External Clock for Atxmega128A1

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What is the maximum frequency can be input on XTAL1?

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Do you mean what does the datasheet specify (actually you can find that out by reading the datasheet!) or what you can actually get away with on a one-off hobby basis? The data says 32MHz, threads here have reported anything up to about 64MHz and possibly beyond.

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Don't most use a "modest" crystal frequency and then crank it up internally? (that might be a good poll question.)

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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clawson wrote:
...(actually you can find that out by reading the datasheet!)...

Where is it written in datasheet?

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Quote:

Where is it written in datasheet?

Page 1 (XA1) wrote:
• Speed performance
– 0 – 12 MHz @ 1.6 – 3.6V
– 0 – 32 MHz @ 2.7 – 3.6V

See also fig 33-1

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It's conspicuously missing from the A1 datasheet. The A4U datasheet (i.e. a completely different chip) says 0-90MHz with VCC from 1.6V to 1.8V and 142MHz with VCC from 2.7V to 3.6V.

Clawson, the external clock capabilities are not the same as the internal clock capabilities. For proof look through the AVR32 datasheets (they can run up to 66MHz but only accept <=50MHz external clock inputs).

Jeff Nichols

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clawson wrote:

Page 1 (XA1) wrote:
• Speed performance
– 0 – 12 MHz @ 1.6 – 3.6V
– 0 – 32 MHz @ 2.7 – 3.6V

See also fig 33-1

Speed performance and external clock this is the same?

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pixel2001n wrote:
The A4U datasheet...

I want to read about it in the DS on A1

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As I say figure 33-1 shows "safe operation" and it's upper limit is 32MHz.

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pixel2001n is correct. The datasheet says you can supply up to 142MHz as long as you divide it down to 32MHz or below for the system clock.

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agentXMEGA wrote:
pixel2001n wrote:
The A4U datasheet...

I want to read about it in the DS on A1

Hey--If if's and but's were candy and nuts, every day would be Christmas.

The pixel-monster already said

Quote:
It's conspicuously missing from the A1 datasheet.

I wouldn't expect that to change. So you could ask Atmel.

But with the errata list of the model you mention, wouldn't the information for the A1U be more pertinent? And that sheet seems to have the same numbers as the mentioned A4 numbers.

===================

It would be more interesting for me if I knew the goal of this quest. I thought that for emissions-control an aim was to minimize the frequency of signals on a board. Perhaps the board already has a fast clock for e.g. programmable logic that you want to share with the Xmega?

===================

One more thing about clocks that is more of a question for my Xmega education: I thought that one of the pluses of the newer Xmega models was that the internal clocks were "good enough" for most use, especially after a calibration. Isn't that an attractive feature? Or put another way: What type(s) of Xmega apps/situations need e.g. an external crystal?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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pixel2001n wrote:
It's conspicuously missing from the A1 datasheet.

ОК
thank you all

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theusch wrote:
I thought that one of the pluses of the newer Xmega models was that the internal clocks were "good enough" for most use, especially after a calibration.

Even after calibration, the frequency is not suitable for an external PLL, which is used to generate video synchronization.

theusch wrote:
What type(s) of Xmega apps/situations need e.g. an external crystal?

When you need a synchronous operation of multiple chips from different manufacturers.