Siemens SIMATIC NET OLM12M Description And Operating Manual page 56

6ZB5530–3AB00–0BA0/01
4.3 Ring Topology (Single-Fiber Ring)
The main application of the optical single-fiber ring is to network passive nodes.
The SIMATIC NET optical link modules are connected together by FO cables with a single fiber.
In the optical 'single-fiber ring', a distinction must be made between an 'Active Node' and at least
one 'Passive Node'.
The optical channel of the module operating as the 'Active Node' must be set to the 'Ring (active)'
mode and functions as the ring coordinator. Both active and passive nodes can be connected only
to the SIMATIC NET optical link module belonging to the 'Active Node'.
Monitoring or echo monitoring errors in the optical single-fiber ring are only indicated by the system
LED and the signaling contact of this SIMATIC NET optical link module.
Please remember that only one optical channel can be set to the 'Ring (active)' mode
per optical single-fiber ring.
Mode settings: A=Ring (active), P=Ring (passive), I=Inactive
Figure 4: Optical Single-Fiber Ring with SIMATIC NET Optical Link Modules
The optical channels that act as 'Passive Nodes' must be set to the 'Ring (passive)' mode. Only
passive nodes (slaves) can be connected to the SIMATIC NET optical link modules belonging to
'Passive Nodes'.
SIMATIC NET OLM12M optical link modules in the 'Ring (passive)'mode can be cascaded in the
single-fiber ring.
Up to 55 SIMATIC NET OLM12M optical link modules can be operated in a single-fiber ring.
Individual DTEs or a complete PROFIBUS segment with a maximum of 31 nodes can be connected
to each SIMATIC NET OLM12M optical link module via the electrical channel with its RS 485
interface.
To avoid noise being coupled into the single-fiber ring via channel 1, it is advisable to connect the
passive nodes to channel 1 over the shortest possible distance (ideal situation: one node via bus
connector and short LAN cable section to OLM12M channel 1).
Coupling in noise can lead to a loss of messages in the single-fiber ring.
In an optical link module or a passive node with an optical interface drops out or if there is a break
on the FO cable, the entire single-fiber ring breaks down.
Unconnected optical channels must be set to the 'Inactive' mode.
Copyright Siemens AG 1997
7
SIMATIC NET OLM12M