RS-485 09: Modbus Slave Mode

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 the use of the Waspmote RS-485 in slave mode.

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. - This example can be executed in Waspmote v15

Code

/*   
 *  ------ [RS-485_09] Modbus Slave Mode -------- 
 *   
 *  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 Waspmote RS-485 in slave mode. 
 * 
 *  Copyright (C) 2016 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 . 
 *   
 *  Version:          3.0 
 *  Implementation:   Ahmad Saad
 */

// Include these libraries for using the RS-485 and Modbus functions
#include <ModbusSlave.h>

// Create new mbs instance 
ModbusSlave mbs(RS485_COM);

// Slave registers
enum 
{        
  MB_0,   // Register 0 
  MB_1,   // Register 1 
  MB_2,   // Register 2 
  MB_3,   // Register 3    
  MB_4,   // Register 4     
  MB_REGS // dummy register. using 0 offset to keep size of array
};

int regs[MB_REGS];

void setup()
{
  // Power on the USB for viewing data in the serial monitor
  USB.ON();  
  USB.println(F("Modbus Slave mode example over RS-485"));
  
  // Modbus slave configuration parameters   
  // SlaveId 
  const unsigned char SLAVE = 2;   
  // Baud rate
  const long BAUD = 9600;    
  // Configure msb
  mbs.configure(SLAVE, BAUD);
}

void loop()
{
  // Pass current register values to mbs
  mbs.update(regs, MB_REGS);

  // Read all the analog Inputs, and store the values in 
  // the Modbus registers
  regs[MB_0] = analogRead(ANALOG1);  
  regs[MB_1] = analogRead(ANALOG2); 
  regs[MB_2] = analogRead(ANALOG3);  
  regs[MB_3] = analogRead(ANALOG4); 
  regs[MB_4] = analogRead(ANALOG5);  
  
  delay(10);
}