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ed-chemnitz / qmodbus

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QModbusTcpServer write to slaves/clients? #30

Closed mancart closed 4 years ago

mancart commented 4 years ago

I am wracking my brain as to how the QModbusTcpServer is suppose to write to the slaves/clients? When I use QModbusTcpServer::setData() it does not send anything to the slaves as far as I can tell.

I can not find an example of how to do this anywhere. The Qt Examples seem like the slave is the only one writing and reading.

Thanks

shiftee commented 4 years ago

TIL that since v5.8 (2017) Qt has Modbus classes.

QModbus is an unrelated standalone Modbus Master program that uses the Qt GUI toolkit but not these classes.

A Modbus TCP server is a slave and only sends responses to the (single) master/client after it receives a request.

setData() is used by the slave side to update the values which can then be read by the master.

e.g. a refrigerator might write its current temperature using setData() every 5 seconds.

That data would only leave the device if a master device like a home automation controller made a request for it.

Looks like the slave would handle that request in QModbusServer::processRequest()