Siemens SIMATIC NET PROFIBUS, Owner'S Manual, Page: 29 / 490

Topologies of SIMATIC NET PROFIBUS Networks
2-3
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Connecting Segments Using RS-485 Repeaters
By using RS-485 repeaters, segments can be interconnected. The RS-485
repeater amplifies the data signals on the LAN cables. You require an RS-485
repeater when you want to attach more than 32 nodes to a network or when the
permitted segment length is exceeded. A maximum of 9 repeaters can be used
between any two nodes. Both bus and tree structures can be implemented.
Figure 2-1 shows a typical topology using the RS-485 technique with 3 segments
and 2 repeaters.
Terminating resistor activated
PG attached via tap line (6ES7 901-4BD00-0XA0)
for maintenance purposes
RS-485
repeater
RS-485
repeater
S7-400 S7-300 S7-300
S7-400
S7-400
Tap line
OP 25
PG
OP 25
OP 25
PG
Figure 2-1 Topology Using the RS-485 Technique
Increasing the overall span of a network by using repeaters can lead to longer
transmission times that may need to be taken into account when configuring the
network (see Chapter 3).
2.1.1 Components for Transmission Rates up to 1.5 Mbps
All SIMATIC NET bus attachment components can be used for transmission rates
≤
1.5 Mbps.