In short
Upgrade legacy Allen-Bradley MicroLogix systems to the modern Micro850 platform. This detailed technical guide covers catalog mapping, hardware wiring differences, and software conversion rules.
Overview
For more than two decades, the Rockwell Automation Allen-Bradley MicroLogix family (MicroLogix 1000, 1100, 1200, 1400, and 1500) served as the industry standard for small-scale, standalone machine control. However, with the exception of the MicroLogix 1400, the majority of this product family has reached end-of-life, discontinued, or "Silver Series" status.
The officially designated replacement path for legacy MicroLogix controllers is the Micro850 platform (specifically the 2080-L50E series). This transition represents more than a hardware replacement; it is an architectural shift from the proprietary, file-based addressing of RSLogix 500 to the modern, tag-based IEC 61131-3 standard native to Connected Components Workbench (CCW) software. This guide provides the technical specifications, mapping configurations, and step-by-step execution steps required to successfully plan and execute a MicroLogix to Micro850 migration.
Legacy Product Information
To execute a clean migration, you must first identify the precise specifications and lifecycle phase of your existing controller. The legacy MicroLogix line includes five primary families:
- MicroLogix 1000 (1761 Series): Discontinued. This was a non-expandable, block-style controller featuring up to 32 fixed I/O points, 1 KB of fixed memory, and a single RS-232 serial port supporting DF1 protocol.
- MicroLogix 1100 (1763 Series): Discontinued/Obsolete. Featuring a small LCD screen, built-in EtherNet/IP (limited to messaging), static web server capabilities, and support for up to four 1762 expansion I/O modules.
- MicroLogix 1200 (1762 Series): Obsolete. A non-Ethernet option featuring high-density I/O configurations and support for up to six 1762 expansion modules, but restricted to RS-232 serial communication.
- MicroLogix 1400 (1766 Series): Active/Mature. Features an LCD screen, dual serial ports, a built-in EtherNet/IP port, and support for up to seven 1762 I/O modules. While still supported, new designs should target the Micro850.
- MicroLogix 1500 (1764 Series): Discontinued. A unique two-piece design utilizing a separate processor unit and base unit. It leveraged 1769 Compact I/O expansion modules, making its physical and electrical replacement distinct from other MicroLogix models.
Common legacy communication protocols encountered during replacement include DF1 Full/Half Duplex, DH-485, and limited Modbus RTU over RS-232/RS-485 interfaces.
Recommended Replacements
When upgrading to the Micro850 platform, look to map fixed I/O configurations, power supply characteristics, and expansion capabilities directly. The table below details direct cross-references from the most common legacy models to modern Micro850 (Series B and L50E) catalog numbers.
| Legacy MicroLogix Catalog | Form Factor & Core Specs | Recommended Micro850 Catalog | Modern Specifications |
|---|---|---|---|
| 1761-L32BWA (ML1000) | 120/240V AC supply, 20x 24V DC inputs, 12x Relay outputs. No expansion. | 2080-L50E-24QWB | 120/240V AC supply, 14x 24V DC inputs, 10x Relay outputs. Supports up to 4 expansion modules and 3 plug-ins. Built-in RJ45 Ethernet port. |
| 1763-L16BWA (ML1100) | 120/240V AC supply, 10x 24V DC inputs, 2x 10V analog inputs, 6x Relay outputs. | 2080-L50E-24QWB + 2080-IF2 Plug-in | Base PLC same as above. Adding the 2080-IF2 (2-channel unipolar analog input plug-in) preserves physical analog inputs without using an expansion slot. |
| 1762-L40BWA (ML1200) | 120/240V AC supply, 24x 24V DC inputs, 16x Relay outputs. | 2080-L50E-48QWB | 120/240V AC supply, 28x 24V DC inputs, 20x Relay outputs. Supports up to 4 expansion modules and 5 plug-ins. |
| 1766-L32BXB (ML1400) | 24V DC supply, 20x 24V DC inputs (including 12 fast), 6x Relay outputs, 6x 24V DC FET outputs (including 3 fast PTO). | 2080-L50E-24QVB | 24V DC supply, 14x 24V DC inputs, 10x 24V DC Source outputs (supports high-speed counter and PTO configurations). |
| 1764-28BXB (ML1500) | 24V DC Base, 12x 24V DC inputs, 12x Relay outputs, 2x 24V DC FET outputs. Uses 1769 expansion. | 2080-L50E-48QVB | 24V DC supply, 28x 24V DC inputs, 20x 24V DC Source outputs. Highly customizable via 2085 expansion modules. |
Compatibility Considerations
16-Bit Register vs. Tag-Based Architecture
The legacy MicroLogix architecture relies on global memory files (e.g., Binary B3, Timer T4, Counter C5, Integer N7). Micro850 uses a modern tag-based database structure following the IEC 61131-3 standard. Memory addresses do not exist natively. Instead, logical names (tags) dynamically allocate program memory.
