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參數(shù)資料
| 型號： | 70V18L15PF8 |
| 廠商： | INTEGRATED DEVICE TECHNOLOGY INC |
| 元件分類： | SRAM |
| 英文描述： | 64K X 9 DUAL-PORT SRAM, 15 ns, PQFP100 |
| 封裝： | TQFP-100 |
| 文件頁數(shù)： | 7/17頁 |
| 文件大小： | 157K |
| 代理商： | 70V18L15PF8 |
15
IDT70V18L
High-Speed 3.3V 64K x 9 Dual-Port Static RAM
Industrial and Commercial Temperature Ranges
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 applica-
tions. In some cases it may be useful to logically OR the
BUSY outputs
together and use any
BUSYindication 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 IDT70V18 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.
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 the R/
W signal. Failure to
observe this timing can result in a glitched internal write inhibit signal
and corrupted data in the slave.
Semaphores
The IDT70V18 is an extremely fast Dual-Port 64K x 9 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 ex-
ample, 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, with both ports
being 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 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
III where
CE and SEM are both HIGH.
Systems which can best use the IDT70V18 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 IDT70V18s
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 IDT70V18 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 indepen-
dent 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 a
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
Width Expansion with Busy Logic
Master/Slave Arrays
When expanding an IDT70V18 RAM array in width while using
BUSY logic, one master part is used to decide which side of the RAMs
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
IDT70V18 RAM 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
Figure 3. Busy and chip enable routing for both width and depth expansion
with IDT70V18 RAMs.
4854 drw 17
MASTER
Dual Port RAM
BUSYR
CE0
MASTER
Dual Port RAM
BUSYR
SLAVE
Dual Port RAM
BUSYR
SLAVE
Dual Port RAM
BUSYR
CE1
CE0
A16
BUSYL
.
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