![](http://datasheet.mmic.net.cn/180000/MT47H128M8HV-187ELIT-E_datasheet_11334050/MT47H128M8HV-187ELIT-E_78.png)
Write Recovery
The WR register is used by the DDR2 SDRAM during WRITE with auto precharge opera-
tion. During WRITE with auto precharge operation, the DDR2 SDRAM delays the inter-
nal auto precharge operation by WR clocks (programmed in bits M9–M11) from the last
WR values of 2, 3, 4, 5, 6, 7, or 8 clocks may be used for programming bits M9–M11. The
user is required to program the value of WR, which is calculated by dividing tWR (in
nanoseconds) by tCK (in nanoseconds) and rounding up a noninteger value to the next
integer; WR (cycles) = tWR (ns)/tCK (ns). Reserved states should not be used as an un-
known operation or incompatibility with future versions may result.
Power-Down Mode
Active power-down (PD) mode is defined by bit M12, as shown in
Figure 35. PD mode
enables the user to determine the active power-down mode, which determines perform-
ance versus power savings. PD mode bit M12 does not apply to precharge PD mode.
When bit M12 = 0, standard active PD mode, or “fast-exit” active PD mode, is enabled.
The tXARD parameter is used for fast-exit active PD exit timing. The DLL is expected to
be enabled and running during this mode.
When bit M12 = 1, a lower-power active PD mode, or “slow-exit” active PD mode, is
enabled. The tXARDS parameter is used for slow-exit active PD exit timing. The DLL can
be enabled but “frozen” during active PD mode because the exit-to-READ command
timing is relaxed. The power difference expected between IDD3P normal and IDD3P low-
power mode is defined in the DDR2 IDD Specifications and Conditions table.
1Gb: x4, x8, x16 DDR2 SDRAM
Mode Register (MR)
PDF: 09005aef821ae8bf
1GbDDR2.pdf – Rev. S 10/09 EN
78
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