Mitsubishi FX5U vs FX3U: iQ-F vs MELSEC-F Series Comparison

By Abdullah Zahid
20 min read
Mitsubishi FX5U MELSEC iQ-F and FX3U MELSEC-F compact PLCs side by side for generation comparison

Mitsubishi FX5U vs FX3U PLC: MELSEC iQ-F vs MELSEC-F Comparison Guide

Controls engineers specifying a compact Mitsubishi PLC for a new machine or upgrade project consistently face the same fork in the road: commit to the MELSEC iQ-F FX5U with its built-in Ethernet, RS-485, and ~34 ns instruction speed, or stay with the proven MELSEC-F FX3U at ~65 ns that already lives in most of your panels. The decision hinges on three things — what your application actually needs today, what it will need in three to five years, and how much migration effort your project can absorb right now. This guide gives you a concrete, scenario-based answer backed by verified specs from both platforms.

Already know which platform you need? Check current pricing and availability for Mitsubishi FX5U and FX3U models at LeadTime.ca — we source and ship worldwide.

FX5U or FX3U — Which Compact PLC Fits Your Project?

The MELSEC iQ-F FX5U is the right choice for most engineers specifying a new machine or planning a substantial upgrade. Choose it when your project meets any of the following criteria:

  • You need built-in Ethernet connectivity for SCADA, HMI, or IIoT integration without adding modules
  • Your machine requires RS-485 Modbus RTU communication to drives, meters, or sensors
  • You need multi-axis pulse outputs — FX5U base units commonly support up to 4 axes at 200 kHz (model-dependent)
  • You want built-in analog I/O (many FX5U CPUs include 2 AI + 1 AO at 12-bit resolution) without a separate analog module
  • Program size is growing beyond ~64K steps or you anticipate logic complexity increasing over the machine lifecycle
  • Data logging, recipe management, or remote diagnostics via SD card are required or likely

The MELSEC-F FX3U remains the correct choice when you are maintaining or lightly expanding an existing FX3U-based system, when the machine is simple discrete I/O with no networking requirement, or when project risk and timeline demand drop-in continuity with minimum change to panels, wiring, and engineering tools. If your team cannot absorb GX Works3 training and project conversion on this build, FX3U has a legitimate role — but plan your migration path now.

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Two Generations, One Ecosystem: Understanding the FX Platform Lineage

The MELSEC-F FX3U compact PLC has been the backbone of Mitsubishi Electric's small controller offering for over a decade. It built its reputation on reliability, a mature expansion module ecosystem, and straightforward ladder programming under GX Works2. Tens of thousands of machines worldwide run on FX3U hardware, and maintenance teams at those facilities know the platform inside out. That installed base is exactly why FX3U remains relevant today, even as it transitions toward legacy status in some regions.

The MELSEC iQ-F FX5U is the direct successor, introduced as Mitsubishi Electric's current-generation compact PLC platform. It was designed to carry the FX family's simplicity and compact form factor forward while addressing the performance and connectivity limits that modern machine requirements expose in FX3U. The key architectural changes are not cosmetic — the FX5U runs a high-speed system bus documented as roughly 150 times faster than the MELSEC-F bus, processes a basic LD instruction in approximately 34 ns versus approximately 65 ns on FX3U, and ships with Ethernet, RS-485, and on many models analog I/O built into the CPU itself. These are not incremental improvements; they change the hardware bill of materials and system architecture for every new machine.

Engineers working in Mitsubishi-standardized facilities today face a practical two-platform reality: FX3U for installed base continuity and FX5U for new work. Understanding exactly where the line falls for your specific project is what this guide is designed to help you draw.

Where These PLCs Sit in a Typical Control System

Both the FX5U and FX3U occupy the compact CPU position in a machine-level control architecture — sitting between the operator interface or SCADA layer above and the physical I/O, drives, and sensors below. The key difference is how much of the surrounding hardware each PLC requires to fulfill that role.

  • Engineering workstation running GX Works3 (FX5U) or GX Works2/GX Developer (FX3U) connects via USB or Ethernet for programming and diagnostics
  • HMI or SCADA connects via built-in Ethernet on FX5U, or via a separate Ethernet adapter module on FX3U
  • FX5U or FX3U CPU handles program execution, I/O scanning, and communication management
  • Right-side expansion modules extend digital and analog I/O; FX5U supports up to 16 intelligent modules (model-dependent), FX3U typically up to 8
  • Field devices — drives, servo amplifiers, sensors, meters — connect via RS-485 Modbus RTU (built-in on FX5U, module-based on FX3U) or via fieldbus modules such as CC-Link on both platforms

Typical Applications and Which PLC Fits Each

Packaging machines with multi-axis indexing, high-speed registration, and Ethernet connectivity to line supervisors represent the clearest case for FX5U. The built-in 4-axis pulse output capability at up to 200 kHz (model-dependent) and native Ethernet reduce both hardware complexity and commissioning time compared to building equivalent functionality on FX3U with add-on modules.

