Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 123)

Full-Duplex Protocol
Chapter 10
10Ć19
Figure 10.11
Message Transfer with Timeout and ENQ
Not Full
DLE ACK
OK
xxxx
DLE ENQ
xxxx
SOURCE XMTR LINK RCVR SINK
10048–I
DL
DLE STX xxxx DLE EXT BCC
(Timeout)
??? CK
In Figure 10.12, retransmission occurs when noise hits both sides of the
line. This type of noise destroys the DLE ACK while also producing
invalid characters at the receiver. The result is that the receiver changes
its last response to NAK and the transmitter retransmits the original
message packet.