Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family
5–11
Clock Feedback Modes
Figure 5–7 shows the external clock outputs for PLLs.
Figure 5–7. External Clock Outputs for PLLs
C0
C1
C2
C3
C4
PLL #
clkena 0 (1)
clkena 1 (1)
PLL #_CLKOUTp (2)
PLL #_CLKOUTn (2)
Notes to Figure 5–7:
(1) These external clock enable signals are available only when using the ALTCLKCTRL megafunction.
(2) PLL#_CLKOUTpand PLL#_CLKOUTnpins are dual-purpose I/O pins that you can use as one single-ended or one
differential clock output.
Each pin of a differential output pair is 180° out of phase. The Quartus II software
places the NOT gate in your design into the I/O element to implement 180° phase
with respect to the other pin in the pair. The clock output pin pairs support the same
I/O standards as standard output pins (in the top and bottom banks) as well as LVDS,
LVPECL, differential HSTL, and differential SSTL.
f
To determine which I/O standards are supported by the PLL clock input and output
pins, refer to the I/O Features in the Cyclone III Device Family chapter.
Cyclone III device family PLLs can drive out to any regular I/O pin through the
GCLK. You can also use the external clock output pins as general purpose I/O pins if
external PLL clocking is not required.
Clock Feedback Modes
Cyclone III device family PLLs support up to four different clock feedback modes.
Each mode allows clock multiplication and division, phase shifting, and
programmable duty cycle.
December 2011 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
