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This question is posted here as a reference question (its actually a follows on from comments in my earlier question "How to expand program memory on an arduino?") -( Edgar Bonet suggested this question and who answered 1 below in the comments there).

I think its a useful question to others new to arduino. I have posted an answer too. But you can of course add your answer too. I dont know everything about arduino- still learning. It does not refer to the version of the Uno that uses a surface mount atmega328-but the version with removable atmega328.

1) If I take out the atmega 328 chip from its socket on the Uno and replace it with using atmega8-16PU instead and I burn a bootloader-does that mean I can use the arduino Uno with the atmega8 like the atmaga328 (but with a subset of the features of the 328)? The atmega8 is of course an older chip than the 328 (and is significantly cheaper) but it still has same pinouts.

2). I am using the 16mhz crystal in my project. So using an Arduino Uno with atmeg8 chip does this mean that the bootloader will set the fuses on the arduino's atmega8 to use the crystal on the arduino Uno pcb? Or does the bootloader set the fuses on the arduino's atmega8 to use its internal oscillator?

3) So hw much memory is left after writing bootlader to atmega8 ?

4) Can I burn the bootloader more than once?

2

1) yes the arduino uno can be used with a blanked at mega8 chip with the NG bootloader burned onto it. You would set the board as NG in the IDE to use the arduino IDE (to upload sketches and so on) with it.

2) A crystal and capacitors is still required -the same values as used for the removed atmega328.

3) The smallest bootloader will leave 7.5kb of program memory left to use on the atmega8.

4) Yes

  • Part 2 of your answer doesn't apply if you edit boards.txt to match whatever oscillator settings you will use. One can use a fuse calculator like at engbedded.com, click to select ATmega8, click to select feature and frequency combination as needed. Edit boards.txt accordingly. – James Waldby - jwpat7 Sep 3 '16 at 22:46
  • @jwpat7 I updated the question- should have mentioned Im using the crystal in the question. And your comment is useful and interesting. – qwerty10 Sep 4 '16 at 2:15

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