Bitzer CM-RC01 Instructions D'installation page 31

4 General Modbus information
1 Gateway + 1 IQ device:
Modbus (RTU)
(2 wire)
gateway
120
Ohm
1 Gateway several IQ devices:
Modbus (RTU)
120
Ohm
gateway
twisted pair
wires
optional, up to
10 IoC devices
termination resistor
must be paces at the
last device
Fig. 5: Correct Modbus wiring
Shielded twisted pair cable must be used. The shield must only be connected in one end of the bus to avoid un-
wanted ground current in shielding. However, the shield must be unbroken along the complete bus length, except
across galvanic isolated repeater.
gateway
Fig. 6: Shielding and earth connection
IQ: IQ MODULE (CM-RC or CM-SW)
FI: frequency inverter
Most controllers, gateways, compressor modules, frequency inverters etc. have no galvanic isolation in the Modbus
interface. Therefore:
• Only data+ and data- wires should be connected to the gateway.
CT-311-5 // PDF Download
device
120
Ohm
(2 wire)
device #1
#2
device
#3
device
120
device
#10
Ohm
shield only connected to gateway chassis
data+, data-
...
IQ device IQ device IQ device
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