dm_modbus – DMPACK

Abstraction layer over libmodbus, for Modbus RTU/TCP communication.

The following types and ranges are used by the Modbus protocol:

Code	Range	Type	Functions
0x01	00001 – 09999	coil	`dm_modbus_read_bit()`, `dm_modbus_read_bits()`
0x02	10001 – 19999	discrete input	`dm_modbus_read_input_bits()`
0x04	30001 – 39999	input register	`dm_modbus_read_input_registers()`
0x03	40001 – 49999	holding register	`dm_modbus_read_registers()`

You may want to use the functions dm_to_signed() and dm_to_unsigned() available in module dm_c to convert unsigned to signed integers and vice versa.

Use Modbus function code 0x03 to read holding registers from a Modbus RTU connection:

integer               :: i, rc, s
integer(kind=u2)      :: data(2)
type(modbus_rtu_type) :: modbus

! Create Modbus RTU context and connect to device 10.
rc = dm_modbus_create(modbus    = modbus,          &
                      path      = '/dev/ttyUSB0',  &
                      baud_rate = TTY_B19200,      &
                      byte_size = TTY_BYTE_SIZE8,  &
                      parity    = TTY_PARITY_EVEN, &
                      stop_bits = TTY_STOP_BITS1)
rc = dm_modbus_connect(modbus)
rc = dm_modbus_set_slave(modbus, slave=10)

! Read and output two registers.
rc = dm_modbus_read_registers(modbus, address=30050, data=data)

do i = 1, size(data)
    s = dm_to_signed(data(i))
    print '("data(", i0, ") = ", i0, " (0x", z0, ")")', i, s, s
end do

! Print the two registers as real in ABCD byte order.
print '(f12.8)', dm_modbus_get_float_abcd(data)

! Disconnect and clean-up.
call dm_modbus_close(modbus)
call dm_modbus_destroy(modbus)

In production, add additional error handling of the return codes.

References

libmodbus Reference Manual

Uses

- iso_c_binding
- dm_kind
- modbus
- modbus_tcp
- dm_modbus_type
- dm_c
- modbus_rtu
- dm_error
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Used by

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Graph Key

Nodes of different colours represent the following:

Solid arrows point from a submodule to the (sub)module which it is descended from. Dashed arrows point from a module or program unit to modules which it uses.

Interfaces

public interface dm_modbus_create

Generic function to create Modbus RTU or TCP context.

public function dm_modbus_create_rtu(modbus, path, baud_rate, byte_size, parity, stop_bits) result(rc)

Creates a new Modbus RTU context.

The function returns the following error codes:

E_INVALID if a given argument is invalid.
E_MODBUS if no Modbus context could be created.

Arguments

Type	Intent		Name
type(modbus_rtu_type),	intent(out)	::	modbus	Modbus RTU type.
character(len=*),	intent(in)	::	path	Device path.
integer,	intent(in)	::	baud_rate	Baud rate enumerator (`TTY_B*`).
integer,	intent(in)	::	byte_size	Byte size enumerator (`TTY_BYTE_SIZE*`).
integer,	intent(in)	::	parity	Parity enumerator (`TTY_PARITY_*`).
integer,	intent(in)	::	stop_bits	Stop bits enumerator (`TTY_STOP_BITS*`).

Return Value integer

public function dm_modbus_create_tcp(modbus, address, port) result(rc)

Creates a new Modbus TCP context.

The function returns the following error codes:

E_INVALID if the given arguments are invalid.
E_MODBUS if no Modbus context could be created.

Arguments

Type	Intent		Name
type(modbus_tcp_type),	intent(out)	::	modbus	Modbus TCP type.
character(len=*),	intent(in)	::	address	IPv4 address.
integer,	intent(in)	::	port	Port number.

Return Value integer

Derived Types

type, public :: modbus_type

Opaque Modbus RTU/TCP context type.

type, public, extends(modbus_type) :: modbus_rtu_type

Opaque Modbus RTU context type.

type, public, extends(modbus_type) :: modbus_tcp_type

Opaque Modbus TCP context type.

