EP3C80 datasheet(92/348 Pages) ALTERA

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5–32

Chapter 5: Clock Networks and PLLs in the Cyclone III Device Family

PLL Reconfiguration

Cyclone III Device Handbook

December 2011

Altera Corporation

Volume 1

Table 5–10 lists the PLL counter selection based on the corresponding

PHASECOUNTERSELECT

setting.

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 tsu and th 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.

PHASESTEP

Logic high enables dynamic phase shifting.

Logic array or I/O

pins

PLL

reconfiguration

circuit

SCANCLK

Free running clock from core used in

combination with PHASESTEP to enable or

disable dynamic phase shifting. Shared with

SCANCLK

for dynamic reconfiguration.

GCLK or I/O pins

PLL

reconfiguration

circuit

PHASEDONE

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.

PLL reconfiguration

circuit

Logic array or

I/O pins

Table 5–9. Dynamic Phase Shifting Control Signals (Part 2 of 2)

Signal Name

Description

Source

Destination

Table 5–10. Phase Counter Select Mapping

PHASECOUNTERSELECT [2]

[1]

[0]

Selects

All Output Counters

M Counter

C0 Counter

C1 Counter

C2 Counter

C3 Counter

C4 Counter

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