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.