Functions

public function dm_modbus_connect(modbus) result(rc)

Connects to Modbus RTU/TCP device.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.

Return Value integer

public function dm_modbus_create_rtu(modbus, path, baud_rate, byte_size, parity, stop_bits) result(rc)

Creates a new Modbus RTU context.

Arguments

Type	Intent		Name
type(modbus_rtu_type),	intent(out)	::	modbus	Modbus RTU type.
character(len=*),	intent(in)	::	path	Device path.
integer,	intent(in)	::	baud_rate	Baud rate enumerator (`TTY_B*`).
integer,	intent(in)	::	byte_size	Byte size enumerator (`TTY_BYTE_SIZE*`).
integer,	intent(in)	::	parity	Parity enumerator (`TTY_PARITY_*`).
integer,	intent(in)	::	stop_bits	Stop bits enumerator (`TTY_STOP_BITS*`).

Return Value integer

public function dm_modbus_create_tcp(modbus, address, port) result(rc)

Creates a new Modbus TCP context.

Arguments

Type	Intent		Name
type(modbus_tcp_type),	intent(out)	::	modbus	Modbus TCP type.
character(len=*),	intent(in)	::	address	IPv4 address.
integer,	intent(in)	::	port	Port number.

Return Value integer

public function dm_modbus_error_message() result(message)

Returns error message from libmodbus.

Arguments

None

Return Value character(len=:), allocatable

public function dm_modbus_flush(modbus) result(rc)

Flushes non-transmitted data.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.

Return Value integer

public function dm_modbus_get_float(data, order, error) result(value)

Returns real value from two registers of given byte order in argument value. The argument byte order must be one of the following:

Arguments

Type	Intent	Optional		Name
integer(kind=u2),	intent(inout)		::	data(2)	Registers to convert.
integer,	intent(in)		::	order	Byte order.
integer,	intent(out),	optional	::	error	Error code.

Return Value real

public function dm_modbus_get_float_abcd(data) result(value)

Returns real value from two registers in ABCD byte order.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(inout)			::	data(2)	Registers to convert.

Return Value real

public function dm_modbus_get_float_badc(data) result(value)

Returns real value from two registers in BADC byte order.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(inout)			::	data(2)	Registers to convert.

Return Value real

public function dm_modbus_get_float_cdab(data) result(value)

Returns real value from two registers in CDAB byte order.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(inout)			::	data(2)	Registers to convert.

Return Value real

public function dm_modbus_get_float_dcba(data) result(value)

Returns real value from two registers in DCBA byte order.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(inout)			::	data(2)	Registers to convert.

Return Value real

public pure elemental function dm_modbus_get_high_byte(data) result(byte)

Returns high byte from 2-byte integer.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(in)			::	data	Register data.

Return Value character(len=1)

public pure function dm_modbus_get_int32_from_int16(data) result(value)

Returns 4-byte integer from two 2-byte registers.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(in)			::	data(2)	Register data.

Return Value integer(kind=i4)

public pure function dm_modbus_get_int64_from_int16(data) result(value)

Returns 8-byte integer from four 2-byte registers.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(in)			::	data(4)	Register data.

Return Value integer(kind=i8)

public pure elemental function dm_modbus_get_low_byte(data) result(byte)

Returns low byte from 2-byte integer.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=u2),	intent(in)			::	data	Register data.

Return Value character(len=1)

public function dm_modbus_get_serial_mode(modbus, mode) result(rc)

Gets the current Modbus RTU serial mode (RS-232 or RS-485).

Arguments

Type	Intent	Optional	Attributes		Name
type(modbus_rtu_type),	intent(inout)			::	modbus	Modbus RTU type.
integer,	intent(out)			::	mode	Modbus RTU mode (`MODBUS_RTU_RS232`, `MODBUS_RTU_RS485`).

Return Value integer

public function dm_modbus_get_slave(modbus, slave) result(rc)

Gets current slave number in the Modbus context.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.
integer,	intent(out)			::	slave	Device id.

Return Value integer

public function dm_modbus_read_bit(modbus, address, value) result(rc)

Reads single input bit from address. The function uses the Modbus function code 0x01 (read coil status).

