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Register Description
D15343-003 85
4.9.16 DRC – DRAM Controller Mode Register (Device #0)
Address Offset:
Default Value:
Access:
Size:
70-73h
00000081h
RO, Read/Write
32 bits
Bit Description
31:30 Revision Number (REV): Reflects the revision number of the format used for DDR SDRAM
register definition (Read Only).
29 Initialization Complete (IC): This bit is used for communication of software state between the
Memory Controller and the BIOS. BIOS sets this bit to 1 after initialization of the DDR SDRAM
Memory Array is complete. Setting this bit to a 1 enables DDR SDRAM Refreshes. On power up
and S3 exit, the BIOS initializes the DDR SDRAM array and sets this bit to a 1. This bit works in
combination with the RMS bits in controlling Refresh state:
IC
Refresh State
0 OFF
1 ON
28:24 Reserved
23:22 Number of Channels (CHAN): Reflects that GMCH supports only one system memory channel.
00: One channel is populated appropriately
Others: Reserved
21:20 DDIM DDR SDRAM Data Integrity Mode:
00: ECC is not supported on this system. Thus, no read-merge-write on partial writes. ECC data
sense-amps are disabled and the data output is tristate (Default).
XX: Reserved
19:16 Reserved
15 RAS Lock-Out Enable: Set to a 1 if all populated rows support RAS Lock-Out. Defaults to 0.
If this bit is set to a 1 the DDR SDRAM Controller assumes that the DDR SDRAM guarantees
tRAS min before an auto precharge (AP) completes (Note: An AP is sent with a Read or a Write
command). Also, the DDR SDRAM Controller does not issue an activate command to the auto pre-
charged bank for tRP.
If this bit is set to a 0 the DDR SDRAM Controller does not schedule an AP if tRAS min is not met.
14:13 Reserved
12 Address Tri-state enable (ADRTRIEN): When set to a 1, the SDRAM Controller will tri-state the
MA, CMD, and CS# (only when all CKEs are deasserted). Note that when CKE to a row is
deasserted, fast chip select assertion is not permitted by the hardware. CKEs deassert based on
Idle Timer and/or max row count control.
0: Address Tri-state Disabled
1: Address Tri-state Enabled
11:10 Reserved