Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 244)

Publication AG-UM008C-EN-P - February 2005
7-18 Configuring Logix Controllers
Use Worksheet 7.2 Logix DF1 Half-Duplex Master Station
Configuration Using Message-based Communication (page D-23) for
an example configuration and to record your station’s configuration.
Table 7.5 Configuring a Logix controller as a master station using message-based
communication mode
Parameter Description Default
Station Address The station address for the serial port on the DF1 master.
Enter a valid DF1 address (0 to 254). 0
Transmit Retries Specifies the number of times a message is retried after the first
attempt before being declared undeliverable.
Enter a value 0 to 127. 3
ACK Timeout Specifies the amount of time you want the controller to wait for an
acknowledgment to its message transmission.
Enter a value 0 to 32767. Limits are defined in 20 ms intervals. 50 (1000 ms)
Reply Message Wait Specifies the amount of time the master station waits after
receiving an ACK to a master-initiated message before polling the
slave station for a reply.
Enter a value 0 to 65535. Limits are defined in 20 ms intervals. 5 (100 ms)
Polling Mode If you want to:
•
accept unsolicited messages from slave stations, choose
MESSAGE BASED (slave can initiate messages)
Slave station-initiated messages are acknowledged and
processed after all master station-initiated (solicited)
messages.
Note: Slave stations can only send messages when they
are polled. If the message-based master station never
sends a slave station a message, the master station will
never send the slave station a poll. Therefore, to regularly
obtain a slave station-initiated message from a slave
station, you should choose to use standard
communications mode instead.
•
ignore unsolicited messages from slave stations, choose
MESSAGE BASED (slave cannot initiate messages)
Slave station-initiated messages are acknowledged and
discarded. The master station acknowledges the slave
station-initiated message so that the slave station
removes the message from its transmit queue, which
allows the next packet slated for transmission into the
transmit queue.
Message Based
(slave can initiate
messages)
Error Detection Select BCC or CRC error detection.
Configure all stations to use the same type of error checking.
BCC: the controller sends and accepts messages that end with a
BCC byte for error checking. BCC is quicker and easier to
implement, but does not detect as many errors as CRC.
CRC: the controller sends and accepts messages with a 2-byte
CRC for error checking. CRC is a more effective error detection
algorithm.
BCC
Enable Duplicate Detection Select whether or not the controller should detect and ignore
duplicate messages. Enabled