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'[PIC]:Has any one ever got a PIC 18F244 chip to wo'
2002\08\02@223455 by Michael Simpson

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I have tried everything including the HS/PLL option using just about every Resonator and Crystal I could get my hands on.

Im using MPLAB and a PICSTART Plus.  
The best I seem to do is 20Mhz

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2002\08\03@095216 by M. Adam Davis

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You'll note, if you inspect the datasheet, that Microchip hasn't listed
any values for oscillators (crystal or resonator) above 20MHz, the
closest they get is listing a 25MHz crystal in the capacitor value table
with valuse of "TBD" as in the capacitor column

I seem to remember that if you wanted to run the chip above 20MHz you
had to use a lower oscillator value and use the PLL to multiply it by 4.

However, you can probably get it going faster if you try a few different
capacitors, and perhaps use a resistor in series.  Check the archives
for crystal problems.

-Adam

Michael Simpson wrote:

{Quote hidden}

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2002\08\03@152548 by Michael Simpson

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Done that, did that.   I have about 100 crystal,cap and resonators.  I tried
using the HS/PLL option.  Cant get it to go above 20mhz.

{Original Message removed}

2002\08\03@172406 by Jim

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Are you sure that any of your "over 20 MHz crystals"
are fundamental crystrals at this "over 20 MHz"
frequency?

Odds are, that all those "higher-frequency crystals"
are actually "overtone" crystals and as such their
"overtone frequency" is stamped on the outside.

I would then place money on a bet that the simple
little oscillator used on the PIC chips *only*
oscillates at the lower "fundamental" frequency
of those crystals ...

(All this comes from the perspective of a radio engineer
who has done work with crystals in communications gear
in the (now-distant) past ...)

RF Jim


{Original Message removed}

2002\08\03@175602 by Michael Simpson

picon face
The question is for the PLL option I am using a 10MHZ Resonator.   IT works
at 10MHZ with or with out the PLL option.

As far as the crystals I have tried about 20 brands and types.  I purchased
about 10 each a few weeks ago so I could test.   At the lower frequencies
they all seem to work. fine.  I have a few 10mhz crystals and again they
work fine at XT or HS as 10MHZ.  But in HS/PLL they are still running at
10MHZ.

What is a good source for fundimental frequency crystals.   I purchased all
the ones Im using from digikey.   I just started picking crystals.



{Original Message removed}

2002\08\03@191257 by Byron A Jeff

face picon face
On Sat, Aug 03, 2002 at 05:46:16PM -0400, Michael Simpson wrote:
> The question is for the PLL option I am using a 10MHZ Resonator.   IT works
> at 10MHZ with or with out the PLL option.
>
> As far as the crystals I have tried about 20 brands and types.  I purchased
> about 10 each a few weeks ago so I could test.   At the lower frequencies
> they all seem to work. fine.  I have a few 10mhz crystals and again they
> work fine at XT or HS as 10MHZ.  But in HS/PLL they are still running at
> 10MHZ.

(sound of head scratching...)

They are supposed to run at 10 Mhz. So what exactly is the problem?

The PLL is internal and uses the 10 Mhz external signal to generate the 40 Mhz
clock internally. So there should be no change in the external appearance of
the external oscialltor.

It's supposed to run at 10 Mhz.

So I only have one question: When you enabled the HS/PLL mode did the chip
get 4 times faster than HS mode?

Lastly did you read the errata page for the 18C chips. There are some issues
on oscillator speed based on whether the chip is industrial or extended. Take
a read if you get a chance...

BAJ

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2002\08\04@021226 by Michael Simpson

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The problem is the Chip does not run 4X internaly.  A 10mhz crystal with HS
and PLL does not run internaly at 40MHZ.


{Original Message removed}

2002\08\04@041301 by Michael Simpson

picon face
OK I got this baby to run at 40MHZ.

Once you program with HS-PLL option you must shutdown the PIC (Reset wont do
it)  This allows the PLL to start up.

Some other observations.
When using crystals and resonators with PLL option  the caps don't seem to
make a difference.

