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fortran-modbus

A collection of Fortran 2018 interface bindings to libmodbus, for Modbus RTU/TCP communication.

Build Instructions

The package libmodbus has to be installed with development headers. On FreeBSD, run:

# pkg install comms/libmodbus

On Linux, instead:

# apt-get install libmodbus5 libmodbus-dev

Build and install the Fortran library using the provided Makefile:

$ make
$ make install PREFIX=/opt

Link your programs against /opt/lib/libfortran-modbus.a -lmodbus. Optionally, overwrite the default compiler and the compiler flags:

$ make FC=ifx FFLAGS="-O3"

Or, use the Fortran Package Manager:

$ fpm build --profile release

Build and run the test program:

$ make test
$ ./test_modbus

Example

The following example program connects to a device via Modbus RTU and outputs two registers as a real number:

! example.f90
program main
    use, intrinsic :: iso_c_binding
    use :: modbus
    use :: modbus_rtu
    implicit none (type, external)

    integer, parameter :: ADDRESS = 50
    integer, parameter :: SLAVE   = 10

    integer                  :: stat
    integer(kind=c_uint16_t) :: regs(2)
    real                     :: f
    type(c_ptr)              :: ctx

    ctx  = c_null_ptr
    stat = -1
    regs = 0

    mb_block: block
        ! Create Modbux RTU context.
        ctx = modbus_new_rtu('/dev/ttyUSB0', 19200, 'E', 8, 1)
        if (.not. c_associated(ctx)) exit mb_block

        ! Connect to device.
        stat = modbus_connect(ctx)
        if (stat == -1) exit mb_block

        ! Set slave number.
        stat = modbus_set_slave(ctx, SLAVE)
        if (stat == -1) exit mb_block

        ! Read registers.
        stat = modbus_read_registers(ctx, ADDRESS, size(regs), regs)
        if (stat == -1) exit mb_block

        ! Convert to real.
        f = modbus_get_float_abcd(regs)
        print '(f12.8)', f
    end block mb_block

    call modbus_close(ctx)
    call modbus_free(ctx)

    if (stat == -1) print '(a)', 'Error: operation failed'
end program main

If the Fortran library is installed to /opt/lib, run:

$ gfortran -o example example.f90 /opt/lib/libfortran-modbus.a -lmodbus

Fortran Package Manager

You can add fortran-modbus as an FPM dependency:

[dependencies]
fortran-modbus = { git = "https://github.com/interkosmos/fortran-modbus.git" }

Licence

ISC