Pins 2 through 9 are output only pins dedicated to providing step and direction signals.
Pins 1, 14, 16, and 17 are output pins for general purpose usage.
Pins 10, 11, 12, 13, and 15 are general purpose inputs. Typically PMDX users will
assign pin 10 as the Emergency Stop input, but this is not mandatory.
You can assign multiple functions to a single input pin provided your machine
is configured accordingly. For example you could have three normally closed
switches wired in series and arranged to trip when X, Y, and Z exceed the
positive travel limits. To configure Mach4 to work with this you would fill in
the same signal assignments on the row in the Input Signals chart for
Motor 0 ++, Motor 1 ++, and Motor 2 ++.