AVR-Chat

If I run this chip off a 32KHz XTAL.. does it multiply up internally, 
or does it actually RUN at 32KHz???

David

On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> If I run this chip off a 32KHz XTAL.. does it multiply up internally, 
> or does it actually RUN at 32KHz???

  AVR microprocessors do not contain PLLs in their clock circuitry.
They run at whatever frequency the clock is running at, unless you
choose to divide that frequency in those chips which support clock
division (which I believe includes the entire line of AVR chips).

Tom

Hi Tom,

AT90PWM3, does have a PLL, It is used for the CPU clock and for the
PSC (PWM controllers).

Regards
Hugo

On 10/6/05, Thomas Keller <tkeller1@neb.rr.com> wrote:
> On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> > If I run this chip off a 32KHz XTAL.. does it multiply up internally,
> > or does it actually RUN at 32KHz???
>
>  AVR microprocessors do not contain PLLs in their clock circuitry.
> They run at whatever frequency the clock is running at, unless you
> choose to divide that frequency in those chips which support clock
> division (which I believe includes the entire line of AVR chips).
>
> Tom
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>

Not true.  Look at the tiny26 oscillator circuit.  They don't use a 32khz
clock for the PLL source, however.


-----------
Larry Barello
www.barello.net

| -----Original Message-----
| From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
| Of Thomas Keller
| Sent: Thursday, October 06, 2005 8:44 AM
| To: AVR-Chat@yahoogroups.com
| Subject: Re: [AVR-Chat] AT90CAN128
| 
| On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
| > If I run this chip off a 32KHz XTAL.. does it multiply up internally,
| > or does it actually RUN at 32KHz???
| 
|   AVR microprocessors do not contain PLLs in their clock circuitry.
| They run at whatever frequency the clock is running at, unless you
| choose to divide that frequency in those chips which support clock
| division (which I believe includes the entire line of AVR chips).
| 
| Tom
| 
| 
| 
| 
| 
| 
| Yahoo! Groups Links
| 
| 
| 
| 
| 
| 
|

On Thu, 2005-10-06 at 17:11 -0700, Larry Barello wrote:

   One of these days I am going to learn not to shoot from the hip, as
it were.   *blush*    I sit corrected (if you think I check my email
while standing, think again!)

Tom

> Not true.  Look at the tiny26 oscillator circuit.  They don't use a
> 32khz
> clock for the PLL source, however.
> 
> 
> -----------
> Larry Barello
> www.barello.net
> 
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
> Behalf
> | Of Thomas Keller
> | Sent: Thursday, October 06, 2005 8:44 AM
> | To: AVR-Chat@yahoogroups.com
> | Subject: Re: [AVR-Chat] AT90CAN128
> | 
> | On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> | > If I run this chip off a 32KHz XTAL.. does it multiply up
> internally,
> | > or does it actually RUN at 32KHz???
> | 
> |   AVR microprocessors do not contain PLLs in their clock circuitry.
> | They run at whatever frequency the clock is running at, unless you
> | choose to divide that frequency in those chips which support clock
> | division (which I believe includes the entire line of AVR chips).
> | 
> | Tom
> | 
> | 
> | 
> | 
> | 
> | 
> | Yahoo! Groups Links
> | 
> | 
> | 
> | 
> | 
> | 
> | 
> 
> 
> 
> 
> ______________________________________________________________________
> YAHOO! GROUPS LINKS
> 
>      1.  Visit your group "AVR-Chat" on the web.
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>      2.  To unsubscribe from this group, send an email to:
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>

*sigh*

  OK.    I suppose now I am going to have to go and read every data
sheet on Atmel's website, so I don't stick my foot in my mount again
like this.

  Query:  are these PLLs used with external crystal or clock sources to
multiply the clock frequency, or are they there for other purposes?
Whyt use an expensive PLL circuits for chips that don't run any faster
than 20 Mhz (except for that one, sweet 48 Mhz chip they just brought
out)?  It's not like a 4 or 5 Mhz cyrstal costs any less than a 20 Mhz
crystal, so why would they bother?

Tom.

On Thu, 2005-10-06 at 20:07 -0300, Hugo Oliveira wrote:
> Hi Tom,
> 
> AT90PWM3, does have a PLL, It is used for the CPU clock and for the
> PSC (PWM controllers).
> 
> Regards
> Hugo
> 
> On 10/6/05, Thomas Keller <tkeller1@neb.rr.com> wrote:
> > On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> > > If I run this chip off a 32KHz XTAL.. does it multiply up
> internally,
> > > or does it actually RUN at 32KHz???
> >
> >  AVR microprocessors do not contain PLLs in their clock circuitry.
> > They run at whatever frequency the clock is running at, unless you
> > choose to divide that frequency in those chips which support clock
> > division (which I believe includes the entire line of AVR chips).
> >
> > Tom
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
> 
> 
> ______________________________________________________________________
> YAHOO! GROUPS LINKS
> 
>      1.  Visit your group "AVR-Chat" on the web.
>           
>      2.  To unsubscribe from this group, send an email to:
>          AVR-Chat-unsubscribe@yahoogroups.com
>           
>      3.  Your use of Yahoo! Groups is subject to the Yahoo! Terms of
>         Service.
> 
> 
> ______________________________________________________________________
>

> On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> > If I run this chip off a 32KHz XTAL.. does it multiply up 
internally, 
> > or does it actually RUN at 32KHz???
> 
>   AVR microprocessors do not contain PLLs in their clock circuitry.
> They run at whatever frequency the clock is running at, unless you
> choose to divide that frequency in those chips which support clock
> division (which I believe includes the entire line of AVR chips).
 
So running the CPU on a watch XTAL gives you a pretty slow computer - I 
assume you can run on the internal osc, and use the 32KHz as a timing 
reference to trim it then?

David

On Fri, 2005-10-21 at 17:58 +0100, David Collier wrote:
> > On Wed, 2005-10-05 at 17:43 +0100, David Collier wrote:
> > > If I run this chip off a 32KHz XTAL.. does it multiply up 
> internally, or does it actually RUN at 32KHz???
> >   AVR microprocessors do not contain PLLs in their clock circuitry.
> > They run at whatever frequency the clock is running at, unless you
> > choose to divide that frequency in those chips which support clock
> > division (which I believe includes the entire line of AVR chips).
> So running the CPU on a watch XTAL gives you a pretty slow computer -
> I assume you can run on the internal osc, and use the 32KHz as a
> timing reference to trim it then?

   If I understand what you are asking, I believe the answer is no.
Depending on WHICH AVR processor you are using, the internalk oscillator
is either fixed, or can be trimmed by writing to the OSCCAL register.
So far as I understand it, the 32 Khz oscillator is used strictly for
the watchdog timer, and to start up the processor from a deep sleep
state (someone who knows more correct me if I am wrong, please?).

Tom