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
integer(kind=i4),	intent(out)	::	value	Bit read.

Return Value integer

public function dm_modbus_read_bits(modbus, address, data, n) result(rc)

Reads many input bits from address. The size of argument data determines the number of bits to read, unless optional argument n is passed. The function uses the Modbus function code 0x01 (read coil status).

Arguments

Type	Intent	Optional		Name
class(modbus_type),	intent(inout)		::	modbus	Modbus RTU/TCP type.
integer,	intent(in)		::	address	Address to read from.
integer(kind=u1),	intent(inout)		::	data(:)	Bits read.
integer,	intent(inout),	optional	::	n	Number of registers to read on input, number of registers read on output.

Return Value integer

public function dm_modbus_read_float(modbus, address, value, order) result(rc)

Reads 4-byte real from input or holding register, depending on the address, and returns result in value. If the address is not in input register or holding register range, it is interpreted as a holding register address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
real(kind=r4),	intent(out)	::	value	Value read from register.
integer,	intent(in)	::	order	Byte order.

Return Value integer

public function dm_modbus_read_input_bits(modbus, address, data, n) result(rc)

Arguments

Type	Intent	Optional		Name
class(modbus_type),	intent(inout)		::	modbus	Modbus RTU/TCP type.
integer,	intent(in)		::	address	Address to read from.
integer(kind=u1),	intent(inout)		::	data(:)	Bits.
integer,	intent(inout),	optional	::	n	Number of registers to read on input, number of registers read on output.

Return Value integer

public function dm_modbus_read_input_registers(modbus, address, data, n) result(rc)

Reads many registers from address. The size of argument data determines the number of registers to read, unless optional argument n is passed. The function uses the Modbus function code 0x04 (read input registers).

Arguments

Type	Intent	Optional		Name
class(modbus_type),	intent(inout)		::	modbus	Modbus RTU/TCP type.
integer,	intent(in)		::	address	Address to read from.
integer(kind=u2),	intent(inout)		::	data(:)	Register values (unsigned).
integer,	intent(inout),	optional	::	n	Number of registers to read on input, number of registers read on output.

Return Value integer

public function dm_modbus_read_int16(modbus, address, value) result(rc)

Reads 2-byte signed integer from input or holding register, depending on the address, and returns result in value. If the address is not in input register or holding register range, it is interpreted as a holding register address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
integer(kind=i2),	intent(out)	::	value	Value read from register.

Return Value integer

public function dm_modbus_read_int32(modbus, address, value) result(rc)

Reads 4-byte signed integer from input or holding register, depending on the address, and returns result in value. If the address is not in input register or holding register range, it is interpreted as a holding register address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
integer(kind=i4),	intent(out)	::	value	Value read from register.

Return Value integer

public function dm_modbus_read_registers(modbus, address, data, n) result(rc)

Arguments

Type	Intent	Optional		Name
class(modbus_type),	intent(inout)		::	modbus	Modbus RTU/TCP type.
integer,	intent(in)		::	address	Address to read from.
integer(kind=u2),	intent(inout)		::	data(:)	Register values (unsigned).
integer,	intent(inout),	optional	::	n	Number of registers to read on input, number of registers read on output.

Return Value integer

public function dm_modbus_read_uint16(modbus, address, value) result(rc)

Reads 2-byte unsigned integer from input or holding register, depending on the address, and returns result in value. Stores the 2-byte unsigned value in a 4-byte signed integer. If the address is not in input register or holding register range, it is interpreted as a holding register address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
integer(kind=i4),	intent(out)	::	value	Value read from register.

Return Value integer

public function dm_modbus_read_uint32(modbus, address, value) result(rc)

Reads 4-byte unsigned integer from input or holding register, depending on the address, and returns result in value. Stores the 4-byte unsigned value in a 8-byte signed integer. If the address is not in input register or holding register range, it is interpreted as a holding register address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
integer(kind=i8),	intent(out)	::	value	Value read from register.

Return Value integer

public function dm_modbus_set_debug(modbus, debug) result(rc)

Sets debug flag of the Modbus context. Returns E_MODBUS on error.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.
logical,	intent(in)			::	debug	Enable debug mode.

