The C5 connector has 5 digital inputs and 3 digital outputs. To these signals is added a differential analog input. All the digital inputs are optically isolated and all have in common a pole (DGT-IN-RTN) which acts as a return; normally is protected by grounding connection. Even for the digital outputs one of the poles is in common for all (see figure on the C5 connector).
Digital Input schematics
Digital Output Schematics
The servo amplifier supplies 3 programmable digital outputs. All outputs are protected against overvoltage and overcurrent.
A dedicated output, called relay Ok, provides a clean contact. In the start sequences you have to take account of the Relay OK contact.
After the auxiliary power supply +24 V to pin C1/1-2 is provided, the servo amplifier makes a check, if there aren't abnormalities the C5/11-12 Relay OK contact is closed allowing the system controller to provide the main power on C4/1-2-3.