7024S55J IDT, 7024S55J Datasheet - Page 18

• Manufacturer Part Number: 7024S55J
• Description: SRAM
• Manufacturer: IDT

Specifications of 7024S55J

• Part # Aliases: IDT7024S55J

is not used, address locations FFE and FFF are not used as mail boxes,
but as part of the random access memory. Refer to Truth Table III for the
interrupt operation.
Busy Logic
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.
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.
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
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 IDT7024 RAM the
BUSY pin is an output if the part is used as a master (M/S pin = V
the BUSY pin is an input if the part used as a slave (M/S pin = V
in Figure 3.
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.
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
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
IDT7024S/L
High-Speed 4K x 16 Dual-Port Static RAM
Busy Logic provides a hardware indication that both ports of the RAM
The use of BUSY logic is not required or desirable for all applications.
The BUSY outputs on the IDT 7024 SRAM in master mode, are push-
When expanding an IDT7024 RAM array in width while using BUSY
If two or more master parts were used when expanding in width, a split
The BUSY arbitration, on a master, is based on the chip enable and
The IDT7024 is an extremely fast Dual-Port 4K x 16 CMOS Static RAM
IL
) as shown
IH
), and
6.42
18
used by one processor to inhibit the other from accessing a portion of the
Dual-Port RAM or any other shared resource.
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 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 I where CE and SEM = V
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 IDT7024's hardware semaphores,
which provide a lockout mechanism without requiring complex program-
ming.
system flexibility by permitting shared resources to be allocated in varying
configurations. The IDT7024 does not use its semaphore flags to control
any resources through hardware, thus allowing the system designer total
flexibility in system architecture.
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
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
BUSY (L)
Figure 3. Busy and chip enable routing for both width and depth
The Dual-Port RAM features a fast access time, and both ports are
Systems which can best use the IDT7024 contain multiple processors
Software handshaking between processors offers the maximum in
An advantage of using semaphores rather than the more common
The semaphore logic is a set of eight latches which are independent
Military, Industrial and Commercial Temperature Ranges
MASTER
Dual Port
RAM
BUSY (L) BUSY (R)
MASTER
Dual Port
RAM
BUSY (L) BUSY (R)
expansion with IDT7024 RAMs.
CE
CE
SLAVE
Dual Port
RAM
BUSY (L) BUSY (R)
SLAVE
Dual Port
RAM
BUSY (L) BUSY (R)
IH
.
CE
CE
BUSY (R)
2740 drw 19
,