Arduino client using Modbus TCP with a server device and Rs485 serial with other servers

Projects General Guidance
1

can you have an Arduino master using modbus tcp with one device and Rs485 serial with others? I have the Ethernet rev2 that I can get to communicate and send data to a Redlion G308 HMI but wanted to also setup an Rs485 communication with other Arduino using MAX485 Module (RS-485 TTL to RS485 MAX485CSA) It’s taken a huge learning curve to get this far and could use some help.
Thanks

2

what do you mean by Modbus TCP master? Modbus TCP has server and clients.

3

Yes this can be done. Its tricky though. I did mitsubishi plc as tcp master and arduino as slave + arduino master for x 2 485 rtu slave devices. But not arduino as tcp slave. You can use the arduino modbus tcp example code for this.

4

@Arrjax

Hope this will help.

5

You did a log of work there but it looks like I am in a little over my head. I can't find
"#include <ModbusSerial.h>" in the library and don't have any experience with GitHub and downloading files to use in my IDE.
So far I only have the Mega 2560 with Ethernet shield as a Client, toggling coils in some tags I set up on a Redlion HMI. I guess i should start with just trying to get holding registers and see if i can read data from the HMI first.

#include <SPI.h>
#include <Ethernet.h>
#include <Modbus.h>
#include <ArduinoRS485.h> // ArduinoModbus depends on the ArduinoRS485 library

#include <ArduinoModbus.h>
const int REG = 528; // Modbus Hreg Offset
// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
// The IP address of Client (will be dependent on your local network)

byte mac[] = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
IPAddress ip(xxx,xxx,x,xxx);
EthernetClient ethClient;
ModbusTCPClient modbusTCPClient(ethClient);

IPAddress server(xxx,xxx,x,xxx); // update with the IP Address of your Modbus server
const int inputPin3 = 3;
int ValveOpenInput = 0;

void setup() {
   pinMode(inputPin3, INPUT);

   
  //Initialize serial and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // start the Ethernet connection and the server:
  Ethernet.begin(mac, ip);

  // Check for Ethernet hardware present
  if (Ethernet.hardwareStatus() == EthernetNoHardware) {
    Serial.println("Ethernet shield was not found.  Sorry, can't run without hardware. :(");
    while (true) {
      delay(1); // do nothing, no point running without Ethernet hardware
    }
  }
  if (Ethernet.linkStatus() == LinkOFF) {
    Serial.println("Ethernet cable is not connected.");
  }
  
}

void loop() {
ValveOpenInput = digitalRead(inputPin3);

  if (!modbusTCPClient.connected()) {
    // client not connected, start the Modbus TCP client
    Serial.println("Attempting to connect to Modbus TCP server");

  
    if (!modbusTCPClient.begin(server, 502)) {
      Serial.println("Modbus TCP Client failed to connect!");
    } else {
   // client connected
      Serial.println("Modbus TCP Client connected");
    }
  } else {
    
  }
   //write to the coil at address 0x00 the value of 0x01
  if (ValveOpenInput == 1 ) {
      (!modbusTCPClient.coilWrite(0x00, 0x01));
    delay(1);
  } else {
      (!modbusTCPClient.coilWrite(0x00, 0x00));
    delay(1);
  }
}
6

Yes you are correct, Modbus Client.

7

So far I only have the Mega 2560 with Ethernet shield as a Client, toggling coils in some tags I set up on a Redlion HMI set as a server. Haven’t figured out how to read registers or inputs in the Arduino so I can toggle bits on the HMI. I’ll look at the examples again and see if I can make heads of it.

8

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.