Data Sheet

Ethernet Controller I210 —Design Considerations
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12.1.3 Other PCIe Signals
The I210 also implements other signals required by the PCIe specification. The I210 signals power
management events to the system using the PE_WAKE_N signal, which operates very similarly to the
familiar PCI PME# signal. Finally, there is a PE_RST_N signal, which serves as the familiar reset
function for the I210.
12.1.4 PCIe Routing
Contact your Intel representative for information regarding the PCIe signal routing.
12.2 Clock Source
All designs require a 25 MHz clock source. The I210 uses the 25 MHz source to generate clocks up to
125 MHz and 1.25 GHz for the PHY circuits. For optimum results with lowest cost, connect a 25 MHz
parallel resonant crystal and appropriate load capacitors at the XTAL1 and XTAL2 leads. The frequency
tolerance of the timing device should be 30 ppm or better. Refer to the Intel® Ethernet Controllers
Timing Device Selection Guide for more information on choosing crystals.
For further information regarding the clock for the I210, refer to the sections about frequency control,
crystals, and oscillators that follow.
12.2.1 Frequency Control Device Design Considerations
This section provides information regarding frequency control devices, including crystals and oscillators,
for use with all Intel Ethernet controllers. Several suitable frequency control devices are available; none
of which present any unusual challenges in selection. The concepts documented herein are applicable to
other data communication circuits, including Platform LAN Connect devices (PHYs).
Intel Ethernet controllers contain amplifiers, which when used with the specific external components,
form the basis for feedback oscillators. These oscillator circuits, which are both economical and reliable,
are described in more detail in Section 12.3.1.
The chosen frequency control device vendor should be consulted early in the design cycle. Crystal and
oscillator manufacturers familiar with networking equipment clock requirements can provide assistance
in selecting an optimum, low-cost solution.
12.2.2 Frequency Control Component Types
Several types of third-party frequency reference components are currently marketed. A discussion of
each follows, listed in preferred order.
12.2.2.1 Quartz Crystal
Quartz crystals are generally considered to be the mainstay of frequency control components due to
their low cost and ease of implementation. They are available from numerous vendors in many package
types and with various specification options.