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Topic: Need help understanding 16mhz vs 8mhz settings (Read 762 times) previous topic - next topic

alparent

If I want to use the internal 8 mhz resonator of a chip. Do I need to just change fuses in the board.txt file or do I also need to create a  new blablabla.hex file (bootloader) for that chip?

I trying to learn how to do this so I wont have to bother you guys every time I want to change something. But I'm kinda lost in the fuses and to what  I need to change to make this happen.


westfw

The bootloader .hex file uses the configured speed of the CPU to generate the serial bitrate.  I *think* you could use the existing 16MHz bootloader with an internal oscillator (just by changing the fuses) if you tell boards.txt that your download speed is half of what you'd otherwise expect (57600 instead of 115200)

retrolefty

#2
Mar 04, 2011, 06:12 pm Last Edit: Mar 04, 2011, 06:14 pm by retrolefty Reason: 1
Quote
I *think* you could use the existing 16MHz bootloader with an internal oscillator (just by changing the fuses) if you tell boards.txt that your download speed is half of what you'd otherwise expect (57600 instead of 115200)


That worked for a poster yesterday on his 644p chip when he converted from external 16Mhz @ 5vdc to 8Mhz @ 3.3vdc in a breadboard setup. He just changed two entries in his boards.txt entry for the 644p board:

xxx.upload.speed=xxxxxx was changed to 1/2 the prior entry baud rate
xxx.build.f_cpu=16000000L was changed to xxx.build.f_cpu=8000000L

He didn't have to change any fuses as he was still using an external crystal.

Lefty

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