User's Manual

Intel

820 Chipset Design Guide 2-13

Layout/Routing Guidelines

2.6.2.3 Direct Rambus* Ground Plane Reference

All RSL signals must be referenced to GND to provide an optimal current return path. The direct

Rambus ground plane reference must be continuous to the Vterm capacitors. The ground reference

island under the RSL signals must be continuous from the last RIMM to the back of the termination

capacitors. Choose the reference island shape such that power delivery to the components is not

compromised. The return current will flow through the Vterm capacitors into the ground island and

under the RSL traces. Any split in the ground island will provide a sub-optimal return path. In a 4

layer board, this will require the Vterm island to be on an outer layer. The Vterm island should

ALWAYS be placed on the top layer. Refer to Section 6.2, “Power Plane Splits” on page 6-7 for an

example of power plane splits.

The ground reference island under the RSL signals MUST be connected to the ground pins on the

RIMM connector and the ground vias used to connect the ground isolation on the 1

and 4

layers.

Figure 2-15. Incorrect Direct Rambus* Ground Plane Referencing

Figure 2-16. Direct Rambus Ground Plane Reference

3.3V Plane

1.8V Plane

MCH

Wrong

RIMM2

RIMM1

Extend GND PLANE

Reference Island Beyond

Vterm Capacitors

GND Plane

1.8V Plane

RIMM1

GND PlaneGND Plane

MCH

Required

Vterm Layer Not Shown

Vterm Resistors

Vterm Capacitors

RIMM2

3.3V Plane