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Intel
®
820E Chipset
R
Design Guide 51
All RSL signals must satisfy the following equation:
Equation 2. RDRAM RSL Signal Trace Length Calculation
Package dimension + board trace length = Nominal RSL length ± 10 mils
Figure 30. Example of RDRAM Trace Length Matching
MCH
Die
MCH
Die
MCH Package
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L3
L4
L1
L2
L1, L2: Packa
g
e dimensions
L3, L4: Board trace length
L1 + L3 = Nominal RSL length ±10 mils
L2 + L4 = Nominal RSL length ±10 mils
Ball
R
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rdram_tr_len.vsd
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Note: Refer to the Intel
®
820 Chipset Family: 82820 Memory Controller Hub (MCH) Datasheet for the
component package dimensions.
The RDRAM clocks (CTM, CTM#, CFM, and CFM#) must be longer than the RDRAM signals, due to
their increased trace velocity (because they are routed as a differential pair). To calculate the length for
each clock, the following formula should be used:
Equation 3. RDRAM Clock Signal Trace Length Calculation
Clock length = Nominal RSL signal length (package + board) × 1.021
This formula yields clock signals 21 mils/inch longer than the nominal length. The lengthening of the
clock signals to compensate for their trace velocity change only applies to routing between the MCH and
the first RIMM. The clock signal lengths should be matched to the RSL signals between RIMMs. For
more detailed clock routing guidelines, refer to Chapter 4 Clocking.
The high-speed CMOS signals must be length-matched to the RSL signals within 1200 mils (1.2 inches),
as the result of a timing requirement between the CMOS and RSL signals during NAP Exit and PDN
Exit.