Modbus extended addressing

Trying to read modbus from a Idec PLC, but it has holding registers of addresses starting at 400000.
The modbus node won't let me define addresses above 65,535
Should I be using some other node?

You should mention which Modbus node you are using. The most comprehensive and used nowadays is node-red-contrib-modbus and being the only one I have used so far I will provide an opinion based on this node.

Considering that holding registers are in the range 400001 - 465535 then reading holding register 400001 should translate to reading address 0000. The Modbus node allows you to select the address from 0 to 65535.

I see no constraint on the contrib node. It could be the opposite in the sense that some devices may not have all the 65536 address numbers available for use.

Perhaps if you post your flow and explain what is not working it would be easier for someone in the forum to provide the best advice. My knowledge in Modbus is somehow limited and have not worked with the PLC model you mentioned.

Yes, that worked.

1 Like