256
Intel
®
855GME Chipset and Intel
®
6300ESB ICH Embedded Platform Design Guide
Platform Clock Routing Guidelines
11.2.4
PCI Clock Group
The PCI clocks are series terminated and routed point-to-point as on the motherboard between the
CK409 and the PCI connectors with dedicated buffers for of the three slots. These clocks are
synchronous to the CLK33 clocks and are length tuned to compensate for the segment on the PCI
daughtercard.
depicts the PCI clock group topology.
presents the PCICLK
clock group routing constraints.
Figure 141. PCI Clock Group Topology
Table 109. PCICLK Clock Group Routing Constraints
Parameter
Definition
Class Name
PCICLK
Class Type
Individual Nets
Topology
Series Terminated Point to Point
Reference Plane
Ground Referenced
Single Ended Trace Impedance (Zo)
55
Ω
±15%
Nominal Inner Layer Trace Width
4.0 mils
Nominal Outer Layer Trace Width
5.0 mils (pin escapes only)
Minimum Spacing (See exceptions below.)
20 mils
Serpentine Spacing
20 mils
Maximum Via Count
4
Series Termination Resistor Value
33
Ω
±5%
Trace Length Limits – L1
Up to 500 mils (breakout segment)
Trace Length Limits – L2
1.5” to 8.0”
Trace Length Limits – L3
2.5” (as per PCI specification)
Total Length Range – L1 + L2
CLK33 – 2.5” (for nominal matching)
Length Matching Required
Yes (Pin to Pin)
Clock to Clock Length Matching
±2.0”
PCICLK to PCICLK to (CLK33 – 2.5”)
Breakout Region Exceptions
5 mil trace with 5 mil space on outers
4 mil trace with 4 mil space in inners
Maximum breakout length is 0.3”
Rs
CK409 PCI
Device
L2
PCI
Connector
Trace on Card
L3
L1
Содержание 6300ESB ICH
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