Connections to 16 of the LabJack’s 20 digital I/O are made at the DB25 connector, and are referred to as D0-D15.
These 16 lines have no overvoltage/short-circuit protection, and can sink or source up to 25 mA each (total sink or source current of 200 mA max for all 16).
This allows the D pins to be used to directly control some relays.
All digital I/O are CMOS output and TTL input except for D13-D15,
which are Schmitt trigger input. Each D pin has a 1 MΩ resistor connected to ground.