WIKA GDT-20 Betriebsanleitung Seite 15

6. Commissioning, operation
After setting up COM ports, the baud rate and the min./max. address or interval, the recording
can be started. For continuous recording, it is possible to record the measured data in the
selected interval in a text file divided by tabs.
The recording is started with the green start symbol. Stop the recording using the red stop
symbol.
6.4.2.4 Modbus register and functional description
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The following documents (available under www.Modbus.org) are recommended for under-
standing the Modbus
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Modbus APPLICATION PROTOCOL SPECIFICATION
■
Modbus over serial line specification and implementation guide
■
The register structure is described in the following.
Communication via messages
General form of the messages
Instrument address
8 Bit
In accordance to Modbus
least 3.5 characters.
The characters within one message may not have spacing of more than 1.5 characters.
Examples of a typical transmission:
Intermission Message 1
Valid function calls
Designation
03 Read holding registers
04 Read input register
06 Write single register
16 Write multiple registers
08 Diagnostic - Sub code 00
23 Read/write multiple registers configuration Writing or reading of one/several register values or the instru-
WIKA operating instructions transmitter, models GDT-20, GDHT-20
architecture which the following chapters will refer to.
Function
8 Bit
specification, separate messages must be divided by a break of at
®
▶
Intermission Message 2
Description
Reading of one or more register values or the instrument
configuration
Reading a register value or the instrument configuration
Writing a register value or the instrument configuration
Writing of one or more register values or the instrument
configuration
Diagnostic function
ment configuration
Data
n x 8 Bit
▶
Intermission
CRC check
16 Bit
Message 3 ...
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