Digital Command Control, some backgrounds

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Digital Command Control gained popularity among railway modellers and not without reason. Digital command control is the logical successor of analogue command control. These analogue systems had their widest following in the USA and only a few are known outside the USA. A few brand names of analogue command control are Dynatrol (by PSI) and the Keller Onboard system, which included loco sound effects built in in the locos. Receivers for these analogue systems are rather large, limiting the use of command control only to H0 scale and larger. Analogue command control systems can only handle locomotives or multiple-units and do not have accessory control and computer interfaces.

How analogue command control works

Analogue command control systems are based on what is called frequency-multiplexing. It works a bit like radio where each station has its own transmitting frequency. To receive that signal, your receiver has to be tuned to filter out the specific frequency of the station you are listening to. Command control works just like that. With analogue command control, a filter circuit in each receiver filters out the information needed from a range of channels (= frequencies). These filter circuits are the complicating factor, requiring expensive precision resistors and capacitors. The voltage across the tracks remains a constant 12 to 15 Volts depending on the system used, not DC but high-frequency AC, with information for the loco receivers coded in. A side effect of the constant voltage is continuous lighting.

History of command control

The first command control system was introduced way back in the early 1960's when General Electric introduced such a system. By then it was real state-of-the-art technology, offering 6 channels to run 6 trains indepently on a single track, without block switches etc. In Europe, Philips introduced a 20-channel system in 1972, but it either never became available or it did not catch on. Does anybody know more on this? In the USA analogue systems did better. The CTC-16, CTC-80, Dynatrol and Keller systems were developed. Analogue systems are more or less limited to about 20 channels, due to a few reasons. Also in 1972, Trix introduced a single channel system, EMS, with receivers small enough for N-scale locomotives. Most N-scale locos had the receiver factory-fitted, a practice now repeated by a few European and American manufacturers nowadays. The major breaktrough came in 1982, when again Trix showed a digital command control system, Selectrix, but this took a little time to become available, so in 1985 Märklin was the first manufacturer to have a digital command control system on the market. The Märklin system is based on a few circuits designed and made by Motorola, so the Märklin system is sometimes called 'Motorola system'. Trix followed in 1987 with their 'Selectrix' system. Major German manufacturer Fleischmann introduced their 'FMZ' system also in 1987. All these systems are not compatible, which causes problems when you want to run your models on someone else's layout.

Digital Command Control

In the 1980's digital components suitable for railway model applications became affordable and model railway manufacturers saw possibilites to develop command control systems with an unprecedented capacity and with lots of extra possiblities when it comes to accessory control. As mentioned above Märklin from Germany was the first to introduce such a system on the market, that was way back in 1985. The pioneering work was not done by Märklin themselves, but by a specialist company named Lenz Elektronik. Lenz designed a system based on chipsets offered by Motorola, the system bacame known as Märklin Digital (trade name) or simply as Motorola or MM system. Use of this system is limited to model railways based on the Märklin electrical system (stud contact central feeder, both outer rails return). This system is not of further interest for those modelling Japanese railways, but the Märklin / Motorola system is quite popular in Europe and it is good to know that this system is the basis of one of the most important developments in railway modelling since the introduction of electrically operated models.

How digital command control works

Digital command control is based on what is technically known as 'time division multiplexing', where commands are given a short stretch of time for transmission to the receiver, in railway modelling known as decoder. Capacity of a typical digital command control system ranges from 80 to over 10,000 channels. The device that generates the signals is often known as command station, the signals are amplified by a booster device and then fed into the track. Larger systems may have more than one booster. Quite often command station and one booster are integrated into one casing, which saves money and space, sometimes one or two loco controllers are built in too.

Available digital command control systems, suitable for N-scale:

There are two different systems available today that have receivers small enough to build in into n-scale locomotives.

1. Selectrix, originally offered only by Trix, but again developed by specialists outside the Trix company. The system is available since 1987 and has its widest following in Germany and a few surrounding countries. Selectrix is not compatible with either ordinary DC and the standard DCC system. Modern Selectrix decoders can be programmed to run on DC, but should be reprogrammed when running on Selectrix, most recent development is a dual-standard loco decoder, which accepts both Selectrix and DCC signals. Selectrix components are nowadays offered by a few firms, all from Germany.

