Mitsubishi GX Works3 function blocks: building reusable

For Mitsubishi Electric GX Works3 V1.080+.

GX Works3 supports IEC 61131-3 function blocks for the iQ-R and iQ-F lines. The FB workflow, scope rules, and how it differs from GX Works2. This page is the working engineer's read — what the menu paths actually are in GX Works3 V1.080+, what the keystrokes do, and the mistakes that bite once the program is on a real CPU. We program iQ-R / iQ-F ourselves, daily; we are not a Mitsubishi Electric sales channel.

What this is and when you need it

GX Works3 supports IEC 61131-3 function blocks for the iQ-R and iQ-F lines. The FB workflow, scope rules, and how it differs from GX Works2. The walkthrough below is the same sequence we use when teaching this on the simulator. Every step names the exact menu path or keystroke; if a name has changed in your version of GX Works3 V1.080+, it is called out. The simulator runs the same logic flow without the licence cost — ladder, FBD, and ST in a browser, with a virtual CPU you can download to.

Walkthrough

1. Create the FB POU

In the Navigator pane, right-click POU > Add New Data > Function Block. Name it MotorStart_FB. Choose language: Ladder, ST (Structured Text), FBD, or SFC. Click OK. The FB editor opens with three panes: header (interface declaration), body (ladder/ST), and label list (instance variables). GX Works3 enforces the IEC 61131-3 split — a clear improvement over GX Works2's looser FB model.

2. Declare the interface

In the header pane, declare VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR (instance-scoped, persists between calls), VAR_TEMP (scratch). VAR_INPUT pins are read-only inside the FB. VAR_IN_OUT pins are pass-by-reference and can be mutated. VAR is the equivalent of Siemens FB Static or AB AOI Local — persistent state per instance.

// MotorStart_FB interface
// VAR_INPUT:  StartPB BOOL, StopPB BOOL, OL_Trip BOOL
// VAR_OUTPUT: RunCmd BOOL, Fault BOOL
// VAR_IN_OUT: MotorRef Motor_UDT
// VAR:        SealLatch BOOL

3. Write the body

Switch to the body pane. In ladder, drop XIC, XIO, OTE elements and reference labels by name (StartPB, SealLatch, RunCmd) without prefixes. In ST, write the equivalent code. The label list pane on the right shows every declared label and its scope. Save with Ctrl+S; GX Works3 validates the FB body against the interface and flags type mismatches inline.

4. Call the FB from a program

Open MainProgram. Drag the FB from the POU list onto a rung. GX Works3 prompts for an instance name — Motor1_FB, Motor2_FB. Each instance gets its own private VAR memory. Wire the input pins (StartPB to %IX0.0 or symbolic StartPB1), output pins (RunCmd to %QX0.0), and in-out pins (MotorRef to global Motor1 of type Motor_UDT). Compile (F4).

5. Watch the cross-reference

Tools > Cross Reference. The output shows every place an FB is called and every instance it owns. Double-click a call site to jump to the rung. If two call sites share the same instance name, GX Works3 flags it at compile time as a duplicate — unlike older GX Works2 which would silently overwrite. Use Tools > Verify Project for a deeper consistency check before download.

Common mistakes

• Putting persistent state in VAR_TEMP thinking it survives scans — VAR_TEMP is scratch and the value is undefined at the start of each call
• Reusing the same FB instance name across two call sites — GX Works3 flags this but a hand-edited project file can slip past and cause memory clobbering
• Declaring an FB in GX Works2 then trying to open in GX Works3 expecting clean conversion — the FB model is different and the conversion needs manual fixup of VAR_IN_OUT pins
• Forgetting that GX Works3 ladder uses %IX0.0 / %QX0.0 IEC addressing, not the X0 / Y0 of GX Works2 — the muscle memory bites every veteran on day one

Each of these mistakes shows up in real projects every week. The simulator catches the first three at compile time; the fourth one only surfaces on hardware, which is why we recommend running the cert packs against a real CPU once you have completed the curriculum modules.

