Gary Crowell wrote:
> If I understand your description correctly, doesn't this mean that the
> return signal paths of all the PIC signals are confined to that single
> pwr/gnd connection point?

Yes, for those signals that go external to the local area of the PIC.  The
crystal lines do not, for example.

This means that the high frequency loop currents caused output signals bein=
g
driven by the PIC do go accross the wide ground plane.  However, note that
they would in a single ground plane scheme too.  The high frequency current
source in the PIC between the power and ground leads is generally much
bigger, and its current will be contained locally and not "contaminate" the
global ground plane.

This kind of board design is all about visualizing the high frequency
current loops, where they are, and what effect they will have.  We are used
to thinking about power current flowing into the Vdd pin and out the Vss pi=
n
of a PIC.  This is true for the DC component, but if you only look at the
high frequency components the PIC actually becomes a current source, as do
other digital ICs.  Letting this current run accross the global ground plan=
e
for a bit it just another way of describing a center fed patch antenna.

--=20
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