IDT IDT7026L55G High-speed 16k x 16 dual-port static ram Datasheet

HIGH-SPEED
16K x 16 DUAL-PORT
STATIC RAM
IDT7026S/L
Integrated Device Technology, Inc.
FEATURES:
• True Dual-Ported memory cells which allow simultaneous access of the same memory location
• High-speed access
— Military: 25/35/55ns (max.)
— Commercial: 20/25/35/55ns (max.)
• Low-power operation
— IDT7026S
Active: 750mW (typ.)
Standby: 5mW (typ.)
— IDT7026L
Active: 750mW (typ.)
Standby: 1mW (typ.)
• Separate upper-byte and lower-byte control for
multiplexed bus compatibility
• IDT7026 easily expands data bus width to 32 bits or
more using the Master/Slave select when cascading
more than one device
• M/S = H for BUSY output flag on Master,
M/S = L for BUSY input on Slave
• On-chip port arbitration logic
• Full on-chip hardware support of semaphore signaling
between ports
• Fully asynchronous operation from either port
• TTL-compatible, single 5V (±10%) power supply
• Available in 84-pin PGA and 84-pin PLCC
• Industrial temperature range (–40°C to +85°C) is available, tested to military electrical specifications
FUNCTIONAL BLOCK DIAGRAM
R/ WL
R/ WR
LBL
CEL
OEL
LBR
CE R
OE R
UBR
UBL
I/O8L-I/O 15L
I/O
Control
I/O8R-I/O 15R
I/O
Control
I/O0L-I/O 7L
BUSY
I/O0R-I/O 7R
(1,2)
L
A13L
A0L
(1,2)
BUSY R
Address
Decoder
MEMORY
ARRAY
14
CEL
SEML
Address
Decoder
A13R
A0R
14
ARBITRATION
SEMAPHORE
LOGIC
CER
M/ S
SEM R
2939 drw 01
NOTES:
1. (MASTER): BUSY is output; (SLAVE): BUSY is input.
2. BUSY outputs are non-tri-stated push-pull.
The IDT logo is a registered trademark of Integrated Device Technology, Inc.
MILITARY AND COMMERCIAL TEMPERATURE RANGES
©1996 Integrated Device Technology, Inc.
For latest information contact IDT’s web site at www.idt.com or fax-on-demand at 408-492-8391.
6.17
OCTOBER 1996
DSC 2939/3
1
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
DESCRIPTION:
The IDT7026 is a high-speed 16K x 16 Dual-Port Static
RAM. The IDT7026 is designed to be used as a stand-alone
Dual-Port RAM or as a combination MASTER/SLAVE DualPort 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, 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 IDT7026 is packaged in a ceramic 84-pin PGA, and a
84-pin PLCC. 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.
A9L
A11L
A10L
A13L
A12L
UBL
LBL
CEL
W
R/ L
SEML
OEL
VCC
I/O1L
I/O0L
GND
I/O3L
I/O2L
I/O4L
I/O5L
INDEX
I/O6L
I/O7L
PIN CONFIGURATIONS (1,2)
12
11 10 9 8 7 6 5 4 3 2 1 84 83 82 81 80 79 78 77 76 75
74
I/O9L
13
73
I/O10L
14
72
I/O11L
15
71
I/O12L
16
70
I/O13L
17
69
GND
18
68
I/O14L
19
I/O15L
20
VCC
21
I/O8L
GND
22
I/O0R
23
67
A8L
A7L
A6L
A5L
A4L
A3L
A2L
A1L
IDT7026
J84-1
66
A0L
65
BUSYL
84-PIN PLCC
TOP VIEW(3)
64
GND
63
M/S
55
I/O8R
54
32
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
UBR
LBR
SEMR
W
I/O9R
A8R
56
31
A9R
30
I/O7R
A10R
57
I/O6R
A11R
29
A13R
A12R
58
I/O5R
CER
59
28
R/ R
GND
27
I/O4R
OER
I/O3R
A0R
A1R
A2R
A3R
A4R
A5R
A6R
A7R
I/O15R
60
GND
26
I/O14R
VCC
I/O12R
I/O13R
61
I/O11R
BUSYR
25
I/O2R
I/O10R
24
62
I/O1R
2939 drw 02
NOTES:
