Rockwell Automation 1789-L10_L30_L60 SoftLogix 5800 System User Manual - Manual (Page 87)

Rockwell Automation Publication 1789-UM002J-EN-P - December 2012 87
Communicate with Serial Devices Chapter 4
If you use a modem to remotely connect the controller to one workstation, use
the Logix Designer application to configure the serial port of the controller for
the DF1 Point-to-Point (full-duplex) protocol, as in the previous example. If the
controller is part of a master/slave serial device, configure the serial port of the
controller for either the DF1 master or DF1 Slave protocol (both half-duplex).
Master and Slave Communication Methods
A master station can communicate with a slave station in these two ways.
Item Description
1 Workstation with Logix Designer application and Logix5550 serial port driver
2 Modem
3 Modem
4 SoftLogix controller
Name Method Benefits
Standard Communication
mode Initiates polling packets to slave stations according to their
position in the polling array.
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 by 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).