"""
.. note:: This section is based on `MODBUS Application Protocol Specification
V1.1b3`_
The Protocol Data Unit (PDU) is the request or response message and is
indepedent of the underlying communication layer. This module only implements
requests PDU's.
A request PDU contains two parts: a function code and request data. A response
PDU contains the function code from the request and response data. The general
structure is listed in table below:
+---------------+-----------------+
| **Field** | **Size** (bytes)|
+---------------+-----------------+
| Function code | 1 |
+---------------+-----------------+
| data | N |
+---------------+-----------------+
Below you see the request PDU with function code 1, requesting status of 3
coils, starting from coil 100.
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> req_pdu = b'\\x01\x00d\\x00\\x03'
>>> function_code = req_pdu[:1]
>>> function_code
b'\\x01'
>>> starting_address = req_pdu[1:3]
>>> starting_address
b'\\x00d'
>>> quantity = req_pdu[3:]
>>> quantity
b'\\x00\\x03'
A response PDU could look like this::
>>> resp_pdu = b'\\x01\\x01\\x06'
>>> function_code = resp_pdu[:1]
>>> function_code
b'\\x01'
>>> byte_count = resp[1:2]
>>> byte_count
b'\\x01'
>>> coil_status = resp[2:]
'b\\x06'
"""
from __future__ import division
import struct
import inspect
import math
try:
from functools import reduce
except ImportError:
pass
from umodbus import conf, log
from umodbus.exceptions import (error_code_to_exception_map,
IllegalDataValueError, IllegalFunctionError,
IllegalDataAddressError)
from umodbus.utils import memoize, get_function_code_from_request_pdu
# Function related to data access.
READ_COILS = 1
READ_DISCRETE_INPUTS = 2
READ_HOLDING_REGISTERS = 3
READ_INPUT_REGISTERS = 4
WRITE_SINGLE_COIL = 5
WRITE_SINGLE_REGISTER = 6
WRITE_MULTIPLE_COILS = 15
WRITE_MULTIPLE_REGISTERS = 16
READ_FILE_RECORD = 20
WRITE_FILE_RECORD = 21
READ_WRITE_MULTIPLE_REGISTERS = 23
READ_FIFO_QUEUE = 24
# Diagnostic functions, only available when using serial line.
READ_EXCEPTION_STATUS = 7
DIAGNOSTICS = 8
GET_COMM_EVENT_COUNTER = 11
GET_COM_EVENT_LOG = 12
REPORT_SERVER_ID = 17
def pdu_to_function_code_or_raise_error(resp_pdu):
""" Parse response PDU and return of :class:`ModbusFunction` or
raise error.
:param resp_pdu: PDU of response.
:return: Subclass of :class:`ModbusFunction` matching the response.
:raises ModbusError: When response contains error code.
"""
function_code = struct.unpack('>B', resp_pdu[0:1])[0]
if function_code not in function_code_to_function_map.keys():
error_code = struct.unpack('>B', resp_pdu[1:2])[0]
raise error_code_to_exception_map[error_code]
return function_code
def create_function_from_response_pdu(resp_pdu, req_pdu=None):
""" Parse response PDU and return instance of :class:`ModbusFunction` or
raise error.
:param resp_pdu: PDU of response.
:param req_pdu: Request PDU, some functions require more info than in
response PDU in order to create instance. Default is None.
:return: Number or list with response data.
"""
function_code = pdu_to_function_code_or_raise_error(resp_pdu)
function = function_code_to_function_map[function_code]
if req_pdu is not None and \
'req_pdu' in inspect.getargspec(function.create_from_response_pdu).args: # NOQA
return function.create_from_response_pdu(resp_pdu, req_pdu)
return function.create_from_response_pdu(resp_pdu)
@memoize
def create_function_from_request_pdu(pdu):
""" Return function instance, based on request PDU.
:param pdu: Array of bytes.
:return: Instance of a function.
