User's Manual

Layout/Routing Guidelines
2-46 Intel
®
820 Chipset Design Guide
2.9 System Bus Design
2.9.1 100/133 MHz System Bus
First, determine the approximate location of the processor and the chip set on the base board. An
example topology is shown in Figure 2-36. This example “star” topology is valid for 133 MHz and
100 MHz 2-way processor/Intel
®
820 chipset designs. The 82820 MCH should be placed
electrically in the center of the bus. The SC242 connectors should be placed on either end of the
bus to allow the processors to terminate each end.
Table 2-12 below provides segment descriptions and length recommendations for the investigated
topology shown in Figure 2-36. Segment lengths are defined at the pins of the devices or
components. For 2-way processor / Intel
®
820 chipset designs, a termination card must be placed
in the unused slot when only one processor is populated. This is necessary to ensure signal integrity
requirements are met.
Figure 2-37 shows the topology and trace lengths required for single processor designs.
Figure 2-36. Intel
®
Pentium
®
III Processor Dual Processor Configuration
Table 2-12. Segment Descriptions and Lengths for Figure 2-36
Segment Description
Min length
(inches)
Max length
(inches)
L1 SC242 connector to Centerpoint 1.5 3.0
L2 SC242 connector to Centerpoint 1.5 3.0
L3 Chip set breakout stub 0.0 1.5
L1+L3 or L2+L3 SC242 distance from MCH 2.0 4.5
L1 + L2 SC242 spacing 5.5
L1
L(1,2,3): Z
0
= 60
Ω
± 15%
MCH
Processor Processor
L2
L3
Figure 2-37. Intel
®
Pentium
®
III Processor Uni-Processor Configuration
L1 Min = 1.75"
L1 Max = 4.5"
L(1): Z
0
= 60
Ω
± 15%
MCH Processor