Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 350)

Publication AG-UM008C-EN-P - February 2005
B-4 Basic DF1 Protocol Troubleshooting
DF1 full- and half-duplex protocols are character-oriented and
combine ASCII characters into two symbol types:
•
control
•
data
A symbol is a sequence of one or more bytes having a specific
meaning to the link protocol. The component characters of a symbol
must be sent one after another with no other characters inserted
between them.
DF1 Half-Duplex Protocol To help you diagnose communication problems, you can use a serial
line analyzer to see the data packets being transmitted on the RS-232
link between the DTE and the DCE. For further details, see the DF1
Protocol and Command Set Reference Manual, Publication
1770-RM516.
Table B.1 Summary of DF1 Half-Duplex Protocol Packet Exchanges
For this information See
different types of communication packet exchanges
between a master station and a remote station Table B.1
definitions of the packets Table B.2
Message Type Master Station’s Packet Remote Station’s Packet
Master station sending a MSG instruction
to a remote station DLE SOH stn DLE STX message DLE ETX
BCC/CRC DLE ACK
Master station sending a poll; remote
station replying to a poll indicating it has
no data to transmit DLE ENQ stn BCC DLE EOT
Master station sending a poll; remote
station sending a MSG instruction as a
reply DLE ENQ stn BCC
DLE ACK
(master station acknowledges receipt of
the remote station’s message)
DLE STX message DLE ETX BCC/CRC