System Bus Length Matching Example - Intel Pentium M Processor Design Manual

12.7.3

System Bus Length Matching Example

Note: Example component values are used in this example and should not be relied upon for actual
design of the system bus.
The system bus source synchronous signal group requires groups of signals and associated strobes
to be length matched within ± 25 mils between components.
Sample: Given that routing has started with DSTBN0# routed between Processor and MCH with a
pad-to-pad route of exactly 4.0 inches, what is the DSTBP0# Processor/MCH
motherboard length?
See Section 12.8
obtained from the Intel
the processor and MCH package trace lengths may be found in the Intel
System Bus Length Matching Spreadsheet. Contact your Intel representative for information about
the Length Matching Spreadsheet tool. For this example, we will use the following processor and
MCH values:
•
Maximum processor package length is this group is 0.722 inch
•
DSTBN0# processor package length is 0.722 inch
•
DSTBP0# processor package length is 0.722 inch
•
Maximum MCH package length is this group is 1.060 inches
•
DSTBN0# MCH package length is 0.842 inch
•
DSTBP0# MCH package length is 0.738 inch
Sample Solution: By definition, the DSTBN0# signal 4-inch route already includes the PLC
motherboard trace components. The MCH PLC values are determined for DSTBN0# and
DSTBP0# using
DSTBN0#
DSTBP0#
The DSTBP0# Processor/MCH motherboard lengths are calculated using
DSTBP0#
Since the system bus data signals must be length matched within ± 25 mils between components,
the DSTBP0# Processor/MCH motherboard length is 4.104 ± 0.025 inch.
The above example demonstrates the importance of the first routed motherboard traces since these
will establish the routing lengths for the remaining signals in the same signal group. Therefore, the
DSTBP0#
avoid multiple iterations of length matching computations for each signal.
Design Guide
®
Intel Pentium
for processor package trace lengths. The MCH package trace lengths may be
®
E7501 Chipset Memory Controller Hub (MCH) Datasheet. Alternatively
Equation 4.
= Maximum in Group
MCH PLC
= 1.060 inch - 0.842 inch = 0.218 inch
= Maximum in Group
MCH PLC
= 1.060 inches - 0.738 inch = 0.322 inch
Processor to MCH PCB Length
– DSTBN0#
MCH PLC
= 4.000 – 0.218 + 0.322 = 4.104 inches
Processor to MCH PCB Length
®
M Processor and Intel
High-Speed Design Concerns
MCH Package Length
MCH Package Length
= DSTBN0#
Processor to MCH PCB Length
+ DSTBP0#
MCH PLC
value should be chosen carefully based on routing studies to
®
E7501 Chipset Platform
®
Pentium M Processor
- DSTBN0#
MCH Package Length
- DSTBP0#
MCH Package Length
Equation 7.
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