Basic electronic stuff

[Posea, David G, SITS]

Some of you may remember I am working on a boost retard device based on a
PIC controller for the Ford DIS ignition. I found a good trigger circuit
that goes to logic 1 when the EEC grounds the trigger wire for a coil. My
question is how do I handle the "open" state on the output side of the
controller? This is the negative side of the coil. If I attach it to an
output pin out on the PIC, won't I be feeding Vbat (+13V)into that same pin
from the coil side? Can I just set the output pin high until time to fire
the coil, then ground it? Or do I need to use the output as the input to a
transistor to switch the negative coil wire to ground?  Something seems
wrong here, and I'm not sure what it is. I'm a programmer by trade with
limited electronic knowlegde. Thanks in advance for any help.

David Posea