White Electronic Designs
DLL ENABLE/DISABLE
The DLL may be enabled or disabled by programming bit
E0 during the LM command, as shown in Figure 7. The
DLL must be enabled for normal operation. DLL enable is
required during power-up initialization and upon returning
to normal operation after having disabled the DLL for the
purpose of debugging or evaluation. Enabling the DLL
should always be followed by resetting the DLL using an
LM command.
The DLL is automatically disabled when entering SELF
REFRESH operation and is automatically re-enabled and
reset upon exit of SELF REFRESH operation.
Any time the DLL is enabled (and subsequently reset), 200
clock cycles must occur before a READ command can be
issued, to allow time for the internal clock to synchronize
with the external clock. Failing to wait for synchronization
to occur may result in a violation of the
t
AC or
t
DQSCK
parameters.
W3H64M72E-XSBX
ADVANCED*
OUTPUT ENABLE/DISABLE
The OUTPUT ENABLE function is defined by bit E12, as
shown in Figure 7. When enabled (E12 = 0), all outputs
(DQs, DQS, DQS#, RDQS, RDQS#) function normally.
When disabled (E12 = 1), all DDR2 SDRAM outputs (DQs,
DQS, DQS#, RDQS, RDQS#) are disabled, thus removing
output buffer current. The output disable feature is intended
to be used during I
CC
characterization of read current.
ON-DIE TERMINATION (ODT)
ODT effective resistance, R
TT
(EFF), is defined by bits
E2 and E6 of the EMR, as shown in Figure 7. The ODT
feature is designed to improve signal integrity of the
memory channel by allowing the DDR2 SDRAM controller
to independently turn on/off ODT for any or all devices.
R
TT
effective resistance values of 50Ω ,75Ω, and 150Ω
are selectable and apply to each DQ, DQS/DQS#, RDQS/
RDQS#, UDQS/UDQS#, LDQS/LDQS#, DM, and UDM/
LDM signals. Bits (E6, E2) determine what ODT resistance
is enabled by turning on/off “sw1,” “sw2,” or “sw3.” The
ODT effective resistance value is elected by enabling
switch “sw1,” which enables all R1 values that are 150Ω
each, enabling an effective resistance of 75Ω (R
TT2
(EFF)
= R2/2). Similarly, if “sw2” is enabled, all R2 values that
are 300Ω each, enable an effective ODT resistance of
150Ω (R
TT2
(EFF) = R2/2). Switch “sw3” enables R1 values
of 100Ω enabling effective resistance of 50Ω Reserved
states should not be used, as unknown operation or
incompatibility with future versions may result.
The ODT control ball is used to determine when R
TT
(EFF)
is turned on and off, assuming ODT has been enabled via
bits E2 and E6 of the EMR. The ODT feature and ODT
input ball are only used during active, active power-down
(both fast-exit and slow-exit modes), and precharge power-
down modes of operation. ODT must be turned off prior to
entering self refresh. During power-up and initialization of
the DDR2 SDRAM, ODT should be disabled until issuing
the EMR command to enable the ODT feature, at which
point the ODT ball will determine the R
TT
(EFF) value.
Any time the EMR enables the ODT function, ODT may
not be driven HIGH until eight clocks after the EMR has
been enabled. See “ODT Timing” section for ODT timing
diagrams.
OUTPUT DRIVE STRENGTH
The output drive strength is defined by bit E1, as shown
in Figure 7. The normal drive strength for all outputs are
specified to be SSTL_18. Programming bit E1 = 0 selects
normal (full strength) drive strength for all outputs. Selecting
a reduced drive strength option (E1 = 1) will reduce all
outputs to approximately 60 percent of the SSTL_18 drive
strength. This option is intended for the support of lighter
load and/or point-to-point environments.
DQS# ENABLE/DISABLE
The DQS# ball is enabled by bit E10. When E10 = 0,
DQS# is the complement of the differential data strobe pair
DQS/DQS#. When disabled (E10 = 1), DQS is used in a
single ended mode and the DQS# ball is disabled. When
disabled, DQS# should be left floating. This function is also
used to enable/disable RDQS#. If RDQS is enabled (E11
= 1) and DQS# is enabled (E10 = 0), then both DQS# and
RDQS# will be enabled.
White Electronic Designs Corp. reserves the right to change products or specifications without notice.
March 2006
Rev. 1
13
White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com
WEDC [ WHITE ELECTRONIC DESIGNS CORPORATION ]
