Datasheet

Dynamic ODT
In certain application cases and to further enhance signal integrity on the data bus, it is desirable that the
termination strength of the device can be changed without issuing an MRS command. This requirement is
supported by the dynamic ODT feature, described below.
Functional Description
The dynamic ODT mode is enabled if bit A9 or A10 of MR2 is set to 1.
 Three R
TT
values are available: R
TT_NOM
, R
TT_WR
, and R
TT_PARK
.
- The value for R
TT_NOM
is preselected via bits MR1 A[10:8].
- The value for R
TT_WR
is preselected via bits MR2 A[11:9].
- The value for R
TT_PARK
is preselected via bits MR5 A[8:6].
 During operation without write commands, the termination is controlled as follows:
- Nominal termination strength R
TT_NOM
or R
TT_PARK
is selected.
- R
TT_NOM
on/off timing is controlled via ODT pin and latencies DODTLon and DODTLoff; and R
TT_PARK
is on
when ODT is LOW.
 When a write command (WR, WRA, WRS4, WRS8, WRAS4, WRAS8) is registered, and if Dynamic ODT is
enabled, the termination is controlled as follows:
- Latency ODTLcnw after the write command, termination strength R
TT_WR
is selected.
- Latency ODTLcwn8 (for BL8, fixed by MRS or selected OTF) or ODTLcwn4 (for BC4, fixed by MRS or
selected OTF) after the write command, termination strength R
TT_WR
is deselected.
- One or two clocks will be added into or subtracted from ODTLcwn8 and ODTLcwn4, depending on write
CRC Mode and/or 2 t
CK
preamble enablement. The following table shows latencies and timing parameters
which are relevant for the on-die termination control in dynamic ODT mode.
The dynamic ODT feature is not supported in DLL-off mode. MRS command must be used to set R
TT_WR
, MR2
A[11:9] = 000, to disable dynamic ODT externally.
Table 65. Latencies and timing parameters relevant for Dynamic ODT with 1t
CK
preamble mode and
CRC disabled
Name and Description
Abbr.
Defined from
Define to
Definition for all
DDR4 speed bins
Unit
ODT Latency for changing from
R
TT_PARK
/R
TT_NOM
to R
TT_WR
ODTLcnw
Registering external
write command
Change R
TT
strength from
R
TT_PARK
/R
TT_NOM
to R
TT_WR
ODTLcnw = WL - 2
t
CK
ODT Latency for change from
R
TT_WR
to R
TT_PARK
/R
TT_NOM
(BL = 4)
ODTLcwn4
Registering external
write command
Change R
TT
strength from
R
TT_WR
to R
TT_PARK
/R
TT_NOM
ODTLcwn4 =
4 + ODTLcnw
t
CK
ODT Latency for change from
R
TT_WR
to R
TT_PARK
/R
TT_NOM
(BL = 8)
ODTLcwn8
Registering external
write command
Change R
TT
strength from
R
TT_WR
to R
TT_PARK
/R
TT_NOM
ODTLcwn8 =
6 + ODTLcnw
t
CK
RTT change skew
t
ADC
ODTLcnw
ODTLcwn
R
TT
Valid
t
ADC(min)
= 0.3
t
ADC(max)
= 0.7
t
CK
Table 66. Latencies and timing parameters relevant for Dynamic ODT with 1t
CK
and 2t
CK
preamble
mode and CRC enabled/disabled
Symbol
1t
CK
Preamble
2t
CK
Preamble
Unit
CRC off
CRC on
CRC off
CRC on
ODTLcnw
WL - 2
WL - 2
WL - 3
WL - 3
t
CK
ODTLcwn4
ODTLcnw +4
ODTLcnw +7
ODTLcnw +5
ODTLcnw +8
t
CK
ODTLcwn8
ODTLcnw +6
ODTLcnw +7
ODTLcnw +7
ODTLcnw +8
t
CK
AS4C256M16D4
Confidential
- 152 of 201 -
Rev.1.0 Aug.2019