Using CIPDriver

The CIPDriver is the base class for the other drivers, so everything on this page also applies to the other drivers as well.

Discovery and Identification

The CIPDriver provides to class methods for discovering and identifying devices. And because they are class methods, they can be used without creating an instance of a driver first. The CIPDriver.discover() method will broadcast a request for all devices on the network to identify themselves. This is similar to how the RSLinx Ethernet/IP driver works. It returns a list of dictionaries, where each dict is the Identity Object of the device.

>>> from pycomm3 import CIPDriver
>>> CIPDriver.discover()

For example, here is a response with 2 devices discovered:

[{'encap_protocol_version': 1, 'ip_address': '10.10.0.120', 'vendor': 'Rockwell Automation/Allen-Bradley',
  'product_type': 'Communications Adapter', 'product_code': 185, 'revision': {'major': 2, 'minor': 7},
  'status': b'T\x00', 'serial': 'aabbcdd', 'product_name': '1763-L16BWA B/7.00', 'state': 0},
 {'encap_protocol_version': 1, 'ip_address': '10.10.1.100', 'vendor': 'Rockwell Automation/Allen-Bradley',
  'product_type': 'Communications Adapter', 'product_code': 191, 'revision': {'major': 20, 'minor': 19},
  'status': b'0\x00', 'serial': 'eeffgghh', 'product_name': '1769-L23E-QBFC1 Ethernet Port', 'state': 3}]

The CIPDriver.list_identity() method is similar, but can be used to identify a specific device. Instead of broadcasting the request to every device, it requires a path to send the request to. This path argument is the same type of CIP path used in creating a driver and detailed in Creating a Driver.

>>> from pycomm3 import CIPDriver
>>> CIPDriver.list_identity('10.10.0.120')
{'encap_protocol_version': 1, 'ip_address': '10.10.0.120', 'vendor': 'Rockwell Automation/Allen-Bradley',
'product_type': 'Communications Adapter', 'product_code': 185, 'revision': {'major': 2, 'minor': 7},
'status': b'T\x00', 'serial': 'aabbcdd', 'product_name': '1763-L16BWA B/7.00', 'state': 0}
>>> CIPDriver.list_identity('10.10.1.100')
{'encap_protocol_version': 1, 'ip_address': '10.10.1.100', 'vendor': 'Rockwell Automation/Allen-Bradley',
'product_type': 'Communications Adapter', 'product_code': 191, 'revision': {'major': 20, 'minor': 19},
'status': b'0\x00', 'serial': 'eeffgghh', 'product_name': '1769-L23E-QBFC1 Ethernet Port', 'state': 3}

Module Identification

For rack-based devices, the CIPDriver.get_module_info() method will return the identity for a slot in the rack. This method is not a class method, so it does require an instance of the driver to be created.

>>> from pycomm3 import CIPDriver
>>> driver = CIPDriver('10.10.1.100')
>>> driver.open()
>>> driver.get_module_info(0)  # Slot 0: PLC
{'vendor': 'Rockwell Automation/Allen-Bradley', 'product_type': 'Programmable Logic Controller', 'product_code': 51,
'revision': {'major': 16, 'minor': 22}, 'status': b'`\x10', 'serial': '00000000',
'product_name': '1756-L55/A 1756-M13/A LOGIX5555'}
>>> driver.get_module_info(1) # Slot 1: EN2T
{'vendor': 'Rockwell Automation/Allen-Bradley', 'product_type': 'Communications Adapter', 'product_code': 166,
'revision': {'major': 5, 'minor': 8}, 'status': b'0\x00', 'serial': '00000000', 'product_name': '1756-EN2T/B'}
>>> driver.close()

Generic Messaging

Generic messaging is a key feature of pycomm3, it allows the user to send custom CIP messages or implement features not included in one of the drivers. In fact, many features available in the drivers are implemented using the generic_message() method. This method operates in a similar way to CIP Generic messages in Logix with the MSG instruction. For more examples see the Generic Messaging section.

To demonstrate how a generic message can be used, below is the process that was used to implement the get_plc_name() feature for the LogixDriver.

First, the Obtaining the Controller’s Program Name article from the Rockwell Knowledge Base shows how to configure a MESSAGE to read the program name from a PLC. It contains all the information we need: CIP service, class, instance, etc.

