IDT IDT70T35L20BFI High-speed 2.5v 8/4k x 18 dual-port 8/4k x 16 dual-port static ram Datasheet

HIGH-SPEED 2.5V
8/4K x 18 DUAL-PORT
8/4K x 16 DUAL-PORT
STATIC RAM
Features
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True Dual-Ported memory cells which allow simultaneous
reads of the same memory location
High-speed access
IDT70T35/34L (IDT70T25/24L)
– Commercial: 20/25ns (max.)
– Industrial: 25ns (max.)
Low-power operation
– IDT70T35/34L (IDT70T25/24L)
Active: 200mW (typ.)
Standby: 600µW (typ.)
Separate upper-byte and lower-byte control for multiplexed
bus compatibility
IDT70T35/34L (IDT70T25/24L) easily expands data bus
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PRELIMINARY
IDT70T35/34L
IDT70T25/24L
width to 36 bits (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 2.5V (±100mV) power supply
Available in a 100-pin Thin Quad Flatpack (TQFP) package
and 100-pin fine pitch Ball Grid Array (fpBGA)
Industrial temperature range (-40°C to +85°C) is available
for selected speeds
Functional Block Diagram
R/WL
UBL
R/WR
UBR
LBL
CEL
OEL
LBR
CER
OER
,
I/O9R-I/O17R(5)
I/O9L-I/O17L(5)
I/O
Control
I/O
Control
I/O0L-I/O8L(4)
I/O0R-I/O8R(4)
(2,3)
BUSYR(2,3)
BUSYL
A12L(1)
A0L
Address
Decoder
MEMORY
ARRAY
13
CEL
OEL
R/WL
SEML
INTL(3)
Address
Decoder
A12R(1)
A0R
13
ARBITRATION
INTERRUPT
SEMAPHORE
LOGIC
M/S
CER
OER
R/WR
SEMR
INTR(3)
5639 drw 01
NOTES:
1. A12 is a NC for IDT70T34 and IDT70T24.
2. (MASTER): BUSY is output; (SLAVE): BUSY is input.
3. BUSY outputs and INT outputs are non-tri-stated push-pull.
4. I/O0x - I/O7x for IDT70T25/24.
5. I/O8x - I/O15x for IDT70T25/24.
DECEMBER 2002
1
©2002 Integrated Device Technology, Inc.
DSC-5639/2
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Description
The IDT70T35/34L (IDT70T25/24L) is a high-speed 8/4K x 18
(8/4K x 16) Dual-Port Static RAM. The IDT70T35/34L (IDT70T25/24L)
is designed to be used as a stand-alone Dual-Port RAM or as a
combination MASTER/SLAVE Dual-Port RAM for 36-bit (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 200mW of power.
The IDT70T35/34L (IDT70T25/24L) is packaged in a plastic 100-pin
Thin Quad Flatpack and a 100-pin fine pitch Ball Grid Array.
IDT70T35/34 Pin Configurations(1,2,3,4)
I/O10L
I/O9L
I/O7L
I/O6L
I/O5L
I/O4L
I/O3L
I/O2L
Vss
I/O1L
I/O0L
OEL
VDD
R/WL
SEML
CEL
UBL
LBL
A12L(1)
A11L
A10L
A9L
A8L
A7L
A6L
12/06/02
Index
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
75
2
74
3
73
1
4
72
5
71
6
70
7
69
8
68
67
9
10
11
IDT70T35/34PF
PN100-1(5)
12
13
14
100-Pin TQFP
Top View(6)
66
65
64
63
62
15
61
16
60
17
59
18
58
19
57
20
56
21
55
22
54
23
53
24
52
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/O9R
I/O10R
I/O11R
I/O12R
I/O13R
I/O14R
I/O15R
Vss
I/O16R
OER
R/WR
Vss
SEMR
CER
UBR
LBR
A12R(1)
A11R
A10R
A9R
A8R
A7R
A6R
A5R
N/C
N/C
I/O8L
I/O17L
I/O11L
I/O12L
I/O13L
I/O14L
Vss
I/O15L
I/O16L
VDD
Vss
I/O0R
I/O1R
I/O2R
VDD
I/O3R
I/O4R
I/O5R
I/O6R
I/O8R
I/O17R
N/C
N/C
NOTES:
