max2009tiny <m...@canor-audio.com> wrote: > 1. when i program and select 4MHz internal RC osc. what OSCAL > constatnt is loaded by reset if Atmel have more constants from > factory?
The AVR hardware only loads the default (i.e., 8 MHz) OSCCAL value itself. It's the responsibility of the developer to maintain the OSCCAL values of the other frequencies outside (e.g. through an EEPROM cell), or somehow perform a run-time calibration (against whatever that could be used as a calibration source, 32 kHz oscillator, external clock of some kind, ...). If you don't want to bother with that, use a more modern AVR: they only have a single (and much better, e.g. regarding the frequency stability vs. Vcc variations) RC oscillator, and thus also only a single OSCCAL value which is loaded automatically. > 2. where in code can change OSCAL and where not You could change it everywhere you want. > 3. exist math function to recalc new OSCAL for a correct freq or > only probing? There is no (guaranteed) mathematical formula for that. > If diference between Tiny Mega ... please write simply about this. I outlined the major difference above: recent AVRs ship with only a single RC oscillator anymore which has been improved. For example, with an ATmega128, it was basically unavoidable to recalibrate the RC oscillator (even the 8 MHz one) if you wanted to use Vcc = 3 V when the calibration value the device ships with has been obtained for Vcc = 5 V. Replacing the ATmega128 by an ATmega1281, there's a good chance you could run an RS-232 communication without recalibrating the RC oscillator even at Vcc = 3 V (but of course, it's not guaranteed it will work). -- cheers, J"org .-.-. --... ...-- -.. . DL8DTL http://www.sax.de/~joerg/ NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-) _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
