Interpolated fine phase shift (IFPS) mode in the MMCM has linear shift behavior independent of the CLKOUT_DIVIDE value, and the phase shift resolution only depends on the VCO frequency. In this mode, the output clocks can be rotated 360° round robin
in linear increments of
.
If the VCO runs at 600 MHz, the phase resolution is approximately (rounded) 30 ps, and at 1.6 GHz is approximately (rounded) 11 ps.
No initial phase shift value can be programmed during configuration. When using fine phase shift, no initial phase shift amount can be set. The phase always starts at zero and can then be dynamically incremented or decremented. The dynamic phase shift is controlled by the PS interface of the MMCME#_ADV. This phase shift mode equally affects all CLKOUT output clocks that are selected for this mode by setting the USE_FINE_PS attribute to TRUE. In interpolated fine phase shift mode, a clock must always be connected to the PSCLK pin of the MMCM. Regardless of the interpolated fine phase shift mode (fixed or dynamic) a clock is in, the clock must always be connected to the PSCLK pin of the MMCM. Each individual CLKOUT counter can independently either select the interpolated phase shift, the previously described static phase shift mode, or none. Fractional divide is not allowed in either fixed or dynamic interpolated fine phase shift mode. Fixed or dynamic phase shifting of the feedback path results in a negative phase shift of all output clocks with respect to CLKIN. The dynamic phase shift interface cannot be used when the phase shift mode is set to fixed.