PLC Indicator Light Control: Ladder Logic and 2026 IO-Link Stack Lights
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Allen-Bradley · Siemens · Schneider · IO-Link · 2026 Update
By KOEED Engineering · 2026-06-30 · 9 min read · How-to
Indicator light control is still the most common entry point for new PLC programmers — but the stack lights themselves have changed. In 2026, IO-Link tower lights (Banner K70 Pro, Schneider XVU, Patlite LR6) replace hardwired 24 Vdc tri-stack lamps, and ladder logic is migrating to structured text with tag-based addressing. This How-to rebuilds the classic indicator-light example with a 2026 hardware bill of materials and a Studio 5000 / TIA Portal ladder snippet you can paste into a real project.
AI Summary
- Hardware changed: 24 Vdc tri-stack lamps are giving way to IO-Link tower lights (Banner K70 Pro, Schneider XVU, Patlite LR6) on PROFINET / EtherNet/IP.
- Logic unchanged: The ladder rung pattern — run input + fault latch + one-shot — still works in Studio 5000 v36 and TIA Portal V19.
- Wiring simplified: One M12 cordset replaces five discrete wires; the AOI maps Run / Fault / Ready / Warn / Override to a single process-data byte.
- 2026 picks: Banner K70 Pro IO-Link for AB racks, Schneider XVU for Modicon M580, Patlite LR6 for Mitsubishi MELSEC iQ-R.
Indicator-light control still teaches PLC scan, latch, and one-shot fundamentals, but 2026 hardware moves from hardwired tri-stack lamps to IO-Link tower lights on PROFINET or EtherNet/IP — one cable, one process-data byte, five colors.
Why the classic example still matters
The "three lights on a panel" exercise has been a PLC training staple since the Modicon 084 era, and for good reason — a tower lamp maps neatly onto the three output patterns every maintenance tech needs: machine running, machine faulted, and operator attention. If you can control three lights reliably, you understand scan order, output latch, and the difference between a level and an edge.
What's changed since the 2024 edition of this article is the physical layer. Discrete 24 Vdc tri-stack lamps with five separate homerun wires are being replaced by IO-Link tower lights: a single M12 cordset carrying both 24 V power and a bidirectional process-data channel. The result is fewer wires in the cabinet, diagnostic data coming back from the lamp (LED health, temperature, runtime hours), and a ladder diagram that drives five colors from one byte instead of five coils.
> Tip
If you're still wiring discrete tri-stack lamps through relay outputs on a 1756-OB16E sink module, keep that circuit in your library — it is still the right answer for retrofits and EOL base plates. New builds in 2026 should default to IO-Link.
What changed since 2024
Three shifts are visible on the shop floor this year.
- IO-Link became the default for new tower lights. Banner Engineering rolled out the K70 Pro IO-Link variant in late 2024; Schneider followed with the XVU series in 2025; Patlite refreshed the LR6 with IO-Link master support in firmware 2.4. Today most U.S. and EU panels use IO-Link rather than discrete wiring.
-
Programming moved from coil-level to tag-level. Studio 5000 v36 and TIA Portal V19 both default to tag-based addressing for new projects. The old
B3:0/0rung now readsLight_Run. The ladder pattern is the same; the tag name is more readable. - Diagnostics came back to the PLC. An IO-Link tower light reports LED failure, internal temperature, and total run hours as process data. Maintenance no longer has to walk to the panel to confirm "is the red lamp actually lit?" — the PLC tells the SCADA whether the lamp is healthy.
Hardware — 2026 picks for a five-color stack
| Brand / Series | Model | Colors | Connection | Fits |
|---|---|---|---|---|
| Banner K70 Pro IO-Link | K70PRO-IOLINK | 5 (R / A / G / B / W) | M12 A-code, IO-Link v1.1 | Allen-Bradley racks (POINT I/O or ArmorBlock) |
| Schneider XVU | XVUC9P5 | 5 modular | M12, IO-Link via TM3 IO-Link master | Schneider Modicon M340 / M580 |
| Patlite LR6 IO-Link | LR6-502IL-RYGBC | 5 tier | M12, IO-Link v1.1 | Mitsubishi MELSEC iQ-R |
| Banner TL50 Pro IO-Link (legacy) | TL50P-IL-RYG-V | 3 tier | M12, IO-Link | Compact retrofits |
All four models mount in a standard 30 mm panel hole and draw less than 80 mA on the IO-Link port. The K70 Pro and LR6 both support firmware updates over the same M12 cable — no laptop, no serial dongle.
Step 1 — Wire the IO-Link master
An IO-Link tower light is a device, not a load — you do not wire it to a digital output module. It must sit behind an IO-Link master, which is the gateway between the fieldbus and the lamp's process-data byte.
On an Allen-Bradley POINT I/O bus, an 1734-4IOL master gives you four IO-Link channels per module; on a Schneider Modicon M340, the TM3AIL4V master gives four channels on a TM3 bus slice; on a Mitsubishi iQ-R, the NZ2GIEFT IO-Link master gives four channels on CC-Link IE Field. In every case, the master appears as a regular I/O module to the CPU — no extra programming environment required.
