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'[PIC]: Will an unprogrammed chip oscillate?'
2002\06\13@095736 by Lawrence Lile

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Will a fresh, unprogrammed chip oscillate if it is powered up?

I have a circuit with ICSP that seems to have two problems - first I can't
get my programmer to successfully program it, and second, I don't find any
signal on the oscillator pins.

The first problem is probably going to fall after I make a shorter
programmer cable, and double check all the connections, and remove some
capacitance that might be in the MCLR line. This has deviled me before. I'll
make sure the chip really has 5V and also double check all the wiring to the
PIC.

Meanwhile, though, I expected the chip would oscillate by default, and I am
wondering if I should be seeing something on the OSC pins or not.  I am
using a 4 MHz crystal, which should require the XT oscillator option.  What
is the default oscillator fuse on a 16F73?


--Lawrence

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2002\06\13@100139 by Michael Rigby-Jones

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{Quote hidden}

Default for an unprogrammed chip is the RC oscillator I believe.

Regards

Mike

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2002\06\13@101415 by Bob Ammerman

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> Meanwhile, though, I expected the chip would oscillate by default, and I
am
> wondering if I should be seeing something on the OSC pins or not.  I am
> using a 4 MHz crystal, which should require the XT oscillator option.
What
> is the default oscillator fuse on a 16F73?
>
>
> --Lawrence
>

Almost certainly whatever you get with all 1 bits in the config word. Taking
a quick look at  P16F73.INC that would appear to be RC oscillator.

Bob Ammerman
RAm Systems

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2002\06\13@104754 by Olin Lathrop

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> Will a fresh, unprogrammed chip oscillate if it is powered up?

It should as long as you hook it up for the oscillator mode that is selected
when all config bits are 1.  On the 16F87x this is RC oscillator mode.


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2002\06\13@110447 by Lawrence Lile

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Thanks! No wonder it won't start.

A re-check of the ICSP lines showed I had some of them crossed, which
explains the failure to program.  Funny, the Microengineering labs EPIC
claims that erasing the chip is OK, and blank check is OK, even if the
target board is unplugged.  I think it is the same with a PICstart.  Too bad
there isn't a way for these programmers to say "Hey! No chip! Plug
somnething into me, dummy!"

--Lawrence

{Original Message removed}

2002\06\13@111051 by Jonathan Starr

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As an experiment I have just put a blank 16F73 into the circuit I'm working on, there was no osc with a ceramic resonator, and no osc with an RC.
So maybe they don't, I'll try and find some more different PIC's and give them a go.

Jon Starr

>>> Olin Lathrop <olin_piclistspamKILLspamEMBEDINC.COM> 13/06/2002 15:47:43 >>>
> Will a fresh, unprogrammed chip oscillate if it is powered up?

It should as long as you hook it up for the oscillator mode that is selected
when all config bits are 1.  On the 16F87x this is RC oscillator mode.


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2002\06\13@131106 by Andre Abelian

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--Lawrence,

Default configuration on blank pic is RC so without programming
it if you put RC it should oscillate.

Andre Abelian





{Original Message removed}

2002\06\13@182339 by Lawrence Lile

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After fixing a few crossed ICSP wires, the chip programs and verifies OK.

Well, the plot thickens.  I had a 4 MHz crystal and two capacitors (22 pF,
IIRC), and still could not get my PIC to oscillate.

I replaced the crystal and caps with a 4 MHZ packaged ceramic resonator with
internal caps, and the oscillator strarts fine.

So what causes one kind of crystal to not oscilate with the PIC, another to
work OK?  I've never really run into this before.

--Lawrence



{Original Message removed}

2002\06\13@183211 by Brendan Moran

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It could be that what you were using before is a parallel cut crystal, since
there is a section in the 16F87x manual stating that only series cut
crystals will operate.  I'd imagine that all the PICs are the same that way,
though I haven't checked.

At least, that's my best guess.

