I am planning to build a project, but it's something quite embedded and I have no need for the extra features or bootloader of a standard Arduino. At the same time, I think I want to use the ATmega 328P rather than an ATTiny, which is what I'm familiar with for this.

I'm running into confusion with the boot size bits and I'm not too sure about the clock setup bits either (normally I run an ATTiny with internal clock). I'm fairly sure I bought some 16MHz crystals and capacitors for this sort of thing a while back, but I'm also sure there will be times that the internal crystal will be fine.

Does anyone have a favored fuse config for this?

I am using an external programmer over the six-pin SPI/ISP port (well, the pins that would be the equivalent of that) for a "boarduino." I only care about the power filtering and external clock (in cases where I need the latter). I'm not bothering with auto-reset or UART since, again, I'm using a programmer.

I would appreciate both configs for 16 MHz (most Arduino-like, I believe) and internal clock at 8MHz. Thanks!

Edit: Here are my settings so far: http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega328p&LOW=FF&HIGH=D6&EXTENDED=FF&LOCKBIT=FF. I think that's normal for a "regular" Arduino (minus some stuff I may have messed up in the high fuse) but I'd like to not bother with any bootloader stuff and have my code run right away.

For the internal clock version I have this so far: http://eleccelerator.com/fusecalc/fusecalc.php?chip=atmega328p&LOW=E2&HIGH=D6&EXTENDED=FF&LOCKBIT=FF

  • 1
    The bootloader is entirely optional. If you don't want to use the bootloader then you don't need to install the bootloader, and you don't need to configure the chip to use a bootloader.
    – Majenko
    Jun 11, 2021 at 21:49
  • I think you need to deselect the Boot Reset vector, to disable the bootloader. That's what I do when I don't use a bootloader. Other than that, those fuses look fine to me. Though I'd enable brownout detection, unless you have a very good reason not to. Note that using the internal RC oscillator will give a less accurate clock, which I found only to be an issue when I was using high speed UART. Most of the time it doesn't matter. I like not having to add a crystal and caps to my PCBs.
    – Gerben
    Jun 12, 2021 at 12:24
  • I don't want the chip configured to have a bootloader, even if I don't use one (not quite sure what happens if it is and I don't, either). It's as simple as turning off the boot reset vector? Like eleccelerator.com/fusecalc/… ? Plus you get more pins without an OSC, admittedly it's less of an issue here. I'll set the BOD as needed, that part I do fortunately understand. Any idea if the internal clock is accurate enough to drive Neopixels or not? I like to use a few as indicators. Jun 13, 2021 at 18:29


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