Modbus Interface manual
LMC341 DIWE
Page 7
5. Connections
All LMC341 DIWE controllers have internally connected
signal ground and protective earth. The signal ground is
hence not needed as protective earth is used as signal
ground.
5.1. Connections on the LMC341
DIWE controller
E
th
er
ne
t
2
x
U
S
B
H
os
t
R
S
48
5
1
2
3
4
+12V
Data+
Data-
GND
Data+
M
od
bu
s
(R
TU
)
Data-
1 2 3 4
Terminal
Description
CN32 - RS485
Modbus connection
GND:
Do not use as all LMC341 DIWE controllers are
grounded(1).
Protective earth is used as signal ground.
Data-
Inverted signal
Data+
Signal
+12V
Power supply for RS485 connection.
Not used for Modbus communication!
Note (1): The LMC341 DIWE controller has internally
connected signal ground to PE (Protective Earth).
5.2. Cable specification
Communication is half duplex.
• Use shielded, tinned copper, twisted-pair cable – twisted
all the way to the controllers.
• Max 200 m cable length. Characteristic impedance
between 100 Ohm and 130 Ohm
• Foil or braided shield – shield grounded at the master
controller
• Shunt capacitance < 100 pF/m, AWG24, 2 * 120 Ohm
termination.
• Receiver impedance >= 12 kOhm.
5.3. Configuration
There can be up to 10 LMC341 DIWE controllers on the
same Modbus string.
If other equipment than LMC341 DIWE controllers are con-
nected on the same string, the maximum current sourcing
of the other equipment must be observed!
The network should be configured in sections, possible with
RS 485 repeaters between sections in large installations
and when connecting different buildings in one network. Up
to 3 repeaters may be used.
5.4. RS485 Repeater
The repeater should be an isolated (galvaniccally isolated)
RS485 repeater to separate the sections of the network.
The following products have been tested and verified to
work right out of the box:
• ICP CON 7510AR
• ICP CON 7510A
• Moxa TCC-120/120I
• BLACK BOX ICD202A
Other RS485 repeater brands and models should be tested
and verified before use in installations.
