Moteino: 16MHz @ 3.3V? Why???

[Tommi76]

Hello all there,

why is the Moteino used with 16 MHz at 3.3V?
This is outside of the specification from Atmel.
At 3.3V the maximum clock frequency is 10 MHz.

Is this going good for long time?
Or is there any special reason for doing that?

All other Arduinos with 3.3V, have a clock frequency of 8 MHz.

Thanks!
Thomas

[luisr320]

Looking at the datasheet, there is no clear answer to your question.
Check this graph from the datasheet:

[TomWS]

Looking at the datasheet, there is no clear answer to your question.
<snip>

It's a valid question.  Given the table, it's fairly easy to interpolate that 13.3333MHz should be the Safe Operating Frequency at 3.3V.  Conversely, 3.78V is the required voltage to operate at 16MHz.

Has anyone done a sufficiently exhaustive test to prove that 16MHz @ 3.3V is 100% reliable?   Clearly it works, otherwise Felix would be flooded with returns, but does it ALWAYS work? 
I suspect that the datasheet covers +/-3 sigma over the complete temperature range, which I doubt that very many of us operate over this complete range.

Tom

[Felix]

I can claim I've extensively tested it at extreme temps with no problems. So the question is not "why" but "why not".

[TomWS]

I can claim I've extensively tested it at extreme temps with no problems. So the question is not "why" but "why not".

Both ends of the temperature range?  And you verified that VDD=3.3V?

Also, I don't think "Why" or "Why not" are the right questions.  "Should" might be more appropriate. ISTM that there must be a corresponding reliability goal before one could answer the question.

Tom

[Felix]

I know it sounds like a back of the envelope answer but I think I've discussed this topic so many times I really don't feel like bothering.
And yes I've had nodes sit for months in extremes of temperature. Not a glitch. So why bother splitting hairs again?

[TomWS]

I know it sounds like a back of the envelope answer but I think I've discussed this topic so many times I really don't feel like bothering.
And yes I've had nodes sit for months in extremes of temperature. Not a glitch. So why bother splitting hairs again?

That which is not documented will oft be repeated...

Someone famous once said that.  But I don't remember who.   

Tom

[Felix]

I wanted to add that if someone is worried about the [email protected] they can set the fuses for the internal 8mhz or do it in firmware, so not really an issue.

Others have standardized 16mhz @ 3.3v and had it widely tested by a large user base as well  (just think jeenodes).

If Moteino would be 8mhz then the question would be "why 8mhz and not 16mhz???"