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Author Topic: ATmega8 at 3.0V can use 8MHz internal oscillator?  (Read 6782 times)

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Offline AdminTopic starter

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ATmega8 at 3.0V can use 8MHz internal oscillator?
« on: January 28, 2009, 04:18:48 AM »
I have an ATmega8 that I want to run at 3.0V (but 3.3V is ok).

I don't want an external oscillator, only internal oscillator, and I want it running at either 7.3728 MHz or 8MHz. I prefer 7.3728 MHz because it has zero error rate for UART. But 8MHz is ok, as the internal oscillator can only do at best 4MHz or 8MHz.

But on the ATmega datasheet, Figure 171 on page 276, it appears to say that I need at least 5V to get 8MHz.

What would happen if I give it just 3.0V? Would it really just give me ~7.2MHz? Will I get about 7.3728 MHz if I gave it 3.3V?

Offline TrickyNekro

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Re: ATmega8 at 3.0V can use 8MHz internal oscillator?
« Reply #1 on: January 28, 2009, 05:01:09 AM »
Basically, you can.... And as you said it will run somewhere near 7.6 to 7.9MHz....
EEeee... One question here....
Can't you somehow output the clock signal out of XTAL2....
I'm not sure...
But if yes.... Just get a scope and measure...... :P
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

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Re: ATmega8 at 3.0V can use 8MHz internal oscillator?
« Reply #2 on: January 28, 2009, 05:34:27 AM »
Basically, you can.... And as you said it will run somewhere near 7.6 to 7.9MHz....
EEeee... One question here....
Can't you somehow output the clock signal out of XTAL2....
I'm not sure...
But if yes.... Just get a scope and measure...... :P
Well, I wanted to know *before* I built the circuit :P

Anyway, I'm looking at the ATmega168 datasheet and it appears it can do exactly 8MHz internal oscillator at 3.3V. Its pin compatible with ATmega8, so no issue making the change. I guess I'll go with that . . .

Although knowing the answer to this question could help me with overclocking in the future!

Offline TrickyNekro

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Re: ATmega8 at 3.0V can use 8MHz internal oscillator?
« Reply #3 on: January 28, 2009, 05:57:14 AM »
Basically, you can overclock about 2MHz every 8MHz....
Once I got an ATMEGA128L to run at 12MHz at 5V while rated for 8MHz...
But it was 5V supply...
Also got the ATMEGA8535 (which is rather old) to run at 22.something.....
But was very prone to noise and reseted a lot....
While when at 20MHz, it could run like charm...

Newer AVR cores should be more easy to overclock... If you have any luck...
please inform....
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

 


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