Guidelines For Intel 82562Et / Intel 82562Em Component Placement; Crystals And Oscillators; Intel 82562Et / Intel 82562Em Termination Resistors - Intel 855PM Design Manual

I/O Subsystem
9.9.3.1.

Guidelines for Intel 82562ET / Intel 82562EM Component Placement

Component placement can affect signal quality, emissions, and temperature of a board design. This
section will provide guidelines for component placement.
Careful component placement can:
Decrease potential problems directly related to electromagnetic interference (EMI), which could
cause failure to meet FCC and IEEE test specifications.
Simplify the task of routing traces. To some extent, component orientation will affect the
complexity of trace routing. The overall objective is to minimize turns and crossovers between
traces.
Minimizing the amount of space needed for the Ethernet LAN interface is important because all other
interfaces will compete for physical space on a motherboard near the connector edge. As with most
subsystems, the Ethernet LAN circuits need to be as close as possible to the connector. Thus, it is
imperative that all designs be optimized to fit in a very small space.
9.9.3.2.

Crystals and Oscillators

To minimize the effects of EMI, clock sources should not be placed near I/O ports or board edges.
Radiation from these devices may be coupled onto the I/O ports or out of the system chassis. Crystals
should also be kept away from the ethernet magnetics module to prevent interference of communication.
The retaining straps of the crystal (if they should exist) should be grounded to prevent the possibility
radiation from the crystal case and the crystal should lay flat against the PC board to provide better
coupling of the electromagnetic fields to the board.
For a noise free and stable operation, place the crystal and associated discrete components as close as
possible to the Intel 82562ET/EM, keeping the trace length as short as possible and do not route any
noisy signals in this area.
9.9.3.3.

Intel 82562ET / Intel 82562EM Termination Resistors

The 100
± 1% receive differential pairs (RDP/RDN) should be placed as close to the Platform LAN connect
component (Intel 82562ET or Intel 82562EM) as possible. This is due to the fact these resistors are
terminating the entire impedance that is seen at the termination source (i.e. Intel 82562ET), including the
wire impedance reflected through the transformer.
216
± 1% resistor used to terminate the differential transmit pairs (TDP/TDN) and the 121
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Intel 855PM Chipset Platform Design Guide
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