In the 18FXX2 manual fig 2.6 does not show the use of caps.  Any one know
any thing about this.

{Original Message removed}

2002\08\04@100609 by Byron A Jeff

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On Sun, Aug 04, 2002 at 04:12:55AM -0400, Michael Simpson wrote:
> OK I got this baby to run at 40MHZ.

Cool!

>
> Once you program with HS-PLL option you must shutdown the PIC (Reset wont do
> it)  This allows the PLL to start up.

That seems to match up with my reading in chapter 2 of the datasheet. The
PLL timer is triggered by power up.

>
> Some other observations.
> When using crystals and resonators with PLL option  the caps don't seem to
> make a difference.
>
> In the 18FXX2 manual fig 2.6 does not show the use of caps.  Any one know
> any thing about this.

I always keep it simple. Always use caps with crystals and resonators all the
time unless the datasheet specifically prohibits their use. There is almost
never a situation where using caps cause problems. OTOH leave them out and
your crystal/resonator circuit may not work.

So always put them in and don't worry about it.

Glad you got it working...

BAJ

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2002\08\04@114744 by iso-8859-1?Q?=D6mer_Yalhi?=

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I have just ordered pic 18f452 and 40mhz xtals (without reading the manual).
do you mean to tell me that I wasted my money on the xtals?  All I need is
just a 10MHz xtal?  I don't get it...

{Original Message removed}

2002\08\04@150858 by Michael Simpson

picon face
I could not get it to clock with 40Mhz Xtals.  Could be that my Xtals were
over tone. (not fundimental) For my application Im gunna use 10MHZ
resonators.

I even got the thing to overclock with a 12MHZ resonator and HS-PLL mode.
IT was fast 48Mhz.  I was playing with other xtals and resonators and got it
up to about 60Mhz internaly.

I have to do some timeing experiments to see how stable it is at 40MHZ with
a UART and other timeing critical stuff.


----- Original Message -----
From: "Ömer Yalhi" <.....oyalhiKILLspamspam.....TEKSAN.COM.TR>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Sunday, August 04, 2002 11:46 AM
Subject: Re: [PIC]:Has any one ever got a PIC 18F244 chip to work at 40mhz


> I have just ordered pic 18f452 and 40mhz xtals (without reading the
manual).
> do you mean to tell me that I wasted my money on the xtals?  All I need is
> just a 10MHz xtal?  I don't get it...
>
> {Original Message removed}

2002\08\04@150914 by Olin Lathrop

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> I have just ordered pic 18f452 and 40mhz xtals (without reading the
manual).

Duh!

> do you mean to tell me that I wasted my money on the xtals?

Yes.

> All I need is just a 10MHz xtal?  I don't get it...

The 18 parts contain a phase lock loop that can multiply the oscillator
frequency by 4 for internal use.  The oscillators themselves top out around
20MHz (I don't remember exactly), which is fine because crystals much above
that are difficult to manufacture or are tricky to use because you have to
resonate them at a harmonic.  To run an 18 PIC at 40MHz, you use a 10MHz
oscillator and turn on the 4x PLL.

Once again, there is no substitute for actually reading the manual.


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2002\08\04@155805 by Byron A Jeff

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On Sun, Aug 04, 2002 at 06:46:50PM +0300, Ömer Yalhi wrote:
> I have just ordered pic 18f452 and 40mhz xtals (without reading the manual).
> do you mean to tell me that I wasted my money on the xtals?
Yup. That's what manuals are for. They won't work.

> All I need is just a 10MHz xtal?

Yup.

>  I don't get it...

The part has a 4x PLL in it. So in HS/PLL mode it'll multiply the input
clock signal by 4 giving up to 40 Mhz.

BAJ

>
> {Original Message removed}

2002\08\04@192202 by Michael Simpson

picon face
One thing that must be concidered is that any error that the Resonator or
crystal has will also be multiplied by 4.   This could effect high speed
serial IO.  As I dig further into this I will post my results.

