MODBUS++ (MODBSPP) V0.2

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.

MODBUS++ is providing a more OOP friendly syntax.

The code has dependencies on libary on Linux for TCP/IP, if you want to use this in Windows, please check out winsock2 and rewrite portion of code of socket to be compatible with Windows operating system.

0.1 Updates

UPDATES in V0.2 compared to V0.1):

1. Cleand up some shitty code
2. Removed exceptions, using error message instead
3. Removed Enums, placing #define instead
4. Fixed some bugs (referencing to @konsolenritter's fix)
5. Combine files into a header only library

0.2 Disclaimer

The code was taken from one of my hack project and wrapped into a header and I take no warranty or responsibility of the code, as mentioned in license. Issues and emails are welcomed, and I will do by best to reply. However I generally do NOT have time to fix it oftenly, due to school and work. The code was written within 5 hours and I knew shit/bugs/issues are in the code, by indicating it with a version number. There are NO points HARRASING me through email for anything unusable.

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:

• Open your command window (cmd, shell, bash, etc.)

  git clone https://github.com/fanzhe98/modbuspp.git

• Directly download from the page.

1.2 Include In your code

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

include "modbus.h"

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

2.2 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);

2. 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);

3. 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);

4. 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);

5. 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);

6. 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);

7. 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);

8. 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);