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Reference Manual
Altera Corporation
Stratix II GX EP2SGX90 Transceiver Signal Integrity Development Board
May 2006
Clocking Circuitry
IC
S
557-03 (U5):
S
p
r
ead
S
pect
ru
m Clock Ge
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ato
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fo
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PCI-Exp
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e
ss
The ICS557-03 is a spread spectrum clock generator supporting PCIe and
Ethernet protocol requirements. The device is used to substantially
reduce electromagnetic interference (EMI) in PC or embedded systems.
The device provides two differential spread spectrum outputs, and is pin-
configured for clock and spread selection. Using phase-locked loop (PLL)
techniques, the device takes a 25 MHz crystal input and produces two
pairs of differential outputs (HCSL) at 25 MHz, 100 MHz, 125 MHz and
200 MHz clock frequencies. The device also provides spread selection of
±0.25
%
, -0.5
%
, -0.75
%
, and no spread.
Table 2–5
lists output clock DIP switch settings.
Table 2–6
lists spread spectrum output selection DIP switch settings.
Table 2–5. Output Clock Setting DIP Switch Pinout (S8)
Switch
25 MHz
100 MHz
125 MHz
200 MHz
SW1
Closed
Open
Closed
Open
SW2
Closed
Closed
Open
Open
Table 2–6. Spread Spectrum Output Selection Setting (S8)
Switch
Center =/-0.25
Down -0.5
Down -0.75
No Spread
SW3
Closed
Open
Closed
Open
SW4
Closed
Closed
Open
Open