../_images/cip_msg_plc_name_msg_cfg.png
  1. The service type is 0x01, which is the Get_Attributes_All service define in the Common Industrial Protocol Specification, Volume 1, Chapter 4: CIP Object Model. See CIP Services and Class Codes for the predefined CIP services, classes, and other objects available in pycomm3. If the service is not already defined, you use either an int or a bytes string (0x01, 1, b'\x01).

  2. The class code, 0x64 is not named in the doc, but is defined as ClassCode.program_name.

  3. The instance number of the class we want, 1.

  4. The attribute is 0, so we can ignore it and not set the attribute parameter.

  5. Since we’re not in the PLC, we’re not storing the response in a tag. If we set the data_type parameter to a DataType, that type will be used to decode the response. Else, the raw response bytes will be returned.

Next, the screenshot below contains enough information for us to determine the data type that can be used to decode the response.

../_images/cip_msg_plc_name_resp.png

While the doc doesn’t specifically say the response type, it’s shows that it is stored in a SINT[50]. The first two bytes contains the length of the string, which corresponds to a integer(INT or UINT). Then the string data is stored in the remainder of the array, since PLCs are limited to fixed-size arrays the destination tag needs to be long enough to contain the maximum size possible. In Python we do not have that limitation, but this information tells us that the response is a string, with 1 byte per character, and the length of the string is stored in the first 2 bytes. That corresponds to the CIP STRING data type, which is a standard type that is already defined and we can just use.

Taking this information, we were able configure the generic_message() method to read the PLC program name:

    @with_forward_open
    def get_plc_name(self) -> str:
        """
        Requests the name of the program running in the PLC. Uses KB `23341`_ for implementation.

        .. _23341: https://rockwellautomation.custhelp.com/app/answers/answer_view/a_id/23341

        :return:  the controller program name
        """

        try:
            response = self.generic_message(
                service=Services.get_attributes_all,
                class_code=ClassCode.program_name,
                instance=1,
                data_type=STRING,
                name="get_plc_name",
            )
            if not response:
                raise ResponseError(f"response did not return valid data - {response.error}")

            self._info["name"] = response.value
            return self._info["name"]
        except Exception as err:
            raise ResponseError("failed to get the plc name") from err

Tip

Setting the name parameter is helpful because it will be used by the built in logging and can help differentiate between calls:

2021-03-09 18:09:50,802 [INFO] pycomm3.cip_driver.CIPDriver.generic_message(): Sending generic message: get_plc_name
2021-03-09 18:09:50,802 [VERBOSE] pycomm3.cip_driver.CIPDriver._send(): >>> SEND >>>
(0000) 70 00 1c 00 00 0b 02 0b 00 00 00 00 5f 70 79 63     p•••••••••••_pyc
(0010) 6f 6d 6d 5f 00 00 00 00 00 00 00 00 0a 00 02 00     omm_••••••••••••
(0020) a1 00 04 00 c1 04 35 01 b1 00 08 00 53 00 01 02     ••••••5•••••S•••
(0030) 20 64 24 01                                          d$•
2021-03-09 18:09:50,803 [DEBUG] pycomm3.cip_driver.CIPDriver.send(): Sent: GenericConnectedRequestPacket(message=[b'S\x00', b'\x01', b'\x02 d$\x01', b''])
2021-03-09 18:09:50,807 [VERBOSE] pycomm3.cip_driver.CIPDriver._receive(): <<< RECEIVE <<<
(0000) 70 00 36 00 00 0b 02 0b 00 00 00 00 00 00 00 00     p•6•••••••••••••
(0010) 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00     ••••••••••••••••
(0020) a1 00 04 00 4a b7 cb 55 b1 00 22 00 53 00 81 00     ••••J••U••"•S•••
(0030) 00 00 0c 00 70 79 63 6f 6d 6d 33 5f 64 65 6d 6f     ••••pycomm3_demo
(0040) 00 00 00 00 02 00 01 00 64 00 02 00 09 00           ••••••••d•••••
2021-03-09 18:09:50,807 [DEBUG] pycomm3.cip_driver.CIPDriver.send(): Received: GenericConnectedResponsePacket(service=b'\x01', command=b'p\x00', error=None)
2021-03-09 18:09:50,807 [INFO] pycomm3.cip_driver.CIPDriver.generic_message(): Generic message 'get_plc_name' completed