pycomm3 0.10.1

A Python Ethernet/IP library for communicating with Allen-Bradley PLCs.

pycomm3 is a Python 3 fork of pycomm, which is a native python library for communicating with PLCs using Ethernet/IP. The initial Python 3 translation was done in this fork, this library seeks to continue and expand upon the great work done by the original pycomm developers. pylogix is another library with similar features (including Python 2 support) for ControlLogix and CompactLogix PLCs. Referencing pylogix code was a big help in implementing some features missing from pycomm. This library is supported on Python 3.6.1 and newer.

This library contains 3 drivers:

LogixDriver

This is the main driver for this library, it supports ControlLogix, CompactLogix, and Micro800 PLCs.

SLCDriver

New in version 0.10.0

This driver can be used for reading/writing data files in SLC 500 or MicroLogix PLCs. This driver is an update to the original pycomm SLC driver with some minor changes to make it similar to the LogixDriver. Some of the more advanced or automatic features are not supported. Even though this driver was newly added, it’s considered legacy and it’s development will be on a limited basis.

CIPDriver

This is the base class for the other two drivers, it handles some common shared services. It can also be used for generic CIP messaging to other non-PLC devices.

Disclaimer

PLCs can be used to control heavy or dangerous equipment, this library is provided ‘As Is’ and makes no guarantees on it’s reliability in a production environment. This library makes no promises in the completeness or correctness of the protocol implementations and should not be solely relied upon for critical systems. The development for this library is aimed at providing quick and convenient access for reading/writing data inside Allen-Bradley PLCs.

Setup

The package can be installed from PyPI using pip: pip install pycomm3 or python -m pip install pycomm3.

Optionally, you may configure logging using the Python standard logging library.

Documentation

This README covers a basic overview of the library, full documentation can be found on Read the Docs.

LogixDriver

Highlighted Features

• simple API, only 1 read method and 1 write method for tags.

  • does not require using different methods for different data types

  • requires the tag name only, no other information required from the user

  • automatically manages request/response size to pack as many requests into a single packet

  • automatically handles fragmented requests for large tags that can’t fit in a single packet

• read support the reading of an entire structure

  • does not require reading of each attribute separately

  • returns a value dict {attribute: value}

• write supports full structure writing

  • value should be a list/tuple of values for each attribute, nested for arrays and other structures

  • not recommended for built-in types (TIMER, CONTROL, COUNTER, etc)

  • all or nothing, does not update only parts of a struct

• generic_message for extra functionality not directly implemented

  • working similar to the MSG instruction in Logix, arguments similar to the MESSAGE properties

  • tested getting/setting drive parameters (see under examples in docs)

  • used internally to implement some of the other methods (get/set_plc_time, forward open/close, etc)

• simplified data types

  • strings use normal Python str objects, does not require reading/writing of the LEN and DATA attributes

  • BOOL arrays use normal Python bool objects, does not require complicated bit shifting of the DWORD value

• uploads the tag list and data type definitions from the PLC

  • no requirement for user to determine tags available (like from an L5X export)

  • controller-scoped tags by default, program-scoped tags are optional

  • definitions are required for read/write methods

• automatically enables/disables different features based on the target PLC

  • Extended Forward Open (EN2T or newer and v20+)

  • Symbol Instance Addressing (Logix v21+)

  • detection of Micro800 and disables unsupported features (CIP Path, Ex. Forward Open, Instance Addressing, etc)

Basic Usage

Connect to a PLC and get some basic information about it. The path argument is the only one required, and it has 3 forms:

• IP Address Only (10.20.30.100) - Use if PLC is in slot 0 or if connecting to CompactLogix

• IP Address/Slot (10.20.30.100/1) - Use if PLC is not in slot 0

• CIP Routing Path (10.20.30.100/backplane/3/enet/10.20.40.100/backplane/0) - Use for more complex routing

  • first 2 examples will be replaced with the full path automatically, they’re there for convenience.

