isoBAT425_D00308_04_M_XXEN/07.2020
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Data access using the Modbus RTU protocol
7. Data access using the Modbus RTU protocol
Requests to the ISOMETER® can be made using the function code 0x03 (read multiple
registers) or the command 0x10 (write multiple registers). The ISOMETER® generates a
function-related answer and sends it back.
7.1 Reading out the Modbus register from the ISOMETER®
The required Words of the process image can be read out from the "Holding registers" of
the ISOMETER® using the function code 0x03. For this purpose, the start address and the
number of the registers to be read out have to be entered. Up to 125 Words (0x7D) can
be read out by one single request.
7.1.1 Command of the master to the
ISOMETER®
In the following example, the master of the ISOMETER® requests the content of the regis-
ter 1003 with the address 3. The register contains the channel description of measuring
channel 1.
7.1.2 The ISOMETER® answers the master
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x03
Byte 2, 3
Start address
0x03EB
Byte 4, 5
Number of registers
0x0001
Byte 6, 7
CRC16 Checksum
0xF598
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x03
Byte 2
Number of data bytes
0x02
Byte 3, 4
Data
0x0047
Byte 7, 8
CRC16 Checksum
0x81B6
7.2 Write Modbus register (parameter setting)
Registers in the device can be modified with the Modbus command 0x10 (set multiple
registers). Parameter registers are available from address 3000. The content of the regis-
ter is
listed in the table on
7.2.1 Command of the master to the ISOMETER®
In this example, the master addresses the ISOMETER® with address 3 and requests that
the content of the register with address 3003 is set to 2.
7.2.2 The ISOMETER® answers the master
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x10
Byte 2, 3
Start register
0x0BBB
Byte 4, 5
Number of registers
0x0001
Byte 6
Number of data bytes
0x02
Byte 7, 8
Data
0x0002
Byte 9, 10
CRC16 Checksum
0x9F7A
Byte Name
Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x10
Byte 2, 3
Start register
0x0BBB
Byte 4, 5
Number of registers
0x0001
Byte 6, 7
CRC16 Checksum
0x722A
