How-To Guide  ·  Allen-Bradley ControlLogix  ·  Platform Migration

SLC 500 to ControlLogix Migration: Hardware, I/O, Wiring, and Software

Part Number: 1756-L83E  ·  Bulletin 1746/1747 → 1756 · 4 Migration Paths

1. Quick Migration Calculator

Skip the catalog cross-referencing. Pick up to 15 of your existing SLC 500 cards from the dropdowns below. We'll suggest the Rockwell-equivalent ControlLogix part numbers, recommend a chassis size and power supply, and pre-fill an RFQ you can submit in one click — all sourced from Rockwell's I/O Wiring Conversion Selection Guide (1492-SG121) and Modernization Profile (MIGRAT-PP003).

This is an initial BOM that should be qualified by a competent engineer. We offer Automation Consulting Services if you would like help understanding or executing the migration process of your system. You can also contact us at any time. Every part PLC Exchange stocks is backed by our 2.5-year warranty.

2. Why Migrate Now

The SLC 500 product line is one of the most successful PLC platforms ever built — but it is at the end of its life. Rockwell Automation's product lifecycle status (documented in publications MIGRAT-PP004 and 1746-RM003) puts every SLC 500 processor and the majority of 1746 I/O modules in the End-of-Life or Discontinued phase. Spare parts on the secondary market are still abundant, but new manufacture has stopped.

What's Driving the Migration

Why Not MicroLogix?

MicroLogix 1100/1400 controllers are sometimes proposed as low-cost SLC replacements. They are not a successor for capital projects: MicroLogix is itself End-of-Life (Discontinued effective 2024 for the 1761/1762 lines, with 1100/1400 in active-mature status), runs RSLogix 500 (not Studio 5000), and tops out at memory and I/O counts well below even a small 1747-L20 application. For a multi-decade plant investment, the migration target should be Logix — ControlLogix 1756 for chassis-based applications, CompactLogix 5380 for compact DIN-rail applications.

3. Migration Path Overview

There are four practical migration paths from SLC 500 to ControlLogix. They differ in how much existing hardware (chassis, I/O, field wiring) you keep versus replace, and in how much risk and downtime the cutover carries. Most real projects use a combination — for example, AENTR adapters on three SLC chassis (path C) plus full hardware replacement on a fourth chassis that has obsolete specialty modules (path A).

How to Choose

1. Inventory your SLC modules. List every 1746 and 1747 catalog number across every chassis. Mark anything that is 1746-HSRV, 1746-BTM, 1747-DCM, 1747-KE, 1747-KFC15, 1747-SDN, 1747-SCNR, 1747-SN, 1747-BSN, 1746-QV, 1746-BLM, 1746-MPM, or 1203-SM1 — these are not supported by the 1747-AENTR adapter (per 1747-UM076 page 28).
2. Decide on a per-chassis basis. Each SLC chassis can use a different path. A chassis with all-supported I/O is a good Path C candidate; a chassis with a 1747-SDN DeviceNet scanner needs Path A or a different scanner strategy.
3. Plan the controller layer. Regardless of how you handle the SLC chassis, you need at least one new 1756 chassis with a ControlLogix processor (1756-L8xE) and an EtherNet/IP communication module (1756-EN2T or 1756-EN2TR). For Path C the EtherNet/IP module is the single point of contact between the new controller and every preserved SLC chassis.
4. Plan the network. Each 1747-AENTR adapter is an EtherNet/IP node and requires an IP address. Plan VLAN, subnet, and switch infrastructure now — the network is permanent.
5. Convert the program. Run RSLogix 500 → Studio 5000 conversion (Save As ‘.SLC’ and import) early in the project, before hardware arrives. The conversion exposes Programming Conversion Errors (PCE) and unsupported instructions you need to refactor manually.

4. Path A — Full Hardware Replacement

In a full hardware replacement, the entire SLC 500 panel is removed and replaced with new ControlLogix hardware. Every field wire is landed on new terminals on new modules in new chassis. This is the most expensive option in capital cost, but it gives you a clean, modern panel with no carry-over of legacy hardware risk.

What You Buy

Pros and Cons

5. Path B — Swing-Arm 1492 Wiring Conversion

The swing-arm conversion is a hybrid: you replace the SLC chassis and all I/O modules with new ControlLogix hardware, but you preserve the existing field wiring by using Bulletin 1492 pre-wired cables and interface modules (IFMs / AIFMs). The pre-wired cable plugs into the new ControlLogix module on one end and into a 1492 IFM (which in turn carries the existing field wiring) on the other end. No field wires are moved.

