Modellbahn Keks
Welcome!
Our cookies offer you a fast, relaxed and full-featured shopping experience. Some are necessary to operate the website and its functions. Others help us to improve our services. If you agree to this, simply consent to the use of cookies for preferences, statistics and marketing by clicking on "OK". Alternatively, you can deactivate individual cookies under "Customise cookies" or all cookies, except those required for the function of our website, under "Reject all".
Imprint  /  Data Privacy
Selectrix Explained Simply: Understanding SX1 & SX2
Minitrix BRAWA ESU Uhlenbrock PIKO
Digital technology for compact and large model railway layouts
Digital format and system bus explained clearly

Selectrix Explained Simply: Understanding SX1 & SX2

Selectrix controls locomotives, turnouts, signals and feedback modules through a rapidly updated digital system. The format is especially well known in N scale. Modern multi-protocol decoders also allow it to be used in TT, H0, 0 scale and large-scale model railways.

Understand Selectrix SX1 and SX2 Select products
Minitrix N scale Class 110 electric locomotive with DCC and Selectrix decoder
A proven digital system with fast response times

What does Selectrix mean in model railways?

Selectrix is a digital control system for model railways. It was originally developed for Trix and is especially closely associated with Minitrix and N scale. The abbreviation SX refers both to the digital track signal and to the data bus through which controllers, occupancy detectors, switching decoders and other layout modules exchange information.

A digital command station continuously transmits data packets through the track. Each locomotive decoder responds to its configured address and converts the transmitted commands into speed, direction of travel, lighting or additional functions. At the same time, the SX bus can communicate the status of turnouts, push buttons and feedback modules to other devices.

A characteristic feature is the cyclic and uniform transmission of system information. Response times therefore remain predictable even when many vehicles and layout modules are involved. Selectrix has consequently been used not only for driving trains, but also for feedback, block operation and computer control.

Why did Selectrix become particularly popular in N scale?

N scale locomotives provide very little installation space. Early Selectrix decoders were comparatively compact while still providing load-regulated, smooth driving characteristics. This made the system attractive for small vehicles. Today, many multi-protocol decoders support DCC, Motorola or M4 in addition to SX.

Is Selectrix still up to date?

Selectrix remains relevant for existing layouts. Many SX components operate reliably and can be supplemented with suitable multi-protocol command stations. When building a completely new layout, consider which new decoders, feedback modules and controllers will be required in the long term. DCC now offers the broader cross-manufacturer range, while Selectrix remains important for existing SX buses and older vehicle collections.

The system consists of more than locomotive decoders

A Selectrix layout can include a command station, handheld controllers, boosters, turnout decoders, occupancy detectors, feedback modules, a computer interface and vehicle decoders. The complete layout concept should therefore always be considered before individual components are replaced.

Rule of thumb for beginners

Selectrix does not control trains alone. The SX bus can also carry switching commands and feedback information for an entire model railway layout.

From the address to the motor

How is a Selectrix locomotive controlled?

A classic SX locomotive does not register automatically. The command station and decoder must use the same address and matching format.

1

Switch on the command station

The digital command station generates the SX track signal and supplies the layout through its internal booster or an additional booster.

2

Set the locomotive address

Assign the decoder an unused SX1 or SX2 address. Duplicate addresses would cause several vehicles to respond together.

3

Select the format

With a multi-protocol decoder, specify whether the vehicle is to operate under SX1, SX2 or another digital format.

4

Transmit the driving command

The command station continuously transmits the address, speed step, direction and functions through the track to the vehicle decoder.

5

The decoder controls the motor

Load regulation compares the requested speed with the motor’s actual behaviour and adjusts the motor control accordingly.

6

Evaluate feedback information

Occupancy detectors and switching modules can communicate their status through the SX bus to controllers, control panels or a computer.

Classifying generations and digital formats

What is the difference between SX1, SX2, DCC and mfx?

SX2 expands the capabilities of the original Selectrix format. Multi-protocol command stations can additionally integrate vehicles using other digital systems.

Format Speed steps Addresses Typical strength
Selectrix 1 31 speed steps 100 locomotive addresses with current D&H decoders A simple, fast and clearly structured SX system for existing layouts.
Selectrix 2 127 speed steps Up to 10,000 addresses Finer speed control and up to 16 additional functions.
DCC 14, 28 or 128 Short and long addresses A very broad cross-manufacturer range for almost every gauge.
mfx / M4 Dependent on the command station and decoder Unique internal identification Automatic registration and transmission of locomotive information.
Motorola Traditionally 14 or an extended mode Dependent on the command station and decoder Compatibility with older Märklin Digital vehicles.
SX2 is not simply another name for SX1

SX2 expands the address range, number of speed steps and available functions. Check the instructions for an existing command station to determine whether it fully supports these capabilities.

Switching, feedback and automation

What role does the SX bus play?

The SX bus connects controllers and layout modules. Driving commands, turnout positions and occupancy feedback can therefore be processed within a shared system.

Occupancy detectors

Feedback modules detect vehicles in monitored track sections and make this information available to other bus participants.

Turnouts and signals

Switching decoders receive commands for solenoid drives, servos, light signals and other electrical devices.

Computer control

A suitable interface allows software to evaluate train positions, set routes and control automated operating sequences.

Block operation

Feedback modules and braking sections enable controlled train sequences and automatic stopping in front of signals.

Handheld controllers

Additional controllers can be connected to suitable command stations so that several people can operate the layout at the same time.

System expansion

Before expanding the system, check bus utilisation, address allocation, power supplies and compatibility between the devices being used.

