I have build simple Arduino ISP programmer, which works fine on ATmega 328 chips (when I select Arduino UNO board) and a ton of others (tiny45, tiny2313). But, when I want to program an ATmega8 chip, it writes it succesfuly, but then the chip runs at 1/16 of the desired speed! (for example a delay(1000) in code takes 16 seconds real-life). I have a 16 MHz crystal oscillator with capacitors connected to the chip, so I thought that the problem is not there but... when I remove the crystal, the chip still runs the same, it still takes 16 seconds. So I assume two possibilities:

  1. the crystal is somehow broken, so the chip runs from some internal thing? But I tried multiple crystals, all the same,


  1. I am doing something wrong, but I really don't know what...

Does somebody have an idea what may be wrong or how to test it? Or feel free for more details...Thanks

EDIT: In IDE, I am selecting "Arduino NG or older" and then I select ATmega8 as processor. I am uploading the sketches directly, without bootloader.

  • 1
    This sounds like a problem with the fuse bit configuration - specifically, that you are running with an internal oscillator and with a divider configuration that gives you a 1 MHz clock rate. Nov 22, 2015 at 18:35
  • Second the fuse bits. Try selecting burn bootloader in the arduino menu, as that should set the correct fuses.
    – Gerben
    Nov 22, 2015 at 20:06
  • I checked it, and in boards.txt, my fuses are set to 0xDF (low) and 0xCA, which, according to this (engbedded.com/fusecalc) should set to external crystal. I even tried to change low to 0x4C, which should run it at 8MHz internally, but it had no effect...
    – user72028
    Nov 22, 2015 at 20:10
  • Gerben: Avrdude returns: "efuse" memory type not defined for part "ATmega8"... I dont know what an efuse is...
    – user72028
    Nov 22, 2015 at 20:11

1 Answer 1


Ok, I finally solved it, so I will write it here so somebody may learn from it in the future :) The problem was really in the fuses, thanks Chris Stratton. Most of my chips were bought already modified for working with Arduino. But this ATmega 8 had the factory fuses, which were setting it for working with internal 1MHz oscillator. You can read and your write your fuse settings with avrdude, so I set them to arduino default (lfuse 0xDF, hfuse 0xCA, from boards.txt). Now it works perfectly even without uploading bootloader.

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