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'[PIC]: 20 MHz clock in a 4 MHz pic'
2001\03\21@132211 by Ander

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Hi. I've allways used 4 MHz pics for my personal proyects, and I've put 14 and
20 MHz clocks on them and they work fine. Now I'm going to use a 16f873 pic with
a 20 MHz clock in my work. Can I use 4 MHz models or do I have to use 20 MHz
modes? I never had problems with it at home, but my proyects have not been working
for days with out stop, so I don't know if they will break after a few days.

Thanks

-- Ander Lozano Pérez
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2001\03\21@133252 by Peter Betts

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A part is given a specific speed grade because it is guaranteed to meet
***ALL*** the specifications detailed in the device data sheet.

Yes you can over clock almost any processor but don't make this your final
solution, temperature differences or batch changes (etc etc) will almost
certainly mean your PIC won't work.

If you need 20MHz then choose a 20MHz device. If you want to just experiment
then do what you like and good luck, you don't have any guarantee it's not
working because your overclocking it.

Specifications are there for a purpose, heed them or put up with the
consequences.

Pete

> {Original Message removed}

2001\03\21@133259 by Dipperstein, Michael

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> From: Ander [ander1spamKILLspamwanadoo.es]

...

> Now I'm going to use a 16f873 pic with a 20 MHz clock in my work.
> Can I use 4 MHz models or do I have to use 20 MHz modes?  I never
> had problems with it at home, but my projects have not been working
> for days with out stop, so I don't know if they will break after a
> few days.

I have been told that the 4MHz and 20MHz parts are made from the same dies.  The
difference is that the 20MHz parts have all been tested and guaranteed to work
at 20MHz across the full temperature range.  It's quite possible a 4MHz part
will work just as well, but it's also possible that it will fail.

-Mike

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2001\03\21@174856 by Bob Ammerman

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This should be a FAQ:

I am intentionally "shouting":

DON'T OVERCLOCK PICS

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\03\21@180520 by David VanHorn

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At 03:36 PM 3/21/01 -0500, Bob Ammerman wrote:
>This should be a FAQ:
>
>I am intentionally "shouting":
>
>DON'T OVERCLOCK PICS

See FAQ:  www.dvanhorn.org/Micros/All/Overclocking.php
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2001\03\21@180536 by Olin Lathrop

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>>
Hi. I've allways used 4 MHz pics for my personal proyects, and I've put 14
and
20 MHz clocks on them and they work fine. Now I'm going to use a 16f873 pic
with
a 20 MHz clock in my work. Can I use 4 MHz models or do I have to use 20 MHz
modes? I never had problems with it at home, but my proyects have not been
working
for days with out stop, so I don't know if they will break after a few days.
<<

What part of "not guaranteed to work above 4MHz" don't you understand!!?


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(978) 742-9014, olinspamspam_OUTembedinc.com, http://www.embedinc.com

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2001\03\21@193625 by shane

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Hi,

We design and manufacture PIC based units.  We have sold just over 1k of units over the past 12 months.   We buy all our chips in at
4Mhz, because they are easier to get hold of.  Now, as everyone knows, 20Mhz and 4Mhz chips are made from the same die.  We run
chips labelled 4Mhz at 16Mhz, and we have never had any problems at all.

Conclusion: running 4Mhz chips at 16Mhz is fine.  This is based on real world experience, not hearsay or witch hunting.

Regards,
Shane.

> {Original Message removed}

2001\03\21@202242 by David VanHorn

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At 12:35 PM 3/22/01 +1200, Shane Tolmie wrote:
>Hi,
>
>We design and manufacture PIC based units.  We have sold just over 1k of
>units over the past 12 months.   We buy all our chips in at
>4Mhz, because they are easier to get hold of.  Now, as everyone knows,
>20Mhz and 4Mhz chips are made from the same die.  We run
>chips labelled 4Mhz at 16Mhz, and we have never had any problems at all.
>
>Conclusion: running 4Mhz chips at 16Mhz is fine.  This is based on real
>world experience, not hearsay or witch hunting.
>
>Regards,
>Shane.

Remind me never to hire you?

This has to be the most blatantly ignorant statement I've heard in nearly
20 years.

