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System Memory Design Guidelines (DDR-SDRAM)
6.1.3.2.2.
Command Topology 2 to Clock Length Matching Requirements
The command signals must be 0.5 inches shorter to 1.0 inches longer than their associated differential
clock pairs.
Length matching equation for SO-DIMM0:
X
= SCK/SCK#[2:0]
1
Y
= Command Signals = L1 + Rs Length + L2 of Figure 82 where:
1
Length matching equation for SO-DIMM1:
X
= SCK/SCK#[5:3]
2
Y
= Command Signals = L1 + L3 of Figure 82 where:
2
For example if the clock length of SCK/SCK#[2:0](X
signal routing to SO-DIMM0 must be between 4.5 inches to 6.0 inches, if SCK/SCK#[5:3](X
inches then the length of command signal routing to SO-DIMM1 must be between 5.0 inches to 6.5
inches. Figure 83 depicts the length matching requirements between the command and clock signals.
The MCH package lengths do not need to be taken into account for routing length matching purposes.
146
( Y
– 1.0" )
X
( Y
+ 0.5" )
1
1
1
( Y
– 1.0" )
X
( Y
+ 0.5" )
2
2
2
) is 5.0 inches then the length of all command
1
®
Intel
855PM Chipset Platform Design Guide
R
) is 5.5
2
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