Re: [avrdude-dev] Calibration bytes on ATmega8

[Theodore A. Roth]

On Tue, 17 Jun 2003, Brian Dean wrote:

> On Tue, May 06, 2003 at 05:40:13PM -0300, Francisco T. A. Silva wrote:
>
> > The Atmega8 has 4 calibration bytes. The atttached patch makes it
> > possible for avrdude to read them all.
>
> The data sheet speaks only of a single calibration byte.  If you can
> show where this is documented somewhere in the datasheet or perhaps in
> an errata somewhere, I have no problem adding this to the
> configuration.  However, I don't think it's wise to deviate from the
> documented data sheets too much.  For example, even if this works for
> some parts, since it's not documented in the data sheet Atmel is free
> to change the behaviour at any time, and we probably should not rely
> on it being there.

Actually, it is in the datasheet (at least for the mega8) which I
just pulled off of Atmel's site:

   Calibration Byte

   The ATmega8 stores four different calibration values for the
   internal RC Oscillator. These bytes resides in the signature row
   High Byte of the addresses 0x000, 0x0001, 0x0002, and 0x0003 for 1,
   2, 4, and 8 Mhz respectively. During Reset, the 1 MHz value is
   automatically loaded into the OSCCAL Register. If other frequencies
   are used, the calibration value has to be loaded manually, see
   Oscillator Calibration Register OSCCAL on page 29 for details.

I haven't verified the other data sheets, but I suspect that any
device which can be fused to select more than one internal osc freq
will have a cal byte for each osc freq.

I don't remember the patch in question though so I can't comment on
it's correctness.

Ted Roth