Ha! I changed the logging level of org.openhab.core.io.transport.modbus to TRACE and can now see the request message/frame being sent from the openhab binding- and that is (as to my limited understanding of modbus) totally off!
Request for holding register 88 being sent:
00 00 00 00 00 06 01 03 00 58 00 01
Should be like that (at least this request is working when being sent by tool Simply Modbus TCP Client):
01 03 00 58 00 01 05 D9
Looks like Modbus binding is sending plain modbus TCP requests and not Modbus RTU requests even though rtuEncoded = true is set in the thing file.
Changing the rtuEncoded setting is not affecting anything in regards to the message/frame being sent - looks like a bug to me.
Is there anyone using modbus tcp binding with rtuEncoded = true ???
I’ve created a seperate post for the rtuEncoded issue with the modbus binding - see Mobus binding with “rtuEncoded=true” not working