VEXcode V5 has a 3-wire Digital In device and a 3-wire Digital Out device.
What Is Digital In/Digital Out
Digital In/Digital Out refers to a digital input signal being received into the 3-wire ports of the V5 Robot Brain and a digital output signal being sent out from a 3-wire port of a V5 Robot Brain.
Digital Input: A digital input detects if a voltage is above/below of a specific threshold. If the voltage is higher, the V5 Robot Brain will detect the digital input as high. If the voltage is lower, the V5 Robot Brain will detect the digital input as low.
Digital Output: A digital output allows you to control a voltage with the V5 Brain. If the V5 Brain instructs the output to be high, the output will produce a 5 volt voltage. If the V5 Brain instructs the output to be low, it outputs no voltage.
Using Digital In
The VEXcode V5 Digital In device is intended for use by advanced users.
One use of the Digital In device would be for Digital In/Digital Out communication between two V5 Robot Brains.
The Digital In device could also be used for Digital In/Digital Out communication with an aftermarket microprocessor.
All of the digital sensors which are available for the VEX V5 system have a sensor device provided in the VEXcode V5 device configuration window. These sensors should use their specific VEXcode V5 sensor device and not the Digital In device.
Using Digital Out
The VEXcode V5 Digital In device is intended for providing control of a 5 volt logic level to external devices or supplying a communication signal out for Digital In/Digital Out communication.
The VEXcode V5 Digital Out device can be used to activate a pneumatic solenoid valve which will control the airflow for a VEX pneumatic system.
For more information about Configuring a Digital In and Digital Out device in VEXcode V5, view this article from the VEX Library.