Development

Communication / RS-485:

» RS-485 06: Modbus Write Single Coil

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 Singles Coil. This function writes a single coil to either ON or OFF.

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_06] Modbus Write Single Coil-------- 
 *   
 *  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 Singles Coil. 
 *  This function writes a single coil to either ON or OFF.
 *  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 readCoils. 
 *  This funtion writes a single coil to either ON or OFF.
 * 
 *  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 
 *  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

// Bit to write 
#define bitData 1

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.writeSingleCoil(address,bitData);

  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.

Quick Publish: