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82563EB/82564EB LAN on Motherboard Design Guide
2.1
Kumeran Reference Clock
The 82563EB/82564EB Gigabit Ethernet Platform LAN Connect uses an embedded clock within
the Kumeran differential signals to recover the data. This reference clock may be generated in one
of two ways dependant on the length of the Kumeran interface board traces as shown in
Figure 2. 631xESB/632xESB Clock Source Diagrams
NOTE: Figure also reflects the same behavior in the single port 82564EB device.
If the length of the Kumeran board traces are 15 inches or less, then the 82563EB/82564EB uses its
25 MHz crystal and internal PLL to provide a 62.5 MHz clock to the 631xESB/632xESB. If the
length of the Kumeran board traces are greater than 15 inches, an oscillator needs to be connected
directly to the 631xESB/632xESB in addition to the 25 MHz crystal that is on the 82563EB/
82564EB. In this case, the 82563EB/82564EB does not provide a direct reference clock to the
631xESB/632xESB. The oscillator at the 631xESB/632xESB is necessary due to the signal quality
degradation as the routed distance is increased.
A 25 MHz crystal is required for the 82563EB/82564EB for both cases as seen in
Table 2. Reference Clocks Required
4
82563EB
631xESB/
632xESB
T X
R X
R X
T X
S E R _ C L K _ IN
P H Y _ C L K _ O U T
6 2 .5 M H z o s c illa to r
T X
R X
R X
T X
X 1
2 5 .0 0 0 M H z
Le ng th > 15
in ch es
Kumeran Length
Less than or equal to 15 inches
More than 15 inches
631xESB/
632xESB
T X
R X
S E R _ C L K _ IN
T X
R X
X 2
L e n g th < 1 5
in c h e s
25 MHz Crystal on
the 82563EB/
82564EB
Yes
Yes
Figure
82563EB
R X
T X
P H Y _ C L K _ O U T
R X
T X
X 1
X 2
2 5 .0 0 0 M H z
Table
2.
62.5 MHz Oscillator on
the 631xESB/632xESB
No
Yes
2.
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