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2001\03\22@025719 by Vasile Surducan

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Usual answer for such interesting comments will be:

IT'S OUT OF SPECIFICATION !

so choose: kill your self or don't tell to anyone else what you know
and already you've tested.
But remember, a specialist from Microchip never made mistakes...
Also a californian energetic engineer...
And the example is fxd1616u routine from Microchip application note
AN 617 which of course it works... ( in the heaven maybe ! )
Vasile


On Wed, 21 Mar 2001, David VanHorn wrote:

{Quote hidden}

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2001\03\22@055104 by Roman Black

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Hi Shane, we manufacture PIC based products too.
We use a 20MHz rated PIC at 16MHz to allow safe
overhead. We sounce/sink maximum current <5mA
total from PIC output pins to reduce PIC die
heating and thermal stresses. All inputs and
outputs are slew rate limited and clamped by
5.1v zener diodes, AC spike regulated by RC
networks. All components are rated for 8x the
heat dissipation they actually get.

And we haven't had a product failure either.
I don't mean to be harsh, but when you talk
about real world experience my real world
experience tells me to use generous ratings
overheads. I respect safty margins in designs
like I respect a good driver that allows
safety margins on the road. Yes, you can miss
hitting the other car by 1 inch and be within
spec. I would rather miss it by a good safe
margin. Sounds like you don't mind hitting
the other car if you don't get whiplash?? ;o)
-Roman




Shane Tolmie wrote:
>
> Hi,
>
> We design and manufacture PIC based units.  We have sold just over 1k of units over the past 12 months.   We buy all our chips in at
> 4Mhz, because they are easier to get hold of.  Now, as everyone knows, 20Mhz and 4Mhz chips are made from the same die.  We run
> chips labelled 4Mhz at 16Mhz, and we have never had any problems at all.
>
> Conclusion: running 4Mhz chips at 16Mhz is fine.  This is based on real world experience, not hearsay or witch hunting.

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2001\03\22@073324 by Bob Ammerman

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Roman,

I think there is quite a difference here, not to defend Shane ;-) :


His product runs off a PC power supply in an office environment.

Yours tend to run on high-power motorcycles out in the real world of mud,
heat, moisture, and who-knows-what-else.

Horses for courses.

BUT DON'T OVERCLOCK (my throat is starting to hurt)

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\03\22@081547 by John Walshe

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Hi,
   The answer to this question really should come from Microchip.

Do they really speed test, and then bin, the die according to their
performance? if the answer to this is truthfully Yes, then you should not
run a device faster than the marked speed.

If however Microchip don't actually test and speed bin, but just stamp
batches as are needed for sales, then all devices must be able to run at top
speed irrespective of the marking.

Most likely however is that they test to select a quantity of devices for
high speed until the required number is achieved, and then mark all the
others at slow speed. If this is the case then all the warnings the guys
have given in earlier replies MUST be heeded, since the device speed is not
tested or guaranteed at higher speeds unless marked.
They may run at higher speed but you maybe running them on the edge of
failure.

I wonder what the real answer is.........

John

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2001\03\22@081812 by Olin Lathrop

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> We design and manufacture PIC based units.  We have sold just over 1k of
units over the past 12 months.   We buy all our chips in at
> 4Mhz, because they are easier to get hold of.  Now, as everyone knows,
20Mhz and 4Mhz chips are made from the same die.  We run
> chips labelled 4Mhz at 16Mhz, and we have never had any problems at all.
>
> Conclusion: running 4Mhz chips at 16Mhz is fine.  This is based on real
world experience, not hearsay or witch hunting.

What company sells these products?  Can you give a URL to your web site?
I'd like to know so that I can make sure I or my customers never buy
anything from you.


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2001\03\22@084504 by uter van ooijen & floortje hanneman
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>     The answer to this question really should come from Microchip.

Their answer is in the datasheets: the device will operate as specified as
long as you operate it within the specs. Outside the specs is 'interesting
territory': very tempting for some hobbyists and maybe for some very special
professional purposes, but otherwise best avoided.