1. All Vcc pins must be connected to the power supply.
2. All GND pins must be connected to the ground supply.
3. This text does not indicate orientation of the actual part-marking.
6.17
2
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
PIN CONFIGURATIONS (CONT'D) (1,2)
63
11
61
I/O7L
66
10
64
I/O10L
67
09
53
GND
47
CEL
52
45
A12L
A10L
77
I/O1R
33
VCC
BUSYL
IDT7026
G84-3
32
84-PIN PGA
TOP VIEW(3)
GND
GND
28
VCC
7
A
5
I/O10R
4
I/O11R
B
11
GND
2
3
A0L
36
M/S
A2L
30
A0R
BUSYR
27
A2R
A3R
I/O7R
I/O8R
A1L
29
A1R
83
I/O9R
A3L
34
26
1
A5L
37
31
I/O4R
I/O6R
39
35
80
I/O5R
A6L
A7L
78
I/O2R
I/O3R
40
A4L
74
GND
A8L
A9L
41
WL
R/
VCC
42
A11L
43
44
A13L
73
I/O14L
I/O0R
84
01
50
UBL
46
LBL
38
70
82
02
49
I/O1L
48
SEML
I/O12L
I/O15L
81
03
56
I/O3L
51
OEL
57
71
79
04
I/O6L
54
I/O0L
68
76
05
59
62
I/O9L
I/O13L
75
06
55
I/O2L
65
72
07
58
I/O4L
I/O8L
I/O11L
69
08
60
I/O5L
8
I/O15R
6
9
I/O14R
C
GND
10
I/O13R
I/O12R
12
R/
WR
15
OER
D
E
25
23
SEMR
14
17
UBR
13
LBR
CER
F
G
A4R
A6R
22
20
A12R
16
A9R
18
A13R
H
24
A7R
19
A11R
J
A5R
21
A10R
A8R
K
L
2939 drw 03
Index
NOTES:
1. All VCC pins must be connected to power supply.
2. All GND pins must be connected to ground supply.
3. This text does not indicate orientation of the actual part-marking.
RECOMMENDED OPERATING
TEMPERATURE AND SUPPLY VOLTAGE
PIN NAMES
Left Port
Right Port
Names
CEL
R/WL
OEL
CER
R/WR
OER
A0L – A13L
A0R – A13R
Address
I/O0L – I/O15L
I/O0R – I/O15R
Data Input/Output
SEML
UBL
LBL
BUSYL
SEMR
UBR
LBR
BUSYR
M/S
Grade
Chip Enable
Read/Write Enable
Military
Output Enable
Commercial
Ambient
Temperature
GND
VCC
–55°C to +125°C
0V
5.0V ± 10%
0°C to +70°C
0V
5.0V ± 10%
2939 tbl 02
Semaphore Enable
Upper Byte Select
Lower Byte Select
Busy Flag
Master or Slave Select
VCC
Power
GND
Ground
2939 tbl 01
6.17
3
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TRUTH TABLE I – NON-CONTENTION READ/WRITE CONTROL
Inputs(1)
CE
R/W
OE
H
X
X
X
X
X
Outputs
UB
LB
SEM
I/O8-15
I/O0-7
X
X
H
High-Z
High-Z
Deselected: Power-Down
H
H
H
High-Z
High-Z
Both Bytes Deselected
Mode
L
L
X
L
H
H
DATAIN
High-Z
Write to Upper Byte Only
L
L
X
H
L
H
High-Z
DATAIN
Write to Lower Byte Only
L
L
X
L
L
H
DATAIN
DATAIN
Write to Both Bytes
High-Z
Read Upper Byte Only
L
H
L
L
H
H
DATAOUT
L
H
L
H
L
H
High-Z
L
H
L
L
L
H
X
X
H
X
X
X
DATAOUT Read Lower Byte Only
DATAOUT DATAOUT Read Both Bytes
High-Z
High-Z
Outputs Disabled
NOTE:
