82583V Datasheet, PDF (325/374 Pages) Intel Corporation – Intel® 82583V GbE Controller

Design Considerations—82583V GbE Controller
11.1.4
11.2
11.2.1
11.2.2
11.2.2.1
11.2.2.2
PCIe Routing
Contact your Intel representative for information regarding the PCIe signal routing.
Clock Source
All designs require a 25 MHz clock source. The 82583V 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 82583V, refer to the sections about
frequency control, crystals, and oscillators that follow.
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 section 11.3.1.
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.
Frequency Control Component Types
Several types of third-party frequency reference components are currently marketed. A
discussion of each follows, listed in preferred order.
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.
Fixed Crystal Oscillator
A packaged fixed crystal oscillator comprises 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.
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