CY7C006A-20(2010) Просмотр технического описания (PDF) - Cypress Semiconductor
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CY7C006A-20 Datasheet PDF : 22 Pages
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CY7C006A/CY7C007A
CY7C016A/CY7C017A
(7FFE) is the mailbox for the left port. When one port writes to
the other port’s mailbox, an interrupt is generated to the owner.
The interrupt is reset when the owner reads the contents of the
mailbox. The message is user defined.
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 CY7C006A, CY7C007A, CY7C016A and CY7C017A
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
will determine which port has access. If tPS is violated, one port
will definitely gain permission to the location, but it is not
predictable which port will get that permission. BUSY will be
asserted tBLA after an address match or tBLC after CE is taken
LOW.
Master/Slave
A M/S pin is provided in order to expand the word width by config-
uring 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
will allow 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 CY7C006A, CY7C007A, CY7C016A and CY7C017A
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
will be available tSWRD + tDOE after the rising 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 relinquished control of the
semaphore (by writing a one), the left side will succeed 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
semaphore address. 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 will
appear 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 will be 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 opera-
tions.
When reading a semaphore, all 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 will definitely be obtained by one
side or the other, but there is no guarantee which side will control
the semaphore.
Document Number: 38-06045 Rev. *F
Page 6 of 22
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