EDWARD,

The "Open-Drain" Scenario was just meant to be an example of a Hardware design that would give you a hard time in Software Development without knowing the schematic.

Desoldering one of the boards and drawing a full schematic is a good idea.
Try to document all type codes of the components before they are all wiped off.

BTW
Here is yet another example for your "Fire" Subroutine
Code:
Fire:
HIGH PortC.2  ' make transistor active
PAUSE 500
INPUT PortC.2 ' PortC.1 as input
PAUSE 500
RETURN