Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 180)

Message Formats
Appendix A
AĆ18
Reply Format:
This is the same as the reply packet format for all reads.
A. Format when the command was successfully executed
DLE C S TNS MD TS TNS STX DLE ETX BCC DATA - Max of 244 bytes or 122 words DST SRC
4F
B. Format when reporting an error
DLE SRC STX DST C
4F
S TNS
MD TS TNS DLE ETX BCC ETX
STS
Where the extended status byte is optional.