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82562EZ(EX)/82547GI(EI) Dual Footprint Design Guide
A.3
Indirect Probing Method
The indirect probing test method is applicable foremost devices that support 100BASE-T. Since
probe capacitance can load the reference crystal and affect the measured frequency, the preferred
method is to use the indirect probing test method when possible.
Almost all Intel LAN silicon that support 1000BASE-T Ethernet can provide a buffered 125 MHz
clock, which can be used for indirect probing of the transmitter reference clock. The buffered 125
MHz clock will be a 5X multiple of the crystal circuit's reference frequency
Different LAN devices may require different register settings, to enable the buffered 125 MHz
reference frequency. Please obtain the settings or instructions that are appropriate for the LAN
controller you are using.
LAN Silicon IEEE Test Out +
2-pin
header
LAN Silicon IEEE Test Out -
Figure 11. Indirect Probing Setup
52
P6246 or similar
high impedance
probe
with less than 1 pF
50 ohm Coaxial
Cable
(Figure
11).
input
Ch.1
input
Ch.2
Power Supply
50 ohm
125.00047
input
Tektronix CMC251
or a similar capability
Frequency Counter
Tektronix
1103
Probe
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