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 sketch shows how to use the function write single coil. This function code is used to write a single holding register in a remote device
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_07] Modbus Write Single Register -------- * * 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 writeSingleRegiter(). * This function code is used to write a single holding register * in a remote device. * * 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 * Design: David Gascon * Implementation: Ahmad Saad */// Include these libraries for using the RS-485 and Modbus functions#include<ModbusMaster.h>// Instantiate ModbusMaster object as slave ID 1ModbusMaster node(RS485_COM,1);// Define one address for reading#defineaddress1// Define the number of bytes to read#definebyteData1voidsetup(){// Power on the USB for viewing data in the serial monitorUSB.ON();// Print hello messageUSB.println(F("Modbus communication over RS-485"));delay(100); // Initialize Modbus communication baud ratenode.begin(9600); }voidloop(){// This variable will store the result of the communication.// result = 0 : no errors. // result = 1 : error occurred. int result =node.writeSingleRegister(address,byteData);if (result !=0) {// If no response from the slave, print an error message. USB.println(F("Communication error"));delay(100); } else { // If all ok USB.print(F("Data written successfully"));delay(100); }USB.print(F("\n"));delay(1000);// Clear the response buffernode.clearResponseBuffer();}
Output
H#
Modbus communication over RS-485
Data written successfully.