
2911 tbl 07
NOTES: 1. VIL> -1.5V for pulse width less than 10ns. 2. VTERM must not exceed Vcc + 0.3V.
VIN = 3dV VOUT = 3dV
NOTES: 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.
DC Electrical Characteristics Over the Operating Temperature and Supply Voltage Range (VCC = 3.3V 0.3V)
70V24S Symbol |ILI| |ILO| VOL VOH Parameter Input Leakage Current
(1)
70V24L Min.
___
Test Conditions VCC = 3.6V, VIN = 0V to VCC
Min.
___
Max. 10 10 0.4
___
Max. 5 5 0.4
___
Unit A A V V
2911 tbl 08
Output Leakage Current Output Low Voltage Output High Voltage
CE = VIH, VOUT = 0V to VCC
IOL = +4mA IOH = -4mA
___
___
___
___
2.4
2.4
NOTE: 1. At VCC < 2.0V input leakages are undefined.
6.42 5
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
DC Electrical Characteristics Over the Operating Temperature and Supply Voltage Range(1) (VCC = 3.3V 0.3V)
70V24X15 Com'l Only Symbol ICC Parameter Dynamic Operating Current (Both Ports Active) Test Condition Version COM'L IND COM'L MIL & IND COM'L MIL & IND COM'L MIL & IND COM'L MIL & IND S L S L S L S L S L S L S L S L S L S L Typ. (2) 150 140
____ ____
70V24X20 Com'l & Ind Typ. (2) 140 130 140 130 20 15 20 15 80 75 80 75 1.0 0.2 1.0 0.2 80 75 80 75 Max. 200 175 225 195 30 25 45 40 110 100 130 115 5 2.5 15 5 115 100 130 115
70V24X25 Com'l & Ind Typ. (2) 130 125 130 125 16 13 16 13 75 72 75 72 1.0 0.2 1.0 0.2 75 70 75 70 Max. 190 165 210 180 30 25 45 40 110 95 125 110 5 2.5 15 5 105 90 120 105
2911 tbl 09a
Max. 215 185
____ ____
Unit mA
CE = VIL, Outputs Open SEM = VIH
f = fMAX
(3)
ISB1
Standby Current (Both Ports - TTL Level Inputs)
CER and CEL = VIH SEMR = SEML = VIH
f = fMAX
(3)
25 20
____ ____
35 30
____ ____
mA
ISB2
Standby Current (One Port - TTL Level Inputs)
CE"A" = VIL and CE"B" = VIH(5)
Active Port Outputs Open, f=fMAX(3) SEMR = SEML = VIH Both Ports CEL and CER > VCC - 0.2V, VIN > VCC - 0.2V or VIN < 0.2V, f = 0 (4) SEMR = SEML > VCC-0.2V
85 80
____ ____
120 110
____ ____
mA
ISB3
Full Standby Current (Both Ports CMOS Level Inputs)
1.0 0.2
____ ____
5 2.5
____ ____
mA
ISB4
Full Standby Current (One Port CMOS Level Inputs)
CE"A" < 0.2V and CE"B" > VCC - 0.2V(5) SEMR = SEML > VCC-0.2V
85 80
____ ____
125 105
____ ____
mA
VIN > VCC - 0.2V or VIN < 0.2V Active Port Outputs Open, f = fMAX(3)
70V24X35 Com'l & Ind Symbol ICC Parameter Dynamic Operating Current (Both Ports Active) Test Condition Version COM'L IND COM'L MIL & IND COM'L MIL & IND COM'L MIL & IND COM'L MIL & IND S L S L S L S L S L S L S L S L S L S L Typ. (2) 120 115 120 115 13 11 13 11 70 65 70 65 1.0 0.2 1.0 0.2 65 60 65 60 Max. 180 155 200 170 25 20 40 35 100 90 120 105 5 2.5 15 5 100 85 115 100
70V24X55 Com'l & Ind Typ. (2) 120 115 120 115 13 11 13 11 70 65 70 65 1.0 0.2 1.0 0.2 65 60 65 60 Max. 180 155 200 170 25 20 40 35 100 90 120 105 5 2.5 15 5 100 85 115 100
2911 tbl 09b
Unit mA
CE = VIL, Outputs Open SEM = VIH
f = fMAX
(3)
ISB1
Standby Current (Both Ports - TTL Level Inputs)
CER and CEL = VIH SEMR = SEML = VIH
f = fMAX
(3)
mA
ISB2
Standby Current (One Port - TTL Level Inputs)
CE"A" = VIL and CE"B" = VIH(5)
Active Port Outputs Open, f=fMAX(3) SEMR = SEML = VIH Both Ports CEL and CER > VCC - 0.2V, VIN > VCC - 0.2V or VIN < 0.2V, f = 0 (4) SEMR = SEML > VCC-0.2V
mA
ISB3
Full Standby Current (Both Ports CMOS Level Inputs)
mA
ISB4
Full Standby Current (One Port CMOS Level Inputs)
CE"A" < 0.2V and CE"B" > VCC - 0.2V(5) SEMR = SEML > VCC-0.2V
mA
VIN > VCC - 0.2V or VIN < 0.2V Active Port Outputs Open, f = fMAX(3)
NOTES: 1. 'X' in part number indicates power rating (S or L) 2. VCC = 3.3V, TA = +25C, and are not production tested. ICC DC = 115mA (typ.) 3. At f = fMAX, address and control lines (except Output Enable) 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".
