ATmega1284 running on 16MHz @ 3.3v outside safe operation

[leonahi]

Hello,

Please correct me if I am wrong.
MoteinoMEGA has 16MHz crystal and it runs on 3.3v using on board regulator (MCP1703), but according to ATmega1284p datasheet, the allowed safe voltage for proper functioning should be more than 3.3v. Perhaps 8MHz @ 3.3v should be a correct combination.

Thank you

[Felix]

Correct. It's "out of spec" but it works without any problem, never saw an issue because of this.
Discussed many times in the forum, please do a basic search for the details, and also search before repeating a question, thank you.

[leonahi]

Thanks for the answer and sorry for repeating this question

[oric_dan]

Sorry that I'm a little late to the party, not been around here for a while....

I've been running mega328 and 1284 chips at Vcc=3.3V, and with 16-MHz xtal for 5-years now, and never had a problem, although I do not operate at temperature extremes. OTOH, I just installed a Moteino-Mega inside my van to use in an alarm system (see related post to appear hereabouts), so I will see whether any problems creep in this winter, at temperatures below 20-degF.

With respect to the d/s, if you look very closely, you'll see that the curve crosses near 13-MHz oscillator frequency for Vcc=3.3V, and is well above 8-MHz. So, all in all, 13-MHz is only 20% distance from 16-MHz, and not 2X as most people round it to be. I should expect that a 20% tolerance is nowheres near a problem.

[Felix]

I think everyone that was worried and tried it, or cared to investigate, had the same experience.
All Moteinos are completely safe at 3.3V/16Mhz, never saw a problem in my own many-year-in-use motes, nor heard of issues of the many thousands of boards sold to customers. Never a return with a MCU frequency problem. They just work without a hitch.