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4.6 RS485 Serial Connection
The following gure shows the RS485 bus connection topology. It is
recommended that the RS485 bus be shielded twisted pairs, with the 485+ and
485- terminals connected by the twisted pairs. Connect a 120 Ω termination
resistor to each end of the bus to prevent signal reection. Connect the reference
grounds of the RS485 signals of all nodes together. Up to 31 nodes can be
connected. The branch distance of every node must be less than 3 m.
485+ 485- GND
485+ 485- GND
485+ 485- GND
GND
485+
485-
120 Ω
resistor
Set a termination resistor
using toggles 1 and 2
of the DIP switch
Master station
120Ω
DIP switch DIP switch
Slave station 1 Slave station N
Use this switch
to set a termination
resistor at network
termination
Figure 9 RS485 connection topology
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