4.2.7. Programmable Duty Cycle
The programmable duty cycle feature allows I/O PLLs to generate clock outputs with a variable duty cycle. This feature is only supported by the I/O PLL post-scale counters, C. fPLLs do not support the programmable duty cycle feature and only have fixed 50% duty cycle.
The I/O PLL C counter value determines the precision of the duty cycle. The precision is 50% divided by the post-scale counter value. For example, if the C0 counter is 10, steps of 5% are possible for duty-cycle options from 5% to 90%. If the I/O PLL is in external feedback mode, set the duty cycle for the counter driving the fbin pin to 50%.
The Quartus® Prime Pro Edition software automatically adjusts the VCO frequency according to the required duty cycle that you enter in the IOPLL IP core parameter editor.
Combining the programmable duty cycle with programmable phase shift allows the generation of precise non-overlapping clocks.
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