How the 1492 System Works

Per Rockwell's MIGRAT-PP004 profile and Bulletin 1492 wiring-system technical data (1492-TD008), the swing-arm conversion uses three components: a 1492 conversion module on the new ControlLogix side, a pre-wired cable in the middle, and a 1492 interface module (IFM or AIFM) on the SLC field side that lands the existing wiring. The original 1746 module is removed; the new ControlLogix module talks to the field through the cable and IFM — the field wiring never changes.

Example 1492 Conversion Pairings

When Path B Makes Sense

Path B works best when (a) the SLC chassis is at end-of-life but the field wiring is in good condition, (b) the application can afford the new ControlLogix I/O cost, and (c) downtime needs to be minimized. It does not work well when the original installation never used 1492 IFMs — if the field wiring lands directly on SLC module RTBs, the IFM has to be installed before path B becomes practical, and at that point Path A or C is usually a better trade-off.

6. Path C — 1747-AENTR Remote SLC Adapter (the marquee path)

Path C is the most popular SLC 500 migration approach Rockwell recommends, and the one most plants choose. The strategy: keep the existing SLC chassis, all 1746/1747 I/O modules, and all field wiring exactly where they are. Replace only the SLC processor (1747-L20/L30/L40/L51 series) with a 1747-AENTR EtherNet/IP adapter in slot 0. The new ControlLogix processor sits in a brand-new 1756 chassis and communicates with the SLC chassis over EtherNet/IP — the SLC chassis becomes a remote I/O drop.

Architecture

From the perspective of Studio 5000 Logix Designer, the SLC chassis appears as an EtherNet/IP node hosting the 1746 I/O modules. The ControlLogix controller produces and consumes I/O data through the 1756-EN2T(R) module, which routes traffic to the 1747-AENTR adapter, which polls the 1746 modules across the SLC backplane just as an SLC processor used to.

1747-AENTR Module Specifications

Per the 1747-UM076 user manual:

Cutover Procedure

1. Build and stage the new ControlLogix chassis on a bench. Mount the 1756 chassis, install the power supply, processor, and 1756-EN2T(R) communication module. Install Studio 5000 Logix Designer v37 (or current) on the engineering workstation.
2. Run the RSLogix 500 to Studio 5000 conversion. Open the existing SLC project in RSLogix 500. File → Save As, set Save as type to .SLC — this produces an export file. Open Studio 5000 Logix Designer, select the new 1756-L8xE controller, and import the .SLC file. Review every Programming Conversion Error (PCE), unsupported instruction (UNK), and message instruction. Per 1756-RM085, expect to manually rework I/O addressing, indirect addressing, and any instructions not in the conversion table.
3. Set the 1747-AENTR network switches. Set the three rotary switches on the front of the adapter to a static host address (e.g., 100 for 192.168.1.100), or leave at 999 to use DHCP. Document the chosen address.
4. Schedule cutover during a planned outage. Per 1747-UM076 page 18, the SLC chassis must be powered down to remove or insert the AENTR adapter.
5. Remove the SLC processor from slot 0. Press the top and bottom releases and pull straight out. Set aside — you may reinstall it for fallback.
6. Install the 1747-AENTR in slot 0. Align the circuit board with the leftmost chassis card guide, slide in, and press evenly until seated. Connect the two Ethernet RJ-45 cables to your network switch (or DLR ring partners).
7. Power up the SLC chassis. The AENTR's 4-character status display should show its IP address after DHCP resolution or static-switch read.
8. In Studio 5000, add the 1747-AENTR to the I/O Configuration tree as a child of the 1756-EN2T module. Then add each 1746 module as a child of the 1747-AENTR. Studio 5000 generates input/output tags for each module automatically.
9. Use BTD, MOV, or CPS instructions to map data between the converted SLC tags and the new I/O module tags (the conversion utility creates SLC-style tag structures, but the live data lives at the new I/O addresses — see 1756-RM085).
10. Download the project to the controller and verify each I/O point against the field. Watch the AENTR's MOD LED (solid green = normal) and the per-channel I/O LEDs on each 1746 module to confirm communication.

1746/1747 I/O Modules NOT Supported by the 1747-AENTR

Per 1747-UM076 page 28, the following modules will NOT communicate through the 1747-AENTR. If your SLC chassis has any of these, you cannot use Path C without first replacing or relocating the unsupported module.

