Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 108)

Full-Duplex Protocol
Chapter 10
10Ć4
DLE ACK – signals that the receiver has successfully received the last
message sent.
DLE NAK – signals that the receiver did not successfully receive the
last message sent.
Link-Layer Message Packets
A link–layer message packet starts with a DLE STX, ends with a DLE
ETX BCC, and includes all link–layer data codes in between. Data codes
can occur only inside a message packet.
Response codes occur inside a message packet. If you select the
embedded responses option with LIST (chapter 2) the response codes can
also occur between a DLE STX and a DLE ETX BCC, but these response
codes are not part of the message packet: they are referred to as embedded
responses.
Figure 10.1 shows the format of a link–layer message packet for
full–duplex protocol, and the layer at which each portion should be
implemented. At the end of each message packet is the one–byte BCC
field.
Figure 10.1
Link Packet Format for Full-Duplex Protocol
10038-I
CMD STS FNC ADDR DATA
DLE STX
Data
DLE ETX BCC (From Network Layer)
DST SRC CMD STS TNS
Data
(From Application Layer)
––––––––––
–––
––––––––––
–––
––––––––––
From
Applicaion
Layer
From
Network
Layer