Memory Controller User's Guide

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4.3 SDRAM Refresh Control Register (SDRCR)
DDR2 Memory Controller Registers
The SDRAM refresh control register (SDRCR) is used to configure the DDR2 memory controller to:
• Enter and Exit the self-refresh state.
• Enable and disable MCLK, stopping when in the self-refresh state.
• Meet the refresh requirement of the attached DDR2 device by programming the rate at which the
DDR2 memory controller issues autorefresh commands.
The SDRCR is shown in Figure 21 and described in Table 27 .
Figure 21. SDRAM Refresh Control Register (SDRCR)
31 30 29 24 23 22 16
SR MCLKSTOPEN Reserved Rsvd Reserved
R/W-0 R/W-0 R-0 R/W-0 R-0
15 0
RR
R/W-884h
LEGEND: R/W = Read/Write; R = Read only; - n = value after reset
Table 27. SDRAM Refresh Control Register (SDRCR) Field Descriptions
Bit Field Value Description
31 SR Self refresh.
0 DDR2 memory controller exits the self-refresh mode.
1 DDR2 memory controller enters the self-refresh mode.
30 MCLKSTOPEN MCLK stop enable.
0 Disables MCLK stopping, MCLK may not be stopped.
1 Enables MCLK stopping, MCLK may be stopped. The SR bit must be set to 1 before setting the
MCLKSTOPEN bit to 1.
29-24 Reserved 0 Reserved
23 Reserved 0 Reserved. Always write 0 to this bit.
22-16 Reserved 0 Reserved
15-0 RR 0-FFFFh Refresh rate. Defines the rate at which the attached DDR2 devices will be refreshed. The value
of this field may be calculated with the following equation:
RR = DDR2 clock frequency (in MHZ) × DDR2 refresh rate (in µ s)
where DDR2 refresh rate is derived from the DDR2 data sheet. Writing a value < 0100h to this
field causes it to be loaded with the value 2 × T_RFC from the SDRAM timing register
(SDTIMR).
SPRUEM4A – November 2007 DDR2 Memory Controller 45
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