6 monitoring the optical link, 1 monitoring the optical receive activity – Siemens SIMATIC NET PROFIBUS User Manual

Page 361

Infrared Link Modul (ILM)

6ZB5530–3AC30–0BA1



by Siemens

5.6

Monitoring the Optical Link

The PROFIBUS ILM has two mechanisms with which it monitors problems on the optical link.

– monitoring of the optical receive activity

– monitoring of the optical link with an acknowledgment pulse

5.6.1

Monitoring the Optical Receive Activity

With the yellow “RX” LED, the PROFIBUS ILM indicates the reception of data via the optical channel of the
PROFIBUS ILM. The pulse for the LED is extended to approximately 300 ms so that it is possible to recognize
data reception even when small amounts of data are received.

Apart from the optical display using the “RX” LED, the PROFIBUS ILM also has integrated monitoring logic that
triggers the signaling contact when problems occur receiving data on the optical channel provided the user
configures this function with a switch. Problems in reception on the optical channel occur when there has been
no change in the status of the optical receive channel for a period of approximately 300 ms, in other words
when no message was received within 300 ms or a received message takes longer than 300 ms.

Note

The “activate signaling contact if problems occur in reception” configuration should not be set on the
PROFIBUS ILM in the master subnet if its partner ILM only has one slave node that is not addressed during
this time.

5.6.2

Monitoring the Optical Link with an Acknowledgment Pulse

During configuration, the user can activate a mechanism so that an acknowledgment pulse is expected from
the receiving station after data have been sent. This acknowledgment must be received within the time set as
the interval between sending and transmitting on PROFIBUS (11 bit times). This acknowledgment pulse is not
passed on to the electrical channels of the sending or receiving PROFIBUS ILM but is restricted exclusively to
the optical transmission link.

Note

The “monitor link with acknowledgment pulse” configuration must be activated on both PROFIBUS ILMs of a
point-to-point link.