Datasheet

CY7C1510KV18, CY7C1525KV18
CY7C1512KV18, CY7C1514KV18
Document Number: 001-00436 Rev. *L Page 10 of 31
Programmable Impedance
An external resistor, RQ, must be connected between the ZQ pin
on the SRAM and V
SS
to enable 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 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 synchro-
nized 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 Switching
Characteristics on page 25.
PLL
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 clocks 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
Application Example
Figure 1 shows two QDR II used in an application.
Figure 1. Application Example
R = 250ohms
Vt
R
R = 250ohms
Vt
Vt
R
Vt = Vddq/2
R = 50ohms
R
CC#
D
A
SRAM #2
R
P
S
#
W
P
S
#
B
W
S
#
ZQ
CQ/CQ#
Q
K#
CC#
D
A
K
SRAM #1
R
P
S
#
W
P
S
#
B
W
S
#
ZQ
CQ/CQ#
Q
K#
BUS
MASTER
(CPU
or
ASIC)
DATA IN
DATA OUT
Address
RPS#
WPS#
BWS#
Source K
Source K#
Delayed K
Delayed K#
CLKIN/CLKIN#
K
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