Wouter

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2001\03\22@165948 by shane

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Overclocking PIC micros

Please allow me to make this statement narrower, ie: retract part of it :)

Our products have a very stable supply, close to 5V, and they all run at room temperature.  We've never had any problems.  Other
customers that run 4Mhz PICs at 20Mhz, and have greater ranges of temperature or voltage, I dont know what will happen. I dont want
to lead anyone astray!  However, I think theres no problem with a hobbyist overclocking the odd 4Mhz chip, considering they are from
the same die. All I know is that all the units we've sold work perfectly, and we've never had any complaints.

Cheers,
Shane.

> {Original Message removed}

2001\03\22@173237 by Matt Pobursky

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Shane,

I've watched this thread with interest and have bitten my tongue up until now.

I've been designing high reliability industrial controls, medical, aerospace
and automotive electronics (and even some VERY high volume consumer devices)
for over 20 years. Sooner or later a "spec related" parts failure will bite
you, no matter how conservative you are on your design tolerances. But always
giving yourself a safety margin, regardless of the pressures of purchasing,
pricing, etc. is just plain good design practice.

>From experience I can tell you that it's not a pleasant experience -- just ask
any of the people on the list with a lot of design experience -- they have most
certainly had such a failure or two. You most likely will never "push the
spec's" again...

I'm not sure what your background or experience level is, but if you design
enough products for a long enough period of time it *WILL* happen.

That said, I agree with most of the others. For hobbyist (personal) use it
really doesn't matter. Feel free to attach a cryogenic cooler to your 4 MHz PIC
and clock it at 100 MHz if you like... ;-)

Matt Pobursky
Maximum Performance Systems

On Fri, 23 Mar 2001 09:58:50 +1200, Shane Tolmie wrote:
{Quote hidden}

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2001\03\22@210611 by Olin Lathrop

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> Our products have a very stable supply, close to 5V, and they all run at
room temperature.  We've never had any problems.

That means you've been lucky so far, but is no guarantee that you will
continue to be lucky in the future.  Maybe all the chips you've gotten
happen to come off the fab line being able to do 20MHz without apparent
problems in your environment.  The next batch could just as well fail at
4.5MHz, whether room temperature and stable 5V supply or not.

What you are doing is irresponsible at best.  Is management aware that you
are shipping product containing parts used outside their specs?  If not, or
if you are advising them to do it you are committing engineering
malpractice.  A lawyer that  knowingly gives blatantly bad advice to a
client can go to jail.  If you have a PE license, you may have similar
exposure.


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2001\03\23@005843 by Bill Westfield

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>> What you are doing is irresponsible at best.

Not necessarilly.  At best, what he's doing is separate "qualification
testing" than microchip does at the factory, using different criteria for
passing (or maybe not.  Who knows what testing microchip does to guarantee
20MHz performance.  The usual suspicion is that 4MHz parts come from the
same from the same fab, and simply have LESS testing, with microchip simply
testing enough "20MHz" parts to meet the perceived demand.)  Presumably the
company in question does SOME testing of their final product before
shipping, so you're not going to run into a situation where the parts flat
out refuse to work at the "overclocked" speed.  For all we know, the testing
of the finished device is more complete than microchip runs on the 20MHz
parts - how much testing can you do on a non-flash part to guarantee
operating speed, anyway?  If the equipment manufacturer guarantees the
product to operate, what does it matter what the chip vendor says about the
operating conditions?  (excepting equipment in life-critical applications,
which you can't do without special permission even with underrated parts...)

I'm not saying that it's a good idea, and I'm not saying that I'd do it, but
I think I believe that it is possible to overclock in a manner "responsible
enough for all practical purposes..."

BillW

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2001\03\23@035219 by Vasile Surducan

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Well done guys, after you killed Shane, now you want to sing on his
tomb too...
( and in your basement, in secret, you test criogenic overclocking at
100Mz on to f84...)
Maybe asking IBM or others how they overclock up to 1,2 GHz without taking
care of consequencies will change a little, your fixed ( but good ) point
of view.

don't overclock...it's out of spec
don't overclock...it's out of spec
don't overclock...it's out of spec
don't overclock...it's out of spec

but if you really want it, why not, final product is guaranteed so will
come back.
Vasile



On Thu, 22 Mar 2001, Bob Ammerman wrote:

{Quote hidden}

> {Original Message removed}

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