Modbus communication issue MAX485

Using Arduino Networking, Protocols, and Devices
1

Dear all,

I am trying to create communication between an arduino Mega and a modbus RTU energy meter by using a MAX485 module.

Firstly, I have checked adresses by usine Modbus doctor and results are following:

modbus doctor
modbus doctor785×467 44.1 KB

As a consequence, slave adress is 0x4B
And register adress is 0x111

When I try this code with on arduino MEGA:


#define DE 3
#define RE 2

ModbusMaster node;


void preTransmission()
{
  digitalWrite(DE,1);
  digitalWrite(RE,1);
}

void postTransmission()
{
  digitalWrite(DE,0);
  digitalWrite(RE,0);
}


void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);
  pinMode(DE,OUTPUT);
  pinMode(RE,OUTPUT);
  digitalWrite(DE,0);
  digitalWrite(RE,0);
  node.begin(0x4B,Serial1);
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}



void loop()
{
  uint8_t Resultat;
  Resultat = node.readHoldingRegisters(0x111, 16);
  if (Resultat == node.ku8MBSuccess)
  {
    Serial.print("connexion");
    Serial.println(Resultat);
  }
  else 
  {
    Serial.print("Echec:");
    Serial.println(Resultat);
  }
  delay(1000);  
}

The Serial response is always 226. I do not suceed to discuss with the energy meter.

Can you help me?

Thank you by advance

2

What is Modbus library do you use?

3

Your screenshot shows even parity.
try:
Serial1.begin(9600, SERIAL_8E1);

4

Just in case, does your device support reading of 16 consecutive registers?

5

226 is 0xE2 which says

/**
    ModbusMaster response timed out exception.

    The entire response was not received within the timeout period, 
    ModbusMaster::ku8MBResponseTimeout. 
    
    @ingroup constant
    */
    static const uint8_t ku8MBResponseTimedOut           = 0xE2;

there might be an mistake in your wiring.
Show us clear pictures of all your modules. We need to see each and every connection.

6

If device is respecting modbus protocol, it should respond with exception. But I agree, we don't know if it does....

7

Thank you, it works with this modification !!

8

Nice to hear!

9

.

please mark @kmin 's answer as solution.