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Topic: How to enable the External Occillation. (Read 984 times) previous topic - next topic


Hello Guys,
I am confused if, atmega328  run around 100mhz with the external crystal Oscillator. is it possible? if is it possible How to enable the External Oscillation in Arduino Register and used external crystal oscillator ?


Udo Klein

No, according to the datasheet the maximum frequency is 20 MHz. The datasheet also describes the fuse setup required for external oscialltors.
Check out my experiments http://blog.blinkenlight.net


The atmega328 will run up to about 20Mhz with a crystal oscillator, depending on version and voltages.  You need to read the
processor specification for the exact parameters.

It will not run at 100MHz.

The arduino board already uses an external crystal oscillator.  To have a standalone atmega328 with an external oscillator you need
to have a 16Mhz crystal, and 2 22pF capacitors.  Look at the microprocessor part of this forum for more details.

You also need to program the fuse bits correctly - if you have an in-circuit programmer this is easy to do, again in the forums, loading a standard bootloader will set the fuse bits correctly on a brand new processor chip.

If you buy a chip with a bootloader already burnt it will be set for an external crystal oscillator already.


Hi Thanks for quick response.  so is there other way to speed the clock speed of atmega328?


so is there other way to speed the clock speed of atmega328?

Is there some part of no that you don't comprehend?

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