Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 147)

Half-Duplex Protocol
Chapter 11
11Ć20
When monitoring half–duplex protocol on a two–wire link, you need to
monitor only one line. the example below shows a message sent by the
master and a reply sent by the slave in answer to a poll. Slave responses
are in bold.
Message from master to slave:
DLE SOH STN DLE STX xxxx DLE ETX BCC DLE ACK
Message sent from slave to master in answer to poll:
DLE ENQ STN BCC DLE STX xxxx DLE ETX BCC DLE ACK
Poll with a DLE EOT answer:
DLE ENQ STN BCC DLE EOT
Line Monitoring