4.9.- RS-485 COMMUNICATIONS
Controller MASTER control VAR FAST units have an RS-485 serial communication output
with the Modbus RTU ® communications protocol
4�9�1� CONNECTIONS
The RS -485 cable should be wired with a twisted pair cable with mesh shield (minimum 3
wires), with a maximum distance between the Controller MASTER control VAR FAST and the
master unit of 1,200 metres.
A maximum of 32 Controller MASTER control VAR FAST units can be connected to this
bus.
Use an intelligent RS-232 to RS-485 network protocol converter (M54020 intelligent converter)
to establish the communications with the master unit. This converter does away with the need
for the Pin 7 connection on the RS-485 side.
B ( - )
A ( + )
S
A( + )
B( - )
S
RS-232 / USB / Ethernet / Profibus ...
PC
RS-485
RS-485
RS-232
USB
Ethernet
Profibus
...
Figure 16: RS-485 Connection diagram�
58
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