Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 36)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 36
3.6. Modbus Master Polling Sequence
Once a Modbus master begins polling, one message from each slave connected to the Master is
executed in turn. This is repeated for all the messages listed for each slave. Once all the messages
for a given slave have been executed, then the list will be repeated from the first message again.
Figure 16 below shows the sequence of three slaves connected to a single master being polled.
Slave 1 Slave 3 Slave 2
msg 3
msg 1 msg 1 msg 1
msg 2 msg 2 msg 2
msg 3
msg 4
continue
Start
Poll
Figure 16 Modbus Master Polling Sequence