Clock Reference Lengths; Figure 21. Memory Clock Trace Length Matching Diagram - Intel 852GME Design Manual

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6.3.1.4.

Clock Reference Lengths

The clock reference length for each SO-DIMM clock group is determined by first determining the
longest total clock length required to complete the clock routing. A table of clock package lengths is
provided in Table 19 to assist in this calculation. Once the longest total length is determined for each
clock group, this becomes a lower bound for the associated clock reference length. At this point it is
helpful to have completed a test route of the SDQ/SDQS bus such that final clock reference lengths can
be defined with consideration of the impact on SDQ/SDQS bus routability. Some iteration may be
required.
Once the reference lengths X0 and X1 are defined then the next step is to tune each clock pairs'
motherboard trace segment lengths as required such that the overall length of each clock equals the
associated clock reference length plus or minus the 25 mil tolerance. Again, the reference length for the
two sets of clocks should be offset by the nominal routing length between SO-DIMM connectors.

Figure 21. Memory Clock Trace Length Matching Diagram

C lo c k R e fe re n c e L e n g th X 0
G M C H P a c k a g e
N o te : A ll le n g th s a re m e a s u re d fro m G M C H d ie -p a d to
S O -D IM M 0 c o n n e c to r p a d s .
C lo c k R e fe re n c e L e n g th X 1
G M C H P a c k a g e
N o te : A ll le n g th s a re m e a s u re d fro m G M C H d ie -p a d to
S O -D IM M 1 c o n n e c to r p a d s .
70
G M C H
D ie
G M C H
D ie
® ®
Intel 852GME, Intel 852GMV and Intel
System Memory Design Guidelines (DDR-SDRAM)
S O -D IM M 0
S C K 0
S C K # 0
S C K 0 L e n g th = X 0
S C K 1
S C K # 0 L e n g th = X 0
S C K # 1 S C K 1 L e n g th = X 0
S C K # 1 L e n g th = X 0
S C K 2
S C K 2 L e n g th = X 0
S C K # 2
S C K # 2 L e n g th = X 0
L e n g th = X 0 + /-2 5 m ils
S O -D IM M 0
S C K 3
S C K 3 #
S C K 4
S C K 4 #
S C K 5
S C K # 5
®
852PM Chipset Platforms Design Guide
S O -D IM M 1
S C K 3 L e n g th = X 1
S C K # 3 L e n g th = X 1
S C K 4 L e n g th = X 1
S C K # 4 L e n g th = X 1
S C K 5 L e n g th = X 1
S C K # 5 L e n g th = X 1
L e n g th = X 1 + /-2 5 m ils