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ze fuses?
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ze fuses?

by eil on Sun Oct 12, 2008 6:54 pm

Hello,

So I'm getting interested in microcontrollers and am doing some reading to further that cause... I keep seeing references to fuses. Near as I can tell, they're 1-bit toggles for low-level chip configuration data (clock speed, etc). But why on earth are they called fuses? Apparently the act of setting them is called "burning the fuses." Burning regular fuses means the fuse is no good afterward, does that mean once you burn a fuse on a microcontroller that you're stuck with those settings for the rest of the chip's life?

Sorry for the noobish question, but teh googles were no help on this one.
eil
 
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Re: ze fuses?

by koolkat on Sun Oct 12, 2008 7:02 pm

You can change fuses of a chip as many times as you want...as long as you can connect to the chip...

It sometimes says youre screwed becuase if you program the wrong fuses you can make it so that the chip is not usable...
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Re: ze fuses?

by The_Don125 on Sun Oct 12, 2008 7:20 pm

I think its because they operate similar to a PLA, they are normally valued at 1, and get set to zero. (if you want to know more about PLAs (Programmable Logic Array), Wikipedia is your friend)

Now, in a fresh PLA, all fuses are are connected. To "program" a PLA, you run a high enough current/voltage through the inputs you want to output a zero to where the internal connections sever "blowing the fuses".
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Re: ze fuses?

by adafruit on Tue Oct 14, 2008 5:14 pm

it used to be a 'permanent' or 'semi-permanent' thing like real glass fuses
but these days its almost always done in flash so you can easily reset them

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Re: ze fuses?

by eil on Tue Oct 14, 2008 7:03 pm

Thanks for the responses, I believe I'm less confused now. :)

***dodges vegetables***
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