6.42 6
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
3.3V 3.3V 590 DATAOUT 435 30pF 435 5pF*
AC Test Conditions
Input Pulse Levels Input Rise/Fall Times Input Timing Reference Levels Output Reference Levels Output Load GND to 3.0V 3ns Max. 1.5V 1.5V Figures 1 and 2
2911 tbl 10
590 DATAOUT
BUSY
INT
, 2911 drw 05
Figure 1. AC Output Test Load (for tLZ, tHZ, tWZ, tOW)
Figure 2. Output Test Load (for tLZ, tHZ, tWZ, tOW) * Including scope and jig.
Timing of Power-Up Power-Down
CE
ICC ISB
2911 drw 06 ,
tPU
50%
tPD
50%
6.42 7
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the Operating Temperature and Supply Voltage Range(4)
70V24X15 Com'l Only Symbol READ CYCLE tRC tAA tACE tABE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA Read Cycle Time Address Access Time Chip Enable Access Time (3) Byte Enable Access Time (3) Output Enable Access Time (3) Output Hold from Address Change Output Low-Z Time(1,2) Output High-Z Time (1,2) Chip Enable to Power Up Time (1,2) Chip Disable to Power Down Time (1,2) Semaphore Flag Update Pulse (OE or SEM) Semaphore Address Access (3) 15
____ ____
70V24X20 Com'l & Ind Min. Max.
70V24X25 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
20
____
____
25
____
____
ns ns ns ns ns ns ns ns ns ns ns ns
2911 tbl 11a
15 15 15 10
____
20 20 20 12
____
25 25 25 13
____
____
____
____
____
____
____
____
____
____
3 3
____
3 3
____
3 3
____
____
____
____
10
____
12
____
15
____
0
____
0
____
0
____
15
____
20
____
25
____
10
____
10
____
10
____
15
20
25
70V24X35 Com'l & Ind Symbol READ CYCLE tRC tAA tACE tABE tAOE tOH tLZ tHZ tPU tPD tSOP tSAA Read Cycle Time Address Access Time Chip Enable Access Time Byte Enable Access Time
(3) (3)
70V24X55 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
35
____
____
55
____
____
ns ns ns ns ns ns ns ns ns ns ns ns
2911 tbl 11b
35 35 35 20
____
55 55 55 30
____
____
____
____
____
Output Enable Access Time (3) Output Hold from Address Change Output Low-Z Time
(1,2) (1,2) (1,2)
____
____
3 3
____
3 3
____
____
____
Output High-Z Time
15
____
25
____
Chip Enable to Power Up Time
0
____
0
____
Chip Disable to Power Down Time (1,2) Semaphore Flag Update Pulse (OE or SEM) Semaphore Address Access
(3)
35
____
50
____
15
____
15
____
35
55
NOTES: 1. Transition is measured 0mV 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 semaphore, CE = VIH or UB and LB = VIH, and SEM = VIL. 4. 'X' in part number indicates power rating (S or L).
