how to clear fuse bits in AVR microcontrollers

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#1
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hi
i want to clear the fuse bits in avr micro controllers which are programmed using AVR dragon.
Is it possible to clear the fuse bits using AVR Dragon or AVRISP mk2 toolkit?
please help me.......

thanks,
prabu

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Depends on what fuses are we talking about. HV/Parallel programing mode can clear most of them (messed up clock's, Brownouts etc.) But I'm not sure it can clear write/read protect fuses. But one never knows...

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"clearing" fuse bits would never be a particularly good idea. On many of the AVRs the CKSEL bits are such that if all cleared (set to 0) it selects an external clock source so you end up needing to pump an oscillator into XTAL1 to regain contact with the chip for ISP programming.

But both Dragon and AVRISPmkII will happily program your selected bit patterns to the fuses in ISP mode. (and, like bloddy-orc says) the Dragon also does HVPP which can be usually be used to recover from a "fuse accident" if you screw up the ISP.

Cliff

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i had clear CKDIV8 fuse bit.is it possible to set that fuse on next time while programming the flash?

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prabu wrote:
i had clear CKDIV8 fuse bit.is it possible to set that fuse on next time while programming the flash?

That's going to depend on what hardware and software you are using to program the chip

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i am using AVRstudio4(WINAVR) and AVRdragon or AVRISP mk2
to my chip.

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Well that's actually the perfect combination for fuse programming. The selection of fuses to set/clear in Studio is done in a far more intutitve way than in any other software. If you want CKDIV8 programmed (so AVR runs at 1/8th clock frequency) you tick the box and if you want the fuse bit unprogrammed you untick the box. What could be simpler? There's no restriction on how often you do this (within practical limits!)

Cliff