Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 60)

Asynchronous Link Protocols
Chapter 4
4-17
Full-Duplex Protocol Diagrams
The following figures show some events that can occur on the various
interfaces. Time is represented as increasing from the top of the figure to
the bottom. Data bytes are represented by “xxxx”; corrupted data by
“???”.
Figure 4.9
Normal Message Transfer
Not Full
DLE ACK
OK
xxxx
DLE STX xxxx DLE ETX BCC
xxxx
SOURCE XMTR LINK RCVR SINK
11561
Figure 4.10
Message Transfer with NAK
Not Full
DLE ACK
OK
xxxx
DLE STX xxxx DLE ETX BCC
xxxx
SOURCE XMTR LINK RCVR SINK
11562
DLE NAK
DLE STX x??x DLE EXT BCC