Return Value integer

public function dm_modbus_set_serial_mode(modbus, mode) result(rc)

Sets the Modbus RTU serial mode to RS-232 or RS-485. This API function is only supported on Linux kernels 2.6.28 onwards.

Arguments

Type	Intent	Optional	Attributes		Name
type(modbus_rtu_type),	intent(inout)			::	modbus	Modbus RTU type.
integer,	intent(in)			::	mode	Modbus RTU mode (`MODBUS_RTU_RS232`, `MODBUS_RTU_RS485`).

Return Value integer

public function dm_modbus_set_slave(modbus, slave) result(rc)

Sets slave number in the Modbus context.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.
integer,	intent(in)			::	slave	Device id.

Return Value integer

public function dm_modbus_version(name) result(version)

Returns libmodbus version as allocatable string.

Arguments

Type	Intent	Optional	Attributes		Name
logical,	intent(in),	optional		::	name	Add prefix `libmodbus/`.

Return Value character(len=:), allocatable

Version string.

public function dm_modbus_write_bit(modbus, address, value) result(rc)

Writes bit value to address using Modbus function code 0x05(force single coil).

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer,	intent(in)	::	value	Value to write (0 or 1).

Return Value integer

public function dm_modbus_write_int16(modbus, address, value) result(rc)

Writes 2-byte signed integer to address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer(kind=i2),	intent(in)	::	value	Value to write.

Return Value integer

public function dm_modbus_write_int32(modbus, address, value) result(rc)

Writes 4-byte signed integer to address.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer(kind=i4),	intent(in)	::	value	Value to write.

Return Value integer

public function dm_modbus_write_register(modbus, address, data) result(rc)

Writes register to address. The function uses the Modbus function code 0x06 (preset single register).

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer(kind=u2),	intent(in)	::	data	Register value (unsigned).

Return Value integer

public function dm_modbus_write_registers(modbus, address, data, n) result(rc)

Writes many registers to address. The size of argument data determines the number of registers to write, unless optional argument n is passed. The function uses the Modbus function code 0x10 (preset multiple registers).

Arguments

Type	Intent	Optional		Name
class(modbus_type),	intent(inout)		::	modbus	Modbus RTU/TCP type.
integer,	intent(in)		::	address	Address to write to.
integer(kind=u2),	intent(inout)		::	data(:)	Register values (unsigned).
integer,	intent(inout),	optional	::	n	Number of registers to write on input, number of registers written on output.

Return Value integer

public function dm_modbus_write_uint16(modbus, address, value) result(rc)

Writes 2-byte unsigned integer to address. The unsigned value must be passed in a 4-byte signed integer.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer(kind=i4),	intent(in)	::	value	Value to write.

Return Value integer

public function dm_modbus_write_uint32(modbus, address, value) result(rc)

Writes 4-byte unsigned integer to address. The unsigned value must be passed in a 8-byte signed integer.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to write to.
integer(kind=i8),	intent(in)	::	value	Value to write.

Return Value integer

Subroutines

public subroutine dm_modbus_close(modbus)

Closes the Modbus RTU/TCP connection.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCPtype.

public subroutine dm_modbus_destroy(modbus)

Destroys the Modbus RTU/TCP context.

Arguments

Type	Intent	Optional	Attributes		Name
class(modbus_type),	intent(inout)			::	modbus	Modbus RTU/TCP type.

public pure subroutine dm_modbus_set_int32_to_int16(value, data)

Writes 4-byte integer to two 2-byte registers.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=i4),	intent(in)			::	value	Value to convert.
integer(kind=u2),	intent(out)			::	data(2)	Returned register data.

public pure subroutine dm_modbus_set_int64_to_int16(value, data)

Writes 8-byte integer to four 2-byte registers.