Assembly stations and test fixtures that require Modbus RTU communication to torque controllers, measurement instruments, or servo drives benefit from FX5U's built-in RS-485 port. On FX3U, adding RS-485 Modbus requires a dedicated communication module, additional wiring, and panel space that a compact fixture often cannot spare.

Conveyors, material handling equipment, and simple gate and door control applications with straightforward discrete I/O and no networking requirement remain a genuine home for FX3U, particularly where an existing FX3U panel needs an I/O count increase or a failed CPU replacement. The engineering effort to migrate to FX5U in this context yields no measurable benefit.

Food and beverage process skids requiring analog inputs for temperature, flow, or pressure measurement, combined with data logging for traceability, are strong FX5U candidates. Many FX5U CPUs include 2 analog inputs and 1 analog output at 12-bit resolution and an SD card slot for logging — functionality that on FX3U requires two separate add-on modules.

Electronics assembly and automotive component manufacturing applications targeting IIoT integration, MES connectivity, or remote diagnostics should standardize on FX5U. The built-in Ethernet port and GX Works3's modern diagnostic tools provide the foundation that FX3U requires additional hardware to approximate.

Application Typical Deployment
New machine with Ethernet HMI and SCADA FX5U — built-in Ethernet eliminates adapter module
Simple discrete conveyor or gate control FX3U — drop-in simplicity, no networking needed
Multi-axis packaging or positioning machine FX5U — up to 4 axes at 200 kHz built-in (model-dependent)
Process skid with analog and data logging FX5U — built-in 2 AI + 1 AO and SD card on many CPUs
Incremental expansion of existing FX3U cabinet FX3U — maintains wiring, modules and GX Works2 workflows
Plant-wide standardization for future machines FX5U — current iQ-F platform, aligned with Mitsubishi roadmap

FX5U vs FX3U Core Specification Comparison

Specification FX3U (MELSEC-F) FX5U (MELSEC iQ-F)
Typical program memory ~64K steps RAM ~128K steps RAM (model-dependent)
Basic instruction speed (LD) ~65 ns ~34 ns
System bus Standard MELSEC-F bus High-speed system bus (~150x faster)
Max I/O points (local + remote) Up to ~384 points Up to ~512 points (CPU and network dependent)
Built-in analog I/O None — requires analog add-on modules 2 AI + 1 AO (12-bit) on many CPUs (model-dependent)
Built-in Ethernet Not built-in — via modules or adapters Built-in Ethernet port
Built-in serial port RS-422 round connector RS-485 terminal block (Modbus-capable)
Intelligent modules supported Up to 8 modules (typical) Up to 16 intelligent modules (model-dependent)
SD card / data logging Via optional add-on modules SD card slot on many FX5U CPUs
Programming software GX Developer / GX Works2 GX Works3 only

Full technical specifications are available on the product page at LeadTime.ca.

Aspect FX3U FX5U
HMI/SCADA connectivity Via serial and optional Ethernet modules Native Ethernet + RS-485; reduced hardware
Fieldbus options CC-Link via dedicated modules CC-Link and other networks via modules with faster system bus
Data logging Via optional modules SD card slot on many FX5U CPUs
Programming tools GX Developer / GX Works2 — ladder-focused legacy environment GX Works3 — function blocks, templates, modern diagnostics
Project migration Not portable to GX Works3 without conversion Can import/convert FX3U projects in GX Works3 with adjustments
Panel space impact Larger — more add-on modules required More compact — fewer modules due to built-in features
Legacy replacement suitability Strong drop-in continuity for FX3U systems Requires migration — better for long-term roadmap

If the FX5U's built-in feature set aligns with your system requirements, check current availability and confirm catalog numbers at LeadTime.ca — we ship worldwide and can confirm lead times before you commit to a build schedule.

