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[General] Running microcontroller with higher than max frequency

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Newbie level 4
Jun 20, 2014
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i was wondering what would happen if i ran a microcontroller with a frequency higher than it's max frequency for example running atmega on more than 20 Mhz,
will be a problem in functionality or just will consume more power?
and what is my limitations of the max frequency , bandwidth of hardware circuits or overheating.....?

It certainly will consume more power but most devices run cool at maximum temperature so the slight increase is unlikely to make them die from overheating. The rated speed is normally the maximum the manufacturer is prepared to guarantee correct operation at. If you push them faster you run the risk of them failing to operate properly although permanent damage is unlikely.

Microcontollers are generally graded according to maximum speed achieved during test, for example, ones that pass tests at 20MHz will be graded "20MHZ" but if the same device failed at 20MHz but worked when retested at 10MHz it might be regraded as "10MHz", in reality it may fail at 20MHz but work fine at 19MHz. The situation is slightly different with microcontrollers with internal clock generators where they must of course work at whatever the top speed of the generator is.

to add a little of my experience,

I managed to make an ATmega to overclock up to 24MHz at 5V and it only got warmer...

I also tried to make an ATmega work in 24MHz at 3.3V... it didn't work at all

the same ATmega at 3.3V but with a crystal of 20MHz, for that it seems that it worked ok, but in reality there were some errors while executing a LPM instruction (that is while accessing const data) those errors where very difficult to catch...

the same ATmega at 3.3V but crystal of 16MHz, also didn't have clear errors (at least the stuff with the LPM was gone, but It failed EVERYTIME My code was a little bigger than 64KB (mind you it was the 256K atmega2561) luckily my code was near 59KB so I didn't test more stuff to make that work...

an ATmega8L worked charm at 3.3V up to 12MHz (you see a lot of it in the V-USB and it seems you can make them work up to 16MHz)

to add a little of my experience,

Ok, I feel it's my turn.
I have successfully run MSP430F5438 at 33 MHz although it's supposed to be 25.
(it failed at 34).
However, according to what I have heard, the limitation is due to flash memory. So one
way to increase the frequency might be to run programs in RAM. That could be done
for exemple for burst transfer of a large amount of data (load a snippet to RAM and
run it from RAM. This code has to first increase the frequency, do what it has to, and
then lower the frequency to come back to flash execution).

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