Overclocking an ATMEGA644P-20PU to 40MHZ, is that possible?

I have seen some people overclock 20MHz Atmel MCUs to 27MHz. I wonder is that possible for the ATMEGA644P-20PU (or any other variation of the ATMEGA644P) to be overclocked to 40MHz?
What could be the maximum clock limit?

Hi,

simple answer:
Read the datasheet.

Any operation beyond the specified values are just "trial and error".

And even if it works once with one device, it doesn´t mean
* that it works tomorrow
* that it works with other temperature
* with modified code
* with onother chip
* and so on....

You will be responsible for any failure.

And if there are hunderd people telling me: it works --> I would never do this for my (industrial) equippment.
..and I hope no other does this with any equippment I use: like: airbag or breaking system in a car, elevator control....

There are already more than enough unreliable devices around, that work most of the time, but fail unexpectedly ... garage opener, kitchen machine, drilling tool .... often by mistreating the devices or because the designer didn´t care about EMC, ESD, heating ....

My personal opinoin: I hate those unreliable devices...They just cause stress.


Klaus

Never overclock if someone else than you will be using the equipment.
The maximum frequency depends heavily on the chip temperature, and it can also be different for different chips.
The max frequency in the data sheet is guaranteed for all chips at the maximum temperature.

The only way to know is to set the chip temperature to the desired maximum and then increase the clock frequency until it fails.
The frequency must be reduced a bit from the found maximum, to have some margin.