1. A12 is a NC for IDT70T34.
2. All VDD pins must be connected to power supply.
3. All VSS pins must be connected to ground.
4. PN100-1 package body is approximately 14mm x 14mm x 1.4mm.
5. This package code is used to reference the package diagram.
6. This text does not indicate orientation of the actual part marking.
6.42
2
N/C
N/C
N/C
N/C
A5L
A4L
A3L
A2L
A1L
A0L
INTL
BUSYL
Vss
M/S
BUSYR
INTR
A0R
A1R
A2R
A3R
A4R
N/C
N/C
N/C
N/C
,
5639 drw 02
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
IDT70T35/34 Pin Configurations(cont'd) (1,2,3,4)
IDT70T35/34BF
BF100(5)
100-Pin fpBGA
Top View(6)
12/06/02
A1
A6R
B1
NC
C1
A3R
D1
A1R
E1
A2
A9R
B2
NC
C2
A4R
D2
INTR
E2
M/S BUSY R
F1
VSS
G1
INTL
H1
A2L
J1
A4L
K1
A7L
F2
BUSYL
G2
A3L
H2
A5L
J2
A8L
K2
A9L
A3
A4
A12R(1) CER
B3
A8R
C3
A5R
D3
A2R
E3
A0R
F3
A0L
G3
A6L
H3
A10L
J3
A11L
K3
A12L(1)
B4
A6
A5
VSS
VSS
B6
B5
A10R SEMR R/WR
C4
A7R
D4
NC
E4
A1L
F4
NC
G4
NC
H4
LBL
J4
C5
C6
UBL
VSS
B7
A8
A9
A10
I/O13R I/O10R I/O7R
B8
B9
B10
OER I/O12R I/O9R
C7
C8
D6
D5
A11R
E5
E6
VSS
VSS
F6
F5
VDD
VSS
G5
G6
VSS
I/O3L
H5
H6
CEL
I/O1L
J5
K5
VDD
LBR
J6
OEL
K6
VDD
D7
D8
I/O14R I/O17R
E7
I/O4R
F7
VDD
G7
NC
H7
I/O7L
J7
I/O4L
K7
I/O0L
E8
I/O2R
F8
I/O6R
C10
C9
UBR I/O16R I/O15R I/O11R I/O8R
SEML R/WL
K4
A7
I/O3R
D9
D10
I/O5R I/O1R
E9
E10
I/O0R
F9
VDD
F10
I/O14L I/O15L I/O16L
G8
I/O12L
H8
I/O8L
J8
I/O6L
K8
I/O2L
G9
VSS
H9
G10
I/O13L
H10
I/O17L I/O11L
J9
VSS
K9
I/O5L
J10
I/O10L
K10
I/O9L
5639 drw 03
NOTES:
1. A12 is a NC for IDT70T34.
2. All VDD pins must be connected to power supply.
3. All VSS pins must be connected to ground.
4. BF-100 package body is approximately 10mm x 10mm x 1.4mm with 0.8mm ball pitch.
5. This package code is used to reference the package diagram.
6. This text does not indicate orientation of the actual part marking.
6.42
3
,
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
IDT70T25/24 Pin Configurations(1,2,3,4)
I/O9L
I/O8L
I/O7L
I/O6L
I/O5L
I/O4L
I/O3L
I/O2L
VSS
I/O1L
I/O0L
OEL
VDD
R/WL
SEML
CEL
UBL
LBL
A12L(1)
A11L
A10L
A9L
A8L
A7L
A6L
12/06/02
Index
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
75
2
74
3
73
1
4
72
5
71
6
70
7
69
8
68
9
67
10
11
IDT70T25/24PF
PN100-1(5)
12
13
14
100-Pin TQFP
Top View(6)
66
65
64
63
62
15
61
16
60
17
59
18
58
19
57
20
56
21
55
22
54
23
53
24
52
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
VSS
I/O15R
OER
R/WR
VSS
SEMR
CER
UBR
LBR
A12R(1)
A11R
A10R
A9R
A8R
A7R
A6R
A5R
N/C
N/C
N/C
N/C
I/O10L
I/O11L
I/O12L
I/O13L
VSS
I/O14L
I/O15L
VDD
VSS
I/O0R
I/O1R
I/O2R
VDD
I/O3R
I/O4R
I/O5R
I/O6R
N/C
N/C
N/C
N/C
NOTES:
1. A12 is a NC for IDT70T24.
2. All VDD pins must be connected to power supply.
3. All VSS pins must be connected to ground.
4. PN100-1 package body is approximately 14mm x 14mm x 1.4mm.
5. This package code is used to reference the package diagram.
6. This text does not indicate orientation of the actual part marking.
6.42
4
N/C
N/C
N/C
N/C
A5L
A4L
A3L
A2L
A1L
A0L
INTL
BUSYL
VSS
M/S
BUSYR
INTR
A0R
A1R
A2R
A3R
A4R
N/C
N/C
N/C
N/C
5639 drw 04
.
