Intel 82925X, Datasheet

Page: 181 / 242

Functional Description
R
Intel
®
82925X/82925XE MCH Datasheet 181
10.3.2 DRAM Clock Generation
The MCH generates three differential clock pairs for every supported DIMM. There are a total of
6 clock pairs driven directly by the MCH to 2 DIMMs per channel.
10.3.3 Suspend to RAM and Resume
When entering the Suspend-to-RAM (STR) state, the SDRAM controller will flush pending
cycles and then enter all SDRAM rows into self refresh. In STR, the CKE signals remain LOW so
the SDRAM devices will perform self-refresh.
10.3.4 DDR2 On-Die Termination
On-die termination (ODT) is a feature that allows a DRAM to turn on/off internal termination
resistance for each DQ, DM, DQS, and DQS# signal for x8 and x16 configurations via the ODT
control signals. The ODT feature is designed to improve signal integrity of the memory channel
by allowing the termination resistance for the DQ, DM, DQS, and DQS# signals to be located
inside the DRAM devices themselves, instead of on the motherboard. The MCH drives out the
required ODT signals, based on memory configuration and which rank is being written to or read
from, to the DRAM devices on a targeted DIMM rank to enable or disable their termination
resistance.
10.3.5 DDR2 Off-Chip Driver Impedance Calibration
The OCD impedance adjustment mode allows the MCH to measure and adjust the pull-up and
pull-down strength of the DRAM devices. It uses a series of EMRS commands to guide the
DRAM through measurement and calibration cycles. This feature is described in more detail in
the JEDEC DDR2 device specification.
The algorithm and sequence of the adjustment cycles is handled by software. The MCH adjusts
the DRAM driver impedance by issuing OCD commands to the DIMM and looking at the analog
voltage on the DQ lines.