9 PLC Dialects Compared: One Motor Circuit, Nine Runnable Formats

PLC platforms often express the same control idea with different instruction names, address formats, and editor conventions. The fastest way to understand those differences is to hold the logic constant.

This guide uses one motor start/stop seal-in program across the nine learning dialects currently runnable in our simulator: IEC 61131-3, Allen-Bradley, Siemens SCL, Mitsubishi, Omron, KEYENCE KV, Schneider Unity, Delta, and Instruction List.

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Scope note: these are educational parser and runtime subsets for learning transferable PLC logic. They do not emulate every vendor instruction, controller firmware behaviour, project-file format, or hardware fault. Validate production work in the target vendor environment and on the real controller.

Compare Them in the Product

You can follow this article with the actual runnable examples:

1. Open the dialect comparison bench.
2. Choose Seal-In (Motor Start/Stop).
3. Switch dialects while keeping the inputs, output, and control objective unchanged.
4. Then open the matching curriculum track and complete its first six lessons free.

The examples below come from the same reference-program source used by our cross-dialect tests, rather than decorative pseudo-code written only for this article.

At a Glance

The Control Problem

The program has three important ideas:

• START requests the motor to run.
• STOP breaks the run condition.
• The MOTOR output is fed back through an OR path, creating the seal-in after START is released.

In ladder, that feedback is normally drawn as a parallel contact. In mnemonic or text formats, the same branch becomes an OR.

1. IEC 61131-3

Learning focus: named variables, explicit declarations, and portable boolean structure.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

| START OR MOTOR AND /STOP | := MOTOR ;

Read it left to right: START or the existing MOTOR state may establish the run request, while /STOP must remain true. The declarations make the physical I/O mapping visible without burying the logic in raw addresses.

2. Allen-Bradley

Learning focus: Logix-style contact and coil mnemonics.

TAG START I:0/0 BOOL
TAG STOP  I:0/1 BOOL
TAG MOTOR O:0/0 BOOL

XIC START OR XIC MOTOR AND XIO STOP OTE MOTOR

XIC checks for a true bit, XIO checks for a false bit, and OTE writes the rung result to the output. The important transfer rule is that the instruction describes the bit test—not the physical shape of the push-button.

3. Siemens SCL / STL

Learning focus: boolean networks using Siemens-oriented A, AN, O, and assignment forms.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

      A     START
      O     MOTOR
      AN    STOP
      =     MOTOR

A contributes an AND condition, O adds the seal-in OR path, AN adds an inverted condition, and = assigns the result. The simulator teaches the reasoning pattern; it is not a replacement for TIA Portal or PLCSIM.

4. Mitsubishi

Learning focus: compact device-oriented mnemonic logic.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

LD   START
OR   MOTOR
ANI  STOP
OUT  MOTOR

The seal-in structure remains obvious: load the start condition, OR the motor feedback, AND the inverse stop condition, then write the output. The curriculum uses a controlled subset for transferable practice rather than claiming full GX Works compatibility.

5. Omron

Learning focus: Omron-oriented boolean instruction sequences.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

LD      START
OR      MOTOR
AND NOT STOP
OUT     MOTOR

The two-word AND NOT form is the most visible difference in this example. The logic is otherwise the same load–OR–stop–output sequence.

6. KEYENCE KV

Learning focus: KV STUDIO-style mnemonic logic using KEYENCE relay and data-memory devices.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

LD   R000
OR   R500
ANB  R001
OUT  R500

R000 is the start input in this exercise, R001 is the stop input, and R500 is both the motor output and its seal-in feedback contact. ANB is the inverse-contact form in this tested KV subset. The simulator also supports MR internal relays, DM data memory, TMR timers, counters, SET/RES, and core arithmetic inside the documented learning boundary.

KEYENCE's public KV Nano specifications describe R relay, MR relay, DM data-memory, timer, and counter areas, while its own controller FAQ demonstrates LD MR000 and OUT MR100 mnemonic form. Exact capacity and I/O allocation vary by KV model, so production addresses must be checked against the target controller and KV STUDIO project.

7. Schneider Unity

Learning focus: IEC-oriented accumulator logic associated with Unity Pro and Control Expert workflows.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

LD   START
OR   MOTOR
ANDN STOP
ST   MOTOR

Here ANDN applies the negated stop condition and ST stores the result. Schneider-specific learning lives inside an IEC-shaped mental model, which makes this a useful bridge from vendor-neutral fundamentals.

8. Delta

Learning focus: DVP-oriented X, Y, M, T, C, and D devices with Delta-style mnemonics.

LD   X0
OR   Y0
ANI  X1
OUT  Y0

X0 is the start input, X1 is the stop input in this exercise, and Y0 is both the motor output and its seal-in feedback. The browser parser translates the supported device addresses and executes the rung so you can test the behaviour.

9. Instruction List

Learning focus: reading accumulator-style IL found in legacy systems.

VAR
  START AT %I0.0 : BOOL;
  STOP  AT %I0.1 : BOOL;
  MOTOR AT %Q0.0 : BOOL;
END_VAR

LD   START
OR   MOTOR
ANDN STOP
ST   MOTOR

Instruction List was deprecated in the third edition of IEC 61131-3, but technicians still encounter it on installed equipment. Learning it is most valuable for maintenance, migration, and troubleshooting—not as the default choice for a new system.

The Translation Pattern

Do not memorise eight programs independently. Translate four roles:

This table is a learning map, not a complete instruction equivalence chart. Timer data structures, edge behaviour, type conversion, scan semantics, and controller-specific instructions need separate treatment.

What Transfers—and What Does Not

Transfers well

• Boolean series and parallel logic
• Seal-in and interlock patterns
• Scan-cycle reasoning
• Timer and counter intent
• Edge detection and one-shot concepts
• Safe naming, comments, and I/O documentation

Must be re-validated on the target platform

• Exact instruction names and operands
• Timer and counter time bases
• Address allocation and retained memory
• Task scheduling and scan order
• Fault handling and startup state
• Vendor project files, libraries, and firmware behaviour

Which Track Should You Learn First?

• No target controller yet: start with IEC 61131-3 to learn the control model.
• North American Logix environment: start with Allen-Bradley.
• Siemens plant or machine builder: start with Siemens SCL / STL.
• MELSEC equipment: start with Mitsubishi.
• Omron-equipped packaging or machine line: start with Omron.
• KEYENCE KV equipment or sensor-heavy OEM machinery: start with KEYENCE KV.
• Modicon / Control Expert environment: start with Schneider Unity.
• Delta DVP equipment: start with Delta.
• Maintaining legacy code: add Instruction List after one modern track.

If you are changing platforms, work through the same three exercises in both tracks: button-to-light, motor seal-in, and an on-delay timer. That gives you a controlled comparison of contacts, branches, outputs, addresses, and time handling before you tackle larger programs.

A Practical Cross-Dialect Exercise

1. Run the seal-in program in your primary track.
2. Turn START on for one scan and confirm MOTOR stays on.
3. Activate STOP and confirm the seal breaks.
4. Switch to a second dialect without changing the expected behaviour.
5. Explain which token performs each of the four roles in the translation table.
6. Rebuild the same circuit visually in the ladder editor using a parallel contact.

That final explanation is the real learning test. If you can identify the roles without relying on a memorised code block, you can move between PLC families much faster.

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Make the comparison executable. Open the tested seal-in reference, switch all nine learning formats, then continue into the track that matches your equipment.

Open the dialect comparison bench →