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
IDT70T25/24 Pin Configurations(cont'd) (1,2,3,4)
IDT70T25/24BF
BF100(5)
100-Pin fpBGA
Top View(6)
12/06/02
A1
A6R
B1
NC
C1
A3R
D1
A1R
E1
A2
A9R
B2
NC
C2
A4R
D2
INTR
E2
M/S BUSY R
F1
VSS
G1
INTL
H1
A2L
J1
A4L
K1
A7L
F2
BUSYL
G2
A3L
H2
A5L
J2
A8L
K2
A9L
A3
A12R(1)
B3
A8R
C3
A5R
D3
A2R
E3
A0R
F3
A0L
G3
A6L
H3
A10L
J3
A11L
K3
A12L(1)
A4
CER
B4
A6
A5
VSS
VSS
B6
B5
A10R SEMR R/WR
C4
A7R
D4
NC
E4
A1L
F4
NC
G4
NC
H4
LBL
J4
SEML
K4
UBL
C5
C6
A7
VSS
B7
A8
D6
LBR
A11R
E5
E6
VSS
F5
VSS
F6
VDD
G5
VSS
G6
VSS
H5
I/O3L
H6
CEL
J5
I/O1L
J6
OEL
R/WL
K6
K5
VDD
VDD
A10
I/O12R I/O9R I/O7R
B8
B9
B10
OER I/O11R I/O8R
C7
C8
UBR I/O15R I/O14R I/O10R
D5
A9
D7
D8
I/O13R
E7
I/O4R
F7
VDD
G7
NC
H7
I/O7L
J7
I/O4L
K7
I/O0L
NC
E8
I/O2R
C9
I/O6R
C10
NC
I/O3R
D9
D10
I/O5R I/O1R
E9
E10
I/O0R
VDD
F8
F9
I/O13L
I/O14L I/O15L
G8
I/O11L
H8
NC
J8
I/O6L
K8
I/O2L
G9
VSS
H9
NC
J9
VSS
K9
I/O5L
F10
G10
I/O12L
H10
I/O10L
J10
I/O9L
K10
I/O8L
5639 drw 05
NOTES:
1. A12 is a NC for IDT70T24.
2. All VDD pins must be connected to power supply.
3. All VSS pins must be connected to ground.
4. BF-100 package body is approximately 10mm x 10mm x 1.4mm with 0.8mm ball pitch.
5. This package code is used to reference the package diagram.
6. This text does not indicate orientation of the actual part marking.
6.42
5
,
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Pin Names
Left Port
Right Port
Names
CEL
CER
Chip Enable
R/WL
R/WR
Read/Write Enable
OEL
OER
Output Enable
A0L - A12L(1)
A0R - A12R(1)
Address
I/O0L - I/O17L(2)
I/O0R - I/O17R(2)
Data Input/Output
SEML
SEMR
Semaphore Enable
UBL
UBR
Upper Byte Select(3)
LBL
LBR
Lower Byte Select(4)
INTL
INTR
Interrupt Flag
BUSYL
BUSYR
Busy Flag
M/S
Master or Slave Select
VDD
Power (2.5V)
VSS
Ground (0V)
5639 tbl 01
NOTE:
1. A12 is a NC for IDT70T34 and IDT70T24.
2. I/O0x - I/O15x for IDT70T25/24.
3. IDT70T35/34L: UBx controls I/O9x - I/O17x
IDT70T25/24L: UBx controls I/O8x - I/O15x
4. IDT70T35/34L: LBx controls I/O0x - I/O8x
IDT70T25/24L: LBx controls I/O0x - I/O7x
6.42
6
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Truth Table I: Non-Contention Read/Write Control
Inputs(1)
Outputs
(3)
I/O9-17
I/O0-8(2)
CE
R/W
OE
UB
LB
SEM
H
X
X
X
X
H
High-Z
High-Z
Deselected: Power Down
X
X
X
H
H
H
High-Z
High-Z
Both Bytes Deselected
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
L
H
L
L
H
H
DATAOUT
High-Z
Read Upper Byte Only
L
H
L
H
L
H
High-Z
DATAOUT
Read Lower Byte Only
L
H
L
L
L
H
DATAOUT
DATAOUT
Read Both Bytes
X
X
H
X
X
X
High-Z
High-Z
Outputs Disabled
Mode
5639 tbl 02
NOTE:
1. A0L — A12L ≠ A0R — A12R for IDT70T35 and IDT70T25; A0L — A11L ≠ A0R — A11R for IDT70T34 and IDT70T24.
2. Outputs for IDT70T25/24 are I/O0x - I/O7x.
3. Outputs for IDT70T25/24 are I/O8x - I/O15x.
Truth Table II: Semaphore Read/Write Control(1)
Inputs
Outputs
CE
R/W
OE
UB
LB
SEM
H
H
L
X
X
L
DATAOUT
DATAOUT
Read Data in Semaphore Flag
X
H
L
H
H
L
DATAOUT
DATAOUT
Read Data in Semaphore Flag
H
↑
X
X
X
L
DATAIN
DATAIN
Write DIN0 into Semaphore Flag
X
↑
X
H
H
L
DATAIN
DATAIN
Write DIN0 into Semaphore Flag
L
____
____
Not Allowed
L
____
____
Not Allowed
L
L
X
X
X
X
L
X
X
L
(1)
I/O9-17
I/O0-8(1)
Mode
5639 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/O17 for IDT70T35/34) and (I/O0-I/O15 for IDT70T25/24). These eight semaphores
are addressed by A0-A2.
