Re: [avr-chat] Avrdude fails to connect to my Dragon...

[Preston Wilson]

"Vincent Trouilliez" wrote:

> On Wed, 11 Mar 2009 10:33:09 +1030
> "Daniel O'Connor" <address@hidden> wrote:
> 
>> Try the -B option, although for me it doesn't seem to make a big difference
>> (although I need -B 10 to program a new part due to the fuse settings).
> 
> Arf... it does make a difference here.. it makes it twice as slow with
> a value of 10, makes the communication fail with 0.1, and with 0.15,
> ...

The uC's frequency has to be at least 4x the frequency generated by the bit
clock.  A bit clock of 1 corresponds to 1 micro second, so that gives you
1MHz, and will work with uC's running at 4MHz or faster.

To get the fastest bit clock value that should work, divide 4 by the
frequency of the uC in MHz.  E.g. If the uC is clocked at 16MHz try 0.25 and
for 8MHz try 0.5.

For a bit clock of 0.1 the uC would need a clock at 40MHz or faster, and for
a bit clock of 0.15 it would need a clock at 27MHz (rounded up) or faster.

-Preston