User's Manual

Intel
®
820 Chipset Design Guide 2-9
Layout/Routing Guidelines
To maintain a nominal 28 Ω trace impedance, the RSL signals must be 18 mils wide. To control
crosstalk and odd/even mode velocity deltas, there must be a 10 mil ground isolation trace routed
between adjacent RSL signals. The 10 mil ground isolation traces must be connected to ground
with a via every 1”. A 6 mil gap is required between the RSL signals and the ground isolation trace.
These signals must be length matched to ±10 mils in line section “A” and ±2 mils in both line
sections labeled “B” using the trace length matching methods in Section 2.6.2.6, “Length Matching
Methods” on page 2-21. To ensure uniform trace lines, trace width variation must be uniform on all
RSL signals at every neck-down for each line section. All RSL signals must have the same number
of vias. It may be necessary to place vias on RSL signals where they are not necessary to meet this
via loading requirement (i.e., dummy vias).
Figure 2-10 shows a top view of the trace width/spacing requirements for the RSL signals.
Figure 2-9. RSL Routing Dimensions
MCH
MCH to
First RIMM
RIMM_0 RIMM_1
A B C
RIMM to
RIMM
RIMM to
Termination
0"-3.50"
0.4"-0.45"
0"-3"
Table 2-2. Placement Guidelines for Motherboard Routing Lengths
Reference Trace Description Maximum Trace Length (in.)
A MCH to first RIMM Connector 0” to 3.50”
B RIMM to RIMM 0.4” – 0.45”
C RIMM to Termination 0” to 3”
Figure 2-10. RSL Routing Diagram
RSL Signal Trace
Space
Ground
Space
RSL Signal Trace
Space
Ground
Space
18 mils
6 mils
10 mils
10 mils
6 mils
6 mils
18 mils
6 mils