We reserve the right to change designs and technical specifications of our products.
15
ENG
7.1.4 Modbus – properties
Properties of Modbus RTU in the client-server network
Network topology
Linear bus with bus termination:
Cable with 120 Ohm resistance at both ends
Transmission medium
For connecting the devices, bus cables suitable for the respective
application must be used and laid professionally, the cross-section must
be AWG 26 (0.129mm²) or more. To increase transmission reliability, it is
recommended to use shielded bus cables twisted in pairs.
Cable lengths (without repeater)
A maximum cable length depends on the baud rate:
-at a baud rate of 9600 bits/s (factory setting), up to 1000m
physical interface
RS-485 with bus connector; connection can be mounted by the
customer, 2-wire and has a 2-screw terminal
Addressings
1 ... 247; the following must be observed:
32 devices in one segment, expandable to 247 with repeater, incl.
client, where address 0 goes as broadcast message to all servers
.
Note:
The respective applicable regulations and standards must be taken into account for laying bus cables
inside buildings (inside/outside cabinets), laying cables outside buildings, potential equalisation,
minimum distances (such as measures against interference voltages), shielding of cables (e.g. shield
connection after expected interference) as well as installation of terminating resistors!
When laying shielded cables, the shield may only be connected to ground at one point!
Work on electrical equipment and connection work is only permitted for authorised and qualified
electricians. The VDE guidelines and the provisions of the responsible energy utility company must
be observed.
The LogoTronic Hub OTC operates with mains voltage. Therefore, always ensure the system is
disconnected from the mains supply when carrying out any maintenance or repair work and secure
it against unauthorised activation
7.2 Modbus for LogoTronic Hub OTC and HIU controllers
These chapters describe the Modbus communication via RS-485 interface with the LogoTronic
controller for electronically controlled interface stations (HIU) that are prepared for communication
via the Modbus RTU client/server protocol.
The Modbus interface offers the following possibilities:
•
User interface with restricted data access to registers
•
Client-server communication between HIU controllers (passing on temperature values), whereby
they form a closed BUS system!
