clientSync.ino

/*
  Modbus Library for Arduino Example - Modbus IP Client (ESP8266/ESP32)
  Read Holding Register from Modbus Server in blocking way

  (c)2020 Alexander Emelianov (a.m.emelianov@gmail.com)
  https://github.com/emelianov/modbus-esp8266
*/

#ifdef ESP8266
 #include <ESP8266WiFi.h>
#else
 #include <WiFi.h>
#else
#error "Unsupported platform"
#endif
#include <ModbusTCP.h>

const int REG = 528;               // Modbus Hreg Offset
IPAddress remote(192, 168, 30, 13);  // Address of Modbus Slave device

ModbusIP mb;  //ModbusTCP object

void setup() {
  Serial.begin(115200);
 
  WiFi.begin("SSID", "PASSWORD");
  
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
 
  Serial.println("");
  Serial.println("WiFi connected");  
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  mb.client();
}

uint16_t res = 0;

void loop() {
  if (mb.isConnected(remote)) {   // Check if connection to Modbus Slave is established
    uint16_t trans = mb.readHreg(remote, REG, &res);  // Initiate Read Hreg from Modbus Server
    while(mb.isTransaction(trans)) {  // Check if transaction is active
      mb.task();
      delay(10);
    }
    Serial.println(res);          // At this point res is filled with responce value
  } else {
    mb.connect(remote);           // Try to connect if no connection
  }
  delay(100);
}