iPEM
4.2 Gb SDRAM-DDR2
Austin Semiconductor, Inc.
AS4DDR264M64PBG1
OUTPUT ENABLE/DISABLE
DLL 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 ICC characterization of read current.
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.
ON-DIE TERMINATION (ODT)
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
ODT effective resistance, RTT (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. RTT 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
(RTT2(EFF) = R2/2). Similarly, if “sw2” is enabled, all R2 values
that are 300Ω each, enable an effective ODT resistance of
150Ω (RTT2(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.
t
t
may result in a violation of the AC or DQSCK parameters.
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 45-60 percent of the SSTL_18 drive strength.
This option is intended for the support of lighter load and/or
point-to-point environments.
The ODT control ball is used to determine when RTT(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 powerdown
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 RTT(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.
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.
Austin Semiconductor, Inc.
● Austin, Texas ● 512.339.1188 ● www.austinsemiconductor.com
AS4DDR264M64PBG1
Rev. 0.5 06/08
11
AUSTIN [ AUSTIN SEMICONDUCTOR ]
