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Communication / RS-485:

» RS-485 07: Modbus Write Single Register

This sketch shows the use of the Modbus communication protocol over RS-485 standard, and the use of the main functions of the library. This sketch shows how to use the function write single coil. This function code is used to write a single holding register in a remote device

Required Materials

1 x Waspmote
1 x Battery
1 x RS-485

Notes

Modbus allows for communication between many devices connected to the same network.
There are many variants of Modbus protocols, but Waspmote implements the RTU format.
Modbus RTU is the most common implementation available for Modbus.

Code

/*   
 *  ------ [RS-485_07] Modbus Write Single Register -------- 
 *   
 *  This sketch shows the use of the Modbus communication protocol over 
 *  RS-485 standard, and the use of the main functions of the library.
 *  Modbus allows for communication between many devices connected
 *  to the same network. There are many variants of Modbus protocols, 
 *  but Waspmote implements the RTU format. Modbus RTU is the most 
 *  common implementation available for Modbus. 
 *  
 *  This example shows the use of the function writeSingleRegiter(). 
 *  This function code is used to write a single holding register 
 *  in a remote device.
 * 
 *  Copyright (C) 2014 Libelium Comunicaciones Distribuidas S.L. 
 *  http://www.libelium.com 
 *   
 *  This program is free software: you can redistribute it and/or modify 
 *  it under the terms of the GNU General Public License as published by 
 *  the Free Software Foundation, either version 2 of the License, or 
 *  (at your option) any later version. 
 *   
 *  This program is distributed in the hope that it will be useful, 
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of 
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 *  GNU General Public License for more details. 
 *   
 *  You should have received a copy of the GNU General Public License 
 *  along with this program. If not, see <http://www.gnu.org/licenses/>. 
 *   
 *  Version:          0.1 
 *  Design:           David Gascon 
 *  Implementation:   Ahmad Saad
 */
 
 
// Include these libraries for using the RS-485 and Modbus functions
#include <Wasp485.h>

#include <ModbusMaster485.h>

// Instantiate ModbusMaster object as slave ID 1
ModbusMaster485 node(1);

// Define one address for reading
#define address 1

//define the number of bytes to read
#define byteData 0

void setup()
{
  // Power on the USB for viewing data in the serial monitor
  USB.ON();

  // Initialize Modbus communication baud rate
  node.begin(9600);

  // Print hello message
  USB.println("Modbus communication over RS-485");
  delay(100);
}


void loop()
{
  // This variable will store the result of the communication
  // result = 0 : no errors
  // result = 1 : error occurred
  int result =  node.writeSingleRegister(address,byteData);

  if (result != 0) {
    // If no response from the slave, print an error message
    USB.println("Communication error");
    delay(100);
  } 
  else { 

    // If all OK 
    USB.print("Data written successfully");
    delay(100);
  }

  USB.print("\n");
  delay(1000);

  // Clear the response buffer
  node.clearResponseBuffer();

}




Output

D#
Modbus communication over RS-485
Data written successfully.

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