"""
function_code = get_function_code_from_request_pdu(pdu)
try:
function_class = function_code_to_function_map[function_code]
except KeyError:
raise IllegalFunctionError(function_code)
return function_class.create_from_request_pdu(pdu)
def expected_response_pdu_size_from_request_pdu(pdu):
""" Return number of bytes expected for response PDU, based on request PDU.
:param pdu: Array of bytes.
:return: number of bytes.
"""
return create_function_from_request_pdu(pdu).expected_response_pdu_size
class ModbusFunction(object):
function_code = None
[docs]class ReadCoils(ModbusFunction):
""" Implement Modbus function code 01.
"This function code is used to read from 1 to 2000 contiguous status of
coils in a remote device. The Request PDU specifies the starting
address, i.e. the address of the first coil specified, and the number
of coils. In the PDU Coils are addressed starting at zero. Therefore
coils numbered 1-16 are addressed as 0-15.
The coils in the response message are packed as one coil per bit of the
data field. Status is indicated as 1= ON and 0= OFF. The LSB of the
first data byte contains the output addressed in the query. The other
coils follow toward the high order end of this byte, and from low order
to high order in subsequent bytes.
If the returned output quantity is not a multiple of eight, the
remaining bits in the final data byte will be padded with zeros (toward
the high order end of the byte). The Byte Count field specifies the
quantity of complete bytes of data."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.1
The request PDU with function code 01 must be 5 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting address 2
Quantity 2
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHH', b'\\x01\\x00d\\x00\\x03')
(1, 100, 3)
The reponse PDU varies in length, depending on the request. Each 8 coils
require 1 byte. The amount of bytes needed represent status of the coils to
can be calculated with: bytes = ceil(quantity / 8). This response
contains ceil(3 / 8) = 1 byte to describe the status of the coils. The
structure of a compleet response PDU looks like this:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Byte count 1
Coil status n
================ ===============
Assume the status of 102 is 0, 101 is 1 and 100 is also 1. This is binary
011 which is decimal 3.
The PDU can packed like this::
>>> struct.pack('>BBB', function_code, byte_count, 3)
b'\\x01\\x01\\x03'
"""
function_code = READ_COILS
max_quantity = 2000
format_character = 'B'
data = None
starting_address = None
_quantity = None
@property
def quantity(self):
return self._quantity
@quantity.setter
def quantity(self, value):
""" Set number of coils to read. Quantity must be between 1 and 2000.
:param value: Quantity.
:raises: IllegalDataValueError.
"""
if not (1 <= value <= 2000):
raise IllegalDataValueError('Quantify field of request must be a '
'value between 0 and '
'{0}.'.format(2000))
self._quantity = value
@property
def request_pdu(self):
""" Build request PDU to read coils.
:return: Byte array of 5 bytes with PDU.
"""
if None in [self.starting_address, self.quantity]:
# TODO Raise proper exception.
raise Exception
return struct.pack('>BHH', self.function_code, self.starting_address,
self.quantity)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
:param pdu: A request PDU.
:return: Instance of this class.
"""
_, starting_address, quantity = struct.unpack('>BHH', pdu)
instance = ReadCoils()
instance.starting_address = starting_address
instance.quantity = quantity
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 2 + int(math.ceil(self.quantity / 8))
def create_response_pdu(self, data):
""" Create response pdu.
:param data: A list with 0's and/or 1's.
:return: Byte array of at least 3 bytes.
"""
log.debug('Create single bit response pdu {0}.'.format(data))
bytes_ = [data[i:i + 8] for i in range(0, len(data), 8)]
# Reduce each all bits per byte to a number. Byte
# [0, 0, 0, 0, 0, 1, 1, 1] is intepreted as binary en is decimal 3.
for index, byte in enumerate(bytes_):
bytes_[index] = \
reduce(lambda a, b: (a << 1) + b, list(reversed(byte)))
log.debug('Reduced single bit data to {0}.'.format(bytes_))
# The first 2 B's of the format encode the function code (1 byte) and
# the length (1 byte) of the following byte series. Followed by # a B
# for every byte in the series of bytes. 3 lead to the format '>BBB'
# and 257 lead to the format '>BBBB'.
fmt = '>BB' + self.format_character * len(bytes_)
return struct.pack(fmt, self.function_code, len(bytes_), *bytes_)
@staticmethod
def create_from_response_pdu(resp_pdu, req_pdu):
""" Create instance from response PDU.
