Hi I am trying to use a sketch based on SimpleModbusMasterExample to interrogate the registers of a flow meter (TUF-2000M) via modbus RTU. the sketch is running on an arduino uno clone (3.3V) with a MAX3485 RS485 driver (3.3v). For debugging I have been using modbus simulation software (trial programs from: http://www.modbustools.com/ running on a PC with a prolific usb to RS485 converter) So the RS485 bus has the pc, arduino & the flow meter connected to it.
The flow meter talks flawlessly to the pc running Modbus poll - all registers can be interrogated!
The arduino talks flawlessly to the pc running Modbus slave - registers can be read!
BUT the arduino will not communicate with the flow meter!
If the flow meter is set to slave 1 & the pc Modbus slave to slave 2 the arduino is clearly sending the correct codes (as seen by the pc) but for some reason the flow meter is not recognising them, even though it recognises identical codes sent from the pc!
The setup is on the bench so I don't think termination is an issue (I have tried various resistors anyway) The ground of the arduino is connected to the flow meter ground I have tried different RS485 drivers on the arduino to no effect
I am not at all sure where the problem is or even if it is hardware or software?
I would be grateful for suggestions as to where to look next?
I don't have a scope at the moment but I will have in a day or two!