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4.7
Maximum network length / device loading
The maximum number of devices that can be connected to a single PROFIBUS-DP
network segment is 32, this includes all nodes and any repeaters. The maximum
lengths of cable for a segment depend on the data rate and are shown in Table 4.2.
Repeaters or fiber optic segments can be used to extend the network, allowing more
than 32 nodes to be connected on the network. The maximum number of nodes on a
single network is 125.
For full details on designing and installing a PROFIBUS-DP network, refer to Installation
NOTE
Guidelines for PROFIBUS-DP/FMS. This document is available from the PROFIBUS
web site at www.profibus.com.
Table 4.2 PROFIBUS-DP maximum network lengths
Data rate (bit/s)
12M
6.0M
3.0M
1.5M
500k
187.5k
93.75k
45.45k
19.2k
9.6K
4.8
Node addressing
SM-PROFIBUS DP-V1 has a valid address range of 1 to 125. Addresses 126 and 0 are
reserved for system use and should not be used. The addressing scheme used is at the
discretion of the end user however it is recommended that nodes are numbered in order
as they appear on the physical network. It is not necessary to use consecutive numbers
and gaps in the addressing scheme may be left to allow for future expansion.
4.9
Spurs
The PROFIBUS-DP specification allows spurs at data rates less than 1.5Mbits/s. At
data rates below 1.5Mbits/s there are specific requirements for capacitance and length
of cable allowed when using spurs. LEROY-SOMER recommend that spurs are not
used as extreme care is required at the design stage to avoid network problems. More
information on spurs can be found on the PROFIBUS web site at www.profibus.com.
4.10
Minimum node to node cable length
The minimum recommended node to node distance is one metre of network cable.
This distance is necessary to avoid multiple nodes generating a single large reflection
on the network, using less than one metre of cable between nodes can have serious
implications for network reliability.
SM-PROFIBUS DP-V1 User Guide
Issue : a
Maximum trunk length (m)
100
100
100
200
400
1000
1200
1200
1200
1200
www.leroy-somer.com
15
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