Pros and Cons

7. Path D — Direct Module-by-Module Replacement

Path D is the slowest and most piecemeal option: keep the existing SLC chassis and processor in service, but replace individual 1746 I/O modules one at a time over a multi-shutdown campaign. This is rarely the right answer for a strategic migration, but it can work as a tactical option when capital is severely constrained.

In practice, this path means buying new-old-stock or refurbished 1746 modules to replace failing ones, while planning a full Path C cutover for some future capital cycle. It is not a path to ControlLogix — it is a strategy for keeping SLC running until a real migration can be funded.

8. Choosing the ControlLogix Controller

The 1756-L8xE family scales from small standalone machines to PlantPAx batch plants. For an SLC migration, where the legacy program is at most 64 KB and uses 16-bit timers and integer math, the right ControlLogix processor is usually one of three: 1756-L81E, 1756-L83E, or 1756-L85E.

Per 5069-AP001 (page 13), “a full 32 KB SLC program converts to a Logix program size of about 360 KB. So in general, SLC programs of less than 32 KB fit into any type of Logix controller while a full 64 KB SLC program fits only in Logix controllers with at least about 800 KB of memory.” Both the L81E (3 MB) and L83E (10 MB) have 4–14× the headroom of a full SLC program after conversion, so memory is rarely the binding constraint. Pick the controller based on EtherNet/IP node count (one per AENTR adapter, plus drives, HMIs, third-party devices) and future expansion needs.

9. Chassis & Power Supply Selection

If you are migrating via Path C (1747-AENTR), the new 1756 chassis only needs to hold the controller, power supply, and EtherNet/IP module — the I/O lives back in the SLC chassis. A 1756-A4 (4-slot) or 1756-A7 (7-slot) is usually sufficient. If you are migrating via Path A or B, size the chassis for the controller plus the new 1756 I/O modules.

Power Supplies

10. 1746 to 1756 I/O Module Equivalents

When migrating individual 1746 modules to 1756 modules (Path A or B), use the following equivalents. These are sourced from Rockwell's 1746-RM003 SLC 500 Hardware Migration Reference Manual and the 1756 I/O technical data publications.

Digital Input Equivalents

Digital Output Equivalents

Analog Input Equivalents

Analog Output Equivalents

11. Software Migration: RSLogix 500 to Studio 5000

The hardware migration is half the project; the other half is converting your RSLogix 500 program into a Studio 5000 Logix Designer project. Per Rockwell's 1756-RM085 reference manual, the conversion is done with the Logix Designer Export utility built into RSLogix 500. The utility produces a syntactically correct import/export file that Studio 5000 can open as a new ACD project.

Architecture Differences

Per 5069-AP001 page 12 and 1756-RM085 page 9, the SLC 500 and Logix architectures differ in several fundamental ways:

Conversion Procedure

1. Open the existing project in RSLogix 500. Use the latest available release of standalone RSLogix 500 (still distributed by Rockwell at the time of writing).
2. Clean up the project before exporting. Delete unused memory (Tools → Delete Unused Memory). Resolve all PCE-prone constructs in the SLC project first — it is cheaper to fix in RSLogix 500 than to fix as PCE errors in Logix.
3. Run the conversion. File → Save As, set Save as type to .SLC. RSLogix 500 produces an export file with the same base name and a .SLC extension.
4. Open Studio 5000 Logix Designer. Create a new project with the target controller (1756-L83E or L85E) and select the appropriate firmware revision. Then File → Open and point to the .SLC export file. Logix Designer imports the file as an ACD project.
5. Review the conversion log. The conversion utility flags every Programming Conversion Error (PCE) and Unknown (UNK) instruction in the rung where the issue occurred. Per 1756-RM085, every PCE/UNK requires manual remediation — do not download to the controller until they are all resolved.
6. Map the I/O. The conversion utility creates SLC-style tag structures (e.g., I:1.0, O:2.0, N7:0). The actual live I/O data lives at the new Logix tag addresses (e.g., Local:1:I.Data, or SLC_Chassis_1:1:I.Data behind a 1747-AENTR). Use BTD, MOV, or CPS instructions to copy data between the converted SLC structures and the live Logix I/O tags.
7. Reconfigure MSG instructions. SLC MSG instructions targeted DH+/DH-485/ControlNet endpoints; Logix MSG instructions target EtherNet/IP nodes by IP address. Every MSG instruction must be reconfigured for the new network topology.
8. Convert SFC and structured text manually. Per 1756-RM085 page 9, the Logix Designer Export converts only ladder instructions. SFC and structured text routines must be re-created from scratch in Studio 5000.
9. Test on the bench. Download to the new controller, with the AENTR adapter and SLC I/O on a test chassis. Force inputs and watch outputs. Compare against the original SLC behavior using the SLC processor still in your spares stock as a reference.

