SM500F
Field mountable paperless recorder Appendix B – Modbus TCP/Modbus 485
IM/SM500F Rev. Z 149
B.3 Modbus Exception Responses
If the recorder detects one of the errors shown in Table B.1 while receiving a message from the host
system, it replies with a response message consisting of the recorder's Modbus address, the function
code, the error code and the error check fields.
Code Name Definition
01 Illegal Function The message function received is not an allowable action
02 Illegal Data Address The address reference in the data field is not an allowable address
03 Illegal Data Value The value referenced in the data field is not allowable in the addressed slave
07 Negative Acknowledgement Received message error
08 Memory Parity Error Parity check indicates an error in one or more of the characters received
Table B.1 Modbus Exception Responses
Note.
Negative numbers are represented in '2's complement' format, for example, 1000 = 03E8 (Hex), –
1000 = FC18 (Hex).
The instrument cannot accept a new message until the current message has been processed and
a reply sent to the master (maximum response time 50ms).
The instrument monitors the elapsed time between receipt of characters from the host. If the
elapsed time between two characters is 3.5 character times, the slave assumes the second
character received is the start of a new message.
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