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Intel
855GME Chipset and Intel
System Memory Design Guidelines (DDR-SDRAM)
Table 38. Command Topology Routing Guidelines (Sheet 2 of 2)
Parallel Termination Resistor (Rt)
Maximum Recommended Motherboard Via Count
Per Signal
Length Matching Requirements
NOTES:
1. Recommended resistor values and trace lengths may change in a later revision of the design guide.
2. Power distribution vias from Rt to Vtt are not included in this count.
3. The overall maximum and minimum length to the DIMM must comply with clock length matching
requirements.
4. It is possible to route using three vias if one via is shared that connects to the DIMM1 pad and parallel
termination resistor.
5.4.6.3
Command Topology Length Matching Requirements
The routing length of the command signals, between the GMCH die-pad and the DIMM must be
within the range defined below, with respect to the associated clock reference length. Refer to
Figure 71
DIMM to the termination resistor need not be length matched.
Length range formula for DIMM0:
X
= SCK[2:0]/SCK[2:0]# total reference length, including package length. Refer to
0
Section 5.4.3.1
Y
= CMD signal total length = GMCH package + L1, as shown in
0
– 1.5") ≤ Y
(X
0
Length range formula for DIMM1:
X
= SCK[5:3]/SCK[5:3]# total reference length, including package length. Refer to
1
Section 5.4.3.1
Y
= CMD signal total length = GMCH package + L1 + L2 + L3, as shown in
1
– 1.5") ≤ Y
(X
1
No length matching is required from DIMM1 to the termination resistor.
length matching requirements between the command signals and clock. A nominal CMD package
length of 500 mils may be used to estimate baseline Mbyte lengths. Refer to
details on package length compensation.
144
®
6300ESB ICH Embedded Platform Design Guide
Parameter
for a definition of the various motherboard trace segments. The length of trace from the
for more information.
≤ (X
+ 1.0")
0
0
for more information.
≤ (X
+ 1.0")
1
1
Routing Guidelines
56 Ω ± 5%
6
CMD to SCK/SCK#
Refer to length matching
Section 5.4.6.3
for details.
Figure
Figure 72
and
Figure 72
71, where:
Figure
71, where:
depicts the
Section 5.3
for more
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