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Topic: ATmega1280 at 8MHz/3.3v (Read 1 time) previous topic - next topic


I am working on a project where I will be implementing the Ethernet shield over SPI and 2 UART connections. Would there be a problem running this at 8MHz?  How would this be done?  Any help would be appreciated.

Thank you,


Why do you want to run at 8MHz?
The art of getting good answers lies in asking good questions.


Because he wants to power it at 3,3V... It's pretty clear in the first or second page of the datasheet.

The question is, how are you going to change the frequency of the clock? The next has to do with the bootloader. I'm not quite sure how that would affect it... Either you'd need to burn a new bootloader, or upload the code at a different baud rate. But considering the current high speed, it might e tricky to get it done. 

You'll probably have to change the code makefiles to get the SPI and UART frequencies accurate in Arduino. Maybe by adding a different profile for your board.
This... is a hobby.


Yes, bubulindo is correct.  I want to be able to power the microcontroller at 3.3 V.  Has anyone had any experience with this?  The frequency of the clock will be changed by using an 8 MHz crystal.  This will be a standalone application, not an Arduino Mega board.  The bootloader is what I am concerned about.  How will it affect my SPI and UART frequencies, and how difficult is it to change the settings to get this to work correctly.  Processing speed isn't the concern, but the porting of 16 MHz code to 8 MHz code is.  I am in the design stage and need to know quickly if I have to try to make a 5 V power rail, but it would require redesign to do so.  I am avoiding the redesign if possible.  Any suggestions?


Like I said, regarding the user program, it is a matter of changing the Makefile to use the correct clock.

But the bootloader is where I have my doubts also. :\
This... is a hobby.

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