EP4SE360F35I4 Datasheet, PDF (150/432 Pages) Altera Corporation – This section provides a complete overview of all features relating to the Stratix IV device family, which is the most architecturlly advanced

5–34
Chapter 5: Clock Networks and PLLs in Stratix IV Devices
PLLs in Stratix IV Devices
Each PLL has one pre-scale counter, n, and one multiply counter, m, with a range of
1 to 512 for both m and n. The n counter does not use duty-cycle control because the
only purpose of this counter is to calculate frequency division. There are seven generic
post-scale counters per left or right PLL and ten post-scale counters per top or bottom
PLL that can feed the GCLKs, RCLKs, or external clock outputs. These post-scale
counters range from 1 to 512 with a 50% duty cycle setting. The high- and low-count
values for each counter range from 1 to 256. The sum of the high- and low-count
values chosen for a design selects the divide value for a given counter.
The Quartus II software automatically chooses the appropriate scaling factors
according to the input frequency, multiplication, and division values entered into the
ALTPLL megafunction.
Post-Scale Counter Cascading
Stratix IV PLLs support post-scale counter cascading to create counters larger than
512. This is automatically implemented in the Quartus II software by feeding the
output of one C counter into the input of the next C counter, as shown in Figure 5–30.
Figure 5–30. Counter Cascading
VCO Output
C0
VCO Output
VCO Output
VCO Output
VCO Output
VCO Output
Note to Figure 5–30:
(1) N = 6 or N = 9
C1
C2
C3
C4
Cn
(1)
from preceding
post-scale counter
When cascading post-scale counters to implement a larger division of the
high-frequency VCO clock, the cascaded counters behave as one counter with the
product of the individual counter settings. For example, if C0 = 40 and C1 = 20, the
cascaded value is C0 × C1 = 800.
1 Post-scale counter cascading is set in the configuration file. You cannot set this using
PLL reconfiguration.
Stratix IV Device Handbook
Volume 1
September 2012 Altera Corporation