I tend to agree with David. While it should work and I've personally never had a problem, the spec does allow for it to drift far enough to start causing issues. You could use a resonator instead of a crystal to improve the accuracy of your clock while saving cost and area. It's somewhat in the middle of the other two options.
On Thu, Mar 14, 2013 at 2:29 PM, David Kelly <[email protected]> wrote: > > On Mar 14, 2013, at 12:04 PM, Rick Mann <[email protected]> wrote: > > > I see that the 32.768 kHz crystal on the dev boards could be used to > automatically calibrate the 32MHz internal clock, although I'm not sure if > they're actually doing that. > > > > I'm laying out a board now, need to know if I should include the crystal > or not. > > Will it kill you to have to make room for the crystal? You don't have to > load it if you don't need it. Plus I find Murphy's Law has a heavy hand in > such things, you can make space for a crystal which you will not need, or > don't and it will almost be certain the onboard RC oscillator is not > accurate enough. > > I brought my first Xmega up on an XPlain board. Wanted a 2.500 MHz SPI > clock so I programmed the oscillator chains for 30.0 MHz as 15 times 2.000 > MHz supposedly corrected using 32 kHz crystal reference. The result was > closer to 31 MHz but close enough to 30 that other things were more > important to make work before doting i's and crossing t's. Since, Atmel has > updated their libraries. I need to drill through the changes to see if the > clock error was theirs or mine. > > Before my PCB is finished I may simply drop a manufactured oscillator on > the board. Brute force. Hit it over the head with a sledgehammer. Its not > worth the extra NRE. > > -- > David Kelly N4HHE, [email protected] > ============================================================ > Whom computers would destroy, they must first drive mad. > > > > > _______________________________________________ > AVR-chat mailing list > [email protected] > https://lists.nongnu.org/mailman/listinfo/avr-chat >
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