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'TTL clock question (and crystals)'
1998\01\11@224826 by Charles Laforge

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Hi

When using a TTL clock oscillator, what option should I use to program
the device?  XT?  HS?  I couldn't find this mentioned anywhere.

Also, does anyone have any prefered Crystals they like to use?
Reliability rate and stuff like that.  I don't know what to look for in
a crystal.  What do you do... look for the cheapest???

Charles

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1998\01\12@015613 by Harold M Hallikainen

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On Sun, 11 Jan 1998 19:48:17 PST Charles Laforge <spam_OUTcjoachimTakeThisOuTspamHOTMAIL.COM>
writes:

>Also, does anyone have any prefered Crystals they like to use?
>Reliability rate and stuff like that.  I don't know what to look for
>in
>a crystal.  What do you do... look for the cheapest???


       I've had great luck with 16 MHz ceramic resonators with built-in
capacitors from muRata.  I'm using them on a 16c74a.  We've probably
shipped a thousand units now with absolutely no problem.  I did find that
the resonators from Integrity Technology and ECS do not seem to work
reliably with the PIC (at least the ones with internal capacitors).  They
may work fine at lower frequencies or with other chips.  The muRata is
something like a 50 cent part and looks like a 3 lead resistor SIP.
Ground the center pin, connect the two other pins to the PIC and you're
running!

Harold

1998\01\12@102200 by John Payson

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>         I've had great luck with 16 MHz ceramic resonators with built-in
> capacitors from muRata.  I'm using them on a 16c74a.  We've probably
> shipped a thousand units now with absolutely no problem.  I did find that
> the resonators from Integrity Technology and ECS do not seem to work
> reliably with the PIC (at least the ones with internal capacitors).  They
> may work fine at lower frequencies or with other chips.

I've found the DigiKey resonators (ECS I think) to work great at 4MHz and
10MHz and not at all at 20MHz.  Haven't tried other frequencies; any idea
what the problem at 20MHz is?

1998\01\12@115440 by Todd Peterson

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>I've found the DigiKey resonators (ECS I think) to work great at 4MHz and
>10MHz and not at all at 20MHz.  Haven't tried other frequencies; any idea
>what the problem at 20MHz is?

We've tested this extensively about 6 months ago.  It seems as though the
Murata brand are the only type which will work with PICs at 20MHz.  The
others are not efficient enough to resonate with the circuitry inside a PIC,
even on HS.   Last I checked the other companies were working on a version
to work with the PIC; anyone heard any new news on this?

-Todd Peterson
E-Lab Digital Engineering, Inc.  (816) 257-9954

EDE300 IC -  PC Interface IC
EDE700 IC -  Serial to LCD Interface IC
EDE1200 IC - Stepper Motor Controller
EDE1400 IC - Serial to Parallel-Printer IC

http://www.elabinc.com

1998\01\12@121145 by myke predko

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face
>>         I've had great luck with 16 MHz ceramic resonators with built-in
>> capacitors from muRata.  I'm using them on a 16c74a.  We've probably
>> shipped a thousand units now with absolutely no problem.  I did find that
>> the resonators from Integrity Technology and ECS do not seem to work
>> reliably with the PIC (at least the ones with internal capacitors).  They
>> may work fine at lower frequencies or with other chips.
>
>I've found the DigiKey resonators (ECS I think) to work great at 4MHz and
>10MHz and not at all at 20MHz.  Haven't tried other frequencies; any idea
>what the problem at 20MHz is?

The problem with the "A" parts (ie 73A) is that the ECS resonators with
built in caps have too much internal capacitance (30 pF+).  I have been able
to get 20 MHz ECS CAPLESS resonators to work with a 73A running up to 20 MHz.

myke

"I was well aware that the processes of puberty are often fatal to psychic
power."
- Sir Arthur Conan Doyle

1998\01\12@121152 by Harold Hallikainen

picon face
>I've found the DigiKey resonators (ECS I think) to work great at 4MHz
>and
>10MHz and not at all at 20MHz.  Haven't tried other frequencies; any
>idea
>what the problem at 20MHz is?
>


       After finding my prototypes worked with the ECS resonator at 16
MHz, we went ahead and built 100 units using them.  They all either
didn't work at all or failed under elevated temperature.  I talked with
ECS, Integrity and muRata.  Both ECS and Integrity said that the
resonators worked in their sample circuit (using a cmos inverter) and if
they didn't work in my circuit (the 16c74a) the problem was my circuit.
In talking with muRata, I found that they work with the semiconductor
companies, getting samples of the chips and modifying the resonator
design as necessary for reliable operation with that chip.  When I spoke
with them a little over a year ago, they had not characterized a device
for use with Microchip as that time.  However, I found that the existing
devices seem to work fine (we've probably shipped about 1,000 systems
with their resonators on the 16c74a).
       As to "what the problem is", I imagine there is not enough gain
in the 16c74a to reliably get over the losses in the other resonators.  I
talked with Microchip about getting plots of input Z, output Z, gain and
phase vs frequency for the oscillator.  They did not have that data and
said it would be expensive to produce.  So, we end up with resonators
that don't work and I wasn't able to give the resonator companies specs
on what WOULD make it work, since Microchip had not completed the tests.
Microchip did correctly point out that they provide about as much
oscillator data as other microcontroller manufacturers (very little).
       So...  we ended up using muRata.

Harold

1998\01\12@122537 by Matt Bonner

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face
Charles Laforge wrote:
> When using a TTL clock oscillator, what option should I use to program
> the device?  XT?  HS?  I couldn't find this mentioned anywhere.

If you're using an external oscillator, you can program the device using
any mode since the fuse just sets the value of the crystal feedback
resistor (which is not being used).  For lower power, use LP.

--Matt

1998\01\12@161302 by Herbert Graf
picon face
> -----Original Message-----
> From: pic microcontroller discussion list
> [.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On Behalf Of Matt Bonner
> Sent: Monday, January 12, 1998 12:25
> To: PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject: Re: TTL clock question (and crystals)
>
>
> Charles Laforge wrote:
> > When using a TTL clock oscillator, what option should I use to program
> > the device?  XT?  HS?  I couldn't find this mentioned anywhere.
>
> If you're using an external oscillator, you can program the device using
> any mode since the fuse just sets the value of the crystal feedback
> resistor (which is not being used).  For lower power, use LP.

       I believe you have to change that from "any mode" to "any mode but RC".
I
don't think you can use an external oscillator with the fuse set to RC. TTYL

1998\01\12@165138 by Matt Bonner

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face
Herbert Graf wrote:
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [.....PICLISTKILLspamspam.....MITVMA.MIT.EDU]On Behalf Of Matt Bonner
> > Sent: Monday, January 12, 1998 12:25
> > To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> > Subject: Re: TTL clock question (and crystals)
> >
> >
> > Charles Laforge wrote:
> > > When using a TTL clock oscillator, what option should I use to program
> > > the device?  XT?  HS?  I couldn't find this mentioned anywhere.
> >
> > If you're using an external oscillator, you can program the device using
> > any mode since the fuse just sets the value of the crystal feedback
> > resistor (which is not being used).  For lower power, use LP.
>
>         I believe you have to change that from "any mode" to "any mode but
RC". I
> don't think you can use an external oscillator with the fuse set to RC. TTYL

You're right.  I keep forgetting about the RC mode because I can't use
it at the temperature extremes my product has to operate in.
--Matt

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