Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 61)

Asynchronous Link Protocols
Chapter 4
4-18
Figure 4.11
Message Transfer with Timeout and ENQ
Not Full
DLE ACK
OK
xxxx
DLE ENQ
xxxx
SOURCE XMTR LINK RCVR SINK
11563
DL
DLE STX xxxx DLE EXT BCC
(Timeout)
??? CK
Figure 4.12
Message Transfer with Retransmission
Not Full
DLE NAK
OK
xxxx
DLE ENQ
xxxx
SOURCE XMTR LINK RCVR SINK
11564
DL
DLE STX xxxx DLE EXT BCC
(Timeout)
??? CK
???
DLE STX xxxx DLE EXT BCC
DLE ACK
(Message Discarded) 1
1 Note that this is detected as a duplicate message.