MT40A512M8RH-075E Datasheet, PDF (144/365 Pages) Micron Technology – DDR4 SDRAM

4Gb: x4, x8, x16 DDR4 SDRAM
Fine Granularity Refresh Mode
Fine Granularity Refresh Mode
Mode Register and Command Truth Table
The REFRESH cycle time (^tRFC) and the average refresh interval (^tREFI) can be pro-
grammed by the MRS command. The appropriate setting in the mode register will set a
single set of REFRESH cycle times and average refresh interval for the device (fixed
mode), or allow the dynamic selection of one of two sets of REFRESH cycle times and
average refresh interval for the device (on-the-fly mode [OTF]). OTF mode must be ena-
bled by MRS before any OTF REFRESH command can be issued.
Table 49: MRS Definition
MR3[8]
0
0
0
0
1
1
1
1
MR3[7]
0
0
1
1
0
0
1
1
MR3[6]
0
1
0
1
0
1
0
1
Refresh Rate Mode
Normal mode (fixed 1x)
Fixed 2x
Fixed 4x
Reserved
Reserved
On-the-fly 1x/2x
On-the-fly 1x/4x
Reserved
There are two types of OTF modes (1x/2x and 1x/4x modes) that are selectable by pro-
gramming the appropriate values into the mode register MR3 [8:6]. When either of the
two OTF modes is selected, the device evaluates the BG0 bit when a REFRESH com-
mand is issued, and depending on the status of BG0, it dynamically switches its internal
refresh configuration between 1x and 2x (or 1x and 4x) modes, and then executes the
corresponding REFRESH operation.
Table 50: REFRESH Command Truth Table
Refresh
Fixed rate
OTF: 1x
OTF: 2x
OTF: 4x
CS_n
L
L
L
L
ACT_n
H
H
H
H
RAS_n/A CAS_n/A
15
14
L
L
L
L
L
L
L
L
WE_n/
A13
H
H
H
H
BG1
V
V
V
V
BG0
V
L
H
H
A10/
AP
V
V
V
V
A[9:0],
A[12:11],
A[20:16]
V
V
V
V
MR3[8:6
]
0vv
1vv
101
110
t_{REFI and} t_{RFC Parameters}
The default refresh rate mode is fixed 1x mode where REFRESH commands should be
issued with the normal rate; that is, ^tREFI1 = ^tREFI(base) (for T_C ≤ 85°C), and the dura-
tion of each REFRESH command is the normal REFRESH cycle time (^tRFC1). In 2x
mode (either fixed 2x or OTF 2x mode), REFRESH commands should be issued to the
device at the double frequency (^tREFI2 = ^tREFI(base)/2) of the normal refresh rate. In 4x
mode, the REFRESH command rate should be quadrupled (^tREFI4 = ^tREFI(base)/4). Per
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4gb_ddr4_dram.pdf - Rev. G 1/17 EN
144
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