Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family
5–31
PLL Reconfiguration
Table 5–7. Loop Filter Control of High Frequency Capacitor
LFC[1]
LFC[0]
Setting (Decimal)
0
0
1
0
1
1
0
1
3
Bypassing PLL Counter
Bypassing a PLL counter results in a multiply (M counter) or a divide (N, C0 to C4
counters) factor of one.
Table 5–8 lists the settings for bypassing the counters in Cyclone III device family
PLLs.
Table 5–8. PLL Counter Settings
PLL Scan Chain Bits [0..8] Settings
Description
LSB
MSB
(1)
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
1
PLL counter bypassed
(1)
0
PLL counter not bypassed
Note to Table 5–8:
(1) Bypass bit.
To bypass any of the PLL counters, set the bypass bit to 1. The values on the other bits
are then ignored.
Dynamic Phase Shifting
The dynamic phase shifting feature allows the output phase of individual PLL
outputs to be dynamically adjusted relative to each other and the reference clock
without sending serial data through the scan chain of the corresponding PLL. This
feature simplifies the interface and allows you to quickly adjust tCO delays by
changing output clock phase shift in real time. This is achieved by incrementing or
decrementing the VCO phase-tap selection to a given C counter or to the M counter.
The phase is shifted by 1/8 the VCO frequency at a time. The output clocks are active
during this phase reconfiguration process.
Table 5–9 lists the control signals that are used for dynamic phase shifting.
Table 5–9. Dynamic Phase Shifting Control Signals (Part 1 of 2)
Signal Name
Description
Source
Destination
PLL
reconfiguration
circuit
Counter Select. Three bits decoded to select
either the M or one of the C counters for
phase adjustment. One address map to select
all C counters. This signal is registered in the
Logic array or I/O
pins
PHASECOUNTERSELECT[2:0]
PLL on the rising edge of SCANCLK
.
Selects dynamic phase shift direction; 1= UP,
0 = DOWN. Signal is registered in the PLL on
PLL
reconfiguration
circuit
Logic array or I/O
pins
PHASEUPDOWN
the rising edge of SCANCLK
.
July 2012 Altera Corporation
Cyclone III Device Handbook
Volume 1
ALTERA [ ALTERA CORPORATION ]
