Rev 03/2022
V1.0 - Page
8
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11
Subject to modifications!
romutec Steuer.-und Regelsysteme GmbH Jochsberger Straße 39 D-91592 Buch am Wald
Subject to technical changes
4.2 Bus connection to Modbus master devices
4.2.1 Communication within Modbus master/slave systems
For communication between a controller (DDC or PLC) and the romutec® RCG32-Bridge devices, it is
necessary to configure an TCP interface of the controller as Modbus master.
To communicate with a slave device connected to the bridge, you have to send the telegrams to the
IP address of the romutec® RCG32-bridge devices. This telegram contains the request message
which is needed for the slave device, including the unique slave ID.
This is done with the programming software of the manufacturer of the controller.
For questions, please consult the manual or contact the manufacturer of the controller.
4.2.2 Terminal assignment of the Modbus RTU (RS485) port
The terminal assignment for the bus connection of the romutec® RCG32-bridge to Modbus RTU slave
devices is as follows:
Type of Interface
Function
Terminal No.
Modbus Slave
RS485-1
Rx-Tx (Net_B )
/Rx-/Tx (Net_A )
I-GND
1.6
1.5
1.8
Data+ (B)
Data- (A)
Bus-GND
RS485-2
Rx-Tx (Net_B)
/Rx-/Tx (Net_A)
GND = supply GND
1.4
1.3
1.1
Data+ (B)
Data- (A)
Bus-GND
The bus interface of serial 1 is electrically isolated. The I-GND terminals must always be wired,
whether with braided shield or individual strands, and connected to ground / earth potential. There is
no internal connection between I-GND of serial 1 and the GND of the power supply.
The terminal 1.7 is connected to the shield of the RJ45 Ethernet socket. To avoid any
unwanted behaviour of the device, connect that terminal direcly to earth potential.
4.2.3 Recommended cable types for bus wiring
For a total length
up to 100m:
more than 100m:
Cable type:
LIYCY 1x2x0,5mm² shielded
CYPIMF 1x2x0,5mm² shielded
Line resistance:
< 4,0Ω / 100m
< 4,0Ω / 100m
Capacitance:
< 13.0nF / 100m
< 6.0nF / 100m
4.2.4 Modbus commands supported
All Modbus commands (aka FC = Function Codes) are supported.
There are no restrictions in the bridge.
