Design Guide

Intel Pentium M/Celeron M Front Side Bus Design Guidelines
R
Intel
®
855GM/855GME Chipset Platform Design Guide 57
Table 17. Processor RESET# Signal Routing Guidelines with ITP700FLEX Connector
L1 L2 + L3 L3 Rs Rtt
1.0” – 6.0” 6.0” max 0.5” max Rs = 22.6 Ω ± 1% Rtt = 220 Ω ± 5%
4.1.5.1. Processor RESET# Routing Example
Figure 19 illustrates a board routing example for the RESET# signal with an ITP700FLEX debug port
implemented. It illustrates how the CPURST# pin of GMCH forks out into two branches on Layer 6 of
the motherboard. One branch is routed directly to the processor RESET# pin amongst the rest of the
common clock signals. Another branch routes below the address signals and vias down to the secondary
side that route to the Rs and Rtt resistors. These resistors are placed in the vicinity of the ITP700FLEX
debug port.
Note: The placement of Rs and Rtt next to each other is to minimize the routing between Rs and Rtt as well as
the minimal routing between Rs and the ITP700FLEX connector. Also, since a transition between Layer
6 and the secondary side occurs, a GND stitching via is added to guarantee continuous ground reference
of the secondary side routing of the RESET# signal to ITP700FLEX connector.
Figure 19. Processor RESET# Signal Routing Example with ITP700FLEX Debug Port
CPU
GMCH
GND VIA
Layer 6
ITPFLEX
Connector
Secondary
Side
VCCP
Rs
Rtt
CPU
L2
L3
Rs
L1
ITPFLEX
CONNECTOR
MCH - M
Rtt
VCCP
RESET#
CPURESET#
RESET#
4.1.6. Processor and GMCH Host Clock Signals
Figure 20 illustrates processor and GMCH host clock signal routing. Both the processor and the
GMCH’s BCLK[1:0] signals are initially routed from the CK-408 clock generator on Layer 3.In the
recommended routing example (Figure 20) secondary side layer routing of BCLK[1:0] is 507 mils long.
To meet length-matching requirements between the processor and GMCH’s BCLK[1:0] signals, a
similar transition from Layer 3 to the secondary side layer is done next to the GMCH package outline.
Routing of the GMCH’s BCLK[1:0] signals on the secondary side is also trace tuned to 507 mils.