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PIKO brand logo ESU brand logo ZIMO brand logo Uhlenbrock brand logo Lenz Elektronik brand logo Märklin brand logo PluX22 Decoders Adapters & Accessories
PIKO SmartDecoder XP 5.1 with a PluX22 interface
Understand NEM 658, the pin assignment and function outputs

PluX22 Interface Explained: Choose the Right Decoder

PluX22 connects the motor, track pickups, lighting, loudspeaker, energy storage and numerous auxiliary functions through a compact plug-in connection. This guide explains how to identify PluX22 and choose a suitable locomotive, function or sound decoder.

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Feature-rich vehicle interface according to NEM 658

What Does PluX22 Mean?

PluX22 belongs to the PluX family defined by NEM 658. The vehicle circuit board carries a two-row female header. The decoder has the matching pins on its underside and is plugged directly into the vehicle circuit board.

The name describes 22 mechanical positions. Position 11 is blocked as the index and has no electrical contact. This leaves 21 electrical connections. The keying prevents the decoder from being inserted after being rotated or shifted sideways.

PluX22 carries both track connections, both motor connections, front and rear lighting, up to seven additional amplified outputs, logic-level or train-bus connections, loudspeaker connections and power-supply contacts for energy storage.

The interface does not determine the digital protocol. A PluX22 decoder may support DCC, Motorola, Selectrix or mfx-compatible registration. The protocol, motor current, dimensions and range of functions must therefore be checked separately.

Check the socket, pins and installation orientation

How Do I Identify a PluX22 Interface?

Vehicle Side

Two-Row Female Header

The locomotive circuit board has two parallel rows with eleven positions in each row.

Check

Position 11 must be blocked or manufactured without a hole.

Decoder Side

Pins Located Under the Decoder

The pin header projects from the underside of the decoder board into the vehicle socket.

Check

Do not confuse it with 21MTC.

Packaging

Look for the PluX22 Designation

Vehicles and decoders should be identified clearly as PluX22 on the packaging or in the instructions.

Check

Compare the production series and article number.

Blanking Plug

Analogue Operation Before Conversion

Analogue vehicles often have a blanking plug that connects the motor and lighting.

Check

Remove the blanking plug straight and with the power off.

Installation Space

Measure the Entire Decoder Area

Circuit-board components, body supports and wires may reduce the usable space.

Check

Measure the length, width and height separately.

Locomotive Circuit Board

Document the Output Assignment

Not every vehicle uses all PluX22 contacts for lighting, couplings or special functions.

Check

Consult the circuit diagram and function description.

PluX22 and 21MTC are not interchangeable: With PluX22, the decoder carries the pins. With 21MTC, the pins are normally located on the vehicle circuit board. The electrical assignments are also different.
Motor, lighting, sound and nine possible function outputs

Pin Assignment of the PluX22 Interface

Why Are the Pin and Contact Missing at Position 11?

Position 11 forms the mechanical key. The pin is omitted on the decoder side, while the corresponding vehicle socket position is blocked. This allows the decoder to be inserted only in the intended orientation.

PluX22 therefore has 22 numbered positions but only 21 electrical contacts. A decoder must never be forced into the interface. Resistance indicates incorrect alignment, bent pins or an unsuitable interface.

Pin Designation Function Output Type Important Note
1 GPIO_C Universal input or output Logic level Do not connect high-current loads directly
2 AUX3 Third auxiliary function output Amplified Observe the decoder output-current rating
3 / 4 GPIO_A and GPIO_B Train bus or additional logic functions Logic level The vehicle circuit board requires suitable amplifiers
5 / 6 GND and Cap+ Decoder negative and energy-storage connection Power supply Connect the energy-storage circuit only according to the instructions
7 / 13 F0 Forward / Reverse Front and rear headlights Amplified Check the direction-dependent assignment
8 / 10 Motor Positive / Negative Decoder motor output stage Regulated Measure the motor current under load
9 U+ Decoder positive after the rectifier Power supply Do not connect it to a separately generated vehicle positive
11 Index Mechanical keying No connection The position remains blocked
12 / 14 Right / Left Track Pickup Current pickup and digital signal Track input Do not confuse these with the motor connections
15 / 17 Loudspeaker A / B Sound-decoder loudspeaker connection Audio Do not connect to the vehicle ground
16 / 18 AUX1 / AUX2 First and second auxiliary functions Amplified Often used for tail lights or cab lighting
19–22 AUX4 to AUX7 Four additional auxiliary functions Amplified Check how the locomotive circuit board actually uses them
Distinguish contact capacity from decoder output: The connector contacts are designed for a maximum of 1 A. The permitted motor current and the capacity of individual function outputs may be considerably lower on a particular decoder.
Distinguish PluX16, PluX22 and 21MTC correctly

