參數(shù)資料
型號(hào)： CY7C028V-20ACT
廠商： CYPRESS SEMICONDUCTOR CORP
元件分類： SRAM
英文描述： 3.3V 32K/64K x 16/18 Dual-Port Static RAM
中文描述： 64K X 16 DUAL-PORT SRAM, 20 ns, PQFP100
封裝： PLASTIC, MS-026, TQFP-100
文件頁(yè)數(shù)： 19/22頁(yè)
文件大小： 635K
代理商： CY7C028V-20ACT
CY7C027V/027AV/028V
CY7C037AV/038V
Document #: 38-06078 Rev. *D
Page 6 of 22
Each port can read the other port’s mailbox without resetting the
interrupt. The active state of the busy signal (to a port) prevents
the port from setting the interrupt to the winning port. Also, an
active busy to a port prevents that port from reading its own
mailbox and, thus, resetting the interrupt to it.
If an application does not require message passing, do not
connect the interrupt pin to the processor’s interrupt request
input pin.
The operation of the interrupts and their interaction with Busy are
summarized in Table 2.
Busy
The CY7C027V/027AV/028V and CY7037AV/038V provide
on-chip arbitration to resolve simultaneous memory location
access (contention). If both ports’ CEs are asserted and an address
match occurs within tPS of each other, the busy logic determines which
port has access. If tPS is violated, one port definitely gains permission to
the location, but it is not predictable which port gets that permission.
BUSY is asserted tBLA after an address match or tBLC after CE is taken
LOW.
Master/Slave
A M/S pin is provided to expand the word width by configuring the
device as either a master or a slave. The BUSY output of the master is
connected to the BUSY input of the slave. This allows the device to
interface to a master device with no external components. Writing to
slave devices must be delayed until after the BUSY input has settled
(tBLC or tBLA), otherwise, the slave chip may begin a write cycle during
a contention situation. When tied HIGH, the M/S pin allows the device
to be used as a master and, therefore, the BUSY line is an output. BUSY
can then be used to send the arbitration outcome to a slave.
Semaphore Operation
The CY7C027V/027AV/028V and CY7037AV/038V provide
eight semaphore latches, which are separate from the dual-port
memory locations. Semaphores are used to reserve resources
that are shared between the two ports.The state of the
semaphore indicates that a resource is in use. For example, if
the left port wants to request a given resource, it sets a latch by
writing a zero to a semaphore location. The left port then verifies
its success in setting the latch by reading it. After writing to the
semaphore, SEM or OE must be deasserted for tSOP before
attempting to read the semaphore. The semaphore value is available
tSWRD + tDOE after therising edge of the semaphore write. If the left port
was successful (reads a zero), it assumes control of the shared
resource, otherwise (reads a one) it assumes the right port has control
and continues to poll the semaphore. When the right side has relin-
quished control of the semaphore (by writing a one), the left side
succeeds in gaining control of the semaphore. If the left side no longer
requires the semaphore, a one is written to cancel its request.
Semaphores are accessed by asserting SEM LOW. The SEM pin
functions as a chip select for the semaphore latches (CE must remain
HIGH during SEM LOW). A0–2 represents the semaphoreaddress. OE
and R/W are used in the same manner as a normal memory access.
When writing or reading a semaphore, the other address pins have no
effect.
When writing to the semaphore, only I/O0 is used. If a zero is written
to the left port of an available semaphore, a one appears at the same
semaphore address on the right port. That semaphore can now only be
modified by the side showing zero (the left port in this case). If the left
port now relinquishes control by writing a one to the semaphore, the
semaphore is set to one for both sides. However, if the right port had
requested the semaphore (written a zero) while the left port had control,
the right port would immediately own the semaphore as soon as the left
port released it. Table 3 shows sample semaphore operations.
When reading a semaphore, all sixteen/eighteen data lines
output the semaphore value. The read value is latched in an
output register to prevent the semaphore from changing state
during a write from the other port. If both ports attempt to access
the semaphore within tSPS of each other, the semaphore is definitely
obtained by one side or the other, but there is no guarantee which side
controls the semaphore.
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