Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 140)

Half-Duplex Protocol
Chapter 11
11Ć13
When the slave transceiver receives a DLE NAK, it takes messages from
the source until the source is empty. It discards each message while
sending an error code back to the source. The master can use this to clear
the message source buffer of each slave after the master has been down.
The following figures show the events that occur on various interfaces.
Control characters are shown in bold type. Link–level data is represented
by xxxx. Line noise is represented by ???. Each message packet is shown
ending in BCC. Time is represented as increasing from the top of the
figure to the bottom. Figure 11.4 shows normal message transfer from the
master to a slave.
Figure 11.4
Normal Message Transfer
Not Full
OK
xxxx
xxxx
SINK MASTER LINK SLAVE SINK
10054–I
DLE ACK
DLE STX xxxx DLE ETX BCC
SOURCE/ SOURCE/
DLE SOH STN
Half-Duplex Protocol Diagrams