6.42
7
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Absolute Maximum Ratings(1)
Symbol
VTERM
Rating
Terminal Voltage
with Respect to GND
(2)
Unit
-0.5 to +3.6
V
-55 to +125
o
C
C
C
Maximum Operating Temperature
and Supply Voltage(1)
Grade
Commercial
Temperature Under Bias
TBIAS(3)
Commercial
& Industrial
TSTG
Storage Temperature
-65 to +150
o
TJN
Junction Temperature
+150
o
IOUT
DC Output Current
50
Ambient
Temperature
GND
VDD
0OC to +70OC
0V
2.5V + 100mV
0V
2.5V + 100mV
O
Industrial
O
-40 C to +85 C
NOTE:
1. This is the parameter TA. This is the "instant on" case temperature.
5639 tbl 05
mA
5639 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 VDD+ 0.3V.
3. Ambient Temperature Under DC Bias. No AC Conditions. Chip Deselected.
Capacitance
Symbol
CIN
COUT
(1)
(TA = +25°C, f = 1.0MHz)
(2)
Parameter
Conditions
Max.
Unit
Input Capacitance
VIN = 3dV
9
pF
VOUT = 3dV
10
pF
Output Capacitance
Recommended DC Operating
Conditions
Symbol
Parameter
Min.
Typ.
Max.
Unit
2.4
2.5
2.6
V
0
0
0
V
VDD
Supply Voltage
VSS
Ground
VIH
Input High Voltage
1.7
____
VDD+0.3(2)
V
VIL
Input Low Voltage
-0.3(1)
____
0.7
V
5639 tbl 06
NOTES:
1. VIL > -1.5V for pulse width less than 10ns.
2. VTERM must not exceed VDD + 0.3V.
5639 tbl 07
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 (VDD = 2.5V ± 100mV)
70T35/34L
(70T25/24L)
Symbol
Parameter
(1)
Test Conditions
Min.
Max.
Unit
|ILI|
Input Leakage Current
VDD = 2.6V, VIN = 0V to V DD
___
5
µA
|ILO|
Output Leakage Currentt(1)
CE = VIH, VOUT = 0V to V DD
___
5
µA
0.4
V
___
V OL
Output Low Voltage
IOL = +2mA
___
VOH
Output High Voltage
IOH = -2mA
2.0
V
5639 tbl 08
NOTE:
1. At VDD < 2.0V leakages are undefined.
6.42
8
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
DC Electrical Characteristics Over the Operating
Temperature and Supply Voltage Range (VDD = 2.5V ± 100mV)
70T35/34L20
(70T25/24L20)
Com'l Only
Symbol
IDD
ISB1
ISB2
ISB3
ISB4
Parameter
Test Condition
Version
70T35/34L25
(70T25/24L25)
Com'l
& Ind
Typ.(2)
Max.
Typ.(2)
Max.
Unit
mA
Dynamic Operating
Current
(Both Ports Active)
CE = VIL, Outputs Disabled
SEM = VIH
f = fMAX(3)
COM'L
L
80
140
70
130
IND
L
____
____
100
160
Standby Current
(Both Ports - TTL
Level Inputs)
CER and CEL = VIH
SEMR = SEML = VIH
f = fMAX(3)
COM'L
L
12
20
7
17
IND
L
____
____
12
25
Standby Current
(One Port - TTL
Level Inputs)
CE"A" = VIL and CE"B" = VIH
Active Port Outputs Disabled,
f=fMAX(3)
SEMR = SEML = VIH
COM'L
L
55
90
40
80
L
____
____
55
100
Both Ports CEL and
CER > VDD - 0.2V,
VIN > VDD - 0.2V or
VIN < 0.2V, f = 0(4)
SEMR = SEML > VDD-0.2V
COM'L
L
0.05
2.5
0.05
2.5
L
____
____
0.2
5.0
CE"A" < 0.2V and
CE"B" > VDD - 0.2V(1)
SEMR = SEML > VDD-0.2V
VIN > VDD - 0.2V or V IN < 0.2V
Active Port Outputs Disabled,
f = fMAX(3)
COM'L
L
55
90
40
80
L
____
____
55
100
(1)
Full Standby Current
(Both Ports CMOS Level Inputs)
Full Standby Current
(One Port CMOS Level Inputs)
IND
IND
IND
mA
mA
mA
mA
5639 tbl 09
NOTES:
1. Port "A" may be either left or right port. Port "B" is the opposite from port "A".
2. VDD = 2.5V, TA = +25°C, and are not production tested. IDD dc = 85mA (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.
AC Test Conditions
50Ω
GND to 2.5V
Input Pulse Levels
3ns Max.
DATAOUT
Input Timing Reference Levels
1.25V
Output Reference Levels
1.25V
BUSY
INT
Input Rise/Fall Times
50Ω
1.25V
10pF / 5pF*
(Tester)
Figure 1
Output Load
5639 tbl 10
Figure 1. AC Output Test Load
*(For tLZ, tHZ, tWZ, tOW)
Timing of Power-Up Power-Down
CE
ICC
tPU
tPD
50%
50%
ISB
5639 drw 07
6.42
9
,
5639 drw 06
,
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the
Operating Temperature and Supply Voltage Range
70T35/34L20
(70T25/24L20)
Com'l Only
Symbol
Parameter
70T35/34L25
(70T25/24L25)
Com'l
& Ind
Min.