6.42 8
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Waveform of Read Cycles(5)
tRC ADDR tAA (4) (4) tACE tAOE
(4)
CE OE
tABE
(4)
UB, LB
R/W tLZ DATAOUT
(1)
tOH VALID DATA
(4) (2)
tHZ
BUSYOUT
tBDD
(3,4) 2911 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 cases 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.
6.42 9
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the Operating Temperature and Supply Voltage(5)
70V24X15 Com'l Only 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)
70V24X20 Com'l & Ind Min. Max.
70V24X25 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
15 12 12 0 12 0 10
____
____ ____ ____ ____ ____ ____ ____
20 15 15 0 15 0 15
____
____ ____ ____ ____ ____ ____ ____
25 20 20 0 20 0 15
____
____ ____ ____ ____ ____ ____ ____
ns ns ns ns ns ns ns ns ns ns ns ns ns
2911 tbl 12a
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 Data Hold Time
(4) (1,2) (1,2) (3)
10
____
12
____
15
____
0
____
0
____
0
____
Write Enable to Output in High-Z Output Active from End-of-Write
10
____ ____
12
____ ____
15
____ ____
(1,2,4)
0 5 5
0 5 5
0 5 5
SEM Flag Write to Read Time SEM Flag Contention Window
____
____
____
70V24X35 Com'l & Ind 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 Data Hold Time
(4) (1,2) (1,2) (3)
70V24X55 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
35 30 30 0 25 0 15
____
____ ____ ____ ____ ____ ____ ____
55 45 45 0 40 0 30
____
____ ____ ____ ____ ____ ____ ____
ns ns ns ns ns ns ns ns ns ns ns ns ns
2911 tbl 12b
15
____
25
____
0
____
0
____
Write Enable to Output in High-Z
15
____ ____
25
____ ____
Output Active from End-of-Write (1,2,4)
0 5 5
0 5 5
SEM Flag Write to Read Time SEM Flag Contention Window
____
____
NOTES: 1. Transition is measured 0mV 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 SRAM, CE = VIL, UB or LB = VIL, SEM = VIH. To access semaphore, CE = VIH or UB and 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 SRAM 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 number indicates power rating (S or L).
6.42 10
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Timing Waveform of Write Cycle No. 1, R/W Controlled Timing(1,5,8)
tWC ADDRESS tHZ (7)
OE
tAW
CE or SEM
(9)
CE or SEM
(9)
tAS (6) R/W tWZ (7) DATAOUT
(4)
tWP (2)
tWR (3)
tOW
(4)
tDW DATAIN
tDH
2911 drw 08
Timing Waveform of Write Cycle No. 2, CE, UB, LB Controlled Timing(1,5)
tWC ADDRESS tAW
(9)
CE or SEM
tAS(6)
tEW (2)
tWR (3)
UB or LB
(9)
R/W tDW DATAIN
2911 drw 09
tDH
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 0mV from low or high-impedance voltage 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 SRAM, CE = VIL, UB or LB = VIL, SEM = VIH. To access semaphore, CE = VIH or UB and LB = VIH and SEM = VIL. Either condition must be valid for the entire tEW time.
6.42 11
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial 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/O0
OE
Write Cycle Read Cycle
2911 drw 10
NOTES: 1. CE = VIH or UB & LB = VIH for the duration of the above timing (both write and read cycle). 2. "DATAOUT VALID" represents all I/O's (I/O0-I/O15)equal to the semaphore value.
Timing Waveform of Semaphore Write Contention(1,3,4)
A0"A"-A2"A" MATCH
SIDE
(2)
"A"
R/W"A"
SEM"A" tSPS A0"B"-A2"B"
(2)
MATCH
SIDE
"B"
R/W"B"
SEM"B"
NOTES: 1. D0R = D0L = VIL, CER = CEL = VIH, or Both UB & LB = VIH. 2. All timing is the same for left or right 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 be granted the semaphore flag.
