CY7C1148KV18/CY7C1150KV18
output impedance is adjusted every 1024 cycles upon power up
to account for drifts in supply voltage and temperature.
DDR Operation
The CY7C1148KV18 enables high-performance operation
through high clock frequencies (achieved through pipelining) and
DDR mode of operation. The CY7C1148KV18 requires two No
Operation (NOP) cycle during transition from a read to a write
cycle. At higher frequencies, some applications require third
NOP cycle to avoid contention.
Echo Clocks
Echo clocks are provided on the DDR II+ to simplify data capture
on high-speed systems. Two echo clocks are generated by the
DDR II+. CQ is referenced with respect to K and CQ is
referenced with respect to K. These are free-running clocks and
are synchronized to the input clock of the DDR II+. The timing for
the echo clocks is shown in the Switching Characteristics on
page 22.
If a read occurs after a write cycle, address and data for the write
are stored in registers. The write information is stored because
the SRAM cannot perform the last word write to the array without
conflicting with the read. The data stays in this register until the
next write cycle occurs. On the first write cycle after the read(s),
the stored data from the earlier write is written into the SRAM
array. This is called a Posted write.
Valid Data Indicator (QVLD)
QVLD is provided on the DDR II+ to simplify data capture on high
speed systems. The QVLD is generated by the DDR II+ device
along with data output. This signal is also edge aligned with the
echo clock and follows the timing of any data pin. This signal is
asserted half a cycle before valid data arrives.
If a read is performed on the same address on which a write is
performed in the previous cycle, the SRAM reads out the most
current data. The SRAM does this by bypassing the memory
array and reading the data from the registers.
PLL
Depth Expansion
These chips use a PLL that is designed to function between 120
MHz and the specified maximum clock frequency. During power
up, when the DOFF is tied HIGH, the PLL is locked after 20 s
of stable clock. The PLL can also be reset by slowing or stopping
the input clock K and K for a minimum of 30 ns. However, it is not
necessary to reset the PLL to lock to the desired frequency. The
PLL automatically locks 20 s after a stable clock is presented.
The PLL may be disabled by applying ground to the DOFF pin.
When the PLL is turned off, the device behaves in DDR I mode
(with one cycle latency and a longer access time). For
information, refer to the application note, PLL Considerations in
QDRII/DDRII/QDRII+/DDRII+.
Depth expansion requires replicating the LD control signal for
each bank. All other control signals can be common between
banks as appropriate.
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 and 350 , with VDDQ = 1.5 V. The
Application Example
Figure 2 shows two DDR II+ used in an application.
Figure 2. Application Example (Width Expansion)
ZQ
ZQ
SRAM#1
SRAM#2
CQ/CQ
CQ/CQ
RQ
RQ
DQ[x:0]
DQ[x:0]
LD
A
LD
R/W BWS
K
K
A
R/W BWS
K
K
DQ[2x:0]
ADDRESS
LD
R/W
BWS
CLKIN1/CLKIN1
CLKIN2/CLKIN2
SOURCE K
SOURCE K
FPGA / ASIC
Document Number: 001-58912 Rev. *I
Page 7 of 29
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