ModBus Test

//Defining header Files

#include <ModbusMaster.h>

#define MAX485_DE_RE 4

ModbusMaster node; //object node for class ModbusMaster

void preTransmission()
{
  digitalWrite(MAX485_DE_RE, HIGH);
}

void postTransmission()
{
  digitalWrite(MAX485_DE_RE, LOW);
}

void setup()
{
  pinMode(MAX485_DE_RE, OUTPUT);

  digitalWrite(MAX485_DE_RE, LOW);

  Serial.begin(115200);
  // Transmission mode: MODBUS-RTU, Baud rate: 9600bps, Data bits: 8, Stop bit: 1, Check bit: no
  Serial1.begin(9600, SERIAL_8N1, 16, 17);

  // Slave address: the factory default is 01H (set according to the need, 00H to FCH)
  node.begin(1, Serial1);
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}
//Setup ends here

void loop()
{
  // The 03H Function Code Example: Read The Atmospheric Temperature, Humidity & Pressure
  // Host Scan Order (Slave addr:0x01): 01 03 00 00 00 03 05CB
  // Slave Response: 01 03 06 01 21 0164 2728 C76E
  // Address of the first register Lo bytes is 00
  // Number of registers of Lo bytes is 03
  uint8_t result = node.readHoldingRegisters( 0, 3 );
  Serial.print("result = ");
  Serial.println( result );

  delay (1000);

  if (result == node.ku8MBSuccess)
  {
    Serial.print("Temperature: ");
    Serial.print(node.getResponseBuffer(0)/10.00);
    Serial.println("degC");
    Serial.print("Humidity: ");
    Serial.print(node.getResponseBuffer(1)/10.00);
    Serial.println("%");
    Serial.print("Pressure: ");
    Serial.print(node.getResponseBuffer(2)/10.00);
    Serial.println("mbar");
  }

  Serial.print("\n");
  delay(1000);
}