Siemens SIMATIC 500 Series Description And Operating Instructions page 15

2 General Functions 2.2 Operating mode related functions
The following functions are only available for the optical ports. Whether the functions can be activated depends on
the operating mode which has been set. Please refer to the following chapters for details.
Line monitoring with echoes
The modules enable the connected optical paths to be actively monitored for interruptions in the fiber line by means
of the functions "Send echo", "Monitor echo" and "Suppress echo".
Send echo
A frame which is received by a module via any port is transmitted to all other ports. If the receiving port is an optical
port, the module sends the frame back to the corresponding optical sender.
Monitor echo
If a module sends a frame - no echo! – to an optical port, the module expects to receive an echo. If the echo is not
received after a predefined time, an echo monitoring error is indicated by a red LED belonging to the port.
Suppress echo
The relevant receiver is separated from the other ports from the moment a frame is sent until the echo has been
received correctly.
Segmentation
If an echo monitoring error or a frame falsification arises at an optical port, the module assumes that the line is faulty
and blocks this port for user data. The connected field bus partial network is then segmented (cut off). This segmen-
tation causes the module at the other end of the optical fiber to be segmented as well.
Both modules connected to the segmented field bus partial network send test frames to the segmented ports. These
test frames – which are to be received regularly – can be used by both modules to check the status of the field bus
partial network.
The segmentation is automatically lifted as soon as the test frames indicate to both modules that the segmented field
bus partial network is no longer disturbed.
If all active bus subscribers are deactivated in a previously active network, the modules are segmented cyclically in
order to check the fiber links to the neighboring modules. If there is no frame traffic, but the fiber links are intact,
the port LEDs of the optical ports flash yellow cyclically.
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