Crosstalk Consideration; Impedances; Line Termination; Terminating Unused Lan Connect Interface Signals - Intel 855GM Design Manual

R

Figure 114. LAN_CLK Routing Example

11.9.2.3.

Crosstalk Consideration

Noise due to crosstalk must be carefully controlled to a minimum. Crosstalk is the key cause of timing
skews and is the largest part of the t
mismatch between LAN_CLK and the LAN data signals. To meet this requirement on the board, the
length of each data trace is either equal to or up to 0.5 inches shorter than the LAN_CLK trace.
Maintaining at least 100 mils of spacing should minimize noise due to crosstalk from non-PLC signals.
11.9.2.4.

Impedances

The motherboard impedances should be controlled to minimize the impact of any mismatch between the
motherboard. An impedance of 55 Ω ± 15% is strongly recommended; otherwise, signal integrity
requirements may be violated.
11.9.2.5.

Line Termination

Line termination mechanisms are not specified for the LAN Connect Interface. Slew rate controlled
output buffers achieve acceptable signal integrity by controlling signal reflection, over/undershoot, and
ringback. A 0-Ω to 33-Ω series resistor can be installed at the driver side of the interface should the
developer have concerns about over/undershoot. Note that the receiver must allow for any drive
strength and board impedance characteristic within the specified ranges.
11.9.2.6.

Terminating Unused LAN Connect Interface Signals

The LAN Connect Interface on the ICH4-M can be left as a no-connect if it is not used.
11.9.3.

Intel 82562ET / Intel 82562 EM Guidelines

For correct LAN performance, designers must follow the general guidelines outlined in Section 11.9.6.
Additional guidelines for implementing an Intel 82562ET or Intel 82562EM Platform LAN Connect
component are provided below.
®
Intel 855GM/855GME Chipset Platform Design Guide
skew parameter. t
RMATCH RMATCH
I/O Subsystem
LAN_CLK LAN_CLK LAN_CLK
LAN_RXD0 LAN_RXD0 LAN_RXD0
is the sum of the trace length
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