Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 27)

Publication AG-UM008C-EN-P - February 2005
Designing Communication 1-9
When the master station is configured for standard-communication
mode, you do not need to program any master-station message
instructions to communicate with slave stations. Communication with
slave stations occurs by the master station sending polling packets to
slave stations. You only need message instructions when you want the
master station to write data to or read data from a location within a
slave station’s data table.
Figure 1.2 Standard Communication Mode
To help you understand See
standard-communication mode Figure 1.2
how a master station requests data Figure 1.3
41181
•
Check for and send
outgoing MSG
•
Select next station
to poll
timeout received and
station inactive
timeout received and
station active and
tries > ‘DF1 message
retries’ make
station inactive
EOT received indicating no MSG to
send make station active
(if inactive)
MSG received and single
poll mode forward data
to or return data from
data table
•
Send poll
•
Start ACK timeout
•
Wait for EOT or
MSG (or timeout)
MSG received and
multiple mode
forward data to or
return data from
data table
timeout received and
station active and tries
< or = ‘DF1 message
retries’