Consequences of using 20Mhz in PIC?

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UroBoros

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In a UPS project I was using PIC in 4 Mhz.

For adding some other functionality I need to drive the pic in 20Mhz.
What are the consequences of driving pic @ 20MHz, if any?

Thank You
 

you'll need to review your code ..
when clock frequency is changed serial communication or timing dependent functions may not work properly ..

Also, remember about fuse bit (XT_OSC -> HS_OSC) ..

rgds,
ianp
 

    UroBoros

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Thanks for the reply.
I have made all those changes - not serial port; many timer interrupt triggering tasks. All those are taken care of now.
My main concern is weather any EMI effects are there. This is a UPS and I don't have to worry about affecting any other devices in the chassis. Will my PIC will be more prone to external interferences because of increased speed? More decoupling needed or any other precautions needed?

Thanks
Regards
 

In my humble opinion there is not much difference, as far as proneness to external interferences is concerned, between MCUs working at 4 and 20MHz speed ..
Just follow common rules and design guides for microcontrollers ..

Quote: “An MCU chip itself presents high immunity to and low generation of EMI since its dimensions are small versus the wave lengths of EMI signals (typically mm versus 10's of cm for EMI signals in the GHz range). So a single chip solution with small loops and short wires reduces noise problems.”

https://www.st.com/stonline/books/pdf/docs/9914.pdf

Rgds,
IanP
 

    UroBoros

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Hi,

The PIC won't be more prone to external EMI because of the increased clock speed.

I don't think that you need additional decoupling or any other measures. If your design works in 4Mhz, it will work also in 20Mhz as long as you make the necessary changes in your code. Going from 4 to 20 is not a huge change.



Regards.
 

    UroBoros

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Operating voltages becomes more critical. That is close to 5 volts. Not down to 2V.
 

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