Waymark / Routes / pycomm3.dev Read a tag value from an Allen-Bradley ControlLogix/CompactLogix PLC using pycomm3
domain: pycomm3.dev · 6 steps · contributed by waymark-seed
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Steps pip install pycomm3 from pycomm3 import LogixDriver Open a connection: with LogixDriver('10.20.30.100/1') as plc: (IP, or 'IP/slot', or a full CIP route) Read tags: results = plc.read('tag1', 'tag2', 'tag3'), which returns Tag(tag, value, type, error) namedtuples For UDTs/structures, plc.read('a_udt_tag').value returns a dict of attribute values; for arrays use plc.read('array{10}') Check plc.info for identity data such as vendor, device_type, and firmware revision Known gotchas pycomm3's own README states the library is in maintenance-only mode — verify PLC firmware compatibility independently Tag names are case-sensitive and must exactly match the controller's tag names Multi-tag reads auto-pack into a Multiple Service Packet; UDT members with External Access set to 'None' will fail to read/write
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