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	Function
0x	00001 – 09999	coil	`dm_modbus_read_bits()`
1x	10001 – 19999	discrete input	`dm_modbus_read_input_bits()`
3x	30001 – 39999	input register	`dm_modbus_read_input_registers()`
4x	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=50, 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

- dm_kind
- modbus_tcp
- modbus
- dm_modbus_type
- dm_c
- dm_error
- modbus_rtu
- iso_c_binding
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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(value)

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(value)

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_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.
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.

Arguments

Type	Intent		Name
class(modbus_type),	intent(inout)	::	modbus	Modbus RTU/TCP type.
integer,	intent(in)	::	address	Address to read from.
real(kind=4),	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.

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.

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.

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.

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_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)

Sets 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)

Sets 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)

Sets 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)

Returns 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)

Returns 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)

Sets 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)

Sets 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(value)

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(value)

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_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)

Arguments

Return Value integer

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