Response PDU is required together with the quantity of coils read.
:param resp_pdu: Byte array with request PDU.
:param quantity: Number of coils read.
:return: Instance of :class:`ReadCoils`.
"""
read_coils = ReadCoils()
read_coils.quantity = struct.unpack('>H', req_pdu[-2:])[0]
byte_count = struct.unpack('>B', resp_pdu[1:2])[0]
fmt = '>' + ('B' * byte_count)
bytes_ = struct.unpack(fmt, resp_pdu[2:])
data = list()
for i, value in enumerate(bytes_):
padding = 8 if (read_coils.quantity - (8 * i)) // 8 > 0 \
else read_coils.quantity % 8
fmt = '{{0:0{padding}b}}'.format(padding=padding)
# Create binary representation of integer, convert it to a list
# and reverse the list.
data = data + [int(i) for i in fmt.format(value)][::-1]
read_coils.data = data
return read_coils
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
:return: Result of call to endpoint.
"""
try:
values = []
for address in range(self.starting_address,
self.starting_address + self.quantity):
endpoint = route_map.match(slave_id, self.function_code,
address)
values.append(endpoint(slave_id=slave_id, address=address,
function_code=self.function_code))
return values
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
[docs]class ReadHoldingRegisters(ModbusFunction):
""" Implement Modbus function code 03.
"This function code is used to read the contents of a contiguous block
of holding registers in a remote device. The Request PDU specifies the
starting register address and the number of registers. In the PDU
Registers are addressed starting at zero. Therefore registers numbered
1-16 are addressed as 0-15.
The register data in the response message are packed as two bytes per
register, with the binary contents right justified within each byte.
For each register, the first byte contains the high order bits and the
second contains the low order bits."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.3
The request PDU with function code 03 must be 5 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting address 2
Quantity 2
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHH', b'\\x03\\x00d\\x00\\x03')
(3, 100, 3)
The reponse PDU varies in length, depending on the request. By default,
holding registers are 16 bit (2 bytes) values. So values of 3 holding
registers is expressed in 2 * 3 = 6 bytes.
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Byte count 1
Register values Quantity * 2
================ ===============
Assume the value of 100 is 8, 101 is 0 and 102 is also 15.
The PDU can packed like this::
>>> data = [8, 0, 15]
>>> struct.pack('>BBHHH', function_code, len(data) * 2, *data)
b'\\x03\\x06\\x00\\x08\\x00\\x00\\x00\\x0f'
"""
function_code = READ_HOLDING_REGISTERS
max_quantity = 0x007D
data = None
starting_address = None
_quantity = None
@property
def quantity(self):
return self._quantity
@quantity.setter
def quantity(self, value):
""" Set number of registers to read. Quantity must be between 1 and
0x00FD.
:param value: Quantity.
:raises: IllegalDataValueError.
"""
if not (1 <= value <= 0x007D):
raise IllegalDataValueError('Quantify field of request must be a '
'value between 0 and '
'{0}.'.format(0x007D))
self._quantity = value
@property
def request_pdu(self):
""" Build request PDU to read coils.
:return: Byte array of 5 bytes with PDU.
"""
if None in [self.starting_address, self.quantity]:
# TODO Raise proper exception.
raise Exception
return struct.pack('>BHH', self.function_code, self.starting_address,
self.quantity)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
:param pdu: A request PDU.
:return: Instance of this class.
"""
_, starting_address, quantity = struct.unpack('>BHH', pdu)
instance = ReadHoldingRegisters()
instance.starting_address = starting_address
instance.quantity = quantity
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 2 + self.quantity * 2
def create_response_pdu(self, data):
""" Create response pdu.
