wtw CL 298, Operating Manual

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pH 298, LF 298, Oxi 298, Cl 298
Communication with Modbus RTU
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6.3 Data transmission
With each query of sensor data via the Modbus protocol, a block of consecutive
registers is read.
Query and
response telegram
The data transmission takes place via query and response telegrams. The form
of the telegrams is determined by the Modbus RTU protocol.
The Modbus master sends a query telegram with a Modbus command to the
Modbus slave (here, the pH 298, LF 298, Oxi 298, Cl 298). The Modbus slave
sends a response telegram with the requested data or an error message.
6.3.1 Query format
Supported
Modbus
commands
The pH 298, LF 298, Oxi 298, Cl 298 provides the data block for read access
only. Write Modbus commands are not carried out.
The following commands are available:
baud rate 9600
19200
38400 Select the baud rate
parity none 1s
none 2s
even 1s
even 2s
odd 1s
odd 2s None, 1 stop bit
None, 2 stop bits
Even, 1 stop bit
Even, 2 stop bits
Odd, 1 stop bit
Odd, 2 stop bits
3 Edit the settings.
4 Quit the menu.
Submenu Selection/Values Explanation
Modbus commands Command code
Read Input Register 04h
Read Holding Register 03h