1. A0L — A13L ≠ A0R — A13R.
2939 tbl 03
TRUTH TABLE II – SEMAPHORE READ/WRITE CONTROL(1)
Inputs
Outputs
CE
R/W
OE
H
H
L
X
X
L
DATAOUT DATAOUT Read Data in Semaphore Flag
X
H
L
H
H
L
DATAOUT DATAOUT Read Data in Semaphore Flag
X
X
X
L
DATAIN
DATAIN
H
X
UB
LB
SEM
I/O0-7
I/O8-15
Mode
Write I/O0 into Semaphore Flag
X
H
H
L
DATAIN
DATAIN
L
X
X
L
X
L
—
—
Not Allowed
Write I/O0 into Semaphore Flag
L
X
X
X
L
L
—
—
Not Allowed
NOTE:
1. 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.
ABSOLUTE MAXIMUM RATINGS(1)
Symbol
VTERM
TA
(2)
Rating
Commercial
Military
Unit
Terminal Voltage –0.5 to +7.0
with Respect
to GND
–0.5 to +7.0
V
Operating
Temperature
–55 to +125
°C
0 to +70
TBIAS
Temperature
Under Bias
–55 to +125
–65 to +135
°C
TSTG
Storage
Temperature
–55 to +125
–65 to +150
°C
IOUT
DC Output
Current
50
50
mA
2939 tbl 04
RECOMMENDED DC OPERATING
CONDTIONS
Symbol
Parameter
Min.
Typ.
Max. Unit
VCC
Supply Voltage
4.5
5.0
5.5
V
GND
Supply Voltage
0
0
0
V
VIH
Input High Voltage
2.2
—
VIL
Input Low Voltage
–0.5(1)
—
(2)
6.0
0.8
NOTES:
1. VIL > -1.5V for pulse width less than 10ns.
2. VTERM must not exceed Vcc + 0.5V.
NOTES:
2939 tbl 05
1. Stresses greater than those listed under ABSOLUTE MAXIMUM
RATINGS may cause permanent damage to the device. This is a stress
rating only and functional operation of the device at these or any other
conditions above those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating
conditions for extended periods may affect reliability.
2. VTERM must not exceed Vcc + 0.5V for more than 25% of the cycle time
or 10ns maximum, and is limited to < 20mA for the period of VTERM > Vcc
+ 0.5V.
V
V
2939 tbl 06
CAPACITANCE(1) (TA = +25°C, f = 1.0MHz)
Symbol
Parameter
Conditions(2) Max.
Unit
CIN
Input Capacitance
VIN = 3dv
9
pF
COUT
Output
Capacitance
VOUT = 3dv
10
pF
NOTES:
2939 tbl 07
1. This parameter is determined by device characterization but is not
production tested.
2. 3dV represents the interpolated capacitance when the input and output
signals switch from 0V to 3V or from 3V to 0V.
6.17
4
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
DC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE (VCC = 5.0V ± 10%)
IDT7026S
Symbol
Parameter
(1)
IDT7026L
Test Conditions
Min.
Max.
Min.
Max.
Unit
VCC = 5.5V, VIN = 0V to VCC
—
10
—
5
µA
CE = VIH, VOUT = 0V to VCC
—
10
—
5
µA
|ILI|
Input Leakage Current
|ILO|
Output Leakage Current
VOL
Output Low Voltage
IOL = 4mA
—
0.4
—
0.4
V
VOH
Output High Voltage
IOH = –4mA
2.4
—
2.4
—
V
NOTE:
1. At Vcc = 2.0V, input leakages are undefined.
2939 tbl 08
DC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1) (VCC = 5.0V ± 10%)
Symbol
ICC
ISB1
ISB2
Parameter
Dynamic Operating
Current
CE = VIL, Outputs Open
SEM = VIH
(Both Ports Active)
f = fMAX(3)
Standby Current
(Both Ports — TTL
CER = CEL = VIH
SEMR = SEML = VIH
Level Inputs)
f = fMAX(3)
Standby Current
(One Port — TTL
Level Inputs)
ISB3
Full Standby Current
(Both Ports — All
CMOS Level Inputs)
ISB4
Test
Condition
Full Standby Current
(One Port — All
CMOS Level Inputs)
7026X20
7026X25
Com'l. Only
Typ.(2) Max. Typ.(2) Max. Unit
Version
CE"A" = VIL and CE"B" = VIH(5)
MIL.
