Mitsubishi vs Allen-Bradley Ladder Logic: A Side-by-Side Guide

If you are deciding which PLC dialect to learn first — or transitioning from one vendor's platform to another — the syntax differences between Mitsubishi and Allen-Bradley can feel significant. They are not. Both are ladder logic dialects. The underlying logic is identical; the notation is different.

This guide walks through the key differences with the same example program written in both dialects so you can see exactly where the gaps are.

The Short Version

The instruction names map one-to-one once you know the pairs — here is the contact, coil and timer naming side by side.

Addressing: The Biggest Difference

Allen-Bradley uses tag-based addressing. Every variable has a programmer-defined name: Start_PB, Motor_Run, Conveyor_Speed. There are no physical memory addresses in the program — the runtime maps tags to memory.

Mitsubishi uses device-based addressing. Inputs are X devices (X0, X1, X2...), outputs are Y devices (Y0, Y1...), internal relays are M devices (M0, M1...), data registers are D devices (D0, D1...). The device number corresponds directly to a physical or virtual memory location.

Practical implication: In Allen-Bradley you can refactor freely because the tag name travels with the logic. In Mitsubishi you need to maintain a separate address map (which GX Works calls a "device comment" file) to avoid re-reading the I/O wiring diagram every time you open a program.

Motor Start/Stop: Side by Side

Here is the classic start/stop motor circuit in both dialects.

Allen-Bradley (Studio 5000)

XIC Start_PB   XIO Stop_PB   XIO Motor_OL   OTE Motor_Contactor
XIC Motor_Contactor

Rung 1 evaluates Start_PB (normally open), Stop_PB (normally closed via XIO), and Motor_OL (overload — normally closed). If all three pass, Motor_Contactor is energised. Rung 2 is the seal-in: Motor_Contactor latches itself.

Mitsubishi (GX Works)

LD   X0   ; Start PB
AND  X2   ; Motor OL (used as normally-closed in wiring, so LD here)
ANI  X1   ; Stop PB (examine if NOT set — ANI = AND Inverse)
OR   Y0   ; Seal-in — Motor_Contactor output
OUT  Y0   ; Motor_Contactor

The logic is identical. The only differences are:

• XIC → LD (load, or AND for second contact in series)
• XIO → ANI (AND inverse — examine if not set)
• OTE → OUT
• Seal-in is an OR Y0 before the OUT rather than a second rung

Timers

Allen-Bradley uses the TON (timer on-delay) function block with a PRE preset and ACC accumulator:

TON
  Timer:    Motor_Start_Delay
  Preset:   T#5S
  Accum:    0

Mitsubishi uses a device-based timer. T0 through T199 are 100ms-resolution timers; T200+ are 10ms-resolution:

LD  X0          ; Input that starts the timer
OUT T0 K50      ; T0 with K50 = 50 × 100ms = 5 seconds
LD  T0          ; Timer contact
OUT Y0          ; Output after timer expires

The Mitsubishi approach ties the timer tightly to a physical device number, which can make large programs harder to track. GX Works 3 (the newer environment for iQ-R) adds symbolic names on top of the device system, bringing it closer to tag-based addressing.

Comparison Operator Syntax

Allen-Bradley uses standard function blocks for comparisons:

EQU  Motor_Speed  100   ; Equal
GRT  Tank_Level   80    ; Greater than
LES  Pressure     200   ; Less than

Mitsubishi uses the CMP (compare) instruction or, in GX Works 3, inline compare contacts:

CMP  D0  K100  M10  ; Compare D0 to 100; result bits M10 (>), M11 (=), M12 (<)
LD   M11            ; If D0 = 100
OUT  Y5

The CMP instruction deposits three result bits into consecutive M devices. This is functional but verbose compared to the AB approach.

Which Should You Learn First?

Learn Allen-Bradley first if:

• You are targeting North American manufacturing (automotive, food & beverage, discrete manufacturing)
• Your employer or target employer runs Rockwell equipment
• You want to learn modern tag-based programming concepts

Learn Mitsubishi first if:

• You are targeting Asia-Pacific manufacturing (electronics, automotive supply chain, food processing)
• You are studying at a Japanese or South-East Asian technical college
• You want to understand device-based addressing, which also applies to Siemens and older Omron systems

Learn both via the simulator: The dialect comparison tool in the simulator lets you write a program once and see it rendered in both Allen-Bradley and Mitsubishi notation side by side. The features/dialects page has a full breakdown of all 8 supported dialects.

The choice often comes down to the surrounding ecosystem — software, PLC families and regional market — as much as the syntax itself.

If you are still unsure which to pick up first, work it backwards from your target region and employer.

Transferring Skills Between Dialects

The core concepts transfer directly:

• A normally-open contact is a normally-open contact in any dialect
• A seal-in rung works identically regardless of syntax
• Timers, counters, and sequencers follow the same logic everywhere

The things that do not transfer automatically are:

• Variable addressing conventions (named tags vs device numbers)
• Timer/counter preset formats (milliseconds vs clock ticks vs preset counts)
• Advanced instructions (motion, networking) which are entirely vendor-specific

If you understand scan cycle execution order, rung evaluation, and output image tables in one dialect, you understand them in all dialects. The PLC scan cycle guide covers this foundation well.

Practice Both in the Simulator

The simulator supports both Allen-Bradley and Mitsubishi dialects. Start a scenario in IEC or Allen-Bradley mode, complete the exercise, then switch to Mitsubishi mode and observe how the same logic is represented. This cross-dialect practice is one of the fastest ways to build transferable skills.

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Try the dialect comparison in the simulator — free. Write a motor start/stop program once and view it in Allen-Bradley, Mitsubishi, Siemens, and 5 more dialects.

Open the dialect comparison tool →