FSB Design Guidelines
R
62
Intel
®
855PM Chipset Platform Design Guide
Table 15. Processor RESET# Signal Routing Guidelines with ITP700FLEX Connector
L1
L2 + L3
L3
Rs
Rtt
1.0” – 6.0”
12.0” max
0.5” max
Rs = 22.6
± 1%
Rtt = 54.9
± 1%
4.1.5.1.
Processor RESET# Routing Example
Figure 27 illustrates a board routing example for the RESET# signal with an ITP700FLEX debug port
implemented. Figure 27 illustrates how the CPURST# pin of Intel 855PM MCH forks out into two
branches on Layer 6 of the motherboard. One branch is routed directly to the processor’s 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 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 27. Processor RESET# Signal Routing Example with ITP700FLEX Debug Port
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Intel P entiu m M
processor
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Intel P entiu m M
processor
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Intel P entiu m M
processor
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Pentium M
855PM
GND
VIA
Layer 6
FO RK
ITPFLEX
connector
Secondary
Side
VCCP
Rs
R tt
CPU
L2
L3
Rs
L1
ITPFLE X
CO NNECTO R
MC H-M
Rtt
VCCP
RESET#
CPURESET #
RESET#
CO M M O N
Clock S ignals
ADD R
Intel
855P M
M C H-M
Intel P entiu m M
processor