Wiring and Expansion I/O
- Terminal Blocks: Physical wiring blocks are not pint-to-pin compatible. Legacy terminal strip arrangements will need to be completely mapped and rewired.
- I/O Signal Types: Pay attention to sourcing vs. sinking styles on DC outputs. MicroLogix configurations often utilized sinking outputs (BXB/BXBA models), whereas standard Micro850 solid-state DC units (QVB catalogs) favor sourcing (sends 24VDC out). Choosing a "QBB" catalog provides sinking output capability if your field wiring cannot be modified.
- Expansion I/O: Legacy systems using 1762 (MicroLogix 1100/1200/1400) or 1769 (MicroLogix 1500) modules must transition to the 2085 Expansion I/O series. 2085 modules offer higher density and isolation parameters but require distinct driver setup in your logic.
Communication Interfaces
MicroLogix controllers rely heavily on serial networks via RS-232 or RS-485 (mini-DIN round connectors pins).
- Micro850 Series B & L50E controllers feature integrated dual-port Ethernet, standard USB programming interfaces, and embedded non-isolated serial RS-232/RS-485 screw-terminal blocks (Modbus RTU master/slave or CIP serial).
- If your legacy system connects to external instruments via DF1 or DH-485, you will need a serial protocol bridge (such as a ProSoft technology module) or you must rewrite the communications to leverage Modbus RTU or standard EtherNet/IP.
Upgrade Benefits
Migrating to the Micro850 provides several immediate system enhancements:
+-------------------------------------------------------------+
| BENEFITS OF MICRO850 MIGRATION |
+-------------------------------------------------------------+
| 1. Fast Ethernet Comms: Standard dual-port EtherNet/IP |
| 2. Modern Programing: Tag-based IEC 61131-3 standard |
| 3. Modular Design: Mix-and-match Plug-ins & Expansion I/O |
| 4. Cost-effective software: CCW Standard Edition is FREE |
| 5. Scalable integration: Direct link with PanelView 800 |
+-------------------------------------------------------------+
- High-Speed Connectivity: Integrated multi-port Ethernet on the 2080-L50E supports up to 16 simultaneous CIP client connections and 32 CIP server connections, providing faster SCADA, HMI, and remote data collection throughput over obsolete DF1 networks.
- Flexible Form Factor with Plug-Ins: You can customize the physical chassis footprint of the Micro850 using 2080 Plug-In modules (e.g., RTD modules, serial expansion, memory modules, additional analog channels) directly inside the controller housing without adding DIN rail width.
- Modernized Programming Environment: Connected Components Workbench (CCW) standard edition is free. It supports Ladder Diagram (LD), Structured Text (ST), and Function Block Diagram (FBD), giving your team access to modern software tools.
- Device-Level Integration: The Micro850 provides deep diagnostic integration with PowerFlex 525 AC drives and PanelView 800 graphic terminals directly over EtherNet/IP networks via built-in setup wizards.
Common Migration Challenges
Ladder Translation Limits & "Undeclared" Instructions
The automated program utilities conversion tool cannot parse complex legacy instructions. Functions such as legacy PID loops, high-speed counters (HSC), real-time clock mapping (RTC values), and MSG (Message) networks will not directly compile and must be rewritten from scratch using CCW system variables or user-defined function blocks (UDFBs).
Analog Input Scaling
Legacy MicroLogix programs leveraged Scale with Parameters (SCP) or Scale (SCL) instructions. CCW does not natively have an SCP or SCL block in its basic library. Developers must write standard algebraic scaling ($Y = mX + c$) or import the Rockwell Automation legacy analog scaling UDFB (RA_Scale_Analogue) from the Rockwell Product Compatibility and Download Center (PCDC).
