MT40A512M16HA-083EIT Datasheet, PDF (149/373 Pages) Micron Technology – Programmable data strobe preambles

8Gb: x4, x8, x16 DDR4 SDRAM
Fine Granularity Refresh Mode
Changing Refresh Rate
If the refresh rate is changed by either MRS or OTF. New ^tREFI and ^tRFC parameters will
be applied from the moment of the rate change. When the REF1x command is issued to
the DRAM, ^tREF1 and ^tRFC1 are applied from the time that the command was issued;
when the REF2x command is issued, ^tREF2 and ^tRFC2 should be satisfied.
Figure 87: OTF REFRESH Command Timing
CK_c
CK_t
Command
DES
REF1
DES
DES
DES
Valid
Valid
REF2
DES
DES
Valid
DES
REF2
DES
t_{RFC1 (MIN)}
t_{RFC2 (MIN)}
t_REFI1
t_REFI2
Don’t Care
The following conditions must be satisfied before the refresh rate can be changed. Oth-
erwise, data retention cannot be guaranteed.
• In the fixed 2x refresh rate mode or the OTF 1x/2x refresh mode, an even number of
REF2x commands must be issued because the last change of the refresh rate mode
with an MRS command before the refresh rate can be changed by another MRS com-
mand.
• In the OTF1x/2x refresh rate mode, an even number of REF2x commands must be is-
sued between any two REF1x commands.
• In the fixed 4x refresh rate mode or the OTF 1x/4x refresh mode, a multiple-of-four
number of REF4x commands must be issued because the last change of the refresh
rate with an MRS command before the refresh rate can be changed by another MRS
command.
• In the OTF1x/4x refresh rate mode, a multiple-of-four number of REF4x commands
must be issued between any two REF1x commands.
There are no special restrictions for the fixed 1x refresh rate mode. Switching between
fixed and OTF modes keeping the same rate is not regarded as a refresh rate change.
Usage with TCR Mode
If the temperature controlled refresh mode is enabled, only the normal mode (fixed 1x
mode, MR3[8:6] = 000) is allowed. If any other refresh mode than the normal mode is
selected, the temperature controlled refresh mode must be disabled.
Self Refresh Entry and Exit
The device can enter self refresh mode anytime in 1x, 2x, and 4x mode without any re-
striction on the number of REFRESH commands that have been issued during the
mode before the self refresh entry. However, upon self refresh exit, extra REFRESH com-
mand(s) may be required, depending on the condition of the self refresh entry.
The conditions and requirements for the extra REFRESH command(s) are defined as
follows:
• In the fixed 2x refresh rate mode or the enable-OTF 1x/2x refresh rate mode, it is rec-
ommended there be an even number of REF2x commands before entry into self re-
fresh after the last self refresh exit, REF1x command, or MRS command that set the
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8gb_ddr4_dram.pdf - Rev. G 1/17 EN
149
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