Built-In Ethernet vs Module-Based: The Communication Divide

This is the specification difference that most directly drives engineers toward the FX5U for new projects. The MELSEC iQ-F FX5U ships with a built-in Ethernet port — no adapter, no additional module, no extra wiring run to a communication card. For a machine that needs to talk to a SCADA system, push data to an MES, or allow remote monitoring via a gateway device, that single fact changes the hardware design from the first revision. The FX3U requires a separate Ethernet module or adapter to achieve the same connectivity, which means additional cost, panel real estate, and a wiring connection that becomes a potential failure point.

The RS-485 situation is similar. The FX5U provides a built-in RS-485 terminal block with Modbus RTU capability, allowing direct connection to variable frequency drives, flow meters, temperature controllers, and other serial field devices. On FX3U, RS-485 Modbus requires a dedicated communication module — and if you also need Ethernet, that is two add-on modules where FX5U uses zero. For compact machine panels where every 35 mm of DIN rail counts, this difference is not abstract.

For CC-Link fieldbus architectures, both platforms support the protocol through dedicated modules. The practical advantage with FX5U is that the high-speed system bus — cited at roughly 150 times faster than the MELSEC-F bus — means the CPU processes data from intelligent modules and fieldbus cards with substantially lower latency, which matters in tight scan-time applications. Engineers building IIoT-connected machines or those planning to add cloud gateway devices should treat the FX5U's native Ethernet as a baseline requirement rather than a feature — it is the on-ramp for every future connectivity option.

Motion Control and High-Speed I/O: Where FX5U Pulls Away

For positioning and motion applications, the generational gap between FX5U and FX3U is most visible. FX5U base units commonly support up to 4 axes of pulse output at up to 200 kHz, model-dependent. FX3U CPUs typically support up to 3 axes, at lower pulse frequencies, with higher-end motion requiring external motion modules. For a machine upgrading from 2-axis to 4-axis motion, or pushing cycle times that require faster pulse rates, the FX5U can often handle the requirement from the base CPU — the same capability would require additional hardware investment on FX3U.

The approximately 34 ns basic instruction execution time on FX5U versus approximately 65 ns on FX3U also matters in motion applications beyond raw axis count. Faster instruction execution means tighter scan times, which translates to more responsive position loops, faster error detection, and more predictable behavior during high-speed coordinated moves. Combined with the high-speed system bus, the FX5U's architecture is substantially better suited to applications where the PLC is managing multiple axes while simultaneously handling communications and analog sampling.

FX3U remains adequate for simple single-axis or two-axis indexing applications where speed requirements are modest and existing motion modules are already installed in the panel. If the upgrade trigger is specifically motion performance — more axes, faster pulse rates, improved coordination — FX5U is the correct platform and the case for migration becomes straightforward to justify.

Analog I/O and Data Logging: Built-In vs Add-On

Many FX5U CPUs include 2 analog inputs and 1 analog output at 12-bit resolution as part of the base unit — no separate analog module required. For a machine with a handful of analog signals — a temperature sensor, a pressure transducer, a speed reference output — this means the hardware design is simpler, the panel is smaller, and the wiring BOM is shorter. On FX3U, each analog function requires a dedicated expansion module, which occupies one of the eight available intelligent module slots, adds terminal blocks, and requires separate configuration in GX Works2.

The FX5U also provides an SD card slot on many CPU models, enabling on-board data logging for quality traceability, recipe storage, and firmware updates without additional hardware. This is a feature that food and beverage, pharmaceutical, and electronics assembly applications increasingly require for regulatory or process quality purposes. On FX3U, achieving equivalent data logging capability requires a dedicated data logging module — again, consuming an expansion slot and adding cost.

The total hardware BOM impact is significant for projects that need both analog and data logging. An FX5U CPU can replace what would be an FX3U CPU plus an analog module plus a data logging module, with fewer terminals, fewer power connections, and a smaller enclosure. Engineers doing panel space calculations on compact machine builds should run this comparison explicitly before selecting FX3U based on familiarity alone.

GX Works2 vs GX Works3: What the Software Change Actually Means

The MELSEC-F FX3U is programmed in GX Works2 or the older GX Developer — both ladder-focused environments that most Mitsubishi-experienced engineers know well. If your maintenance team has been modifying and troubleshooting FX3U programs for years, GX Works2 is already part of your workflow. That familiarity has real value during commissioning, fault finding, and minor machine modifications in the field.

