Bender ISOMETER isoCHA425 Manual page 20

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 ISOMETER® "holding
registers" 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 ISOMETER® master requests the content of the register
1003 with the address 3. The register contains the channel description of measuring
channel 1.
Byte Name
Byte 0 ISOMETER® Modbus address
Byte 1 Function code
Byte 2, 3 Start address
Byte 4, 5 Number of registers
Byte 6, 7 CRC16 Checksum
7.1.2 Answer of the ISOMETER® to the Master
Byte Name
Byte 0 ISOMETER® Modbus address
Byte 1 Function code
Byte 2 Number of data bytes
Byte 3, 4 Data
Byte 7, 8 CRC16 Checksum
20
Example
0x03
0x03
0x03EB
0x0001
0xF598
Example
0x03
0x03
0x02
0x0047
0x81B6
Data access using the Modbus RTU protocol
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 page 22.
7.2.1 Command of the Master to the ISOMETER®
In this example, in the ISOMETER® with address 3 the content of the register address 3003
is set to 2.
Byte Name
Byte 0 ISOMETER® Modbus address
Byte 1 Function code
Byte 2, 3 Start register
Byte 4, 5 Number of registers
Byte 6 Number of data bytes
Byte 7, 8 Data
Byte 9, 10 CRC16 Checksum
7.2.2 ISOMETER® answer to the Master
Byte Name
Byte 0 ISOMETER® Modbus address
Byte 1 Function code
Byte 2, 3 Start register
Byte 4, 5 Number of registers
Byte 6, 7 CRC16 Checksum
Example
0x03
0x10
0x0BBB
0x0001
0x02
0x0002
0x9F7A
Example
0x03
0x10
0x0BBB
0x0001
0x722A
isoCHA425_D00352_01_M_XXEN/10.2019