Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 142)

Half-Duplex Protocol
Chapter 11
11Ć15
Figure 11.6 shows a message transfer in which the acknowledgment was
destroyed by noise. After a timeout, the message is retransmitted and the
DLE ACK response is detected.
Figure 11.6
Message Transfer with ACK Destroyed
Not Full
OK
xxxx
xxxx
SINK MASTER LINK SLAVE SINK
10056–I
DLE ACK
SOURCE/ SOURCE/
DLE STX xxxx DLE ETX BCC DLE SOH STN
(Timeout)
DL ??? CK
DLE STX xxxx DLE ETX BCC DLE SOH STN
Figure 11.7 shows a slave being polled, and responding with DLE EOT
because it has no messages to transfer.
Figure 11.7
Poll with No Message Available
No Message
Not Full
SINK MASTER LINK SLAVE SINK
10057–I
DLE EOT
SOURCE/ SOURCE/
BCC DLE ENQSTN