Max.
Min.
Max.
Unit
READ CYCLE
tRC
Read Cycle Time
20
____
25
____
ns
tAA
Address Access Time
____
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 (3)
____
12
____
13
ns
tOH
Output Hold from Address Change
3
____
3
____
ns
tLZ
Output Low-Z Time (1,2)
3
____
3
____
ns
____
12
____
15
ns
0
____
0
____
ns
____
20
____
25
ns
10
____
ns
____
25
ns
(1,2)
tHZ
Output High-Z Time
tPU
Chip Enab le to Power Up Time (1,2)
tPD
Chip Disable to Power Down Time (1,2)
tSOP
Semaphore Flag Update Pulse (OE or SEM)
10
____
tSAA
Semaphore Address Access (3)
____
20
5639 tbl 11
NOTES:
1. Transition is measured 0mV from Low or High-impedance voltage with Output Test Load (Figure 1).
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 & LB = VIH, and SEM = VIL.
Waveform of Read Cycles(5)
tRC
ADDR
(4)
CE
tAA
(4)
tACE
tAOE
(4)
OE
tABE
(4)
UB, LB
R/W
tLZ
tOH
(1)
DATAOUT
VALID DATA
(4)
tHZ
(2)
BUSYOUT
tBDD
(3,4)
5639 drw 08
NOTES:
1. Timing depends on which signal is asserted last, OE, CE, LB, or UB.
2. Timing depends on which signal is de-asserted first, CE, OE, LB, or UB.
3. tBDD delay is required only in case where opposite port is completing a write operation to the same address location for simultaneous read operations BUSY has no
relation to valid output data.
4. Start of valid data depends on which timing becomes effective last tABE, tAOE, tACE, tAA or tBDD.
5. SEM = VIH.
6.42
10
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the
Operating Temperature and Supply Voltage
Symbol
Parameter
70T35/34L20
(70T25/24L20)
Com'l Only
70T35/34L25
(70T25/24L25)
Com'l
& Ind
Min.
Max.
Min.
Max.
Unit
WRITE CYCLE
tWC
Write Cycle Time
20
____
25
____
ns
tEW
Chip Enable to End-of-Write (3)
15
____
20
____
ns
tAW
Address Valid to End-of-Write
15
____
20
____
ns
0
____
0
____
ns
15
____
20
____
ns
0
____
0
____
ns
15
____
15
____
ns
____
12
____
15
ns
0
____
0
____
ns
____
12
____
15
ns
0
____
0
____
ns
5
____
5
____
ns
5
____
5
____
tAS
tWP
tWR
tDW
tHZ
tDH
tWZ
Address Set-up Time
(3)
Write Pulse Width
Write Recovery Time
Data Valid to End-of-Write
Output High-Z Time
Data Hold Time
(1,2)
(4)
(1,2)
Write Enable to Output in High-Z
tOW
Output Active from End-of-Write
tSWRD
SEM Flag Write to Read Time
tSPS
SEM Flag Contention Window
(1,2,4)
ns
5639 tbl 12
NOTES:
1. Transition is measured 0mV from Low or High-impedance voltage with the Output Test Load (Figure 1).
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 & 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.
6.42
11
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
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
CE or SEM
(9)
(9)
tAS
(6)
tWP
(3)
(2)
tWR
R/W
tWZ
(7)
tOW
(4)
DATAOUT
(4)
tDW
tDH
DATAIN
5639 drw 09
Timing Waveform of Write Cycle No. 2, CE, UB, LB Controlled Timing(1,5)
tWC
ADDRESS
tAW
(9)
CE or SEM
tAS (6)
tWR (3)
tEW (2)
(9)
UB or LB
R/W
tDW
tDH
DATAIN
5639 drw 10
NOTES:
1. R/W or CE or UB & LB must be HIGH during all address transitions.
2. A write occurs during the overlap (tEW or tWP) of a LOW UB or LB and a LOW CE and a LOW R/W for memory array writing cycle.
3. tWR is measured from the earlier of CE or R/W (or SEM or R/W) going HIGH to the end-of-write cycle.
4. During this period, the I/O pins are in the output state and input signals must not be applied.
5. If the CE or SEM LOW transition occurs simultaneously with or after the R/W LOW transition the outputs remain in the HIGH-impedance state.
6. Timing depends on which enable signal is asserted last, CE, R/W, or UB or LB.
7. This parameter is guaranteed by device characterization, but is not production tested. Transition is measured 0mV from steady state with Output Test Load
(Figure 1).
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, and SEM = VIH. To access Semaphore, CE = VIH or UB and LB = VIH, and SEM = VIL. tEW must be met for either condition.
