Circutor Computer SMART III FAST 12, Instruction Manual

Page: 55 / 112

4�9�- RS-485 COMMUNICATIONS
Computer SMART III 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
Computer SMART III FAST
and the master unit of 1,200 metres.
A maximum of 32 Computer SMART III 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�
55
Instruction Manual
Computer SMART III FAST