The parallel breakout board allows for 4 input connections. Each input connection can have an unlimited number of switches, but if you need to separate the switch circuit for, say, all of the home switches, you can use another input pin. There is no need to add another breakout board to add more switches unless you need to use the input pins for totally unique conditions that may or may not be related to CNC functions.
To Clarify: I need to set up 3 home switches which can double for limits (that's 3 pins.). Another pin for a probe. That's 4 pins used. Now I need to set up the other limit and E-stop switches. No pins left, how do I do that? Can a ground pin be doubled up on?
Plus, I have a SuperPID. Another pin?
You can put all of your limit switches (including the E-stop which serves the same purpose as the limit switches) and home switches on a single pin. When homing, mach3 will move the axis it wants to home, hit the switch, pull away from the switch, then move the next axis and repeat the steps for the next two axes.
The probe is on the 2nd pin. The SuperPID is on the 3rd pin and now you have another pin remaining.
The GND terminal can be doubled up.
how about a diagram to reference showing the pin-out to use
Here is the diagram for the parallel breakout board (pins 10 through 13 are used for input):
The circuit is from the GND to the input
Here is the diagram for the Mach3 USB board (pins I1 through I4 are used for input):
The circuit is from the V- to the input pin