  • enet/backplane (or bp) are for port selection, easy to remember symbols for standard CIP routing pairs

from pycomm3 import LogixDriver

with LogixDriver('10.20.30.100/1') as plc:
    print(plc)
    # OUTPUT:
    # Program Name: PLCA, Device: 1756-L83E/B, Revision: 28.13

    print(plc.info)
    # OUTPUT:
    # {'vendor': 'Rockwell Automation/Allen-Bradley', 'product_type': 'Programmable Logic Controller',
    #  'product_code': 166, 'version_major': 28, 'version_minor': 13, 'revision': '28.13', 'serial': 'FFFFFFFF',
    #  'device_type': '1756-L83E/B', 'keyswitch': 'REMOTE RUN', 'name': 'PLCA'}

By default, when creating the LogixDriver object, it will open a connection to the plc, read the program name, get the controller info, and get all the controller scoped tags. By reading the tag list first, this allows us to cache all the tag type/structure information, including the instance ids for all the tags. This information allows the read/write methods to require only the tag name. If your project will require program-scoped tags, be sure to set the init_program_tags kwarg. By default, only the controller-scoped tags will be retrieved and cached.

Reading/Writing Tags

Reading or writing tags is as simple as calling the read and write methods. Both methods accept any number of tags, and will automatically pack multiple tags into a Multiple Service Packet Service (0x0A) while making sure to stay below the connection size. If there is a tag value that cannot fit within the request/reply packet, it will automatically handle that tag independently using the Read Tag Fragmented (0x52) or Write Tag Fragmented (0x53) requests.

Both methods will return Tag objects to reflect the success or failure of the operation.

class Tag(NamedTuple):
    tag: str
    value: Any
    type: Optional[str] = None
    error: Optional[str] = None

Tag objects are considered successful if the value is not None and the error is None. Otherwise, the error will indicate either the CIP error or exception that was thrown. Tag.__bool__() has been implemented in this way. type will indicate the data type of the tag and include [<length>] if multiple array elements are requested. value will contain the value of the tag either read or written, structures (read only) will be in the form of a { attribute: value, ... } dict. Even though strings are technically structures, both reading and writing support automatically converting them to/from normal string objects. Any structures that have only the attributes LEN (DINT) and DATA (array of SINT) will automatically be treated as strings. Reading of structures as a whole is supported as long as no attributes have External Access set to None (CIP limitation). Writing structures as a whole is not supported (for the time being) except for string objects.

Examples:

with LogixDriver('10.20.30.100') as plc:
    plc.read('tag1', 'tag2', 'tag3')  # read multiple tags
    plc.read('array{10}') # read 10 elements starting at 0 from an array
    plc.read('array[5]{20}) # read 20 elements starting at elements 5 from an array
    plc.read('string_tag')  # read a string tag and get a string

    # writes require a sequence of tuples of [(tag name, value), ... ]
    plc.write(('tag1', 0), ('tag2', 1), ('tag3', 2))  # write multiple tags
    plc.write(('array{5}', [1, 2, 3, 4, 5]))  # write 5 elements to an array starting at the 0 element
    plc.write(('array[10]{5}', [1, 2, 3, 4, 5]))  # write 5 elements to an array starting at element 10
    plc.write(('string_tag', 'Hello World!'))  # write to a string tag with a string
    plc.write(('string_array[2]{5}', 'Write an array of strings'.split()))  # write an array of 5 strings starting at element 2

Note

Tag names for both read and write are case-sensitive and are required to be the same as they are named in the controller. This may change in the future. (pull requests welcome)

Tag Definitions and Data Types

Tag definitions are uploaded from the controller automatically when connecting. This allows the read/writing methods to work. These definitions contain information like instance ids and structure size and composition. This information allows for many optimizations and features that other similar libraries do not offer. The old pycomm API does not depend on these, but the new read/write methods do. The tag definitions are accessible from the tags attribute. The tags property is a dict of {tag name: definition}.

Definitions for structures are accessible from the data_types attribute. These include things like User-Defined Data Types (UDT), Add-On Instructions (AOI), strings, and pre-defined types (TIMER, COUNTER, etc). For structure tags (tag['tag_type'] == 'struct'), the data type definition will be stored in the data_type attribute. ('atomic' tags will only have a string with their data type name: 'DINT', 'REAL', ...).

For details on the information contained and the structure of the definitions, refer the to the Documentation.

Unit Testing

pytest is used for unit testing. The tests directory contains an L5X export of the Pycomm3_Testing program that contains all tags necessary for testing. The only requirement for testing (besides a running PLC with the testing program) is the environment variable PLCPATH for the PLC defined.

Note

Test coverage is not complete, pull requests are welcome to help improve coverage.

TODO

• (wip) - improve documentation and include more real-world example scripts

• (not started) - make API case insensitive

License

pycomm3 is distributed under the MIT License