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Communication / RS-485:

» RS-485 08: Modbus Several Slaves

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 example shows how to create a network with several slaves, and how to get data from them.

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_08] Modbus Several Slaves -------- 
 *   
 *  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 how to create a network with several slaves, 
 *  and how to get data from them. 
 * 
 *  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 temperatureSensor(1); 

// Instantiate ModbusMaster object as slave ID 2
ModbusMaster485 co2Sensor(2); 


// Define addresses for reading
#define tempRegister 10
#define co2Register  0

// Define the number of bits 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
  temperatureSensor.begin(9600);
  co2Sensor.begin(9600);

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


void loop()
{
//              Reading from the temperature sensor 
// *****************************************************************************************

  // This variable will store the result of the communication.
  // result = 0 : no errors
  // result = 1 : error occurred  
  int result =  temperatureSensor.readInputRegisters(tempRegister,bytesQty);

  if (result != 0) {
    //If no response from the slave, print an error message. 
    USB.println("Communication error. Couldn't read from temperature sensor");
    delay(100);
  } 
  else { 

    // If all OK
    USB.print("Temperature read from slave ID 1: ");

    // Print the read data from the slave 
    USB.print(temperatureSensor.getResponseBuffer(0));
    delay(100);
  }

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


//              Reading from the co2 sensor          
// *****************************************************************************************

  // result = 0 : no errors
  // result = 1 : error occurred 
  result =  co2Sensor.readHoldingRegisters(co2Register,bytesQty);

  if (result != 0) {
    // If no response from the slave, print an error message. 
    USB.println("Communication error. Couldn't read from the C02 sensor");
    delay(100);
  } 
  else { 

    // If all OK. 
    USB.print("CO2 data read from slave ID 2: ");

    // Print the read data from the slave 
    USB.print(co2Sensor.getResponseBuffer(0));
    delay(100);
  }

  USB.print("\n");
  delay(1000);
  
  // Clear the response buffer
  temperatureSensor.clearResponseBuffer();
  co2Sensor.clearResponseBuffer();

}




Output

D#
Modbus communication over RS-485
Temperature read from slave ID 1: 223
CO2 data read from slave ID 2: 134

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