Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 89)

Publication AG-UM008C-EN-P - February 2005
Configuring MicroLogix 1100/1200/1500 Controllers 3-21
Define the parameters shown in Table 3.4 when configuring a
MicroLogix 1100/1200/1500 controller as a master station using
message-based communication mode to talk to slave stations.
Table 3.4 Configuring a MicroLogix 1100/1200/1500 as a Master Using Message-based Communication Mode
Parameter Selections
Baud Rate Select a communication rate that all devices in your system support. Configure all devices in the
system for the same communication rate.
Parity Parity provides additional message packet error detection. To implement even parity checking,
choose Even. To implement no parity checking, choose None.
Node Address A node address identifies the controller on the DF1 half-duplex link. Each station on a link must
have a unique address. Choose an address between 0
10
and 254
10.
Node address 255
10
is the
broadcast address, and cannot be selected as a station’s individual address.
Control Line This parameter defines the mode in which the driver operates. Choose a method appropriate for
your system’s configuration:
•
If you are not using a modem, choose NO HANDSHAKING.
•
If the master modem is full duplex, choose FULL-DUPLEX MODEM (RTS On).
•
If all the modems in the system are half-duplex, choose HALF-DUPLEX MODEM
(RTS/CTS Handshaking).
See page 3-8 for descriptions of control line operation settings.
Error Detection With this selection, you choose the how the processor checks the accuracy of each DF1 packet
transmission.
BCC: This algorithm provides a medium level of data security. It cannot detect:
•
transposition of bytes during transmission of a packet
•
the insertion or deletion of data values of zero within a packet
CRC: This algorithm provides a higher level of data security.
Select an error detection method that all devices in your configuration can use.
When possible, choose CRC.
Polling Mode If you want to:
•
accept unsolicited messages from slave stations, choose MESSAGE BASED (ALLOW
SLAVES TO 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
communication mode instead.
•
ignore unsolicited messages from slave stations, choose MESSAGE BASED (DO NOT
ALLOW SLAVES TO 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.
Duplicate Packet
Detect Duplicate Detect lets the controller detect if it has received a message that is a duplicate of its
most recent message from another station. If you choose duplicate detect, the processor will
acknowledge (ACK) the message but will not act on it since it has already performed the
message’s task when it received the command from the first message.
If you want to detect duplicate packets and discard them, check this parameter. If you want to
accept duplicate packets and execute them, leave this parameter unchecked.