Is there a reason to use an external 32Mhz crytal for Xmega?

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I have some 32 MHz Crystal. But since the Xmega itself can generate 32Mhz signal. Is there really a need to use an external 32MHz Crystal(Is it better in acurracy? Power consumption?)

Using PLL i can generate all sort of frequency, right? So besides those special one like a RTC, is there a reason to buy external crytal even for Xmega chips?

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More accuracy is the obvious answer.

The xmega internal oscillator is quite a bit better than the previous generation so they are accurate enough for UARTs mostly.

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Quote:
The 0.4 - 16 MHz Crystal Oscillator is a driver intended for driving both external resonators and
crystals ranging from 400 kHz to 16 MHz.

(from XMEGA A Datasheet Preliminary - Section 10.3.4)

In other words, you actually can't use a 32MHz external crystal oscillator with the XMEGA (16MHz is the maximum).

Nick

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dmginc wrote:
Quote:
The 0.4 - 16 MHz Crystal Oscillator is a driver intended for driving both external resonators and
crystals ranging from 400 kHz to 16 MHz.

(from XMEGA A Datasheet Preliminary - Section 10.3.4)

In other words, you actually can't use a 32MHz external crystal oscillator with the XMEGA (16MHz is the maximum).

Nick

Wait....so i can't use a 32MHz external crystal?

So the only thing that an external crystal is good at is to be more accurate?

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No you can't...

What is your application? Are you using the UART? If so, the internal 32MHz oscillator is accurate enough (as Gordon said above) ;)

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cheungupdt wrote:

Wait....so i can't use a 32MHz external crystal?

So the only thing that an external crystal is good at is to be more accurate?

No, but you can still use the PLL with a 16MHz crystal to get a 32MHz system clock.

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Although I haven't tried it, apparently you can run the peripherals at a faster rate than the CPU clock.

Maybe there are implications there?

Besides, aren't 32MHz xtals comparatively hard to find (cf 8MHz, 16MHz)?

-- Damien

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dmginc wrote:
No you can't...

What is your application? Are you using the UART? If so, the internal 32MHz oscillator is accurate enough (as Gordon said above) ;)

No, i don't have any actual application yet. I just have some crystals. It probably has no point to put any crystal with xmegas besides the RTC.

Thanks, guys!

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Fundamental 32MHz crystals do exist but are uncommon. They are probably 3rd overtone. The regular AVR crystal oscillator does not discriminate against the fundamental frequency. So I would guess that most 32MHz crystals would oscillate at 10.667 MHz unless you put a tuned circuit in the path.

As Gordon suggested, use a 8Mhz crystal and the x4 PLL to get 32MHz.
Or the "32MHz crystal" at 10.667MHz with x3 PLL to get 32MHz.

David.

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I'm using an 8MHz crystal and PLL.