Data access using the Modbus RTU protocol
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isoEV425_D00126_09_M_XXEN/03.2019
7.2.2 ISOMETER® answers the Master
7.3 Exception code
If a request cannot be answered for whatever reason, the ISOMETER® will send
a so-called exception code with which possible faults can be narrowed down.
7.3.1 Structure of the exception code
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
Exception
code
Description
0x01 Impermissible function
0x02 Impermissible data access
0x03 Impermissible data value
0x04 Internal fault
0x05
Acknowledgement of receipt (answer will be time-delayed)
0x06
Request not accepted (repeat request, if necessary)
Byte Name Example
Byte 0 ISOMETER® Modbus address 0x03
Byte 1 Function code (0x03) + 0x80 0x83
Byte 2 Data (exception code) 0x04
Byte 3, 4 CRC16 Checksum 0xE133
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