120
Hardware Design Guide
IXP28XX Network Processor
PCI
6.2.3
cPCI Bus Interface
The compact PCI (cPCI) interface can be a 32- or 64-bit bus, which can operate at either 33 or 66
MHz. When the base card is not connected to a host, V
IO
for this bus comes from the base card 3.3
V power supply. When there is a host present, resistor R2401 and R2305 need to be removed and
V
IO
is provided by the host.
6.2.3.1
cPCI Signals
Figure 70
illustrates the topology for the cPCI signal.
Table 45
provides routing guidelines for the cPCI signal group parameters.
Figure 70.
cPCI Signal Topology
B0520-01
Intel
®
21555
PCI-to-PCI
Bridge
CPCI Host
Connector
B
A
R
S
Table 45.
cPCI Signal Group Guidelines
Parameter
Routing Guidelines
Signal Group
cPCI Signals
Topology
Point-to-Point
Reference Plane
Dual-referenced, PWR–SIG–GND
Characteristic Trace Impedance
60
Ω
± 10%
Nominal Trace Width
3.5 mils
Nominal Trace Separation
9 mils
Spacing to Other Groups
20 mils
Trace Length A
Maximum = 1200 mils
Trace Length B
Maximum = 500 mils
Resistor R
S
10
Ω
± 10%
Maximum Via Count per Signal
3 vias
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