Siemens SIMATIC NET PROFIBUS Owner's Manual page 358

Infrared Link Modul (ILM)
6ZB530–3AC30–0BA1
5.2.2 Point–to–Multipoint Link
Instead of the multiple use of point-to-point links, the point-to-multipoint link can also be used. Optical isolation
between the infrared transmission links is not necessary. If the configuration is correct, only one slave node
responds to the request of a master node and because there is only one PROFIBUS ILM on the master
network segment, there are no synchronization problems with the response.
The advantage of this arrangement is that with n slave segments only n)1 PROFIBUS ILMs are required.
The disadvantages of this arrangement are not only the restrictions in the arrangement of the slave PROFIBUS
ILMs to a solid angle of )/–10 degrees but also from the point of view of the master PROFIBUS ILM the
poorer monitoring of the link because the acknowledgment pulse mechanism cannot be used (see Section
5.6.2).
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