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Exception codes
MODBUS protocol manual
MODBUS TCP
Values contained in Response messages are in hexa format.
Response example in case of MODBUS TCP: 010000000003018302
Example Byte Description No. of bytes
01 - Transaction identifier 1
00 High
Protocol identifier 4
00 Low
00 High
00 Low
03 - No. of byte of next data in this string 1
01 - Unit identifier 1
83 - Function code (80+03) 1
02 - Exception code 1
Exception codes for MODBUS TCP are following described:
01 ILLEGAL FUNCTION: the function code is unknown by the server.
02 ILLEGAL DATA ADDRESS: the data address received in the query is not an allowable
address for the instrument (i.e. the combination of register and transfer length is
invalid).
03 ILLEGAL DATA VALUE: a value contained in the query data field is not an allowable value
for the instrument.
04 SERVER FAILURE: the server failed during the execution.
05 ACKNOWLEDGE: the server accepted the server invocation but the service requires a
relatively long time to execute. The server therefore returns only an aknowledgement
of the service invocation receipt.
06 SERVER BUSY: the server was unable to accept the MB request PDU. The client application
has the responsability of deciding if and when re-sending the request.
0A GATEWAY PATH UNAVAILABLE: the ETHERNET interface is not configured or cannot
communicate.
0B GATEWAY TARGET DEVICE FAILED TO RESPOND: the instrument is not available in the
network.
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