PIC32MK clock speed and requirement for guard trace

[perdrix]

The data sheet for the PIC32MK series (page 608) says the external crystal or clock frequency can be up to 64MHz.

I realise that there's a PLL internally so I can feed it with 8MHz, 12MHz, or pretty much any multiple of 4MHz.   What's the general wisdom on choosing the frequency?

The data sheet for the PIC32MK (figure 2.3 on page 31) strongly suggests the use of a guard trace that passes between pads of the 0.5mm pitch QFN or TQFP64 footprint when a crystal is being used  which rather requires 3 mil track and clearance rules.   Is this also a requirement when an external clock source is being used as below:



Thanks
David

[perdrix]

Any other comments on best choice of external clock speed - I'm leaning towards 12MHz but have not got a strong basis for that choice ...

D.

[free_electron]

running traces between 0.5mm pitch tqfp ? don't go there.
you are using an active oscillator so no need for guard traces. it drives hard enough.

if you use a crystal the reason for the guard is to shield the input pin from external factors. the guard needs to be tied to the oscillator OUTPUT. you need ot check the datasheet to see which of the two it is.