6.42
12
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Timing Waveform of Semaphore Read after Write Timing, Either Side(1)
tOH
tSAA
A0 - A2
VALID ADDRESS
tAW
VALID ADDRESS
tWR
tACE
tEW
SEM
tSOP
tDW
DATA0
DATA OUT
VALID(2)
DATAIN VALID
tAS
tWP
tDH
R/W
tSWRD
OE
tAOE
tSOP
Write Cycle
Read Cycle
5639 drw 11
NOTES:
1. CE = VIH or UB & LB = VIH for the duration of the above timing (both write and read cycle).
2. “DATAOUT VALID” represents all I/O's (I/O0-I/O17 for IDT70T35/34) and (I/O0-I/O15 for IDT70T25/24) equal to the semaphore value.
Timing Waveform of Semaphore Write Contention(1,3,4)
A0"A"-A2"A"
(2)
SIDE
"A"
MATCH
R/W"A"
SEM"A"
tSPS
A0"B"-A2"B"
(2)
SIDE
"B"
MATCH
R/W"B"
SEM"B"
5639 drw 12
NOTES:
1. DOR = DOL = VIL, CER = CEL = VIH, or both UB & LB = VIH.
2. All timing is the same for left and right port. Port “A” may be either left or right port. Port “B” is the opposite from port “A”.
3. This parameter is measured from R/W"A" or SEM"A" going HIGH to R/W"B" or SEM"B" going HIGH.
4. If tSPS is not satisfied, there is no guarantee which side will obtain the semaphore flag.
6.42
13
,
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the
Operating Temperature and Supply Voltage Range
70T35/34L20
(70T25/24L20)
Com'l Only
Symbol
Parameter
70T35/34L25
(70T25/24L25)
Com'l
& Ind
Min.
Max.
Min.
Max.
Unit
20
____
20
ns
20
____
20
ns
20
ns
BUSY TIMING (M/S = VIH)
tBAA
BUSY Access Time from Address Match
____
tBDA
BUSY Disable Time from Address Not Matched
____
tBAC
BUSY Access Time from Chip Enable LOW
____
20
____
tBDC
BUSY Disable Time from Chip Enable HIGH
____
17
____
17
ns
tAPS
Arbitration Priority Set-up Time (2)
5
____
5
____
ns
tBDD
BUSY Disable to Valid Data(3)
____
30
____
30
ns
tWH
Write Hold After BUSY
15
____
17
____
ns
(5)
BUSY TIMING (M/S = VIL)
tWB
BUSY Input to Write (4)
0
____
0
____
ns
tWH
Write Hold After BUSY(5)
15
____
17
____
ns
____
45
____
50
ns
35
____
35
PORT-TO-PORT DELAY TIMING
tWDD
tDDD
Write Pulse to Data Delay(1)
Write Data Valid to Read Data Delay
(1)
____
ns
5639 tbl 13
NOTES:
1. Port-to-port delay through SRAM cells from writing port to reading port, refer to "TIMING WAVEFORM OF WRITE PORT-TO-PORT READ AND
BUSY (M/S = VIH)".
2. To ensure that the earlier of the two ports wins.
3. tBDD is a calculated parameter and is the greater of 0, 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.
Timing Waveform of Write Port-to-Port Read and BUSY(2,4,5) (M/S = VIH)
tWC
ADDR"A"
MATCH
tWP
R/W"A"
tDH
tDW
DATAIN "A"
VALID
tAPS
(1)
ADDR"B"
MATCH
tBAA
tBDA
tBDD
BUSY"B"
tWDD
DATAOUT "B"
VALID
(3)
tDDD
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
5639 drw 13
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Timing Waveform of Write with BUSY
tWP
R/W"A"
tWB
(3)
BUSY"B"
tWH
R/W"B"
(1)
(2)
5639 drw 14
,
NOTES:
1. tWH must be met for both master 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.
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
BUSY"B"
5639 drw 15
Waveform of BUSY Arbitration Cycle Controlled by Address Match
Timing(1) (M/S = VIH)
ADDR"A"
ADDRESS "N"
tAPS
(2)
ADDR"B"
MATCHING ADDRESS "N"
tBAA
tBDA
BUSY"B"
5639 drw 16
NOTES:
1. All timing is the same for left and right ports. Port “A” may be either the left or right port. Port “B” is the port opposite from “A”.
2. If tAPS is not satisfied, the BUSY signal will be asserted on one side or another but there is no guarantee on which side BUSY will be asserted.
6.42
15
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
AC Electrical Characteristics Over the
Operating Temperature and Supply Voltage Range
70T35/34L20
(70T25/24L20)
Com'l Only
Symbol
Parameter
70T35/34L25
(70T25/24L25)
Com'l
& Ind
Min.
Max.
Min.
Max.
