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About changing clocks and programming
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About changing clocks and programming

by jdumond3 on Thu Jan 28, 2010 1:57 am

I want to upgrade from an internal clock to an external crystal on an atmeag168. I have a few questions regarding this process.

1.) When I program and burn new fuse settings for the chip for the new external crystal does the crystal have to be in the circuit?
2.) If I were again to switch sources to a different external crystal which one would have to be in circuit when programming the chip? Similarly if I was to switch back to the internal clock would an external clock have to be present during programming?

I guess this can just be generalized as what do I do when changing clocks sources?
jdumond3
 
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Re: About changing clocks and programming

by jgotthardt on Thu Jan 28, 2010 8:34 am

jdumond3 wrote:1.) When I program and burn new fuse settings for the chip for the new external crystal does the crystal have to be in the circuit?


No. To be able to program a device using ISP it must be running from the currently selected clock source. Once programming is complete the device will not function until the newly selected clock source is properly connected.

jdumond3 wrote:2.) If I were again to switch sources to a different external crystal which one would have to be in circuit when programming the chip? Similarly if I was to switch back to the internal clock would an external clock have to be present during programming?


As stated above, the device must be running from the currently selected clock source. Be careful though! An "external clock" and "external crystal oscillator" are different clock sources.
John

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Location: Massachusetts

Please be positive and constructive with your questions and comments.