Length Matching Equation - Intel Pentium M Processor Design Manual

To compensate for package-induced skew, all source synchronous motherboard trace lengths are
adjusted by the exact amount of Package Length Compensation (PLC).
a particular signal. Signal X is any signal in the group that does not have the longest package
length. This includes the strobe signals.
Equation 4. Package Length Compensation (PLC) Definition
SignalX
The signals with a package length less than the longest package trace in that group will require
additional motherboard trace length equal to SignalX
signal with the longest package length. So the signal with the longest package length would require
no amount of additional motherboard trace length.
the longest package trace and strobe signal as "Signal X".
Figure 160. Example of PLC Compensation on the Motherboard
Component A
Die Pad
Die Pad
12.7.2

Length Matching Equation

This section explains the length matching compensation scheme, associated equations, and an
explanation for determining the motherboard trace lengths. Processor Length Matching is only
dependant upon a signals PLC. To determine an actual PCB length, the designer may use one
signal as a reference signal to calculate the PCB length of the remaining signals in a group. For
simple illustrative purposes, the formulas and examples used are based upon the shortest PCB trace
length. However, the formulas could be based off any signal in the group. For simple illustrative
purposes, the example also assumes the shortest and longest signals on the processor package are
the shortest and longest for the MCH package as well. This is not necessarily the case.
Figure 161
trace lengths. The signal whose motherboard trace length between. All source synchronous signals
with less than the longest processor and MCH package length require varying amounts of PLC
motherboard length segments added to
Design Guide
®
Intel Pentium
= Maximum_Signal_in_Group
PLC
Data Signal
Longest Pac kage T race
Strobe Signal
Shortest Pac kage T race
contains the final length matching example that account for PLC in the motherboard
®
M Processor and Intel
High-Speed Design Concerns
- SignalX
Package Length
. Equation 4
PLC
Figure 160 illustrates PLC using a data signal as
Delta
Component Pin
PLC
Delta
Shortest Signal
Processor to MCH PCB Length
®
E7501 Chipset Platform
Equation 4 defines PLC for
Package Length
yields a zero PLC for the
Shortes t Motherboard T race
Routes to
Component B
Shortest Motherboard T rac e
respectively.
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