Routing Styles And Topology; Figure 2-30. Daisy Chain Routing Example; Figure 2-31. Point-To-Point And Multi-Drop Topology Examples; Figure 2-32. Alternate Multi-Drop Topology Example - VIA Technologies Apollo Pro133A Design Manual

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2.3.3 Routing Styles and Topology

High-speed bus signals are sensitive to transmission line stubs, which can result in ringing on the rising edge caused by the high
impedance of the output buffer in the high state. In order to maintain better signal quality, transmission stubs should be kept under
1.5 inches. Therefore, daisy chain style routing is strongly recommended for these signals. Figure 2-30 below shows an example
of a daisy chain routing.
Topology is the physical connectivity of a net or a group of nets. Basically, there are two types of topologies for a motherboard
layout: point-to-point and multi-drop. An example of these topologies is shown in Figure 2-31.
If daisy chain routing is not allowed in some circumstances, different routings may be considered. An alternative topology is
shown in Figure 2-32. The branch point in this case is somewhere between both ends. It may be near the source or near the loads.
Being close to the load side is best. The separated traces should be equal length.
Preliminary Revision 0.5, November 19, 1999
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Connector

Figure 2-30. Daisy Chain Routing Example

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Point-to-Point

Figure 2-31. Point-to-Point and Multi-Drop Topology Examples

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Somewhere in
the middle

Figure 2-32. Alternate Multi-Drop Topology Example

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Trace Length
Short Stub
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or or
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Multi-Drop
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or or
Connector Connector
Equal Length
40
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Motherboard Design Guidelines