--Brendan

{Original Message removed}

2002\06\14@104811 by Lawrence Lile

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Series cut .. Parallel cut - How does one figure out which applies to the
crystal in question.  I just looked at EVERY crystal in Digikey, and NONE
(i.e. diddlysquat, Nada, Nichts, Nyet, Zip, Zilcho) specify whether the
crystal is parallel or serial cut.  Now there are a few that allude to
"When run in parallel mode.."  "Effective series resistance"  And one has a
whole paragraph of rubber language which basically says "Your Mileage May
Vary" when run in parallel or series mode, but none of them just come right
out and say one or the other.

I guess the correct method is to use a CRYSTAL ball.  <Groan>

--Lawrence


{Original Message removed}

2002\06\14@115231 by Olin Lathrop

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> It could be that what you were using before is a parallel cut crystal,
since
> there is a section in the 16F87x manual stating that only series cut
> crystals will operate.  I'd imagine that all the PICs are the same that
way,
> though I haven't checked.

Parallel versus series "cut" really has nothing to do with how the crystal
is cut but rather which operating mode is required to achieve the specified
frequency.  The series resonant and parallel resonant frequencies are
slightly different.


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2002\06\14@115826 by Alan B. Pearce

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>Series cut .. Parallel cut - How does one figure out which applies to the
>crystal in question.  I just looked at EVERY crystal in Digikey, and NONE

Every crystal will run in both modes, but.....
as I understand it when the crystal is ground to frequency there are tweaks
they can do to minimize the spurious responses in each mode, and what is
best for parallel mode ain't necessarily best for series mode. It also
affects things like the ESR in series mode, and similar parameters in
parallel mode that may determine if it will oscillate in that mode unless
you have a very determined oscillator circuit.

This is apart from the slightly different frequency of operation between the
two modes. For PIC use unless you are going for absolute frequency accuracy
then you will not see the difference in frequency.


>I guess the correct method is to use a CRYSTAL ball.  <Groan>

I think this comes into the "see through a glass darkly" mode.

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2002\06\14@120852 by Pic Dude

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Isn't it the other way? -- that the Microchip docs state that
a PARALLEL-cut crystal is required as a series cut may cause
incorrect timing?

Cheers,
-Neil.




{Original Message removed}

2002\06\14@122850 by Olin Lathrop

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> Series cut .. Parallel cut - How does one figure out which applies to the
> crystal in question.  I just looked at EVERY crystal in Digikey, and NONE
> (i.e. diddlysquat, Nada, Nichts, Nyet, Zip, Zilcho) specify whether the
> crystal is parallel or serial cut.

Parallel resonant crystals are specified with the capacitance value they
require to achieve the appropriate phase shift, and series resonant crystals
are not.


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2002\06\14@125003 by Anno, Jeff

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<I guess the correct method is to use a CRYSTAL ball.>

Series Cut Crystal Ball or Parallel Cut Crystal Ball?

{Original Message removed}

2002\06\14@125009 by Brendan Moran

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Quite right.  I misread that I guess

"The PIC16F87X oscillator design requires the use of a parallel
cut crystal. Use of a series cut crystal may give a
frequency out of the crystal manufacturers specifications."

Regards,

--Brendan


----- Original Message -----
From: "Pic Dude" <@spam@picdudeKILLspamspamAVN-TECH.COM>
To: <KILLspamPICLISTKILLspamspammitvma.mit.edu>
Sent: Friday, June 14, 2002 9:07 AM
Subject: Re: [PIC]: Will an unprogrammed chip oscillate?


> Isn't it the other way? -- that the Microchip docs state that
> a PARALLEL-cut crystal is required as a series cut may cause
> incorrect timing?
>
> Cheers,
> -Neil.
>
>
>
>
> {Original Message removed}

2002\06\14@125711 by Lawrence Lile

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Is Zero frequency usually considered to be outside the manufacturer's
specifications?

--Lawrence

----- Original Message -----
From: "Brendan Moran" <RemoveMEannirakTakeThisOuTspamBIGFOOT.COM>
To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Friday, June 14, 2002 11:42 AM
Subject: Re: [PIC]: Will an unprogrammed chip oscillate?


{Quote hidden}

> > {Original Message removed}

2002\06\14@130458 by adam

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Zero frequency <-> No oscillation <-> DC

If you're talking about for a PIC then DC would be the same as applying
+5V and ground to the crystal pins; this wouldn't accomplish anything.
As for other "manufactures," some devices operate at DC levels
(sometimes oscilloscopes, etc.) while other things have higher minimum
frequencies (although they can still be pretty low, i.e. 20Hz for
speakers).

