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MODBUS++ (MODBSPP) v0.3

CMake

0 Info, Updates and Discalimer

0.0 Info

MODBUS++ (MODBUSPP) is an header-only open source c++ class/ library making an encapsulation of Modbus TCP Protocol for client.

MODBUS++ is providing a more OOP friendly syntax.

The code now is modified to extend for Windows! However, the code for running on Windows is not throughly tested.

0.1 Updates

UPDATES in v0.3 compared to V0.2:

  1. Bug Fixing
  2. Type fixing
  3. Initial Windows support (in dev, not fully tested)
  4. Logging as Option
  5. Cmake install script
  6. Pasting licensing information in file

1 Usage

To use the library, please follow the steps below. Please note current library is only compatible with Linux distributions because of the socket library dependencies.

1.1 Download

Download the MODBUS++, you can:

1.2 Include In your code

  1. Copy the "moodbus.h" to your include directory and include the code whenever appropriate:

    include "modbus.h"

  2. On Linux platform, you could also use 
    mkdir build
cd build
cmake ..
sudo make install
    This will install the header under usr/local/include and include the code whenever appropriate

    include "modbuspp/modbus.h"

1.3 Logging as Option

To enable logging, simply set ENABLE_MODBUSPP_LOGGING in your compile option, see CMakeLists.txt with example.

2 Getting Started with a Example

2.1 Getting the Example

Checkout example.cpp for a example usage of MODBUSPP. Please note that the code should be compiled using c++11 compilers. A sample CMakeLists.txt is included. To build example:

2.1.1 CMAKE

mkdir build
cd build
cmake ..
make

2.1.2 G++

g++ example.cpp --std=c++11 -o example

2.1.3 MSCV

Open your Visual Studio to compile the project

2.2 Tutorials

Let's break the code down, before you read this, reference to example.cpp. The example shows basic usages of how to create a modbus client connecting to a modbus server and perform modbus operations in your program.

Include the header

To start with, be sure to include the modbus.h header in your program

#include "modbus.h"

This line includes the header modbus.h from the library, this will tell the compiler to look for functions and variables in the related file.

Create and connects a mobus server

Before performing any modbus operations, a connection needed to be setup between the modbus client(your program) and a modbus server(could be a controller).

modbus mb = modbus("127.0.0.1", 502); mb.modbus_set_slave_id(1); mb.modbus_connect();

These lines creates local modbus client with target IP address at 127.0.0.1 and port at 502, a server with id 1.

Performe Mobus Operations

Modbus usually have 2 types of operations, reading and writing. Reading operations include reading a coil, reading input bits, reading holding registers, and reading input registers. Writing Operations include writing sigle coil, wirting single register, writing multiple coil, and writing multiple registers. Be sure to create a connection before performing any operations. Modbus is relatively low-level protocols. It is useful to have strong computer structure knowledge to understand it.

  1. The following line show how to read a coil (function 0x01). These lines read a bit from the coil at address 0.

bool read_coil; mb.modbus_read_coils(0, 1, &read_coil);

  1. The following lines show how to read input bits(discrete input) (function 0x02). These lines read a bit from discrete inputs at address 0.

bool read_bits; mb.modbus_read_input_bits(0, 1, &read_bits);

  1. The follwing lines show how to read holding registers (function 0x03). These lines read a word(16 bits) from holding registers starting at address 0.

uint16_t read_holding_regs[1]; mb.modbus_read_holding_registers(0, 1, read_holding_regs);

  1. The following lines show how to Read input registers (function 0x04). These lines read a word(16 bits) from input registers starting at address 0.

uint16_t read_input_regs[1]; mb.modbus_read_input_registers(0, 1, read_input_regs);

  1. The following lines show how to write single coil (function 0x05). These lines write a bit to the coil at address 0.

mb.modbus_write_coil(0, true);

  1. The following lines show how to write single register (function 0x06). These lines write a word(16 bits) to the register at address 0.

mb.modbus_write_register(0, 123);

  1. The following lines show how to write multiple coils (function 0x0F). These lines write multiple bits to the coil starting from address 0, for a length of 4.

bool write_cols[4] = {true, true, true, true}; mb.modbus_write_coils(0,4,write_cols);

  1. The following lines show how to write multiple regs (function 0x10). These lines write multiple words to the register starting from address 0, for a length of 4.

uint16_t write_regs[4] = {123, 123, 123}; mb.modbus_write_registers(0, 4, write_regs);