4.8.6 RS-485 Serial Communication
Up to 32 nodes can be connected as a bus, or via drop
cables from a common trunk line to one network segment.
Repeaters can divide network segments. Each repeater
functions as a node within the segment in which it is
installed. Each node connected within a given network must
have a unique node address across all segments.
•
Connect RS-485 serial communication wiring to
terminals (+)68 and (-)69.
•
Terminate each segment at both ends, using either
the termination switch (bus term on/off, see
Figure 4.14) on the adjustable frequency drives, or a
biased termination resistor network.
•
Connect a large surface of the shield to ground, for
example with a cable clamp or a conductive cable
connector.
•
Apply potential-equalizing cables to maintain the
same ground potential throughout the network.
•
Use the same type of cable throughout the entire
network to prevent impedance mismatch.
Cable
Shielded twisted pair (STP)
Impedance
120 Ω
Max. cable length
[m]
1200 (including drop lines)
500 station-to-station
Table 4.4 Cable Information
Electrical Installation
VLT
®
HVAC Drive Instruction Manual
22 MG11AJ22 - Rev. 2013-09-13
44
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