127
Peripheral Local Bus
8.2
Topology Layout Guidelines
This section provides the topologies for routing the Address/Data bus for single load, latched single
load and dual load latched topologies. Note that no length matching is required between the AD
lines.
Figure 64.
Peripheral Bus Unlatched Bidirectional Single Load Topology
TL1
Flash
Table 73.
Routing Guideline Bidirectional Single Load
Parameter
Routing Guidelines
Reference Plane
Route over unbroken ground plane or power plane. If
routing over power plane maintain this consistency
throughout the topology.
Breakout
5 mils on 5 mils spacing. Maximum length of breakout
region is 500mils.
Routing
Microstrip or stripline or combination of microstip and
stripline.
Motherboard Impedance (for both microstrip and
stripline)
50 ohms +/- 15%
Add-in card Impedance (for both microstrip and
stripline)
60 ohms +/- 15%
Trace Spacing (center to center)
•
> 12 mils between all AD lines
•
> 20 mils must be maintained from all other
signals or vias.
Trace Length TL1
2.0” to 10.0”
Trace Length to strapping resistors
0.5” to 3.0” from the last device on the bus.
Routing Recommendations
Number of vias for microstrip < 2
Number of vias for stripline < 4
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