:param data: A list with values.
:return: Byte array of at least 4 bytes.
"""
log.debug('Create multi bit response pdu {0}.'.format(data))
fmt = '>BB' + conf.TYPE_CHAR * len(data)
return struct.pack(fmt, self.function_code, len(data) * 2, *data)
@staticmethod
def create_from_response_pdu(resp_pdu, req_pdu):
""" Create instance from response PDU.
Response PDU is required together with the number of registers read.
:param resp_pdu: Byte array with request PDU.
:param quantity: Number of coils read.
:return: Instance of :class:`ReadCoils`.
"""
read_holding_registers = ReadHoldingRegisters()
read_holding_registers.quantity = struct.unpack('>H', req_pdu[-2:])[0]
read_holding_registers.byte_count = \
struct.unpack('>B', resp_pdu[1:2])[0]
fmt = '>' + (conf.TYPE_CHAR * read_holding_registers.quantity)
read_holding_registers.data = list(struct.unpack(fmt, resp_pdu[2:]))
return read_holding_registers
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
:return: Result of call to endpoint.
"""
try:
values = []
for address in range(self.starting_address,
self.starting_address + self.quantity):
endpoint = route_map.match(slave_id, self.function_code,
address)
values.append(endpoint(slave_id=slave_id, address=address,
function_code=self.function_code))
return values
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
[docs]class WriteSingleCoil(ModbusFunction):
""" Implement Modbus function code 05.
"This function code is used to write a single output to either ON or
OFF in a remote device. The requested ON/OFF state is specified by a
constant in the request data field. A value of FF 00 hex requests the
output to be ON. A value of 00 00 requests it to be OFF. All other
values are illegal and will not affect the output.
The Request PDU specifies the address of the coil to be forced. Coils
are addressed starting at zero. Therefore coil numbered 1 is addressed
as 0. The requested ON/OFF state is specified by a constant in the
Coil Value field. A value of 0XFF00 requests the coil to be ON. A value
of 0X0000 requests the coil to be off. All other values are illegal and
will not affect the coil.
The normal response is an echo of the request, returned after the coil
state has been written."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.5
The request PDU with function code 05 must be 5 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Address 2
Value 2
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHH', b'\\x05\\x00d\\xFF\\x00')
(5, 100, 65280)
The reponse PDU is a copy of the request PDU.
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Address 2
Value 2
================ ===============
"""
function_code = WRITE_SINGLE_COIL
format_character = 'B'
address = None
data = None
_value = None
@property
def value(self):
if self._value == 0xFF00:
return 1
return self._value
@value.setter
def value(self, value):
if value not in [0, 1, 0xFF00]:
raise IllegalDataValueError
value = 0xFF00 if value == 1 else value
self._value = value
@property
def request_pdu(self):
""" Build request PDU to write single coil.
:return: Byte array of 5 bytes with PDU.
"""
if None in [self.address, self.value]:
# TODO Raise proper exception.
raise Exception
return struct.pack('>BHH', self.function_code, self.address,
self._value)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
:param pdu: A response PDU.
"""
_, address, value = struct.unpack('>BHH', pdu)
value = 1 if value == 0xFF00 else value
instance = WriteSingleCoil()
instance.address = address
instance.value = value
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 5
def create_response_pdu(self):
""" Create response pdu.
:param data: A list with values.
:return: Byte array of at least 4 bytes.
"""
fmt = '>BHH'
return struct.pack(fmt, self.function_code, self.address, self._value)
@staticmethod
def create_from_response_pdu(resp_pdu):
""" Create instance from response PDU.
:param resp_pdu: Byte array with request PDU.
:return: Instance of :class:`WriteSingleCoil`.
"""
write_single_coil = WriteSingleCoil()
address, value = struct.unpack('>HH', resp_pdu[1:5])
value = 1 if value == 0xFF00 else value
write_single_coil.address = address
write_single_coil.data = value
return write_single_coil
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
"""
endpoint = route_map.match(slave_id, self.function_code, self.address)
try:
endpoint(slave_id=slave_id, address=self.address, value=self.value,
function_code=self.function_code)
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
[docs]class WriteSingleRegister(ModbusFunction):
""" Implement Modbus function code 06.
