Intel 820E Benutzerhandbuch

116  

Design 

Guide 

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. 

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. 

 

IO_subsys_82562ET-82562EM_term

Intel® 
82562ET

 

Magnetics

module

 

RJ45

 

Place termination resistors as

 

close as possible to Intel 82562ET.

 

LAN connect

interface

 

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.