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Adventurer
Adventurer
248 Views
Registered: ‎10-31-2017

Zynq MMCM with variable input frequency

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I have a use case where I need to vary the input frequency of the PL within a certain range, 60 to 100MHz.

Does the PL accept such a wide range for a given configuration of the MMCM?

Looking at the clock wizard, the VCO is being set to 960MHz (multiplier 12), from an input clock of 80MHz. The data sheet of the part I am using (-1) states FVCO range from 600 to 1200MHz. Am I right to assume MMCM VCO will lock with the aforementioned input frequency fange (60-100MHz)?

 

 

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Scholar drjohnsmith
Scholar
236 Views
Registered: ‎07-09-2009

Re: Zynq MMCM with variable input frequency

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You dont say which part your using, there is a spec in the data sheet for the input range to the MMCM,

Having said that, a clock of 60 to 100 MHz sounds no problem,
and if you keep the same dividers in the MMCM, the on fpga clock will change acordingly,

timing wise, set the constraints to the fastest clock in,

BUT

One thing you need to be careful of is how fast you switch / sweep the input clock,

the MMCM can go out of lock whilst you do that,

which you need to monitor via the outputs of the MMCM, and force a reset ,

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
2 Replies
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Scholar drjohnsmith
Scholar
237 Views
Registered: ‎07-09-2009

Re: Zynq MMCM with variable input frequency

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You dont say which part your using, there is a spec in the data sheet for the input range to the MMCM,

Having said that, a clock of 60 to 100 MHz sounds no problem,
and if you keep the same dividers in the MMCM, the on fpga clock will change acordingly,

timing wise, set the constraints to the fastest clock in,

BUT

One thing you need to be careful of is how fast you switch / sweep the input clock,

the MMCM can go out of lock whilst you do that,

which you need to monitor via the outputs of the MMCM, and force a reset ,

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
Adventurer
Adventurer
192 Views
Registered: ‎10-31-2017

Re: Zynq MMCM with variable input frequency

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Hello @drjohnsmith 

 

Thank you for your comments; I did have the right understanding of the specs. OK about resetting after changing the clocks and also about timing constraints.

 

FWIW the part is XC7Z020-1CLG484I.

 

 

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