I checked out this document and came across a circuit which generates the clock frequency from an external crystal oscialltor. Can someone explain the circuit to me?
Where is this circuit?
Where did you come across the "Document"?... both "little" details are probably necessary to answer a question as vague as your question? is...
Doc
Yeah, in the Atmel data sheets... An ATMega328P-PU is probably as good an example as any of the examples. although you'll find very similar circuitry used on most 8 bit controllers and a great many others as well it's just a pair of inverters in series to provide a 360 deg phase shift, Biased into the linear operating range (1/2 Vcc) and some loading capacitors to keep the crystal happy..
Doc
Hmm...your answer didn't help much...Can you be a bit more clear.
Not until you can understand what I wrote...
Here :
An ATMega328P-PU is probably as good an example as any of the examples. although you'll find very similar circuitry used on most 8 bit controllers and a great many others as well it's just a pair of inverters in series to provide a 360 deg phase shift, Biased into the linear operating range (1/2 Vcc) and some loading capacitors to keep the crystal happy..
No I cannot, some parts of programming require a basic knowledge of electronics that you have so far been unable to demonstrate.
There are from device to device minor variations on the same basic scheme.
Perhaps it might help for you to understand the Barkhausen criterion for oscillation as it is the governing physics used to describe a two port oscillator (Wiki : Barkhausen stability criterion - Wikipedia. Where the feedback is the crystal or resonating element(s) and the losses incurred in using those networks represent the required gain to meet the oscillation criteria.
The differences in the two circuits are due to the feedback mechanism itself. IE gain and impedance matching of the resonant component(s).
I would caution you that the subject is quite complex...
This was the origin of my comments about where and what as that information might have been from several different possible sources.
For now, accept that there are differences in the methods used to drive different types of resonant networks and when your electronics education has grown to encompass those differences you will have the necessary theoretical background to look and be able to say "Of Course... This is what is required".
You have the choice to either use the recommended applications or understand why they are necessary. When I was learning, this was the method I used.that worked for me. As a point of fact it is still my preferred method.
I said before Mr Google is your friend but you need to learn how to properly formulate your questions first.
I would note in passing that your questions speak very highly to your lack of knowledge of general electronics theory and IMO are of little general interest to anyone else reading this thread.... RTFM "Read That 'Fine'Manual", First. Then ask questions.
Most digital engineers don't even learn the little I have given you so far. The preferred course of action is generally to follow the MFR's recommendations for each type of oscillator.
Doc
Is your original question based on you wanting to generate a frequency and hoping to derive a design from what you've found in that datasheet, or understand how the external clock works with Atmel's processors?
Geoff
I want to know how clock is generated from external crystal in Atmega microcontrolers.
sreedevk:
I want to know how clock is generated from external crystal in Atmega microcontrolers.
Hi
In that case, how crystal oscillators work (Wikipedia) and this article on why you need a clock source from AVRfreaks might make helpful reading.
Cheers ! Geoff