S
L
—
—
—
—
170
170
345
305
COM’L.
S
L
180
180
315
275
170
170
305
265
MIL.
S
L
—
—
—
—
25
25
100
80
COM’L.
S
L
30
30
85
60
25
25
85
60
MIL.
S
L
—
—
—
—
105
105
230
200
COM’L.
S
L
115
115
210
180
105
105
200
170
MIL.
S
L
—
—
—
—
1.0
0.2
30
10
COM’L.
S
L
1.0
0.2
15
5
1.0
0.2
15
5
MIL.
S
L
—
—
—
—
100
100
200
175
COM’L.
S
110
185
100
170
L
110
160
100
145
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
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)
mA
mA
mA
mA
mA
NOTES:
2939 tbl 09
1. "X" in part numbers indicates power rating (S or L).
2. VCC = 5V, TA = +25°C, and are not production tested. ICCDC = 120mA (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".
6.17
5
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
DC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(1)(Con't.) (VCC = 5.0V ± 10%)
7026X35
Symbol
ICC
ISB1
ISB2
Parameter
Typ.(2) Max. Typ.(2) Max. Unit
Version
CE = VIL, Outputs Open
SEM = VIH
MIL.
S
L
160
160
335
295
150
150
310
270
(Both Ports Active)
f = fMAX(3)
COM’L.
S
L
160
160
295
255
150
150
270
230
Standby Current
(Both Ports — TTL
CEL = CER = VIH
SEMR = SEML = VIH
MIL.
S
L
20
20
100
80
13
13
100
80
Level Inputs)
f = fMAX(3)
COM’L.
S
L
20
20
85
60
13
13
85
60
CE"A"=VIL and CE"B"=VIH(5)
MIL.
S
L
95
95
215
185
85
85
195
165
COM’L.
S
L
95
95
185
155
85
85
165
135
MIL.
S
L
1.0
0.2
30
10
1.0
0.2
30
10
COM’L.
S
L
1.0
0.2
15
5
1.0
0.2
15
5
MIL.
S
L
90
90
190
165
80
80
175
150
mA
COM’L.
S
L
90
90
160
135
80
80
135
110
mA
Standby Current
(One Port — TTL
Full Standby Current
(Both Ports — All
CMOS Level Inputs)
ISB4
7026X55
Dynamic Operating
Current
Level Inputs)
ISB3
Test
Condition
Full Standby Current
(One Port — All
CMOS Level Inputs)
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
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)
NOTES:
1. "X" in part numbers indicates power rating (S or L).
2. VCC = 5V, TA = +25°C, and are not production tested. ICCDC = 120mA (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".
6.17
mA
mA
mA
mA
2939 tbl 10
6
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
AC TEST CONDITIONS
5V
Input Pulse Levels
5V
GND to 3.0V
Input Rise/Fall Times
893Ω
5ns Max.
Input Timing Reference Levels
1.5V
Output Reference Levels
1.5V
Output Load
893Ω
DATAOUT
BUSY
INT
DATAOUT
347Ω
30pF
347Ω
5pF
Figures 1 and 2
2939 tbl 11
2939 drw 04
2939 drw 05
Figure 1. AC Output Load
Figure 2. Output Test Load
(for tLZ, tHZ, tWZ, tOW)
* Including scope and jig.
AC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(4)
Symbol
IDT7026X20
Com'l. Only
Min.
Max.
Parameter
IDT7026X25
Min.
Max.
Unit
READ CYCLE
tRC
Read Cycle Time
tAA
Address Access Time
20
—
25
—
ns
—
20
—
25
ns
tACE
Chip Enable Access Time
(3)
—
20
—
25
ns
tABE
Byte Enable Access Time(3)
—
20
—
25
ns
tAOE
Output Enable Access Time
—
12
—
13
ns
tOH
Output Hold from Address Change
3
—
3
—
ns
tLZ
Output Low-Z Time(1, 2)
3
—
3
—
ns
tHZ
Output High-Z Time(1, 2)
—
12
—
15
ns
(2)
tPU
Chip Enable to Power Up Time
0
—
0
—
ns
tPD
Chip Disable to Power Down Time(2)
—
20
—
25
ns
tSOP
Semaphore Flag Update Pulse (OE or SEM)
10
—
12
—
ns
tSAA
Semaphore Address Access Time
—
20
—
25
ns
Symbol
Parameter
IDT7026X35
IDT7026X55
Min.
