Rockwell Automation AADvance Controller Configuration Guide - Manual (Page 192)

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Issue 07
Configuration Guide (AADvance Controller)
The illustration shows the message scheduling for a master with three slaves needing
four, two and three messages.
The total number of messages that the master has to send in a complete poll cycle is
equal to the largest number of messages scheduled for any one slave, multiplied by the
total number of slaves. So, in this example the total number of messages is 4
 3 = 12.
There are nine messages defined for the three slaves; the message scheduling
mechanism sends three of these messages twice to make the total of twelve. The
sequence of messages seen on the serial communications link in this example is listed
in the table.
Table 22: Message Sequence for Example Modbus Master
Sequence
Number Slave Message Remarks
1 Slave 1 Message 1
2 Slave 2 Message 1
3 Slave 3 Message 1 End of first pass through all slaves
4 Slave 1 Message 2
5 Slave 2 Message 2 End of pass through slave 2
6 Slave 3 Message 2
7 Slave 1 Message 3