[SOLVED] ppm requirement for PIC microcontrollers

[embeddedlover]

I was going through datasheet of pic micro-controller (PIC32MX795F512L) ans was wondering what the requirement of ppm for main clock (main clock i meant because there is also RTC crystal) was?? :bang:

I have gone through few pic micro datasheets and found that none of them mention the ppm requirement for external crystal.

Does anyone based on your exposure have idea about the requirement of external crystal ppm for pic micros?

 

[FvM]

Crystal tolerance is up to your application requirements.

 

[D.A.(Tony)Stewart]

• for >1kpc orders typ.
• Unsorted crystals 100ppm 0.10$
• Watch crystals may be room~body temp only .. 0.25$

​https://www.digikey.com/product-search/en/crystals-and-oscillators/crystals/852333?k=Crystal

 

[embeddedlover]

Crystal tolerance is up to your application requirements.

That is fair, agree with your application requirement view... have seen processors/uCs vendors suggesting a required ppm rating for their respective clocking scheme irrespective of application but still i don't see it specified with pic micro controllers.. ppm always give me a data of how much clock deviation is allowed for that processor/uC over a period of time, which is very relevant... and if i want to use the pic controller at higher temperatures i want to know what max. deviation is allowed w.r.t crystal? so, if the requirement of ppm is high it helps me choose crystal of lower cost/loose constraints.

To put it in other way, if my main clock is 24 MHz and i want to know up to what frequency {24 MHz ± x Hz} my controller will work stable. Now my choice is like have a low ppm crystal as specification is not mentioned.

 

[chuckey]

If your controller has no critical timers, then ANY old tolerance would do. If its just running timers for heating , for instance, then +-1% would do. If you are running a real time clock, to time tag data, then you have to consider how far you can allow your clock to get out of step with real time, and more to the point how you can re time it (reset the time). The electric clocks you see on the wall cannot be relied upon to be with 30 seconds of the true time, as the mains frequency runs slow during the day and fast at night JUST to get the clocks correct. But the overall accuracy over a year would be spot on, unlike a crystal in a CPU which will drift continuously.
Frank

 

[Tunelabguy]

To put it in other way, if my main clock is 24 MHz and i want to know up to what frequency {24 MHz ± x Hz} my controller will work stable. Now my choice is like have a low ppm crystal as specification is not mentioned.

Any crystal or ceramic resonator will have more than enough frequency stability to work with a PIC. The PIC microcontrollers can be clocked all the way down to DC and all the way up to the maximum frequency allowed for that particular PIC and supply voltage combination.