Siemens SIMATIC NET 12M Operating Instructions Manual page 18

Installation
2.2 Mounting and attaching the bus cable(s)
Note
The same wires (green or red) must always be connected to the same terminal A or B in all
bus terminals (and with all bus connectors) and be uniform throughout the segment.
Note
The 12M bus terminal may only be plugged into a PROFIBUS interface when the power is
off.
The following scheme is recommended for a PROFIBUS LAN:
● Connector A: green wire
● Connector B: red wire
18
Operating Instructions, 07/2013, C79000-G8976-C333-01
12M bus terminal