PluX22 Interface Comparison

Interface Positions Typical Installation Space Strengths Important Consideration
NEM 652 8 contacts Depends on the wired decoder Simple and widely used Only a few functions in the basic connector
PluX12 12 positions Up to 20 × 11 × 4.2 mm Compact Not preferred for new vehicle designs
PluX16 16 positions Up to 20 × 11 × 4.2 mm Sound and several functions Fewer amplified outputs than PluX22
PluX22 22, including one index position 30 or 35 × 16 × 6 mm Motor, sound, energy storage and many functions Check the standard and vehicle space together
21MTC 22 positions with 21 contacts Separate NEM dimensions Feature-rich H0 models Pins are located on the vehicle circuit board
PluX16 in PluX22: A smaller PluX16 decoder may be mechanically usable with a standards-compliant arrangement. However, AUX3 to AUX7 and other PluX22 functions will not be available in full.
Combine the application, protocol and equipment

Which PluX22 Decoder Fits My Locomotive?

Which task?
Which digital system?
What is particularly important?
Open the Detailed Decoder Finder

Your Recommendation

View Suitable Products →
Seven criteria in addition to the plug-in connection

Choose a PluX22 Decoder Safely

Motor

Measure Continuous and Starting Current

The decoder requires sufficient reserve for the motor under realistic load conditions.

Installation Space

Distinguish Between 30 and 35 Millimetres

The vehicle space and the dimensions of the specific decoder must be checked together.

Functions

Assign Each Output Individually

Headlights, tail lights, cab lighting, couplings and smoke units require suitable outputs.

Output Type

Do Not Load Logic Levels Directly

GPIO connections frequently require an amplifier circuit on the vehicle circuit board.

Sound

Plan the Loudspeaker and Project Together

The impedance, sound enclosure, sound project and available space must all be compatible.

Energy Storage

Observe Cap+, U+ and GND

Energy-storage modules may only be connected according to the manufacturer's circuit diagram.

Protocol

Match the Command Station and Decoder

DCC, Motorola, Selectrix and mfx are decoder features, not properties of the PluX22 socket.

Focus on H0 with individual applications above and below it

PluX22 Applications by Gauge

Gauges Z and N

PluX22 is usually too large. Next18, E24, NEM 651 or wired decoders are more common.

Exception

Very large multiple units or specialist vehicles.

Gauges TT and H0e

Some modern vehicles use PluX22, although PluX12, PluX16 and Next18 are more common.

Check

Available decoder length and body height.

Gauge H0

PluX22 is particularly widespread in modern diesel, electric and steam locomotives.

Advantage

Numerous independently controlled lighting and sound functions.

Gauge 0

Some compact Gauge 0 models may use PluX22. The motor current must be checked particularly carefully.

Check

Continuous current, starting current and heat dissipation.

Gauges 1 and G

High-capacity decoders with wires, screw terminals or PluG are generally more suitable for large-scale railways.

Reason

Multiple motors and high auxiliary currents.

Cross-Gauge Rule

The socket fitted is only the first step. The output capacity, installation space and vehicle circuit board remain decisive.

Safest Method

Open the locomotive, photograph and measure it, and compare the instructions.

Insert it straight, with the power off and without pressure

Install a PluX22 Decoder in Six Steps

Step 1

Test the Vehicle in Analogue Operation

The motor, current pickup and lighting must operate reliably.

Step 2

Open the Body Carefully

Release screws, clips and wires according to the instructions.

