Communication Errors; Figure 35: Rtu Error Response Format - Emerson PACSystems RX3i User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual
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6.3.5

Communication Errors

Serial link communication errors are divided into three groups:
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6.3.5.1 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.
6.3.5.1.1 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.
Serial I/O, SNP & RTU Protocols
Invalid Query Message
Serial Link Time Outs
Invalid Transaction
Invalid Function Code
Invalid Address Field
Invalid Data Field
Query Processing Failure

Figure 35: RTU Error Response Format

Address Exception
Func
Subcode
1
2
3
4
Error Error
Subcode Check
Section 6
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