The areset signal is the reset or resynchronization input for each PLL. The device input pins or internal logic can drive these input signals.
When areset is driven high, the PLL counters reset, clearing the PLL output and placing the PLL out-of-lock. The VCO is then set back to its nominal setting. When areset is driven low again, the PLL resynchronizes to its input as it re-locks.
You must assert the areset signal every time the PLL loses lock to guarantee the correct phase relationship between the PLL input and output clocks. You can set up the PLL to automatically reset (self-reset) after a loss-of-lock condition using the Intel® Quartus® Prime IP Catalog.
You must include the areset signal if either of the following conditions is true:
- PLL reconfiguration or clock switchover is enabled in the design
- Phase relationships between the PLL input and output clocks must be maintained after a loss-of-lock condition
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