So I have this genuine Arduino 2560 in my hand. Looks like one, quacks like one, and the box was very Arduino'ish 
It does not have a crystal to clock it (or I cant see it on the board). The pictures & description in the hardware section do mention a crystal.
I skimmed a thread (cant find it again) a while ago that claimed the Mega2560 didnt have a crystal and thus timings are a bit uncertain.
Questions:
- Was there a series made without crystals (or is it just me that cant see it - SMD can be tiny?)
- What is the uncertainty in micros() timing if there "only" is a capacitor/resonator?
- I have seen three wods - capacitor, crystal and resonator. In my vocabulary resonator is a small circuit that acts similar to a crystal but not as accurate at the specified frequency. Have I understood resonator correct?
Does it look like this:
The crystal, which is shown in the schematic, is that little metal can to the lower left of the processor. It looks like in this picture the capacitors are integrated into the crystal package. It looks like there are also solder pads for a larger crystal and external loading capacitors if the small integrated units are not available.
The little can just underneath the USB/Serial converter with "SPK6.000Y" written on it (which I take to be 16Mhz) on the standard picture you refer to is what I thought is the crystal.
Attached a closeup of that region on my board. (Yeah a bit shaky, but clear enough for the purpose) As you see it has a much smaller component and a few unused pads in comparison. Is it just a capacitor? It has 6 legs?
Either way, it is not the same as the "advertised pictures" 
But is it significant?
That crystal is the one for the tiny ATmega processor being used as a USB to Serial converter.
Both areas of the circuit board have pads for both large crystals with external capacitors and small crystals with integrated capacitors. Your board just happens to have the small version in both places. The 'official portrait' has a large crystal on the USB interface and a small crystal on the main processor. Either one will work in either or both places.
and small crystals with integrated capacitors.
I strongly suspect the 'small crystals with integrated caps' is really a ceramic resonator with internal caps.
Lefty
retrolefty:
I strongly suspect the 'small crystals with integrated caps' is really a ceramic resonator with internal caps.
You are probably right. I've just never seen a ceramic resonator in a metal can. All the ones I have seen look like fat ceramic disk capacitors with three pins. I guess I never saw a surface mount resonator before.