HMI Protocol Mapping
Legacy HMIs communicating directly via DF1 mapped directly to physical files like N7:0. If the HMI is not being replaced immediately, you must enable Logical Address Mapping in CCW. This feature allows you to map specific tag arrays to match old RSLogix 500 address formats (e.g., map a 50-element array of integers directly to data file N7).
Step-by-Step Replacement Procedure
Follow this systemized engineering process to execute the changeover:
[1. Backup & Export] --> [2. CCW Conversion Utility] --> [3. Tag Mapping]
|
v
[6. System Startup] <-- [5. Cabinet Installation] <-- [4. Bench Testing]
Phase 1: Software Conversion and Prep
- Backup Existing System: Connect to your legacy MicroLogix using RSLogix 500. Upload the current running program, save the project file as
.RSP, and export the database as a.CSVfile for instruction comment reference. - Run the Conversion Utility: Open Connected Components Workbench. Navigate to Tools > MicroLogix Library Converter. Select your legacy
.RSPor.ACHfile. - Resolve Compilation Errors:
- Review the generated compilation output log. Locate any unmapped data references.
- Manually program analog scaling code to convert raw input words (typically 0-65535 or 0-16384 depending on the legacy card resolution) to real physical units.
- Set up any HMI bridging parameters via CCW's Logical Address Map settings.
Phase 2: Hardware Preparation and Bench Test
- Confirm I/O Configurations on the Bench: Supply power to the new Micro850 on a test bench. Using a USB standard Type-A to Type-B cable or Ethernet, download your newly compiled program.
- Simulate and Force System Points: Use CCW’s Global Variables monitoring screen to verify logic executes properly without hardware errors. Resolve internal clock or math execution division-by-zero faults.
Phase 3: Field Installation
- De-energize Control Panels: Lockout/tagout the main breaker supplying the system cabinet. Verify with a calibrated digital multimeter that no AC or DC power remains in the field I/O circuit.
- Identify and Label Field Wiring: Label each wire clearly based on the existing terminal block assignments before disconnecting them.
- Mount New DIN Rail/Chassis: Remove the old MicroLogix chassis. Drill new template mounting holes or clip a stable length of standard 35mm DIN rail to mount the Micro850.
- Land Field Terminal Signals: Connect all physical wires to the Micro850 terminal block. Install expansion modules and terminate power supplies (check for 24VDC polarity matches to prevent internal fuse trip-outs).
- Power Up and Commission: Power on the controller. Configure your network gateway parameters using the front panel and CCW software. Run live I/O validation steps, checking limit switches and analog signals before running full machine processes.
Frequently Asked Questions
Q: Can I reuse existing 1762 expansion modules with the Micro850?
A: No. 1762-series modules are inoperable with Micro850 controllers. The Micro850 uses 2085-series expansion modules or 2080 Plug-In modules.
Q: Can I convert my legacy files using the free version of Connected Components Workbench?
A: Yes. The free CCW Standard Edition includes the MicroLogix Library Converter tool. A paid license (Developer Edition) is only required if you require advanced features like Online Editing during system diagnostics.
Q: How do I handle PID conversion during migration?
A: Because RSLogix 500 PID loops function on different internal algorithms than the CCW PID instruction, you must manually rebuild loop loops using the standard CCW function block execution loop structure and manually re-tune the proportional, integral, and derivative parameters on-site.
Q: Do Micro850 controllers support DH-485 protocol directly?
A: No. If you have legacy network drops communicating via run-length DH-485, you must integrate an external gateway device (such as the ProSoft PLX51-DF1-ENI module) to interface with the modern industrial Ethernet framework of the Micro850.
Related Products & Families
- Allen-Bradley PanelView 800 Graphic Terminals: High-speed display interfaces designed to integrate directly with Micro850 systems via CCW.
- 2085 Expansion Modules: Analog, digital, thermocouple, and RTD expansion options to scale your physical I/O layout.
- 2080 Plug-in Modules: Compact functional modules (including non-isolated serial, digital input/output, or analog plug-ins) that insert directly into the front face of the Micro850 controller.
Need Help?
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