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| 型号： | IDT70V26L25J |
| 厂商： | IDT, Integrated Device Technology Inc |
| 文件页数： | 14/17页 |
| 文件大小： | 0K |
| 描述： | IC SRAM 256KBIT 25NS 84PLCC |
| 标准包装： | 15 |
| 格式 - 存储器： | RAM |
| 存储器类型： | SRAM - 双端口，异步 |
| 存储容量： | 256K（16K x 16） |
| 速度： | 25ns |
| 接口： | 并联 |
| 电源电压： | 3 V ~ 3.6 V |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 84-LCC（J 形引线） |
| 供应商设备封装： | 84-PLCC（29.21x29.21） |
| 包装： | 管件 |
| 其它名称： | 70V26L25J |
IDT70V26S/L
High-Speed 16K x 16 Dual-Port Static RAM
write operations can be prevented to a port by tying the BUSY pin for
that port LOW.
The BUSY outputs on the IDT 70V26 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.
Width Expansion with BUSY Logic
Master/Slave Arrays
When expanding an IDT70V26 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
Industrial and Commercial Temperature Ranges
are completely independent of each other. This means that the activity
on the left port in no way slows the access time of the right port. Both
ports are identical in function to standard CMOS Static RAM and can
be read from, or written to, at the same time with the only possible
conflict arising from the simultaneous writing of, or a simultaneous
READ/WRITE of, a non-semaphore location. Semaphores are pro-
tected against such ambiguous situations and may be used by the
system program to avoid any conflicts in the non-semaphore portion
of the Dual-Port SRAM. These devices have an automatic power-
down feature controlled by CE , the Dual-Port SRAM enable, and SEM ,
the semaphore enable. The CE and SEM pins control on-chip power
down circuitry that permits the respective port to go into standby mode
when not selected. This is the condition which is shown in Truth Table
I where CE and SEM are both HIGH.
Systems which can best use the IDT70V26 contain multiple
MASTER
Dual Port
RAM
BUSY L
CE
BUSY R
SLAVE
Dual Port
RAM
BUSY L
CE
BUSY R
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 IDT70V26's
hardware semaphores, which provide a lockout mechanism without
requiring complex programming.
BUSY L
MASTER
Dual Port
RAM
BUSY L
CE
BUSY R
SLAVE
Dual Port
RAM
BUSY L
CE
BUSY R
BUSY R
,
Software handshaking between processors offers the maximum in
system flexibility by permitting shared resources to be allocated in
varying configurations. The IDT70V26 does not use its semaphore
flags to control any resources through hardware, thus allowing the
2945 drw 16
Figure 3. Busy and chip enable routing for both width and depth expansion
with IDT70V26 RAMs.
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
IDT70V26 SRAM the BUSY pin is an output if the part is used as a
master (M/ S pin = H), and the BUSY pin is an input if the part used as
a slave (M/ S pin = L) as shown in Figure 3.
If two or more master parts were used when expanding in width, a
split decision could result with one master indicating BUSY on one side
of the array and another master indicating BUSY on one other side of
the array. This would inhibit the write operations from one port for part
of a word and inhibit the write operations from the other port for 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 IDT70V26 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 SRAM to claim a privilege over the other
processor for functions defined by the system designer’s software. As
an example, the semaphore can be used by one processor to inhibit
the other from accessing a portion of the Dual-Port SRAM or any other
shared resource.
The Dual-Port SRAM features a fast access time, and both ports
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 indepen-
dent 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 IDT70V26 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
14
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| IDT70V26L25J8 | 功能描述:IC SRAM 256KBIT 25NS 84PLCC RoHS:否 类别:集成电路 (IC) >> 存储器 系列:- 标准包装:1,000 系列:- 格式 - 存储器:RAM 存储器类型:SRAM - 双端口，同步 存储容量:1.125M（32K x 36） 速度:5ns 接口:并联 电源电压:3.15 V ~ 3.45 V 工作温度:-40°C ~ 85°C 封装/外壳:256-LBGA 供应商设备封装:256-CABGA（17x17） 包装:带卷 (TR) 其它名称:70V3579S5BCI8 |
| IDT70V26L25JI | 功能描述:IC SRAM 256KBIT 25NS 84PLCC RoHS:否 类别:集成电路 (IC) >> 存储器 系列:- 标准包装:1,000 系列:- 格式 - 存储器:RAM 存储器类型:SRAM - 双端口，同步 存储容量:1.125M（32K x 36） 速度:5ns 接口:并联 电源电压:3.15 V ~ 3.45 V 工作温度:-40°C ~ 85°C 封装/外壳:256-LBGA 供应商设备封装:256-CABGA（17x17） 包装:带卷 (TR) 其它名称:70V3579S5BCI8 |
| IDT70V26L25JI8 | 功能描述:IC SRAM 256KBIT 25NS 84PLCC RoHS:否 类别:集成电路 (IC) >> 存储器 系列:- 标准包装:1,000 系列:- 格式 - 存储器:RAM 存储器类型:SRAM - 双端口，同步 存储容量:1.125M（32K x 36） 速度:5ns 接口:并联 电源电压:3.15 V ~ 3.45 V 工作温度:-40°C ~ 85°C 封装/外壳:256-LBGA 供应商设备封装:256-CABGA（17x17） 包装:带卷 (TR) 其它名称:70V3579S5BCI8 |
| IDT70V26L35G | 功能描述:IC SRAM 256KBIT 35NS 84PGA RoHS:否 类别:集成电路 (IC) >> 存储器 系列:- 标准包装:3,000 系列:- 格式 - 存储器:EEPROMs - 串行 存储器类型:EEPROM 存储容量:8K (1K x 8) 速度:400kHz 接口:I²C，2 线串口 电源电压:1.7 V ~ 5.5 V 工作温度:-40°C ~ 85°C 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 供应商设备封装:8-SOIC 包装:带卷 (TR) |
| IDT70V26L35J | 功能描述:IC SRAM 256KBIT 35NS 84PLCC RoHS:否 类别:集成电路 (IC) >> 存储器 系列:- 标准包装:1,000 系列:- 格式 - 存储器:RAM 存储器类型:SRAM - 双端口，同步 存储容量:1.125M（32K x 36） 速度:5ns 接口:并联 电源电压:3.15 V ~ 3.45 V 工作温度:-40°C ~ 85°C 封装/外壳:256-LBGA 供应商设备封装:256-CABGA（17x17） 包装:带卷 (TR) 其它名称:70V3579S5BCI8 |
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