WIKA GDT-20 Mode D'emploi page 39

5. Commissioning, operation
5.4.2.4 Modbus register and functional description
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The following documents (available under www.Modbus.org) are recommended for
understanding the Modbus
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
intermission of at 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 ▶ Intermission Message 2 ▶ Intermission Message 3 ...
Valid function calls
Function Designation
03 Read holding registers
04 Read input register
06 Write single register
16 Write multiple registers Writing of one or more register values or the instrument
08 Diagnostic -
Sub code 00
23 Read/write multiple
registers configuration
WIKA operating instructions transmitter, models GDT-20 and GDHT-20
architecture which the following chapters will refer to.
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Function Data
8 bit n x 8 bit
specification, separate messages must be divided by an
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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
configuration
Diagnostic function
Writing or reading of one/several register values or the
instrument configuration
CRC check
16 bit
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