CY7C006A-20JXC(2013) Просмотр технического описания (PDF) - Cypress Semiconductor
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CY7C006A-20JXC Datasheet PDF : 22 Pages
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CY7C006A
If a location is being written to by one port and the opposite port
attempts to read that location, a port-to-port flowthrough delay
must occur before the data is read on the output; otherwise the
data read is not deterministic. Data will be valid on the port tDDD
after the data is presented on the other port.
Read Operation
When reading the device, the user must assert both the OE and
CE pins. Data will be available tACE after CE or tDOE after OE is
asserted. If the user wishes to access a semaphore flag, then the
SEM pin must be asserted instead of the CE pin, and OE must
also be asserted.
Interrupts
The upper two memory locations may be used for message
passing. The highest memory location (3FFF) is the mailbox for
the right port and the second-highest memory location (3FFE) 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 Interrupt Operation Example on page 16.
Busy
The CY7C006A provides 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
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 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 provides 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 relin-
quished 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. Semaphore Operation Example on page 16
shows sample semaphore operations.
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. *G
Page 5 of 22
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