Siemens SIMATIC NET PROFIBUS - Manual (Page 41)

Topologies of SIMATIC NET PROFIBUS Networks
2-15
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Infrared
link
0.5 to 15 m
PROFIBUS
master network segment PROFIBUS
slave network segment
ILM ILM
Master
S7-400
Master OP 25
Master
PG/PC/OP Slave
ET 200M
Slave
ET 200S
Terminating resistor activated
А
А
А
А
2 LAN cable for PROFIBUS
2
2
2
2
2
À
Figure 2-9 Point-to-Point Link with Two PROFIBUS ILMs
Figure 2-9 illustrates the typical structure of a PROFIBUS network with master and
slave nodes and an infrared link with two PROFIBUS ILMs. The infrared link is
implemented as a point-to-point link between the two PROFIBUS ILMs. The two
PROFIBUS ILMs replace a cable connection between the two network segments.
Remember that only slave nodes are permitted in the slave network segment.
Point-to-Multipoint Link
Several ILMs are positioned opposite to a single ILM so that several ILMs are in
the infrared light cone of another ILM. Only the ILMs positioned opposite each
other can exchange data. A data exchange between adjacent ILMs is only possible
by using a surface that reflects infrared light. If you consider this option, remember
that the length of the link is the path from the ILM to the reflector and from the
reflector to the partner ILM. Signal attenuation will also occur since the reflector
can only reflect part of the infrared light to the partner ILM. Such losses mean a
reduction in the maximum length of a link.