Data access using the Modbus RTU protocol
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isoPV425_D00028_09_M_XXEN/05.2018
7.2.2 ISOMETER® answer to 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 Function not allowed
0x02 Data access not allowed
0x03 Data value not allowed
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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