> The manual does not explains explicitly about the difference
> in-between the different oscillator modes.

It does. What are you missing ? Point us to a specific
part of the text that is unclear. I'm not saying that
it is *not* clear, just that I don't understand what part
of it that *you* do not find clear.


>
> Each PIC device operates at a particular clock frequency
> range. Now we could
> either have an internal or an external clock source as input
> to PIC device.

Correct. As the data sheet says.

> The clock is required for the device to execute instructions
> and for the peripherals to function.

Yes. (but I'll think you'll better wait a little with the sleep mode :-) )

> For example a PIC operates with an external 4Mhz
> clock input connected at its OSC1 and OSC2 pins.

No !
If you use an *external* clock source (not very common), you
connect that to one of the OSC pins. The other pin will be used
as a clock OUT pin *or* as a general I/O pin, it's up to you.

Or are you confusing an "external clock source" with "a crystal" ?
That are two different things. As said before, see the data sheet.

> Now if the change the value of C1 and C2

What C1 and C2 ? You mean the two caps that should be used
together with a crystal ? They shold never be changed. Use the
value specified in the manual.

> such that the clock frequency increases (more than the clock
> range as specified for the device), how would PIC behave and WHY?

????? When ? Using what clock source (osc mode) ?
What are you reading that made you come up with *that* question ?

I'm sure everyone here would be happy to help, but you realy
must be more specific. Point to a specific sentencs or part
of the data sheet that you find unclear, and we'll sort that out.

You are asking questions like you havn't read the data sheet at
all. I'm not saying that you have *not*, just that it sounds like
that.

But just take it easy, continue asking, and we'll sort this out !

Best Regards
Jan-Erik.

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