Development v12

Warning - Product Update

All the resources present on this section belong to Waspmote v12, Waspmote Plug & Sense! v12 and Meshlium v3.8.

If you have a Waspmote v15, Waspmote Plug & Sense! v15 or Meshlium v4.0 please go to the new Development Section.

Check what is your version and what are the differences between the old and the new one in this document.

» RS-485 04: Modbus Read Coils (v12)

This example shows the use of the function readCoils. This function requests the ON/OFF status of discrete coils from the slave device.

Required Materials

1 x Waspmote
1 x Battery
1 x RS-485

Notes

- Waspmote must be powered with a battery
- 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 can be executed in Waspmote v12

Code

/*   
 *  ------ [RS-485_04] Modbus Read Coils -------- 
 *   
 *  This sketch shows the use of the Modbus communication protocol over 
 *  RS-485 standard, and the use of the main funcions 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 readCoils. This function 
 *  requests the ON/OFF status of discrete coils from the slave 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 addres for reading
#define address 1 

// Define the number of bits to read
#define bitQty 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.readCoils(address, bitQty);

  if (result != 0) {
    // If no response from the slave, print an error message 
    USB.println("Communication error");
    delay(1000);
  } 
  else { 

    // If all ok 
    USB.print("Read value: ");

    // Print the read data from the slave 
    USB.print(node.getResponseBuffer(0));
    delay(1000);
  }

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

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

}

Output

E#
Modbus communication over RS-485
Read value : 223
Read value : 224

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