Fuses

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What are "Fuses" really? "Flash Fuse bits"?
Like CKSEL I've read about. I understand the meaning of it and
I understand that I need to store some bits somewhere to
tell the AVR things (like clock-source) right from the start, but
I can not find where this information goes in the AVR?

Hope anyone can explain this to me, sorry if it's a stupid question.

WFR: Mikael

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Possible explanation: Once upon a time in a far far away galaxy... oops wrong line, well the old style EPROMS of the last quarter of the last century did store info by basically blowing little fuses inside the chip, which on occasion would regrow causing pain to the users. Then EEPROM and FLASH were invented but the term remained as an understanding that those bits would only be normally set once as if a fuse was blown. Anyone with a better story? :D

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Ah, thanks that helped!

But how are they stored nowadays? In the program or boot flash
somewhere? And where?

WFR: Mikael

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It's really not a stupid question, and answering it is hard. I had a quick look at the mega8 datasheet and didn't find much about how/where the fuse bits are stored.

As the fuse bits can't be accessed in "normal" running mode it seems this never was a problem for anyone. They can only be accessed via ISP and from within the boot loader section at the end of the AVR Flash (for those AVRs which support boot loading). They're definitely not stored in the program Flash space.

Christoph

I tend to post off-topic replies when I've noticed some interesting detail.
Feel free to stop me.

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Fuses are stored somewhere inside the chip, I guess. And, of course, there must be a tiny fuseholder somewhere near the ISP pins, under the plastic. Dissolve the case and you will certainly find it! :-)))) :D

Cats never lie. At least, they do this rarely.