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 05: Modbus Read Input Registers (v12)

This sketch shows the use of the Modbus communication protocol over RS-485 standard, and the use of the main functions of the library.

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_05] Modbus Read Input Registers -------- 
 *   
 *  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 readInputRegisters. 
 *  This function code is used to read contiguous input registers 
 *  in a slave.
 * 
 *  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 10

// Define the number of bytes to read
#define bytesQty 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.readInputRegisters(address, bytesQty);

  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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