PluX Interface

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PluX Interface


The NMRA and MOROP have adopted a newer standard interface called PluX22, and its subsets, PluX16 and PluX8. (MOROP's NEM 658 also defines PluX12, however, NMRA Standard S-9.1.1 does not.)

PluX Interfaces


The purpose of the PluX interface is to provide a uniform interface for safe, secure and rapid installation of decoders adhering to the PluX Standard.


The PluX22 connector consists of two rows of 11 pins. PluX16 and PluX8 connectors consist of two rows of 8 pins and 4 pins respectively. The smaller connectors are subsets of the larger interface. Mechanically, the interface defines male pins on the decoder which are meant to interface directly with a female connector on a locomotive's receiving board. The preferred board-to-board orientation being that the decoder pins pass through holes in the receiving board's PCB and enter the bottom of the female connector. This would keep the height to a minimum.

  • PluX8 offers no advantages over the NEM 651 interface, so it not used.

The interface is designed for direct plug-in installation. Connection via a cable is not provided for, and are outside the PluX Standard.

The Standard sets maximum dimensions for the decoder -- both footprint and thickness. This allows for small, drop-in decoders.

The PluX interface supports one motor, up to 9 function outputs and one sensor input.

Also defined are the installation space and size of the decoder. Packaging must be labelled indicating a PluX16 or PluX22 device.

Mechanical Details

The interface on the locomotive side consists of a 16 or 22-pin double row female header with the pitch of 1.27, mm and decoder side of the matching male header. Misalignment is avoided with the omission of pin 11 and blocking the associated socket. According to the number of contacts including index, the two types are called Plux16 and PluX22.

The pins have a minimum length of 3 mm, maximum 4 mm and either one square profile with 0.40 mm edge length or a round profile with a diameter of 0.43 mm. Pins and jacks have a gold plated contact surface and a contact load capacity of 1A maximum.

The locomotive should provide enough space that the decoder can be easily mounted, and allow for removal without tools.


The maximum dimensions of the decoder amount

  • PluX22: maximum of 30 (l) x 16 (w) x 6.0 (h) mm
  • PluX16: maximum 20 X 11 X 4.2 mm
Compact Variant a PluX Decoder

The compact decoder variation is only 1mm in depth, for the lowest possible height. The female socket is under the interface board.

High Version

If the decoder has components that require additional clearances, and the space is available, a taller version can be used. Unlike the compact version, the female socket is on top of the interface board. There should be enough space under the board to accommodate pins of the maximum length allowed.

Operation without a Decoder Installed

For operation without a decoder, a jumper plug must be used which has at least the connections from track 1 (pin 12) to motor 1 (pin 8) and track 2 (pin 14) to motor 2 (pin 10). If there is vehicle lighting, F0f (pin 7) with track 2 (pin 14) and F0r (Pin 13) to track 1 (pin 12). Terminal V + (pin 9) is via two diodes


The 22-pin interface can also be used as a SUSI interface according to [RCN600 ]Only four signals: GND, V+, train bus clock and Train bus data are connected to the motor or function decoder. In particular, track connections are not connected when used as a SUSI interface. All other connections can be used for the functions of the SUSI module.


PluX22 PluX16 Name Description Group
1 GPIO/C General I/0 4
2 AUX Output 3 5
3 3 GPIO/B Train bus clk 7
4 4 Example Train bus data 7
5 5 Ground Decoder ground tap to rectifier
6 6 Capacitor Pos. Storage Cap positive connection 2
7 7 F0f Forward Lighting 5
8 8 Mtr 1 Motor positive 3
9 9 VPLUS Decoder positive rectifier tap
10 10 Mtr 2 Motor negative 3
11 11 Index Coding, not used
12 12 Track 1 Right rail pickup 1
13 13 F0r Reverse Lighting 5
14 14 Track 2 Left rail pickup 1
15 15 Loudspeaker Spkr A 6
16 16 AUX1 Output 1 5
17 17 Loudspeaker Spkr B 6
18 18 AUX2 Output 2 5
19 AUX4 Output 4 5
20 AUX5 Output 5 5
21 AUX6 Output 5
22 AUX7 Output 7 5
Group Description
1 AC Traction: Center Rail pickup
2 Cap. + for connecting storage capacitors. This connection should be switchable, so that the storage capacitor can be disabled the programming track. Maximum potential equal to the track voltage.
3 AC Traction: Mtr1 (pin 8) is field coil A, Mtr 2 (pin 10) is the field coil B.
4 GPIO / C can be an output or input. The input resistance should be approx. 100 kΩ. As an output: TTL-compatible logic levels, maximum 0.5 mA
5 These outputs are in the switched-on state decoder with GND connected. The voltage for the switched load is Track voltage at V +.
6 Speaker impedance is determined by the manufacturer.
7 The processor pins of the train bus have a maximum series impedance of 470 Ω. The levels correspond to TTL-compatible logic levels
Voltage Levels, Decoder GPIO Ports
Decoder Output External Circuit, Input
Function OFF <= 0.4 volts <= 0.8 volts
Function ON > = 2.4 volts > = 2.0 volts

Additional Details

  • The PluX interface is based on the connector used by Marklin.
  • The sixteen pin PluX16 adds sound, two additions functions, SUSI and a storage capacitor.
  • Decoders with the twenty two pin PluX22 connector are premium sound decoders with up to 10 functions, and full SUSI.

You can insert a PluX8 decoder, or a PluX16 decoder into a PluX22 socket, as both are subsets of the larger connector. This gives the consumer choice as to the type of decoder to be installed while giving the manufacturer a single decoder interface for all decoder types. The index ensures correct alignment.

If a PluX16 decoder is plugged into a Plux22 interface, functions on pins 1, 2 and 19 to 22 are not controlled. If there are holes available, a PluX22 decoder can also be inserted into a PluX16.

Important Notes

As this is a standard, RCN-122 Decoder interface PluX16 & PluX22 the the authoritative document.

Locomotives with a PluX12 interface cannot carry a compliance logo.

NMRA S-9.1.1 Draft Connectors Standard