Unit
0
____
0
____
ns
0
____
0
____
ns
20
____
20
ns
20
____
20
ns
INTERRUPT TIMING
tAS
tWR
Address Set-up Time
Write Recovery Time
tINS
Interrupt Set Time
____
tINR
Interrupt Reset Time
____
5639 tbl 14
Waveform of Interrupt Timing(1)
tWC
ADDR"A"
INTERRUPT SET ADDRESS
(2)
(3)
tAS
tWR
(4)
CE"A"
R/W"A"
tINS (3)
INT"B"
5639 drw 17
tRC
INTERRUPT CLEAR ADDRESS
ADDR"B"
(2)
tAS(3)
CE"B"
OE"B"
tINR
(3)
INT"B"
5639 drw 18
NOTES:
1. All timing is the same for left and right ports. Port “A” may be either the left or right port. Port “B” is the port opposite from “A”.
2. See Interrupt Flag 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
16
IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Truth Table III — Interrupt Flag(1)
Left Port
Right Port
R/WL
CEL
OEL
A12L-A0L(4)
INTL
R/WR
CER
OER
A12R-A0R(4)
L
L
X
1FFF
X
X
X
X
X
X
X
X
X
X
X
X
X
L
L
L(2)
Set Right INTR Flag
X
L
L
1FFF
H
Reset Right INTR Flag
L
L
X
1FFE
X
Set Left INTL Flag
(2)
X
X
X
X
X
Reset Left INTL Flag
L
1FFE
Function
(3)
X
X
INTR
H
(3)
5639 tbl 15
NOTES:
1. Assumes BUSYL = BUSYR = VIH.
2. If BUSYL = VIL, then no change.
3. If BUSYR = VIL, then no change.
4. A12 is a NC for IDT70T34 and IDT70T24, therefore Interrupt Addresses are FFF and FFE.
Truth Table IV — Address BUSY
Arbitration
Inputs
Outputs
(4)
CEL
CER
A12L-A0L
A12R-A0R
BUSYL(1)
BUSYR(1)
Function
X
X
NO MATCH
H
H
Normal
H
X
MATCH
H
H
Normal
X
H
MATCH
H
H
Normal
L
L
MATCH
(2)
(2)
Write Inhibit(3)
5639 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
IDT70T35/34L (IDT70T25/24L) 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. H if the inputs to the opposite port became stable after the
address and enable inputs of this port. If tAPS is not met, either BUSYL or BUSYR = LOW will result. BUSYL and BUSYR outputs cannot be LOW simultaneously.
3. Writes to the left port are internally ignored when BUSYL outputs are driving LOW regardless of actual logic level on the pin. Writes to the right port are internally ignored
when BUSYR outputs are driving LOW regardless of actual logic level on the pin.
4. A12 is a NC for IDT70T34 and IDT70T24. Address comparison will be for A0 - A11.
Truth Table V — Example of Semaphore Procurement Sequence(1,2,3)
D0 - D17 Left(2)
D0 - D17 Right(2)
No Action
1
1
Semaphore free
Left Port Writes "0" to Semaphore
0
1
Left port has semaphore token
Right Port Writes "0" to Semaphore
0
1
No change. Right side has no write access to semaphore
Left Port Writes "1" to Semaphore
1
0
Right port obtains semaphore token
Left Port Writes "0" to Semaphore
1
0
No change. Left port has no write access to semaphore
Right Port Writes "1" to Semaphore
0
1
Left port obtains semaphore token
Left Port Writes "1" to Semaphore
1
1
Semaphore free
Right Port Writes "0" to Semaphore
1
0
Right port has semaphore token
Right Port Writes "1" to Semaphore
1
1
Semaphore free
Left Port Writes "0" to Semaphore
0
1
Left port has semaphore token
Left Port Writes "1" to Semaphore
1
1
Semaphore free
Functions
Status
5639 tbl 17
NOTES:
1. This table denotes a sequence of events for only one of the eight semaphores on the IDT70T35/34L (IDT70T25/24L).
2. There are eight semaphore flags written to via I/O0 and read from all I/O's (I/O0-I/O17 for IDT70T35/34) and (I/O0-I/O15 for IDT70T25/24). 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 Tables.
6.42
17
MASTER
Dual Port
SRAM
BUSYL
BUSYL
PRELIMINARY
Industrial and Commercial Temperature Ranges
CE
SLAVE
CE
Dual Port
SRAM
BUSYR
BUSYL
BUSYR
MASTER
CE
Dual Port
SRAM
BUSYR
BUSYL
SLAVE
CE
Dual Port
SRAM
BUSYR
BUSYL
DECODER
IDT70T35/34L(IDT70T25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
BUSYR
,
5639 drw 19
Figure 3. Busy and chip enable routing for both width and depth expansion with IDT70T35/34L (IDT70T25/24L) SRAMs.
Functional Description
The IDT70T35/34L (IDT70T25/24L) 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 IDT70T35/34L (IDT70T25/24L)
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.
operations can be prevented to a port by tying the BUSY pin for that port
LOW.
The BUSY outputs on the IDT70T35/34L (IDT70T25/24L) SRAM in
master mode, are push-pull type outputs and do not require pull up
resistors to operate. If these SRAMs are being expanded in depth, then
the BUSY indication for the resulting array requires the use of an external
AND gate.
