Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 32)

Publication AG-UM008C-EN-P - February 2005
1-14 Designing Communication
Figure 1.6 Effect of MSGs on Logix, PLC-5, SLC 500, and MicroLogix Polling
41185
1. Polled station 1; ready to poll station 2.
2. MSG sent to station 3 (MSG was waiting in queue).
Polling List
Polling List
Master
Station
Master
Station
slave
station 1 slave
station 2 slave
station 3
slave
station 1 slave
station 2 slave
station
Modem
Modem
Stn 1
Stn 2
Stn 3 Return Data Packet
or DLE EOT to
Master
Poll to slave
MSG to slave
Modem Modem Modem
Modem Modem Modem
Polling List
Master
Station
slave
station 1 slave
station 2 slave
station 3
Modem
Stn 1
Stn 2
Stn 3
Return Data Packet
to Master
Poll to slave
Modem Modem Modem
4. Master station polls station 3.
5. Station 3 replies with data.
3. Master station continues polling where it left off in the polling
sequence, e.g., station 2.
6. Master station returns to beginning of the poll list.
Stn 1
Stn 2
Stn 3