2. NMRA DCC,developed by Lenz Elektronik from Germany, and accepted by the NMRA as a standard for digital command control. This means that there is more than one manufacturer that offers components for the system and that components are interchangeable to a certain level. In the NMRA DCC system loco decoders and accessory decoders should be interchangeable. Manufacturers are free to use their own standards for connecting the command station and boosters, the control network in which hand-held controllers can be plugged in and feedback buses that feed back the status of block detectors, accessory decoders etc. into the command station, which may be connected to a computer using an interface, which normally has an RS-232 connection on the computer side. There are generation differences in the NMRA DCC system, which include the number of speed steps and available adresses.

3. Märklin Motorola and Märklin Systems. These systems are developed for Märklin to be used with their 3-rail stud-contact AC system At the moment (2005) Märklin has 'gone digital' almost completely and there are hardly any analogue products (at least in HO and Gauge 1) available. After 20 years of success, the old Märklin Motorola (MM) system is successed by the new Märklin Systems (mfx) system. These systems are compatible, meaning that locos and accessories (not yet, after introducton of 'Central Station' master control unit) can be controlled with both types of command stations. The new 'mfx'  format offer easier control, more loco adresses available (only 80 with MM, some 10,000 with mfx) and more speedsteps (mfx command station driving mfx decoders). The reason to mention these systems is that the old MM format is the base of a do-it-yourself system that could be great fun to build and operate. More on this 'EDiTS' and 'EDiTS Pro' systems the EDiTS section. The new mfx system promises to be the new approach to model railway control, with long alphanumerical loco names instead of short address numbers, fast Ethernet computer connection etc.


Advantages and drawbacks of Selectrix, NMRA DCC and Märklin Digital systems

Both Selectrix and NMRA DCC systems have their pros and cons. Here is a short list that may assist you in making the right choice, I can not take any responsibilty for your choice, which is of course completely yours.


Pro: smallest decoders available, all manufacturers use the same connections between 'land-based' components. As far as I know all Selectrix or Sx components are compatible without major problems. System offers smooth control and is easy to operate. Clever and flexible control bus wiring system, which is used by all manfacturers of Selectrix control systems, at the moment there are 4 of them. Interest of the German model industry is slowly growing. The latest loco decoders offer a basic transponding feature. Transponding compatible track-circuits are offered by only one manufacturer (Müt).

Con: only one manufacturer of loco decoders, which are offered under several trade names. Components are nearly inavailable outside the European continent, loco decoders are more expensive than those for the NMRA DCC system, the difference is somewhere between 5 and 10 Euro.  You will probably need many loco decoders, so sharp calculating may pay off. Documentation is only available in the German language.


Pro: more than one manufacturer that offer a complete range of products, so when one supplier ceases production, you may use the products offered by others. A very wide choice of products is available. Published standards ensure interoperateabililty.

Con: different 'cab buses' in use by various manufacturers. Meanwhile at least 5 different systems have developed; XpressNet / X-Bus which is used by Lenz, Arnold / Lima and ZTC, LocoNet, used by Digitrax, Uhlenbrock, Fleischmann and a few smaller manufacturers, CAN bus used by Zimo, which is based on a technology used in the automotive industry and simply 'Cab bus', used by NCE and Wangrow.CVP's Easy DCC has its own cab bus, which uses coaxial cable to connect the sockets. LocoNet seems to be the most versatile system, but I can not see the 'big difference' yet. Components of different manufacturers are not 100% compatible, so you have to inform in advance to ensure yourself that a product will work with your system. Programming more advanced functions may not be easy, and is best done with a computer tool. A new development is transponding, which is feedback of train-based adresses into the command station. Today transponding is offered by Zimo, Digitrax and Lenz, but all 3 use a different system and these are not compatible. Transponding is very suitable for computer-control applications. The NMRA is working on a standard for transponding and its applications.

rood Märklin Motorola (MM)  and Märklin Systems (mfx):

Pro: MM is a system with a wide following among Märklin fans. Cheap decoders and equipment available from 3rd party manufacturers. mfx offers new standards in control ergonomics, but a full range is not yet available. The new mfx system is a Märklin-only system and not of interest for those using a 2-rail system, either HO or N-scale, as it can control DCC locos.

