I've got a couple of Modbus/tcp devices on the network, but the 'node scan' doesn't see anything when pointed at the correct IP address. Does anyone know what the 'node scan' is attempting to do/ how it works? (I need to work out if it's not working because the devices don't support the 'scan' request, or if there is some other problem)
Modbus Node Scan
Hi ChargeRegulator, welcome to the forum!
The Modbus scan tool is going through the slave IDs from 0 to 240 one at a time sending read holding registers at offset zero for one register: https://github.com/infiniteautomation/modbus4j/blob/master/Modbus4J/src/com/serotonin/modbus4j/ModbusMaster.java#L185
It will use the retry and timeout settings from the data source configuration, so if you are hoping it will discover a slave with a high slave ID, it may be many minutes before it even tries that ID.
OK, got the device set up correctly and the node scan finds it now! On to the next step..