AVR-Chat

AVR-Chat@yahoogroups.com wrote:
> Hi Tim,
> 
> As I understand it, the chip only loads the osccal value for
> it's lowest internal oscillator speed (1MHz usually). You
> have to write a different value to the OSCCAL register for
> running at faster oscillator speeds.
> 
> Also remember that the oscillator cal byte will be wrong if
> your not using the supply voltage your meant to use. (Usually 5V)
> 
> The way ive done this in the past when not using the correct
> voltage is I go into a loop that outputs the osccal value to
> the serial port, I then incriment the osccal value and keep
> outputting it until I can read the value in my terminal
> program. When you can read the values, pick one in the middle
> of the bunch and it will be accurate enough.
> 

Thanks... The 1MHz thing is true for most of the megas but the mega162
seems to be a bit of an oddity in that the RC oscillator is fixed at
8MHz. You can then divide it down to a lower speed if you want using the
CLKPS3..0 bits. 

I am using 5V supply, but according to the graphs in the data sheet, it
should be pretty much dead on over the whole voltage range. Even at 85
degrees C it should be closer than it was for me.

-- 
Tim Mitchell
tim@sabretechnology.co.uk
http://www.sabretechnology.co.uk