IDT7015S Datasheet, PDF (17/20 Pages) Integrated Device Technology – HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM

IDT7015S/L
HIGH-SPEED 8K x 9 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
MASTER
CE
Dual Port
R_BUAM_{SY (L) BUSY (R)}
SLAVE
CE
Dual Port
R_BUAM_{SY (L) BUSY (R)}
BUSY (L)
MASTER ^CE
Dual Port
R_BUAM_{SY (L) BUSY (R)}
SLAVE
CE
Dual Port
R_BUAM_{SY (L) BUSY (R)}
BUSY (R)
2954 drw 19
Figure 3. Busy and chip enable routing for both width and depth expansion with IDT7015 RAMs.
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 opera-
tion 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 IDT7015 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 IDT7015 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 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 IDT7015 RAM 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 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 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 IDT7015 are extremely fast Dual-Port 8Kx9 Static
RAMs 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 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, 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 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 where CE
and SEM are both high.
Systems which can best use the IDT7015 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 IDT7015's hardware semaphores, which pro-
vide a lockout mechanism without requiring complex pro-
gramming.
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