----- Original Message -----
From: "Byron A Jeff" <@spam@byronKILLspamspamCC.GATECH.EDU>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Sunday, August 04, 2002 3:56 PM
Subject: Re: [PIC]:Has any one ever got a PIC 18F244 chip to work at 40mhz


> On Sun, Aug 04, 2002 at 06:46:50PM +0300, Ömer Yalhi wrote:
> > I have just ordered pic 18f452 and 40mhz xtals (without reading the
manual).
{Quote hidden}

> > {Original Message removed}

2002\08\04@193431 by Spehro Pefhany

picon face
At 07:21 PM 8/4/02 -0400, you wrote:
>One thing that must be concidered is that any error that the Resonator or
>crystal has will also be multiplied by 4.   This could effect high speed
>serial IO.  As I dig further into this I will post my results.

Not true. If the oscillator frequency is 300ppm off, the serial comms will
also be off by 300ppm. One for one, to a first approximation (ignoring
second order effects in the PLL).

Best regards,

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2002\08\04@202131 by Michael Simpson

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Kewl.  But I wont believe it till I see it.  :)

----- Original Message -----
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To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Sunday, August 04, 2002 7:46 PM
Subject: Re: [PIC]:Has any one ever got a PIC 18F244 chip to work at 40mhz


{Quote hidden}

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2002\08\04@232419 by Jim Ewald

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That power reset after programming the PLL bit me a couple of times
here. Note to anyone using the ICD2 - be sure to power off your target
circuit AND pull the RJ-45 connector from the target circuit after
programming the PLL. The ICD2 will still provide power to the chip after
your target power is removed.

I have been using resonators without external caps. I'm running a 10 MHz
crystal on an 18F452 with 22pf caps. The chip won't run without them.
Maybe there is enough stray capacitance on the breadboard to get your
clock running?

Jim

{Original Message removed}

2002\08\05@030233 by Wouter van Ooijen

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> One thing that must be concidered is that any error that the
> Resonator or
> crystal has will also be multiplied by 4.   This could effect
> high speed
> serial IO.  As I dig further into this I will post my results.

Bullocks. The relative error, which is the important figure, remains the
same. But I guess a PLL will add some frequency jitter, but that should
not matter except maybe at very high baudrates (megabauds instead of
kilobauds).

Wouter van Ooijen

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2002\08\05@074946 by Olin Lathrop

face picon face
>>
One thing that must be concidered is that any error that the Resonator or
crystal has will also be multiplied by 4.   This could effect high speed
serial IO.  As I dig further into this I will post my results.
<<

In absolute terms, yes, but that is not relevant.  A 10MHz crystal with
100Hz error will generate a 40MHz clock with 400Hz error.  But the
percentage error is still the same, which is all that matters for things
like serial I/O - whether high speed or not.


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2002\08\05@081657 by Olin Lathrop

face picon face
> > >One thing that must be concidered is that any error that the Resonator
or
> > >crystal has will also be multiplied by 4.   This could effect high
speed
> > >serial IO.  As I dig further into this I will post my results.
> >
> > Not true. If the oscillator frequency is 300ppm off, the serial comms
will
> > also be off by 300ppm. One for one, to a first approximation (ignoring
> > second order effects in the PLL).
>
> Kewl.  But I wont believe it till I see it.  :)

I don't know what your problem is here.  This is just plain grade school
math.  There are no real world part tolerance issues in this argument.


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2002\08\05@101829 by Josh Koffman

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(Disclaimer: I haven't read the datasheet yet, but I _HAVE_ printed it,
and I _DO_ intend to read it...when I get the time :)

So does the PLL multiply by 4, then the PIC divides by four? Or is
instructions/clock cycle different on the 18f?

Josh
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Olin Lathrop wrote:
> The 18 parts contain a phase lock loop that can multiply the oscillator
> frequency by 4 for internal use.

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2002\08\05@112324 by Olin Lathrop

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> (Disclaimer: I haven't read the datasheet yet, but I _HAVE_ printed it,
> and I _DO_ intend to read it...when I get the time :)

Look, this list isn't a substitute for doing your homework.  It's rather
arrogant to ask 2000 people to drop what they are doing to answer a question
you were too lazy to look up.

