Intel
®
810A3 Chipset Design Guide
3-3
SC242 Processor Design Guidelines
3.2
Determine General Topology and Layout
Figure 3-1
provides segment descriptions and length recommendations for the investigated
topology shown. Segment lengths are defined at the pins of the devices or components. To ensure
processor signal integrity requirements, it is highly recommended that all system bus signal
segments to be referenced to the ground plane for the entire route.
NOTE: 1 - All AGTL+ bus signals should be referenced to the ground plane for the entire route.
3.3
Solution Space
•
AGTL+ signals should be routed with trace lengths within the range specified for L1 from the
processor pin to the chipset.
•
Use an intragroup AGTL+ spacing to line width to dielectric thickness ratio of at least 2:1:1
for microstrip geomety. If
ε
r
= 4.5, this should limit coupling to 3.4%. For example, intragroup
AGTL+ routing could use 10 mil spacing, 5 mil traces, and a 5 mil prepreg between the signal
layer and the plane it references (assuming a 4-layer motherboard design).
•
The trace width is recommended to be 5 mils and not greater than 6 mils.
Table 3-5
contains the trace width:space ratios assumed for this topology. The crosstalk cases
considered in this guideline involve three types: Intragroup AGTL+, Intergroup AGTL+, and
AGTL+ to non-AGTL+. Intragroup AGTL+ crosstalk involves interference between AGTL+
signals within the same group. Intergroup AGTL+ crosstalk involves interference from AGTL+
signals in a particular group to AGTL+ signals in a different group. An example of AGTL+ to non-
AGTL+ crosstalk is when CMOS and AGTL+ signals interfere with each other.
Figure 3-1. Intel
®
Pentium
®
III Uni-Processor Configuration
Table 3-4. Segment Descriptions and Lengths for Figure 3-2
1
Segment
Description
Min length (inches)
Max length (inches)
L1 (100 MHz)
GMCH to SC242
1.50
3.00
L1 (100 MHz only)
GMCH to SC242
1.50
5.00
G M C H
L(1): Z0=60 W ±15%.
1.5" < L1 < 3.0" (100 MHz)
1.5" < L1 < 5.0" (100 MHz only)
Core
Rtt
Vtt
S C 2 4 2
Table 3-5. Trace Width:Space Guidelines
Crosstalk Type
Trace Width:Space Ratios
Intragroup AGTL+ signals (same group AGTL+)
5:10 or 6:12
Intergroup AGTL+ signals (different group AGTL+)
5:15 or 6:18
AGTL+ to non-AGTL+
5:20 or 6:24
Содержание 810A3
Страница 1: ...Intel 810A3 Chipset Platform Design Guide July 2000 Order Number 298186 002...
Страница 11: ...1 Introduction...
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Страница 25: ...2 PGA370 Processor Design Guidelines...
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Страница 41: ...3 SC242 Processor Design Guidelines...
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Страница 51: ...4 Layout and Routing Guidelines...
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