[Al Skierkiewicz]

This is very common practice for interfacing unknown inputs to a complex circuit for digital or status inputs. The input circuit is designed to look for a closing contact to ground or common. The input is designed so that no voltage need be applied from the external circuitry and therefore no crosstalk or voltage interaction that could cause the power supply of the robot controller to induce misc data in any input or affect the operation of the controller. For this reason, applying any voltage, even if it is 5 volts or less, runs the risk of causing errors or damage to the controller or it's power supply.