Allen-Bradley Logix 5000

What you can build

• Catch a stalled line from its own counters

  Read part counters and state DINTs on a cycle, notice when a count stops moving inside a running state, and open a downtime record for your review.

  With Line Downtime

• Watch cycle time drift on one machine

  Read a cycle timer's accumulated value each cycle, compare it with its baseline, and flag drift before it shows up in throughput.

  With Cycle Drift

• Queue a maintenance proposal from fault words

  Read fault and warning words from a drive or machine UDT, map bits to known faults, and propose a work order in your CMMS.

  With Predictive Maintenance

• Change a setpoint with a receipt

  Propose a Write Tag to a recipe or setpoint DINT, show the current and new value, and record who approved it and how to reverse it.

  With Changeover Plan

Requirements

• A ControlLogix, GuardLogix, CompactLogix, or SoftLogix controller reachable over EtherNet/IP from where the connector runs
• Tags you want read set to External Access Read Only or Read/Write; tags set to None are invisible to outside clients
• Logix Designer version 21 or later if you want Symbol Instance addressing for large tag counts
• A path through any intervening switches and firewalls for CIP explicit messaging to the controller

Authentication

No credential in the protocol itself: access is governed per tag by the External Access attribute (Read/Write, Read Only, None) set in Studio 5000 Logix Designer, and by network reach to the controller.

Limits

• A single packet carries roughly 500 bytes; larger tags need the fragmented services and a series of requests
• Program-scope tags are not directly addressable; the manual has them copied to controller-scope tags first
• Tag names run up to 40 characters, and longer names cost packet space and parsing time in the controller
• When CPU Lock is on, controller memory cannot be altered and the change-detection request returns General Status 0x10, Device State Conflict

Questions and answers

Which CIP services does the connector use to read and write Logix tags?

The five vendor-specific services in the Logix 5000 Data Access manual: Read Tag (0x4c), Read Tag Fragmented (0x52), Write Tag (0x4d), Write Tag Fragmented (0x53), and Read Modify Write Tag (0x4e). Several requests can be grouped in one Multiple Service Packet (0x0a). Rockwell recommends connected messaging where possible.

How does the connector discover which tags exist?

It walks Symbol object instances (Class ID 0x6B) with Get_Attribute_List, paging because one packet cannot return every instance, then reads Template object instances (Class ID 0x6C) to learn each structure's members. It re-reads controller object attributes to notice when the program changed.

Can a tag be hidden from the connector?

Yes. In Logix Designer version 21 and later, each tag carries an External Access attribute: Read/Write, Read Only, or None. Tags set to None are absent from the symbol list and cannot be read or written from outside the controller. Logix Designer itself keeps full access.