129
Peripheral Local Bus
Figure 66.
Peripheral Bus Latched Bidirectional Two Load Topology
Table 75.
Routing Guideline Latch Bidirectional Two Loads
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 minimize the layer changes.
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)
16 mils (for microstrip 60 ohms or stripline 50/60
ohms) to 20 mils (for microstrip 50 ohms)
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 TL2, TL3
0.5” to 2.0”
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
Route as daisy-chain only.
Address latches for 16 bit implementations may be in
any of the device locations for ease of routing.
TL1
TL
2
Latch
Flash
TL3
Flash2
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