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Burning Fuses?
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Burning Fuses?

by mikeyp on Thu Jan 31, 2008 4:17 pm

Okay so I'm new to playing with microcontrollers, and I've got one question which is bugging me, and that's what exactly is all this talk about burning fuses? From reading about the minipov3 and if you're building from components not supplied my Limor, you're supposed to "burn" the fuses before you can program the chip, but I can't find any sort of explanation why this is necessary or what exactly it does to the chip? I'd sort of like to know what I'm doing to my chip before I do any permanent damage to it. Can anyone tell me what this is about or at least point me to something that will?
Thanks :)
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by CCarlson on Thu Jan 31, 2008 5:52 pm

Read here.

The rest of the tutorials are good, as well.
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by mikeyp on Thu Jan 31, 2008 8:22 pm

ok cool, I understand. Next question not answered as far as I could see there, once set, can the fuses be changed? Say I wanted to reuse the chip for a different project and needed a different clock speed?
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by dol-sen on Sun Feb 24, 2008 12:19 pm

Actually it was answered there.

from the Introductio:
You only need to set them once, but if you don't do it right, it's a disaster!


and from "What is a fuse"
there are also 3 bytes of permanent storage called the fuses
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by magician13134 on Sun Feb 24, 2008 12:44 pm

Dumb question alert: Why do you need a proper fuse attached to program it? Couldn't you at least reprogram the fuse without having the right fuse?
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by mikeyp on Sun Feb 24, 2008 1:03 pm

dol-sen wrote:Actually it was answered there.

from the Introductio:
You only need to set them once, but if you don't do it right, it's a disaster!


and from "What is a fuse"
there are also 3 bytes of permanent storage called the fuses


Believe it or not I was seeking clarification on this as that could be interpreted several ways. Some people think of permanent storage as that which doesn't lose its information when the batteries die.

What I was not looking for was a "RTFM you idiot" comment by some smart ass thinking he's clever a month after the thread died.

get a life.
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by mikeyp on Sun Feb 24, 2008 1:05 pm

magician13134 wrote:Dumb question alert: Why do you need a proper fuse attached to program it? Couldn't you at least reprogram the fuse without having the right fuse?


What do you mean by a "proper fuse"?
I've never had a fuse on my projects. The fuses are a form internal storage within the chip that can only be set once. They define how the chip will work for a particular project.
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by oPossum on Sun Feb 24, 2008 1:15 pm

magician13134 wrote:Dumb question alert: Why do you need a proper fuse attached to program it? Couldn't you at least reprogram the fuse without having the right fuse?


If reset is disabled or debug wire is enabled, then the chip can not be programmed with a low voltage programmer (LVP) like the tinyusb, DASA or simple parallel programmer. A high voltage programmer (HVP) can still program it because it can supply high voltage on the reset pin to put it in programming mode.

There are a few other fuse settings that can also cause some problems.

The fuses can be programmed many times - they are not OTP (one time programmable).
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by mikeyp on Sun Feb 24, 2008 3:54 pm

oPossum wrote:The fuses can be programmed many times - they are not OTP (one time programmable).


Ah thank you! That's what I wanted to hear! :D
That's good news because I can potentially use the chip for other projects now :)
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by darus67 on Sun Feb 24, 2008 4:59 pm

oPossum wrote:The fuses can be programmed many times - they are not OTP (one time programmable).


Thats one thing that has always bugged me about their choice of terminology.
The term "fuse" implies that they're a one-shot deal, when in reality they are
just non-volatile configuration registers that are set using an external programmer.


mikeyp wrote:Ah thank you! That's what I wanted to hear! :D
That's good news because I can potentially use the chip for other projects now :)


You do have to use some caution. As oPossum mentioned, there are some
fuse settings that can lock you out.
"He's just this guy. You know?"
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by mikeyp on Sun Feb 24, 2008 6:28 pm

darus67 wrote:You do have to use some caution. As oPossum mentioned, there are some
fuse settings that can lock you out.

True, words of wisdom appreciated :) and you do have to be careful of those. What I was getting at was if for example I wanted to take the chip from the minipov and use it with something else that needed an external clock or change the clock speed, then I could.
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by dol-sen on Sun Feb 24, 2008 11:31 pm

What I was not looking for was a "RTFM you idiot" comment by some smart ass thinking he's clever a month after the thread died.


No Where in my post did I "RTFM you idiot". I know you were seeking clarification. From my knowledge of electronics (old & nearly outdated) and the portions I quoted it did very well seem to answer your query. As for the "dead thread", I had not noticed the date, and since this forum seems to be a low volume site, microcontroller noobs like myself will see it also looking for clarification and furthering their knowledge. I was not trying to be a "smart ass".

Thank you oPossum for the great explanation.

I too, think the term fuse is very misleading.
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by adafruit on Mon Feb 25, 2008 3:19 pm

ive updated the page to be a little more clear about what 'permanent' means

yay

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by dol-sen on Thu Feb 28, 2008 10:53 am

Also to complete this thread a little more...

There is also some instructions here about fixing incorrect fuses.
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