Max.
Min.
Max.
Unit
READ CYCLE
tRC
Read Cycle Time
35
—
55
—
ns
tAA
Address Access Time
—
35
—
55
ns
—
55
ns
(3)
—
35
tABE
(3)
Byte Enable Access Time
—
35
—
55
ns
tAOE
Output Enable Access Time
—
20
—
30
ns
tOH
Output Hold from Address Change
3
—
3
—
ns
tLZ
Output Low-Z Time(1, 2)
3
—
3
—
ns
tHZ
Output High-Z Time(1, 2)
—
15
—
25
ns
tACE
Chip Enable Access Time
(2)
tPU
Chip Enable to Power Up Time
0
—
0
—
ns
tPD
Chip Disable to Power Down Time(2)
—
35
—
50
ns
tSOP
Semaphore Flag Update Pulse (OE or SEM)
15
—
15
—
ns
tSAA
Semaphore Address Access Time
—
35
—
55
ns
NOTES:
1. Transition is measured ±200mV 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 and SEM = VIH. To access semaphore, CE = VIH and SEM = VIL.
4. "X" in part numbers indicates power rating (S or L).
6.17
2939 tbl 12
7
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
WAVEFORM OF READ CYCLES(5)
tRC
ADDR
tAA (4)
(4)
tACE
CE
tAOE
OE
(4)
tABE
(4)
, LB
UB
W
R/
tOH
tLZ (1)
DATAOUT
VALID DATA
(4)
tHZ (2)
BUSYOUT
tBDD (3, 4)
2939 drw 06
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 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
ICC
tPU
tPD
50%
50%
ISB
2939 drw 07
6.17
8
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE (5)
Symbol
IDT7026X20
Com'l. Only
Min.
Max.
Parameter
IDT7026X25
Min.
Max.
Unit
WRITE CYCLE
20
—
25
—
ns
tEW
(3)
Chip Enable to End-of-Write
15
—
20
—
ns
tAW
Address Valid to End-of-Write
15
—
20
—
ns
—
0
—
ns
tWC
Write Cycle Time
(3)
tAS
Address Set-up Time
0
tWP
Write Pulse Width
15
—
20
—
ns
tWR
Write Recovery Time
0
—
0
—
ns
tDW
Data Valid to End-of-Write
15
—
15
—
ns
(1, 2)
tHZ
Output High-Z Time
—
12
—
15
ns
tDH
Data Hold Time(4)
0
—
0
—
ns
tWZ
Write Enable to Output in High-Z(1, 2)
—
12
—
15
ns
tOW
Output Active from End-of-Write(1, 2, 4)
0
—
0
—
ns
5
—
5
—
ns
5
—
5
—
ns
tSWRD
tSPS
SEM Flag Write to Read Time
SEM Flag Contention Window
Symbol
Parameter
IDT7026X35
IDT7026X55
Min.
Min.
Max.
Max.
Unit
WRITE CYCLE
tWC
Write Cycle Time
35
—
55
—
ns
tEW
Chip Enable to End-of-Write(3)
30
—
45
—
ns
tAW
Address Valid to End-of-Write
30
—
45
—
ns
tAS
Address Set-up Time(3)
0
—
0
—
ns
tWP
Write Pulse Width
25
—
40
—
ns
tWR
Write Recovery Time
0
—
0
—
ns
tDW
Data Valid to End-of-Write
15
—
30
—
ns
—
15
—
25
ns
tHZ
(1, 2)
Output High-Z Time
(4)
tDH
Data Hold Time
0
—
0
—
ns
tWZ
Write Enable to Output in High-Z(1, 2)
—
15
—
25
ns
tOW
tSWRD
tSPS
(1, 2, 4)
Output Active from End-of-Write
SEM Flag Write to Read Time
SEM Flag Contention Window
0
—
0
—
ns
5
—
5
—
ns
5
—
5
—
ns
NOTES:
2939 tbl 13
1. Transition is measured ±200mV 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 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).
