PLLs in Stratix II and Stratix II GX Devices
Clock Source Control For Enhanced PLLs
The clock input multiplexer for enhanced PLLs is shown in Figure 1–43.
This block allows selection of the PLL clock reference from several
different sources. The clock source to an enhanced PLL can come from
any one of four clock input pins CLK[3..0], or from a logic-array clock,
provided the logic array clock is driven by an output from another PLL,
a pin-driven dedicated global or regional clock, or through a clock control
block, provided the clock control block is fed by an output from another
PLL or a pin-driven dedicated global or regional clock. An internally
generated global signal cannot drive the PLL. The clock input pin
connections to the respective enhanced PLLs are shown in Table 1–20
above. The multiplexer select lines are set in the configuration file only.
Once programmed, this block cannot be changed without loading a new
configuration file. The Quartus II software automatically sets the
multiplexer select signals depending on the clock sources that a user
selects in the design.
Figure 1–43. Enhanced PLL Clock Input Multiplex Logic
(1)
4
clk[3..0]
inclk0
core_inclk
To the Clock
Switchover Block
(1)
inclk1
4
Note to Figure 1–43:
(1) The input clock multiplexing is controlled through a configuration file only and
cannot be dynamically controlled in user mode.
Clock Source Control for Fast PLLs
Each center fast PLL has five clock input sources, four from clock input
pins, and one from a logic array signal, provided the logic array signal is
driven by an output from another PLL, a pin-driven dedicated global or
regional clock, or through a clock control block, provided the clock
control block is fed by an output from another PLL or a pin-driven
dedicated global or regional clock. An internally generated global signal
cannot drive the PLL. When using clock input pins as the clock source,
you can perform manual clock switchover among the input clock sources.
Altera Corporation
July 2009
1–73
Stratix II Device Handbook, Volume 2
ALTERA [ ALTERA CORPORATION ]
