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isoPV425_D00028_09_M_XXEN/05.2018
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 ISO-
METER® 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 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 have to be entered. Up to
125 Words (0x7D) can be read by one single request.
7.1.1 Master sends a command to the ISOMETER®
In the following example, the master addresses the ISOMETER® with address
3 and the requests the contents of register 1003. The register contains the
channel description of measuring channel 1.
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
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