> So does the PLL multiply by 4, then the PIC divides by four? Or is
> instructions/clock cycle different on the 18f?

RTFM!



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2002\08\05@114313 by Jennifer L. Gatza

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> > So does the PLL multiply by 4, then the PIC divides by four? Or is
> > instructions/clock cycle different on the 18f?

Maybe RTFM is the better answer, but maybe just a quick reminder...  each
instruction is executed in four quarter-cycles (Q-cycles).

If you weren't using the PLL, your 10 MHz would execute 2.5M instructions
per second.  With the PLL, you still get 10M instructions/second.

[maybe a little oversimplified, but just enough to jog your memory]  :)

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2002\08\05@120909 by Harold M Hallikainen

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On Sat, 3 Aug 2002 14:44:19 -0400 Michael Simpson <RemoveMEmsimpsonspam_OUTspamKILLspamHIS.COM>
writes:
> Done that, did that.   I have about 100 crystal,cap and resonators.
> I tried
> using the HS/PLL option.  Cant get it to go above 20mhz.

       You tried a 10 MHz crystal and HSPLL? That should give you 40 MHz clock
(or one instruction every 100ns). I've now built over a thousand boards
with 18C452 and 18F452 with 10 MHz resonators with internal capacitors.
No problems...

Harold


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2002\08\05@124235 by Harold M Hallikainen

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On Sun, 4 Aug 2002 19:21:21 -0400 Michael Simpson <RemoveMEmsimpsonTakeThisOuTspamspamHIS.COM>
writes:
> One thing that must be concidered is that any error that the
> Resonator or
> crystal has will also be multiplied by 4.   This could effect high
> speed
> serial IO.  As I dig further into this I will post my results.
>

       But, the percentage error remains the same. If I'm off by 0.5% at 10
MHz, I'll also be off 0.5% at 40 MHz. The absolute error is multiplied,
but the relative error (as percentage of frequency) is not. A UART will
work properly with up to about 5% bit rate error, so the 0.5% error of a
typical resonator is no problem.

Harold


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2002\08\05@130621 by Josh Koffman

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Ok, admittedly I slipped on this one. I shouldn't have asked. Sorry all.

Josh
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Olin Lathrop wrote:
<snip>

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2002\08\05@143751 by Hazelwood Lyle

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OK, just for the record..

RTFM should always be the first step. I try to, at least.

Your posting and the ensuing discussion were valuable to me.
I also purchased some 40MHZ XTals in anticipation
of my recently arrived PIC18F parts. Had I not read your post,
I would surely have fallen into the same predicament.

This morning I read the manual(41159a.pdf), and while an explanation of the PLL feature was there, there was no
statement that it is required. Granted, the tables show
testing of resonators and crystals only up to 25MHZ, and
only up to 10 with HS4 enabled.. But there was nothing
that I read stating that you couldn't do regular HS at
40 MHZ.

Also, the higher clock rates in the table were marked "TBD"
or something similar.

Perhaps I'm using a dated datasheet. I DL'ed the latest, sure
enough, this was updated to 41159b.pdf. Still marked as
"preliminary", but apparently the latest as I just got it from
the Microchip website. The "Oscillator Options" are the same.

Am I looking in the wrong place? In the wrong document?
Is it just a Monday thing?

Any feedback, corrective or otherwise, is welcomed.
Lyle Hazelwood


{Original Message removed}

2002\08\05@161753 by Michael Simpson

picon face
As I said in other posts I got it to work by powering down the chip and
powering it backup.   Works good.

I found that if you use other xtals/resonators you can over clock the chip
as well.  I have got it to run at 60Mhz.


{Original Message removed}

2002\08\05@162618 by Michael Simpson

picon face
This is one of MicroChips main failing.  Look at the 16F628.  It has been
out for a while and still says preliminary.

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To: <RemoveMEPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Monday, August 05, 2002 2:36 PM
Subject: Re: [PIC]:Has any one ever got a PIC 18F244 chip to work at 40mhz


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> {Original Message removed}

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