December 2004
®
AS7C251MFT18A
2.5V 1M x 18 flowthrough burst synchronous SRAM
Features
•
•
•
•
•
•
Organization: 1,048,576 words x18 bits
Fast clock to data access: 7.5/8.5/10 ns
Fast OE access time: 3.5/4.0 ns
Fully synchronous flow-through operation
Asynchronous output enable control
Available 100-pin TQFP package
•
•
•
•
•
Individual byte write and global write
Multiple chip enables for easy expansion
2.5V core power supply
Linear or interleaved burst control
Snooze mode for reduced power-standby
Logic block diagram
LBO
CLK
ADV
ADSC
ADSP
A[19:0]
CLK
CS
CLR
Burst logic
Q
20
CS
Address
D
20
18 20
1M
x
18
Memory
array
18
18
register
CLK
GWE
BW
b
BWE
BW
a
CE0
CE1
CE2
D
DQb
Q
CLK
D
DQa
Q
Byte Write
registers
Byte Write
registers
CLK
D
2
OE
CE
CLK
D
ZZ
Enable
register
Q
Output
buffers
Input
registers
CLK
Power
down
Enable
Q
delay
register
CLK
OE
18
DQ[a,b]
Selection guide
-75
Minimum cycle time
Maximum clock access time
Maximum operating current
Maximum standby current
Maximum CMOS standby current (DC)
8.5
7.5
275
90
60
-85
10
8.5
250
80
60
-10
12
10
230
80
60
Units
ns
ns
mA
mA
mA
12/24/04, v. 1.2
Alliance Semiconductor
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Copyright © Alliance Semiconductor. All rights reserved.
AS7C251MFT18A
®
16 Mb 2.5V Synchronous SRAM products list
1,2
Org
1MX18
512KX32
512KX36
1MX18
512KX32
512KX36
1MX18
512KX32
512KX36
1MX18
512KX32
512KX36
1MX18
512KX32
512KX36
Part Number
AS7C251MPFS18A
AS7C25512PFS32A
AS7C25512PFS36A
AS7C251MPFD18A
AS7C25512PFD32A
AS7C25512PFD36A
AS7C251MFT18A
AS7C25512FT32A
AS7C25512FT36A
AS7C251MNTD18A
AS7C25512NTD32A
AS7C25512NTD36A
AS7C251MNTF18A
AS7C25512NTF32A
AS7C25512NTF36A
Mode
PL-SCD
PL-SCD
PL-SCD
PL-DCD
PL-DCD
PL-DCD
FT
FT
FT
NTD-PL
NTD-PL
NTD-PL
NTD-FT
NTD-FT
NTD-FT
Speed
166/133 MHz
166/133 MHz
166/133 MHz
166/133 MHz
166/133 MHz
166/133 MHz
7.5/8.5/10 ns
7.5/8.5/10 ns
7.5/8.5/10 ns
166/133 MHz
166/133 MHz
166/133 MHz
7.5/8.5/10 ns
7.5/8.5/10 ns
7.5/8.5/10 ns
1 Core Power Supply: VDD = 2.5V + 0.125V
2 I/O Supply Voltage: VDDQ = 2.5V + 0.125V
PL-SCD
PL-DCD
FT
NTD
1
-PL
NTD-FT
:
:
:
:
:
Pipelined Burst Synchronous SRAM - Single Cycle Deselect
Pipelined Burst Synchronous SRAM - Double Cycle Deselect
Flow-through Burst Synchronous SRAM
Pipelined Burst Synchronous SRAM with NTD
TM
Flow-through Burst Synchronous SRAM with NTD
TM
1NTD: No Turnaround Delay. NTD
TM
is a trademark of Alliance Semiconductor Corporation. All trademarks mentioned in this document are the property of
their respective owners.
12/24/04, v. 1.2
Alliance Semiconductor
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AS7C251MFT18A
®
Pin configuration for 100-pin TQFP
NC
NC
NC
V
DDQ
V
SSQ
NC
NC
DQb0
DQb1
V
SSQ
V
DDQ
DQb2
DQb3
NC
V
DD
NC
V
SS
DQb4
DQb5
V
DDQ
V
SSQ
DQb6
DQb7
DQPb
NC
V
SSQ
V
DDQ
NC
NC
NC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
A
A
CE0
CE1
NC
NC
BWb
BWa
CE2
V
DD
V
SS
CLK
GWE
BWE
OE
ADSC
ADSP
ADV
A
A
TQFP 14 x 20mm
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
54
53
52
51
A
NC
NC
V
DDQ
V
SSQ
NC
DQPa
DQa7
DQa6
V
SSQ
V
DDQ
DQa5
DQa4
V
SS
NC
V
DD
ZZ
DQa3
DQa2
V
DDQ
V
SSQ
DQa1
DQa0
NC
NC
V
SSQ
V
DDQ
NC
NC
NC
12/24/04, v. 1.2
LBO
A
A
A
A
A1
A0
NC
NC
V
SS
V
DD
A
A
A
A
A
A
A
A
A
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Alliance Semiconductor
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AS7C251MFT18A
®
Functional description
The AS7C251MFT18A is a high-performance CMOS 16-Mbit synchronous Static Random Access Memory (SRAM) device organized as
1,048,576 words x18 bits
.
Fast cycle times of 8.5/10/12 ns with clock access times (t
CD
) of 7.5/8.5/10 ns. Three chip enable (CE) inputs permit easy memory expansion.
Burst operation is initiated in one of two ways: the controller address strobe (ADSC), or the processor address strobe (ADSP). The burst
advance pin (ADV) allows subsequent internally generated burst addresses.
