Intel 820E manual Intel 82562ET/82562EM Component Termination

Intel® 820E Chipset

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2.22.4.2.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 also should be kept away from the Ethernet magnetics module, to prevent communication interference. The crystal’s retaining straps (if they exist) should be grounded to prevent possible radiation from the crystal case, and the crystal should lie flat against the PC board to provide better coupling of the electromagnetic fields to the board.

For noise-free and stable operation, place the crystal and associated discretes as close as possible to the Intel 82562ET or Intel 82562EM component, keeping the trace length as short as possible. Do not route any noisy signals in this area.

2.22.4.3.Intel® 82562ET / Intel® 82562EM Component Termination Resistors

The 120 Ω (1%) resistor used to terminate the differential transmit pairs (TDP/TDN) and the 100 Ω (1%) receive differential pairs (RDP/RDN) should be placed as close as possible to the LAN connect component (Intel 82562ET or Intel 82562EM component). The reason is that these resistors terminate the entire impedance seen at the termination source (i.e., Intel 82562ET component), including the wire impedance reflected through the transformer.

Figure 72. Intel® 82562ET/82562EM Component Termination

LAN connect interface

Intel®

82562ET

Magnetics module

RJ45

Place termination resistors as close as possible to Intel 82562ET.

IO_subsys_82562ET-82562EM_term

2.22.4.4.Critical Dimensions

As shown in Figure 73, two dimensions must be considered during layout: distance ‘B’ from the line RJ45 connector to the magnetics module, and distance ‘A’ from the Intel 82562ET or Intel 82562EM component to the magnetics module.

116 Design Guide