Hello,
I try to finely tune a frequency with using the CDCE6214. For this I wanted to use the Fractional Divider, and play with the Numerator.
I got it worked, with 25MHz input generating 24.576MHz output +/- 500ppm.
However it seems that it's not possible to get the PLL automatically follow the newly programmed fraction without resetting the PLL with the R0.SWRST bit. In this case the PLL recalibrates and unlocks and the output is broken.
=> Q1. Is it possible to force the PLL to re-read the Numerator register without reset ?
So I tried the DCO, with programmed increment or decrement value and pulsing . It works but there are major lacks which make it unsafe :
- it seems that the Numerator Register does not reflect the actual numerator value, so we don't know what is actually programmed (what is the total increment).
=> Q2. Is it possible to know the actual numerator value (or DCO delta) after DCO increment/decrement was used ?
- Numerator increment / decrement is not limited. I thought it would wrap around after 2^24, but you can pull it very far beyond 100%, so far that the PLL goes out of operational range, and unlocks.
- Resetting the PLL with the R0.SWRST bit does not reset the DCO increment, so it's out of control. Also tried to disable DCO but the DCO value is still active.
=> Q3. Is it possible to reset the DCO ?
Thank you,
Eric Heurtel - SOUND4
