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'[PIC] XTAL question'
2006\03\15@132439 by pic

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part 1 171 bytes content-type:text/plain; (decoded 7bit)

When I need to connect a crystal to a pic, can I use an oscillator
that has 4 connection? and what does it mean RoHS compilant?
Simon.

part 2 9555 bytes content-type:image/jpeg; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2006\03\15@133201 by Michael Rigby-Jones

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Yes, you can used a "canned" oscillator, you just need to set the PIC's configuration fuses appropriately.  Beware that these canned oscillators take considerably more current than using a normal 2 pin crystal with the PIC's built in oscillator circuit.

RoHS is a relatively recent set of standards controlling the amount of toxic materials in electronic equipment.  See http://www.netregs.gov.uk/netregs/legislation/380525/477158/?lang=_e

Regards

Mike



>{Original Message removed}

2006\03\15@144137 by Chris Levin

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pic wrote:

>When I need to connect a crystal to a pic, can I use an oscillator
>that has 4 connection? and what does it mean RoHS compilant?
>Simon.
>
>
> ------------------------------------------------------------------------
>

As mentioned, you can use these with a PIC. Also, in case you don't have
or know the pin out here it is:

Pin 1 is the pin with the DOT on it. It is a "no connection" pin.
Pin 2 is the lower right pin. It is the ground connection.
Pin 3 is the upper right pin. It is the oscillator out pin. Connect this
to the  PIC's OSC pin.
Pin 4 is the upper left pin. It connects to +5 volts.

Hopefully this diagram will come through ok.

    +---------------+
+5V | 4           3 | Output
    |               |
N/C | 1           2 | Ground
    +---------------+

I like using these on breadboards when prototyping. It makes it easy to
plug in different frequencies  while testing and the one  wire
connection to the PIC is easy to manage. I will also use them
occasionally in a final circuit if power is not an issue.

As mentioned these use lots more power than a crystal AND if you put
the  PIC in sleep mode, they continue to run.

-Chris

2006\03\15@171657 by pic

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Hi, thank you for replying,

Do I consider it to be an external oscillator, as opposed to HS
(configuration bits) i.e. this is not "crystal" mode, is it?

Also, would it work with 3.3v as well, and does anyone know
if I can connect it to 2 devices at once, i.e. I need to connect
it to pic18f4620 and to enc28J60 at the same time?
Simon.

2006\03\15@180319 by alan smith

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and along the same thread...sorta...but not really.
 
 Do the resonators require excitation like a crystal does?  Case being, wanting to put the chip to sleep, conserving power so a crystal would stop oscillating...thus not drawing power.  A resonator goes across the same leads, and I would assume that it needs excittion as well to work...so resonators being smaller and cheaper could be a better choice.  If thats how they work.
 
 except, once a time ago, we had a discussion on using a resonator for doing serial comms and i thought it was decided that resonators do not have the stabilty for reliable baud rate generation.?

               
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2006\03\15@202927 by Russell McMahon

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>  except, once a time ago, we had a discussion on using a resonator
> for doing serial comms and i thought it was decided that resonators
> do not have the stabilty for reliable baud rate generation.?

Any normal resonators are stable enough for async coms.
You need *about* 50/total_bits %  stability.

So for 1 + 8 + 1 = 10 bits you need 10/50 = 2%.
Any resonator that won't do better than that should be quickly buried
at the nearest cross roads (stake optional).



       RM


Could a vegetarian vampire be killed with a beef-steak?


2006\03\15@202930 by Russell McMahon

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> ... and what does it mean RoHS compilant?

Suggestion: ALWAYS ask Google questions like that before asking the
list.
It makes you look smarter, smarter and feel smarter.

ROHS = Restriction Of Hazardous Substances.

Google knows
(It also means "harder to solder with 'real' solder" :-) ).


       RM

2006\03\15@211116 by Chris Levin

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pic wrote:

>Hi, thank you for replying,
>
>Do I consider it to be an external oscillator, as opposed to HS
>(configuration bits) i.e. this is not "crystal" mode, is it?
>
>Also, would it work with 3.3v as well, and does anyone know
>if I can connect it to 2 devices at once, i.e. I need to connect
>it to pic18f4620 and to enc28J60 at the same time?
>Simon.
>  
>
Hi,

Checking my notes I see that the canned oscillators work for me using
all PIC oscillator modes so I generally follow the data sheet rules and
use LP for 4 MHz or less and XT for all others.
You can drive multiple sources with one of these. I've driven 2 PICs
without any issues. I don't know if they run on 3.3 volts but you can
try it and it will not hurt anything. Check the output with an
oscilloscope and if the waveform looks ok then you should be good to go.

-Chris

2006\03\15@211516 by Chris Levin

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alan smith wrote:

>and along the same thread...sorta...but not really.
>  
>  Do the resonators require excitation like a crystal does?  Case being, wanting to put the chip to sleep, conserving power so a crystal would stop oscillating...thus not drawing power.  A resonator goes across the same leads, and I would assume that it needs excittion as well to work...so resonators being smaller and cheaper could be a better choice.  If thats how they work.
>  
>  except, once a time ago, we had a discussion on using a resonator for doing serial comms and i thought it was decided that resonators do not have the stabilty for reliable baud rate generation.?
>
>                
>---------------------------------
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> Use Photomail to share photos without annoying attachments.
>  
>
Hi,

The canned oscillators are totally self contained. If you apply power
then you get a waveform from the output pin. I've even used them as
simple morse code transmitters by simply attaching a short wire to the
output and turning them on and off via a control signal. Of course, this
means that even when your chip is sleeping the oscillator is still
oscillating and consuming power.

Also, they are stable enough for serial comms. My "standard" baud rate
for serial output when debugging or building something that needs serial
communications is 9600 baud. I've never had a problem talking between a
PIC and PC or a PIC and PIC.

-Chris

2006\03\16@052229 by Michael Rigby-Jones

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>-----Original Message-----
>From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]
>Sent: 15 March 2006 22:17
>To: Microcontroller discussion list - Public.
>Subject: Re: [PIC] XTAL question
>
>
>Hi, thank you for replying,
>
>Do I consider it to be an external oscillator, as opposed to
>HS (configuration bits) i.e. this is not "crystal" mode, is it?
>
>Also, would it work with 3.3v as well, and does anyone know
>if I can connect it to 2 devices at once, i.e. I need to
>connect it to pic18f4620 and to enc28J60 at the same time? Simon.

You need to check the datasheet, you can get canned oscilliators that run from 3.3volts.  The outputs from these are reasonably well buffered so you should be able to drive two devices.  Keep the connection between the output and the two devices as short as possible, and don't forget a decoupling capacitor accross the oscillator supply rails.

You should choose the PIC option for an external oscillator, if it exists, which can also free up another pin.  Many of the older PIC's did not have this option, so you had to use the HS or XT option and ignore the other pin.

Regards

Mike

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2006\03\16@072401 by olin piclist

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Chris Levin wrote:
> I don't know if they run on 3.3 volts but you can
> try it and it will not hurt anything. Check the output with an
> oscilloscope and if the waveform looks ok then you should be good to go.

For that unit, at that temperature, at that phase of the moon.  If it's not
specified in the data sheet, relying on it is a bad idea, whether it works
in one instance or not.


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