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Communication / RS-232:

» RS-232 06: Modbus Write Single Register

This sketch shows the use of the Modbus communication protocol over RS-232 standard, and the use of the main functions of the library. Modbus allows for communication between many devices connected to the same network.

Required Materials

1 x Waspmote
1 x Battery
1 x RS-232

Notes

This example shows how to configure the Waspmote as a Modbus master device. The Waspmote read the ACC values and the battery level from a Modbus slave.
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-232_06] Modbus Write Single Register -------- 
 *   
 *  This sketch shows the use of the Modbus communication protocol over 
 *  RS-232 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-232 and Modbus functions
#include <Wasp232.h>
#include <ModbusMaster232.h>

// Instantiate ModbusMaster object as slave ID 1
ModbusMaster232 node(1);

// Define one adders 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, SOCKET0);

  // Print hello message
  USB.println("Modbus communication over RS-232");
  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-232
Data written successfully.

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