[quote:011054f799="kos19"]I would like tu use external oscilator.
Until now I used only internal oscilators.
Which fuse bit I have to set?[/quote:011054f799]
One should notice the difference between [b:011054f799]oscillator[/b:011054f799] and [b:011054f799]crystal/resonator[/b:011054f799].
In Atmel nomenclature internal clock is provided either by an internal oscillator, an external oscillator, or a crystal/resonator.
The internal oscillator is build up by an [b:011054f799]r[/b:011054f799]esistor/[b:011054f799]c[/b:011054f799]apacitor combination, that's why it's called RC-oscillator.
An external oscillator in contrary is a self-contained part, which provides a clock signal, as soon supplied with power. The clock signal is then fed into CLKI of the µC.
In case fuses are set to external oscillator, but a crystal is connected, the bug will play dead.
Alternatively any other suitable signal from a clock-source can be used for the setting "external oscillator".
A crystal or resonator needs two connections to the µC, as it is powered by a circuitry within the µC, fuse settings have to be to crystal/resonator and not oscillator.
The difference between crystal and resonator is, the latter is cheaper, sometimes smaller and always less precise.
That said - if Mark would not have guessed what you actually want, the µC would have been already a (at least temporarily) dead bug.
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