Eos –Gate Installation and operation manual
All the information provided with this document are property of Carlo Gavazzi Controls SpA
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10.1.6 RS-485 termination
A termination is needed at each end of the bus. Termination must not be placed in other places.
Suggested terminations have the following characteristics:
Suggested terminations for MODBUS over RS485 serial line
Description
Type
Connection
Suggested termination
Notes
Bidirectional
termination,
resistor only
Between the two conductors of
the balanced line (near each end
of the bus)
R = 150 ohm/0.5W
(resistor)
Preferred
without line
polarization
2W RS-485
Bidirectional
termination,
serial
capacitor
with resistor
Between the two conductors of
the balanced line (near each end
of the bus)
R = 120 ohm, 0.25W
(resistor)
in series with
C = 1 nF, 10V
(capacitance)
Preferred
with line
polarization
Bidirectional
termination,
resistor only
Between each pair of conductors
of the balanced line (near each
end of the bus)
R = 150 ohm/0.5W
(resistor)
Preferred
without line
polarization
4W RS-485
Bidirectional
termination,
serial
capacitor
with resistor
Between each pair of conductors
of the balanced line (near each
end of the bus)
R = 120 ohm, 0.25W
(resistor)
in series with
C = 1 nF, 10V
(capacitance)
Preferred
with line
polarization
10.1.7 RS-485 MODBUS line polarization.
Every MODBUS device must
document if the device needs line
polarization, and if it implements
such a line polarization.
If one or several devices need
polarization, the following resistors
must be connected on the RS-485
balanced pair:
•
Pull-up resistor to 5V voltage
( from 450 ohm to 650 ohm)
•
Pull-down resistor to the
common circuit ( from 450
ohm to 650 ohm)
The two resistors must be connected at one location for the whole bus (possibly near to the
master). Other devices must not implement any polarization.
10.1.8 RS-485 wiring procedure
Suitable wire sleeves must be used for wiring. If any wire splice is to be used, this splice must be
soldered, taking special care to cover splice with cable shield and to ensure proper continuity.
