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'[EE] Source for 40 Mhz Xtal for PIC18F252 ?'
2003\08\21@134819 by Philip Galanter

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Electronics amateur having a bit of trouble finding, 40 Mhz Crystals
for use with an 18F252 at its top speed.

Would also appreciate any pointers to resonators at this same speed.

I need maybe 10-20 of these.  For now at least.

I'd appreciate it if you could note if you've actually used the given
part or if it "should work".

thanks!  Phil

p.s. Extra credit questions....

I did find a catalog entry for 40Mhz "oscillators" from Kyocera in a
14 pin dip sized package for use with "microprocessors"...4 pins...+5
V, Ground, "output", and a do-nothing pin presumably just for
mechanical connection to the PCB.  $1 each and said to drive CMOS and
TTL.  Other than size any gotcha's with these?  (Power consumption
maybe?)

Also the 18F252 has a PLL mode where a 10 Mhz crystal is turned into
a 40 Mhz signal.  My understanding is that this uses more power, and
is really there for those concerned about emitting higher frequency
interference.  I'd consider using it, except I can't find 10 Mhz
crystals either!  They seem to exist mostly as multiples of
4...comments about this option, or 10 Mhz crystals?

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2003\08\21@140023 by D. Jay Newman

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> Electronics amateur having a bit of trouble finding, 40 Mhz Crystals
> for use with an 18F252 at its top speed.

Maybe I'm mistaken, but I thought that you needed a 10 MHz crystal with
the PLL set to 4.

> Would also appreciate any pointers to resonators at this same speed.

Both should be available at Digikey.

I've used the resonators.

> I need maybe 10-20 of these.  For now at least.

> Also the 18F252 has a PLL mode where a 10 Mhz crystal is turned into
> a 40 Mhz signal.  My understanding is that this uses more power, and
> is really there for those concerned about emitting higher frequency
> interference.  I'd consider using it, except I can't find 10 Mhz
> crystals either!  They seem to exist mostly as multiples of
> 4...comments about this option, or 10 Mhz crystals?

I had no problem finding 10 or 20 MHz crystals.
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2003\08\21@143659 by Wouter van Ooijen

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> Electronics amateur having a bit of trouble finding, 40 Mhz Crystals
> for use with an 18F252 at its top speed.

You do know that the 18F's (at least most of them, but that's another
story) can use Xtals up to 25 MHz, and can use their *4 internal
multiplier to run up to 40 MHz *internally* (which requires a 10 MHz
crystal).

I guess this cancels your question rather than answering it :)

And I will put this in the still very small faq at
http://www.voti.nl/picfaq

Wouter van Ooijen

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2003\08\21@155738 by Philip Galanter

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At 8:37 PM +0200 8/21/03, Wouter van Ooijen wrote:
>  > Electronics amateur having a bit of trouble finding, 40 Mhz Crystals
>>  for use with an 18F252 at its top speed.
>
>You do know that the 18F's (at least most of them, but that's another
>story) can use Xtals up to 25 MHz, and can use their *4 internal
>multiplier to run up to 40 MHz *internally* (which requires a 10 MHz
>crystal).
>
>I guess this cancels your question rather than answering it :)
>
>And I will put this in the still very small faq at
>http://www.voti.nl/picfaq
>
>Wouter van Ooijen


Aha!  Very useful info indeed.  I wonder why the references I saw
seemed focused on noting how the PLL mode helps reduce RFI and didn't
emphasize it is the *only* way to get top speed at all.

Thanks!  Off to find 10 Mhz Xtals...only 4's and 20's in my stash...

Phil

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2003\08\21@160540 by Mark Samuels

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That isn't the *only* way to get top speed...
external CRYSTAL (HS setting) max speed is 25MHz, but you can still apply a
40MHz clock from an external oscillator (EC or ECIO setting).

-Mark


At 03:11 PM 8/21/03 -0400, you wrote:
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2003\08\21@180705 by Jinx

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> except I can't find 10 Mhz crystals either!  They seem to
> exist mostly as multiples of  4...comments about this
> option, or 10 Mhz crystals?

I've no trouble finding 10MHz from any number of sources
around NZ. A local retail chain (Dick Smith), who STILL
stocks the 16F84 as weapon of choice, stocks just 3 crystals -
32k, 4M and 10M (I must tell them about the 628-20 one day)

Rather than run the 252 flat out all the time, you speed freak, as
well as the 10MHz look around for a 9.8304MHz (also should be
easy to find). This will run a x4 252 at 39.3216MHz which is
both high speed and a base clock for RS232

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2003\08\21@194227 by Philip Galanter

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At 10:06 AM +1200 8/22/03, Jinx wrote:
>  > except I can't find 10 Mhz crystals either!  They seem to
>>  exist mostly as multiples of  4...comments about this
>>  option, or 10 Mhz crystals?
>
>I've no trouble finding 10MHz from any number of sources
>around NZ. A local retail chain (Dick Smith), who STILL
>stocks the 16F84 as weapon of choice, stocks just 3 crystals -
>32k, 4M and 10M (I must tell them about the 628-20 one day)
>
>Rather than run the 252 flat out all the time, you speed freak, as
>well as the 10MHz look around for a 9.8304MHz (also should be
>easy to find). This will run a x4 252 at 39.3216MHz which is
>both high speed and a base clock for RS232

I'll admit I didn't look that hard for 10MHz Xtals...I wrongly thought
it would be better to use 40MHz ones...

The need for speed here is that I have to get a 40 KHz signal out of
the hardware PWM unit AND try to retain as close to 10 bits of duty
cycle resolution as possible.

Phil

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2003\08\21@221736 by Bob Ammerman

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The PIC18's are not specced for crystals all the way up to 40MHz. Above a
certain frequency you must use an external oscillator, or the PLL.

Bob Ammerman
RAm Systems

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