ABB AC 800M

RS485 limits and network design Section 3 Fieldbus Topologies
70 3BDS009029R5001 B
RS485 limits and network design
As described in the PROFIBUS RS485 specification, each bus segment can have a
maximum of 32 active devices. In order to be able to connect a larger number of
PROFIBUS DP devices, it is necessary to segment the bus. The segments are then
interconnected with repeaters which amplify and refresh the data signals. Repeaters
can also be used for galvanic isolation of bus segments or bus sections. Each
repeater allows the PROFIBUS system to be extended by an additional bus segment
with the maximum admissible cable length and the maximum number of fieldbus
devices. Repeaters increase the signal propagation times. This should be taken into
account during planning.
Table 8. General Data PROFIBUS DP
Maximum number of stations
participating in the exchange
of user data
DP: 126 (addresses from 0 .. 125)
Maximum number of stations
per segment including
repeaters
32
Available data transfer rates
in kbit/s
9.6 19.2 45.4
5
93.7
5
187.
5
500 1500
3000 6000 12000
Max. RS485 segment length in
m *
1200 1000 400 200
185 * 120 * 100
Max. spur lines length Dependent on the data transmission rate. The use of passive bus
spur lines should be avoided.
Max. fibre optic cable length in
m
44 (plastic),1700 (glass) up to 15000 (PCF)
Max. number of segments
in series
9
According to EN 50170, a maximum of 9 repeaters are allowed
between any two stations.