SLC 500 to ControlLogix: Instruction Set Conversion Table
Conversion reference for Allen-Bradley SLC 500 instructions to ControlLogix/CompactLogix equivalents. Covers addressing, data types, timers, counters, math, and file instructions.
SLC 500 to ControlLogix: Instruction Set Conversion Table
When migrating from Allen-Bradley SLC 500 (RSLogix 500) to ControlLogix or CompactLogix (Studio 5000 Logix Designer), most instructions have direct equivalents — but the addressing system is fundamentally different. This reference covers the key instruction and addressing changes.
Addressing System Change
This is the single biggest difference between SLC 500 and ControlLogix:
| Concept | SLC 500 (RSLogix 500) | ControlLogix (Studio 5000) |
|---|---|---|
| Addressing | File-based: N7:0, B3:0/0, T4:0 | Tag-based: MyInteger, MyBool, MyTimer |
| I/O | Fixed slot: I:1/0, O:2/0 | Module path: Local:1:I.Data[0] |
| Integers | 16-bit INT: N7:0 (-32768 to +32767) | 32-bit DINT (default) |
| Data files | Numbered: N7, B3, T4, C5, R6, F8 | Named tags: any descriptive name |
| Bit addressing | B3:0/0 | MyBoolArray[0].0 or named BOOL tag |
Migration trap: SLC 500 uses 16-bit integers (INT). ControlLogix defaults to 32-bit DINT. Arithmetic involving negative numbers or bit manipulation may behave differently. The Logix Designer Export tool creates "SLC-Type" tags that preserve the 16-bit behavior, but these should be converted to native DINT tags for optimal performance.
Instruction Mapping
Bit Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| XIC (Examine If Closed) | XIC | Identical |
| XIO (Examine If Open) | XIO | Identical |
| OTE (Output Energize) | OTE | Identical |
| OTL (Output Latch) | OTL | Identical |
| OTU (Output Unlatch) | OTU | Identical |
| OSR (One-Shot Rising) | ONS | Name changed, same function |
Timer/Counter Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| TON (Timer On Delay) | TON | Same — but timer structure changes |
| TOF (Timer Off Delay) | TOF | Same |
| RTO (Retentive Timer On) | RTO | Same |
| RES (Reset) | RES | Same |
| CTU (Count Up) | CTU | Same |
| CTD (Count Down) | CTD | Same |
Timer structure change: SLC 500: T4:0.ACC, T4:0.PRE, T4:0.DN. ControlLogix: MyTimer.ACC, MyTimer.PRE, MyTimer.DN. Same fields, tag-based names.
Math Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| ADD | ADD | Same — but watch INT→DINT overflow |
| SUB | SUB | Same |
| MUL | MUL | Same |
| DIV | DIV | Same — ControlLogix DIV can return REAL |
| NEG | NEG | Same |
| SQR | SQR | Same |
| CPT (Compute) | CPT | Same — more powerful in ControlLogix |
Comparison Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| EQU | EQU | Same |
| NEQ | NEQ | Same |
| GRT | GRT | Same |
| GEQ | GEQ | Same |
| LES | LES | Same |
| LEQ | LEQ | Same |
| LIM (Limit Test) | LIM | Same |
Move/Copy Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| MOV (Move) | MOV | Same |
| COP (Copy File) | COP | Same — tag-based addressing |
| FLL (Fill File) | FLL | Same |
| MVM (Masked Move) | MVM | Same |
File/Array Instructions
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| FAL (File Arithmetic/Logic) | FAL | Same — uses tag arrays instead of file numbers |
| FSC (File Search/Compare) | FSC | Same |
| COP with file # | COP with array tag | Address syntax changes |
Communication
| SLC 500 | ControlLogix | Notes |
|---|---|---|
| MSG (Message) | MSG | Restructured — EtherNet/IP replaces DH+/DH485 |
| DH+ protocol | EtherNet/IP (CIP) | Network change required |
| DH485 | EtherNet/IP | DH485 is obsolete |
Instructions NOT Available in SLC 500
ControlLogix adds instructions not available in SLC 500: AOI (Add-On Instructions) for reusable code, PIDE (PID Enhanced), MOD (Modulo), structured text in rungs, UDTs (User-Defined Types), PHASE/EQUIPMENT for ISA-88, and CIP Motion instructions.
Frequently Asked Questions
Does the Logix Designer Export tool convert everything automatically?
No. The tool converts ladder logic only — not SFC or Structured Text. It produces SLC-Type tags that need manual cleanup. I/O configuration must be remapped manually. The tool saves hundreds of hours but is not a complete solution.
Can I keep my SLC 500 I/O modules with a ControlLogix processor?
Not directly. SLC 500 (1746) I/O is not compatible with ControlLogix (1756) backplanes. You need 1756-series I/O modules or a 1756-SYNCH bridge module for legacy integration.
Analyze Your Allen-Bradley Code
PLCcheck Pro supports Allen-Bradley SLC 500 and PLC-5 program analysis. Upload your .RSS or .RSP file for documentation and migration guidance.
Part of the Allen-Bradley Reference. Maintained by PLCcheck.ai. Not affiliated with Rockwell Automation.
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