The MELSEC iQ-F FX5U requires GX Works3 exclusively. GX Works3 is a more capable environment — it supports structured text, function blocks, modern library management, improved motion configuration, and significantly better built-in diagnostics compared to GX Works2. Engineers who invest the time to learn it consistently report improved development productivity and easier troubleshooting once they clear the initial learning curve. The trade-off is that the learning curve is real: new device structures, different project organization, and revised diagnostic workflows require deliberate training time before a team is productive.

Project migration from GX Works2 to GX Works3 is possible — GX Works3 includes an import and conversion function for FX3U projects. However, conversion is not automatic in the sense that the result is immediately production-ready. Instruction differences, device type changes, and structural adjustments mean that every migrated project requires review, testing, and validation before it can be considered equivalent to the original. Engineering teams planning a migration should budget time for this process, run a pilot conversion on a representative machine, and ensure at least one engineer per facility is properly trained on GX Works3 before the migration program begins.

Migrating from FX3U to FX5U: Module Reuse, Project Conversion, and Panel Impact

One of the most common questions engineers ask when evaluating an FX3U to FX5U upgrade is whether existing FX3-series I/O modules can be reused on the new platform. The answer is: some can, with the FX5-CNV-BUS adapter module, which allows certain FX3-series expansion I/O units to connect to an FX5U CPU. However, compatibility is not universal — each module must be checked against Mitsubishi's official compatibility documentation. Assuming that all existing FX3U hardware transfers directly to an FX5U system is the most common and most expensive mistake in FX series migrations.

Key points to assess before committing to a migration:

  • Verify each FX3-series module against the FX5-CNV-BUS compatibility list in Mitsubishi's official documentation before assuming reuse is possible
  • The RS-422 round connector on FX3U becomes RS-485 terminal block on FX5U — existing HMI cables may require adapters or replacement
  • Terminal block layouts and wiring points differ between generations; allow time for wiring verification and labeling updates
  • Project conversion in GX Works3 requires review of every instruction and device reference — plan for a structured validation process, not a simple import
  • Panel grounding practices and power supply wiring should be verified against FX5U hardware manual requirements, as specifications may differ from FX3U installations

When a direct FX3U drop-in replacement is genuinely the right answer — failed CPU in a running production line, minimal I/O changes, no new connectivity requirements — there is no compelling reason to trigger a full FX5U migration in that moment. The case for switching to FX5U becomes clear when the scope of the change already justifies panel rework, new communication requirements are being added, or the machine's performance ceiling is being approached.

Expert Verdict: When to Choose FX5U and When FX3U Still Makes Sense

The MELSEC iQ-F FX5U is the right platform for the majority of new machine designs and substantial upgrades today. Its approximately 34 ns instruction speed, high-speed system bus, built-in Ethernet, RS-485, and analog I/O, plus SD card data logging on many models, eliminate the module layers that make FX3U-based designs more complex and less maintainable over time. The engineers who benefit most from FX5U are those building machines that will need network connectivity, analog measurement, motion beyond 3 axes, or any form of data-driven diagnostics — which, increasingly, describes most new machines. If GX Works3 is new to your team, treat training as a project task with real hours allocated, not an afterthought.

The MELSEC-F FX3U still has a well-defined and legitimate role. For maintenance engineers keeping installed MELSEC-F systems running, engineers doing small I/O expansions in panels already wired for FX3U modules, or OEM projects where the machine is genuinely simple, the network-free, the analog-free, and the team's GX Works2 skills are an asset rather than a liability — FX3U is the lower-risk, faster-to-execute choice. The wrong reason to choose it is inertia. If you know the machine will need Ethernet or analog in the next product revision, design it on FX5U now rather than paying the migration cost twice.

From a procurement and lifecycle standpoint, FX5U is Mitsubishi Electric's current small PLC platform and the one receiving active development, new module support, and long-term software investment through GX Works3. FX3U remains available and stocked through distribution, but its legacy trajectory is established. Engineers planning five to ten year machine lifecycles should base new designs on FX5U with confidence. For current pricing, catalog number confirmation, and lead time verification on both platforms before you lock in a BOM, check availability at LeadTime.ca — we ship worldwide and can confirm stock before you commit to a build schedule.

For volume pricing, project BOM reviews, or help confirming the right catalog numbers for your migration, contact the LeadTime.ca team directly.