Common Instructions: SLC to Logix

12. Wiring Preservation Detail

The single largest source of post-cutover defects in any PLC migration is wiring error — a wire landed on the wrong terminal, a missed shield drain, a swapped polarity. The 1747-AENTR strategy (Path C) eliminates this risk entirely by leaving every field wire on its existing 1746 RTB. Path B (1492 swing-arm) eliminates it by using factory-built pre-wired cables that maintain pin-for-pin continuity from the new ControlLogix module to the existing 1492 IFM. Path A is the only path that requires hands-on field-wiring rework.

1492 Pre-Wired Cable Sizing

1492 conversion cables are sized by length (typically 0.5 m, 1 m, 2.5 m, or 5 m), conductor count (matched to the SLC module's I/O count plus commons), and shield type. Per 1492-TD008, common cable selections include:

Color Coding and Polarity

When using 1492 swing-arm cables for analog inputs (Path B), per 1492-TD008 the typical color code is: red = current/voltage input (+), black = current/voltage input (-), shield drain to module ground terminal. Verify the exact color code on the cable's spec sheet before commissioning — cable color codes vary by IFM family.

13. Sample Migration: 64-Point Water Treatment Plant

To make the AENTR strategy concrete, here is a realistic example: a small water treatment plant with two existing SLC 500 chassis, 64 I/O points total, currently controlled by a 1747-L532 SLC 5/03 processor. The plant runs 24/7 and can take a 4-hour outage maximum for cutover.

Existing System

New System (Path C — 1747-AENTR)

Bill of Materials — New Hardware Only

Cutover Timeline

1. Week 1–3 (offline): Engineering. Run RSLogix 500 conversion to Studio 5000. Resolve PCE/UNK errors. Configure I/O tree for both AENTR adapters and all 1746 modules. Build new 1756 chassis on the bench. Configure network switch and IP addresses.
2. Week 4 (offline): Bench FAT. Connect bench AENTR adapter to a test SLC chassis loaded with spare 1746 modules. Verify every input read, every output write, every alarm.
3. Outage hour 0: Plant shutdown. Lock-out/tag-out main and secondary SLC chassis power.
4. Hour 0–1: Pull 1747-L532 from main chassis slot 0. Install 1747-AENTR (rotary switches set to 200 for 192.168.1.200). Pull old 1747-ACN from secondary chassis slot 0. Install second 1747-AENTR (set to 201). Connect both adapters to the Stratix 5200 switch in DLR ring topology.
5. Hour 1–2: Mount new 1756-A4 chassis in main MCC. Land power. Connect Stratix 5200 to 1756-EN2TR.
6. Hour 2–3: Power up. Verify both AENTR MOD LEDs solid green. Verify 1756-EN2TR network LEDs. Download Studio 5000 project to 1756-L83E.
7. Hour 3–4: Functional test — cycle each pump start/stop, verify each alarm contact, verify each analog reading, verify each chemical pump output. Hand back to operations.
8. Fallback: If anything fails, pull both AENTRs, reinstall 1747-L532, restore the old DH-485 cable, and the plant is back on SLC inside an hour.

14. Related Guides

These ControlLogix guides on plcexchange.net cover related products and topics:

1. 1756-L85E ControlLogix 5580 for PlantPAx & Batch Process — If your migration target is a PlantPAx batch plant, this guide covers L85E sizing, redundancy, and FactoryTalk Batch integration.
2. 5069-AENTR Compact 5000 EtherNet/IP Adapter Guide — For Compact 5000 remote I/O drops in a mixed ControlLogix architecture.
3. 5069-IB16 Digital Input Module Guide — Companion if your project includes new Compact 5000 I/O alongside the migrated SLC chassis.

For the authoritative migration references, download Rockwell's 1756-RM085 Converting PLC-5 or SLC 500 Logic to Logix-Based Logic, 1746-RM003 SLC 500 Hardware Migration Reference Manual, and 1747-UM076 SLC 500 EtherNet/IP Adapter User Manual from the Rockwell Automation literature library.

Reference Documentation

The following Rockwell Automation publications were used as references for this guide. These are the official manufacturer documents for the hardware covered in this article.