Siemens 500 NIM - Manual (Page 53)

Installation 3-18 SIMATIC TIWAY I Series 500 NIM User Manual
3.7 Connecting the Network Cables
Network cabling should already be in place before NIM installation is
begun. If you need information concerning network cabling, see the
SIMATIC TIWAY I Systems Manual (TIWAY–8101).
There are two communication ports on the Series 500 NIM, one on the top of
the module (Port A) and one on the bottom (Port B). Depending on the
model you have, these ports accept either an RS-232-C or Local Line
connection. Plug the network interface cables into one of these two ports.
For media redundancy, both ports are used.