Guide

System Memory Design Guidelines (DDR-SDRAM)
R
Intel
®
852GM Chipset Platform Design Guide 109
7.3.6.3. Command Topology 1 Length Matching Requirements
The routing length of the command signals, between the GMCH die pad and the SO-DIMM must be
within the range defined below, with respect to the associated clock reference length. Refer to Figure 53
for a definition of the various motherboard trace segments. The length of trace from the SO-DIMM to
the termination resistor need not be length matched. The length matching requirements are also depicted
in Figure 54. Refer to Section 7.1 for more details on length matching requirements.
Length range formula for SO-DIMM0:
X0 = SCK/SCLK#[2:0] total reference length, including package length. See clock Section 7.3.1.
Y0 = CMD signal total length = GMCH package + L1, as shown in Figure 53,
where: ( X
0
– 1.0” ) ≤ Y
0
≤ ( X
0
+ 2.0” )
Length range formula for SO-DIMM1:
X1 = SCK/SCLK#[5:3] total reference length, including package length. See clock Section 7.3.1.
Y1 = CMD signal total length = GMCH package + L1 + L2 + L3, as shown in Figure 53,
where: ( X
1
– 1.0” ) ≤ Y
1
≤ ( X
1
+ 2.0” )
No length matching is required from SO-DIMM1 to the termination resistor. Figure 54 on the following
page depicts the length matching requirements between the command signals and clock. A nominal
CMD package length of 500 mils can be used to estimate baseline MB lengths. Refer to Section 7.2 for
more details on package length compensation.