"This function code is used to write a single holding register in a
remote device. The Request PDU specifies the address of the register to
be written. Registers are addressed starting at zero. Therefore
register numbered 1 is addressed as 0. The normal response is an echo
of the request, returned after the register contents have been
written."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.6
The request PDU with function code 06 must be 5 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Address 2
Value 2
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHH', b'\\x06\\x00d\\x00\\x03')
(6, 100, 3)
The reponse PDU is a copy of the request PDU.
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Address 2
Value 2
================ ===============
"""
function_code = WRITE_SINGLE_REGISTER
address = None
data = None
_value = None
@property
def value(self):
return self._value
@value.setter
def value(self, value):
""" Value to be written on register.
:param value: An integer.
:raises: IllegalDataValueError when value isn't in range.
"""
try:
struct.pack('>' + conf.TYPE_CHAR, value)
except struct.error:
raise IllegalDataValueError
self._value = value
@property
def request_pdu(self):
""" Build request PDU to write single register.
:return: Byte array of 5 bytes with PDU.
"""
if None in [self.address, self.value]:
# TODO Raise proper exception.
raise Exception
return struct.pack('>BH' + conf.TYPE_CHAR, self.function_code,
self.address, self.value)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
:param pdu: A response PDU.
"""
_, address, value = \
struct.unpack('>BH' + conf.MULTI_BIT_VALUE_FORMAT_CHARACTER, pdu)
instance = WriteSingleRegister()
instance.address = address
instance.value = value
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 5
def create_response_pdu(self):
fmt = '>BH' + conf.TYPE_CHAR
return struct.pack(fmt, self.function_code, self.address, self.value)
@staticmethod
def create_from_response_pdu(resp_pdu):
""" Create instance from response PDU.
:param resp_pdu: Byte array with request PDU.
:return: Instance of :class:`WriteSingleRegister`.
"""
write_single_register = WriteSingleRegister()
address, value = struct.unpack('>H' + conf.TYPE_CHAR, resp_pdu[1:5])
write_single_register.address = address
write_single_register.data = value
return write_single_register
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
"""
endpoint = route_map.match(slave_id, self.function_code, self.address)
try:
endpoint(slave_id=slave_id, address=self.address, value=self.value,
function_code=self.function_code)
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
[docs]class WriteMultipleCoils(ModbusFunction):
""" Implement Modbus function 15 (0x0F) Write Multiple Coils.
"This function code is used to force each coil in a sequence of coils
to either ON or OFF in a remote device. The Request PDU specifies the
coil references to be forced. Coils are addressed starting at zero.
Therefore coil numbered 1 is addressed as 0.
The requested ON/OFF states are specified by contents of the request
data field. A logical '1' in a bit position of the field requests the
corresponding output to be ON. A logical '0' requests it to be OFF.
The normal response returns the function code, starting address, and
quantity of coils forced."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.11
The request PDU with function code 15 must be at least 7 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting Address 2
Byte count 1
Quantity 2
Value n
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHHBB', b'\\x0f\\x00d\\x00\\x03\\x01\\x05')
(16, 100, 3, 1, 5)
The reponse PDU is 5 bytes and contains following structure:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting address 2
Quantity 2
================ ===============
"""
function_code = WRITE_MULTIPLE_COILS
starting_address = None
_values = None
_data = None
@property
def values(self):
return self._values
@values.setter
def values(self, values):
if not (1 <= len(values) <= 0x7B0):
raise IllegalDataValueError
for value in values:
if value not in [0, 1]:
raise IllegalDataValueError
self._values = values
@property
def request_pdu(self):
if None in [self.starting_address, self._values]:
raise IllegalDataValueError
bytes_ = [self.values[i:i + 8] for i in range(0, len(self.values), 8)]
# Reduce each all bits per byte to a number. Byte
# [0, 0, 0, 0, 0, 1, 1, 1] is intepreted as binary en is decimal 3.
for index, byte in enumerate(bytes_):
bytes_[index] = \
reduce(lambda a, b: (a << 1) + b, list(reversed(byte)))
fmt = '>BHHB' + 'B' * len(bytes_)
return struct.pack(fmt, self.function_code, self.starting_address,
len(self.values), (len(self.values) // 8) + 1,
*bytes_)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
This method requires some clarification regarding the unpacking of
the status that are being passed to the callbacks.
