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debevv / nanoMODBUS

A compact MODBUS RTU/TCP C library for embedded/microcontrollers
MIT License
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arduino c embedded embedded-c embedded-systems microcontroller microcontrollers modbus modbus-library modbus-rtu modbus-tcp stm32

readme

nanoMODBUS - A compact MODBUS RTU/TCP C library for embedded/microcontrollers

If you found this library useful, buy me a coffee on

nanoMODBUS is a small C library that implements the Modbus protocol. It is especially useful in embedded and resource-constrained systems like microcontrollers.
Its main features are:

At a glance

#include <stdio.h>

#include "nanomodbus.h"
#include "my_platform_stuff.h"

int main(int argc, char* argv[]) {
    // Set up the TCP connection
    void* conn = my_connect_tcp(argv[1], argv[2]);
    if (!conn) {
        fprintf(stderr, "Error connecting to server\n");
        return 1;
    }

    // my_transport_read() and my_transport_write() are implemented by the user 
    nmbs_platform_conf platform_conf;
    platform_conf.transport = NMBS_TRANSPORT_TCP;
    platform_conf.read = my_transport_read;
    platform_conf.write = my_transport_write;
    platform_conf.arg = conn;    // Passing our TCP connection handle to the read/write functions

    // Create the modbus client
    nmbs_t nmbs;
    nmbs_error err = nmbs_client_create(&nmbs, &platform_conf);
    if (err != NMBS_ERROR_NONE) {
        fprintf(stderr, "Error creating modbus client\n");
        return 1;
    }

    // Set only the response timeout. Byte timeout will be handled by the TCP connection
    nmbs_set_read_timeout(&nmbs, 1000);

    // Write 2 holding registers at address 26
    uint16_t w_regs[2] = {123, 124};
    err = nmbs_write_multiple_registers(&nmbs, 26, 2, w_regs);
    if (err != NMBS_ERROR_NONE) {
        fprintf(stderr, "Error writing register at address 26 - %s", nmbs_strerror(err));
        return 1;
    }

    // Read 2 holding registers from address 26
    uint16_t r_regs[2];
    err = nmbs_read_holding_registers(&nmbs, 26, 2, r_regs);
    if (err != NMBS_ERROR_NONE) {
        fprintf(stderr, "Error reading 2 holding registers at address 26 - %s\n", nmbs_strerror(err));
        return 1;
    }

    // Close the TCP connection
    my_disconnect(conn);

    return 0;
}

Installation

Just copy nanomodbus.c and nanomodbus.h inside your application codebase.

API reference

API reference is available in the repository's GitHub Pages.

Platform functions

nanoMODBUS requires the implementation of 2 platform-specific functions, defined as function pointers when creating a client/server instance.

Transport read/write

int32_t read(uint8_t* buf, uint16_t count, int32_t byte_timeout_ms, void* arg);
int32_t write(const uint8_t* buf, uint16_t count, int32_t byte_timeout_ms, void* arg);

These are your platform-specific functions that read/write data to/from a serial port or a TCP connection.
Both methods should block until either:

A value < 0 for byte_timeout_ms means no timeout.

Their return value should be the number of bytes actually read/written, or < 0 in case of error.
A return value between 0 and count - 1 will be treated as if a timeout occurred on the transport side. All other values will be treated as transport errors.

Callbacks and platform functions arguments

Server callbacks and platform functions can access arbitrary user data through their void* arg argument. The argument is useful, for example, to pass the connection a function should operate on.
Their initial values can be set via the nmbs_set_callbacks_arg and nmbs_set_platform_arg API methods.

Tests and examples

Tests and examples can be built and run on Linux with CMake:

mkdir build && cd build
cmake ..
make

Please refer to examples/arduino/README.md for more info about building and running Arduino examples.

Misc