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PICList Thread
'Crystal PIC'
1998\12\14@062855 by Goovaerts

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How do I connect my crystal (20 MHz) to a PIC16C63 ? I also have two
capacitors of
22 pF. How do I connect everything to the PIC and haven't I forgotten any
components ??

Glenn !!

1998\12\14@094054 by Stefan Sczekalla-Waldschmidt

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Hi Glenn,

Goovaerts wrote:
>
> How do I connect my crystal (20 MHz) to a PIC16C63 ? I also have two
> capacitors of
> 22 pF. How do I connect everything to the PIC and haven't I forgotten any
> components ??
>
> Glenn !!

Xtal as close as possible to the Pic, capacitors form each pin of the
xtal to gnd.
thc capacitors also close to pic and xtal.

By following th PIC-List I saw/read many questions you wrote. Your
questions give me
the Idea, that you eventually don4t now about the datasheet4s available
from the
microchip web-site. They have also a lot of application-notes where you
may wish to
have a look at. There you4ll find a lot of comprehensive stuff.

Kind regards

       Stefan

1998\12\15@170615 by Marc

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> Xtal as close as possible to the Pic, capacitors form each pin of the
> xtal to gnd.
> thc capacitors also close to pic and xtal.

It might be worth mentioning that it's a good idea to run the caps' ground
to the PIC ground directly, with no other connections inbetween (other
chips' ground pins). Do not route them to your power supply or any other
ground, use the PIC ground pin!

1998\12\15@172805 by dave vanhorn

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>It might be worth mentioning that it's a good idea to run the caps' ground
>to the PIC ground directly, with no other connections inbetween (other
>chips' ground pins). Do not route them to your power supply or any other
>ground, use the PIC ground pin!


It's not just a good idea, it's the LAW.
If you want to pass part 15, and have a reliable osc.


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1998\12\16@173559 by Russell McMahon

picon face
On the subject of crystal connection to a PIC, if you're really
serious, when doing a PCB layout, consider minimising the area of the
loop formed by the circuit from the PIC pins to the crystal and
capacitors. This area forms an RF radiator and the larger the area
the greater the radiation (its more complex than that of course but
that's a good guide). Turning the crystal at 90 degrees physically to
the PIC may be an effective way of doing this.

   Russell McMahon
From: Marc <spam_OUTmarcTakeThisOuTspamAARGH.FRANKEN.DE>

>> Xtal as close as possible to the Pic, capacitors form each pin of
the
>> xtal to gnd the capacitors also close to pic and xtal.
>
>It might be worth mentioning that it's a good idea to run the caps'
ground
>to the PIC ground directly, with no other connections inbetween
(other
>chips' ground pins). Do not route them to your power supply or any
other
>ground, use the PIC ground pin!
>

1998\12\17@073923 by wwl

picon face
On Thu, 17 Dec 1998 09:16:29 +1300, you wrote:

>On the subject of crystal connection to a PIC, if you're really
>serious, when doing a PCB layout, consider minimising the area of the
>loop formed by the circuit from the PIC pins to the crystal and
>capacitors. This area forms an RF radiator and the larger the area
>the greater the radiation (its more complex than that of course but
>that's a good guide). Turning the crystal at 90 degrees physically to
>the PIC may be an effective way of doing this.
>
It's a shame they put the power pins the wrong way round on the 18 pin
devices, isn't it?

1998\12\17@090141 by paulb

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Mike Harrison wrote:

> It's a shame they put the power pins the wrong way round on the 18 pin
> devices, isn't it?

 It's irrelevant.  The caps are most conveniently returned to pin 14;
Vdd which is adjacent to pin 15; Osc2.  You couldn't have it any more
opportune.  The term "CMOS" refers to "Complementary MOS" which means
that either Vss or Vdd can be used as ground; it's as simple as that.

 It's probably a very good idea to lead traces from Vss and Vdd
underneath the chip footprint to the pin 1/ 18 end of the chip where a
decoupling capacitor can be fitted.  Even better, put the decoupling cap
and the crystal loading caps on the underneath of the PCB, within the
footprint, as SMDs.

Marc wrote:
> It might be worth mentioning that it's a good idea to run the caps'
> ground to the PIC ground directly, with no other connections inbetween
> (other chips' ground pins).

 Doing so would of course "tap" such other connections into the crystal
resonant circuit.

> Do not route them to your power supply or any other ground, use the
> PIC ground pin!

 I doubt in saying this, Mark was precluding use of the Vdd pin, rather
decrying long lanky traces.

 The suggestion to orient the crystal perpendicular to the PIC
certainly has merit; the two loading caps can be mounted together beside
the crystal and their common taken directly to Vdd.
--
 Cheers,
       Paul B.

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