Circutor Computer SMART III 14 - RS-485 and Modbus RTU Protocol

4.9.- COMMUNICATIONS
Computer SMART III devices 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 Computer SMART III and the master device of 1200 metres.
A maximum of 32 Computer SMART III devices 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 device. 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 19: RS-485 Connection diagram
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Instruction Manual
Computer SMART III