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Communication / RS-485:

» RS-485 11: Modbus Master ACC & Battery Level

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 configure the Waspmote as a Modbus master device. The Waspmote read the ACC values and the battery level from a Modbus slave.

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.
See the example RS485_10_modbus_slave_acc_battery_level

Code

/*   
 *  ------ [RS-485_11] Modbus Master ACC and Battery level -------- 
 *   
 *  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 configure the Waspmote as a Modbus 
 *  master  device. The Waspmote read the ACC values and the battery
 *  level from a Modbus slave.
 *
 *  Note: See the example RS-485_10_modbus_slave_acc_battery_level
 * 
 *  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 slave(1); 

// Define addresses for reading
#define accX 0 
#define accY 1 
#define accZ 2
#define bateryLevel 3

// Define the number of bits to read
#define bytesQty 4

void setup()
{
  // Power on the USB for viewing data in the serial monitor
  USB.ON();

  // Initialize Modbus communication baud rate
  slave.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 
  // Read 4 bytes
  int result =  slave.readHoldingRegisters(accX ,bytesQty);

  if (result != 0) {
    // If no response from the slave, print an error message. 
    USB.println("Communication error. Couldn't read from slave");
    delay(100);
  } 
  else { 
    USB.println("\n \t0X\t0Y\t0Z\tBatery %"); 
    USB.print(" ACC\t"); 
    USB.print(slave.getResponseBuffer(accX), DEC);
    USB.print(F("\t")); 
    USB.print(slave.getResponseBuffer(accY), DEC);
    USB.print(F("\t")); 
    USB.print(slave.getResponseBuffer(accZ), DEC);
    USB.print(F("\t")); 
    USB.println(slave.getResponseBuffer(bateryLevel), DEC);
  }

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

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

}

Output

D#
Modbus communication over RS-485

0X 0Y 0Z Batery %
ACC 65292 329 953 89

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