Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 31)

Publication AG-UM008C-EN-P - February 2005
Designing Communication 1-13
Choosing Single or Multiple Message Transfer
Depending on your application’s requirement, you can choose the
number of messages you want to receive from a slave station during
its turn.
Planning for Timing Issues
Two types of timing categories exist.
•
Protocol timers, which specify how long a master station will
wait to ‘hear’ from a slave station.
•
Request to send (RTS) timers, which you can use to make sure
the modem is ready to accept data or has passed on the data
(does not apply when control line is configured for No
Handshaking).
Set and adjust these timing values as necessary for your application.
Set your RTS times based on the communication media and modem
you are using.
Design Considerations
•
Define a polling list type to use (normal or priority).
•
Define a station list.
•
Use Figure 1.6 to help understand how the MSGs are handled
using standard communication.
If you want to receive Choose
only one message from a slave station per poll
per a station’s turn.
single transfer
Choose this method only if it is critical to keep the
poll list scan time to a minimum.
as many messages from the slave station as it has
in its queue. multiple transfer