Connect a TCXO to a AVR

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#1
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Hello,

Is there any one that have experience with connecting a TCXO or other high precision crystal to a AVR (I use a atmega1280). I need this to achieve a high precision real time clock better then +-1 ppm.

Br Leif G

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Just connect it to XTAL1 and program the fuse to external clock.

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Ok that sounds easy. Should xtal2 be unconnected?
Thanks for the reply.

Br Leif G

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Most likely unconnected, but do read what the datasheet says about using external clock signals.

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The datasheet says that it could be left open. I might migrate to a xmega and then I also could use it as a IO. Thanks again.

Br Leif G

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Quote:

I might migrate to a xmega and then I also could use it as a IO.

???
Didn't someone above say:
Quote:

Most likely unconnected, but do read what the datasheet says about using external clock signals.

What does it say about using XTAL2 as I/O on e.g. Mega88?

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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Many TCXOs have a low level (< 1Vpp) sinewave output instead of a full swing CMOS squarewave output. To use such TCXOs as an AVR clock source you need to place a capacitor (1 nF or so) between the TCXO and XTAL1 and configure your AVR clock as external crystal (not as external clock!). In this case the XTAL1 input inverting amplifier will be self biased due to an internal feedback resistor, and will have enough gain to shape the input sinewawe to output squarewave. Of course the XTAL2 will be an amplifier's output and couldn't be used as an i/o pin.

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