Modbus MS Card
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3.2 RS485 link configuration and connection
3.2.1 RS485 connection
Normally, the master of the network sets the polarity of the line. The Modbus MS
card is a slave equipment and don’t have
polarisation resistor.
The two ends of the line must be terminated. Allow for 1 or 2 terminators to avoid mismatching the line when any equipment at
the end of the line is disconnected.
The next figure gives the detail of the RS485 connector and the internals drivers:
Pin number
Function
1
R- : Receiver - (input)
2
R+ : Re (input)
3
T- : Transmitter - (output)
4
T+ : Trans
(output)
5
0 V
Important notes:
Use twisted pair cable (cable specification 0.3mm
2
and capacitance 42pF/m)
The transmission range will increase if a cable with lower capacitance and larger diameter is used.
Use shielded cable in heavy industrial environments.
