#include <SPI.h>
#include <Ethernet.h>
#include <ModbusEthernet.h>

byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
IPAddress ip(192, 168, 30, 177);
ModbusEthernet mb;

void setup() {
  Serial.begin(115200);     // Open serial communications and wait for port to open
  #if defined(AVR_LEONARDO)
  while (!Serial) {}        // wait for serial port to connect. Needed for Leonardo only
  #endif
  Ethernet.init(5);        // SS pin
  Ethernet.begin(mac, ip);  // start the Ethernet connection
  delay(1000);              // give the Ethernet shield a second to initialize
  mb.server();              // Act as Modbus TCP server
  mb.addReg(HREG(100));     // Add Holding register #100
}

void loop() {
  mb.task();                // Server Modbus TCP queries
  delay(50);
}