Rockwell Automation Allen-Bradley DriveLogix 5730, Руководство пользователя

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5-8 Communicating with Devices on a Serial Link
Master/Slave Communication Methods
A master station can communicate with a slave station in two ways:
Configuring a DF1 Slave Station
Name: This method: Benefits:
standard
communication mode Initiates polling packets to slave stations
according to their position in the polling array(s).
Polling packets are formed based on the contents
of the normal poll array and the priority poll array. This communication method is most often used for point-to-multipoint
configurations.
This method provides these capabilities:
•
slave stations can send messages to the master station (polled
report-by-exception)
•
slave stations can send messages to each other via the master
•
master maintains an active station array
The poll array resides in a user-designated data file. You can configure
the master:
•
to send messages during its turn in the poll array
or
•
for between-station polls (master transmits any message that it
needs to send before polling the next slave station)
In either case, configure the master to receive multiple messages or a
single message per scan from each slave station.
message-based
communication mode initiates communication to slave stations using
only user-programmed message (MSG)
instructions.
Each request for data from a slave station must
be programmed via a MSG instruction.
The master polls the slave station for a reply to
the message after waiting a user-configured
period of time. The waiting period gives the slave
station time to formulate a reply and prepare the
reply for transmission. After all of the messages in
the master’s message-out queue are transmitted,
the slave-to-slave queue is checked for messages
to send. If your application uses satellite transmission or public
switched-telephone-network transmission, consider choosing
message-based communication. Communication to a slave station
can be initiated on an as-needed basis.
Also choose this method if you need to communicate with
non-intelligent remote terminal units (RTUs).
This field: Description:
Station address The station address for the serial port on the DF1 slave.
Enter a valid DF1 address (0-254). Address 255 is reserved for broadcast messages. The default is 0.
Transmit retries The number of times the remote station retries a message after the first attempt before the station declares the message
undeliverable.
Enter a value 0-127. The default is 3.
Slave poll timeout Specifies the amount of time the slave station waits to be polled by a master before indicating a fault.
Enter a value 0-32767. Limits are defined in 20ms intervals. The default is 3000 (60,000ms).
EOT suppression Select whether or not to suppress sending EOT packets in response to a poll. The default is not to suppress sending
EOT packets.
Error detection Select BCC or CRC error detection.
Configure both 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 in a computer driver. This is the default.
CRC: the controller sends and accepts messages with a 2-byte CRC for error checking. CRC is a more complete
method.
Enable duplicate
detection Select whether or not the controller should detect duplicate messages. The default is duplicate detection enabled.