Step 3

Document the Socket

Photograph the index position, blanking plug and circuit-board markings.

Step 4

Remove the Blanking Plug

Pull it straight out of the female header and retain it safely.

Step 5

Insert the Decoder Evenly

Align the pins and never press on components or the pins themselves.

Step 6

Use the Programming Track

Read the address and test the motor, lighting and functions individually.

Before closing the body: Check that the decoder, loudspeaker, wires and energy-storage module do not touch the flywheel, cardan shaft, gears or body supports.
Avoid mechanical and electrical damage

Common Mistakes with PluX22

Confusing 21MTC with PluX22

The pin side and electrical assignment are completely different.

Forcing the Decoder into the Socket

This can bend the pins or damage circuit-board tracks.

Ordering by Locomotive Name Alone

Different production series may have different circuit boards.

Loading Logic Outputs Directly

GPIO pins frequently require an amplifier circuit.

Buying Sound Without Planning the Space

The loudspeaker and sound enclosure require additional room.

Connecting the Energy-Storage Capacitor Incorrectly

The polarity, voltage and charging circuit must suit the decoder.

20 suitable locomotive, function and sound decoders

PluX22 Decoders for H0, TT and Gauge 0

The selection includes universal locomotive decoders, function decoders for control cars, blank sound decoders and model-specific sound solutions. The linked product cards do not contain an availability statement.

Universal and Model-Specific Sound Decoders

Blank decoders and prepared sound projects for H0 vehicles and individual Gauge 0 models.

Explore decoder selection and digitisation in greater depth

Suitable Product Categories and Guides

Decoder Finder → Decoders Without Sound → Sound Decoders → Adapters and Accessories → Digital Decoder Guide → Digitise a Locomotive → Understand DCC → Installation and Repair →
Answers before ordering and installing a decoder

Frequently Asked Questions about the PluX22 Interface

How many contacts does PluX22 really have?

PluX22 has 22 numbered positions. Position 11 is blocked as the mechanical index, leaving 21 electrical contacts.

How large may a PluX22 decoder be?

NEM 658 provides for dimensions of up to 35 × 16 × 6 mm. RCN-122 uses a maximum of 30 × 16 × 6 mm for harmonisation with 21MTC.

Can a PluX16 decoder be used in a PluX22 socket?

This may be mechanically possible. The additional outputs and functions of the PluX22 interface will then remain unused.

Does a PluX22 decoder fit a PluX16 socket?

Only when the vehicle circuit board, unused holes and installation space expressly permit it. It must never be inserted with force.

Is PluX22 suitable for sound?

Yes. The interface provides two loudspeaker connections and numerous contacts for sound, lighting and auxiliary functions.

Can an energy-storage module be connected?

PluX22 provides GND, U+ and Cap+. The specific circuit must, however, comply with the decoder instructions.

What is the difference from 21MTC?

With PluX22, the pins are located on the decoder. With 21MTC, the vehicle circuit board normally carries the pins.

Which outputs are amplified?

F0 forward, F0 reverse and AUX1 to AUX7 are generally intended as amplified outputs. GPIO connections provide logic levels.

Is PluX22 always DCC?

No. The interface is independent of the protocol. Decoders may support DCC, Motorola, Selectrix or mfx.

Which gauge uses PluX22 most frequently?

PluX22 is particularly widespread in modern H0 locomotives. Individual TT, H0e and Gauge 0 vehicles may also be equipped with it.

Why does a lighting function not work?

Possible causes include missing function mapping, an unassigned vehicle circuit board connection, a logic-level output or a different circuit-board assignment.

When is professional installation advisable?

Professional installation is advisable when pins are bent, the circuit-board assignment is unknown, the motor current is high, the vehicle is valuable or a complex sound conversion is planned.

Technical Basis

The contact assignment, index position, dimensions and installation guidance of NEM 658, 2025 edition were considered.

Update Date

Content status: 17 July 2026. Check the current vehicle and decoder instructions before installation.

PluX22 Identified – Continue Planning the Decoder and Digital Project

The main guide covers locomotive decoders, sound decoders, digital command stations, protocols, digitisation and layout planning.

Go to the Main Guide