Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 195)

Error Reporting
Chapter 7
7Ć40
The remote station then formatted a reply with the STS byte containing
some error code. Local errors mean that the network controller was
unable to transmit the message to the remote station. The local station
then turns the command around, stuffs the STS byte with the appropriate
error code, and returns it to the sender (computer). The error code format
is as follows:
When the error is local, the high nibble (7-4) is zero; and the reference to
a particular code is in the low nibble as a hex value. When the error is
remote, the low nibble is zero; and the error code is in the high nibble.
Since the full-duplex message packet is actually transmitted on the
highway itself (in an encapsulated form), the contents of the STS byte is
what other (PC) network stations use to generate the error word in the PC
application program. To decode the contents of the STS byte, refer in
“ERROR WORD in User Programming (1771-KG, 1771-KA, 1771-KA2,
1774-KA Modules)” to error codes (80-8B) for remote errors and error
codes (90-97) for local errors
For remote station errors, make sure the error codes correspond to the
processor type at that station (either PLC/PLC-2 or PLC-3/PLC-5).
Match the last digit of the error code with value in hex in the appropriate
nibble. For example, if the STS byte contains 04H, the low nibble = 4
and the high nibble is 0, indicating a local error. Referring to the local
error codes (90-91), 04H matches Error 94 (contention on the highway).
PLCĆ3 and PLCĆ5
Important: With PLC-2 Compatibility mode for the 1775-KA, PLC-2
level commands addressed to a PLC-3 will return only errors, as described
above; that is, in the STS byte format.
In addition to the above, PLC-3 can also create a second layer of error
codes, 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 EXT STS.
If there is a non-zero error value in the EXT STS byte, the STS byte will
contain F0H (which, in effect, functions as a flag that there has been an
error value generated). If the STS byte is zero, then the EXT STS will
also be zero.