Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 156)

Network and Application Layer Protocols
Chapter 12
12Ć9
Remote errors mean that a command was successfully delivered by the
network, but the remote station was unable to execute the command. The
remote station then placed an error code in the high nibble of the STS
byte.
Local errors mean that your network layer was unable to deliver the
message to the remote station. Your network layer then turns the
command around, stuffs the low nibble of the STS byte with the
appropriate error code, and returns it to your application.
All error codes are listed in appendix B.
When you receive a reply message from a PC station, check the STS byte
at the application layer. If the STS byte is non–zero, refer to appendix B
for the type of error that has occurred.
If your application layer receives a command message and detects an
error, it should format a reply message with a remote error code in the
high nibble of the STS byte.
ETX STS (extended status)
If the PLC–3 receives PLC/PLC–2 commands, error codes for those
commands are returned in the STS byte only.
The PLC–3 can also create a second layer of error codes, however,
relative to PLC–3 type commands (CMD byte–15). If the command is a
PLC–3 level command addressed to a remote PLC–3, then the remote
error returned from the 1775–KA will have an additional status byte
stuffed into the data area, called an ETX STS.
If the STS byte is zero, then the ETX STS will also be zero, indicating no
error. If the STS bytes contain the value F0 hex, this is a flag to indicate
that the ETX STS contains the non–zero code.
To decode the contents of the STS byte and the ETX STS byte relating to
the application programs of specific processors, refer to Appendix B error
codes (80–88) for remote errors and error codes (90–97) for local errors.