Modbus library

Tiny Modbus RTU and ASCII library in C.

Goals

They are many existing Modbus libraries out there. This one will differ from them on these aspects:

• Pure C99 software implementation, no OS specific calls
• Just one function to call!
• BSD license

Features

• Modbus TCP, RTU and ASCII (maybe broken) packets
• Slave functions 3, 4, 6 and 16
• Exception

TODO

• More unit tests
• Coils support
• Master support

Install

Just add the two modbus.c and modbus.h files in your project.

Example

Here is a minimal example:

#include <string.h>
#include <stdio.h>

struct app_data_t
{
    uint16_t hop;
    uint16_t hip;
} app_data = {1000U, 4U};


static const modbus_section_t section = { (uint16_t *)&app_data, 0x0000U, SECTION_SIZE(app_data), MDB_READ_WRITE };

const modbus_ctx_t context = { 12U, MODBUS_TCP, &section, 1U };

int main(void)
{
    static const uint8_t read_holding[] = { 0x00, 0x12, 0x00, 0x00, 0x00, 0x06, 0x0C, 0x03, 0x00, 0x00, 0x00, 0x0A };

    uint8_t data[MAX_DATA_LENGTH];

    memcpy(data, read_holding, sizeof(read_holding));

    int32_t ret = modbus_process(&context, data, sizeof(read_holding));

    if (ret >= 0)
    {
        printf("Success! response size is %d bytes.\r\n", (int)ret);
    }
}

Copy paste this code snippet in a file called main.c, then in call gcc -o modbus modbus.c main.c.

License

Copyright (c) 2017, Anthony Rabine All rights reserved.

This software may be modified and distributed under the terms of the BSD license. See LICENSE.txt for more details.