Communication Errors - GE PACSystems RX7i Reference Manual

6.3.5 Communication Errors

Serial link communication errors are divided into three groups:
▪
Invalid Query Message
▪
Serial Link Time Outs
▪
Invalid Transaction
Invalid Query Message
When the communications module receives a query addressed to itself, but cannot process the query, it
sends one of the following error responses:
The format for an error response to a query is as follows:
The address reflects the address provided on the original request. The exception function code is equal
to the sum of the function code of the query plus 128. The error subcode is equal to 1, 2, 3, or 4. The value
of the subcode indicates the reason the query could not be processed.
Invalid Function Code Error Response (1)
An error response with a subcode of 1 is called an invalid function code error response. This response is
sent by a slave if it receives a query whose function code is not equal to 1- 8, 15, 16, 17, or 67.
Note: Starting with Release 6.70 for the RX3i, the invalid function code error response is not used.
Instead, undefined and unsupported function codes are ignored, and no response is
generated.
GFK-2222AD
Invalid Function Code
Invalid Address Field
Invalid Data Field
Query Processing Failure
Address
Exception
Func
Figure 64: RTU Error Response Format
April 2018
Chapter 6. Serial I/O, SNP & RTU Protocols
Subcode
1
2
3
4
Error Error
Subcode Check
253