Re: [avr-chat] fuse broke my AVRISP?

[Matthew MacClary]

On Wed, Jun 08, 2005 at 12:26:02PM -0400, Christopher X. Candreva wrote:
> > What can
> > I do to fix this problem? I have never used fuses (i've only had a
> > programmer for 2 days!) and I'm not sure what I have done.
> 
> I manage to do the same thing to a mega16 some time ago. I've been told that 
> if you mess up  the osc fuse bits bad enough the only way to recover is with 
> parallel/high voltage programming mode.

    We use a parallel port programmer that is apparentely close enough
to the stk200 to use the "-dprog=stk200" option under uisp.  I haven't
hosed my fuse bits since I started using uisp, but here is how I used
to tell people to fix the problem:

-Matt


    Here is an effective method for fixing AVR boards have had their
fuse bits scrambled:
    Take a good board, and lightly solder a wire between its XTAL2 pin
(pin 23 for the mega128) and the XTAL1 pin (pin 24) on the broken
board.  Then blow the CKOPT fuse bit on the good board.  This makes
the clock output pin on the good board swing from Vcc to ground with
the system clock on the good board.  When you turn both boards on,
you should be able to reset the fuse bits on the broken board.
    It is a good idea to reset the CKOPT bit on the good board when
you are done, to decrease its power consumption.  It might be a good
idea to connect the two boards to a common ground, but I haven't ever
done that.