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5 - ELECTRICAL CONNECTIONS
5.12 MODBUS - RS485
LED BSP communication with AP1 module
green communication ok
yellow software ok but communication with AP1 down
red flashing : software error
fixed : hardware error
LED BUS communication with MODBUS
green communication ok
yellow startup / channel not communicating
red communication down
Every RS485 serial line must be set up using the 'In/Out'
bus system. Other types of networks are not allowed,
such as Star or Ring networks
The difference in potential between the earth of the two
RS485 devices that the cable shielding needs to be
connected to must be lower than 7 V
Suitable arresters must be set up to protect the serial lines
from the effects of the atmospheric discharges
A 120 ohm resistance must be located on the end of the
serial line. Alternatively, when the last serial board is
equipped with an internal terminator, it must be enabled
using the specific jumper, dip switch or link
The cable must have insulation features and non-flame
propagation in accordance with applicable regulations
The RS485 serial line must be kept separate from the
power conductors or powered by different voltages
The RS485 serial line must be kept as far away as
possible from sources of electromagnetic interference
MODBUS Cable requirements
Conductors twisted and shielded
Section of conductor 0.22mm2…0,35mm2
Nominal capacity between conductors < 50 pF/m
nominal impedance 120 Ω
Recommended cable BELDEN 3106A
A unit
B metal conduit
C metal septums
D metal-lined sheath
(sleeve)
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