WIKA GD-20 Operating Instructions Manual page 56

5. 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.
5.4.2.4 Modbus
EN
The following documents (available under www.Modbus.org) are recommended for understanding the Modbus
architecture which the following chapters will refer to.
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
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
Function Designation
03 Read holding registers
04 Read input register
06 Write single register
16 Write multiple registers
56
register and functional description
®
Function
8 bit
specification, separate messages must be divided by a break of at least 3.5 characters.
®
▶
Intermission
Data
n x 8 bit
▶
Message 2 Intermission
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
WIKA operating instructions gas density sensor, model GD-20
®
CRC check
16 bit
Message 3 ...