pcom 0.11

A basic PCOM implementation in Python

PCOM

A very basic Unitronics PCOM protocol implementation for Python 3.

How to use

from pcom import commands
from pcom.plc import EthernetPlc

with EthernetPlc(address=('192.168.5.43', 1616)) as plc:
    # Read realtime clock
    c = commands.ReadRtc()
    res = plc.send(c)
    print(res)
    
    # Set realtime clock
    c = commands.SetRtc(value=datetime.now())
    plc.send(c)
    
    # Set MB 300 through 304
    values = [True, False, True, True, False]
    c = commands.SetBits(code=commands.SetBits.MEMORY, address=300, values=values)
    plc.send(c)

When entering the with block, the plc instance connects to the PLC and the connection is closed when the block is done, or when an error occurs within the block.

You can also manually call the connect() and close() methods:

from pcom import commands
from pcom.plc import EthernetPlc

plc = EthernetPlc(address=('192.168.5.43', 1616))
try:
  plc.connect()
  # Read realtime clock
  c = commands.ReadRtc()
  res = plc.send(c)
  print(res)
finally:  # Always close the connection.
  plc.close()

See the commands Python package for available commands.

Datatable commands are in the commands.datatables package. To work with a datatable, its structure has to be defined. Here's an example:

from pcom import commands
from pcom.plc import EthernetPlc


with EthernetPlc(address=('192.168.5.47', 1616)) as plc:
    table_structure = commands.datatables.DatatableStructure("My table", offset=19000, rows=2, columns=[
        commands.datatables.Int(),
        commands.datatables.Int(2),
        commands.datatables.Int(),
        commands.datatables.Int(),
        commands.datatables.Long(),
    ])
    c = commands.datatables.ReadDatatable(structure=table_structure, row_count=2)
    res = plc.send(c)
    print('My table', res)

Writing to a datatable is very much alike:

from pcom import commands
from pcom.plc import EthernetPlc


with EthernetPlc(address=('192.168.5.47', 1616)) as plc:
    table_structure = commands.datatables.DatatableStructure("My table", offset=19000, rows=2, columns=[
        commands.datatables.Int(2),
        commands.datatables.Int(),
        commands.datatables.String(5),
        commands.datatables.Int(),
        commands.datatables.Int(),
        commands.datatables.Long(),
    ])

    rows = [
        [[11, 12], [13], "hello", [14], [15], [-673542]],
        [[11, 14], [15], "bye  ", [16], [17], [655666]],
    ]
    c = commands.datatables.WriteDatatable(structure=table_structure, data=rows)
    try:
        plc.send(c)
    except datatables.WriteDatatableError as ex:
        print(ex)

Known limitations

• General:
  • Serial communication is not implemented yet.
• Datatables:
  • "Part of project" columns are not supported.
  • Reading a datatable structure is not supported.

Changelog

Version 0.11

• Fix: IndexError when reading OneBitRequests (MB, SB...)

Version 0.10

• Add hint about requested data being too large in binary command exception.
• Fix: is_online should not be True when connect() fails.

Version 0.9.1

• Add support for WriteIntegers and WriteFloats commands

Version 0.8

• Start of changelog
• BREAKING: Methods _connect() and _close() have been renamed to connect() and close(). Unless you have subclasses that overrides those methods, this has no impact.