Data Sheet

Ethernet Controller I210 —Design Considerations
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12.3 Crystal Support
12.3.1 Crystal Selection Parameters
All crystals used with Intel Ethernet controllers are described as AT-cut, which refers to the angle at
which the unit is sliced with respect to the long axis of the quartz stone. Table 12-19 lists crystals which
have been used successfully in other designs (however, no particular product is recommended):
For information about crystal selection parameters, see Section 11.6.5 and Table 11-15.
12.3.1.1 Vibrational Mode
Crystals in the above-referenced frequency range are available in both fundamental and third overtone.
Unless there is a special need for third overtone, use fundamental mode crystals.
At any given operating frequency, third overtone crystals are thicker and more rugged than
fundamental mode crystals. Third overtone crystals are more suitable for use in military or harsh
industrial environments. Third overtone crystals require a trap circuit (extra capacitor and inductor) in
the load circuitry to suppress fundamental mode oscillation as the circuit powers up. Selecting values
for these components is beyond the scope of this document.
12.3.1.2 Nominal Frequency
Intel Ethernet controllers use a crystal frequency of 25.000 MHz. The 25 MHz input is used to generate
a 125 MHz transmit clock for 100BASE-TX and 1000BASE-TX operation – 10 MHz and 20 MHz transmit
clocks, for 10BASE-T operation.
12.3.1.3 Frequency Tolerance
The frequency tolerance for an Ethernet Platform LAN Connect is dictated by the IEEE 802.3
specification as ±50 parts per million (ppm). This measurement is referenced to a standard
temperature of 25° C. Intel recommends a frequency tolerance of ±30 ppm.
12.3.1.4 Temperature Stability and Environmental Requirements
Temperature stability is a standard measure of how the oscillation frequency varies over the full
operational temperature range (and beyond). Several optional temperature ranges are currently
available, including -40° C to +85° C for industrial environments. Some vendors separate operating
temperatures from temperature stability. Manufacturers may also list temperature stability as 50 ppm
in their data sheets.
Table 12-19. Crystal Manufacturers and Part Numbers
Manufacturer Part No.
KDS America DSX321G
NDK America Inc. 41CD25.0F1303018
TXC Corporation - USA
7A25000165
9C25000008