What Engineers Are Saying About FX3U and FX5U

Across automation forums including Reddit's r/PLC and r/industrialautomation, as well as PLCTalk and Mitsubishi-focused community discussions, the consensus view on FX3U is consistent: it is a platform engineers trust because they know it. Maintenance teams at facilities running FX3U-standardized lines value the fact that spare CPUs are readily available, that documentation is thorough and well-understood, and that any controls technician with Mitsubishi experience can work on the program without retraining. The recurring complaint is equally consistent — getting Ethernet and analog onto FX3U requires extra modules, extra wiring, and extra panel space, and for modern machine designs that baseline expectation feels like an unnecessary tax on project cost and panel real estate.

Feedback on FX5U in the same communities is broadly positive once engineers have cleared the GX Works3 learning curve. The performance improvement, the built-in connectivity, and the reduced module count are cited as genuine engineering quality-of-life improvements. The complaints are specific: GX Works3 has a steeper onboarding curve than GX Works2, the project structure is different enough that engineers familiar only with older Mitsubishi tools take time to become productive, and migrating large FX3U projects into GX Works3 requires more hands-on testing than engineers sometimes budget for. These are transition costs, not permanent limitations — but they are real costs that should appear in project estimates.

The most consistent theme in migration discussions is that engineers who have completed the switch to FX5U generally do not go back. Improved diagnostic visibility, faster troubleshooting through GX Works3's modern tools, and the ability to connect machines to higher-level systems without hardware additions are outcomes that teams report as making the migration effort worthwhile. The common practical advice from the community: standardize on FX5U for all new builds now, keep FX3U expertise alive in the maintenance team for the installed base, and plan GX Works3 training as a near-term investment rather than a future-state item.

The Most Costly Selection Mistakes — and How to Avoid Them

Four selection errors appear repeatedly in FX3U and FX5U project decisions. Each one is preventable with a focused pre-specification review.

The first and most common mistake is specifying FX3U for a new machine that the project team already knows will need Ethernet connectivity and data logging — just not in revision one. The initial I/O count looks fine on FX3U, the team knows the platform, and the add-on modules for connectivity feel manageable. By revision two or three, the panel is full of modules, the next Ethernet card has no slot, and the machine needs to be redesigned anyway. If SCADA, IIoT, or data logging appear anywhere in the machine's five-year requirement list, FX5U is the correct starting point.

The second mistake is assuming that all FX3-series modules from an existing panel will transfer directly to an FX5U. The FX5-CNV-BUS adapter enables reuse of certain FX3-series I/O modules, but compatibility is module-specific and must be verified against Mitsubishi's official documentation for each catalog number. Engineers who skip this step commit to a wiring and hardware plan that may need to be rebuilt from scratch when incompatibilities surface during commissioning.

The third mistake is underestimating GX Works3 conversion effort for complex FX3U projects. GX Works3 includes an import function, but instruction differences, device structure changes, and diagnostic reconfigurations mean that migrated projects require thorough review and testing. Teams that treat conversion as a quick export-import step typically discover issues during commissioning rather than during controlled testing, which is a significantly more expensive place to find them.

The fourth mistake goes in the other direction: over-specifying FX5U for a machine that is genuinely simple — a few digital inputs, a few outputs, no networking, no analog, no motion beyond a single pulse output. For that application profile, FX5U's added capability delivers no measurable value, and if the FX3U hardware is already in the warehouse, the total cost comparison may favor staying with the legacy platform. Feature richness has value only when the application actually uses the features.

Wrong-Part Prevention Checklist Before You Order

Work through each item before finalizing your PLC selection to avoid the most common and costly specification errors on FX3U and FX5U projects:

  1. Confirm required communication (Ethernet, Modbus, CC-Link, RS-485) and ensure chosen PLC supports these natively or via modules.
  2. Check program size and logic complexity; if approaching FX3U limits, favor FX5U's larger memory.
  3. Verify motion and high-speed I/O needs (axes, pulse frequency, counters) against each PLC's specific model capabilities.
  4. Assess ability and budget to convert projects and train staff on GX Works3 (for FX5U).
  5. Confirm compatibility or reuse strategy for FX3-series I/O modules and extension units if upgrading to FX5U.
  6. Review lifecycle status: FX3U is legacy in some regions, FX5U is the current small PLC platform.
  7. Consider future modifications (data logging, remote diagnostics, IIoT); avoid FX3U if these will be mandatory later.

If you have worked through this checklist and are ready to confirm catalog numbers and check availability, view current FX5U and FX3U stock at LeadTime.ca — or contact us directly if your project requires cross-referencing multiple catalog numbers before committing to a BOM.

Frequently Asked Questions

Can FX3U programs be converted and run directly on FX5U?

