EP3C120F484C7 Datasheet, PDF (92/274 Pages) Altera Corporation – Cyclone III Device Handbook

5–32
Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family
PLL Reconfiguration
Table 5–9. Dynamic Phase Shifting Control Signals (Part 2 of 2)
Signal Name
PHASESTEP
SCANCLK
PHASEDONE
Description
Source
Destination
Logic high enables dynamic phase shifting.
Logic array or I/O
pins
PLL
reconfiguration
circuit
Free running clock from core used in
combination with PHASESTEP to enable or
disable dynamic phase shifting. Shared with
SCANCLK for dynamic reconfiguration.
When asserted, it indicates to core logic that
the phase adjustment is complete and PLL is
ready to act on a possible second adjustment
pulse. Asserts based on internal PLL timing.
Deasserts on rising edge of SCANCLK.
GCLK or I/O pins
PLL reconfiguration
circuit
PLL
reconfiguration
circuit
Logic array or
I/O pins
Table 5–10 lists the PLL counter selection based on the corresponding
PHASECOUNTERSELECT setting.
Table 5–10. Phase Counter Select Mapping
PHASECOUNTERSELECT [2]
[1]
[0]
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
Selects
All Output Counters
M Counter
C0 Counter
C1 Counter
C2 Counter
C3 Counter
C4 Counter
To perform one dynamic phase shift step, you must perform the following
procedures:
1. Set PHASEUPDOWN and PHASECOUNTERSELECT as required.
2. Assert PHASESTEP for at least two SCANCLK cycles. Each PHASESTEP pulse allows one
phase shift.
3. Deassert PHASESTEP after PHASEDONE goes low.
4. Wait for PHASEDONE to go high.
5. Repeat steps 1 through 4 as many times as required to perform multiple phase-
shifts.
PHASEUPDOWN and PHASECOUNTERSELECT signals are synchronous to SCANCLK and must
meet the t_su and t_h requirements with respect to the SCANCLK edges.
1 You can repeat dynamic phase-shifting indefinitely. For example, in a design where
the VCO frequency is set to 1,000 MHz and the output clock frequency is set to
100 MHz, performing 40 dynamic phase shifts (each one yields 125 ps phase shift)
results in shifting the output clock by 180, in other words, a phase shift of 5 ns.
Cyclone III Device Handbook
Volume 1
July 2012 Altera Corporation