6.17
9
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TIMING WAVEFORM OF WRITE CYCLE NO. 1, R/W CONTROLLED TIMING(1,5,8)
tWC
ADDRESS
tHZ
(7)
OE
tAW
CE
or SEM
UB
or LB
(9)
(9)
(3)
tWP(2)
tAS (6)
tWR
W
R/
tWZ (7)
DATAOUT
tOW
(4)
(4)
tDW
tDH
DATAIN
2939 drw 08
TIMING WAVEFORM OF WRITE CYCLE NO. 2, CE, UB, LB CONTROLLED TIMING(1,5)
tWC
ADDRESS
tAW
CE or SEM
(9)
(6)
tAS
tWR(3)
tEW (2)
UB or LB (9)
R/
W
tDW
tDH
DATAIN
2939 drw 09
NOTES:
1. R/W or CE or UB and LB 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.
6.17
10
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TIMING WAVEFORM OF SEMAPHORE READ AFTER WRITE TIMING, EITHER SIDE(1)
tOH
tSAA
A0-A2
VALID ADDRESS
tWR
tAW
tEW
SEM
VALID ADDRESS
tACE
tSOP
tDW
DATAIN
VALID
I/O0
tAS
W
tWP
DATAOUT
VALID(2)
tDH
R/
tSWRD
tAOE
OE
Write Cycle
Read Cycle
2939 drw 10
NOTES:
1. CE = VIH or UB and 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"
(2)
SIDE
“A”
MATCH
W"A"
R/
SEM"A"
tSPS
A0"B"-A2"B"
(2)
SIDE
“B”
MATCH
W"B"
R/
SEM"B"
2939 drw 11
NOTES:
1. DOR = DOL = VIL, CER = CEL = VIH, or both UB & LB = VIH.
2. All timing is the same for left and right ports. Port “A” may be either left or right port. Port “B” is the opposite from port “A”.
3. This parameter is measured from R/W"A" or SEM"A" going HIGH to R/W"B" or SEM"B" going HIGH.
4. If tSPS is not satisfied, there is no guarantee which side will be granted the semaphore flag.
6.17
11
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
AC ELECTRICAL CHARACTERISTICS OVER THE
OPERATING TEMPERATURE AND SUPPLY VOLTAGE RANGE(6)
Symbol
IDT7026X20
Com'l. Only
Min.
Max.
Parameter
IDT7026X25
Min.
Max.
Unit
BUSY TIMING (M/S = VIH)
tBDC
BUSY Access Time from Address Match
BUSY Disable Time from Address Not Matched
BUSY Access Time from Chip Enable Low
BUSY Disable Time from Chip Enable High
tAPS
Arbitration Priority Set-up Time(2)
tBAA
tBDA
tBAC
BUSY Disable to Valid Data(3)
Write Hold After BUSY(5)
tWH
BUSY TIMING (M/S = VIL)
BUSY Input to Write(4)
tWB
Write Hold After BUSY(5)
tWH
tBDD
—
20
—
20
ns
—
20
—
20
ns
—
20
—
20
ns
—
17
—
17
ns
5
—
5
—
ns
—
30
—
30
ns
15
—
17
—
ns
0
—
0
—
ns
15
—
17
—
ns
PORT-TO-PORT DELAY TIMING
tWDD
Write Pulse to Data Delay(1)
—
45
—
50
ns
tDDD
Write Data Valid to Read Data Delay(1)
—
30
—
35
ns
Symbol
Parameter
IDT7026X35
IDT7026X55
Min.
Max.
Min.
Max.
Unit
—
20
—
45
ns
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
(2)
Arbitration Priority Set-up Time
BUSY Disable to Valid Data(3)
Write Hold After BUSY(5)
—
20
—
40
ns
—
20
—
40
ns
—
20
—
35
ns
5
—
5
—
ns
—
35
—
40
ns
25
—
25
—
ns
BUSY TIMING (M/S = VIL)
tWB
tWH
BUSY Input to Write(4)
Write Hold After BUSY(5)
0
—
0
—
ns
25
—
25
—
ns
PORT-TO-PORT DELAY TIMING
tWDD
Write Pulse to Data Delay(1)
—
60
—
80
ns
tDDD
Write Data Valid to Read Data Delay(1)
—
45
—
65
ns
NOTES:
1. Port-to-port delay through RAM cells from writing port to reading port, refer to "Timing Waveform 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).
