Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 329)

Publication AG-UM008C-EN-P - February 2005
Using Dial-up Telephone Communication 10-9
Report-by-Exception and/or
Master Station-Initiated
Communication
Report-by-exception communication refers to the remote stations
initiating a dial-up connection to the master station upon change of
input status or process data in order to update the master station’s
data table.
Master station-initiated communication refers to the master station
initiating the dial-up connections to each of the remote stations on a
round robin or time-scheduled basis in order to update the master
station’s data table.
A combination of report-by-exception and master station-initiated
communication is possible but requires two communication ports and
modems (one for dial-in and one for dial-out) at the master station in
order to be effective. This can be accomplished using a 1785-KE
module with a PLC-5 processor, a 1747-KE module with an SLC 5/03,
or a dual-port processor such as a MicroLogix 1500 LRP or a
CompactLogix L31.