Mobile Intel Pentium 4 Processor - M and Intel 845MP/MZ Chipset Platform Design Guide

Mobile Intel

Pentium

4 Processor-M and Intel

845MP/845MZ Chipset Platform

Design Guide 67

5.2.3.1. Command Topology 1 Solution

5.2.3.1.1. Routing description for Command Topology 1

Refer to Figure 28 and Figure 31 for clarification of the description below. The command signal routing

should transition from an external layer to an internal signal layer under the MCH-M. Keep to the same

internal layer until transitioning back to an external layer immediately prior to connecting the appropriate

pad of the SO-DIMM0 connector. At the SO-DIMM0 layer transition continue the signal route on the

same internal layer to the series resistor Rd2d, collocated to SO-DIMM1. At this resistor the signal

should transition to an external layer immediately prior to the pad of Rd2d. After the series resistor,

Rd2d, continue the signal route on the external layer landing on the appropriate connector pad

of SO-

DIMM1. After SO-DIMM1, transition to the same internal layer or stay on the external layer and route

the signal to Rt.

External trace lengths should be minimized. It is suggested that the parallel termination(Rt) be placed on

both sides of the board to simplify routing and minimize trace lengths. All internal and external signals

should be ground referenced to keep the path of the return current continuous. It is suggested that

command be routed on same internal layer.

Resistor packs are acceptable for the series (Rd2d) and parallel (Rt) command termination resistors but

command signals can’t be placed within the same Rpacks as data, strobe or control signals. The diagrams

and tables below depict the recommended topology and layout routing guidelines for the DDR-SDRAM

command signals routing to SO-DIMM0 and SO-DIMM1 for topology 1.Collocating the series resistor,

Rd2d, and SO-DIMM1 allows for the elimination of one via from the signal route.

Figure 28. Command Signal Routing Topology 1

Rd2d

SO-DIMM1 PAD SO-DIMM0 PAD

Vtt

MCH-M

Pad

MCH-M Package