Intel 855GME User Manual

254
Intel
®
855GME Chipset and Intel
®
6300ESB ICH Embedded Platform Design Guide
Platform Clock Routing Guidelines
11.2.2 CLK66 Clock Group
The 66 MHz clocks are series terminated and routed point-to-point on the motherboard, with
dedicated buffers for each of the loads. These clocks are all length tuned to match each other and
the CLK33 clocks. Figure 139 depicts the CLK66 clock group topology. Table 107 presents the
CLK66 clock group routing constraints.
Figure 139. CLK66 Clock Group Topology
Table 107. CLK66 Clock Group Routing Constraints
Parameter Definition
Class Name CLK66
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 (per side)
Series Termination Resistor Value 33
Ω ±5%
Trace Length Limits – L1 Up to 500 mils (breakout segment)
Trace Length Limits – L2 4.0” to 8.5”
Total Length Range – L1 + L2 4.0” to 9.0”
Length Matching Required Yes (Pin to Pin)
Clock to Clock Length Matching ±100 mils
CLK66 to CLK66
Breakout Region Exceptions.
(Reduced spacing for GMCH and ICH breakout
region)
5 mil trace with 5 mil space on outers
4 mil trace with 4 mil space in inners
Maximum breakout length is 0.3”
NOTE: The overall length of CLK66 is considered the reference length for CLK66 and CLK33, except
USBCLK and CLK14. The length of this clock should be set within the range and then used as the
basis for defining the length of all other length matched clocks.
L1
Rs
CK409
GMCH
Intel
®
6300ESB
L2

Intel 855GME Specifications

General

Brand	Intel
Model	855GME
Category	Computer Hardware
Language	English