Configuration Of Modbus Address; Reading The Measured Values - Thies CLIMA Hygro-Thermo Transmitter-compact Instructions For Use Manual

6.3 Configuration of MODBUS address

Every sensor has its own MODBUS address which can be changed through the MODBUS protocol.
With write access to the register „0205" (see table 1), you can change the MODBUS address of the
respective sensor.
The write command to the address register of the respective sensor presumes a valid target
address in the MODBUS network. Please make sure at this point that the newly assigned MODBUS
address is not already taken. If the current target address of the sensor is unknown, the MODBUS
sensors can always be activated using the MODBUS address 255.
For this reason, the address 255 is excluded from the regular address-allocation in the
network with the application of these sensors. With address 255 all sensors of this type are
activated at the same time.
The only exception to this rule is when you are operating a single sensor per network segment, for
example during mainte- nance via the service interface, starting up a test network or as a
permanent single sensor solution. In figure 1 the structure of a MODBUS frame is given with the
write command to change the MODBUS address:
MODBUS Function code Register address Argument
address
8 bit 8 bit
e.g. 255 6

6.4 Reading the measured values

The registers of the MODBUS sensors can be read using the MODBUS function code "03" (Read
Holding Register) or the MODBUS function code "04" (Read Input Register). The range for the
register to be read can be specified in the argument of both function codes. All registers between
the start and stop address of the argument, including the registers with both addresses themselves,
are read. This means that all measured values with their alarm registers and the serial number
(address range 0000 to 0007) are read through information retrieval. If the start and stop address
are identical, then only one register with the corresponding address is read.
In the following example, the first two MODBUS registers (0000-0001) are read which together
represent the measured value for the temperature in Float32 format. The MODBUS address of the
sensor has been set arbitrarily at 119.
MODBUS Function code Start address
address
8 bit 8 bit
119 3
16 bit
205
Figure 1: A llocation of a new MODBUS address
register
16 bit
00 00
Figure 2: Reading the measured values
7 - 14
(new
MODBUS address)
16 bit
1-254 (255 reserved)
Stop address register CRC
16 bit
00 01
CRC Check-sum
16 bit
CRC Check-sum
Checksum
16 bit
CRC
Checksumme
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