How this fits the broader curriculum

Mitsubishi GX Works3 function blocks: building reusable logic is one of the building blocks. The full Mitsubishi Electric curriculum on the simulator covers: programming-language fundamentals (ladder, FBD, ST), tag and variable scope, HMI tag binding, comms setup (Profinet / EtherNet/IP / Modbus depending on the platform), and the brownfield troubleshooting pathway. Each is its own module with worked examples and a portfolio piece. The cert packs at the Pro tier align to the ISA CCST exam content outline. Reference: isa.org.

For the platform-pick decision — when Mitsubishi Electric is the right call versus a different brand — see the brand hub. For region-specific context on where Mitsubishi Electric dominates the SA install base, see the relevant city pages under /brands/mitsubishi/training-in-* and the sector pages under /industries.

Where this sits in a working week

A technician who has finished this module typically spends the next three to four working days running the same logic flow on hardware. The simulator's value is the dry run — getting the keystrokes and the IDE conventions into muscle memory before you sit down with a live CPU. The first time you build this on hardware, expect the IO mapping and the addressing conventions to slow you down for a session or two; the simulator's project tree mirrors the same shape so the transition is short.

The full Mitsubishi Electric curriculum runs roughly 60 to 100 hours of focused practice. That breaks into bit logic and timers in the first 20 hours, FBs and structured data in the next 20, comms and HMI in the next 20, and a portfolio piece in the last block. Pace yourself — three or four hours per session, four sessions a week, and you finish in eight weeks. Most of our learners report that the bottleneck is not understanding the IDE, it is building reflex around the conventions: where Mitsubishi Electric expects you to put state, how it scopes variables, what naming patterns the OEMs in the sector use.

Vendor reference

Mitsubishi Electric's own documentation is the canonical reference once you are working on real hardware: Mitsubishi Electric Factory Automation Support. The simulator covers the basics; the vendor docs cover everything specific to a hardware revision, a firmware update, or a CPU-specific quirk. Bookmark both. The IEC 61131-3 standard that governs all the Mitsubishi Electric programming languages is at iec.ch.

What we don't claim

This site is not SAQA-registered, not MerSETA-accredited, and not an NQF-registered qualification provider. Our completion certificates are course-level only — they describe what you covered, not an NQF Level X qualification. The CCST cert from ISA is the portable industry credential we recommend; we are not an ISA cert delivery partner either, but our cert packs are CCST-aligned. The walkthrough above is brand-specific because Mitsubishi Electric's tooling has its own conventions; do not assume the same menu paths exist in another brand's IDE.

How to start

You can be running mitsubishi gx works3 function blocks: building reusable logic in the simulator in 5 minutes. Free tier covers the basics, no card, no install. Once you are 20 minutes in you will know whether the platform fits how you learn. The full Mitsubishi Electric curriculum is the Basic tier (USD 12 / month). The cert packs and portfolio export sit in the Pro tier (USD 29 / month). For institutional buyers — TVET colleges, private training providers, in-house engineering training departments — the bulk-licence option is the Teams tier, USD 199 per seat per year, minimum 5 seats. The training-centres page has the institutional pitch and the contact form.

Honest expectations on the local job market

Petrochem, mining, FMCG, automotive, and water-utility sectors all carry Mitsubishi Electric install bases somewhere in their stack. Knowing the IDE conventions on this page does not get you a job by itself; it gets you past the first technical screen. The portfolio piece — a working program you built yourself, with a wiring track, a tag list, an HMI screen, and a short README explaining the design choices — is what lands the second interview. The simulator's portfolio export bundles all of that into a single folder you can hand a hiring engineer. Recruiters in this space skim the README first; if your design choices are coherent, they read the code.

Load-shedding has reshaped what gets built first in Mitsubishi Electric programs across SA. Power-recovery patterns — controlled shutdown on UPS hold, state recovery from retentive memory, sequenced restart of motor groups — now belong in the same module as the basics. Mitsubishi GX Works3 function blocks: building reusable logic fits into that shape: every line of code you write needs to consider what state the controller is in when it powers up after a 2.5-hour cut, not just what state it is in when running. The simulator's restart-from-cut mode lets you exercise this without bricking real hardware.