Altera Stratix II GX EP2SGX90 Transceiver Signal Integrity Development Board - Manual (Page 20)

2–10 Reference Manual Altera Corporation
Stratix II GX EP2SGX90 Transceiver Signal Integrity Development Board May 2006
Clocking Circuitry
ICS557-03 (U5): Spread Spectrum Clock Generator for PCI-Express
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