Electronic – arduino – ATSAM3X8E: Custom Arduino Due Design

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I'm currentlry doing a redesign of the Arduino Due board to include some additional features I need. Browsing through the Datasheet of the ATMSAM3X8E atmel chip, I noticed that the 12Mhz Oszillator used for the Arduino Due differs from the descriptions in the datasheet. The Due oszillator has a load cap. of 20pF and they use two 22pF externals caps. The datasheet specifies an allowed crystal capacitance load of 12.5 to 17.5 pF and external caps < 10pF (Datasheet p.1397).

Every schematic I found doing an adaption of the arduino due uses the same setup as the Arduino Due.

I already have a first prototype made where I used the setup from the Due schematic and it seems to work. Now that I discovered this, I'm not sure wether to adapt this and risk that the redesign does not work for some reason or just ignore this…

Does anyone have experience with this or any thoughts?

Thanks

EDIT:
It gets better :-). Apparently the BOM I used for the first prototype was an older one and had even another crystal in it. So the current prototype runs with an 12MHz Oszillator with a load cap. of 10pF together with two 22pF external caps. Apparently this does not cause any (at least obvious) problems. I really do not have any experience regarding those crystals and wonder why those faults obviously dont matter… 🙂

Best Answer

My experience is limited to using rather than designing the "Due compatible" Duet board designed by Think3DPrint3D and RepRapPro using the same microcontroller, it uses 10pF external caps https://github.com/T3P3/Duet/blob/master/Duet0.8.5/Duet0.8.5_Schematic.pdf digging around you could find the crystal capacitance pretty quickly, but as you and the other responder point out, if what you have works (and presuming the vast tranche of Due's work) then all's good.

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