Arguments

Type	Intent	Optional	Attributes		Name
integer(kind=i8),	intent(in)			::	value	Value to convert.
integer(kind=u2),	intent(out)			::	data(4)	Returned register data.

public subroutine dm_modbus_set_float(value, data, order, error)

Writes real value to registers of given byte order. The argument order must be one of the following:

Arguments

Type	Intent	Optional		Name
real,	intent(in)		::	value	Real value to set.
integer(kind=u2),	intent(out)		::	data(2)	Registers to write to.
integer,	intent(in)		::	order	Byte order.
integer,	intent(out),	optional	::	error	Error code.

public subroutine dm_modbus_set_float_abcd(value, data)

Writes real value to registers in ABCD byte order.

Arguments

Type	Intent	Optional	Attributes		Name
real,	intent(in)			::	value	Real value to set.
integer(kind=u2),	intent(out)			::	data(2)	Registers to write to.

public subroutine dm_modbus_set_float_badc(value, data)

Writes real value to registers in BADC byte order.

Arguments

Type	Intent	Optional	Attributes		Name
real,	intent(in)			::	value	Real value to set.
integer(kind=u2),	intent(out)			::	data(2)	Registers to write to.

public subroutine dm_modbus_set_float_cdab(value, data)

Writes real value to registers in CDAB byte order.

Arguments

Type	Intent	Optional	Attributes		Name
real,	intent(in)			::	value	Real value to set.
integer(kind=u2),	intent(out)			::	data(2)	Registers to write to.

public subroutine dm_modbus_set_float_dcba(value, data)

Writes real value to registers in DCBA byte order.

Arguments

Type	Intent	Optional	Attributes		Name
real,	intent(in)			::	value	Real value to set.
integer(kind=u2),	intent(out)			::	data(2)	Registers to write to.

dm_modbus Module

Contents

Interfaces

Derived Types

Functions

Subroutines

References

Uses

Used by

Interfaces

public interface dm_modbus_create

public function dm_modbus_create_rtu(modbus, path, baud_rate, byte_size, parity, stop_bits) result(rc)

Arguments

Return Value integer

public function dm_modbus_create_tcp(modbus, address, port) result(rc)

Arguments

Return Value integer

Derived Types

type, public :: modbus_type

type, public, extends(modbus_type) :: modbus_rtu_type

type, public, extends(modbus_type) :: modbus_tcp_type

Functions

public function dm_modbus_connect(modbus) result(rc)

Arguments

Return Value integer

public function dm_modbus_create_rtu(modbus, path, baud_rate, byte_size, parity, stop_bits) result(rc)

Arguments

Return Value integer

public function dm_modbus_create_tcp(modbus, address, port) result(rc)

Arguments

Return Value integer

public function dm_modbus_error_message() result(message)

Arguments

Return Value character(len=:), allocatable

public function dm_modbus_flush(modbus) result(rc)

Arguments

Return Value integer

public function dm_modbus_get_float(data, order, error) result(value)

Arguments

Return Value real

public function dm_modbus_get_float_abcd(data) result(value)

Arguments

Return Value real

public function dm_modbus_get_float_badc(data) result(value)

Arguments

Return Value real

public function dm_modbus_get_float_cdab(data) result(value)

Arguments

Return Value real

public function dm_modbus_get_float_dcba(data) result(value)

Arguments

Return Value real

public pure elemental function dm_modbus_get_high_byte(data) result(byte)

Arguments

Return Value character(len=1)

public pure function dm_modbus_get_int32_from_int16(data) result(value)

Arguments

Return Value integer(kind=i4)

public pure function dm_modbus_get_int64_from_int16(data) result(value)

Arguments

Return Value integer(kind=i8)

public pure elemental function dm_modbus_get_low_byte(data) result(byte)

Arguments

Return Value character(len=1)

public function dm_modbus_get_serial_mode(modbus, mode) result(rc)

Arguments

Return Value integer

public function dm_modbus_get_slave(modbus, slave) result(rc)

Arguments

Return Value integer

public function dm_modbus_read_bit(modbus, address, value) result(rc)

Arguments

Return Value integer

public function dm_modbus_read_bits(modbus, address, data, n) result(rc)

Arguments

Return Value integer

public function dm_modbus_read_float(modbus, address, value, order) result(rc)

Arguments

Return Value integer

public function dm_modbus_read_input_bits(modbus, address, data, n) result(rc)