2911 drw 11
6.42 12
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the Operating Oemperature and Supply Voltage Range(6)
70V24X15 Com'l Ony Symbol Parameter Min. Max. 70V24X20 Com'l & Ind Min. Max. 70V24X25 Com'l & Ind Min. Max. Unit
BUSY TIMING (M/S = VIH)
tBAA tBDA tBAC tBDC tAPS tBDD tWH
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)
____
15 15 15 15
____
____
20 20 20 17
____
____
20 20 20 17
____
ns ns ns ns ns ns ns
____
____
____
____
____
____
____
____
____
5
____
5
____
5
____
BUSY Disable to Valid Data(3)
Write Hold After BUSY
(5)
18
____
30
____
30
____
12
15
17
BUSY TIMING (M/S = VIL)
tWB tWH
BUSY Input to Write(4)
Write Hold After BUSY
(5)
0 12
____
0 15
____
0 17
____
ns ns
____
____
____
PORT-TO-PORT DELAY TIMING tWDD tDDD Write Pulse to Data Delay(1) Write Data Valid to Read Data Delay (1)
____ ____
30 25
____ ____
45 35
____ ____
50 35
ns ns
2911 tbl 13a
70V24X35 Com'l & Ind Symbol Parameter Min. Max.
70V24X55 Com'l & Ind Min. Max. Unit
BUSY TIMING (M/S = VIH)
tBAA tBDA tBAC tBDC tAPS tBDD tWH
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)
____
20 20 20 20
____
____
45 40 40 35
____
ns ns ns ns ns ns ns
____
____
____
____
____
____
5
____
5
____
BUSY Disable to Valid Data
Write Hold After BUSY
(5)
(3)
35
____
40
____
25
25
BUSY TIMING (M/S = VIL)
tWB tWH
BUSY Input to Write (4)
Write Hold After BUSY(5)
0 25
____
0 25
____
ns ns
____
____
PORT-TO-PORT DELAY TIMING tWDD tDDD Write Pulse to Data Delay (1) Write Data Valid to Read Data Delay
(1)
____ ____
60 45
____ ____
80 65
ns ns
2911 tbl 13b
NOTES: 1. Port-to-port delay through SRAM 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 = VIL)". 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 during contention. 5. To ensure that a write cycle is completed after contention. 6. 'X' in part number indicates power rating (S or L).
6.42 13
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Timing Waveform of Read with BUSY(2,4,5) (M/S = VIH)
tWC ADDR"A" MATCH tWP R/W"A" tDW DATAIN "A" tAPS ADDR"B" tBAA
(1)
tDH VALID
MATCH tBDA tBDD
BUSY"B"
tWDD DATAOUT "B" tDDD (3)
2911 drw 12
VALID
NOTES: 1. To ensure that the earlier of the two ports wins. tAPS is ignored for M/S = VIL (slave). 2. CEL = CER = VIL. 3. OE = VIL for the reading port. 4. If M/S = VIL (slave), BUSY is an input. Then for this example BUSY"A" = VIH and BUSY"B" input is shown above. 5. All timing is the same for both left and right ports. Port "A" may be either the left or right Port. Port "B" is the port opposite from port "A".
6.42 14
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Timing Waveform of Slave Write (M/S = VIL)
tWP R/W"A" tWB(3)
BUSY"B"
tWH(1)
R/W"B"
NOTES: 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. tWB is only for the "slave" version.
(2) 2911 drw 13
Waveform of BUSY Arbitration Controlled by CE Timing(1) (M/S = VIH)
ADDR"A" and "B" ADDRESSES MATCH
CE"A"
tAPS (2)
CE"B"
tBAC tBDC
2911 drw 14
BUSY"B"
Waveform of BUSY Arbitration Cycle Controlled by Address Match Timing(1) (M/S = VIH)
ADDR"A" tAPS ADDR"B" tBAA
(2)
ADDRESS "N"
MATCHING ADDRESS "N" tBDA
2911 drw 15
BUSY"B"
NOTES: 1. All timing is the same for left and right ports. Port "A" may be either the left or right port. Port "B" is the port opposite from "A". 2. If tAPS is not satisfied, the BUSY signal will be asserted on one side or another but there is no guarantee on which side BUSY will be asserted.
6.42 15
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the Operating Temperature and Supply Voltage Range(1)
70V24X15 Com'l Only Symbol INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0
____ ____
70V24X20 Com'l & Ind Min. Max.
