Best practicw for managing modbus slaves

2 posts in this topic


One of our systems can have 12 modbus slaves, schneider VFD. Is ir common to disable slaves that are not used?

How does the modbus work when a slave is offline? Does offline slaves slow down the traffic?

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Modbus master/clients all have a time-out setting that in the absence of a reply from a slave will skip over it (instead of waiting forever for the reply) and go onto the next task/action.   Assuming that the time-out can be flagged, It would take some programming to recognize some number of reply-failures and then drop the missing slave from the line-up. 

Yes, slave loss slows down 'throughput' because the master waits the entire time-out interval before moving onto the next action.  The 'next' action might be a re-try or it might be 'ignore and proceed'.

Slaves can be wired on an RS-485 multidrop network without affecting the network if the slave is not enabled.   But disabling the slave's comm will not speed up the Master's actions.  The bad slave has to be taken out of the Master's 'line-up' to avoid the time the master waits for a reply that might not be forthcoming.

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