MT40A256M16GE-075E Datasheet, PDF (48/365 Pages) Micron Technology – Temperature controlled refresh (TCR)

4Gb: x4, x8, x16 DDR4 SDRAM
Mode Register 1
Table 10: MR1 Register Definition (Continued)
Mode
Register
10, 9, 8
7
6, 5
4, 3
2, 1
0
Description
Nominal ODT (R_TT(NOM) – Data bus termination setting
000 = R_TT(NOM) disabled
001 = RZQ/4 (60 ohm)
010 = RZQ/2 (120 ohm)
011 = RZQ/6 (40 ohm)
100 = RZQ/1 (240 ohm)
101 = RZQ/5 (48 ohm)
110 = RZQ/3 (80 ohm)
111 = RZQ/7 (34 ohm)
Write leveling (WL) – Write leveling mode
0 = Disabled (normal operation)
1 = Enabled (enter WL mode)
RFU
0 = Must be programmed to 0
1 = Reserved
Additive latency (AL) – Command additive latency setting
00 = 0 (AL disabled)
01 = CL - 1¹
10 = CL - 2
11 = Reserved
Output driver impedance (ODI) – Output driver impedance setting
00 = RZQ/7 (34 ohm)
01 = RZQ/5 (48 ohm)
10 = Reserved (Although not JEDEC-defined and not tested, this setting will provide RZQ/6 or 40 ohm)
11 = Reserved
DLL enable – DLL enable feature
0 = DLL disabled
1 = DLL enabled (normal operation)
Note: 1. Not allowed when 1/4 rate gear-down mode is enabled.
DLL Enable/DLL Disable
The DLL must be enabled for normal operation and is required during power-up initial-
ization and upon returning to normal operation after having the DLL disabled. During
normal operation (DLL enabled with MR1[0]) the DLL is automatically disabled when
entering the SELF REFRESH operation and is automatically re-enabled upon exit of the
SELF REFRESH operation. Any time the DLL is enabled and subsequently reset, ^tDLLK
clock cycles must occur before a READ or SYNCHRONOUS ODT command can be is-
sued to allow time for the internal clock to be synchronized with the external clock. Fail-
ing to wait for synchronization to occur may result in a violation of the ^tDQSCK, ^tAON,
or ^tAOF parameters.
During ^tDLLK, CKE must continuously be registered HIGH. The device does not require
DLL for any WRITE operation, except when R_TT(WR) is enabled and the DLL is required
for proper ODT operation.
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4gb_ddr4_dram.pdf - Rev. G 1/17 EN
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