Read cycles are initiated with ADSP (regardless of WE and ADSC) using the new external address clocked into the on-chip address register
when ADSP is sampled LOW, the chip enables are sampled active, and the output buffer is enabled with OE. In a read operation, the data
accessed by the current address registered in the address registers by the positive edge of CLK is carried to the data-out buffers. ADV is
ignored on the clock edge that samples ADSP asserted, but it is sampled on all subsequent clock edges. Address is incremented internally for
the next access of the burst when ADV is sampled LOW and both address strobes are HIGH. Burst mode is selectable with the LBO input.
With LBO unconnected or driven HIGH, burst operations use an interleaved count sequence. With LBO driven LOW, the device uses a linear
count sequence.
Write cycles are performed by disabling the output buffers with OE and asserting a write command. A global write enable GWE writes all
18 bits regardless of the state of individual BW[a,b] inputs. Alternately, when GWE is HIGH, one or more bytes may be written by asserting
BWE and the appropriate individual byte BWn signals.
BWn is ignored on the clock edge that samples ADSP LOW, but it is sampled on all subsequent clock edges. Output buffers are disabled
when BWn is sampled LOW, regardless of OE. Data is clocked into the data input register when BWn is sampled LOW. Address is
incremented internally to the next burst address if BWn and ADV are sampled LOW.
Read or write cycles may also be initiated with ADSC instead of ADSP. The differences between cycles initiated with ADSC and ADSP are
as follows:
• ADSP must be sampled HIGH when ADSC is sampled LOW to initiate a cycle with ADSC.
• WE signals are sampled on the clock edge that samples ADSC LOW (and ADSP HIGH).
•
Master chip enable
CE0 blocks ADSP, but not ADSC.
The AS7C251MFT18A family operates from a core 2.5V power supply. These devices are available in a 100-pin TQFP package.
TQFP capacitance
Parameter
Input capacitance
I/O capacitance
* Guaranteed not tested
Symbol
C
IN*
C
I/O*
Test conditions
V
IN
= 0V
V
OUT
= 0V
Min
-
-
Max
5
7
Unit
pF
pF
TQFP thermal resistance
Description
Thermal resistance
(junction to ambient)
1
Thermal resistance
(junction to top of case)
1
1 This parameter is sampled
Conditions
Test conditions follow standard test methods
and procedures for measuring thermal
impedance, per EIA/JESD51
1–layer
4–layer
Symbol
θ
JA
θ
JA
θ
JC
Typical
40
22
8
Units
°C/W
°C/W
°C/W
12/24/04, v. 1.2
Alliance Semiconductor
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AS7C251MFT18A
®
Signal descriptions
Signal
CLK
A,A0,A1
DQ[a,b]
CE0
CE1, CE2
ADSP
ADSC
ADV
GWE
BWE
BW[a,b]
OE
LBO
ZZ
NC
I/O Properties
Description
I
I
I/O
I
I
I
I
I
I
I
I
I
I
I
-
CLOCK
SYNC
SYNC
SYNC
SYNC
SYNC
SYNC
SYNC
SYNC
SYNC
SYNC
ASYNC
STATIC
ASYNC
-
Clock. All inputs except OE, ZZ, and LBO are synchronous to this clock.
Address. Sampled when all chip enables are active and when ADSC or ADSP are asserted.
Data. Driven as output when the chip is enabled and when OE is active.
Master chip enable. Sampled on clock edges when ADSP or ADSC is active. When CE0 is
inactive, ADSP is blocked. Refer to the “Synchronous truth table” for more information.
Synchronous chip enables. Active HIGH and active LOW, respectively. Sampled on clock
edges when ADSC is active or when CE0 and ADSP are active.
Address strobe processor. Asserted LOW to load a new bus address or to enter standby
mode.
Address strobe controller. Asserted LOW to load a new address or to enter standby mode.
Advance. Asserted LOW to continue burst read/write.
Global write enable. Asserted LOW to write all 18 bits. When HIGH, BWE and BW[a,b]
control write enable.
Byte write enable. Asserted LOW with GWE HIGH to enable effect of BW[a,b] inputs.
Write enables. Used to control write of individual bytes when GWE is HIGH and BWE is
LOW. If any of BW[a,b] is active with GWE HIGH and BWE LOW, the cycle is a write
cycle. If all BW[a,b] are inactive, the cycle is a read cycle.
Asynchronous output enable. I/O pins are driven when OE is active and the chip is in read
mode.
Selects Burst mode. When tied to V
DD
or left floating, device follows interleaved Burst order. When
driven LOW, device follows linear Burst order.
This signal is internally pulled High.
Sleep. Places device in LOW power mode; data is retained. Connect to GND if unused.
No connects
Snooze Mode
SNOOZE MODE is a low current, power-down mode in which the device is deselected and current is reduced to I
SB2
. The duration of
SNOOZE MODE is dictated by the length of time the ZZ is in a High state.
The ZZ pin is an asynchronous, active high input that causes the device to enter SNOOZE MODE.
When the ZZ pin becomes a logic High, I
SB2
is guaranteed after the time t
ZZI
is met. After entering SNOOZE MODE, all inputs except ZZ is
disabled and all outputs go to High-Z. Any operation pending when entering SNOOZE MODE is not guaranteed to successfully complete.
Therefore, SNOOZE MODE (READ or WRITE) must not be initiated until valid pending operations are completed. Similarly, when exiting
SNOOZE MODE during t
PUS
, only a DESELECT or READ cycle should be given while the SRAM is transitioning out of SNOOZE MODE.
12/24/04, v. 1.2
Alliance Semiconductor
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