A coil status can be 0 or 1. The request PDU contains at least 1 byte,
representing the status for 1 to 8 coils.
Assume a request with starting address 100, quantity set to 3 and the
value byte is 6. 0b110 is the binary reprensention of decimal 6. The
Least Significant Bit (LSB) is status of coil with starting address. So
status of coil 100 is 0, status of coil 101 is 1 and status of coil 102
is 1 too.
coil address 102 101 100
1 1 0
Again, assume starting address 100 and byte value is 6. But now
quantity is 4. So the value byte is addressing 4 coils. The binary
representation of 6 is now 0b0110. LSB again is 0, meaning status of
coil 100 is 0. Status of 101 and 102 is 1, like in the previous
example. Status of coil 104 is 0.
coil address 104 102 101 100
0 1 1 0
In short: the binary representation of the byte value is in reverse
mapped to the coil addresses. In table below you can see some more
examples.
# quantity value binary representation | 102 101 100
== ======== ===== ===================== | === === ===
01 1 0 0b0 - - 0
02 1 1 0b1 - - 1
03 2 0 0b00 - 0 0
04 2 1 0b01 - 0 1
05 2 2 0b10 - 1 0
06 2 3 0b11 - 1 1
07 3 0 0b000 0 0 0
08 3 1 0b001 0 0 1
09 3 2 0b010 0 1 0
10 3 3 0b011 0 1 1
11 3 4 0b100 1 0 0
12 3 5 0b101 1 0 1
13 3 6 0b110 1 1 0
14 3 7 0b111 1 1 1
:param pdu: A request PDU.
"""
_, starting_address, quantity, byte_count = \
struct.unpack('>BHHB', pdu[:6])
fmt = '>' + (conf.SINGLE_BIT_VALUE_FORMAT_CHARACTER * byte_count)
values = struct.unpack(fmt, pdu[6:])
res = list()
for i, value in enumerate(values):
padding = 8 if (quantity - (8 * i)) // 8 > 0 else quantity % 8
fmt = '{{0:0{padding}b}}'.format(padding=padding)
# Create binary representation of integer, convert it to a list
# and reverse the list.
res = res + [int(i) for i in fmt.format(value)][::-1]
instance = WriteMultipleCoils()
instance.starting_address = starting_address
instance.quantity = quantity
instance.values = res
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 5
def create_response_pdu(self):
""" Create response pdu.
:param data: A list with values.
:return: Byte array 5 bytes.
"""
return struct.pack('>BHH', self.function_code, self.starting_address,
len(self.values))
@staticmethod
def create_from_response_pdu(resp_pdu):
write_multiple_coils = WriteMultipleCoils()
starting_address, data = struct.unpack('>HH', resp_pdu[1:5])
write_multiple_coils.starting_address = starting_address
write_multiple_coils.data = data
return write_multiple_coils
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
"""
for index, value in enumerate(self.values):
address = self.starting_address + index
endpoint = route_map.match(slave_id, self.function_code, address)
try:
endpoint(slave_id=slave_id, address=address, value=value,
function_code=self.function_code)
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
[docs]class WriteMultipleRegisters(ModbusFunction):
""" Implement Modbus function 16 (0x10) Write Multiple Registers.
"This function code is used to write a block of contiguous registers (1
to 123 registers) in a remote device.
The requested written values are specified in the request data field.
Data is packed as two bytes per register.
The normal response returns the function code, starting address, and
quantity of registers written."