6.17
BUSY
2939 tbl 15
(M/S = VIH)".
12
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TIMING WAVEFORM OF WRITE WITH PORT-TO-PORT READ AND BUSY (M/S = VIH)(2,4,5)
tWC
MATCH
ADDR"A"
tWP
W"A"
R/
tDW
tDH
VALID
DATAIN "A"
tAPS (1)
MATCH
ADDR"B"
tBAA
tBDA
tBDD
BUSY"B"
tWDD
DATAOUT "B"
VALID
tDDD (3)
NOTES:
1. To ensure that the earlier of the two ports wins. tAPS is ignored for M/S = VIL (slave).
2. CEL = CER = VIL.
3. OE = VIL for the reading port.
4. If M/S = VIL (slave), BUSY is an input. Then for this example BUSY"A" = VIH and BUSY"B" input is shown above.
5. All timing is the same for left and right ports. Port "A" may be either the left or right port. Port "B" is the port opposite from port "A".
2939 drw 12
TIMING WAVEFORM OF WRITE WITH BUSY (M/S = VIL)
tWP
W
R/ "A"
tWB(3)
BUSY"B"
tWH (1)
W
R/ "B"
(2)
2939 drw 13
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.
6.17
13
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
WAVEFORM OF BUSY ARBITRATION CONTROLLED BY CE TIMING (M/S = VIH)(1)
ADDR"A"
and "B"
ADDRESSES MATCH
CE"A"
tAPS(2)
CE"B"
tBAC
tBDC
BUSY"B"
2939 drw 15
WAVEFORM OF BUSY ARBITRATION CYCLE CONTROLLED BY ADDRESS MATCH TIMING
(M/S = VIH)(1)
ADDRESS "N"
ADDR"A"
tAPS
(2)
MATCHING ADDRESS "N"
ADDR"B"
tBAA
tBDA
BUSY"B"
2939 drw 15
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.
TRUTH TABLE III — EXAMPLE OF SEMAPHORE PROCUREMENT SEQUENCE(1,2)
Functions
No Action
D0 - D15 Left
1
D0 - D15 Right
1
Status
Semaphore free
Left Port Writes "0" to Semaphore
0
1
Left port has semaphore token
Right Port Writes "0" to Semaphore
0
1
No change. Right side has no write access to semaphore
Left Port Writes "1" to Semaphore
1
0
Right port obtains semaphore token
Left Port Writes "0" to Semaphore
1
0
No change. Left port has no write access to semaphore
Right Port Writes "1" to Semaphore
0
1
Left port obtains semaphore token
Left Port Writes "1" to Semaphore
1
1
Semaphore free
Right Port Writes "0" to Semaphore
1
0
Right port has semaphore token
Right Port Writes "1" to Semaphore
1
1
Semaphore free
Left Port Writes "0" to Semaphore
0
1
Left port has semaphore token
Left Port Writes "1" to Semaphore
1
1
Semaphore free
NOTES:
1. This table denotes a sequence of events for only one of the eight semaphores on the IDT7026.
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.
6.17
2683 tbl 16
14
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
WIDTH EXPANSION WITH BUSY LOGIC
MASTER/SLAVE ARRAYS
Inputs
Outputs
CEL
CER
A0L-A13L
A0R-A13R
X
X
NO MATCH
H
H
Normal
H
X
MATCH
H
H
Normal
X
H
MATCH
H
H
Normal
L
L
MATCH
(2)
(2)
Write Inhibit(3)
BUSYL(1) BUSYR(1)
Function
NOTES:
2683 tbl 17
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 IDT7026 are push pull, not open drain outputs. On slaves the BUSYX
input internally inhibits writes.
2. LOW if the inputs to the opposite port were stable prior to the address and
enable inputs of this port. HIGH 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.
When expanding an IDT7026 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 IDT7026 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.