Con: not intended for use with N-scale or smaller or with 2-rail systems. Selectrix or NMRA-DCC would be a better choice, the Märklin Systems Central Station can be used as a DCC base station (if you want to spend € 700.- + on the unit).

prpl Use in Japanse outline models

At this moment, DCC is not very popular among Japanese modellers. As far as I know, Digitrax and Lenz have agents in Japan to co-ordinate their sales. Digitrax co-operates with Kato and offers a starter kit aimed at the Japanese market, named 'Zephyr' (now superseeded by the Zephyr Xtra).  No N-scale Japanese model loco or MU has a socket fitted to 'plug in' one of the modern decoders, but some Kato H0 have the standard 8-pin plug fitted. Digitrax ref. DN-163K0 fits a number of Japanese-outline Kato locos, albeit only the newer ones. Kato has information on DCC conversions on their Japanese website, Kato can supply Digitrax decoder fitted locos from their 'Kato Hobby Center'. For all other models you will need skill and creativity to convert your models to digital command control, whatever system you choose. Use of DCC in MUs is a bit complicated, as you need to fit function-only decoders in the end cars as well. Usually, the Japanese manufacturers have made no provision for fitting a DCC decoder. The hardest to convert are the smaller diesel locos, like the DE10 or DD16, where there is very little room to fit a decoder. Usual practice is to cut away part of the chassis to make room for the decoder. Fortunately very small decoders have become more affordable recently. These sell at prices around US $ 25,- or even less. Point motor control is quite easy, due to the popularity of Kato's 'Unitrack' in the US. There are several accessory decoders available that can drive Kato and Tomix point motors. These are offered by CVP (model AD4K), Lenz (LS150) and Digitrax (DS51K and DS52). Digitrax also offers a signal decoder for those who want operating signals on their layout. Littfinki Datentechnik from Germany also offer a suitable accessory decoder (1-DEC-DC) in both kit and built-up versions.

Recent development: In the summer of 2005, Kato announced a set of decoders, especially made for use in their MU models. The set consists of 3 different decoders that are sold seperately, a motor-only decoder that fits between the power pickups and the printed circuit board that is used in MU-models made from 2005 onwards, a decoder for head and tail lights and a 1-function decoder to switch interior lighting. A few more websites in Japanese on DCC conversions: DCC Model describes several DCC conversions, mainly using Digitrax components and SNJPN, which is a japanese manufacturer of DCC decoders. SNJPN offers a custom-made decoder for the Tomix track cleaner.

More detailed information:

On the following pages I put in more detailed information on digital command control, split up by the different systems.

NMRA DCC page, overview of manufacturers and N-scale suitable loco decoders, includes links to manufacturers.

Selectrix page, overview of manufacturers and suitable loco decoders, links to manufacturers also included.

DCC Model, a japanese page with lots of information on fitting decoders in japanese model trains, geared towards the use of Digitrax products, but very informative.

Digital direct to loco control

Direct to loco control has been re-introduced by 2 manufacturers I would like to mention: Ring Engineering with their RailPro system and Layout-IoE, who offer a complete control solution. 

Ring Engineering uses radio-signal that are transmitted form a special controller and special loco receivers that are a lot like a DCC decoder.  RailPro also offer accessory modules that can control 3-wire solenoid devices, like point motors. The RailPro controller is a hand-held device with a colour touchscreen and a control knob. Setting up a loco is alot easier than in a DCC system and very straightforward. You have the choice of loco modules with or without sound. A capable power supply completes the range.

railpro Ring Engineering RailPro handheld controller (source: Ring Engineering

Layout-IoE has a slightly different approach: convert your layout with all trains and accessories into a 'Internet of Thngs', all controllers have an IP-address and communicate by the IP-protocol.  Layout-IoE has no dedicated controllers, but instead a smartphone or tablet are used to control trains and accessories. Layout-IoE las has announced track-circuits that fit within the system. In my opnion Layout-IoE offers the better system when compared to RailPro. Both systems have the same drawback: they are non-standard and loco modules are still on the bulky side and quite costly.

wifitrax WifiTrax offer a complete Wifi-based layout control solution, that not only controls locos, but also your points and other accessories. The accessory modules are compatible with Kato and Tomix point motors (bi-polar solenoids) You may even control DC locos without decoders ore receivers with this system. Control is by an app or software on Android or Windows 10 devices. More information on

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> a short history of NMRA DCC

> Overview of DCC systems

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