EP2S90F1020C5 Datasheet, PDF (299/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

PLLs in Stratix II and Stratix II GX Devices
VCO operates within the recommended range of 500 to 1,000 MHz.
You should also set the m and n counters accordingly to keep the
VCO operating frequency in the recommended range.
Figure 1–18 shows an example waveform of the switchover feature when
using the automatic clkloss detection. Here, the inclk0 signal gets
stuck low. After the inclk0 signal is stuck at low for approximately two
clock cycles, the clock sense circuitry drives the clk0_bad signal high.
Also, because the reference clock signal is not toggling, the clk_loss
signal goes low, indicating a switch condition. Then, the switchover state
machine controls the multiplexer through the clksw signal to switch to
the secondary clock.
Altera Corporation
July 2009
1–35
Stratix II Device Handbook, Volume 2