Arduino Uno as Modbus Slave TCP

Projects Networking, Protocols, and Devices
1

I'm trying to find a library for running a Uno + W5100 shield as Modbus Slave . I need to use FC03 (read holding registers) and fc16( write multiple register) as this

FC3 --> reg 40000 length 100
FC16 --> reg 44000 length 10

I've found ,many GitHub, the better working is this My Arduino Projects - Website dedicated to my arduino projects - A ModBus TCP library for the Arduino system but on writing (FC16 --> reg 44000 length 10) it seems overwrite register 40000...

the I found ArduinoModbus - Arduino Reference : someone has some sample of it?

2

install it in IDE and the examples are in File menu

3

I've got a look but samples are referred to wifi only (for Modbus TCP) never to W5100 RJ45 shield

4

fleaP75:
I've got a look but samples are referred to wifi only (for Modbus TCP) never to W5100 RJ45 shield

replace WiFiCliient with EthernetClient. and you know how to connect to network with Ethernet

5

mm .it doesn0t work so much.. do you have some sample with ModbusTCPServer?

6

I use Modbus TCP with my own functions, because two years ago when I wrote my project I could not find a working Modbus TCP library. From your post I discovered that Arduino created a modbus library last year.

So I tested it now. It is not good for AVR boards. It works, but it is large and uses dynamic memory allocation.

#include <Ethernet.h>
#include <ArduinoModbus.h>

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };

EthernetClient ethClient;
ModbusTCPClient modbus(ethClient);

const IPAddress serverAddress(192,168,1,7);
const byte CONSUMPTION_METER_UID = 241;
unsigned int AC_POWER_REGISTER_ADDR = 40087;
unsigned int AC_POWER_SF_REGISTER_ADDR = 40091;
const byte AC_POWER_REQUEST_LENGTH = AC_POWER_SF_REGISTER_ADDR - AC_POWER_REGISTER_ADDR + 1;

void setup() {
  Serial.begin(115200);

  // start the Ethernet connection:
  Serial.println("Initialize Ethernet with DHCP:");
  Ethernet.init(10);
  if (Ethernet.begin(mac) == 0) {
    Serial.println("Failed to configure Ethernet using DHCP");
      while (true) {
        delay(1); // do nothing, no point running without Ethernet hardware
      }
  } else {
    Serial.print("  DHCP assigned IP ");
    Serial.println(Ethernet.localIP());
  }

}

void loop() {
  int err = modbusConnection();
  if (err != 0) {
    Serial.println(err);
  } else {
    int l = modbus.requestFrom(241, HOLDING_REGISTERS, AC_POWER_REGISTER_ADDR, AC_POWER_REQUEST_LENGTH);
    if (l != AC_POWER_REQUEST_LENGTH) {
      Serial.println(modbus.lastError());
    } else {
      short val = modbus.read();
      for (int i = 0; i < AC_POWER_REQUEST_LENGTH - 2; i++) {
        modbus.read();
      }
      short scaleFactor = modbus.read();
      Serial.println(val * pow(10, scaleFactor));
    }
  }
  delay(15000);
}

int modbusConnection() {
  if (!modbus.connected()) {
    modbus.stop();
    if (!modbus.begin(serverAddress))
      return -1;
  }
  return 0;
}
7

Juray, is the code for running Arduino as Client?

8

fleaplc:
Juray, is the code for running Arduino as Client?

yes, sorry you want a server. (modbus TCP has server and client, not slave and master). I missed that you want a server (slave).
but the library is not suitable for Uno.