70V24X25 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
0 0
____
____
0 0
____
____
ns ns ns ns
2911 tbl 14a
____
____
____
15 15
20 20
20 20
____
____
____
70V24X35 Com'l & Ind Symbol INTERRUPT TIMING tAS tWR tINS tINR Address Set-up Time Write Recovery Time Interrupt Set Time Interrupt Reset Time 0 0
____ ____
70V24X55 Com'l & Ind Min. Max. Unit
Parameter
Min.
Max.
0 0
____
____
ns ns ns ns
2911 tbl 14b
____
____
25 25
40 40
____
____
NOTES: 1. 'X' in part number indicates power rating (S or L).
6.42 16
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Waveform of Interrupt Timing(1)
tWC ADDR"A" tAS (3) INTERRUPT SET ADDRESS
(2)
tWR (4)
CE"A"
R/W"A" tINS
(3)
INT"B"
2911 drw 16
tRC ADDR"B" tAS (3) INTERRUPT CLEAR ADDRESS
(2)
CE"B" OE"B"
tINR(3)
INT"B"
2911 drw 17
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 III. 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.
6.42 17
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Truth Table III Interrupt Flag(1)
Left Port R/WL L X X X CEL L X X L OEL X X X L A11L-A0L FFF X X FFE INTL X X L(3) H(2) R/WR X X L X CER X L L X Right Port OER X L X X A11R-A0R X FFF FFE X INTR L
(2) (3)
Function Set Right INTR Flag Reset Right INTR Flag Set Left INTL Flag Reset Left INTL Flag
2911 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.
Truth Table IV Address BUSY Arbitration
Inputs Outputs A0L-A11L A0R-A11R NO MATCH MATCH MATCH MATCH
CEL
X H X L
CER
X X H L
BUSYL(1)
H H H (2)
BUSYR(1)
H H H (2)
Function Normal Normal Normal Write Inhibit(3)
2911 tbl 16
NOTES: 1. Pins BUSYL and BUSYR are both outputs when the part is configured as a master. Both are inputs when configured as a slave. BUSY outputs on the IDT70V24 are push pull, not open drain outputs. On slaves the BUSY 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. VIH 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(1,2,3)
Functions No Action Left Port Writes "0" to Semaphore Right Port Writes "0" to Semaphore Left Port Writes "1" to Semaphore Left Port Writes "0" to Semaphore Right Port Writes "1" to Semaphore Left Port Writes "1" to Semaphore Right Port Writes "0" to Semaphore Right Port Writes "1" to Semaphore Left Port Writes "0" to Semaphore Left Port Writes "1" to Semaphore D0 - D15 Left 1 0 0 1 1 0 1 1 1 0 1 D0 - D15 Right 1 1 1 0 0 1 1 0 1 1 1 Semaphore free Left port has semaphore token No change. Right side has no write access to semaphore Right port obtains semaphore token No change. Left port has no write access to semaphore Left port obtains semaphore token Semaphore free Right port has semaphore token Semaphore free Left port has semaphore token Semaphore free
2911 tbl 17
Status
NOTES: 1. This table denotes a sequence of events for only one of the eight semaphores on the IDT70V24. 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. 3. CE = VIH, SEM = VIL to access the semaphores. Refer to the Semaphore Read/Write Control Truth Table.
6.42 18
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
MASTER Dual Port SRAM
CE BUSYR
BUSYL
SLAVE Dual Port SRAM
CE BUSYR
BUSYL
MASTER Dual Port SRAM
CE BUSYR
BUSYL
BUSYL
SLAVE Dual Port SRAM
CE
BUSYL
BUSYR
BUSYR
2911 drw 18
Figure 3. Busy and chip enable routing for both width and depth expansion with IDT70V24 SRAMs.
Functional Description
The IDT70V24 provides two ports with separate control, address and I/O pins that permit independent access to any location in memory. The IDT70V24 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.
prevented to a port by tying the BUSY pin for that port LOW. The busy outputs on the IDT 70V24 SRAM in master mode, are pushpull 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.
Interrupts
If the user chooses 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 FFE (HEX), where a write is defined as the CE=R/W=VIL per Truth Table III. The left port clears the interrupt by accessing address location FFE 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 memory location FFF (HEX) and to clear the interrupt flag (INTR), the right port must read the memory location FFF. The message (16 bits) at FFE or FFF is user-defined, since it is an addressable SRAM location. If the interrupt function is not used, address locations FFE and FFF are not used as mail boxes, but as part of the random access memory. Refer to Truth Table IIII for the interrupt operation.