MASTER
Dual Port
RAM
BUSYL
MASTER
Dual Port
RAM
BUSYL
BUSYL
CE
BUSYR
CE
BUSYR
SLAVE
Dual Port
RAM
BUSYL
SLAVE
Dual Port
RAM
BUSYL
CE
BUSYR
DECODER
TRUTH TABLE IV —
ADDRESS BUSY ARBITRATION
CE
BUSYR
BUSYR
2939 drw 16
FUNCTIONAL DESCRIPTION
The IDT7026 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 IDT7026 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.
BUSY LOGIC
Busy Logic provides a hardware indication that both ports
of the RAM have accessed the same location at the same
time. It also allows one of the two accesses to proceed and
signals the other side that the RAM is “Busy”. The busy pin can
then be used to stall the access until the operation on the other
side is completed. If a write operation has been attempted
from the side that receives a busy indication, the write signal
is gated internally to prevent the write from proceeding.
The use of busy logic is not required or desirable for all
applications. In some cases it may be useful to logically OR
the busy outputs together and use any busy indication as an
interrupt source to flag the event of an illegal or illogical
operation. If the write inhibit function of busy logic is not
desirable, the busy logic can be disabled by placing the part
in slave mode with the M/S pin. Once in slave mode the BUSY
pin operates solely as a write inhibit input pin. Normal operation can be programmed by tying the BUSY pins HIGH. If
desired, unintended write operations can be prevented to a
port by tying the busy pin for that port LOW.
The busy outputs on the IDT 7026 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.
Figure 3. Busy and chip enable routing for both width and depth
expansion with IDT7026 RAMs.
If two or more master parts were used when expanding in
width, a split decision could result with one master indicating
busy on one side of the array and another master indicating
busy on one other side of the array. This would inhibit the write
operations from one port for part of a word and inhibit the write
operations from the other port for the other part of the word.
The busy arbitration, on a master, is based on the chip
enable and address signals only. It ignores whether an access
is a read or write. In a master/slave array, both address and
chip enable must be valid long enough for a busy flag to be
output from the master before the actual write pulse can be
initiated with either the R/W signal or the byte enables. Failure
to observe this timing can result in a glitched internal write
inhibit signal and corrupted data in the slave.
SEMAPHORES
The IDT7026 is an extremely fast Dual-Port 16K x 16
CMOS Static RAM with an additional 8 address locations
dedicated to binary semaphore flags. These flags allow either
processor on the left or right side of the Dual-Port RAM to claim
a privilege over the other processor for functions defined by
the system designer’s software. As an example, the semaphore can be used by one processor to inhibit the other from
accessing a portion of the Dual-Port RAM or any other shared
resource.
The Dual-Port RAM features a fast access time, and both
ports are completely independent of each other. This means
that the activity on the left port in no way slows the access time
of the right port. Both ports are identical in function to standard
6.17
15
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
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 IDT7026 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 IDT7026'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 IDT7026 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 IDT7026 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
6.17
16
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
L PORT
R PORT
SEMAPHORE
REQUEST FLIP FLOP
D0
D
Q
SEMAPHORE
REQUEST FLIP FLOP
Q
D
WRITE
SEMAPHORE
READ
D0
WRITE
SEMAPHORE
READ
Figure 4. IDT7026 Semaphore Logic
2939 drw 17
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
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 IDT7026’s Dual-Port
RAM. Say the 16K x 16 RAM was to be divided into two 8K
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 8K 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 8K. 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 8K 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 8K 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.
6.17
17
IDT7026S/L
HIGH-SPEED 16K x 16 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
ORDERING INFORMATION
IDT XXXXX
Device
Type
A
999
A
A
Power
Speed
Package
Process/
Temperature
Range
Blank
Commercial (0°C to +70°C)
B
Military (–55°C to +125°C)
Compliant to MIL-STD-883, Class B
G
J
84-pin PGA (G84-3)
84-pin PLCC (J84-1)
20
25
35
55
Commercial Only
S
L
Standard Power
Low Power
7026
256K (16K x 16) Dual-Port
RAM
Speed in nanoseconds
2939 drw 18
6.17
18
Similar pages