Re: [avr-chat] Urgent clock-related questions

[Rick Mann]

On Apr 8, 2013, at 20:18 , Graham Davies <address@hidden> wrote:

> Yes, this will be fine.  The following is for information only and I'm not 
> suggesting you deviate from your plan, but you can meet your goals with no 
> crystal at all.  Synchronize the 32 MHz oscillator to the USB start-of-frame 
> and run it at 48 MHz to drive the USB sub-system.  Then, synchronize the 2 
> MHz oscillator to the 32.768 kHz internal oscillator and use the PLL to 
> multiply by 16 to get a 32 MHz CPU and peripheral clock.  This will be 
> accurate enough for UARTs because the 32.768 kHz internal oscillator is 
> factory calibrated and is fairly stable with temperature and voltage. Again, 
> this is just so that you know that this is possible (I have done exactly 
> this) but I'm not suggesting you do it.  Your plan with the external crystal 
> is fine, probably better.

Hahahaha, that's a lot of work! But clever, assuming you have actual USB 
traffic. For me USB is an infrequent use. But good to know something like that 
can be done.

Might even be better, if the USB device you're talking to is off a bit.

-- 
Rick