EP4SE360F35I4 Datasheet, PDF (169/432 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

Chapter 5: Clock Networks and PLLs in Stratix IV Devices
PLLs in Stratix IV Devices
5–53
1 You can repeat dynamic phase-shifting indefinitely. For example, in a design where
the VCO frequency is set to 1000 MHz and the output clock frequency is 100 MHz,
performing 40 dynamic phase shifts (each one yields 125 ps phase shift) results in
shifting the output clock by 180°, which is a phase shift of 5 ns.
The PHASESTEP signal is latched on the negative edge of SCANCLK (a,c) and must remain
asserted for at least two SCANCLK cycles. De-assert PHASESTEP after PHASEDONE goes low.
On the second SCANCLK rising edge (b,d) after PHASESTEP is latched, the values of
PHASEUPDOWN and PHASECOUNTERSELECT are latched and the PLL starts dynamic
phase-shifting for the specified counters and in the indicated direction. PHASEDONE is
de-asserted synchronous to SCANCLK at the second rising edge (b,d) and remains low
until the PLL finishes dynamic phase-shifting. Depending on the VCO and SCANCLK
frequencies, PHASEDONE low time may be greater than or less than one SCANCLK cycle.
You can perform another dynamic phase-shift after the PHASEDONE signal goes from
low to high. Each PHASESTEP pulse enables one phase shift. PHASESTEP pulses must be
at least one SCANCLK cycle apart.
Figure 5–43. Dynamic Phase Shifting Waveform
SCANCLK
PHASESTEP
PHASEUPDOWN
PHASECOUNTERSELECT
PHASEDONE
a
b
c
d
PHASEDONE goes low synchronous with SCANCLK
t _CONFIGPHASE
Depending on the VCO and SCANCLK frequencies, PHASEDONE low time may be greater
than or less than one SCANCLK cycle.
After PHASEDONE goes from low to high, you can perform another dynamic phase shift.
PHASESTEP pulses must be at least one SCANCLK cycle apart.
f For information about the ALTPLL_RECONFIG MegaWizard Plug-In Manager, refer
to the Phase-Locked Loops Reconfiguration (ALTPLL_RECONFIG) Megafunction User
Guide.
September 2012 Altera Corporation
Stratix IV Device Handbook
Volume 1