I am working on a home made project,where i am using Atmega2560V-8AU (note the suffix, this part has an 8 MHz maximum clock rate) as my main controller, supplying 3.3V to this chip.

I want this controller to work exactly same as standard Atmega2560-16AU like on Arduino Mega(perhaps at a slower baud rate on account of the slower clock)

Does there already exist a suitable bootloader image and board definition for an ATmega2560 operating from an 8 MHz crystal?

If not, what changes would need to be made to the usual 16 MHz bootloader and boards definition to support 8 MHz operation, both for the bootloader and for correct time functions and serial buad rates in sketches?

  • @Gerben - how do you propose the lower clock speed be handled? If you are suggesting there is already an option for it, mentioning that would be clearer. Jun 9, 2017 at 15:35
  • @Gerben - you seem to be ignoring the whole point of the question - the poster wants to use an atypical chip which cannot operate at the normal clock rate. It either needs a custom bootloader to operate at a usual baud rate, or programming support for a slower baud rate. Your responses so far have been the exact opposite of helpful. Jun 9, 2017 at 15:57
  • In actual fact, the ordinary bootloader will work, but the problem will come when then trying to talk to it - it will be operating at half the expected baud rate due to the 8 MHz vs expected 16 MHz clock, so the usual board definitions won't allow the IDE to talk to it. What the poster needs is a good board definition package for an 8 MHz Arduino Mega. Jun 9, 2017 at 15:58
  • There is a fair amount of coverage here and elsewhere for 8 MHz / 3.3v usage of the ATMega328p - the situation with the 2560 will be similar enough that those solutions could be used as a model for the necessary modifications or workarounds, but of course an ATMega328p board package won't actually work on a 2560. Jun 9, 2017 at 16:05
  • Hello, I am sorry for not providing enough information my task! I am using 8Mhz crystal and the chip runs on 3.3V, I cannot upload bootloaders of Atmega2560-16AU which runs on 16Mhz cystal. Yes! the ordinary boorloaders should work! but i need to change 16Mhz set to 8Mhz set somewhere in some files of ARduino IDE How do i dot that.? and is there any more things i have to do like Fuses etc.? and I am using my Arduino UNO as "Arduino as ISP" programmer in the list, which will have +5V on the SPI lines and I am running my target chip on 3.3V, Does it hurts to my chip.? Thank you Jun 9, 2017 at 16:26

1 Answer 1


I have used megacore bootloaders, and it solved the problem

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