CY7C1511AV18, CY7C1526AV18
CY7C1513AV18, CY7C1515AV18
Document Number: 001-06985 Rev. *C
Page 9 of 31
and C HIGH at power on. This function is a strap option and not
alterable during device operation.
Concurrent Transactions
The read and write ports on the CY7C1513AV18 operates
completely independently of one another. As each port latches
the address inputs on different clock edges, the user can read or
write to any location, regardless of the transaction on the other
port. If the ports access the same location when a read follows a
write in successive clock cycles, the SRAM delivers the most
recent information associated with the specified address
location. This includes forwarding data from a write cycle that
was initiated on the previous K clock rise.
Read access and write access must be scheduled such that one
transaction is initiated on any clock cycle. If both ports are
selected on the same K clock rise, the arbitration depends on the
previous state of the SRAM. If both ports are deselected, the
read port takes priority. If a read was initiated on the previous
cycle, the write port takes priority (as read operations can not be
initiated on consecutive cycles). If a write was initiated on the
previous cycle, the read port takes priority (as write operations
can not be initiated on consecutive cycles). Therefore, asserting
both port selects active from a deselected state results in alter-
nating read or write operations being initiated, with the first
access being a read.
Depth Expansion
The CY7C1513AV18 has a port select input for each port. This
enables for easy depth expansion. Both port selects are sampled
on the rising edge of the positive input clock only (K). Each port
select input can deselect the specified port. Deselecting a port
does not affect the other port. All pending transactions (read and
write) are completed before the device is deselected.
Programmable Impedance
An external resistor, RQ, must be connected between the ZQ pin
on the SRAM and VSS to allow the SRAM to adjust its output
driver impedance. The value of RQ must be 5X the value of the
intended line impedance driven by the SRAM, the allowable
range of RQ to guarantee impedance matching with a tolerance
of ±15% is between 175
Ω and 350Ω, with V
DDQ =1.5V. The
output impedance is adjusted every 1024 cycles upon power up
to account for drifts in supply voltage and temperature.
Echo Clocks
Echo clocks are provided on the QDR-II to simplify data capture
on high-speed systems. Two echo clocks are generated by the
QDR-II. CQ is referenced with respect to C and CQ is referenced
with respect to C. These are free-running clocks and are
synchronized to the output clock of the QDR-II. In the single clock
mode, CQ is generated with respect to K and CQ is generated
with respect to K. The timing for the echo clocks is shown in the
Switching Characteristics on page 24.
DLL
These chips use a DLL that is designed to function between 120
MHz and the specified maximum clock frequency. During power
up, when the DOFF is tied HIGH, the DLL is locked after 1024
cycles of stable clock. The DLL can also be reset by slowing or
stopping the input clocks K and K for a minimum of 30 ns.
However, it is not necessary to reset the DLL to lock to the
desired frequency. The DLL automatically locks 1024 clock
cycles after a stable clock is presented. The DLL may be
disabled by applying ground to the DOFF pin. When the DLL is
turned off, the device behaves in QDR-I mode (with one cycle
latency and a longer access time). For information refer to the
application note DLL Considerations in QDRII/DDRII.
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