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4.0
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).
The 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
The Intel® Ethernet controllers also have bus clock input functionality, however a discussion of
this feature is beyond the scope of this document, and will not be addressed.
The chosen frequency control device vendor should be consulted early in the design cycle. Crystal
and oscillator manufacturers familiar with networking equipment clock requirements may provide
assistance in selecting an optimum, low-cost solution.
4.1
Frequency Control Component Types
Several types of third-party frequency reference components are currently marketed. A discussion
of each follows, listed in preferred order.
4.2
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.
4.3
Fixed Crystal Oscillator
A packaged fixed crystal oscillator is comprised of an inverter, a quartz crystal, and passive
components conveniently packaged together. The device renders a strong, consistent square wave
output. Oscillators used with microprocessors are supplied in many configurations and tolerances.
Crystal oscillators should be restricted to use in special situations, such as shared clocking among
devices or multiple controllers. As clock routing can be difficult to accomplish, it is preferable to
provide a separate crystal for each device.
82563EB/82564EB LAN on Motherboard Design Guide
"Crystal Selection
Parameters".
15
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