46
PCI-X Layout Guidelines
Table 8.
PCI-X Clock Layout Requirements Summary (Sheet 1 of 2)
Parameter
Routing Guidelines
Signal Group
PCI Clock S_CLKO[3:0].
Reference Plane
Route over unbroken ground plane.
Preferred Topology
Stripline
Breakout
5 mils on 5 mils spacing. Maximum length of breakout region is
500mils.
Motherboard Impedance (for both
microstrip and stripline).
50 ohms +/- 15%.
Add-in card Impedance (for both
microstrip and stripline).
57 ohms +/- 15%.
Stripline Trace Spacing: Separation
between two different clock lines, “d”
clock lines.
25 mils edge to edge from any other signal.
Stripline Trace Spacing: Separation
between two segments of the same
clock line (on serpentine layout), “a”
dimension.
25 mils edge to edge from any other signal.
Stripline Trace Spacing: Separation
between clocks and other lines.
50 mils edge to edge from any other signal.
Length Matching Requirements for
Topologies having NO Slot
•
Each of the Clock out (Clk0 - Clk3) should be length matched
to the Feedback Clk (Feedback Clock is that running from
CLKOUT to CLKIN). The length matching should be within 25
mills.
Length Matching Requirements for
Topologies having only Slot
•
Each of the Clock out (Clk0 - Clk3) to the Slots should be
length matched to within 25mils.
•
The Feedback Clk (Feedback Clock is that running from
CLKOUT to CLKIN) should be routed 3.5” longer than the
Clocks running to the Slots. This should be done to a tolerance
of within 25 mills.
Length Matching Requirements for
Topologies having both Slots and
Embedded Devices
•
Each of the Clock out (Clk0 - Clk3) to the Slots (if more than 1
slot) should be length matched to within 25mills.
•
The Clock out to the Embedded Device(s) should be routed
3.5” longer than the Clocks running to the Slots. This should be
done to a tolerance of within 25 mills.
•
The Feedback Clk (Feedback Clock is that running from
CLKOUT to CLKIN) should be routed 3.5” longer than the
Clocks running to the Slots. This should be done to a tolerance
of within 25 mills.
Total Length of 80331 PCI CLKs on a
motherboard (or embedded design).
Less than 14.0” maximum.
Total Length of Clock Line in an
Add-in Card.
2.4” minimum to 2.6” maximum.
Series Termination.
22 ohms 1%
Trace Length from driver to series
termination.
1” maximum.
S_CLKIN Series Termination.
Connect S_CLKIN to one end of a 22 ohm resistor and the other
end connected to S_CLKOUT.
Maximum skew for PCIX.
0.3 ns.
Содержание 80331
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