ZIEHL-ABEGG MODBUS RTU System, Technical Information, Page: 3 / 16

1 General description
1.1 Intended use
This technical information is only complete together with the corresponding operating instruc-
tions of the connected components. Therefore the safety information in the operating instruc-
tions of the connected components must also be observed.
1.2 Explanations of symbols
Safety instructions are highlighted with warning triangles and are depicted according to the degree of
hazard as follows.
Attention!
General hazardous area. Death or severe injury or signi fi cant property damage can occur if the
corresponding precautions are not taken!
Information
Important additional information and advice for user.
2 MODBUS RTU (Remote Terminal Unit)
2.1 Introduction
MODBUS RTU is an international, open fi eld bus standard. MODBUS is used successfully world-wide
as an easy to implement fi eld bus protocol.
The area of application includes production, process and building automation. MODBUS distinguishes
between master and slave devices.
Master devices determine the data transfer on the bus. A master can send messages without an
external request.
Slave devices are peripheral devices. Typical slave devices are input-output devices, valves, drives
and transducers. They receive no bus access authorisation, i.e. they may only acknowledge received
messages or send messages to the master when it requests them to.
In general:
•
Only one master may be active on a bus branch (monomaster bus system)
•
Up to 247 slaves can be addressed on a bus branch
•
Communication always comes from the master; the slaves must respond to requests from the
master
•
Protection function: Checksum and parity bit
Network addressing is performed, unless speci fi ed otherwise, by the master in the address range
from 1 to 247, whereby 0 may not be used and address 247 indicates the address preset by the
manufacturer (
chapter 3.4.2.2)
Information
Every member on the bus is addressed by its bus address ( fi eld devices address). This address may
only exist once per bus (channel). The slave addresses must always be set to ensure that the bus
master can access the slaves connected to the bus line.
Technical information MODBUS RTU System – model series General description
R-TIL08_01-GB 1215 Part.-No.
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