Rockwell-automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM Instrukcja Użytkownika Strona 28

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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’
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