Question re: AVR's w/ multiple clock sources

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#1
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Total votes: 0

Hi,

I was wondering: If the default internal 1MHz RC oscillator fuse setting was left intact AND a 8MHz crystal w/ 2 caps (of proper value) was put across XTAL1/XTAL2...would you see the proper (crystal) frequency signal on XTAL2? I realize the AVR would operate on the internal 1MHz clock.

I looked in the datasheet (used mega8 as an example) and I could only find block diagrams, no schematics (of course that doesn't mean they are not there...I just didn't see them). I just now thought about looking in Sleep sections...I will go look now.

I only have a STK500/501 and there isn't really a way to (easily) connect a crystal and caps directly to an AVR, otherwise I would test this for myself.

My apologies if this turns out to be in the datasheet somewhere. I spent 10 or 15 minutes browsing around.

Regards,
Steve

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Total votes: 0

Hi,

I think I have convinced myself that there should NOT be a waveform on XTAL2. I base this on a hint I saw in the Electrical Characteristics section. I realized Atmel couldn't make guarantees about current consumption in Sleep modes if it would be possible for that circuit to function if the fuses were set to tell it to be off.

I was asking because there is a thread over in the GCC forum that made me wonder if someone could actually see a 8MHz clock when the AVR was running on the internal RC oscillator.

Regards,
Steve