Operating Manual
Compact Weather Station
90
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany
18.7 Communication in Modbus Mode
For a simpler integration of WS family Compact Weather Stations into a PLC environment
the Modbus communication protocol has been made available.
Measurement values are mapped to Modbus Input Registers. The range of values available
is basically the same as for the UMB protocol, including different unit systems.
In the interest of simple and safe integration the use of register pairs for floating point values
or 32 bit integers, which is not part of the Modbus standard, has not been applied. All
measurement values are mapped to 16bit integers using suitable scaling factors.
18.7.1 Modbus Communication Parameters
The WSxxx can be configured for MODBUS-RTU or for MODBUS-ASCII.
The base configuration has to be done using the UMB Config Tool.
When selecting MODBUS RTU or MODBUS-ASCII with the UMB Config Tool
communicationparameters 19200 Bd, evenparity, will be preselected.
Modbus operating modes:
MODBUS-RTU, MODBUS-ASCII
Baudrate:
19200 (9600, 4800 or lower)
Interface Setting
8E1, 8N1
NOTE:
The Modbus communication has been tested for a poll rate of 1 sec. The proper
function of the Compact Weather Station with higher Modbus poll rates has not been tested.
We suggest to set the poll rate to 10 sec or slower, as, with the exception of the channels
„wind speed / wind directions fast“, which are provided for special purposes, the update rate
of the data is >= 10sec. Anyway for most of the weather data significant changes have tob e
expected more in the range of minutes.
18.7.2 Modbus Functions
The functions of conformance class 0 and 1 havebeen implemented as far as they are
applicable for WSxxx, i.e. all functions operating on register level.
Conformance Class 0
0x03
Read Holding Registers
Selected configuration settings
0x16
Write Multiple Registers
Selected configuration settings
Conformance Class 1
0x04
Read Input Registers
Measurement values and statusinformation
0x06
Write Single Register
Selected configuration settings
0x07
Read Exception Status
Currently not used
Diagnostics
0x11
Report Slave ID
(responds also tobroadcastaddress)
18.7.2.1 Function 0x03 Read Holding Registers
The Holding Registers are used to make a selected set of adjustable parameters available
for Modbus access. As for the measurement values the parameters are mapped to 16bit
integers.