Width Expansion with BUSY Logic Master/Slave Arrays
When expanding an IDT70V24 SRAM array in width while using busy logic, one master part is used to decide which side of the SRAM 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 IDT70V24 SRAM the BUSY pin is an output if the part is used as a master (M/S pin = VIH), and the BUSY pin is an input if the part used as a slave (M/S pin = VIL) 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.
Busy Logic
Busy Logic provides a hardware indication that both ports of the SRAM 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 SRAM 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 attemp-ted 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 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
Semaphores
The IDT70V24 is an extremely fast Dual-Port 4K 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 SRAM 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 SRAM or any other shared resource.
6.42 19
DECODER
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
The Dual-Port SRAM 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 accessed to, at the same time with the only possible conflict arising from the simultaneous writing of, or a simultaneous READ/WRITE of, a nonsemaphore 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 SRAM. These devices have an automatic power-down feature controlled by CE, the Dual-Port SRAM 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 I where CE and SEM are both HIGH. Systems which can best use the IDT70V24 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 IDT70V24's hardware semaphores, which provide a lockout mechanism without requiring complex programming. Software handshaking between processors offers the maximum in system flexibility by permitting shared resources to be allocated in varying configurations. The IDT70V24 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 SRAM. 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 IDT70V24 in a separate memory space from the Dual-Port SRAM. 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 Truth Table V). 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 discussion 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 Truth Table V). 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
6.42 20
IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
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 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 SemaphoresSome Examples
Perhaps the simplest application of semaphores is their application as resource markers for the IDT70V24's Dual-Port SRAM. Say the 4K x 16 SRAM was to be divided into two 2K 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 2K of Dual-Port SRAM, 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 2K. 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 2K 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 2K blocks of Dual-Port SRAM 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 SRAM 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 SRAM segments at full speed. Another application is in the area of complex data structures. In this case, block arbitration is very important. For this application one processor may be responsible for building and updating a data structure. The other processor then reads and interprets that data structure. If the interpreting processor reads an incomplete data structure, a major error condition may exist. Therefore, some sort of arbitration must be used between the two different processors. The building processor arbitrates for the block, locks it and then is able to go in and update the data structure. When the update is completed, the data structure block is released. This allows the interpreting processor to come back and read the complete data structure, thereby guaranteeing a consistent data structure.
L PORT SEMAPHORE REQUEST FLIP FLOP D0 WRITE
D Q
R PORT SEMAPHORE REQUEST FLIP FLOP
Q D
D0 WRITE
SEMAPHORE READ
Figure 4. IDT70V24 Semaphore Logic
SEMAPHORE READ 2911 drw 19
,
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IDT70V24S/L High-Speed 4K x 16 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
Ordering Information
IDT XXXXX Device Type A Power 999 Speed A Package A Process/ Temperature Range Blank I PF G J 15 20 25 35 55 S L Commercial (0C to +70C) Industrial (-40C to +85C) 100-pin TQFP (PN100-1) 84-pin PGA (G84-3) 84-pin PLCC (J84-1) Commercial Only Commercial & Industrial Commercial & Industrial Commercial & Industrial Commercial & Industrial Standard Power Low Power
Speed in nanoseconds
70V24 64K (4K x 16) 3.3V Dual-Port RAM
2911 drw 20
Datasheet Document History
3/8/99: Initiated datasheet document history Converted to new format Cosmetic and typographical corrections Pages 2 and 3 Added additional notes to pin configurations Changed drawing format Page 2 TQFP for corrected pinout (no pin 55 was shown) Page 1 Changed 660mW to 660W Replaced IDT logo Added 15 and 20ns speed grades Upgraded DC parameters Added Industrial Temperature information Changed 200 mV to 0mV in notes CORPORATE HEADQUARTERS 2975 Stender Way Santa Clara, CA 95054 for SALES: 800-345-7015 or 408-727-6116 fax: 408-492-8674 www.idt.com for Tech Support: 831-754-4613 DualPortHelp@idt.com
6/10/99: 8/1/99: 8/30/99: 11/12/99: 3/10/00:
The IDT logo is a registered trademark of Integrated Device Technology, Inc.
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