Design Guide

System Memory Design Guidelines (DDR-SDRAM) for SO-DIMM configuration
R
Intel
®
855GM/855GME Chipset Platform Design Guide 113
Length Matching Requirements
CPC to SCK/SCK# [5:0]
See length matching Section 6.3.7.3 and
Figure 51 for details.
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. It is possible to route using 2 vias if one via is shared that connects to the SO-DIMM pad and parallel
termination resistor.
4. The overall maximum and minimum length to the SO-DIMM must comply with clock length matching
requirements.
6.3.7.3. CPC to Clock Length Matching Requirements
The total length of the CPC signals, between the GMCH die pad and the SO-DIMM must fall within the
range defined below, with respect to the associated clock reference length. Refer to Figure 50 for a
definition of the various trace segments. The length the trace from the SO-DIMM to the termination
resistor need not be length matched. The length matching requirements are also depicted in
Figure 51. Refer to Section 6.1 for more details on length matching requirements. A table of CPC
signal package length is provided in Section 6.3.7.4.
Length range formula for SO-DIMM0:
X
0
= SCK/SCK#[2:0] total reference length, including package length.
Y
0
= SMA[5,4,2,1] total length = GMCH package + L1 + S1, as shown in
Figure 51,
where: ( X
0
– 1.0” ) ≤ Y
0
≤ ( X
0
+ 0.5” ) for DDR 200/266
( X
0
– 2.0” ) ≤ Y
0
≤ ( X
0
- 1.0” ) for DDR 200/266/333
Length range formula for SO-DIMM1:
X
1
= SCK/SCK#[5:3] total reference length, including package length.
Y
1
= SMAB[5,4,2,1] total length = GMCH package + L1 + S1, as shown in
Figure 51,
where: ( X
1
– 1.0” ) ≤ Y
1
≤ ( X
1
+ 0.5” ) for DDR 200/266
( X
1
– 2.0” ) ≤ Y
1
≤ ( X
1
- 1.0” ) for DDR 200/266/333
No length matching is required from SO-DIMM1 to the termination resistor.
Figure 51 on the following page depicts the length matching requirements between the CPC signals and
clock. A nominal CPC package length of 500 mils can be used to estimate baseline MB lengths. Refer
to Section 6.2 for more details on package length compensation.