def create_response_adu(self, meta_data, response_pdu):
""" Build response ADU from meta data and response PDU and return it.
:param meta_data: A dict with meta data.
:param request_pdu: A bytearray containing request PDU.
:return: A bytearray containing request ADU.
"""
first_part_adu = struct.pack('>B', meta_data['unit_id']) + response_pdu
return first_part_adu + get_crc(first_part_adu)
def create_response_adu(self, meta_data, response_pdu):
""" Build response ADU from meta data and response PDU and return it.
:param meta_data: A dict with meta data.
:param request_pdu: A bytearray containing request PDU.
:return: A bytearray containing request ADU.
"""
first_part_adu = struct.pack(">B", meta_data["unit_id"]) + response_pdu
return first_part_adu + get_crc(first_part_adu)
def _create_request_adu(slave_id, req_pdu):
""" Return request ADU for Modbus RTU.
:param slave_id: Slave id.
:param req_pdu: Byte array with PDU.
:return: Byte array with ADU.
"""
first_part_adu = struct.pack('>B', slave_id) + req_pdu
return first_part_adu + get_crc(first_part_adu)
def _create_request_adu(slave_id, req_pdu):
""" Return request ADU for Modbus RTU.
:param slave_id: Slave id.
:param req_pdu: Byte array with PDU.
:return: Byte array with ADU.
"""
first_part_adu = struct.pack('>B', slave_id) + req_pdu
return first_part_adu + get_crc(first_part_adu)
def _create_request_adu(slave_id, req_pdu):
""" Return request ADU for Modbus RTU.
:param slave_id: Slave id.
:param req_pdu: Byte array with PDU.
:return: Byte array with ADU.
"""
aes = AES.new(key, AES.MODE_CBC, IV)
first_part_adu = struct.pack(
'>B', slave_id) + aes.encrypt(req_pdu + b'\x00' *
(16 - len(req_pdu) % 16))
return first_part_adu + get_crc(first_part_adu)
def test_get_crc():
""" Test if correct CRC is calculated. """
# Values are equal to those used in example in MODBUS over serial line
# specification and implementation guide V1.02, chapter 6.2.2.
assert struct.unpack('<H', get_crc(b'\x02\x07')) ==\
struct.unpack('<H', b'\x41\x12')