From the smallest decoder to a large-scale locomotive

Which gauges are suitable for Selectrix?

The format is not tied to a specific model railway scale. However, decoder dimensions, motor current and output power must be suitable for the vehicle.

Gauge Prevalence Important selection criteria Recommendation
Z scale Specialist application Extremely small dimensions, low motor current and a suitable track voltage. Use only nano decoders expressly designed for this application.
N scale Traditionally very widespread NEM 651, Next18, installation height and heat dissipation. Very suitable for existing SX layouts and compact decoders.
TT scale Regularly used through multi-protocol decoders NEM 651, Next18, PluX and the available installation space. Compare SX1, SX2 and DCC support when selecting a decoder.
H0 scale Broad multi-protocol range AC or DC system, interface, motor current, sound and functions. Select 21MTC, PluX22 or NEM 652 to match the vehicle.
H0e and H0m Easily implemented with compact decoders Installation space, current consumption and reliable current pickup. Use compact multi-protocol decoders or specialist narrow-gauge solutions.
0 scale Possible with high-performance decoders Motor current, lighting, servos, smoke generators and speakers. Use LokSound L or a comparable high-performance decoder.
Gauge 1 and G scale Multi-protocol operation High motor current, robust connections and a suitable track voltage. Select XL decoders and powerful command stations or boosters.
The interface alone is not a sufficient selection criterion

Also check the decoder dimensions, maximum motor current, track voltage, lighting outputs, sound, speaker specifications and supported protocols. The Decoder Finder helps narrow down the available options.

Matching the decoder and command station correctly

How do you set up a Selectrix locomotive?

First determine whether the decoder supports SX1, SX2 or both formats. With a multi-protocol decoder, it is also important to know which track format was programmed most recently. Some decoders do not switch automatically between SX and DCC during digital operation.

Place the locomotive on a separate programming track. Select the appropriate Selectrix format on the command station and assign an unused address. You can then configure acceleration delay, braking delay, maximum speed and any additional parameters.

What must be checked during a decoder conversion?

Determine the interface and motor type before opening the vehicle. Common interfaces include NEM 651, NEM 652, Next18, 21MTC and PluX22. If the locomotive does not have an interface, the decoder must be hard-wired and the motor must be safely isolated from the track.

When is a multi-protocol command station useful?

It is useful when older Selectrix locomotives are to operate alongside new DCC, Motorola or mfx vehicles. Digital command stations such as the ESU ECoS or Uhlenbrock Intellibox support several formats and make a gradual change of system easier.

Document addresses clearly

A list containing the vehicle, catalogue number, address, decoder, format and interface prevents duplicate addresses and makes subsequent maintenance easier.

Vehicles, decoders and digital command stations

21 suitable products for Selectrix layouts

The selection includes ready-to-run vehicles, compact decoders for N and TT, powerful H0 sound decoders, command stations and large-scale decoders. The interface, electrical system and actual range of supported SX functions are always decisive.

Small scales

Selectrix products for N and TT scale

Compact dimensions and low current consumption make these products suitable for small locomotives and space-saving layouts.

1:87 scale

Locomotives and decoders for H0 scale

H0 offers powerful multi-protocol decoders and ready-to-run sound locomotives with SX1 and SX2 support.

Control systems and digitising large vehicles

Command stations, 0 scale, G scale and narrow-gauge technology

Powerful command stations support mixed vehicle collections. L and XL decoders provide sufficient output for large motors, sound, lighting, smoke generators and additional functions.

Answers for beginners and layout converters

Frequently asked questions about Selectrix

The most important answers about SX1, SX2, DCC, addresses, feedback, gauges and modern multi-protocol layouts.

What does the abbreviation SX stand for?

SX is derived from the name Selectrix. The designation is used for the digital track signal and in connection with the SX system bus.

How many speed steps does Selectrix 1 provide?

SX1 operates with 31 true speed steps in each direction. Modern decoders can regulate more finely internally and generate intermediate values for smoother operation.

How many addresses does SX2 support?

Current SX2-compatible D&H decoders support up to 10,000 addresses, 127 speed steps and 16 additional functions.

Can a Selectrix locomotive be controlled using DCC?

Only when the installed decoder also supports DCC. A pure SX1 decoder does not respond to DCC commands.

Can a DCC locomotive operate on a Selectrix layout?

This is possible when the command station can additionally transmit DCC. Otherwise, the vehicle decoder must be replaced with an SX-compatible model.

Does Selectrix register automatically?

A classic SX locomotive is added using its address. Automatic registration with the locomotive name and functions is not one of the basic SX1 features.

Is Selectrix suitable only for N scale?

No. The format can be used in almost any gauge with a suitable decoder. N scale is simply its best-known field of application.

What is a Selectrix braking diode?

It modifies the track signal within a braking section. A compatible decoder detects this condition and brings the vehicle to a controlled stop.

Can the SX bus be used for feedback?

Yes. Occupancy detectors and other modules can transmit status information through the bus to controllers, control panels or computer software.

Is Selectrix worthwhile for a new layout?

This depends on the existing vehicle collection and the desired modules. For a completely new layout, compare the current availability of Selectrix, SX2 and DCC products carefully.

Digital decoders Digitising locomotives Analogue or digital? Gauge comparison Digital command stations ESU brand range Uhlenbrock brand range Minitrix brand range

Technical foundations and manufacturer information

Further information is available from Döhler & Haass , in the Trix service documents and in the MOROP NEM 680 documentation on the SX signal .

Discover more digital topics and model railway basics

The central model railway guide covers gauges, digital technology, layout planning, track, vehicles, scenery construction and maintenance.

Go to the model railway guide