Regards,
Adam Smith

> {Original Message removed}

2002\06\14@130919 by Brendan Moran

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> Is Zero frequency usually considered to be outside the manufacturer's
> specifications?

Nah, it's like a 0 ohm resistor, they make them just to show they can. ;P

--Brendan

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2002\06\14@190937 by Doug Butler

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What take real skill is to make a 0 ohm resistor to within a 5% tollerance!

Doug Butler
Sherpa Engineering


> {Original Message removed}

2002\06\15@050223 by Peter L. Peres

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On Fri, 14 Jun 2002, Lawrence Lile wrote:

>Series cut .. Parallel cut - How does one figure out which applies to the
>crystal in question.  I just looked at EVERY crystal in Digikey, and NONE
>(i.e. diddlysquat, Nada, Nichts, Nyet, Zip, Zilcho) specify whether the
>crystal is parallel or serial cut.  Now there are a few that allude to
>"When run in parallel mode.."  "Effective series resistance"  And one has a
>whole paragraph of rubber language which basically says "Your Mileage May
>Vary" when run in parallel or series mode, but none of them just come right
>out and say one or the other.
>
>I guess the correct method is to use a CRYSTAL ball.  <Groan>

Last time I checked Mouser specified both cut and required capacitance.

The correct method to determine crystal cut is a spectrum analyzer with
tracking generator (or a noise box) which will tell you what you want to
know immediately. You can substitute a VXO for the specan using the same
crystal (buy two) and a RF signal meter. When you use the VXO the second
crystal will be between it and the signal meter. You will have one peak
and one trough. The peak is the serial f. and the trough the parallel f.
Make sure that the reactive crystal load does not pull the VXO (use a
buffer). A counter will tell you exactly where you are. Note that you are
doing exactly what the specan is doing. Some grid dip meters will work as
VXO if you fit a crystal. Mine does not ...

hope this helps,

Peter

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2002\06\15@062618 by Peter L. Peres

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On Fri, 14 Jun 2002, Doug Butler wrote:

>What take real skill is to make a 0 ohm resistor to within a 5% tollerance!

<g>! Actually an opamp wired as a negative resistor and near zero gain
should do it.

Peter

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2002\06\15@080309 by Bob Ammerman

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----- Original Message -----
From: "Peter L. Peres" <RemoveMEplpspam_OUTspamKILLspamACTCOM.CO.IL>
To: <RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU>
Sent: Saturday, June 15, 2002 4:48 AM
Subject: Re: [PIC]: Will an unprogrammed chip oscillate?


> On Fri, 14 Jun 2002, Doug Butler wrote:
>
> >What take real skill is to make a 0 ohm resistor to within a 5%
tollerance!
>
> <g>! Actually an opamp wired as a negative resistor and near zero gain
> should do it.
>
> Peter
>

No it won't.... 5% of 0 ohms is 0 ohms. So you'd need your circuit tuned to
_exactly_ zero ohms, with _no_ tolerance. This isn't going to happen in the
real world!

Bob Ammerman
RAm Systems

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2002\06\15@102833 by Peter L. Peres

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On Sat, 15 Jun 2002, Bob Ammerman wrote:

>----- Original Message -----
>From: "Peter L. Peres" <RemoveMEplpKILLspamspamACTCOM.CO.IL>
>To: <PICLISTSTOPspamspamspam_OUTMITVMA.MIT.EDU>
>Sent: Saturday, June 15, 2002 4:48 AM
>Subject: Re: [PIC]: Will an unprogrammed chip oscillate?
>
>
>> On Fri, 14 Jun 2002, Doug Butler wrote:
>>
>> >What take real skill is to make a 0 ohm resistor to within a 5%
>tollerance!
>>
>> <g>! Actually an opamp wired as a negative resistor and near zero gain
>> should do it.
>>
>> Peter
>>
>
>No it won't.... 5% of 0 ohms is 0 ohms. So you'd need your circuit tuned to
>_exactly_ zero ohms, with _no_ tolerance. This isn't going to happen in
the
>real world!

<g> Caught me there !

Peter

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