Interrupts
Width Expansion with Busy Logic
Master/Slave Arrays
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
1FFE (HEX)(FFF for IDT70T34 and IDT70T24), where a write is defined
as the CER = R/WR = VIL per Truth Table III. The left port clears the interrupt
by an address location 1FFE access when CEL = OEL = VIL, R/WL is a
"don't care". Likewise, the right port interrupt flag (INTR) is set when the
left port writes to memory location 1FFF (HEX) (FFF for IDT70T34 and
IDT70T24) and to clear the interrupt flag (INTR), the right port must read
the memory location 1FFF. The message to the interrupt mail box is userdefined, since it is an addressable SRAM location. If the interrupt function
is not used, the interrupt address locations are not used as mail boxes but
as part of the random access memory.
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 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
When expanding an IDT70T35/34L (IDT70T25/24L) 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 IDT70T35/34L (IDT70T25/24L) 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.
Semaphores
The IDT70T35/34L (IDT70T25/24L) is an extremely fast Dual-Port
8/4K x 18 (8/4K 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
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PRELIMINARY
Industrial and Commercial Temperature Ranges
to inhibit the other from accessing a portion of the Dual-Port SRAM or any
other shared resource.
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
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 nonsemaphore 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 IDT70T35/34L (IDT70T25/24L)
contain multiple processors or controllers and are typically very highspeed systems which are software controlled or software intensive. These
systems can benefit from a performance increase offered by the IDT70T35/
34L (IDT70T25/24L)'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 IDT70T35/34L (IDT70T25/24L) 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 IDT70T35/34L
(IDT70T25/24L) 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
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PRELIMINARY
Industrial and Commercial Temperature Ranges
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 IDT70T35/34L (IDT70T25/24L)’s DualPort SRAM. Say for example, the 8K x 18 SRAM was to be divided into
two 4K x 18 blocks which were to be dedicated at any one time to servicing
either the left or right port. Semaphore 0 could be used to indicate the side
which would control the lower section of memory, and Semaphore 1 could
be defined as the indicator for the upper section of memory.
To take a resource, in this example the lower 4K of Dual-Port
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 4K. Meanwhile the right processor was attempting
to gain control of the resource after the left processor, it would read back
a one in response to the zero it had attempted to write into Semaphore 0.
At this point, the software could choose to try and gain control of the second
4K section by writing, then reading a zero into Semaphore 1. If it succeeded
in gaining control, it would lock out the left side.
Once the left side was finished with its task, it would write a one to
Semaphore 0 and may then try to gain access to Semaphore 1. If
Semaphore 1 was still occupied by the right side, the left side could
undo its semaphore request and perform other tasks until it was able
to write, then read a zero into Semaphore 1. If the right processor
performs a similar task with Semaphore 0, this protocol would allow the
two processors to swap 4K blocks of Dual-Port 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 RAM segments at full speed.
Another application is in the area of complex data structures. In this
case, block arbitration is very important. For this application one
processor may be responsible for building and updating a data
structure. The other processor then reads and interprets that data
structure. If the interpreting processor reads an incomplete data
structure, a major error condition may exist. Therefore, some sort of
arbitration must be used between the two different processors. The
building processor arbitrates for the block, locks it and then is able to
go in and update the data structure. When the update is completed, the
data structure block is released. This allows the interpreting processor
to come back and read the complete data structure, thereby guaranteeing a consistent data structure.
L PORT
R PORT
SEMAPHORE
REQUEST FLIP FLOP
D0
D
SEMAPHORE
REQUEST FLIP FLOP
Q
Q
D
WRITE
D0
WRITE
SEMAPHORE
READ
SEMAPHORE
READ
,
Figure 4. IDT70T35/34L (IDT70T25/24L) Semaphore Logic
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IDT70T35/34L (IDT70T/25/24L)
High-Speed 2.5V 8/4K x 18 (8/4K x 16) Dual-Port Static RAM
PRELIMINARY
Industrial and Commercial Temperature Ranges
Ordering Information(1)
IDT XXXXX
Device
Type
A
999
A
A
Power
Speed
Package
Process/
Temperature
Range
Blank
I
Commercial (0°C to +70°C)
Industrial (-40°C to +85°C)
PF
BF
100-pin TQFP (PN100-1)
100-pin fpBGA (BF100)
20
25
Commercial Only
Commercial & Industrial
L
Low Power
70T35
70T34
70T25
70T24
144K (8K x 18-Bit) 2.5V Dual-Port RAM
72K (4K x 18-Bit) 2.5V Dual-Port RAM
128K (8K x 16-Bit) 2.5V Dual-Port RAM
64K (4K x 16-Bit) 2.5V Dual-Port RAM
,
Speed in Nanoseconds
5639 drw 21
Preliminary Datasheet: Definition
"PRELIMINARY' datasheets contain descriptions for products that are in early release.
Datasheet Document History
07/18//02:
12/06/02:
Initial Public Offering
Consolidated mutiple devices into one data sheet
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