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Modbus
7.4 Modbus
The Modbus protocol is a communications protocol. It is based on a
Master/Slave or Client/Server architecture. Since 1979, Modbus, because of
its open protocol has become a de facto standard in the industry.
Using (
) Modbus a master (e.g. a PC) and several slaves (e.g. measurement
and control systems) can be connected to each other. The DURAG Modbus
uses a
serial interface
(RS-485) for this.
The data are transmitted in binary form
. Using this technique a higher data
throughput rate can be achieved than if the data were in (
This form of Modbus is referred to as
RTU
(RTU: Remote Terminal Unit).
Because the data is in a binary structure the information transmitted and
processed by Modbus must then be converted into a form readable by
humans.
The Modbus receives its power from the supply unit; see Table 6.3 on page 57
and section 7.4.6 from page 83.
7.4.1 General information on the Modbus protocol
In this section we have summarised the essential information for setting up
and operating the Modbus for DURAG devices, and here especially for the
D
−
R 800 system. The section is intended for operators and maintenance
personnel who have experience with DURAG measurement systems and who
possess the necessary basic knowledge of information processing and
networking. Basic information about Modbus is therefore not presented at this
point, but is assumed for understanding this manual.
Basic information about Modbus can be obtained from the Internet at the home
page of the
Modbus Independent User Organisation (IDA) *.
"Modbus Protocol Specifications"
http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b.pdf
(describes the datagrams (protocol data units) that are exchanged
between master and slave).
"Modbus over Serial Line Specification and Implementation Guide"
http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf
(describes how the datagrams are packed into telegrams (application data
units)).
*(We offer no guarantee of the correctness of the Internet addresses). We take
no liability for the contents of the pages listed. The presenters of those pages
take sole responsibility for them).
7.4.2 Technische Beschreibung DURAG Modbus für D
−
R 800
Interface
serial (RS-485)
Baud rate selectable
9600 /
19200
Baud
Number of data bits
8
Number of stop bits
1
Parity
none
D
−
R 800
81
Содержание D-R 800
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