Step 2 — Map the process-data byte
Once the master is on the network, the lamp's process data shows up as one input byte and one output byte. The bit mapping below is consistent across Banner K70 Pro, Schneider XVU, and Patlite LR6:
| Bit | Color | Typical signal |
|---|---|---|
| Bit 0 | Red | Fault / stop |
| Bit 1 | Amber | Warning / attention |
| Bit 2 | Green | Running |
| Bit 3 | Blue | Override / service |
| Bit 4 | White | Manual mode |
| Bit 5 | Buzzer | Audible horn |
| Bit 6–7 | Reserved | Vendor diagnostics |
Step 3 — Ladder logic (Studio 5000 v36)
The ladder below maps five boolean inputs (Machine_Running, Machine_Faulted, Operator_Warn, Override_Active, Manual_Mode) into the single output byte Tower_Light.Out that the IO-Link master writes to the lamp:
// Rung 1 — pack tower light output byte
MOV(Machine_Running, Tower_Light.Out.2); // green
MOV(Machine_Faulted, Tower_Light.Out.0); // red
MOV(Operator_Warn, Tower_Light.Out.1); // amber
MOV(Override_Active, Tower_Light.Out.3); // blue
MOV(Manual_Mode, Tower_Light.Out.4); // white
// Rung 2 — fault latch with acknowledge
XIC(Machine_Faulted) OTE(Light_Red_Latch);
XIC(Machine_Faulted) OTL(Fault_Latch);
XIC(Operator_Ack) OTU(Fault_Latch);
// Rung 3 — one-shot for amber on rising edge
ONS(Warn_Trigger) OTE(Tower_Light.Out.1);
// Rung 4 — diagnostic read-back from lamp
MOV(Tower_Light.In.0, Lamp_Red_Healthy); // lamp reports red LED OK
MOV(Tower_Light.In.1, Lamp_Green_Healthy); // lamp reports green LED OK
! Warning
Never wire an IO-Link tower light to a sinking digital output module (e.g. 1756-OB16E) directly. The lamp expects a process-data byte from an IO-Link master, not 24 Vdc on a single terminal. Doing so will not light the LED and may damage the master port over time.
Step 4 — Siemens and Mitsubishi equivalents
In Siemens TIA Portal V19, the same pattern uses the "AT" view on the IO-Link master device description (IODD). You split the input byte IB100 into Lamp.Running, Lamp.Fault, etc. The ladder rung is identical to the AB example above.
In Mitsubishi GX Works 3, an IO-Link master on CC-Link IE Field appears as a remote I/O station; the process-data byte is bound to a link register (e.g. W100) and the bits are read with SMOV or a dedicated FB. Most system integrators wrap the bit-decode inside an FB so that the same function block runs on every machine, regardless of PLC brand.
Step 5 — Test, troubleshoot, deploy
Run the PLC in simulation mode first. Force each input bit individually and confirm the matching LED lights — both visually and through the lamp's read-back status bit. If a color does not respond, check the IODD version on the master (mismatched IODDs are the single most common cause of an IO-Link lamp not coming up).
Once simulated, deploy to the physical machine. IO-Link commissioning tools (Banner BSI, Siemens PRONETA, Mitsubishi IO-Link Configurator) all let you poll the lamp's diagnostic page over USB or the network — no need to climb a ladder with a flashlight.
Common pitfalls in 2026
Note
Three things we still see on site:
- M12 cordset longer than 20 m — IO-Link spec says 20 m max. Use a repeater, not a longer cable.
- Shared 24 Vdc supply on the lamp's power pin and the IO-Link master's logic — common ground noise trips the master. Use a dedicated PSU.
- Mixing tri-stack and IO-Link on the same panel — looks inconsistent and confuses operators. Pick one technology per cell.
Where to buy the hardware
Banner, Schneider, and Patlite tower lights are stocked by KOEED alongside the PLCs that drive them. We carry active production, last-time-buy, and EOL inventory for Allen-Bradley, Siemens, Schneider, Mitsubishi, and Omron. Send your BOM (lamp model + master + PLC + IO module) and we quote all of it in one email within 24 hours.
Wiring up an IO-Link tower light project?
Send your BOM to Moritta@KOEED.COM. Active stock, EOL stock, and cross-references — all in one quote within 24 hours.
Send My BOM →Related on KOEED Blog
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- KOEED AI Diagnostic Tool — 24/7 fault-helper
Frequently asked questions
Do I need an IO-Link master to use a 2026 tower light?
Yes. IO-Link tower lights are class-A devices and need a master — e.g. 1734-4IOL (AB), TM3AIL4V (Schneider), or NZ2GIEFT (Mitsubishi) — to handle the process-data handshake and IODD file.
Can I reuse my 2024 ladder code with 2026 IO-Link lamps?
Yes. Rung logic is unchanged; only the output address differs. Instead of five discrete bits on a 1756-OB16E, you write one byte to the IO-Link master. KOEED can supply AOI and FB translations.
What is the maximum cable length for an IO-Link tower light?
IO-Link v1.1 allows 20 m unshielded between master and device. For longer runs, add an IO-Link repeater or move the master closer. The 5-pin M12 A-coded cordset is the industry standard.
Is the Banner K70 Pro IO-Link still in production in 2026?
Yes. The K70 Pro IO-Link (late 2024) is in active production in 2026. Banner typically keeps each K70 generation available 8–10 years. KOEED stocks both K70 Pro and TL50 Pro IO-Link.
Where can I get the IODD file for a Patlite LR6?
Patlite publishes IODD files on its IODD Finder portal. The same file works in Banner BSI, Siemens PRONETA, Mitsubishi IO-Link Configurator, and any FDT/DTM tool. KOEED can ship it on USB if needed.
KOEED Engineering
Industrial automation editor at KOEED. Writes about PLC sourcing, cross-reference, and legacy system support. Reach the team at Moritta@KOEED.COM.