Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 28)

Publication AG-UM008C-EN-P - February 2005
1-10 Designing Communication
Figure 1.3 How a Master Station Requests Data
To design a communication scheme using standard-communication
mode, you must do the following:
•
design a polling scheme
•
plan for timing issues
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•
Ladder logic
triggers MSG
•
Master driver
formats command
packet
Master data table
ACK timeout received and
tries > ‘DF1 message
retries’ return error
indication
•
Send command
packet
•
Start ACK timer
•
Wait for ACK (or
timeout)
•
Start reply timer
•
Resume polling
•
Wait for reply (or
timeout)
reply packet
received return
data
reply timeout received
return error
indication
ACK received
ACK timeout received
and station active and
tries < or = ‘DF1 message
retries’