-- MODBUS Application Protocol Specification V1.1b3, chapter 6.12
The request PDU with function code 16 must be at least 8 bytes:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting Address 2
Quantity 2
Byte count 1
Value Quantity * 2
================ ===============
The PDU can unpacked to this:
..
Note: the backslash in the bytes below are escaped using an extra back
slash. Without escaping the bytes aren't printed correctly in the HTML
output of this docs.
To work with the bytes in Python you need to remove the escape sequences.
`b'\\x01\\x00d` -> `b\x01\x00d`
.. code-block:: python
>>> struct.unpack('>BHHBH', b'\\x10\\x00d\\x00\\x01\\x02\\x00\\x05')
(16, 100, 1, 2, 5)
The reponse PDU is 5 bytes and contains following structure:
================ ===============
Field Length (bytes)
================ ===============
Function code 1
Starting address 2
Quantity 2
================ ===============
"""
function_code = WRITE_MULTIPLE_REGISTERS
starting_address = None
_values = None
_data = None
@property
def values(self):
return self._values
@values.setter
def values(self, values):
if not (1 <= len(values) <= 0x7B0):
raise IllegalDataValueError
for value in values:
try:
struct.pack(">" + conf.MULTI_BIT_VALUE_FORMAT_CHARACTER, value)
except struct.error:
raise IllegalDataValueError
self._values = values
self._values = values
@property
def request_pdu(self):
fmt = '>BHHB' + (conf.TYPE_CHAR * len(self.values))
return struct.pack(fmt, self.function_code, self.starting_address,
len(self.values), len(self.values) * 2,
*self.values)
@staticmethod
def create_from_request_pdu(pdu):
""" Create instance from request PDU.
:param pdu: A request PDU.
:return: Instance of this class.
"""
_, starting_address, quantity, byte_count = \
struct.unpack('>BHHB', pdu[:6])
# Values are 16 bit, so each value takes up 2 bytes.
fmt = '>' + (conf.MULTI_BIT_VALUE_FORMAT_CHARACTER *
int((byte_count / 2)))
values = list(struct.unpack(fmt, pdu[6:]))
instance = WriteMultipleRegisters()
instance.starting_address = starting_address
instance.values = values
return instance
@property
def expected_response_pdu_size(self):
""" Return number of bytes expected for response PDU.
:return: number of bytes.
"""
return 5
def create_response_pdu(self):
""" Create response pdu.
:param data: A list with values.
:return: Byte array 5 bytes.
"""
return struct.pack('>BHH', self.function_code, self.starting_address,
len(self.values))
@staticmethod
def create_from_response_pdu(resp_pdu):
write_multiple_registers = WriteMultipleRegisters()
starting_address, data = struct.unpack('>HH', resp_pdu[1:5])
write_multiple_registers.starting_address = starting_address
write_multiple_registers.data = data
return write_multiple_registers
def execute(self, slave_id, route_map):
""" Execute the Modbus function registered for a route.
:param slave_id: Slave id.
:param eindpoint: Instance of modbus.route.Map.
"""
for index, value in enumerate(self.values):
address = self.starting_address + index
endpoint = route_map.match(slave_id, self.function_code, address)
try:
endpoint(slave_id=slave_id, address=address, value=value,
function_code=self.function_code)
# route_map.match() returns None if no match is found. Calling None
# results in TypeError.
except TypeError:
raise IllegalDataAddressError()
function_code_to_function_map = {
READ_COILS: ReadCoils,
READ_DISCRETE_INPUTS: ReadDiscreteInputs,
READ_HOLDING_REGISTERS: ReadHoldingRegisters,
READ_INPUT_REGISTERS: ReadInputRegisters,
WRITE_SINGLE_COIL: WriteSingleCoil,
WRITE_SINGLE_REGISTER: WriteSingleRegister,
WRITE_MULTIPLE_COILS: WriteMultipleCoils,
WRITE_MULTIPLE_REGISTERS: WriteMultipleRegisters,
}