GX Works3 includes an import and conversion function for FX3U projects developed in GX Works2. The conversion is not automatic in a production-ready sense — instruction differences, device type changes, and structural adjustments require review and testing of every converted project. Plan for a structured validation process; do not treat the import function as a one-click migration. Running a pilot conversion on a representative machine before committing to a full program migration is the recommended approach.

Can FX3U I/O modules be reused on an FX5U system?

Some FX3-series expansion I/O modules can be reused on FX5U using the FX5-CNV-BUS adapter module. Compatibility is module-specific and must be verified against Mitsubishi Electric's official compatibility documentation for each catalog number. Do not assume all FX3-series hardware transfers without checking — this is the most common hardware planning mistake in FX platform migrations.

Does FX5U fully replace FX3U for all applications?

For new machine designs and substantial upgrades, FX5U is the recommended platform in virtually all cases. However, FX3U remains the practical choice for maintaining or lightly expanding existing FX3U-based systems, where drop-in compatibility, existing module inventory, and GX Works2 maintenance workflows outweigh the benefit of migrating to a new platform. FX5U does not replace FX3U in every scenario — it replaces it for new work.

Which programming software do I need for each platform?

The MELSEC-F FX3U is programmed using GX Works2 or the older GX Developer. The MELSEC iQ-F FX5U requires GX Works3 exclusively — GX Works2 cannot program FX5U CPUs. If your team is currently using GX Works2, adopting FX5U requires a software change, a learning investment, and a separate license. Budget both the training time and the software procurement as real project costs.

How many axes of motion can each PLC support without an external motion module?

FX3U CPUs typically support up to 3 axes of pulse output at the base CPU level on supported models. FX5U base units commonly support up to 4 axes at up to 200 kHz pulse output, model-dependent. Both platforms can extend motion capability through dedicated motion modules, including SSCNET-based options for integration with Mitsubishi servo drives. Verify your specific CPU variant's axis and frequency specifications against the relevant hardware manual before finalizing your motion architecture.

Is FX3U still supported and available through distribution?

The MELSEC-F FX3U remains available through industrial automation distribution channels and is commonly stocked as a spare and replacement part for existing installations. Its lifecycle status varies by region — in some markets it is formally classified as legacy. Availability and lead times for specific FX3U catalog numbers should be confirmed with a distributor before including them in a new project BOM. For current stock status, check with LeadTime.ca or contact us for a lead time confirmation.

Why Order Through LeadTime.ca

  • LeadTime.ca sources and ships Mitsubishi Electric FX5U and FX3U PLCs, expansion modules, and accessories worldwide — not limited to any single region or market
  • We can confirm current stock levels and lead times for specific FX5U and FX3U catalog numbers before you finalize your BOM — reducing project schedule risk
  • Our team supports cross-referencing between FX3U and FX5U catalog numbers for engineers working through migration or upgrade projects
  • Volume pricing is available — contact us directly for project-level quotes on multi-unit builds or standardization programs
  • Hard-to-find and longer lead time Mitsubishi modules are a sourcing specialty — if it is in the catalog, we can help you find it

At-a-Glance Summary

  • FX5U processes a basic LD instruction in approximately 34 ns; FX3U takes approximately 65 ns — roughly double the instruction speed on FX5U
  • FX5U system bus is documented as approximately 150 times faster than the MELSEC-F bus used on FX3U
  • FX5U typical program memory is approximately 128K steps; FX3U is approximately 64K steps (model-dependent for both)
  • FX5U includes built-in Ethernet and RS-485 Modbus RTU; FX3U requires separate modules for both functions
  • Many FX5U CPUs include 2 analog inputs and 1 analog output at 12-bit resolution; FX3U has no built-in analog
  • FX5U supports up to 4 axes at up to 200 kHz pulse output on base units (model-dependent); FX3U typically up to 3 axes at lower frequencies
  • FX5U supports up to 16 intelligent expansion modules (model-dependent); FX3U typically up to 8
  • FX5U is programmed exclusively in GX Works3; FX3U uses GX Works2 or GX Developer
  • FX3-series module reuse on FX5U is possible for some modules via the FX5-CNV-BUS adapter — verify each catalog number against official compatibility documentation
  • FX5U is Mitsubishi Electric's current compact PLC platform; FX3U is legacy in some regions but remains available and widely installed
  • Use FX5U for new designs requiring networking, analog, motion performance, or IIoT capability; use FX3U for continuity in existing MELSEC-F installations where migration is not justified

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