Please I have a technical question about Modbus Slave-Timeout. It is possible as for some bus system to detect the presence of a no longer existing master by a Modbus slave device during a communication? Because I still not find mention, in particular about this scenario in thr Modbus protocol.

Thank you,

 

That would be a watchdog function. There is nothing in the Modbus specification about that because if the master (client) isn't communicating, there are no Modbus messages to be interpreted by the slave (server), are there?

Something like that would have to be a feature of the slave, and may be called a "watchdog". For example, if the slave did not receive a valid poll within a set period of time, it could fault and then perform some action (e.g. turn off its outputs).

The Modbus spec is all about what the messages look like as they go over the wire. A watchdog function would be product and application specific, and is outside the scope of a communications protocol. You would need to look at each manufacturer's product literature to see if they support something like that. It's not a feature that many people have a use for.