Datasheet
ODT R
TT_NOM
Values
The device is capable of providing three different termination values: R
TT_PARK
, R
TT_NOM
, and R
TT_WR
. The
nominal termination value, R
TT_NOM
, is programmed in MR1. A separate value, R
TT_WR
, may be programmed in
MR2 to enable a unique R
TT
value when ODT is enabled during Write operations. The R
TT_WR
value can be
applied during Write commands even when R
TT_NOM
is disabled. A third R
TT
value, R
TT_PARK
, is programmed in
MR5. R
TT_PARK
provides a termination value when the ODT signal is Low.
Additive Latency
The Additive Latency (AL) operation is supported to make command and data bus efficient for sustainable
bandwidths in the device. In this operation, the device allows a Read or Write command (either with or without
auto precharge) to be issued immediately after the Activate command. The command is held for the time of AL
before it is issued inside the device. Read latency (RL) is controlled by the sum of the AL and CAS latency (CL)
register settings. Write latency (WL) is controlled by the sum of the AL and CAS Write latency (CWL) register
settings. Additive Latency is not supported for x16 device.
Write Leveling
For better signal integrity, the device uses fly-by topology for the commands, addresses, control signals,
and clocks. Fly-by topology benefits from a reduced number of stubs and their lengths, but it causes flight-time
skew between clock and strobe at every DRAM on the DIMM. This makes it difficult for the controller to
maintain tDQSS, tDSS, and tDSH specifications. Therefore, the device supports a write leveling feature that
allows the controller to compensate for skew.
Output Disable
The device outputs may be enabled/disabled by MR1[12] as shown in the MR1 Register Definition table.
When MR1[12] is enabled (MR1[12] = 1) all output pins (such as DQ and DQS) are disconnected from the
device, which removes any loading of the output drivers. For example, this feature may be useful when
measuring module power. For normal operation, set MR1[12] to 0.
AS4C256M16D4
Confidential
- 18 of 201 -
Rev.1.0 Aug.2019