Modbus RTU sensor, MAX485, Controllino MAXI(Arduino Mega 2560 PLC)

[Nur_Alya]

Hi. I was given a task to do a school project using Controllino MAXI/Arduino Mega 2560 with MAX485 and a Modbus RTU sensor where the objective is to get some reading from the sensor.

Here I am struggling with coding and connection for it. I wanted to ask for advice, opinion on the things I've done with it at the moment. As I am lost with on how to use the one MAX485 as transmitter/receiver in getting values from the sensor to the Controllino.

At the moment;
Sensor: Brown -> External power supply, B -> B MAX485, A -> A MAX485, Black -> GND Controllino
MAX485: DE & RE -> GND, DI -> TX3 Controllino, RO -> RX Controllino, VCC -> 5V RS485 Controllino, GND -> GND Controllino
Controllino : No connection at the moment

Is it true? Or fine with what I am doing at the moment?

 

[FvM]

Because RS485 is half duplex, DE must be dynamically controlled, activated during transmit.

 

[KlausST]

Hi,

you need a schematic.
and you need to read modbus specification and go through some tutorials. There are even videos.

Klaus

 

[FvM]

I expect that existing Arduino MODBUS RTU client examples bring all what you want, as a starting point see

ArduinoModbus - Arduino Reference

The Arduino programming language Reference, organized into Functions, Variable and Constant, and Structure keywords.

www.arduino.cc

 

[prakashvenugopal]

Hi,

Short the RE and DE pin in the MAXRS-485 IC and give to one Controller pin to control the Receive/Transmit

If that pin High --> Transmit
If that pin Low --> Receive

Regards,
V. Prakash