Hi all,
I need to generate a 20MHz clock from a 10MHz clock on a V2Pro.
Plan is to use 2 DCMs:
1st DCM: 10MHz into CLKIN Use CLKFX output with default of M = 4 and D = 1 to get 40MHz. I need to leave CLKFB unconnected because CLK0 and CLK2X will be below 24MHz. Also, since I am using CLKFX, I can leave CLKFB open since it is ok for CLKFX clock to be out of phase with the input 10MHz clock.2nd DCM:
40MHz into CLKIN 20MHz out of CLKDV CLKFB gets CLK0.First question - will that work?
Next question:
The input 10MHz clock can be varied by +/- 25 parts per million to give a frequency offset.
So, input period is (1/10e6) +/- 2.5ps.
The +/-2.5 ps seems to be way less than the cycle and period jitter spec of the DCM so I am not worried about that.
The input clock will be held at each offset for 20ms minimum. Also, there is 800us available for the DCMs to adjust to the new input frequency.
I see that the lock time of the DCM is 10ms and I assume this is just at configuration time?
So, am i right in thinking that my DCM cascade will track my freq offset when it is applied? Is there a spec somewhere that states how long it will take to adjust to the new input freq or is it instantaneous since the variance is only +/- 2.5ps?
Thanks for your time guys,
Ken