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running pic18f46k22 at 20 mhz pll x4

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garg29

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Hi,

I'm running a project on PIC18F46k22 with 20Mhz Quartz crystal, In configuration I have selected :
1. HS Oscillator (high power > 16Mhz)
2. Oscillator 4X PLL Enable - Oscillator multiplied by 4

Is now the system running at 20 x 4 = 80Mhz or is it at its maximum frequency 64 MHz (as described in datasheet)

I'm bit confused please reply me.

regards.
 

You cannot run it with the 4x PLL with a 20MHz clock. The maximum internal clock allowed is 64MHz.

Keith
 
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    garg29

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thanks keith for replying. As i said I know that the maximum allowed frequency is 64MHz but when I'm putting 20Mhz with 4x PLL the system is running very fast , I just want to know is it at 64Mhz or any other arbitrary frequency. (actually I'm not having 16Mhz xtal and my supplier also doesn't have the same).

Thanks

Regards.
 

It will be trying to run at 80MHz and probably will manage it under certain conditions. However, it will be unreliable. Unless you need high accuracy from the clock you could use the internal 16MHz clock & the 4x PLL to get 64MHz. Otherwise you need to find a 16MHz crystal or external clock module.

Keith.
 
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Thanks once again for replying.

Regards
 
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